Imidazoquines as antimalarial and antipneumocystis agents. Facile regioselective synthesis of a novel chitosan-pexiganan conjugate with potential interest for the treatment of infected skin lesions. Electrospray ionization mass spectrometry as a valuable tool in the characterization of novel primaquine peptidomimetic derivatives. Schistosoma haematobium: Identification of new estrogenic molecules with estradiol antagonistic activity and ability to inactivate estrogen receptor in mammalian cells.
MedChemComm, 1 3 , Molecular docking and 3D-quantitative structure activity relationship analyses of peptidyl vinyl sulfones: Plasmodium Falciparum cysteine proteases inhibitors. Falcipains, plasmodium falciparum cysteine proteases as key drug targets against malaria. Covalent immobilization of human lactoferrin-derived peptide hLF for the development of an antimicrobial surface. Erratum: Viral surface glycoproteins, Gp and Gp41, as potential drug targets against HIV Brief overview one quarter of a century past the approval of zidovudine, the first anti-retroviral drug European Journal of Medicinal Chemistry Covalent immobilization of antimicrobial peptides AMPs onto biomaterial surfaces.
Acta Biomaterialia, 7 4 , Synthesis of an O-alkynyl-chitosan and its chemoselective conjugation with a PEG-like amino-azide through click chemistry. Synthesis and thermochemical study of quinoxaline-N-oxides: Enthalpies of dissociation of the N-O bond. Peptidomimetic and organometallic derivatives of primaquine active against Leishmania infantum.
MedChemComm, 3 9 , Novel potent metallocenes against liver stage malaria. New times, new trends for ethionamide: In vitro evaluation of drug-loaded thermally carbonized porous silicon microparticles. Comparative analysis of in vitro rat liver metabolism of the antimalarial primaquine and a derived imidazoquine. Drug Metabolism Letters, 6 1 , ChemMedChem, 7 9 , Tumour-like phenotypes in urothelial cells after exposure to antigens from eggs of Schistosoma haematobium: An oestrogen-DNA adducts mediated pathway?.
Toward the discovery of inhibitors of babesipain-1, a Babesia bigemina cysteine protease: In vitro evaluation, homology modeling and molecular docking studies. Recycling antimalarial leads for cancer: Antiproliferative properties of N-cinnamoyl chloroquine analogues. Bioorganic and Medicinal Chemistry Letters, 23 24 , N-cinnamoylated aminoquinolines as promising antileishmanial agents.
N-Cinnamoylated chloroquine analogues as dual-stage antimalarial leads. Metabolism of the antituberculosis drug ethionamide. Mass spectrometry techniques in the survey of steroid metabolites as potential disease biomarkers: A review. In vitro efficiency of 9- N-cinnamoylbutyl aminoacridines against blood- and liver-stage malaria parasites.
Bioorganic and Medicinal Chemistry Letters, 23 3 , Imidazolium-based functional monomers for the imprinting of the anti-inflammatory drug naproxen: Comparison of acrylic and sol-gel approaches. Hydration water and peptide dynamics-two sides of a coin. A neutron scattering and adiabatic calorimetry study at low hydration and cryogenic temperatures. Experimental and computational study of the energetics of hydantoin and 2-thiohydantoin. Development of plasmodium falciparum protease inhibitors in the past decade Density functional treatment of interactions and chemical reactions at interfaces.
Urinary estrogen metabolites and self-reported infertility in women infected with Schistosoma haematobium. PLoS One, 9 5. Selective albumin-binding surfaces modified with a thrombin-inhibiting peptide. Acta Biomaterialia, 10 3 , N-cinnamoylation of antimalarial classics: Quinacrine analogues with decreased toxicity and dual-stage activity. ChemMedChem, 9 2 , Killing of mycobacterium avium by lactoferricin peptides: Improved activity of arginine- and d-Amino-Acid-containing molecules.
Interaction of chitosan and chitin with Ni, Cu and Zn ions: A computational study. Characterization of hLF immobilization onto chitosan ultrathin films, and its effects on antimicrobial activity. Acta Biomaterialia, 10 8 , Antimicrobial peptides: A new class of antimalarial drugs?. Frontiers in Pharmacology, 5 DEC. Aminoglutethimide-imprinted xerogels in bulk and spherical formats, based on a multifunctional organo-alkoxysilane precursor. ImmunoPEGliposomes for the targeted delivery of novel lipophilic drugs to red blood cells in a falciparum malaria murine model.
Anti-Pneumocystis carinii and antiplasmodial activities of primaquine-derived imidazolidinones. Bloodstream infections caused by multidrugresistant Enterobacteriaceae: report from two Portuguese hospitals. Unanticipated stereoselectivity in the reaction of primaquine alpha-aminoamides with substituted benzaldehydes: A computational and experimental study. Influence of feeding strategies of mixed microbial cultures on the chemical composition and microstructure of copolyesters P 3HB-co-3HV analyzed by NMR and statistical analysis. Predicting the secondary structure of proteins using Machine Learning algorithms.
International Journal of Data Mining and Bioinformatics, 6, A novel fluorescein-based dye containing a catechol chelating unit to sense iron III. Potential effects of non-conjugated metabolites of propofol in clinical variables. Carbohydrate particles as protein carriers and scaffolds: physico-chemical characterization and collagen stability. Synthesis of new hydroxycinnamoyl oseltamivir amides and evaluation of their antioxidant and antiviral activities. Amides of antiviral drug oseltamivir with antioxidant active aminoacids: synthesis and biological activities.
Discrimination of fluorescence light-up effects induced by pH and metal ion chelation on a spirocyclic derivative of rhodamine B. Chitosan conjugates for DNA delivery. NMR study of the supramolecular structure of dual drug-loaded poly butylcyanoacrylate nanoparticles. Disproportionation route to monodispersed copper nanoparticles for the catalytic synthesis of propargylamines. RSC Advances, 3, Rhodamine labeling of 3-hydroxypyridinone iron chelators is an important contribution to target Mycobacterium avium infection. Exploiting the use of 3,4-HPO ligands as nontoxic reagents for the determination of iron in natural waters with a sequential injection approach.
Anti-tyrosinase, antioxidant and antimicrobial activities of hydroxycinnamoylamides. PLoS One, 8. Photosensitized oxidation of phosphatidylethanolamines monitored by electrospray tandem mass spectrometry. Distinctive EPR signals provide an understanding of the affinity of bis- 3-hydroxypyridinonato copper II complexes for hydrophobic environments.
Efficiency of trypsin digestion for mass-spectrometry-based identification and quantification of oxidized proteins: evaluation of the digestion of oxidized bovine serum albumin. Silica nanostructures synthesis and CdTe quantum dots immobilization for photocatalytical applications. RSC Advances, 4, Endo-benzonorbornenol as an efficient non-natural chiral auxiliary in the asymmetric aza-Diels-Alder reactions between cyclopentadiene and 1-phenylethyl iminoacetates.
Biomembrane simulations of 12 lipid types using the general amber force field in a tensionless ensemble. Structural characterization of inclusion complexes between cyanidinglucoside and beta-cyclodextrin. Frontiers in Pharmacology, 5. An efficient eco-sustainable oxidative desulfurization process using mu-oxo-bridged Fe III complex of meso-tetrakis pentafluorophenyl porphyrin. Indigo dye production by enzymatic mimicking based on an iron III porphyrin. The glycation site specificity of human serum transferrin is a determinant for transferrin's functional impairment under elevated glycaemic conditions.
Synthesis and N-functionalization of isoxazolidines: a new approach to nucleoside analogues. Development of insulino-mimetic zinc II complexes of the class 3-hydroxypyridinone ligands: In vitro cytotoxicity studies for safety assessment. Tuning the limits of pH interference of a rhodamine ion sensor by introducing catechol and 3-hydroxypyridinone chelating units. A green and sustainable method for the oxidation of 1,3-dihydrobenzo[c] thiophenes to sulfones using metalloporphyrin complexes. Vanadyl cationic complexes as catalysts in olefin oxidation.
Structural characterization of functionalized gold nanoparticles for drug delivery in cancer therapy: a NMR based approach. Antimycobacterial activity of rhodamine 3,4-HPO iron chelators against Mycobacterium avium: analysis of the contribution of functional groups and of chelator's combination with ethambutol. MedChemComm, 6, Surface modified poly butyl cyanoacrylate nanoparticles loaded with indomethacin: preparation and physicochemical characterization.
Bulgarian Chemical Communications, 47, Iron speciation by microsequential injection solid phase spectrometry using 3-hydroxy-1 H methylpyridinone as chromogenic reagent. Synthesis and spectroscopic characterization of a new tripodal hexadentate iron chelator incorporating catechol units. Nutritional parameters of infusions and decoctions obtained from Fragaria vesca L. Novel serine-based gemini surfactants as chemical permeation enhancers of local anesthetics: A comprehensive study on structure-activity relationships, molecular dynamics and dermal delivery.
ChemMedChem, 10, Role of the sphingomyelinase Isc1p in the regulation of iron homeostasis. Supramolecular self-assembly between an amino acid-based surfactant and a sulfonatocalixarene driven by electrostatic interactions. Chlorogenic acid-arabinose hybrid domains in coffee melanoidins: Evidences from a model system. The influence of hyperthermia on the vascular effects of MDMA and its metabolites. Neurotoxicity of amphetamine and its metabolite 4-hydroxynorephedrine on differentiated SH-SY5Y dopaminergic cells.
DoD SBIR Solicitation | iqegumybiwyf.ml
A mild cumulative dose of mitoxantrone leads to age-dependent cardiac injury in mice. Synthesis and characterization of a 3-hydroxypyridinone chelator functionalized with a polyethylene glycol PEG chain aimed at sequential injection determination of iron in natural waters.
Stem Cells International. Primaquine-based ionic liquids as a novel class of antimalarial hits. RSC Advances, 6, But, Where Should We Target?. PLoS One, Iron speciation in natural waters by sequential injection analysis with a hexadentate 3-hydroxypyridinone chelator as chromogenic agent.
Uncovering novel 3-hydroxypyridinone metal ion complexes with potential anti-inflammatory properties. Bacteria-targeted biomaterials: Glycan-coated microspheres to bind Helicobacter pylori. Acta Biomaterialia, 33, Enhancing glioblastoma cell sensitivity to chemotherapeutics: A strategy involving survivin gene silencing mediated by gemini surfactant-based complexes. Antimicrobial properties and death-inducing mechanisms of saccharomycin, a biocide secreted by Saccharomyces cerevisiae. Journal of Chemistry. The Anticancer Potential of Ionic Liquids. ChemMedChem, 12, Saccharomyces cerevisiae accumulates GAPDH-derived peptides on its cell surface that induce death of non-Saccharomyces yeasts by cell-to-cell contact.
Ultrasound-assisted green bromination of N-cinnamoyl amino acid amides - Structural characterization and antimicrobial evaluation. Microsequential injection lab-on-valve system for the spectrophotometric bi-parametric determination of iron and copper in natural waters. Targeted O-glycoproteomics explored increased sialylation and identified MUC16 as a poor prognosis biomarker in advanced-stage bladder tumours. Molecular Oncology, 11, Cardiovascular Toxicology, 17, Design of oligoaziridine-PEG coatings for efficient nanogold cellular biotagging.
RSC Advances, 5, Untangling interactions of a zinc II complex containing a coumarin-porphyrin unit with alkaloids in water solutions: a photophysical study. Recent progress in the field of glycoconjugates. Journal of Chemical Information and Modeling, 55, Pre-treatment of the paper pulp in the bleaching process using biodegradable chelating agents.
International Journal of Environmental Science and Technology, 12, ChemPlusChem, 81, Synthesis, characterization and biological evaluation of cationic porphyrin-terpyridine derivatives. Ring Opening of 6-Azabicyclo[3. Porphyrin-rhodamine conjugates as new materials with sensing ability. Catalyst-free aziridination and unexpected homologation of aziridines from imines. Thermal rearrangement of an N-hydroxyimidazole thiocarbamoyl derivative as a simple entry into the 4-thioimidazole motif. A Review of Recent Work. Geographical classification of weathered crude oil samples with unsupervised self-organizing maps and a consensus criterion.
Metabolic interactions between ethanol and MDMA in primary cultured rat hepatocytes. Antioxidant mechanisms of Quercetin and Myricetin in the gas phase and in solution - a comparison and validation of semi-empirical methods. Synthesis and biodegradation studies of new copolymers based on sucrose derivatives and styrene. Combining Kohonen neural networks and variable selection by classification trees to cluster road soil samples. Demethylation of theophylline 1,3-dimethylxanthine to 1-methylxanthine: the first step of an antioxidising cascade. Scavenging activity of aminoantipyrines against hydroxyl radical.
Recovery of lupanine from Lupinus albus L. Microwave-based methodology for the preparation of organoselenium compounds. Antioxidant activity of unexplored indole derivatives: Synthesis and screening. Synthesis and properties of new functionalized guanidinium based ionic liquids as non-toxic versatile organic materials. A new insight on the hypochlorous acid scavenging mechanism of tryptamine and tryptophan derivatives.
Library of mild and economic protocols for the selective derivatization of sucrose under microwave irradiation. Synthesis and characterization of versatile MgO-ZrO2 mixed metal oxide nanoparticles and their applications. Analysis of the antioxidant activity of an indole library: cyclic voltammetry versus ROS scavenging activity. New chiral imidazolium ionic liquids from isomannide. QSAR modeling of antitubercular activity of diverse organic compounds. Online chemical modeling environment OCHEM : web platform for data storage, model development and publishing of chemical information.
Ionic Liquids as Active Pharmaceutical Ingredients. ChemMedChem, 6, Synthesis of a new pyranoanthocyanin dimer linked through a methyl-methine bridge. Fast synthesis employing a microwave assisted neat protocol of new monomers potentially useful for the preparation of PDLC films. Use of a porphyrin platform and 3,4-HPO chelating units to synthesize ligands with N-4 and O-4 coordination sites. Synthesis of geminal bisphosphonates via organocatalyzed enantioselective Michael additions of cyclic ketones and 4-piperidones.
Highly active zinc alkyl cations for the controlled and immortal ring-opening polymerization of epsilon-caprolactone. Synthesis and structural characterisation of aryl-BIAN copper I complexes and their application as catalysts for the cycloaddition of azides and alkynes. Multivariate statistical approaches for wine classification based on low molecular weight phenolic compounds.
Corroles as anion chemosensors: exploiting their fluorescence behaviour from solution to solid-supported devices. A facile synthesis of cysteine-ferrite magnetic nanoparticles for application in multicomponent reactions-a sustainable protocol. RSC Advances, 2, Synthesis of a 3-hydroxyl-free N-acetyl glucosamine disaccharide. Molecular Informatics, 31, Pro-oxidant effects of Ecstasy and its metabolites in mouse brain synaptosomes.
New quinoline alpha-diimine ligands as fluorescent probes for metal ions: Ultrasound-assisted and conventional synthetic methods. Unexpected reactivity of trifluoromethylated olefins with indole: a mechanistic investigation. Pereira, MMA. Immobilized Ionic Liquids in Organic Chemistry. Indole based cyclooxygenase inhibitors: Synthesis, biological evaluation, docking and NMR screening.
Preparation of N-arylamines from 2-oxoazobicyclo[4. ChemPlusChem, 77, Synthesis of catecholamine conjugates with nitrogen-centered bionucleophiles. Journal of Chemical Information and Modeling, 52, Selective derivatization of D-galactose towards a practical synthesis of C-6 L-fucose analogues.
First application of core-shell Ag Ni magnetic nanocatalyst for transfer hydrogenation reactions of aromatic nitro and carbonyl compounds. Nano-magnetite Fe3O4 as a support for recyclable catalysts in the development of sustainable methodologies. Magnetically recyclable magnetite-ceria Nanocat-Fe-Ce nanocatalyst - applications in multicomponent reactions under benign conditions.
Benign by design: catalyst-free in-water, on-water green chemical methodologies in organic synthesis. Influence of a thioether function in short-bite diphosphine ligands on the nature of their silver complexes: structure of a trinuclear complex and of a coordination polymer. Revisiting Heck-Mizoroki reactions in ionic liquids. Pd-catalysed amination on a soluble polymer support: arylation of anilines with PEG-supported aryl halides. Dual on-off and off-on switchable oligoaziridine biosensor.
NavMol 2. Antioxidising activity of cinnamic acid derivatives against oxidative stress induced by oxidising radicals. A big data approach to the ultra-fast prediction of DFT-calculated bond energies. Journal of Cheminformatics, 5. Mechanisms of P-gp inhibition and effects on membrane fluidity of a new rifampicin derivative, 1,8-dibenzoyl-rifampicin. ChemPlusChem, 78, Efficient microwave assisted synthesis of novel 1,2,3-triazole-sucrose derivatives by cycloaddition reaction of sucrose azides and terminal alkynes.
Applied Sciences-Basel, 3, Synthesis and biological evaluation of alpha-hydroxyalkylphosphonates as new antimicrobial agents. ChemSusChem, 7, Preparation and ion recognition features of porphyrin-chalcone type compounds as efficient red-fluorescent materials. Journal of Materials Chemistry C, 2, Surfactant-free polymeric nanoparticles composed of PEG, cholic acid and a sucrose moiety. Journal of Materials Chemistry B, 2, Magnetically recyclable magnetite-palladium Nanocat-Fe-Pd nanocatalyst for the Buchwald-Hartwig reaction.
PLoS One, 9. Alternative chelating agents: Evaluation of the ready biodegradability and complexation properties. ChemCatChem, 6, New coumarin-corrole and -porphyrin conjugate multifunctional probes for anionic or cationic interactions: synthesis, spectroscopy, and solid supported studies. New gallium III corrole complexes as colorimetric probes for toxic cyanide anion. International Journal of Environmental Research, 8, Design, synthesis and biological evaluation of novel isoniazid derivatives with potent antitubercular activity. Controlled ring-opening polymerization of trimethylene carbonate and access to PTMC-PLA block copolymers mediated by well-defined N-heterocyclic carbene zinc alkoxides.
Group 13 metal Al, Ga, In, Tl complexes supported by heteroatom-bonded carbene ligands. Amide-linked N-methacryloyl sucrose containing polymers. Isoxazolidine-fused meso-tetraarylchlorins as key tools for the synthesis of mono- and bis-annulated chlorins. P,O-Phosphinophenolate zinc II species: synthesis, structure and use in the ring-opening polymerization ROP of lactide, epsilon-caprolactone and trimethylene carbonate.
Enantiopure synthesis of 7- 1-pyrindanyl propargyl ethers as rasagiline analogues via chemical or enzymatic resolution of 1-pyrindanol. Synthesis and antimalarial evaluation of prodrugs of novel fosmidomycin analogues. Formulation of functionalized PLGA polymeric nanoparticles for targeted drug delivery.
Formation of spherical and core-shell polymeric microparticles from glycopolymers.
Investigation of cationic Claisen-type electrophilic rearrangements of amides. Synthesis of cross-linked polymeric microparticles containing hexa-O-benzylsucrose. Antimicrobial and cytotoxic activities of 1,2,3-triazole-sucrose derivatives. L-Serine functionalized clays: Preparation and characterization. Synthesis and structural characterization, by spectroscopic and computational methods, of two fluorescent 3-hydroxypyridinone chelators bearing sulphorhodamine B and naphthalene. On the scope of oxidation of tertiary amines: Meisenheimer rearrangements versus Cope elimination in 2- cyanoethyl azanorbornanes.
Organic Chemistry Frontiers, 3, Hypoxia enhances the malignant nature of bladder cancer cells and concomitantly antagonizes protein O-glycosylation extension. Oncotarget, 7, Chemistry-An Asian Journal, 11, Novel L-prolyl-L-leucylglycinamide PLG tripeptidomimetics based on a 2-azanorbornane scaffold as positive allosteric modulators of the D2R. Journal of Chemical Information and Modeling, 57, Medicinal Chemistry, 13, Toxicity of the amphetamine metabolites 4-hydroxyamphetamine and 4-hydroxynorephedrine in human dopaminergic differentiated SH-SY5Y cells.
Assessing gelling properties of chia Salvia hispanica L. Organic Chemistry Frontiers, 4, N,N'-Dihydroxy-N,N'-diisopropylhexanediamide, a siderophore analogue, as a possible iron chelating agent for hydroponic conditions: metal equilibrium studies. Journal of the Iranian Chemical Society, 14, Frontiers in Microbiology, 8. Developments in the Reactivity of 2-Methylimidazolium Salts. Gemcitabine anti-proliferative activity significantly enhanced upon conjugation with cell-penetrating peptides. Is caffeic acid, as the major metabolite present in Moscatel wine protein haze hydrolysate, involved in protein haze formation?.
Effects of novel triple-stage antimalarial ionic liquids on lipid membrane models. Effect of thermal and high hydrostatic pressure treatments on mango bars shelf-life under refrigeration. Polymeric nanoparticles: A study on the preparation variables and characterization methods. Medicinal Chemistry, 12, Directed electrostatic activation in enantioselective organocatalytic cyclopropanation reactions: a computational study.
Molecular Informatics, 35, Optimisation of gellan gum edible coating for ready-to-eat mango Mangifera indica L. Doxorubicin-loaded galactose-conjugated poly d,l-lactide-co-glycolide nanoparticles as hepatocyte-targeting drug carrier. Marine Drugs, 14, The challenging SO2-mediated chemical build-up of protein aggregates in wines. Synthesis of capsular polysaccharide at the division septum of Streptococcus pneumoniae is dependent on a bacterial tyrosine kinase.
Development of novel ionic liquids based on ampicillin. MedChemComm, 3, Evaluation of solubility and partition properties of ampicillin-based ionic liquids. Chemistry-An Asian Journal, 7, Magnetite-supported sulfonic acid: a retrievable nanocatalyst for the Ritter reaction and multicomponent reactions. Mixed metal MgO-ZrO2 nanoparticle-catalyzed O-tert-Boc protection of alcohols and phenols under solvent-free conditions.
An efficient and expeditious Fmoc protection of amines and amino acids in aqueous media. Convenient Synthesis of 3-Vinyl and 3-Styryl Coumarins. Derepression of a baker's yeast strain for maltose utilization is associated with severe deregulation of HXT gene expression. Membrane partition of bis- 3-hydroxypyridinonato zinc ii complexes revealed by molecular dynamics simulations.
RSC Advances, 8 48 , Chiral monooxazolines as modular copper I -heterocomplex building blocks: investigations on the catalytic asymmetric cyclopropanation of alkenes. Expeditious and novel synthesis of alpha-hydroxyesters via rhodium-NHC catalyzed arylation of ethyl glyoxalate. Transition-metal-catalyzed intramolecular cyclization of amido hetero arylboronic acid aldehydes to isoquinolinones and derivatives. RSC Advances, 5 26 , The benzilic ester rearrangement: Synthesis of labelled compounds and theoretical studies.
Recent multiple transition metal catalysed single-pot reactions. Novel chiral P,O-ligands for homogeneous Pd 0 catalysed asymmetric allylic alkylation reactions. New route to N-alkylated trans-pyrrolidine diols from 2,2,3,3- tetramethoxybutane-protected dimethyl tartrate. Mechanistic and synthetic aspects of the benzilic acid and ester rearrangements. Burke, Anthony J. Chiral oxoperoxomolybdenum VI complexes for enantioselective olefin epoxidation: Some mechanistic and stereochemical reflections.
Approaches towards catalytic asymmetric epoxidations with methyltrioxorhenium VII MTO : Synthesis and evaluation of chiral non-racemic 2-substituted pyridines. Stereoselective alkylation of tartrate derivatives. Organic and Biomolecular Chemistry, 4 12 , Synthesis, characterisation and reactivity of oxodiperoxo-[2- 1-pyrazolyl - 6-menthylpyridine]molybdenum VI : The first chiral 2- 1-pyrazole pyridineoxodiperoxomolybdenum VI complex. Asymmetric synthesis and applications of beta-amino Weinreb amides: asymmetric synthesis of S -coniine.
An efficient and selective method for the epoxidation of olefins using urea-hydrogen peroxide and methyltrioxorhenium VII MTO catalyst with heterocyclic aromatic amines. Isbut-Box: A new chiral C-2 symmetric bis-oxazoline for catalytic enantioselective synthesis. Asymmetric synthesis of anti- 2S,3S - and syn- 2R,3S -diaminobutanoic acid.
Highly stereoselective aldol reaction for the synthesis of gamma-lactones starting from tartaric acid. ChemistrySelect, 1, E methoxy alpha-methoxybenzylidene benzo[b]furan-2 3H -one at K. Thermostabilization of proteins by diglycerol phosphate, a new compatible solute from the hyperthermophile Archaeoglobus fulgidus. Flavonoid epoxides. Part Establishment of the configuration of the diastereomeric solvolysis products of 2-arylmethylenebenzo[b]furan-3 2H -one aurone epoxides.
Some unusual reactions of dimethyldioxirane DMD with flavonoid compounds. Fetching data from CrossRef. This may take some time to load. Jump to main content. Jump to site search. Journals Books Databases. Search Advanced. Current Journals. Archive Journals. All Journals. New Titles. Pick and Choose. Literature Updates. For Members. For Librarians. RSS Feeds. Chemistry World. Education in Chemistry. Open Access. Historical Collection.
Thus, for the purpose of kinetic analysis the reversibility of cleavage cannot be dismissed a priori. In several systems where the possibility of reversibility has been explicitly tested [29, 99, , ] none was found. The absence of reversibility of fragmentation implies that other reactions of the fragments also have low activation energies. These processes include reactions of the radical and ionic fragments with both solvent and the non-cleaving radical ion component of the initial ion pair. The reactions with neutral radical ion precursors are less common.
The most prevalent reactions encompass proton transfer, nucleophile-electrophile reactions, radical-radical ion coupling reactions and ET reactions between fragments and the radical ion components of the initial ion pair Sect. Dioxygen, if present, may additionally complicate the outcome [, ].
It is not surprising, therefore, that a variety of products are obtained in PET systems involving radical ion fragmentations [77, 78, ]. The products may depend on the solvation status of the fragmenting radical ion. In general, the processes in CIP are likely to favor reactions between the fragments and the radical ions.
The lifetimes of fragments are usually too short to allow for reencounter of the reactive intermediates once they separate. Those redox reactions between the fragments and the non-cleaving radical ion that occur in the direction opposite to the original PET warrant a special mention. Such reactions lead to "catalytic" PET systems, i. These reactions may be considered as light-assisted "catalytic" processes wherein the component not directly absorbing the photon energy undergoes a very rapid fragmentation that is equivalent to the homolysis or heterolysis which is excruciatingly slow at ambient temperatures .
A possible mechanistic complication which must be considered in such situations is bond reformation between the "secondary" fragments pair or radicals or ions leading to the apparent reversibility of the cleavage [ b]. This quantum-yield26 Fragmentations by Photoinduced Electron Transfer lowering process should be distinguished from the "true" reversibility of the radical ion fragmentation.
Specific products of a given PET system are generally difficult to predict, since rate constants of the processes involved are only rarely known. Qualitative arguments are not always sufficient because the rates of many competing processes are similar and even small solvent or temperature variations may affect the outcome. The situation should improve, however, with the increasing number of kinetic and redox data that are rapidly becoming available. If predictions are still on shaky ground, the rationalization of the observed products is usually easier, and commonly serves to deduce mechanistic details of the fragmentation reaction.
- New & Forthcoming Titles.
- Instructions for Authors?
- Ethics of the Real: Kant and Lacan (Radical Thinkers)!
- Main navigation!
- Change Password.
The overall quantum yield depends on the efficiency of using the photon energy to generate the reactive intermediates as well as on the efficiency of the cleavage step in relation to other reactions of reactive intermediates, BET being usually the most important competitor. The previous sections described the basic considerations concerning the elementary steps involved in the PET fragmentations.
In practice however, PET systems are usually much more complex than the analysis of elementary steps would suggest. The complications reflect the dynamic nature of these systems. The reactive intermediates are produced in various solvation and spin states. The various ion pairs interconvert in competition with the fragmentation and back-electron-transfer reactions. Other reactions, like proton transfer, radical ion coupling, nucleophilic trapping, etc. A simplified scheme of a PET system includes at least five kinetically defined intermediates which may undergo fragmentation reaction Scheme 3.
In principle, all reactions of Scheme 3 except kbe0 may be reversible. A detailed kinetic analysis is usually not practical under such circumstances. In nonpolar solvents contact ion pairs dominate. As discussed previously Sect. The fragmentation rates are usually assumed to be independent of ion pairing, although quantitative information on that respect is not available. In photochemical systems the steady-state concentrations of reactive intermediates are very low typically less than M with conventional lamps or less than 5 M with intense laser sources.
Such low concentrations essentially exclude any kinetically second-order processes between the reactive intermediates geminate processes dominate and minimize the probability of re27 P. The SSIP separation ksep is rather structure insensitive, providing that typical aromatic compounds are involved. The solvent interpenetration between the reactive intermediates depends on the charge status of the pair. If one of the components is uncharged, the viscosity of the medium is the dominant factor. If the components have opposite charges the polarity of the solvent plays a major role.
In non-polar solvents such as benzene, chlorobenzene or hexane these rates are not measurable  too slow to compete with other processes. The rates seem to be affected by the ability of the system to stabilize the charge internally within the components of the ion pair. Thus, the more "stable" ions larger internal delocalization are solvated slower [53, 59], although the effect may be small or even absent in some systems .
Added salts are able to intercept CIP giving rise to "salt effects" [52, 53]. These effects usually manifest themselves in solvents of moderate polarity. In such situations, the reactive ions within the geminate ion pairs are exchanged by redox inactive ones. Again the solvent polarity plays the dominant role. The typical values ofksep vary from ca. The empirical Weller equation  Eq. Several strategies have been developed to increase the efficiency of the follow up reaction based on perturbation of ion-pair dynamics. All of them intend to increase the fraction of more solvated ions or increase the rate of ion separation.
The strategies include using polar solvents , adding salts [20, b, ], using charged acceptors or donors to eliminate Coulombic attraction , increasing steric bulk  in the non-cleaving acceptor or donor and using secondary acceptors [, ] or donors  whose radical ions will serve as the ultimate redox agent for the cleaving component. The spin status of the ion pair is another crucial variable affecting the overall efficiency of the process. The forward electron transfer from or to a diamagnetic molecule is not affected by the spin status of the excited component.
The back electron transfer, however, is forbidden within the triplet ion pairs it would violate Pauli's exclusion principle. In situations like that the intersystem crossing will very often determine the efficiency of BET. In practice, the triplet state acceptors or donors lead to overall efficiencies that are higher than those observed with singlet state acceptors or donors [38,78, , , ]. An additional bonus is the fact that triplet states have longer lifetimes  and are efficiently ET-quenched with lower concentrations of the ground state component.
Quinones and ketones are the most common triplet acceptors, while aromatic amines often serve as triplet donors. The ion pair spin multiplicity may be a valuable tool to affect the BET rates and to probe the ion pair dynamics via magnetic field effects . Even weak magnetic fields are known to influence relative probabilities of singlet and triplet reactions .
Many bond scission reactions and rearrangements in cyclic radical ions have been successfully explored using this approach. Both structural data spin densities and approximate kinetic informations are indirectly available from such experiments . These reactions are chain processes and photoinduced ET is involved only in the initiation step, which is usually poorly defined.
The reactions may also be initiated by other means, not involving absorption of a photon. The SRNI reactions and related redox-activation processes have been recently extensively reviewed [72a, , ] and will not be discussed here. Maslak There are also several reviews dealing with various facets of fragmentation reactions in photogenerated radical ions  as well as more general reviews touching on that subject .
The examples discussed below were arbitrarily chosen to illustrate certain fundamental and practical aspects summarized in the previous sections. If one of the a-substituents is hydrogen, deprotonation reactions often compete [, ] leading often to protonation and further reduction of the radical anion of the acceptor.
The C-C fragmentations are thermally activated . The apparent activation barriers determined from the temperature dependence of the reaction efficiency are almost identical to the estimated AGe's or AHm'S . The ability of the system to delocalize the charge in the transition state facilitates the cleavage [, ]. Thus, electron donating substituents Y accelerate the reaction even in cases where the Y-substituted fragments will become radicals after the C-C bond scission .
In most cases only one pair of the possible four primary products Scheme 4 is formed . The electron apportionment to the fragments is determined by thermodynamic stability of the two possible ions. Only in cases where both ions have similar stability the reduction potentials within mV of each other are all four products formed . In chemically "clean" systems the ratio of cationic fragments may be used to determine the difference in their reduction potentials .
The "cleanness" of the system is determined by the secondary reactions of the fragments. The cations are usually trapped by MeOH, giving high yield of ethers. The reaction of diphenylmethyl or cumyl cations with MeOH commonly present in molar concentration is slower than the diffusion limit s s- 1 M - a [, ] , but apparently sufficiently rapid to prevent their reduction by the radical anion of the cyanoaromatic component.
Since this redox process is exergonic by 1. The reduction products of the primary cationic fragment are observed in systems where the fragmentation is rapid enough [b, , ] to compete with ion solvation. In the absence of alcohol in the medium, or in cases where the benzyl fragment carries an a-OH substituent, a rapid deprotonation of the cation is often observed . The fate of the primary radical fragment depends on its reduction potential.
Thus, if the reduction of the radical by the radical anion of the cyanoaromatic component is exergonic diphenylmethyl derivatives , cumene derivatives with electron-withdrawing Y substituents [b] , the carbanion produced is rapidly protonated by the solvent Scheme 4. If the reduction is endergonic the 31 P. Maslak radical-radical anion coupling takes place [, ], often in the ipso position, which is followed by the expulsion of CN-. The characteristic radical-radical coupling products are also commonly detected [, ]. The reaction is often run in the presence of dioxygen which serves as a secondary acceptor, intercepting the cyanoaromatic radical anions and trapping the radical fragments [, ].
Alcohols, peroxides, aldehydes and ketones derived from the fragments are observed under such conditions. The unpaired electron is strongly localized on the amine nitrogen, and the bond cleavage is of the re-re type. The loss of H in the form of a proton or hydrogen atom is a common competing reaction, since the electron removal from the amine activates both the geminal N - H and the vicinal C - H bonds for heterolysis and homolysis .
A variety of acceptors, from inorganic ruthenium complexes via organic dyes thioindigo to quinones fl-lapachone and cyanoaromatics serve as excited-state component of the PET systems. Based on thermodynamic considerations the primary fragments should consist of the amine-stabilized cation an iminium ion if the fl-C-C bond is cleaved and the radical derived from the other fragment. Since this radical often carries an amino or hydroxy substituent Scheme 5 it is susceptible to further oxidation followed by hydrolysis.
Thus, two-electron oxidation products are often encountered. These include aldehydes, ketones, dealkylated amines etc. The chemical yields are usually high and quantum yields vary from low to moderate, often strongly depending on the solvent and identity of the acceptor. A characteristic feature of some of these reactions is the dependence of their efficiency on the basicity of the radical anion .
The differences are especially manifested in non-polar solvents, where the CIP are expected to dominate. Some of these cleavage processes are more efficient than expected, based on the thermodynamic evaluations of the unassisted fragmentation Sect. Also a stereochemical preference for cleavage is observed for erythro isomers as compared to the threo isomers Scheme 6.
The stereochemical preference disappears in acetonitrile if biphenyl is used as a co-sensitizer . These observations are accounted for by radical anion base assisted fragmentations, where anti stereochemistry, analogous to that in elimination reactions, is favored. The intramolecular hydrogen bonding in the threo isomers leads to gauche arrangements of the reactive substituents, diminishing the rate of assisted fragmentation . In more polar solvents and under circumstances where the free ions are produced Ph-Ph co-sensitization , the unassisted process is observed providing that the energetics are not prohibitive.
The iodonium and sulfonium salts Scheme 7 are the most widely studied, but other salts derived from halogens chloronium and bromonium , or other elements N, P etc behave similarly . These salts may act as electron acceptors, giving a neutral reduction product. Although neutral, these species may, therefore, be considered as "radical anions" as discussed in Sect.
In some instances ET may be dissociative. The cleavage of these species may produce a radical and a neutral most likely or an anion and a radical cation less likely. The photochemistry of these salts is, however, rather complicated [7, ]. Both direct and energy-transfer sensitized cleavages are observed with heterolysis and homolysis products detected, but the details are not yet completely understood.
Many of these salts are able to rapidly generate Bronsted acids by rather complicated pathways and are used to initiate Rz. The borate salts Scheme 7 constitute an analogous group of electron donors [8, 29, ]. In this case, PET from the anions to cationic acceptors Sect. If one of the substituents is an alkyl group the one-electron bond breaks rapidly possibly in a dissociative process , forming a radical and a neutral.
These systems also find applications in imaging. A related, "reverse-charge" situation is found in systems where the acceptor and donor are directly connected via a scissile bond. The intramolecular electron transfer generates a zwiterionic intermediate Scheme 8. This intermediate may be considered to be doubly activated for fragmentation [77, ]. Thermodynamic analysis Sect. Both homolytic cleavage giving a pair of ions and heterolytic cleavage giving a pair of radicals may have highly negative free-energies and high rates of fragmentation [77, ].
The homolytic alternative may have a larger driving force than the heterolytic path if the fragments are stable ions . The dynamics of such a system may be quite complex, with various deactivation pathways available [77, ]. The radical anion fragments rapidly z P. Maslak takes place.
Occupational Exposures in Petroleum Refining; Crude Oil and Major Petroleum Fuels
Thus, the triad is equivalent to the contact ion pair and the geminate radical pair at the same time. The dynamics of this triad has been probed in detail for various anthracene donors , providing direct data for the ion pair interconversions Sect. The fate of the triad is determined by the stability of the radical cation component and the solvent polarity. The resulting cyclohexadienyl cation may lose a proton, giving the nitration product directly, or may be trapped by the trinitromethanide, giving the adduct that can spontaneously eliminate nitroform, and lead also to the nitration product.
In less polar solvents or in the case of less stable radical cations such as anisole derivatives the ion collapse process dominates. The cyclohexadienyl radical produced transfers a hydrogen atom to NO2, giving an aromatic trinitromethyl derivative. If the radical cation contains also a scissile bond, as found in the bicumene derivatives [d], aromatic nitration or trinitromethylation depending on solvent polarity may compete with bond scission. Thus, in addition to the products of aromatic substitution benzylic derivatives are observed. If the C - C bond cleavage is rapid a tetrad of reactive intermediates two ions and two radicals forms.
The reactivity of the tetrad is dominated by the ion-collapse processes. The carbon-centered radicals are oxidized by TNM present in large excess, leading to a triad of reactive intermediates similar to the original tetrad Scheme The competition between the various processes is governed by solvent polarity as well as by the rates of C - C bond cleavage, which in turn are controlled by substitution patterns [d]. The C - C bond cleavage of pinacol or bicumene derivatives have been used to compare the overall efficiency of two alternative methods of generating reactive radical ions [, a].
This generalization applies to systems involving singlet excited states  as well as triplet excited states [, a-l, the latter having the advantage of the spin-forbidden nature of BET. Nevertheless, the results of such analyses agree with the data obtained for BET by different methods Sect. Thus, the difference between BET in singlet 37 P. The complexity of the ion pair dynamics may be illustrated by the photoinduced ET from the excited state tetramethylbenzidine TMB to cyanobicumene BC derivatives Fig.
At low concentrations of acceptors, only TMB 3 is quenched yielding triplet ion pairs. The fragmentation of the radical anion or ion separation see below competes with BET. Since BET is spinforbidden, the overall reaction is relatively efficient. At higher concentration of the acceptor, more excited state molecules of TMB are quenched, but an increasing fraction of them is in the singlet state.
This fraction gives singlet ion pairs, within which BET is more efficient. The overall efficiency of the photoreaction, therefore, does not increase linearly with increasing concentration of the acceptor . Thus the quantum yields for these compounds reflect a competition between BET and ion separation. The quantum yield for disappearance of BC as a function of [BC].
The rates of cleavage of BC-d and BC-e are faster than the rate of ion separation and the quantum yields reflect the competition between BET and mesolysis. In general, BET within triplet pairs is most likely controlled by intersystem crossing rates, and thus will strongly depend on the system under investigation, with such factors as presence of heavy atoms or magnetic fields playing an important role.
The research in the author's laboratory was sponsored by grants from the National Science Foundation and the Petroleum Research Fund. The contributions of my coworkers H. Abdel, S. Asel, B. Bocknack, W. Chapman, Jr. Funke, J. Kula, D. Malinski, J. Narvaez, T. Vallombroso and B. Watson are acknowledged with gratitude. Mariano PS ed and Advances in electron transfer chemistry.
Mattay J ed Top. Marcel Dekker, New York, vol 6, p 7. Saeva FD Top. Elsevier, Amsterdam, p See for example: a Roth HD Acc. Maslak Chem. JAI Press, vol 2. Faraday Soc. Eberson L Electron transfer reactions in organic chemistry. Springer, Berlin Heidelberg New York Depending on the value of V, only the first few terms are of importance.
Elsevier, Amsterdam, p 1. Acta 45A: Marcel Dekker, New York, vol 6, p For a review see: Chibisov K i Russ. Vondenhof M Top. Marcus Y Ion solvation. Wiley, Chichester Elsevier, Amsterdam, p ; d Balzani V Tetrahedron Maslak Academic Press, New York, vol 2, p A: Chem. Am, Chem. Acta 41A: Acta Sav6ant J-M J. See for example: a Nelsen SF Acc. See for example: a Clark T A handbook of computational chemistry. Cheng J-P J. Marcel Dekker, New York For a computational approach to radical ion fragmentation see: a Clark T J. Kimura N, Takamuku S Bull. Masnovi J J. Chapman, WH, Jr. Takamuku S J.
Perkin Trans. ACS symposium series, vol Weller A Pure Appl. Recent work on the mechanisms of the photohydrodehalogenation of haloarenes, with an emphasis on polyhaloarenes, and the related mechanisms of phototransformations of aliphatic hatocompounds are reviewed. Attention is focused on the nature of the excimer in the photochemical transformations of haloarenes without additional electron transfer reagent and on the nature of the exciplex formed in phototransformations in the presenceof electron transfer reagent.
Applications of surface catalyzed photochemical transformations and photohydrodehalogenation of polyhaloarenes to toxic waste disposal is discussed. Topics in Current Chemistry, Vol. Freeman and S. A, Hatlevig 1 Introduction The photodehalogenation of haloarenes has attracted the attention of scientists interested in reaction mechanisms, synthesis, and environmental processes .
Considerable effort has been devoted to developing our understanding of the mechanism of photodehalogenation of monohaloarenes. Since in the environment polyhaloarenes are of more importance than their monohalo parents, interest has been stimulated in applying current theory to achieving an understanding of the mechanistic features of the phototransformation of polyhaloarenes. In the case of monochloroarenes, the initial view of the mechanistic options was that the excited singlet usually possesses sufficient energy to undergo C-C1 bond homolysis, but the triplet state formed by intersystem crossing is generally too low in energy to react in this manner without help in the form of additional thermal energy, exciplex formation, or strain relief.
The C-C1 bond homolysis of the singlet generates aryl radical which leads to products Eq. The radical anion is viewed as undergoing fission to aryl radical and chloride ion Eq. Direct irradiation of 1 in acetonitrile at nm gives 1,2,3,5-tetrachloro- 2 , 1,2,4,5-tetrachloro- 3 and 1,2,3,4-tetrachtorobenzene 4 as the only products at low conversions of 1. In addition, the quantum yield of disappearance of 1 was found to increase with increasing concentrations of 1 accompanied by a steady change in the relative ratios of the regioisomers .
The kinetic scheme which has evolved is illustrated in Scheme 1. Since butyrophenone absorbs all the incident light at this wavelength range, the 48 Photochemistryof polyhalocompounds C I. Actual measurement of the quantum yield of intersystem crossing of 1 in acetonitrile using the eis-trans isomerization of cis-piperylene , however, gave a value of 0. Further, the reaction was quenched very efficiently by the triplet quencher fumaronitrile .
Figure 1 shows the Stern-Volmer quenching plot for the reaction at nm. The function is linear with an intercept of 1 at low quencher concentrations, but as the concentration is increased is concave downward. Using steady-state methods, it can be demonstrated that this quenching pattern signals the presence of both singlet and triplet reactions . The plateau in Fig. It thus appears that the observed quantum yield is the sum of the quantum yields of singlet and triplet processes .
Reaction from the singlet state could occur through direct fission of the C-C1 bond which is feasible in terms of the energy of the singlet state 49 P.
In order to determine the possibility of reaction via a singlet excimer species similar to that depicted for the triplet state, the fluorescence lifetime of 1 was measured as a function of its concentration in ethanol. The reaction from the singlet state thus occurs through the direct fission of the C-C1 bond. Hatlevig The simplest mechanistic picture is that of a three way competition which involves direct homolysis of singlet and triplet states and C-C1 fragmentation of the radical anion-like moiety of the excimer.
The major routes to product are via direct fission of triplet state and reaction through the intermediary of excimer with only a minor contribution of singlet . The scope of the photohydrodehalogenation process has been tested by an investigation of the photochemistry of pentafluorobenzene 5.
This clearly supports product formation via an excimer with no competition from direct fission . Since the reported quantum yield of the intersystem crossing process for biphenyl is 0. Actual measurement of the quantum yield of intersystem crossing did indeed give a value of 0.
The triplet energy of 4-bromobiphenyl Thus, direct formation of product from the triplet state may be inhibited. However, excimer formation through an electron transfer process from the ground state to the triplet state of BpBr may provide an alternative pathway to the product. Application of the steady state assumption provides us with Eq. Also irradiation of a very dilute solution of BpBr 1 x 10 -4 M gave no biphenyl photoproduct. The involvement of only one excited state for debromination was supported by quenching studies using cis1,3-pentadiene  and fumaronitrile  in acetonitrile solvent.
This result is in harmony with the view that the triplet excimer is the sole product determining intermediate for the debromination of 4-bromobiphenyl. If reaction were to occur from the singlet state as well as via triplet excimer, the Stern-Volmer plot would be linear, with a positive slope, at low concentrations of the quencher but would flatten out as the concentration of the quencher increases. Evidence bearing on the nature of the bromobiphenyl excimer was obtained by determining the dependence of the rate constant for the formation of excimer k2 upon solvent polarity.
Solvents of differing polarity based on the E x polarity scale  were chosen and the quantum yields were determined as a function of concentration of BpBr for each solvent, plots of the inverse of the quantum yield versus the inverse of the concentration of BpBr 53 P. Freemanand S. Hatlevig exhibiting a linear relationship for each solvent system. Using the least squares method, the best fitted first order equation correlating the inverse of quantum yield and the inverse of concentration for each solvent system was obtained.
The k2 values derived from Eqs. A comparison of equation D with E and G reveals that the cavity term is more important than nucleophilic solvent participation since there is a considerably greater decrease in the correlation coefficient when the cavity term is omitted. The positive term in 62 is consistent with the reorganization of solvent-solute and solvent-solvent interactions in the formation of triplet excimer.
Hatlevig s-O-. H A solvent molecules on the inside faces of the two benzene rings would be stripped away providing a larger number of solvent-solvent interactions. A small amount of charge transfer might well induce the solvent nucleophilic assistance illustrated in A. Overall a comparison with the solvolysis of tert-butyl halides reveals that the solvent effects for excimer formation are quite muted. In a complementary study an interest in the mechanistic pathways which are operative in micellar media led to a characterization of the triplet pentachlorobenzene excimer.
Pentachlorobenzene 1 was irradiated in 0. The major dechlorinated products were the tetrachlorobenzenes 24 with an accompanying trace of trichlorobenzenes. Bromotetrachlorobenzenes were observed as byproducts . Building on our results in homogeneous solution, the mechanism for photohydrodehalogenation is represented in Scheme 3.
An approach based upon the statistics of pentachlorobenzene distribution in the CTAB solution was employed . Using Poisson statistics, the distribution of pentachlorobenzene is given by Eq. The total probability of encounters between excited and ground state haloarene is given in Eq. Unexpectedly in the photolysis of pentachlorobenzene in CTAB, bromotetrachlorobenzenes 7, 8 and 9 were formed as byproducts. The composition of the bromotetrachlorobenzene fraction at three different concentrations of 1 is listed in Table 2.
One might consider homolysis of the C-C1 bond in the triplet, followed by electron transfer from the aryl radical to chlorine to generate aryl cation which then reacts with bromide ion, using as a model the mechanism put forward to explain the phenol products from the photolysis of 4-chlorobiphenyl in water . However, this mechanism seems unlikely, since the excited chloroarene is in the micellar interior and such a mechanism has not been observed in hydrocarbon solvents.
In addition, this 57 P. Hatlevig Table 2. Distributions of byproduct bromotetrachlorobenzene Local concentration of I Cm Percentage ratio of products" 0, 0. Instead, a mechanism similar to that put forward by Soumillion and Wolf, who reported that photoreduction and photosubstitution occurred simultaneously in the irradiation of chlorobenzene and chloroanisoles, is favored .
Subsequent to excimer formation, the bromide ion reacts with the radical cationic moiety of the excimer to produce a pentadienyl radical species which loses chlorine to form product Scheme 4. Three additional experiments were run to test this mechanism: a a solution of 2. In experiment a the concentration of pentachlorobenzene is in the region where excimer formation is dominant . In experiments b and c photochemical hydrodechlorination is achieved without the generation of excimer.