|
| ||
|
|
||
Cation Radical (cation + radical)
Selected AbstractsChemInform Abstract: Decarboxylative Reduction of Free Aliphatic Carboxylic Acids by Photogenerated Cation Radical.CHEMINFORM, Issue 15 2008Yasuharu Yoshimi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Cation Radical [3 + 2] Cycloaddition of Chalcone Epoxides: A Facile Synthesis of Highly Substituted Tetrahydrofurans.CHEMINFORM, Issue 25 2004Congde Huo Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Asymmetric Cyclization via Oxygen Cation Radical: Enantioselective Synthesis of cis-4b,9b-Dihydrobenzofuro[3,2-b]benzofurans.CHEMINFORM, Issue 21 2002Kouta Masutani Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Voltammetric Assay of Naproxen in Pharmaceutical Formulations Using Boron-Doped Diamond ElectrodeELECTROANALYSIS, Issue 11 2005V. Suryanarayanan Abstract The electrooxidation of naproxen was studied, for the first time, using boron-doped diamond (BDD) electrode by cyclic and differential pulse voltammetry (CV and DPV) in nonaqueous solvent supporting electrolyte system. The results were also compared with glassy carbon electrode (GC) under the same conditions. Naproxen undergoes one electron transfer resulting in the formation of cation radical for the first electrooxidation step, which follows other chemical and electrochemical steps such as deprotonation, removal of another electron and the attack of nucleophile (ECEC mechanism). BDD electrode provided higher signal to background ratio, well resolved and highly reproducible cyclic voltammograms than the GC electrode. With a scan rate of 50,mV s,1 and pulse height of 50,ms, respectively, the DPV technique was able to determine the naproxen concentrations in the range of 0.5 to 50,,M with a detection limit of 30,nM. The influence of interference compounds namely 2-acetyl-6-methoxy naphthalene (AMN) on naproxen oxidation can also be followed successfully. Moreover, the percentage of AMN present in the standard chemical form of a mixture containing naproxen can be found accurately. Rapidity, precise and good selectivity were also found for the determination of naproxen in pharmaceutical formulations. [source] BODIPY-Tetrazine Multichromophoric DerivativesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2010Cécile Dumas-Verdes Abstract New dyes based on BODIPY and tetrazine fluorophores connected through a phenyl spacer have been synthesized and their absorption, emission and electrochemical properties characterized. BODIPY can be reversibly oxidized into a stable cation radical whereas tetrazine can be reduced to a stable anion radical. The electrochemical and absorption studies demonstrate that both fluorophores behave independently. The bichromophoric compounds show an expected very weak emission by the BODIPY core that is quenched by the phenoxytetrazine mainly through energy transfer. DFT calculations and spectroelectrochemistry experiments demonstrate that photoinduced electron transfer and energy transfer remain possible when the tetrazine moiety is reduced electrochemically, which prevents switching on of the fluorescence of the BODIPY unit. [source] Properties of pyranose dehydrogenase purified from the litter-degrading fungus Agaricus xanthodermaFEBS JOURNAL, Issue 3 2007Magdalena Kujawa We purified an extracellular pyranose dehydrogenase (PDH) from the basidiomycete fungus Agaricus xanthoderma using ammonium sulfate fractionation and ion-exchange and hydrophobic interaction chromatography. The native enzyme is a monomeric glycoprotein (5% carbohydrate) containing a covalently bound FAD as its prosthetic group. The PDH polypeptide consists of 575 amino acids and has a molecular mass of 65 400 Da as determined by MALDI MS. On the basis of the primary structure of the mature protein, PDH is a member of the glucose,methanol,choline oxidoreductase family. We constructed a homology model of PDH using the 3D structure of glucose oxidase from Aspergillus niger as a template. This model suggests a novel type of bi-covalent flavinylation in PDH, 9- S -cysteinyl, 8-,- N3-histidyl FAD. The enzyme exhibits a broad sugar substrate tolerance, oxidizing structurally different aldopyranoses including monosaccharides and oligosaccharides as well as glycosides. Its preferred electron donor substrates are d -glucose, d -galactose, l -arabinose, and d -xylose. As shown by in situ NMR analysis, d -glucose and d -galactose are both oxidized at positions C2 and C3, yielding the corresponding didehydroaldoses (diketoaldoses) as the final reaction products. PDH shows no detectable activity with oxygen, and its reactivity towards electron acceptors is rather limited, reducing various substituted benzoquinones and complexed metal ions. The azino-bis-(3-ethylbenzthiazolin-6-sulfonic acid) cation radical and the ferricenium ion are the best electron acceptors, as judged by the catalytic efficiencies (kcat/Km). The enzyme may play a role in lignocellulose degradation. [source] Plasma antioxidative activity during atorvastatin and fluvastatin therapy used in coronary heart disease primary preventionFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 1 2004Jan Kowalski Abstract We estimated the effect of atorvastatin and fluvastatin on plasma antioxidative activity used in coronary heart disease (CHD) primary prevention. Anti-oxidative activity of blood plasma was determined by Bartosz et al. method [Curr. Top. Biophys. (1998)22:11,13], based on reduction of preformed cation radical of 2,2,azinobis(3-ethylbenzothiazoline-6-sulphonic acid) by blood plasma. The study comprised 35 patients with CHD risk who were randomly divided into two groups. The atorvastatin group comprised 17 patients who were administered the drug orally in a daily dose of 10 mg and the fluvastatin group consisted of 18 patients on an oral dose of 40 mg once daily. The control group comprised 12 healthy subjects with no drug administration. Blood samples were collected from cubital vein before and after 6-week therapy. Significantly (P < 0.05) increased , in comparison with the initial values , antioxidative activity of blood plasma was found in atorvastatin and fluvastatin groups after 6-week therapy. Moreover, the increase in antioxidative plasma activity in atorvastatin group was significantly higher in comparison with the fluvastatin group. The results of our study have demonstrated that atorvastatin and fluvastatin have an additional mechanism independent of the effect on cholesterol concentration. Thus, we presume that administration of these statins in CHD risk patients may have a beneficial effect. [source] Investigation of the electropolymerization of o -toluidine and p -phenylenediamine and their electrocopolymerization by in situ ultraviolet,visible spectroelectrochemistryJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Guirong Zhang Abstract Under the conditions of potentiostatic electrolysis, the electropolymerization of o -toluidine (OT) and para -phenylenediamine (PPDA) and the electrocopolymerization between OT and PPDA on an indium tin oxide (ITO) conductive glass electrode at potentials of 0.7, 0.8, and 0.9 V were studied in detail by in situ ultraviolet,visible (UV,vis) spectrometry in 0.5 mol/L sulfuric acid media. It was shown that both OT and PPDA could be electropolymerized on the ITO electrode, which depended on the applied electrolysis potential and the concentration of the monomer. Furthermore, in situ UV,vis spectra indicated that the electrocopolymerization between OT and PPDA could happen. The presence of PPDA not only promoted polymerization but also accelerated polymerization, which was attributed to the formation of an intermediate result from the coupling of PPDA and the toluidine monomer cation radical. PPDA could be incorporated into the copolymer to make the copolymer have a phenazine or phenazine-like cyclic structure, which was proven by the reflectance Fourier transform infrared spectra of the polymer and copolymer. The scanning electron microscopy morphology images of the polymers obtained showed that, in addition to accelerating polymerization, PPDA also could change the method of nucleation for the polymer to make the copolymer possess a fibrous surface morphology. The diameter of the fibroid copolymer was about 100 nm, and the length of that reached about 1000 nm. In the article, a newer concerned mechanism of copolymerization was proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Triplet state and phenoxyl radical formation of 3, 4-methylenedioxy phenol: a combined laser flash photolysis and pulse radiolysis studyJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2007Ravi Joshi Abstract Formations of triplet state, molecular cation radical, and phenoxyl radical of 3,4-methylenedioxy phenol (sesamol, SOH) in organic solvents have been investigated by laser photolysis as well as pulse radiolysis techniques. Photolysis of SOH in cyclohexane has been found to produce both triplet state (,max,,,480,nm) and phenoxyl radical (425,430,nm) of SOH by mono-photonic processes. However, radical cation (,max,=,450,nm) and phenoxyl radical of SOH have been observed on radiolysis in cyclohexane. Further, radiolysis of SOH in benzene has been found to produce phenoxyl radical only. Mechanism of phenoxyl radical formation by photo-excitation of SOH has been studied and triplet energy level of SOH is estimated to lie between 1.85 and 2.64,eV. Copyright © 2007 John Wiley & Sons, Ltd. [source] Multi-frequency EPR and Mössbauer spectroscopic studies on freeze-quenched reaction intermediates of nitric oxide synthase ,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005C. Jung Abstract It is believed by analogy to chloroperoxidase (CPO) from Caldariomyces fumago that the electronic structure of the intermediate iron-oxo species in the catalytic cycle of nitric oxide synthase (NOS) corresponds to an iron(IV) porphyrin- , -cation radical. Such species can also be produced by the reaction of ferric NOS with external oxidants within the shunt pathway. We present multi-frequency EPR (9.6, 94, 285 GHz) and Mössbauer spectroscopic studies on freeze-quenched intermediates of the oxygenase domain of nitric oxide synthase which has reacted with peroxy acetic acid within 8,200 ms. The intermediates of the oxygenase domain of both the cytokine inducible NOS (iNOSox) and the neuronal NOS (nNOSox) show an organic radical signal in the 9.6-GHz spectrum overlapping with the spectrum of an unknown species with g -values of 2.24, 2.23 and 1.96. Using 94- and 285-GHz EPR the organic radical signal is assigned to a tyrosine radical on the basis of g -values (i.e. Tyr*562 in nNOSox and Tyr*341 in iNOSox). Mössbauer spectroscopy of 57Fe-labeled unreacted nNOSox shows a ferric low-spin heme-iron (, = 0.38 mms,1, ,EQ = 2.58 mms,1). The reaction of nNOSox with peroxy acetic acid for 8 ms leads to the disappearance of the magnetic background characteristic for native nNOSox and a new species with , = 0.27 mms,1 and ,EQ = 2.41 mms,1 is detected at 4.2 K which does not resemble the parameters typical for a Fe(IV) center. It is proposed that this intermediate species corresponds to a ferric low-spin species which magnetically couples to an amino acid radical (presumably Trp*409). Copyright © 2005 John Wiley & Sons, Ltd. [source] Primary Photophysical Properties of Moxifloxacin, A Fluoroquinolone AntibioticPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2008Fernando Lorenzo The photophysical properties of the fluoroquinolone antibiotic moxifloxacin (MOX) were investigated in aqueous media. MOX in water, at pH 7.4, shows two intense absorption bands at 287 and 338 nm (, = 44 000 and 17 000 dm3 mol,1 cm,1, respectively). The absorption and emission properties of MOX are pH-dependent, pKa values for the protonation equilibria of both the ground (6.1 and 9.6) and excited singlet states (6.8 and 9.1) of MOX were determined spectroscopically. MOX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Phosphorescence from the excited triplet state in frozen ethanol solution has a quantum yield of 0.046. Laser flash photolysis and pulse radiolysis studies have been carried out to characterize the transient species of MOX in aqueous solution. On laser excitation, MOX undergoes monophotonic photoionization with a quantum yield of 0.14. This leads to the formation of a long-lived cation radical whose absorption is maximum at 470 nm (,470 = 3400 dm3 mol,1 cm,1). The photoionization process releases hydrated electron which rapidly reacts (k = 2.8 × 1010 dm3 mol,1 s,1) with ground state MOX, yielding a long-lived anion radical with maximum absorption at 390 nm (,390 = 2400 dm3 mol,1 cm,1). The cation radical of MOX is able to oxidize protein components tryptophan and tyrosine. The bimolecular rate constants for these reactions are 2.3 × 108 dm3 mol,1 s,1 and 1.3 × 108 dm3 mol,1 s,1, respectively. Singlet oxygen sensitized by the MOX triplet state was also detected only in oxygen-saturated D2O solutions, with a quantum yield of 0.075. [source] Theoretical studies on high-valent manganese porphyrins: Toward a deeper understanding of the energetics, electron distributions, and structural features of the reactive intermediates of enzymatic and synthetic manganese-catalyzed oxidative processesISRAEL JOURNAL OF CHEMISTRY, Issue 1 2000Abhik Ghosh We present here a relatively comprehensive theoretical study, based on nonlocal density functional theory calculations, of the energetics, electron distributions, and structural features of the low-lying electronic states of various high-valent intermediates of manganese porphyrins. Two classes of molecules have been examined: (a) compounds with the general formula [(P)MnX2]0 (P = porphyrin; X = F, Cl, PF6) and (b) high-valent manganese-oxo species. For [(P)Mn(PF6)2]0, the calculations reveal a number of nearly equienergetic quartet and sextet states as the lowest states, consistent with experimental results on a comparable species, [(TMP)Mn(ClO4)2]0 (TMP = tetramesitylporphyrin). In contrast, [(P)MnCl2]0 and [(P)MnF2]0 have a single well-defined S = 3/2 Mn(IV) ground state, again in agreement with experiment, with the three unpaired spins largely concentrated (>90%) on the manganese atom. Manganese(IV)-oxo porphyrins have an S = 3/2 ground state, with the three unpaired spins distributed approximately 2.3:0.7 between the manganese and oxygen atoms. The metal-to-oxygen spin delocalization, as measured by the oxygen spin population, for MnIV = O porphyrins is less than, but still qualitatively similar to, that in analogous iron(IV)-oxo intermediates, indicating that the MnIV = O bond is significantly weaker than the FeIV = O bond in an analogous molecule. Thus, the optimized metal,oxygen bond distances are 1.654 and 1.674 Å for (P)FeIV(O)(Py) and (P)MnIV(O)(Py), respectively (Py = pyridine). This is consistent with the experimental observation that MnIV = O stretching frequencies are over 10% lower than FeIV = O stretching frequencies for analogous compounds. For [(P)Mn(O)(PF6)]0, [(P)Mn(O)(Py)]+, and [(P)Mn(O)(F)]0, the ground states clearly correspond to a (dxy)2 Mn(V) configuration and the short Mn,O distances of 1.541, 1.546, and 1.561 Å for the three compounds, respectively, reflect the formal triple bond character of the Mn,O interaction. Interestingly, the corresponding Mn(IV)-oxo porphyrin cation radical states are calculated to be a few tenths of an electrovolt higher than the Mn(V) ground states, suggesting that the Mn(IV)-oxo porphyrin cation radicals are not likely to exist as ground-state species. [source] ESR/DFT study of bis-iminophosphorane cation radicalsMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2007Adil Matni Abstract Bis-iminophosphoranes containing various types of linkers between two R3PN moieties were electrochemically oxidized at controlled potential in situ in the electron spin resonance (ESR) cavity. For linkers constituted of phenylenes, conjugated phenylenes or merely a dicyanoethylenic bond, this oxidation led to well-resolved ESR spectra which were characterized by their g values and by their 1H, 14N and 31P isotropic hyperfine constants. These coupling constants agree with those calculated by DFT for the corresponding cation radicals. Experimental and theoretical results clearly indicate that in these species the unpaired electron is mostly delocalized on the bridge and on the nitrogen atoms while the spin density on the phosphorus atoms is particularly small. Cyclic voltammetry and ESR spectra show that the nature of the bridge between the two iminophosphoranes considerably influences the oxidation potential of the compound as well as the stability of the radical cation. Information about the conformation of the precursor containing two Ph3PN moieties separated by a C(CN)C(CN)group was obtained from its crystal structure. Copyright © 2007 John Wiley & Sons, Ltd. [source] Oxidative polymerization of N -vinylcarbazole in polymer matrixPOLYMER INTERNATIONAL, Issue 6 2001Belkis Ustamehmeto Abstract A new class of soluble conductive poly(N -vinylcarbazole) (PVCz) compounds has been developed by oxidative matrix polymerization of N -vinylcarbazole (NVCz) by Ce(IV) in the presence of poly(ethylene glycol) (PEG). PEG was found to be a more suitable matrix with which to obtain a stable homogenous ternary complex solution when compared with poly(acrylic acid) (PAA) and poly(vinylpyrrolidone) (PVP). The role of PEG, NVCz and Ce(IV) concentration, order of component addition, the structure of the polymer matrix, molecular weight of polymer and the effect of solvent have been investigated. Obtaining soluble PEG,Ce(III),PVCz ternary complexes was shown by cyclic voltammetric measurements, and the initial rate of formation NVCz cation radicals as calculated using UV,visible spectrophotometry. Advantageously with these soluble complexes, conductivities could be measured both in solution and in the solid state. © 2001 Society of Chemical Industry [source] Oligo- and Polyselenophenes: A Theoretical StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2009Sanjio Abstract Recently, a family of conducting polyselenophenes was synthesized, and they were shown to have a number of interesting properties. Here we have studied oligoselenophenes, their cation radicals and dications up to the 50-mer (50,Se), as well as polyselenophene at the B3LYP/6-31G(d) level of theory, and compared them with the corresponding oligothiophenes. Although the calculations reveal many similarities between oligo- and polyselenophenes and their thiophene-based counterparts, they also show the important differences between those two types of conjugated systems. Oligo- and polyselenophenes have a more quinoid character, lower band gap, and importantly, they are more difficult to twist. The theoretical results suggest that the HOMO,LUMO gap (band gap), bond-length alternation (BLA), and charge distribution in oligo- and polyselenophenes are strongly dependent on inter-ring twisting, yet twisting costs little energy. The inter-ring distances in oligo- and polyselenophenes are shorter than the related distances in oligothiophenes, whereas the bond lengths within the selenophene rings are comparable to those of the corresponding oligothiophenes. [source] Selective Inclusion of Electron-Donating Molecules into Porphyrin Nanochannels Derived from the Self-Assembly of Saddle-Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin DicationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2007Takahiko Kojima Prof. Abstract A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p -hydroquinone and p -xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated. This result indicates that the PNC can recognize the electronic character and steric hindrance of the guest molecules during the course of inclusion. ESR measurements (photoirradiation at ,>340,nm at room temperature) of the PNC that contains p -hydroquinone, catechol, and tetrafluorohydroquinone guest molecules gave well-resolved signals, which were assigned to cation radicals formed without deprotonation based on results from computer simulations of the ESR spectra and density functional theory (DFT) calculations. The radicals are derived from photoinduced electron transfer from the guest molecules to the singlet state of H4DPP2+. Transient absorption spectroscopy by femtosecond laser flash photolysis allowed us to observe the formation of 1(H4DPP2+)*, which is converted to H4DPP+. by electron transfer from the guest molecules to 1(H4DPP2+)*, followed by fast disproportionation of H4DPP+., and charge recombination to give diamagnetic species and the triplet excited state 3(H4DPP2+)*, respectively. [source] | |||||||||||||||||||||||||