Fluorescence and excitation spectra of cinnamyl and α-styryl radicals

Radiolysis of solutions in alkane glasses at 77 K provides a convenient source of radicals derived from olefins, either by loss or by gain of a hydrogen atom. Fluorescence excitation spectroscopy has been used to trace absorption bands of radicals related to benzyl. Spectra of cinnamyl (1-phenyl-allyl) radicals derived from allyl-benzene, 1- and 2-phenyl-butadiene, are reported. Attempts at observing atropyl(2-phenyl-allyl) radicals were unsuccessful. The assignment of thermoluminescent emission of phenyl-acetylene solutions to α-styryl radicals is supported by their excitation spectra. Diphenyl acetylene gives similar phenyl-α-styryl radicals.     

Electron paramagnetic resonance (EPR) study of γ-radiation-induced radicals in 1,3,5-trithiane and its derivatives

Radicals formed in γ-irradiated 1,3,5-trithiane (TT) and its three derivatives, α- and β-2,4,6-trimethyl-1,3,5-trithiane (α-TMT and β-TMT), and 2,4,6-trimethyl-2,4,6-triphenyl-1,3,5-trithiane (TMTPT), were studied by the electron paramagnetic resonance (EPR) method in the solid state. The sulfur radical cations (>S^+•) were identified in all compounds at 77 K. In TT and its two derivatives, α-TMT and β-TMT, the >S^+• decay via deprotonation-forming C-centered radicals. Further increase of temperature up to 293 K results in the appearance of thiyl-type radicals (RS^•). In TMTPT, the >S^+• are stable up to 250 K. They formed the intermolecularly three-electron-bonded dimeric radical cations (S∴S)⁺ while RS^• radicals were not observed. Some of the radical assignments and their EPR parameters (g and a hyperfine splittings) obtained support from the DFT calculations.     

ESR study of the free radicals formed in the photolysis of α-ketofluorosulfates

ESR spectroscopy was used to establish that the UV irradiation of -ketofluorosulfates containing an OSO ₂ F group at a tertiary carbon atom gives radicals formed upon cleavage of the C-OSO ₂ F bond. If the OSO ₂ F group is attached to a primary or secondary carbon atom, we observe ordinary photodecomposition with cleavage of the acyl—carbon bond. The ESR spectra of the new radicals were studied. Replacement of fluorine by the OSO ₂ F group in the trifluoromethyl radical leads to compression of the radical site. Branched -oxoperfluoroalkyl radicals are not heteroallylic and the unpaired electron is localized largely on the carbon atom. The [(CF ₃ ) ₂ CF] ₂ C(O)CF ₃ radical is stable in the air.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 757–761, March, 1992.     

Angular dependence of the β-proton hyperfine coupling constant in β-substituted ethyl radicals

The β-proton hyperfine coupling constants in β-substituted ethyl radicals Ḣ₂-CH₂-X (X = CH₃, NH₂, OH, F, SiH₃, PH₂, SH, Cl) were computed as a function of the rotational angle α about the C_αC_β bond by ab initio calculations at the UHF/DZ + d level. They follow the relation a_H⨿(θ,α) = A + Bcos²θ + C cosθcosα, where A and B are not significantly affected by the substituent, and C is closely related to the electronegativity of the heteroatom.     

Interaction of hydroxyaryl aldehydes with α-hydroxyethyl radicals

The effect of some hydroxylated aromatic aldehydes on the radiation-chemical transformations of deaerated ethanol during continuous radiolysis has been studied. The data obtained show that these compounds effectively inhibit radiation-induced processes involving α-hydroxyethyl radicals (α-HER). Benzaldehyde and its hydroxylated derivatives (II, III) predominantly oxidize, and compounds containing the cinnamic moiety, (IV–VI), add α-HER to a carbonyl group or -C=C bond.     

On the extraction of spectra of components from spectra of mixtures. A development in factor theory—II

The theory of factor analysis developed in Part I [A. Muller and D. Steele, Spectrochim. Acta 46A, 817 (1990) [1] is extended to cases where m > 3, m being the number of factors. The effect of increasing the number of independent parameters by m(m-1) for T′ and the subsequent changes produced in the transformed eigenspectra, are investigated. Applications to actual spectra of mixtures of: (A) butan-2-one, ethyl ethanoate, cyclohexane and oct-1-ene (B) butan-2-one, ethyl ethanoate, cyclohexane and 2-methylpentane and (C) oct-1-ene, butan-2-one, ethyl ethanoate, cyclohexane and 2-methyl-pentane are presented. Using standard target techniques, an alternative approach is developed for the m> 3 case. This is based on transformation of the leading three eigenspectra, followed by identification and elimination of a component in a repetitive manner, until completion. The problems associated with the implementation of the Beer-Lambert Law are explored the need for accurate determination of a suitable wavenumber block to ensure the removal of the correct amount of each component, is examined. The ability to recognize at least one of the m component spectra per programme cycle is demonstrated.     

On the extraction of spectra of components from spectra of mixtures. A development in factor theory—I

The theory of factor analysis is extended to permit the computer based extraction of the spectra of pure components from spectra of mixtures. A simultaneous linear, non-orthogonal transformation of the eigenspectra and eigenvectors is used to generate all positive absorbances and concentrations within noise level. Applications to actual spectra of mixtures of: (A) ethyl ethanoate, butan-2-one and oct-1-ene; (B) ethyl ethanoate, butan-2-one and cyclohexane; and (C) butan-2-one, cyclohexane and 2-methylpentane are presented. The effects of changes in signs of the constrained diagonal elements of the transformation matrix is investigated. To explore the ability of the software to cope with component spectra in which there are no wavenumbers at which one component dominates an artificial set of mixtures is examined. Recognizable spectra are extracted. It appears that, even when there are no wavenumbers at which one component dominates, the condition of finding “the sum of squares of negative absorbances/concentrations” near zero is adequate to yield useful spectra for library searches.     

Effect of flavonols on radiation-induced reactions with the participation of α-hydroxyl-containing organic radicals

The effects of flavonols and structurally related model compounds on the formation of the final radiolysis products of ethanol and aqueous ethylene glycol and 2-methoxyethanol solutions were studied. It was found that the test compounds actively interact with the -hydroxyl-containing radicals of parent substances by several mechanisms to change the direction of radiolytic processes. The applicability of flavonols to the inhibition of radiation-induced free-radical fragmentation of organic compounds was demonstrated for the first time. Mechanisms were proposed to explain the observed effects.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 3, 2005, pp. 171–175.Original Russian Text Copyright © 2005 by Grintsevich, Shadyro.     

Aminopyridines as amino components in the catalytic synthesis of α-aminophosphonates

6h-Aminophosphonates containing alicyclic, aromatic, and heterocyclic fragments were obtained in high yields by the Kabachnick—Fields reaction of the corresponding carbonyl compounds with 2-, 3- and 4-aminopyridines and diethyl phosphite using tetra- tert-butyl- phthalocyanine aluminum chloride as the catalyst. 2-, 3-, 4-Aminopyridines were found to vary in their reactivity with ketones and diethyl phosphite in the catalytic three-component one-pot process.     

Radical stabilization is crucial in the mechanism of action of lysine 5,6-aminomutase: role of tyrosine-263α as revealed by electron paramagnetic resonance spectroscopy

Adenosylcobalamin- and pyridoxal-5'-phosphate-dependent lysine 5,6-aminomutase utilizes free radical intermediates to mediate 1,2-amino group rearrangement, during which an elusive high-energy aziridincarbinyl radical is proposed to be central in the mechanism of action. Understanding how the enzyme participates in stabilizing any of the radical intermediates is fundamentally significant. Y263F mutation abolished the enzymatic activity. With isotope-edited EPR methods, the roles of the Tyr263α residue in the putative active site are revealed. The Tyr263α residue stabilizes a radical intermediate, which most likely is the aziridincarbinyl radical, either by acting as a spin-relay device or serving as an anchor for the pyridine ring of pyridoxal-5'-phosphate through aromatic π-stacking interactions during spin transfer. The Tyr263α residue also protects the radical intermediate from interception by molecular oxygen. This study supports the proposed reaction mechanism, including the aziridincarbinyl radical, which has eluded detection for more than two decades.     

The interaction of radiation-generated radicals with myoglobin in aqueous solution—VI: The reduction of ferrimyoglobin by α-hydroxyalkyl radicals

G-values of the formation of ferromyoglobin (Mb^II) have been determined for the continuous γ-radiolysis of N₂O-saturated neutral aqueous solutions containing ferrimyoglobin (Mb^III) and a series of aliphatic alcohols (RH) under conditions such that the competition for the primary ^.OH radicals favors RH. A comparison of the efficiencies of reduction of Mb^III by the secondary organic radicals formed via H-abstraction reactions with estimates from the literature of the fraction of ^.OH attack at the C-atom α to the —OH group indicates that α-hydroxyalkyl radicals are primarily responsible for the observed reduction. Significantly lower reduction yields are observed when RH = 1,2-diol, compared with the expected yields of strongly reducing 1,2-dihydroxyalkyl radicals; the initial reducing radicals convert into inactive β-alkanonyl analogues so that the reduction of Mb^III is not kinetically competitive with the β-elimination process. Mb^III is useful as a probe of the occurence of slow conversion processes involving radiolytically-generated radicals.     

Application of reductive,single electron transfer processes to the generation and cyclization of ω-unsaturated α-amino radicals

Subjection of ω-unsaturated iminium salts 1 to dissolving metal reduction with samarium diiodide in the presence of camphorsulfonic acid afforded the corresponding α-amino radicals 2, which underwent facile cyclization via a 5-exo mode of closure leading to heterocyclic products of the general type 4.     

Some anomalies in the vibrational spectra of α, β-unsaturated ketones

Summary Some anomalies in the intensities of the bands of the C=C and C=O bonds in the vibrational spectra of , -unsaturated ketones have been explained by a difference in the sequence of the frequencies of the in-phase (_s) and out-of-phase (_as) vibrations of the multiple bonds in their cis (_s<_as) and trans (_s>_as) arrangements.     

Study on the resonance Rayleigh scattering spectra and resonance non-linear spectra of congo red-amikacin system and its analytical application

The interaction between congo red (CR) and amikacin (AMK) was studied by resonance Rayleigh scattering (RRS), frequency doubling scattering (FDS) and second-order scattering (SOS) combining with absorption spectrum. In a weak acidic medium, CR combined with AMK to form an ion association complex with the composition ratio of 1∶1 by electrostatic interaction, hydrophobicity and charge transferring effect. As a result, the new spectra of RRS, FDS, and SOS appeared and their intensities were enhanced greatly. The maximum wavelengths of RRS, FDS and SOS were located at 563 nm, 475 nm and 940 nm, and the scattering intensities were proportional to the concentration of AMK. These three methods have very high sensitivities, and the detection limits were 4.0 ng·mL?1 for RRS, 3.6 ng·mL?1 for FDS and 1.9 ng·mL?1 for SOS, respectively. At the same time, the methods have better selectivity. A new method for the determination of trace amounts of AMK with congo red by resonance scattering technique has been developed. The recovery for the determination of AMK in blood serum and urine sample was between 95.5% and 105.5%. In this study, the properties, such as enthalpy of formation, charge distribution and mean polarizability, were calculated by AM1 quantum chemistry method. In addition, the reaction mechanism and the reasons for the enhancement of scattering spectra were discussed.     

Where does the electron go? Electron distribution and reactivity of peptide cation radicals formed by electron transfer in the gas phase

We report the first detailed analysis at correlated levels of ab initio theory of experimentally studied peptide cations undergoing charge reduction by collisional electron transfer and competitive dissociations by loss of H atoms, ammonia, and N-C alpha bond cleavage in the gas phase. Doubly protonated Gly-Lys, (GK + 2H) (2+), and Lys-Lys, (KK + 2H) (2+), are each calculated to exist as two major conformers in the gas phase. Electron transfer to conformers with an extended lysine chain triggers highly exothermic dissociation by loss of ammonia from the Gly residue, which occurs from the ground ( X ) electronic state of the cation radical. Loss of Lys ammonium H atoms is predicted to occur from the first excited ( A ) state of the charge-reduced ions. The X and A states are nearly degenerate and show extensive delocalization of unpaired electron density over spatially remote groups. This delocalization indicates that the captured electron cannot be assigned to reduce a particular charged group in the peptide cation and that superposition of remote local Rydberg-like orbitals plays a critical role in affecting the cation-radical reactivity. Electron attachment to ion conformers with carboxyl-solvated Lys ammonium groups results in spontaneous isomerization by proton-coupled electron transfer to the carboxyl group forming dihydroxymethyl radical intermediates. This directs the peptide dissociation toward NC alpha bond cleavage that can proceed by multiple mechanisms involving reversible proton migrations in the reactants or ion-molecule complexes. The experimentally observed formations of Lys z (+*) fragments from (GK + 2H) (2+) and Lys c (+) fragments from (KK + 2H) (2+) correlate with the product thermochemistry but are independent of charge distribution in the transition states for NC alpha bond cleavage. This emphasizes the role of ion-molecule complexes in affecting the charge distribution between backbone fragments produced upon electron transfer or capture.     

Thermolyses of α-phosphorylmethyl tetrazolyl sulfoxides in the presence of 2,3-dimethyl-1,3-butadiene and their reactions with several amines

We have synthesized α-(phosphoryl)methyl tetrazolyl sulfoxides and examined the reactivities in the thermolyses and in the presence of several amines, such as aniline, benzylamine, piperidine, pyrrolidine, and morpholine. Thermolyses of the derivatives in the presence of 2,3-dimethyl-1,3-butadiene afforded 2-phosphoryl substituted 4,5-dimethyl-3,6-dihydro-2H-thiopyran S-oxide. In addition, novel phosphinecarbothioamides were obtained in the reaction of the derivatives with amines.     

Solvent effects in the reactivity of phenylethyl hydroperoxide, II. Reactivity and β-scission of α-phenylethoxy radicals in the solutions of α-phenylethylhydroperoxide

Efficient cleavage of -phenylethoxy radicals (HRO^.) was observed in CH₃CN at 304 K. From measurements of the quantum yields of product formation, it was calculated that      

ESR study of the structure and reactivity of spin-adducts of element- and metal-centered radicals with perfluorinated α-triketones

The addition of element-centered radicals to perfluorinated α-triketones (CF₃)₂CFCOCOCOC₂F₅ (1) and (CF₃)₂CFCOCOCO(CF₃)₂ (2) was studied by the ESR method. In the case of Si-centered radicals, α-siloxydiketomethyl radicals are formed, which are characterized by the highest delocalization of an unpaired electron. The dimerization of these radicals is characterized by a low value of the enthalpy of the radical—dimer equilibrium (2.7 kcal mol⁻¹). The Ge(C₆F₅)₃ and ·Mn(CO)₅ radicals are added to1 at the carbonyl group directly bound to the pentafluoroethyl substituent. The hindered rotation of the (CF₃)₂CF group was observed for the spin-adduct of ·Ge(C₆F₅)₃ with2. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 474–477, March, 1999.