ACTION SPECTRA AND CHROMOPHORES FOR LETHAL PHOTOSENSITIZATION OF Candida albicans BY DNA MONOADDUCTS FORMED BY 8-METHOXYPSORALEN AND MONOFUNCTIONAL FUROCOUMARINS

The red-shift of furocoumarin action spectra, compared with their absorption spectra, has been investigated. An action spectrum for 8-methoxypsoralen (8-MOP) monoadduct formation in the yeast Candida albicans has been determined. The yeast cells were initially exposed to sublethal doses of monochromatic UVA at different wavelengths. Monoadduct formation was monitored by growth inhibition induced, after washing out any unbound 8-MOP, by re-irradiation with a constant second (non-lethal) dose of 330 nm radiation. A comparison between this action spectrum and the absorption spectrum of the dark complex of 8-MOP and DNA was made. In addition, the action spectra of monoadduct formation of five monofunctional compounds including a coumarin derivative have been determined. These action spectra were compared with their respective DNA dark complex absorption spectra. In general, the peaks of the furocoumarin DNA dark complexes show a red-shift when compared with the free furocoumarin molecule and the action spectra show peaks which correspond with the peaks of the dark complexes. Such data indicate that the DNA dark complex is the chromophore for growth inhibition in yeast rather than the free furocoumarin. The similarity of the 8-MOP monoadduct formation action spectrum and 8-MOP action spectra suggests that spectral dependence for the photobiological effects (including the red-shift) is dependent on monoadduct formation rather than, as previously suggested by several authors, crosslink formation. The action spectrum for the coumarin derivative 4-methyl N-ethylpyrrolo (3,2-g) coumarin (PCNEt) correlated well with the free molecule absorption spectrum rather than DNA dark complex indicating that the free molecule is the chromophore.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electron spin resonance study of γ-irradiated poly(methacrylic acid)

Low temperature relaxations in poly(methacrylic acid) (PMAA) have been studied by electron spin resonance (ESR) spectroscopy. The observed 8 line ESR spectra of irradiated PMAA in the temperature range 77-300K (LNT-RT) is attributed to the free radicals of the type ～ CH₂? CH? CH₃. Assignment of ESR spectra to free radicals has been made on the basis of magnetic parameters employed to simulate ESR spectra at different temperatures. Further, ESR spectra below LNT have been simulated, using the set of parameters employed to simulate the experimental spectrum at LNT. Magnetic parameters of the ESR spectra at LNT and below LNT indicate γ- and δ-relaxations of PMMA chains. © 1994 John Wiley & Sons, Inc.     

L-tryptophan radical cation electron spin resonance studies: connecting solution-derived hyperfine coupling constants with protein spectral interpretations

Fast-flow electron spin resonance (ESR) spectroscopy has been used to detect a free radical formed from the reaction of l-tryptophan with Ce (4+) in an acidic aqueous environment. Computer simulations of the ESR spectra from l-tryptophan and several isotopically modified forms strongly support the conclusion that the l-tryptophan radical cation has been detected by ESR for the first time. The hyperfine coupling constants (HFCs) determined from the well-resolved isotropic ESR spectra support experimental and computational efforts to understand l-tryptophan's role in protein catalysis of oxidation-reduction processes. l-Tryptophan HFCs facilitated the simulation of fast-flow ESR spectra of free radicals from two related compounds, tryptamine and 3-methylindole. Analysis of these three compounds' beta-methylene hydrogen HFC data along with equivalent l-tyrosine data has led to a new computational method that can distinguish between these two amino acid free radicals in proteins without dependence on isotope labeling, electron-nuclear double resonance, or high-field ESR. This approach also produces geometric parameters (dihedral angles for the beta-methylene hydrogens) that should facilitate protein site assignment of observed l-tryptophan radicals as has been done for l-tyrosine radicals.     

Positron annihilation in ionic conductivity polymers

Positron annihilation lifetime spectra and ionic conductivity have been measured for poly(etherurethane)-LiClO₄ as a function of temperature. The effects of Li salt on glas transition free volume and ionic conductivity have been discussed. A correlation between fractional free volume and ionic conductivity was first experimentally confirmed by using the free volume theory.Supported by the National Natural Science Foundation of China.     

PHOTOCHEMISTRY OF BIOLOGICAL MOLECULES – II. PHOTOLYSIS OF DIPEPTIDES IN THE SOLID STATE

Abstract— Photolysis with light of 2537 Å of a series of aliphatic dipeptides in the solid state has been shown to lead to bond rupture and free radical formation. The structures of the radicals have been determined by ESR techniques and in general, the free electron has been shown to reside on the carbon atom attached to the nitrogen atom of the peptide bond. Dipeptides containing phenylalanine residues show ESR spectra typical of the free amino-acid in the terminal position.     

Vibrational spectra of ethyl dihaloacetates

Vibrational spectra of ethyl dihaloacetates have been studied. Infrared spectra in vapour and liquid phases, solutions in different solvents, and Raman spectra of these compounds have been recorded in order to assign the fundamental bands. The existence of different rotamers about the CC bonds joining the dihalomethyl and carbonyl groups produces a splitting in some bands of the spectra. It yields a more complex profile but, to some extent, it allows an easier assignment of bands which present that splitting. A theoretical study of the potential barrier hindering free rotation about that bond has been made in order to predetermine the number and orientation of the rotamers in each compound.     

Free carboxylate stretching modes

We report the first IR spectroscopic observation of carboxylate stretching modes in free space, i.e., in the complete absence of solvent or counterions. Gas-phase spectra of a series of benzoate anions have been recorded and compared to condensed-phase spectra, revealing the profound influence of the environment on the symmetric and antisymmetric carboxylate stretch modes.     

Formation of free radicals in photoirradiated cellulose. VIII. Mechanisms

Photoinduced free radicals in cellulose were studies by means of ESR spectroscopy. Plausible mechanisms have been suggested for each type of intermediate radical to account for the ESR spectra observed and for the product balances. Based on the principles of photochemistry of cellulose, coupled with the findings of the ESR spectra, it becomes evident that localization of the energy absorbed in the cellulose molecule leads to formation of free radicals in terms of chain scission, dehydrogenation, dehydroxylation, and dehydroxymethylation. Emphasis has been placed on the correlation of the mechanisms of photodegradation and the mechanisms of photoinduced graft copolymerization.     

Application of SERS and SEF Spectroscopy for Detection of Water-Soluble Fullerene–Chlorin Dyads and Chlorin e6

Free fluorescence spectra in solution and surface-enhanced Raman scattering (SERS) and surface enhanced fluorescence (SEF) spectra of chlorin e6 and water-soluble covalent fullerene–chlorin dyads have been studied. It has been demonstrated that chlorin e6 and covalent fullerene–chlorin dyads have similar characteristic SERS spectra. The fullerene–chlorin dyads show a pronounced SEF signal, while native chlorin e6 has no fluorescence on surface, which is consistent with the theory predicting an inverse dependence of the SEF intensity on the free fluorescence quantum yield. The concentration dependence of the SEF intensity is linear for the dyads in the range 0.1–2.0 μmol/L. These effects allow one to determine, with high sensitivity, the content of fullerene–chlorin dyads with a low quantum yield of free fluorescence in solutions, which opens wide opportunities for study of biological properties of fullerene–chlorin dyads and their applications in medicine.     

The application of Fourier transform Raman spectroscopy to the identification and characterization of polyamides—I. Single number nylons

High quality Fourier transform Raman spectra, free from fluorescence, have been obtained for a series of commercial polyamides of the single number nylon type from nylon 3 to nylon 12. With this newly developed technique, it is now possible to record spectra routinely and to characterize each nylon spectrum thus to identify them for analytical purposes. The characteristic trends observed in some regions of the Fourier transform Raman spectra obtained for this series of nylons are investigated and discussed.     

The application of Fourier transform Raman spectroscopy to the identification and characterisation of polyamides—II. Double-number nylons

High quality Fourier transform Raman spectra, substantially free from fluorescent background, have been obtained for twelve double-number nylons ranging from nylon 1,3 to nylon 10,10. These spectra, obtainable on a routine basis, prove to be highly characteristic and therefore of considerable value for analytical purposes. The characteristic trends observed in some regions of this series of spectra are investigated and discussed. A less detailed study suggests that Fourier transform Raman spectroscopy should also be of value for the characterisations of nylon co-polymers.     

ELECTRON SPIN RESONANCE STUDIES OF ULTRAVIOLET IRRADIATED KERATIN AND RELATED PROTEINS

Abstract— The formation of free radicals in keratin and related proteins by exposure to u.v. light has been examined by electron spin resonance spectroscopy. From a comparison of the spectra obtained and the effects of different wavelengths and the stabilities of the radicals produced, it has been shown that several species of free radicals are produced by the u.v. irradiation of keratin. However it has been possible to identify only those free radicals associated with the cystine residues. The free radicals produced in keratin by exposure to shorter wavelength irradiation (below 3250 Å) were found to be quite different to those produced at longer wavelengths.     

The characterization of polycyclic aromatic hydrocarbons by Raman spectroscopy

High quality Raman spectra, substantially free from fluorescence interference, have been obtained from 11 polycyclic aromatic hydrocarbons, in the solid state, using a Fourier Transform spectrometer. These spectra are rich in sharp bands and, merely by utilizing the limited number of strong peaks it is possible to characterize each hydrocarbon uniquely. The presence of an appreciable number of peaks of medium intensity in each spectrum considerably increases the specificity. The scope and limitations of these spectra for analytical purposes are discussed.     

Interaction of some complementary constituents of nucleic acids in aqueous solution: UV and IR hypochromicities

Ultraviolet spectra of mixtures of monomeric units of nucleic acids and dinucleoside monophosphates, containing the complementary nucleobases adenine and uracil, have been obtained in aqueous solution. Hypochromicity of spectra of the mixtures with respect to free components has been determined, introducing the correction corresponding to selfassociation of these compounds. Hypochromicity of mixtures can be considered an experimental evidence of the existence of heteroassociation processes.Infrared spectra of some complementary constituents of nucleic acids in aqueous solution also reveal hypochromic effects, which provide information about the molecular groups involved in the heteroassociation.     

High resolution electronic absorption spectra of aniline, anilino and silicon dioxide

High resolution electronic absorption spectra of aniline and anilino free radical have been recorded in the vapor phase at room temperature by flash photolysis technique, and subsequent reactions have been investigated by kinetic spectroscopy. It was possible to follow the kinetics of the anilino radical's decay which occurred predominantly by bimolecular recombination. Decay parameters of anilino free radical were measured from the absorption bands.     

Vibrational analysis of free and hydrogen bonded complexes of nicotinamide and picolinamide

Harmonic and anharmonic vibrations of free nicotinamide (NIA) and picolinamide (PIA) molecules together with their hydrogen bonded complexes H₂O–NIA and H₂O–PIA have been studied by means of density functional method. The calculation results of the vibrational spectra of free molecules have been investigated and are compared to the available experimental spectra. The vibrational wavenumbers of both molecules have also been calculated by polarizable continuum model (PCM) that represents the solvent as a polarizable continuum and places the solute in a cavity within the solvent (water is chosen as the solvent in this study). The results of PCM calculations and the H₂O–NIA, H₂O–PIA complexes, are used to investigate the H-bonding interactions of both molecules with the water molecule. The harmonic wavenumbers have been scaled by proper factors obtained by comparing the observed versus calculated wavenumbers and it is shown that anharmonic corrections on the vibrational spectra provided a better agreement between the observed and calculated wavenumbers compared to the results obtained by scaling factor method.     

Sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) of thiol and thioether compounds

The speciation and quantification of sulfur species based on sulfur K-edge x-ray absorption spectroscopy is of wide interest, particularly for biological and petroleum science. These tasks require a firm understanding of the sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of relevant species. To this end, we have examined the gas phase sulfur 1s NEXAFS spectra of a group of simple thiol and thioether compounds. These high-resolution gas phase spectra are free of solid-state broadening, charging, and saturation effects common in the NEXAFS spectra of solids. These experimental data have been further analyzed with the aid of improved virtual orbital Hartree-Fock ab initio calculations. The experimental sulfur 1s NEXAFS spectra show fine features predicted by calculation, and the combination of experiment and calculation has been used to improve assignment of spectroscopic features relevant for the speciation and quantification of the sulfur compounds.     

Sequencing of oligosaccharides by collision-induced dissociation matrix-assisted laser desorption/ionization mass spectrometry

A study of the collision-induced dissociation post-source decay (PSD) spectra of free oligosaccharides is presented. These spectra, when obtained with helium as collision gas, show (1,5)X fragments containing the reducing end sugar. The presence of these fragments permits Y ions and, consequently, B and C peaks to be identified. This is a common behaviour from which it has been possible to delineate a general method for the easy assignment of the peaks in PSD spectra of underivatized neutral sugars, allowing the sequence of a real unknown to be obtained.     

Infrared studies on Co and Cd complexes of sulfamethoxazole

In this study, the new Co and Cd complexes of sulfamethoxazole (SMX) (drug substance) [4-amino-N-(5-methyl-3-isoxazolyl) benzenesulfonamide] have been prepared for the first time and their infrared spectra have been investigated. The infrared spectra of the samples were recorded in the range 4000-400 cm(-1) and their fundamental vibrational wave numbers were obtained. The vibrational assignments were determined by using the group frequency tables and compared with the wave numbers of SMX found in the literature. The SMX wave numbers observed in the infrared spectra of the metal complexes were compared with those of free SMX. Investigations of the infrared spectra of the metal complexes indicated the vibrations due to the amino and sulfonamido groups are shifted with respect to the free molecule in line with their coordination to the metal. In the cadmium complex, the active binding sites of SMX are the sulfonamide nitrogen and sulfonic oxygen; in cobalt compound, the metal atom coordinates through the sulfonamide and amino nitrogens. The low energy calculations were also carried out by using geometry optimization. It is shown that the proposed structure for the metal complexes of SMX derived from the infrared spectra are consistent with the theoretical results.     

Observations on the mass spectrometry of monensin and related compounds

Monensin and nigericin are structurally related compounds belonging to a family of biologically active, polycylic, monocarboxylic acids produced by Streptomyces. Partial interpretation of their mass spectra has been achieved with the aid of high resolution data and by correlation with spectra of derivatives. These results have been applied to structure elucidation of several minor factors produced along with monensin. An interesting aspect of the mass spectrometry of these compounds is that their alkali-metal salts are sufficiently volatile to yield mass spectra. Fragmentation of the salts is markedly different from that of the free acids and their derivatives. A scheme is proposed to account for the formation of a number of fragment ions which contain the metal atom.