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At least 685 records · Page 38Linked to original sources
PubMed2004

Biolocalisation and photochemical properties of two novel macrocyclic photosensitisers: a spectroscopic study.

Biolocalisation and photochemical properties of novel macrocyclic photosensitisers, guanidiniocarbonyl-substituted tetraphenylporphyrin (1) and sugar-substituted sapphyrin (2) were investigated by spectroscopic methods. Both photosensitisers absorb in far visible region and showed good tumour localisation. Photosensitiser 2 demonstrated significantly larger absolute and relative to normal tissue (T/N) amount in tumour (330 microg g(-1) wet tissue, T/N=19.0) than photosensitiser 1 did (13 microg g(-1) wet tissue, T/N=2.1). According to iodometric and uric acid assays, compound 1 produced large amount of 1O2 (phidelta=0.60-0.68), while compound 2 showed non-significant 1O2 production (phidelta=0.04). The electronic spectroscopic study confirms that only photosensitiser 1 is able to mediate photooxidation of model compounds (BSA, poly(Trp), Tyr, Trp, and GMP) after light irradiation. Pour photochemical activity of compound 2 was explained by its self-aggregation. Raman spectroscopic study indicated that monomerised photosensitiser 2 effectively damaged BSA and calf thymus DNA after light excitation at the conditions of high excess of these macromolecules.

Absorption↗
PubMed2005

Growth and spectroscopic characterization of a new organic nonlinear optical crystal--8-hydroxyquinoline.

A novel organic nonlinear optical crystal 8-hydroxyquinoline having good optical quality has been grown by slow evaporation solution technique using methanol as solvent. The morphology of the grown crystals were identified by X-ray diffraction method. Solubility studies were made under various solvents and solvent mixtures at different temperatures. Functional groups present in the grown material have been identified using FTIR and FT Raman spectra. Transparency was tested using UV-vis spectrophotometer and the second harmonic generation was also verified.

Crystallization↗
PubMed2006

Spectroscopic and structural impact of a stem base-pair change in DNA hairpins: GTTC-ACA-GAAC versus GTAC-ACA-GTAC.

Successive investigations over the last decade have revealed and confirmed a stable loop closure in a family of d-[GTAC-5Pur6N7N-GTAC] hairpins, where 5Pur6N7N is a AAA, GAG and AXC loop (X being any nucleotide). The trinucleotide loop is characterized by a well defined 5Pur-7N mispairing mode, and by upfield chemical shifts for three sugar protons of the apical nucleotide 6N. The GTTC-ACA-GAAC DNA hairpin, of interest for its likely involvement in Vibrio cholerae genome mutations, has now been investigated. The GTAC-ACA-GTAC DNA hairpin has also been studied because it is intermediate between the other structures, as it contains the loop of the hairpin under consideration and the stem of the above family. The two hairpins with the ACA loop are stable. They show the same mispairing mode and similar upfield shifts as the previous family, but GTTC-ACA-GAAC seems to be slightly less compact than any other. GTTC-ACA-GAAC is remarkable in that it exhibits a B(II) character for the phosphate-ester conformation at 8Gp9A, together with a swing of the upper hairpin into the major groove that, in particular, brings 6CH1' roughly as close to 7AH2 as to 6CH6. These unexpected structural features are qualitatively deduced from (1)H and (31)P NMR spectra, and confirmed by Raman spectroscopy. This comparative study shows that not only the loop sequence but also the stem sequence may control hairpin structures.

Base Pairing↗
PubMed2006

Density functional theory study of vibronic structure of the first absorption Qx band in free-base porphin.

Harmonic vibrational frequencies and vibronic intensities in the first S(0)-->S(1) (pipi( *)) absorption band of free-base porphin (H(2) P) are investigated by hybrid density functional theory (DFT) with the standard B3LYP functional. The S(0)-S(1) transition probability is calculated using time-dependent DFT with account of Franck-Condon (FC) and Herzberg-Teller (HT) contributions to the electric-dipole transition moments including displacements along all 108 vibrational modes. Two weak wide bands observed in the gas phase absorption spectra of the H(2) P molecule at 626 and 576 nm are interpreted as the 0-0 band of the X(1) A(g)-->1B(3u) transition and the 0-1 band with largest contributions from the nu(10)(a(g))=1610 cm(-1) and nu(19)(b(1g))=1600 cm(-1) modes, respectively, in agreement with previous tentative assignments. Both bands are induced by the HT mechanism, while the FC contributions are negligible. A number of fine structure bands, including combination of two vibrational quanta, are obtained and compared with available spectra from supersonic jet and Shpolskij matrices. Both absorption and fluorescence spectra are interpreted on ground of the linear coupling model and a good fulfillment of the mirror-symmetry rule.

Chemical Phenomena↗
PubMed2006

Anharmonic analysis of the vibrational spectrum of ketene by density functional theory using second-order perturbative approach.

The paper reports main results of a comprehensive study of the vibrational spectrum of ketene computed using second-order perturbation theory treatment based on quartic, cubic and semidiagonal quartic force constants. Two different models--a homogeneous model using the same density functionals and basis functions for the harmonic calculations and anharmonic corrections, and a hybrid model in which the two parts of the calculation are conducted using different density functionals and basis sets--have been employed in the present calculations. Different DFT and CCSD methods and DZ and TZ extended basis sets involving diffuse and polarization functions have been used to calculate optimized and vibrationally averaged geometrical parameters, the harmonic and anharmonic vibrational frequencies and the spectroscopic constants such as anharmonicity constants, rotational constants, rotation-vibration coupling constants, Nielsen's centrifugal distortion constants and Coriolis coupling constants. Homogeneous model is found to be superior to the hybrid model in several respects. Difficulties in the hybrid model may arise due to one of the following reasons: (a) the basic requirement that the geometry optimization and frequency calculations must be done at the same level of theory to have valid frequencies is not met in the hybrid model; (b) the molecular structure gets reoptimized at the low level for anharmonic corrections; (c) in addition, the perturbation could also diverge for the above reasons, particularly for the very low, very anharmonic terms where the harmonic approximation is not close enough to make the perturbation work.

Ethylenes↗
PubMed2003

Comparison of ligand polarization and enzyme activation in medium- and short-chain acyl-coenzyme A dehydrogenase-novel analog complexes.

Spectroelectrochemical and off-resonance Raman indicate that substrate/product binding to medium-chain acyl-coenzyme A (CoA) dehydrogenase (pMCAD) results in ligand polarization and positive flavin potential shifts, which activate the enzyme for electron transfer. Bacterial short-chain acyl-CoA dehydrogenase (bSCAD) typically exhibits smaller potential shifts upon substrate/product binding that have not been linked to ligand polarization. To further investigate the roles of ligand binding and polarization in activation, several novel aromatic carboxyloyl-CoAs were designed. These analogs allowed for the first direct comparison of pMCAD and bSCAD mechanisms. The results indicate that pMCAD activation can occur without perceptible analog polarization. bSCAD data provide the first spectral evidence of ligand polarization. The potential alterations exhibited by ligand-bound bSCAD are smaller than those of pMCAD, while their directionality and magnitude suggest differing enzyme-analog interactions. Such data provide the first indication of variations in the activation mechanism of these enzymes, which were thought to be comparable in both structure and function.

Acyl-CoA Dehydrogenase↗
PubMed2000

Chromophore reorientation during the photocycle of bacteriorhodopsin: experimental methods and functional significance.

Light-induced isomerization leads to orientational changes of the retinylidene chromophore of bacteriorhodopsin in its binding pocket. The chromophore reorientation has been characterized by the following methods: polarized absorption spectroscopy in the visible, UV and IR; polarized resonance Raman scattering; solid-state deuterium nuclear magnetic resonance; neutron and X-ray diffraction. Most of these experiments were performed at low temperatures with bacteriorhodopsin trapped in one or a mixture of intermediates. Time-resolved measurements at room temperature with bacteriorhodopsin in aqueous suspension can currently only be carried out with transient polarized absorption spectroscopy in the visible. The results obtained to date for the initial state and the K, L and M intermediates are presented and discussed. The most extensive data are available for the M intermediate, which plays an essential role in the function of bacteriorhodopsin. For this intermediate the various methods lead to a consistent picture: the curved all-trans polyene chain in the initial state straightens out in the M intermediate (13-cis) and the chain segment between C(5) and C(13) tilts upwards in the direction of the cytoplasmic surface. The kink at C(13) allows the positions of beta-ionone ring and Schiff base nitrogen to remain approximately fixed.

Bacteriorhodopsins↗
PubMed2003

The structure of DNA within cationic lipid/DNA complexes.

The structure of DNA within CLDCs used for gene delivery is controversial. Previous studies using CD have been interpreted to indicate that the DNA is converted from normal B to C form in complexes. This investigation reexamines this interpretation using CD of model complexes, FTIR as well as Raman spectroscopy and molecular dynamics simulations to address this issue. CD spectra of supercoiled plasmid DNA undergo a significant loss of rotational strength in the signal near 275 nm upon interaction with either the cationic lipid dimethyldioctadecylammonium bromide or 1,2-dioleoyltrimethylammonium propane. This loss of rotational strength is shown, however, by both FTIR and Raman spectroscopy to occur within the parameters of the B-type conformation. Contributions of absorption flattening and differential scattering to the CD spectra of complexes are unable to account for the observed spectra. Model studies of the CD of complexes prepared from synthetic oligonucleotides of varying length suggest that significant reductions in rotational strength can occur within short stretches of DNA. Furthermore, some alteration in the hydrogen bonding of bases within CLDCs is indicated in the FTIR and Raman spectroscopy results. In addition, alterations in base stacking interactions as well as hydrogen bonding are suggested by molecular dynamics simulations. A global interpretation of all of the data suggests the DNA component of CLDCs remains in a variant B form in which base/base interactions are perturbed.

Cations↗
PubMed1985

Do vibrational spectroscopies uniquely describe protein dynamics? The case for myoglobin.

We develop a quasi-harmonic description of protein dynamics and apply this description to the anomalous Mössbauer, infrared, x-ray diffraction, and EXAFS (extended x-ray absorption fine structure spectroscopy) data that are available for myoglobin (Mb) and its interactions with carbon monoxide (CO). In the quasi-harmonic approximation the dynamical parameters derived from these spectroscopic data are relevant in the calculation of reaction rates, and we give a quantitative description of the nonexponential kinetics of Mb-CO binding observed at low temperatures. All these data have previously been interpreted in terms of the more complex conformational substates model for protein dynamics. We point out several problems with this model and propose experiments that can provide detailed tests of the quasi-harmonic theory proposed here.

Iron↗
PubMed2005

[Emerging endoscopic techniques. The arrival of virtual histology].

Endoscopic technology has evolved in such a way that gastroenterologists can now visualize and store high-resolution images of the gastrointestinal tract. This has improved the approach to precancerous and cancerous lesions of the gastrointestinal tract and biliary tree. However, certain difficulties remain, especially in relation to diagnosis. In the last few years, multiple techniques have been developed that, using the properties of light, enable an instantaneous histologic diagnosis to be made while endoscopy is being performed. What has been called the "optical biopsy" allows highly exact information to be obtained, both from the morphological and functional point of view. Some of these techniques, such as chromoendoscopy and magnification, are already being performed in clinical practice while others are still under investigation. The aim of the present article is to review the underlying principles and applications of these emerging techniques.

Endoscopy, Gastrointestinal↗
PubMed2002

Spectroscopic characterisation of the monoclinic and orthorhombic forms of paracetamol.

The metastable orthorhombic form of paracetamol was prepared from the melt of the commercially available monoclinic form. Distinct differences were observed in the infrared spectra of both forms, especially in the region 1260-1225 cm(-1), in which is observed three strong absorptions of approximately equal intensity in spectra of the monoclinic form, and two absorptions, one strong and one medium, in spectra of the orthorhombic form. No diagnostically useful differences were observed in the Raman spectra of the two forms. A 13C CP/MAS solid-state NMR spectrum of the monoclinic form and a spectrum of a mixture of forms prepared from a melt were obtained. A spectrum of the orthorhombic form was obtained from these spectra by difference spectroscopy. The spectra show that the carbons in the paracetamol molecules are all in unique chemical environments in both crystalline forms, and that clear well-resolved differences in the chemical shifts of particular carbons in both forms can be observed.

Acetaminophen↗
PubMed2003

Use of FTIR, FT-Raman and 13C-NMR spectroscopy for identification of some seaweed phycocolloids.

Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce polysaccharides the main components of which are galactose (galactans)-agar and carrageenan. In addition, alginic acid is extracted from members of the Phaeophyceae. This is a binary polyuronide made up of mannuronic acid and guluronic acid. The wide uses of these phycocolloids are based on their gelling, viscosifying and emulsifying properties, which generate an increasing commercial and scientific interest. In this work, the FTIR and FT-RAMAN spectra of carrageenan and agar, obtained by alkaline extraction from different seaweeds (e.g. Mastocarpus stellatus, Chondrus crispus, Calliblepharis jubata, Chondracanthus acicularis, Chondracanthus teedei and Gracilaria gracilis), were recorded in order to identify the type of phycocolloid produced. The spectra of commercial carrageenan, alginic acid and agar samples (SIGMA and TAAB laboratories) were used as references. Special emphasis was given to the 500-1500 cm(-1) region, which presents several vibrational modes, sensitive to the type of polysaccharide and to the type of glycosidic linkage. The FT-Raman spectra present a higher resolution than FTIR spectra, this allowing the identification of a larger number of characteristic bands. In some cases, phycocolloids can be identified by FT-Raman spectroscopy alone.

Agar↗
PubMedDate not supplied

Effect of pegylation on the structure and function of horse cytochrome c.

The preparation and spectrophotometric characterization of (both Fe2+ and Fe3+ forms) poly(ethylene glycol) (PEG; av FW 5000)-modified horse cytochrome c (cyt c(PEG)n) with different degrees of modification (nav = 6, 19) by UV-vis spectroscopy, circular dichroism spectroscopy, resonance Raman spectroscopy, and cyclic voltammetry are described. Extensive modification (nav = 19) of cyt c causes gross structural deformation of the heme as evidenced by major spectral changes in the UV-vis and circular dichroism spectral signatures of both the Fe2+ and Fe3+ forms. Modification of cyt c by six PEG residues, however, produces a protein in which the heme active site is structurally and functionally intact (UV-vis, circular dichroism, and resonance Raman) and which exhibits at least quasireversible direct electron transfer (Eo' = 338 +/- 5 mV vs SHE; (2.1 +/- 0.6) x 10(-3) cm/s) at bis(4-pyridyl) disulfide-modified Au electrodes.

Animals↗