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At least 235 records · Page 13Linked to original sources
PubMed2004

Gold nanoparticle embedded, self-sustained chitosan films as substrates for surface-enhanced Raman scattering.

In this work, self-sustained, biocompatible, biodegradable films containing gold nanostructures have been fabricated for potential application in nanobioscience and ultrasensitive chemical and biochemical analysis. We report a novel synthesis of gold nanoparticles mediated by the biopolymer chitosan. Self-supporting thin films are formed from the resultant gold-chitosan nanocomposite solutions and characterized by UV-visible surface plasmon absorption, transmission electron microscopy, atomic force microscopy, infrared absorption, and Raman scattering measurements. Results demonstrate control over the size and distribution of the nanoparticles produced, which is promising for several applications, including the development of biosensors. As a proof of principle, we demonstrate that gold-chitosan films can be employed in trace analysis using surface-enhanced Raman scattering.

Biocompatible Materials↗
PubMed2003

Fourier transform Raman spectrometry for the quantitative analysis of oil content and humidity in olives.

A method for the direct and fast determination of oil content and humidity in olives using Fourier transform Raman spectrometry is reported. The only sample preparation step required was crushing of the olives using a hammer mill. The crushed olives were placed in a dedicated sample cup, which was rotated excentrically to the horizontal laser beam during spectrum acquisition. This allowed us to sample an increased volume and thus compensate for sample inhomogeneities. In this way the reproducibility of Raman spectra taken from crushed olives was significantly improved. Partial least-squares (PLS) regression was used for the chemometric evaluation of the Raman spectra. Standard errors of prediction for the validation set of 0.81% for oil content (in the range 19.68-35.71%) and 1.54% for humidity (in the range 29.23-51.49%), both expressed as weight percentage referred to fresh matter, were obtained.

Food Analysis↗
PubMed1987

Raman spectroscopic study on the conformation of 11 S form acetylcholinesterase from Torpedo californica.

Vibrational Raman spectroscopy has been used to study the conformation of the 11 S form of acetylcholinesterase from Torpedo californica. Secondary structure analysis by the method of Williams [(1983) J. Mol. Biol. 166, 581-603] shows 49% alpha-helical structure, 23% beta-sheets, 11% turns and 15% undefined structure. Secondary structure estimates obtained for this enzyme by Raman spectroscopy and circular dichroism have been analyzed.

Acetylcholinesterase↗
PubMed1986

Characteristics and variations of B-type DNA conformations in solution: a quantitative analysis of Raman band intensities of eight DNAs.

Raman spectra were obtained from four bacterial DNAs varying in GC content and four periodic DNA polymers in 0.1 M NaCl at 25 degrees C. A curve fitting procedure was employed to quantify and compare Raman band characteristics (peak location, height, and width) from 400 to 1600 cm-1. This procedure enabled us to determine the minimum number of Raman bands in regions with overlapping peaks. Quantitative comparison of the Raman bands of the eight DNAs provided several new results. All of the DNAs examined required bands near 809 (+/- 7) and 835 (+/- 5) cm-1 to accurately reproduce the experimental spectra. Since bands at these frequencies are associated with A-family and B-family conformations, respectively, this result indicates that all DNAs in solution have a mixture of conformations on the time scale of the Raman scattering process. Band characteristics in the 800-850-cm-1 region exhibited some dependence on CG content and base pair sequence. As previously noted by Thomas and Peticolas [Thomas, G. A., & Peticolas, W. L. (1983) J. Am. Chem. Soc. 105, 993], the poly[d(A)].poly[d(T)] spectra were qualitatively distinct in this region. The A-family band is clearly observed at 816 cm-1. The intensity of this band and that of the B-family band at 841 cm-1 were similar, however, to intensities in the natural DNA spectra. Three bands at 811, 823, and 841 cm-1 were required to reproduce the 800-850-cm-1 region of the poly[d(A-T)].poly[d(A-T)] spectra. This may indicate the presence of three backbone conformations in this DNA polymer. Analysis of intensity vs. GC content for 42 Raman bands confirmed previous assignments of base and backbone vibrations and provided additional information on a number of bands.

DNA, Bacterial↗
PubMed2000

Raman and IR spectroscopic investigation of zinc(II)-carnosine complexes.

The zinc(II)-L-carnosine system was investigated at different pH and metal/ligand ratios by Raman and IR spectroscopy. The Raman and IR spectra present some marker bands useful to identify the sites involved in metal chelation at a specific pH value. In particular, the neutral imidazole group gives rise to some Raman bands, such as the nu C(4)===C(5) band, that change in wave number, depending on whether the imidazole ring takes the tautomeric form I or II. Even if tautomer I is predominant in the free ligand, metal coordination can upset tautomeric preference and N(tau)- and N(pi)-ligated complexes can be identified. Although weak compared to those of aromatic residues, these Raman marker bands may be useful in analyzing metal-histidine interaction in peptides and proteins. On the basis of the vibrational results, conclusions can be drawn on the species existing in the system. Depending on the available nitrogen atoms, various complexes can be formed and the prevalent form of the species depends mainly on the pH. At basic pH carnosine gives rise to two different neutral complexes: a water-insoluble polymeric species, [ZnH(-1)L](0)(n), and a dimer, [Zn(2)H(-2)L(2)](0). The first is predominant and involves the tautomeric I form of the imidazole ring in metal chelation; the second contains tautomer II and increases its percentage by going from a 2 to 0.25 metal/ligand ratio. Conversely, the dimeric species dominates at pH 7, whereas two charged species, [ZnHL](2+) and [ZnL](+), are formed under slightly acidic conditions. In the [ZnHL](2+) complex the imidazole ring takes part in the Zn(II) coordination in the tautomeric I form, whereas in [ZnL](+) the ring is protonated and not bound to the Zn(II) ion. In addition, the curve fitting analysis of the 1700-1530 cm(-1) Raman region was helpful in indicating the predominant species at each pH.

Anti-Ulcer Agents↗
PubMed2005

Excited-state mixed valence in a diphenyl hydrazine cation: Spectroscopic consequences of coupling and transition dipole moment orientation.

A quantitative model of mixed-valence excited-state spectroscopy is developed and applied to 2,3-diphenyl-2,3-diazabicyclo[2.2.2]octane. The lowest-energy excited state of this molecule arises from a transition from the ground state, where the charge is located on the hydrazine bridge, to an excited state where the charge is associated with one phenyl group or the other. Coupling splits the absorption band into two components with the lower-energy component being the most intense. The sign of the coupling, derived by using a neighboring orbital model, is positive. The transition dipole moments consist of parallel and antiparallel vector components, and selection rules for each are derived. Bandwidths are caused by progressions in totally symmetric modes determined from resonance Raman spectroscopic analysis. The absorption, emission, and Raman spectra are fit simultaneously with one parameter set.

Cations↗
PubMed2000

In situ Raman microspectroscopic identification and localization of carotenoids: approach to monitoring of UV-B irradiation stress on Antarctic fungus.

The in situ Raman microspectroscopic properties of an Antarctic fungus are investigated to assess the nature and the spatial localization of the main chromophores and to study their spectral changes under enhanced UV-B irradiation. The Raman spectroscopic features of spores in situ are consistent with those of carotenoid-like pigments. In particular, the Raman shifts seem to be related either to the frequency modes of long conjugated double-bond carotenoids or to protein bound beta-carotene. The spectroscopic analysis at different spore depths clearly shows the strongest Raman signal arises from cell wall and membrane structures. The intensity of such a signal shows a drastic reduction upon UV-B irradiation without any significant frequency change. The use of Raman microspectroscopy for nondestructively monitoring the UV-B effects on Arthrobotrys ferox spores is also discussed.

Antarctic Regions↗
PubMed1998

Molecular dynamics simulations of biomembrane models.

A molecular force field dedicated to molecular dynamics simulation of biomembranes was developed. It was parameterized on model compounds related to phospholipids and was able to reproduce at the same time structures, energies, and vibrational spectra. Cross terms in the potential energy function were introduced by solving the redundancy problem among internal coordinates. This force field was used in the 400-ps molecular dynamics simulation of a hydrated bilayer in the gel and liquid crystal phases. The conformational properties of the polar head groups were in particular agreement with the experimental observations using Raman scattering.

Gels↗