Search results for "matrix"
showing 10 items of 3205 documents
Polycyclic Aromatic Hydrocarbons in Sediments of Marine Coastal Lagoons in Messina, Italy: Extraction and GC/MS Analysis, Distribution and Sources
2004
The content of 21 polycyclic aromatic hydrocarbons (PAHs) has been determined in 16 samples of sediments collected from Ganzirri and Faro marine coastal lagoons in Messina (Italy). Analysis was performed by gas chromatography/mass spectrometry (GC/MS) in selected ion monitoring (SIM) mode. The total concentration of polycyclic aromatic hydrocarbons (PAHs) ranged from 74 to 5755 ...g/Kg of dry matrix. The resulting distributions and molecular ratios of specific compounds have been discussed in terms of sampling location and origin of organic matter. The results obtained show that levels of contamination are not homogeneous throughout the stations, while the relative distributions of PAH are…
Pencil Lead as a Matrix for MALDI-ToF Mass Spectrometry of Sensitive Functional Polymers
2007
With the increase in complexity of functional polymers in recent years, MALDI-ToF has become an important tool for gaining precise information on polymer functionality, end groups, and, in special cases, molecular weights. Here we describe how pencil lead, deposited by simply drawing with a regular pencil onto conventional MALDI-ToF targets, can be used as a very attractive matrix for MALDI-ToF mass spectrometry of synthetic polymers. Highly sensitive polymers such as silyl hydride functional poly(styrene), poly(butadiene), and poly(isoprene) have been investigated using conventional MALDI-ToF matrices as well as pencil lead. In all cases, the use of pencil lead prevented oxidation of the h…
Vibrational relaxation of matrix-isolated carboxylic acid dimers and monomers.
2009
Femtosecond mid-IR transient absorption spectroscopy was used to probe the vibrational dynamics of formic acid and acetic acid isolated in solid argon following excitation of the fundamental transition of the carbonyl stretching mode. Carboxylic acids form extremely stable H-bonded dimers, hindering the study of the monomeric species at equilibrium conditions. The low-temperature rare-gas matrix isolation technique allows for a unique control over aggregation enabling the study of the monomer vibrational dynamics, as well as the dynamics of two distinct dimer structures (cyclic and open chain). This study provides insight into the role of the methyl rotor and hydrogen bonding in the vibrati…
Ferrochirality: A simple theoretical model of interacting dynamically invertible helical polymers, 1. The basic effects
1994
The effect of interaction between reversible helical polymers of the poly(hexyl isocyanate) type is investigated by using a molecular field model. It is shown that for interacting helices a critical temperature exists below which they must adopt a common helix-sense spontaneously, even in the absence of any external or intrinsic chiral force
Contact sites of peptide-oligoribonucleotide cross-links identified by a combination of peptide and nucleotide sequencing with MALDI MS.
1997
We have investigated peptide–oligoribonucleotide complexes isolated from cross-linked Escherichia coli 30S ribosomal subunits in order to identify the contact sites of these complexes at the molecular level. For this purpose, reversed-phase (RP) HPLC-purified peptide–oligoribonucleotide complexes were submitted to N-terminal amino acid sequencing in order to determine the cross-linked peptide moiety and were analyzed using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) for calculation of the nucleotide composition of the cross-linked complex. Subsequently, for nucleotide sequence information the complexes were partially hydrolyzed or treated with exonucleases and a…
An ab initio softness metric to measure the similarity between all pairs of amino acids
2010
Abstract The search for quantitative index of similarity between molecular moeties is important for its applications in pharmacology. Similarity is also an important concept in computational biology to measure the exchangeability of an amino acid by another in a protein sequence. In the present work, a distance between two molecules based on local and global softnesses of their fragments is defined. The method proposed is general and could be applied to any molecular library. It is first applied to compute the distance between the 190 pairs of different amino acids in their neutral states. Two amino acids belonging to the one of the biochemical class (aliphatic, sulfur-containing, acidic, ……
Anisotropic Effect after Stretching of the Spin-Crossover Compound [Fe(II)(2,6-bis-(benzimidazol-2′-yl)pyridine)2] (C1O4)2 in Polyvinylalcohol Polyme…
1999
Abstract [Fe(II)(2,6-bis-(benzimidazol-2′-yl)-pyridine)2](C1O4)2 diffused into a poly(vinyl)alcohol polymer matrix, exhibits an thermally induced spin-crossover. After stretching the matrix, the compound orients itself in the matrix. Polarised UV/VIS spectra measured parallel and perpendicular to the stretching direction allowed to calculate the distortion of the molecule in the matrix by means of semi-empirical PPP SCF-CI calculations.
Irradiation of low density and high density polyethylenes in presence of carbon dioxide in subcritical and supercritical conditions
1998
Abstract The grafting of carboxylated and oxygenated functions on low density and high density polyethylenes is carried out by gamma irradiation in the presence of carbon dioxide. Both crosslinking and grafting of oxidised groups occur. The extent of these molecular modifications depends on the physical conditions of the gas phase and on the nature of the polymer matrix.
Shear flow characterization of blends containing liquid crystal polymers
1992
A simple phenomenological approach is proposed in order to predict the presence of minima in the viscosity-composition curves of blends of thermoplastic with liquid crystal polymer (LCP). When the viscosity of the liquid crystal polymer is larger than that of the thermoplastic matrix, a minimum is observed. A possible explanation of the presence of yield stress in the flow curves of these blends is also given.
Time-monitoring sensor based on oxygen diffusion in an indicator/polymer matrix
2013
Abstract A time-monitoring sensor based on the oxidation of leuco methylene blue (LMB) to methylene blue (MB) was developed. The sensor changes its color from yellow to green in the presence of oxygen and was integrated into a poly(vinyl alcohol) matrix. The diffusion of the oxygen in the polymer matrix as well as the oxygen uptake due to the oxidation reaction determines the time monitoring of the sensor. A physical model has been developed that accounts for both the diffusion as well as the oxidation reaction. For this purpose, the reaction kinetics was determined experimentally. Moreover, the diffusion coefficient of oxygen was determined and concentration profiles in the polymer matrix …