Search results for "molecule"
showing 10 items of 5162 documents
Miscibility of cyanine dyes in two-dimensional aggregates
1995
Mixed aggregates of cyanine dyes at a charged lipid monolayer surface are studied by absorption spectroscopy, fluorescence microscopy and electron diffraction. We show that slight variations of the molecular structure can convert a system from being fully miscible to being immiscible, and also that the concentrations of dyes in the solution and in the crystal may deviate considerably. The different concentration in the solution and crystal was observed for a molecule where force field calculations indicated the existence of two isomers in solution and where probably only one fits into the lattice.
Line intensities of CH3D in the Triad region: 6–10μm
2004
Abstract Line intensities of the three lowest fundamentals of the 12CH3D Triad are modeled with an RMS of 3.2% using over 2100 observed values retrieved by multispectrum fitting of enriched sample spectra recorded with two Fourier transform spectrometers. The band strengths of the Triad in units of 10−18 cm−1/(molecule cm−2) at 296 K are, respectively, 2.33 for ν6 (E) at 1161 cm−1, 1.75 for ν3 (A1) at 1307 cm−1 and 0.571 for ν5 (E) at 1472 cm−1. The total calculated absorption arising from 12CH3D Triad fundamentals is 4.65×10−18 cm−1/(molecule cm−2) at 296 K. In addition, some 740 intensities of nine hotbands are fitted to 8.1%; most of the hotband measurements belong to 2ν6−ν6 and ν3+ν6−ν3…
Investigation of molecular dimers by ensemble and single molecule spectroscopy
2002
International audience; We have investigated molecular dimers with different electronic coupling strengths by bulk and single molecule spectroscopy. In one of the dimers the two monomers (perylene-monoimide) are directly connected via a single bond while in the other one they are separated by the benzil motif. The close proximity of the monomers in the first case gives rise to excitonic band splitting which is clearly observable in the bulk absorption spectra. For the benzil structure the electronic interactions are governed by Förster-type energy hopping between the monomers. Fluorescence intensity trajectories at the single molecule level show one-step and two-step bleaching behaviour whi…
Temperature and pH Dependence XAFS Study of Gd(DOTA)(-) and Gd(DTPA)(2)(-) Complexes: Solid State and Solution Structures.
1998
We present an X-ray absorption spectroscopy study of the local structures of Gd(DTPA)(2)(-) and Gd(DOTA)(-) complexes in the crystalline state (at room and low temperatures) and in aqueous solutions exhibiting various pH values (0.15-7) at different temperatures (25-90 degrees C). Using X-ray absorption fine structure (XAFS) analysis procedures and ab initio multiple scattering calculations of XAFS spectra at the Gd L(3) edge, we reconstructed the Gd(3+) local environment, and compared it with existing structural models. From neutral pH to a value of 1.5, we found that the local environment and complex dynamics around the gadolinium ions were conserved up to 4.5 Å, and the structure agreed …
Vacuum-ultraviolet absorption of interstitial O2 and H2O molecules in SiO2 glass
2006
Abstract Vacuum-ultraviolet (VUV) absorption of O 2 and H 2 O molecules incorporated in interstitial voids in SiO 2 glass by thermal annealings was examined. Interactions of the interstitial molecules with the surrounding SiO 2 glass network lead to a redshift of the VUV absorption band of interstitial O 2 , while a blueshift of that of interstitial H 2 O, both accompanied by an increase in the intensity of the absorption bands. The Coulomb repulsion, London dispersion, and hydrogen bonding are the main interactions responsible for the modification of the VUV absorption bands.
Interactions of amino acids with aluminum octacarboxyphthalocyanine hydroxide. Experimental and DFT studies
2017
The influence of albumin and amino acids (l-serine, glycine, l-histidine, l-tryptophan, l-cysteine) on the properties of aluminum octacarboxyphthalocyanine hydroxide (Al(OH)PcOC) was investigated in a phosphate buffer (pH 8.0). Particular attention was paid to the spectroscopic properties and photostability of Al(OH)PcOC. The effect of albumin or amino acids on the photodegradation of Al(OH)PcOC was examined in water using red light: 685 nm and daylight irradiation. Analysis of kinetic curves indicated that interaction with those molecules increases the photostability of Al(OH)PcOC. The molecular structure of Al(OH)PcOC complexes (in vacuum and in water) with axially or equatorially coordin…
Optical method for predicting the composition of self-assembled monolayers of mixed thiols on surfaces coated with silver nanoparticles.
2012
With a simple optical method, based on UV-vis absorption spectra on glass slides, it is possible to predict the composition of self-assembled monolayers of mixed thiols, grafted on monolayers of silver nanoparticles. Glass slides are modified with the layer-by-layer technique, first forming a monolayer of mercaptopropyltrimethoxysilane, then grafting a monolayer of silver nanoparticles on it. These surfaces are further coated by single or mixed thiol monolayers, by dipping the slides in toluene solutions of the chosen thiols. Exchange constants are calculated for the competitive deposition between the colorless 1-dodecanethiol or PEG5000 thiol and BDP-SH, with the latter being a thiol-beari…
Reversible isomerization of metal nanoclusters induced by intermolecular interaction
2021
Most inorganic nanoparticles are directly surface-terminated (and -stabilized) by protecting ligands, which could greatly affect the atomic packing and physical/chemical properties of their inorganic cores. Here, we show that the intermolecular interactions between the adsorbed molecules and surface ligands can also affect the core structure of inorganic nanoparticles. Through the coupling/decoupling of cationic surfactants (cetyltrimethylammonium cations, CTA+) and anionic surface ligands (para-mercaptobenzoic acid, p-MBA) in the aqueous phase, we have achieved a reversible transformation between two isomers of [Au25(p-MBA)18]− nanoclusters. The interconversion process between the two isom…
Electronic signature of the instantaneous asymmetry in the first coordination shell of liquid water
2013
Interpretation of the X-ray spectra of water as evidence for its asymmetric structure has challenged the conventional symmetric nearly-tetrahedral model and initiated an intense debate about the order and symmetry of the hydrogen bond network in water. Here, we present new insights into the nature of local interactions in water obtained using a novel energy decomposition method. Our simulations reveal that while a water molecule forms, on average, two strong donor and two strong acceptor bonds, there is a significant asymmetry in the energy of these contacts. We demonstrate that this asymmetry is a result of small instantaneous distortions of hydrogen bonds, which appear as fluctuations on …
Detection of deuterated molecules, but not of lithium hydride, in the z = 0.89 absorber toward PKS 1830−211
2020
Deuterium and lithium are light elements of high cosmological and astrophysical importance. In this work we report the first detection of deuterated molecules and a search for lithium hydride, 7LiH, at redshift z=0.89 in the spiral galaxy intercepting the line of sight to the quasar PKS1830-211. We used ALMA to observe several submillimeter lines of ND, NH2D, and HDO, and their related isotopomers NH2, NH3, and H2^18O, in absorption against the southwest image of the quasar, allowing us to derive XD/XH abundance ratios. The absorption spectra mainly consist of two distinct narrow velocity components for which we find remarkable differences. One velocity component shows XD/XH abundances that…