The spectrum of allene near 5 μm

The infrared bands of allene between 1920 and 2028 cm^?1 were measured on a large grating spectrometer with effective resolution of 0.006–0.007 cm^?1 after deconvolution. The main band in this region is the antisymmetric CC stretching fundamental ν₆ of symmetry B₂, accompanied on the high-frequency side by the overtone band 2ν₉ of the degenerate CH₂ rocking vibration. The overtone has three components of species B₂, B₁, and A₁, of which B₂ is in Fermi resonance with ν₆, B₁ has second-order Coriolis interaction with ν₆, while A₁ is in l-type interaction with the B₁ and B₂ components. Additional perturbations by other unobserved states were detected in the spectrum. The observed transitions were analyzed with the aid of a general computer program system SYMTOP designed for analysis of symmetric-top spectra. The main program effects a least-squares refinement of the spectroscopic constants for a set of bands whose upper states interact through arbitrary matrix elements. Two sets of spectroscopic constants for the ν₆, 2ν₉ states were calculated. One, based only on those lines which appear to be unperturbed by unknown and unobserved states, and a second, obtained after inclusion in the H matrix of two perturbing states designed to simulate the effect of the perturbations on all of the data. Comparison indicates that the lower-order constants based merely on the “unperturbed” data are quite satisfactory. Molecular constants for the ν₉ vibration of C₃H₄ are reported.     

Laminar boundary layers of co-current gas-liquid stratified flows—I. Theory

The flow in the developing laminar boundary layers on a flat moving gas-liquid interface is studied theoretically. Analysis of the equations shows that flows depend on two parameters, each less than unity. Using a perturbation method, an analytical solution with accuracy to the third power of the small parameters is obtained and is in close agreement with the exact solution of the problem.     

Transmembrane potential measurement with carbocyanine dye diS-C3-(5): fast fluorescence decay studies

The mechanism of carbocyanine dye diS-C3-(5) fluorescence intensity variations with transmembrane potential changes has been studied using time-resolved fluorescence spectroscopy. Clear evidence is given of the transmembrane-potential-dependent partition of the dye among various sites with different fluorescence lifetimes. It was found that fluorescence decay profiles reflect the transmembrane potential changes.     

Folding structures of isolated peptides as revealed by gas-phase mid-infrared spectroscopy.

To understand the intrinsic properties of peptides, which are determined by factors such as intramolecular hydrogen bonding, van der Waals bonding and electrostatic interactions, the conformational landscape of isolated protein building blocks in the gas phase was investigated. Here, we present IR-UV double-resonance spectra of jet-cooled, uncapped peptides containing a tryptophan (Trp) UV chromophore in the 1000-2000 cm(-1) spectral range. In the series Trp, Trp-Gly and Trp-Gly-Gly (where Gly stands for glycine), the number of detected conformers was found to decrease from six (Snoek et al., PCCP, 2001, 3, 1819) to four and two, respectively, which indicates a trend to relaxation to a global minimum. Density functional theory calculations reveal that the O-H in-plane bending vibration, together with the N-H in-plane bend ing and the peptide C=O stretching vibrations, is a sensitive probe to hydrogen bonding and, thus, to the folding of the peptide backbone in these structures. This enables the identification of spectroscopic fingerprints for the various conformational structures. By comparing the experimentally observed IR spectra with the calculated spectra, a unique conformational assignment can be made in most cases. The IR-UV spectrum of a Trp-containing nonapeptide (Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu) was recorded as well and, although the IR spectrum is less well-resolved (and it probably results from different isomers), groups of amide I (peptide C=O stretching) and amide II (N-H in-plane bending) bands can still be recognised, in agreement with predictions at the AM1 level.