Sweep Tests on Vibrating Systems with Power-Law Damping

The non-stationary response in vibrating systems with power-law damping, subjected to sweep tests is considered. Using the method of averaging, it is shown that the bifurcation delay persists in all forms of power-law damping, viz., Coulomb, orifice and cubic damping models. Experimental investigations on a soft type of isolator confirm the existence of delay in the jump phenomenon. These results also indicate that the softening nature of non-linearity can be profitably employed in the design of isolators and vehicle suspensions.     

Recognition of flexible peptides in water by transition metal complexes

This paper describes the design, synthesis, and evaluation of transition metal complexes capable of recognizing flexible histidine-containing peptides in aqueous medium (25 mM HEPES buffer, pH = 7.0, 25 degrees C). When the pattern of metal ions on a complex matches with the pattern of histidine moieties on the peptide, strong interaction (K = 1.2 x 10(6) M-1) can be achieved. The complex was highly selective (> 200:1) in discriminating similar flexible peptides differing only by one glycine unit.     

3-[4-Bromo-α(<Emphasis Type="Italic">R</Emphasis>*)-methoxybenzyl]-6-chloro-3(<Emphasis Type="Italic">S</Emphasis>*),4(<Emphasis Type="Italic">S</Emphasis>*)-dihydroxychroman: X-ray and DFT Studies

Sodium borohydride reduction of E-3-benzylidenechromanone epoxides in dry methanol has afforded 3(S*), 4(S*)-dihydroxy-3-[α(R*)-methoxybenzyl]chromans as an interesting class of products, the structures of which have been assigned mainly from spectral data and consideration of the mechanistic aspects. X-ray diffraction study of one of them, 3-[4-bromo-α(R*)-methoxybenzyl]-6-chloro-3(S*),4(S*)- dihydroxychroman, is performed. The title compound crystallizes in the monoclinic sp. gr. P2₁/n, with a = 13.336(6) Å, b = 10.866(5) Å, c = 27.166(11) Å, β = 95.193(6)°, V = 3920(3) ų, and Z = 8. Supramolecular construction of the compound involves O–H···O intermolecular hydrogen bonds as well as three other types of non-covalent interactions which are responsible for crystal packing. Density functional theory was applied for geometry optimization, molecular orbital calculations, and prediction of UV spectral features. The geometric parameters (bond lengths, bond angles, and dihedral angles) for the representative compound obtained from density functional theory with B3LY6-31G basis set were in good agreement with experimental values.     

Controllable shape selectivity based on highly ordered carbonyl and methyl groups in simple β-structural polypeptide on silica

Poly(l-alanine)-grafted porous silica (Sil-Ala₂₂) was prepared by polymerization of N-carboxyanhydride of l-alanine initiated by 3-aminopropylated silica. The retention behaviors of the column packed with Sil-Ala₂₂ were investigated by using alkylbenzenes and polycyclic aromatic hydrocarbons as injection samples in liquid chromatography. The Ala₂₂ phase was in a rigid β-form structure and thus provided specific interaction sites, which were derived from the highly ordered carbonyl and methyl groups. These interaction sites bring unique molecular-shape discriminations: molecular-length and non-planarity selectivity, which are controllable by altering organic solvent used as a part of mobile phase.