A sharp inequality for the variance with respect to the Ewens sampling formula

Lithuanian Mathematical Journal - We examine the variance of a linear statistic defined on the symmetric group endowed with the Ewens probability. Despite the dependence of the summands, it can be...     

Chitin/cellulose blend fibers prepared by wet and dry‐wet spinning

We describe the wet and dry‐wet spinning of multifilament cellulosic composite fibers, namely chitin/cellulose fibers. The direct solution process for the two biopolymers based on an ionic liquid as solvent represents an environmentally friendly and alternative technology to the industrially applied viscose and lyocell process. Both cellulose and chitin possess good solubility in 1‐ethyl‐3‐methylimidazolium propionate ([C₂C₁Im][OPr]) and were spun into multifilament composite fibers. Moreover, for the first time, pure chitin multifilament fibers were obtained by dry‐wet spinning. The effect of chitin addition on the filament properties was investigated and evaluated by microscopic, spectroscopic, and mechanical analyses.     

Physicochemical Properties of Dodecylammonium Picrate

A novel surfactant, dodecylammonium picrate (DDAP), was synthesized and its crystal structure was determined by X-ray diffraction analysis. DDAP's physicochemical properties were examined by spectral (infrared and nuclear magnetic resonance), thermal, microscopic, and conductometric studies. The results revealed the influence of counterion specificity on thermal solid-state transitions and solution properties: the Krafft point, the aqueous solubility, the critical micelle concentration, the degree of counterion binding, and thermodynamic parameters of micellization. Copyright 2000 Academic Press.     

Linear Stereo-co-oligopeptides with Alternating D- and L-Residues. I. Synthesis and Mass Spectrometric Behavior of the Members of a Series with Valine Residues

The synthesis of the protected stereo-co-oligopeptides with alternating D - and L -valine residues Boc-(D -Val)_m-(L -Val-D -Val)_n-OMe (m = 0; n = 1,2,3,4,6,8, and m = 1; n = 1,2,3,4) is described. The synthesis has been carried out by using conventional solution methods. The co-oligopeptides up to the nonapeptide (m = 1; n = 4) have been prepared in a stepwise fashion. The dodecapeptide (m = 0; n = 6) and the hexadecapeptide (m = 0; n = 8) have been prepared by condensation of smaller peptides, and the criteria used for assessing their stereochemical purity are discussed. Preliminary characterization data are presented. Even the co-oligopeptides with six or more residues, up to the dodecapeptide included, have given EI/MS. showing the molecular ion peak. The possible reasons for this uncommon behavior are examined.     

Discrimination between an Antiparallel and a Parallel β5.6-Helix Using 1Hα-NMR Spin-Lattice Relaxation

The ¹H-NMR spectrum of Boc-(L -Val-D -Val)₄-OH in CDCl₃ can be attributed either to an antiparallel or to a parallel double-stranded β^5.6-helical structure. To resolve this ambiguity, T₁-measurements have been carried out for the α-protons of Boc-(L -Val-D -Val)₄-OH and its monodeuterated analogue Boc-(L -Val-D -Val)₂ -α-²H-L -Val-D -Val-L -Val-D -Val-L -Val-D -Val-OH. The results show that the H^α of the fifth residue in one strand is close to the H^α of the seventh residue in the other strand, as expected for an antiparallel arrangement, a conclusive demonstration that the correct structure of Boc-(L -Val-D -Val)₄-OH is antiparallel.     

A New Weil Cohomology Theory

There is a Weil cohomology theory with coefficients in a pseudofinitefield of characteristic zero. 2000 Mathematics Subject Classification14F20 (primary), 03C20 (secondary).     

Some Cyclic Oligopeptide with S2n Symmetry

Some cyclic oligopeptides formed by an equal number of alternating D- and L-amino-acid residues have been synthesized by using the hydrochloride of the open-chain peptide acid as precursor and the mixed-anhydride condensation method. The cyclic oligopeptides (tetra-, hexa-, and octavaline, hexaleucine, and hexaphenylalanine) form very stable H-bonded structures (IR-amide band at 3270–3290 cm^?1) which are insoluble in common organic solvents. In CF₃COOH/CDCI₃ (25°), they yield ¹H-NMR spectra snowing the expected equivalency of the various amino-acid residues.     

β-Helical structures of Boc-(L-Val-D-Val)6-OMe in the crystalline state and in chloroform

A conformational study was carried out on Boc-(L -Val-D -Val)₆-OMe in the crystalline state by X-ray and IR. and by ¹H-NMR. in chloroform. The dodecapeptide crystallizes from CHCl₃/EtOAc with a left-handed helical structure of the type ↑↓ β^5.6, and from CHCl₃/MeOH (or MeOH) with a different structure. In chloroform it forms three slowly interconverting species: one is a ↑↓ β^5.6 left-handed helical species, and the other two are most likely single-stranded β^4.4 helical species of opposite handedness. The double-stranded helical species is predominant in fresh solutions of samples obtained from CHCl₃/EtOAc. Because of the slow conversion or formation of this species some hours are needed to reach the conformational equilibrium in chloroform at 25°.