Leitf?higkeit

Ohne Zusammenfassung     

Study of the molecular conformation of an aromatic polyamide–hydrazide by intrinsic viscosity

The persistence length of poly(terephthaloyl p-amino benzhydrazide) (X-500) in dimethyl sulfoxide (DMSO) has been determined from intrinsic viscosities measured for several whole-polymer samples. An approximate correction is applied for excluded volume effects, and these corrected values are fitted using the viscosity treatments of Yamakawa and Fujii and of Eizner and Ptitsyn. Both give for the persistence length of X-500 values in the range 30–35 Å. Revised treatment of our previous light scattering data for the same polymer yields 49 Å for the persistence length. Thus the chain extension of X-500 falls between those of para-linked polyamides and those of typical freely coiling macromolecules. Phase diagram studies indicate the solubility of X-500 in DMSO decreases with rising temperature, and can be increased by the addition of LiCl. No anisotropic phase is found in DMSO at the highest volume fraction of polymer, v₂ = 0.19, which can be obtained with 4 g/dl LiCl. The critical concentration of X-500 needed for the appearance of the anisotropic phase depends upon solvent since Morgan reported an anisotropic phase for this polymer in 100% H₂SO₄ when v₂ ≈ 0.13.     

Ein Modell für Bindegewebe-Systeme: Messung des Ionenflusses durch Membrane von Gelen,die Proteoglykan enthalten

Ohne Zusammenfassung     

Effects of heavy-atom substituents on matrices used for matrix-assisted laser desorption—Ionization mass spectrometry

The data reported show that heavy-atom substitution on matrices that are used for matrix-assisted laser desorption-ionization mass spectrometry enhance [M + H]⁺ ion yields of both Leu—enkephalin and vitamin B₁₂. Heavy-atom substitution alters the excited state relaxation dynamics of the matrices as indicated by measured decreases in the measured luminescence (fluorescence and/or phosphorescence) observed for heavy atoms that contain matrices relative to the nonheavy-atom-substituted matrices. The results presented are consistent with the direct involvement of an electronically excited state of the matrix in the formation of analyte [M + H]⁺ ions.     

Calculation of the electric polarizability of a charged spherical dielectric particle by the theory of colloidal electrokinetics

Dielectrophoresis (DEP) is increasingly being explored as a means to manipulate or separate colloidal particles. The direction and strength of the DEP force depend strongly on the induced dipole strength, K, of a polarized particle, and predictions of DEP forces require carefully computed values for K. In this paper, we present the calculation of the dipole strength using the full electrokinetic theory of Mangelsdorf and White for both static and oscillating electric fields. The effects of particle zeta potential, radius, Debye length and electrolyte composition on the magnitude and sign of Re(K) are discussed. The full theory model is compared with the extended Maxwell-Wagner (EMW) model and the results show that the EMW model can fail to predict the full Re(K) variation with frequency, even predicting Re(K) with the incorrect sign depending on system parameters. A program for the dipole strength calculation shown in this paper is available from the authors.