Heterogeneity in the binding of chymotrypsin and related proteins to affinity chromatographic media

The binding of a series of related proteins, namely, α-chymotrypsin, chymotrypsinogen A, DIP-chymotrypsin, and TPCK-chymotrypsin,² to affinity gels consisting of 4-phenylbutylamine or ε-aminocaproyl-d-tryptophanmethylester covalently attached to Sepharose 4B was investigated. Considerable heterogeneity in the binding was observed, both at the level of the affinity adsorbent and with respect to the proteins themselves. Both the aromatic moiety of the ligand and the positively charged isourea group introduced during the coupling of the ligand to the gel play a part in the stabilization of the binding of α-chymotrypsin. At least a part of the binding involves the substrate binding site of the enzyme. The existence of secondary binding sites on the proteins, capable of interaction with gel-bound ligand, is suggested by the observation that at fairly high levels of substitution of gel by ligand the zymogen and covalently modified enzyme species are also bound quite strongly. Since the level of gel substitution is difficult to control, the results emphasize the necessity of a thorough investigation of the binding properties of a given affinity medium prior to use in the separation of active chymotrypsin from inactive derivatives.     

Synthesis,processing, and third-order nonlinear optical properties of benzobisthiazole polymers containing thiophene moieties

Benzobisthiazole polymers containing mono-, bi-, and terthiophene moieties were synthesized through polycondensation in polyphosphoric acid of 2,5-diamino-1,4-benzenedithiol dihydrochloride with thiophene-2,5-dicarboxylic acid, 2,2′-bithiophene-5,5′-dicarboxylic acid, and 2,2′:5′,2″-terthlophene-5,5″-dicarboxylic acid, or their corresponding diacid chlorides, respectively. Intrinsic viscosities of up to 8.1 dL/g (methanesulfonic acid, 30°C) were recorded. Polymer structures were verified by elemental analysis and spectroscopic comparison of the polymers with appropriate model compounds. Onset of breakdown under thermogravimetric analysis in air occurred in the 460–590°C range with the benzobisthiazole polymers containing a monothiophene linkage being the most stable. Films suitable for third-order optical susceptibility measurements could be prepared by extrusion techniques from the benzobisthiazole polymer containing a monothiophene linkage. Degenerate four wave mixing measurements on this film yielded a third order optical susceptibility χ⁽³⁾ of approximately 4.5 × 10^?10 esu. © 1993 John Wiley & Sons, Inc.     

Thermodynamics of solute transfer between chloroform and water

The apparent enthalpies, free energies and entropies of transfer from water saturated chloroform to chloroform saturated aqueous buffer (pH 7) were determined for five primary alcohols and six other organic nonelectrolytes using an isoperibol flow microcalorimeter. A linear relationship between the enthalpies and free energies of transfer is found for the homologous series of alcohols indicating that the occurrence of enthalpy-entropy compensation in solute transfer is not restricted to solvent systems of low mutual solubility. The apparent thermodynamics of transfer from chloroform to aqueous buffer were compared with those from 2,2,4-trimethylpentane to aqueous buffer and were rationalized in terms of solvation interactions.     

Interaction between carbon dioxide and naphthalene: A molecular modeling approach

The formation of a charge-transfer complex between carbon dioxide and naphthalene was studied using a molecular modeling program, with the aim of studying the solubility of naphthalene in supercritical carbon dioxide. The orbitals involved in the formation of the complex were studied using MINDO/3 as the semi-empirical method. A solvent cage was constructed, and the maximum number of carbon dioxide molecules to surround naphthalene was found to be 20. The heat of interaction of the complex was obtained using MINDO/3. © 1994 by John Wiley & Sons, Inc.     

Speciation of protein-bound trace elements by gel electrophoresis and atomic spectrometry

The metabolism of trace elements, in particular their binding to proteins in biological systems is of great importance in biochemical, toxicological, and pharmacological studies. As a result there has been a sustained interest over the last two decades in the speciation of protein-bound metals. Various analytical approaches have been employed, combining efficient separation of metalloproteins by liquid chromatography or electrophoresis with high-sensitivity elemental detection. Slab-gel electrophoresis (GE) is a key platform for high-resolution protein separation, and has been combined with autoradiography and various atomic spectrometric techniques for in-gel determination of protein-bound metals. Recently, the combination of GE with state-of-the-art inductively coupled plasma-mass spectrometry (ICP-MS), particularly when linked to laser ablation (LA) for direct gel interrogation, has opened up new opportunities for rapid characterization of metalloproteins. The use of GE and atomic spectrometry for the speciation of protein-bound trace elements is reviewed in this paper. Technical requirements for gel electrophoresis/atomic spectrometric measurement are considered in terms of method compatibilities, detection capability and potential usefulness. The literature is also surveyed to illustrate current status and future trends.     

Evolution of surface morphologies in multivariant assemblies of surface-tethered diblock copolymers after selective solvent treatment

We study systematically the topography behavior of PHEMA-b-PMMA block as a function of the PHEMA and PMMA block lengths after selectively collapsing the top (PMMA) block by using surface-anchored assemblies of poly(2-hydroxyethyl methacrylate-b-methyl methacrylate), PHEMA-b-PMMA, block copolymer with orthogonally varying lengths of each block. Our experimental results are in excellent qualitative agreement with topology diagrams predicted by self-consistent field calculations of Zhulina and co-workers.     

Quasiparticle lifetimes in pure Al and Pb

We present results of theoretical calculations of the quasiparticle lifetimes in pure Al and Pb which are due to the electron-phonon interaction. A four-plane-wave model is used to describe the electronic structure and the coupling with the phonons. The lattice dynamics is taken from inelastic neutron scattering data. At a given temperature (T) the lifetimes (τ) display considerable variation with position on the Fermi surface (FS). At several points on the FS we obtain through a least-squares fit to our numerical output on the low temperature variation of τ, the best power law of the form AT^α with A and α constants. The exponent α is found to vary significantly from point to point.     

The Personality of O.R. Workers—Are They Different?

This paper is a preliminary attempt to compare the personality of O.R. workers with research scientists and other professionals in the management area. It is based on 16PF personality tests carried out on 56 U.K. operational research workers. The results indicate that this group has a personality profile which is significantly different from the published profiles of the professional groupings. It is believed that the results are highly indicative and justify further research.     

Foreword

Journal of the Operational Research Society -