Peptide mapping by reversed-phase high-performance liquid chromatography employing silica rod monoliths

In this paper, a general procedure is described for the generation of peptide maps of proteins with monolithic silica-based columns. The peptide fragments were obtained by tryptic digestion of various cytochrome c species with purification of the tryptic fragments achieved by reversed-phase high-performance liquid chromatographic methods. Peak assignment of the various peptides was based on evaluation of the biophysical properties of the individual peptides and via mass spectrometric identification. The performance of several different monolithic sorbents prepared as columns of identical cross-sectional dimensions were investigated as part of these peptide mapping studies and the data evaluated by applying solvent strength theory. These studies revealed curvilinear dependencies in the corresponding relative resolution maps. These findings directly impact on the selection of specific sorbent types or column configurations for peptide separations with silica rod monoliths. Moreover, the influence of variations in the amino acid sequence of the cytochrome cs were evaluated with respect to their effect on intrinsic hydrophobicity, the number of experimental observed tryptic cleavage sites, detection limits of the derived fragments in relation to their molecular size, and the chromatographic selectivity and resolution of the various peptides obtained following enzymatic fragmentation of the parent protein. Finally, the scope of these approaches in method development was examined in terms of robustness and efficiency.     

Coulomb interactions in metallic VO2

The intra-cationic coulomb energy in the metallic phase of VO₂ is estimated using a model in which the observed spin susceptibility and its temperature dependence arise from correlation modified exchange enhancement of the spin susceptibility of the d - subbands.     

A subgradient algorithm for certain minimax and minisum problems

We present a subgradient algorithm for minimizing the maximum of a finite collection of functions. It is assumed that each function is the sum of a finite collection of basic convex functions and that the number of different subgradient sets associated with nondifferentiable points of each basic function is finite on any bounded set. Problems belonging to this class include the linear approximation problem and both the minimax and minisum problems of location theory. Convergence of the algorithm to an epsilon-optimal solution is proven and its effectiveness is demonstrated by solving a number of location problems and linear approximation problems.This research was partially supported by the Army Research Office, Triangle Park, NC, under contract number DAH-CO4-75-G-0150, and by NSF grants ENG 16-24294 and ENG 75-10225.     

Carbon-13 chemical shifts of some propargyl alcohol derivatives

The natural abundance ¹³C chemical shifts of a range of propargyl alcohol derivatives have been determined and individual resonances assigned. The shielding effects of the triple bond and hydroxyl group on neigbouring carbons have been characterised. The observed for these compounds are compared to those of alkyl or allyl alcohols.     

Rapid chromatographic isolation and immunoblot characterization of immunoreactive fibroblast growth factor-related polypeptides from various tissues

Procedures to rapidly isolate fibroblast growth factor (FGF)-like activity from a number of tissue sources (lung, plasma, brain, ovary, corpus luteum, pituitary, chondrosarcoma) of bovine, porcine or rat origin are described. In addition, immunoblotting experiments using well characterized and specific rabbit polyclonal anti-fibroblast growth factor beta (anti-FGF-beta) sera have been performed. Besides documenting the first report of the isolation of FGF-beta from bovine lung and plasma, these studies provide evidence for the existence of higher-molecular-mass proteins with FGF-beta-like immunoreactivity. For example, in addition to new truncated forms of the acidic and basic FGF (FGF-alpha and FGF-beta), respectively, other higher-molecular-mass immunoreactive proteins were detected in bovine, pig and rat brain, and in rat chondrosarcoma. The tissue distribution of these immunoreactive proteins and their competitive inhibition characteristics mitigate against the possibility that the polyclonal antisera are cross-reacting non-specifically with common cellular proteins. Rather, the data suggest that the immunoblotting technique is either detecting other proteins structurally related to FGF-beta or alternatively FGF-beta is strongly bound to specific carrier proteins (e.g. heparan sulphate proteoglycan fragments) associated with their transport and recognition at the cellular level.     

A new ring opening reaction of N-aminophthalimide hydrazones

Araldehyde hydrazones III of N-aminophthalimide underwent rapid ring opening reactions initiated by the addition of excess base to their refluxing methanolic solutions. The products were conveniently isolated through liquid-liquid extraction as the stable sodium salts V, and acidification precipitated the resulting phthalic acid congeners VI from aqueous solution. Compounds III readily exchanged one hydrazine moiety for another. For example, IIId reacted with 2,4-dinitrophenylhydrazine to give the 2,4-dinitrophenylhydrazone of 4-chlorobenzaldehyde (VIId, 93%). Nonetheless, IIIg reacted exclusively at the carboxaldehyde function to give products VIIIa and VIIIb.     

Permeation through homopolymer latex films

The helium permeabilities of homopolymer films cast from polymer solutions and latex dispersions have been measured as a function of time. The permeability coefficients of most polymer latex films started off at a value which was considerably higher than that of the corresponding solvent-cast film, but then dropped at a rate dependent on the polymer concerned. The permeability coefficients levelled off at a value which was closer to, but still higher than that of the equivalent solvent-cast film. Solvent-cast film permeabilities remained constant for the period of several months over which time they were examined. The reduction in the permeability of latex films is attributed to ageing processes occurring within the film after casting. The fact that latex film permeability coefficients are always higher than those of solvent-cast films suggests that latex films never become completely homogeneous. The effect on permeability of the latex type and characteristics, and preparation and storage conditions has been examined. The polymer molecular weight, particle size, and surface-change density did not appear to exert any influence, within experimental error. However, the time-dependent permeability behavior was affected by the film preparation and storage temperatures.     

Mechanism of emulsion polymerization of styrene in soap-free systems

The formation and growth of monodisperse polystyrene latex particles in the absence of added surfactant has been studied by sampling polymerization reactions at different times and determining the surface and bulk properties of the latex. A large number of nuclei in excess of 5 × 10¹²/ml were generated during the first minute of reaction, but this fell due to coagulation until a constant number (10¹¹?10¹²/ml) was reached. The rate of polymerization per particle was then found to be proportional to the particle radius. Gel-permeation chromatography has shown that the initial particles consist mainly of material of MW 1000 with a small amount of polymer up to MW 10⁶, and the presence of this low molecular weight polymer, which in many cases can still be detected after 100% conversion, is taken as being indicative of particle formation via a micellization-type mechanism involving short-chain (MW 500) free-radical oligomers. M?_n values determined for the latex particles throughout the course of reactions show that the molecular weight increases to a maximum of about 10⁵ as the particles grow. The presence of anomalous regions within the particles has been confirmed by transmission electron microscopy, scanning electron microscopy, and gas adsorption studies. It has also been found possible to re-expose these regions within apparently homogeneous particles by stirring with styrene monomer; this is indicative of a molecular weight heterogeneity within the latex particles. The presence of sulfate, carboxyl, and hydroxyl groups upon the latex particle surfaces has been determined by conductometric titration.     

Measuring rates of reaction in supercooled organic particles with implications for atmospheric aerosol

The kinetics of heterogeneous reactions involving supercooled organic droplets is reported for the first time. Reactions between ozone and internally-mixed sub-micrometre particles containing an unsaturated alkenoic acid, oleic acid, and an n-alkanoic acid, myristic acid, were studied as a simple model for the oxidation of meat-cooking aerosol. The reactions were followed by monitoring the rate of oleic acid loss using an Aerosol CIMS (chemical ionization mass spectrometry) instrument for real-time particle analysis. Evidence of as much as 32 degrees C supercooling at room temperature was observed depending on particle composition. FTIR spectra of the aerosol also demonstrate features indicative of supercooling. Particles in which crystallization was induced by cooling below room temperature demonstrated decreased reactivity by a factor of 12 compared to supercooled particles of the same composition. This drastic difference in reactivity could have significant implications for the lifetimes of reactive species in ambient aerosol as well as for the accurate source apportionment of particulate matter.