Semisimilarity of molecular bodies: Scaling–nesting similarity measures

A simple, new technique for the evaluation of the similarity of molecular shapes is presented. The concept of semisimilarity (asymmetric similarity) is applied within the topological–geometrical framework of scaling–nesting similarity measures of molecules. The practical application of these similarity measures is illustrated by the examples of the three-dimensional formal bodies of electronic charge densities of a set of simple molecules. © 1994 John Wiley & Sons, Inc.     

Contribution to the study of the mechanism of curing of unsaturated polyester resins

The mechanism of copolymerization of monomethyl and dimethyl maleates and fumarates with styrene was studied by analysis of the conformation of the acid units of the resulting copolymers. The absorption bands for C?O stretching and OH stretching in the spectra of the copolymers are fully identical. They are quite different from the spectra of the copolymers obtained from maleic anhydride and styrene that are subsequently treated with absolute methanol to give the monoester which is then esterified with diazomethane to give the diester. The acid units of the copolymers derived from maleic anhydride exist in a gauche configuration; copolymers derived from fumaric units exist in a trans conformation. The identity of copolymers derived from maleic units with those derived from fumaric units but not with those derived from maleic anhydride indicates that the first step in the copolymerization of the maleic units is an isomerization to fumaric units, which are actually the genuine comonomers.     

Automated direct determination of chromium in blood and urine by electrothermal atomic absorption spectrometry

A simple direct procedure for the determination of chromium in whole blood and urine by graphite-furnace atomic absorption spectrometry is described. Whole blood samples are diluted with 0.1% Triton-X solution before injection, whereas urine samples are injected directly. Calibration is done by direct comparison against matrix-matched standards. Between-run precision is 5.4% at 154 nmol l^?1 for urine and 3.6% at 142 nmol l^?1 for blood. The detection limits are 3.8 nmol l^?1 for urine and 11.5 nmol l^?1 for blood, each for a 20μl sample. The calibration range extends up to 770 nmol l^?1 for both blood and urine. This allows the determination of chromium in both occupationally exposed and unexposed groups. The graphite-furnace conditions for each matrix are similar. Elimination fo sample pretreatment minimizes the risk of contamination and allows a rapid sample throughput of 50–60 samples per day. The methods described are particularly suited for the screening and surveying of populations occupationally exposed to chromium.     

Inhibition and labeling of enzymes and abzymes by phosphonate diesters

Reactive phosphonate diesters were designed and prepared as inhibitors of serine proteases and esterases. Inactivation of trypsin, chymotrypsin, and butyrylcholinesterase was determined by residual enzymaticactivity as well as by the release of a chromogenic or fluorogenic product of the inhibition reaction. Second-order rate constants were determined from rates of nitrophenol formation. Application of the reaction for active-site titration of enzyme preparations is demonstrated. A basic functional group present in the nitrophenyl tropane phosphonate diester was shown to confer selectivity for inactivation of try psin and chymotrypsin. Biotinylated derivatives of the phosphonate diesters were prepared to permitanalysis of proteins modified in the inhibition reaction. Labeled polypeptides were resolved by SDSPAGE, electroblotted, and detected by streptavidin-peroxidase staining. A detection limit of less than 4 ng, corresponding to 20 nM of trypsin, was demonstrated. Pretretment of enzymes with DFP or nonbiotinylated phosphonates specifically blocks the labeling. This technique permits identification of serine proteases in complex mixtures with good sensitivity and specificity.     

Improved detection of multi-phosphorylated peptides in the presence of phosphoric acid in liquid chromatography/mass spectrometry

In contrast to lower phosphorylation states (e.g. the tryptic monophosphopeptide FQpSEEQQQTEDELQDK from bovine beta-casein), the specific detection of multi-phosphorylated peptides (e.g. the tetraphosphopeptide RELEELNVPGEIVEpSLpSpSpSEESITR from tryptic digestion of bovine beta-casein) has often been problematic for liquid chromatographic mass spectrometric (LC/MS) analysis owing to their high affinity for adsorption to exposed surfaces. We observed an enhancement in the overall detection of phosphopeptides on addition of phosphoric acid (0.1-1.0%) to the sample solution; a 10-fold increase in sensitivity was determined for the detection of two tryptic phosphopeptides and also a significant improvement in the detection of the tetraphosphopeptide. Using capillary LC with ion trap tandem MS for detection and identification, the achievable detection limits were 50 fmol and 50 pmol for the monophosphopeptide and the tetraphosphopeptide, respectively. Phosphoric acid is believed to act as a blocking agent to available silanol groups on both the silica capillary surface and the C(18)-bonded stationary phase silica surface.     

Generalizing a realization result of B. Zimmermann and K. B. Lee to infranilmanifolds

Let M be a closed infranilmanifold. We show that each finite subgroup G of the outer automorphism group Out ₁(M) admits a finite inflation pHG which can be effectively geometrically realized as a group of affine diffeomorphisms of M. This generalizes an analogous result obtained earlier for closed flat Riemannian manifolds by Lee ([7]) and Zimmermann ([12]). Using the Seifert construction we construct explicitly an example of such a manifold for which Nielsen's realization problem fails. This shows the need for such inflations and can be seen as a complementary example to those in [9].     

Complex 2 plane bundles over CP(n)

The purpose of this note is to construct examples of non-trivial rank 2 complex bundles over CP(n) with vanishing Chern classes for all n5.     

The spectrophotometric determination of chromium in ilmenite

A new diphenylcarbazide procedure free from iron interference is described for the determination of chromium in low-chrome ilmenite. After fusion of the sample, chromium is oxidised with permanganate and most of the iron is eliminated by extraction of chromium(VI) with MIBK Residual iron causes fading of the final colour, this can be avoided by using a phosphoric acid medium at temperatures below 15°. When iron levels are less than 200 μg, temperature control (10°) suffices to prevent iron interference if the concentration of the usual sulphuric acid medium is increased to 0.2 M. However, the phosphoric acid-low temperature method gives wider tolerance to acidity variations and maximum stability with time.     

Time-dependent master equation simulation of complex elementary reactions in combustion: application to the reaction of 1CH2 with C2H2 from 300-2000 K

Computational simulations of the title reaction are presented, covering a temperature range from 300 to 2000 K. At lower temperatures we find that initial formation of the cyclopropene complex by addition of methylene to acetylene is irreversible, as is the stabilisation process via collisional energy transfer. Product branching between propargyl and the stable isomers is predicted at 300 K as a function of pressure for the first time. At intermediate temperatures (1200 K), complex temporal evolution involving multiple steady states begins to emerge. At high temperatures (2000 K) the timescale for subsequent unimolecular decay of thermalized intermediates begins to impinge on the timescale for reaction of methylene, such that the rate of formation of propargyl product does not admit a simple analysis in terms of a single time-independent rate constant until the methylene supply becomes depleted. Likewise, at the elevated temperatures the thermalized intermediates cannot be regarded as irreversible product channels. Our solution algorithm involves spectral propagation of a symmetrized version of the discretized master equation matrix, and is implemented in a high precision environment which makes hitherto unachievable low-temperature modelling a reality.     

Virus Particles Monitored by Fluorescence Spectroscopy: A Potential Detection Assay for Macromolecular Assembly¶

Native fluorescence spectroscopy was used for in situ investigations of two lipid‐containing bacteriophages from the cystovirus family as well as their Pseudomonad host cells. Both the viruses φ6 and φ12 and their bacterial host proteins contain the amino acid tryptophan (trp), which is the predominant fluorophore in UV. Within proteins, trp's structural environment differs, and the differences are reflected in their spectroscopic signatures. It was observed that the peak of the trp emission from both viruses was at 330 nm, a significantly shorter wavelength than trp in either the Pseudomonad host cells or the amino acid's chemical form. This allowed us to monitor the viral attachment process and subsequent lytic release of progeny virus particles by measurement of the trp emission spectra during the infection process. This work demonstrates that fluorescence may offer a novel tool to detect viruses and monitor viral infection of cells and may be part of a biodefense application.