Determination of the proteins in mixtures of meat,soymeal and rind from their chromatographic amino-acid pattern by the partial least-squares method

The simultaneous determination of muscle protein and rind protein in mixtures of muscle, soymeal and rind is described. Hydrolysates are derivatized with dansyl chloride and separated by reversed-phase liquid chromatography. The chromatographic pattern is subjected to multivariate evaluation. An indirect calibration method, partial least-squares modelling in latent variables (p.l.s.), is used. The rind protein is determined accurately regardless of sample composition. The accuracy of muscle protein determinations is lower when high concentrations of soymeal are present in the samples, because of the similarity in amino acid composition between soy protein and muscle. The method not only predicts the concentrations of the constituents but also calculates a measure of the similarity between the calibration set and each unknown sample. This gives an indication of the reliability of the predicted concentrations.     

Minimal and maximal methods of interpolation

We show that several interpolation functors, including the widely used real and complex methods, are minimal or maximal extensions from a single couple of Banach spaces. Various consequences are drawn from this property.     

Levels and transitions in136Ba

Excited states of¹³⁶Ba are studied in the beta decay of¹³⁶Cs. The gamma spectrum is measured with high-resolution and coincidence techniques. Several new transitions are suggested to be connected with two recently reported levels. Gamma-gamma directional correlations are performed in an attempt to determine the characteristics of these levels, and in order to determine mixing ratios. The lifetime of the 2207.5 keV state is remeasured, and the lifetime of the 2140.5 keV state is measured for the first time.     

The birth of the giant component

Limiting distributions are derived for the sparse connected components that are present when a random graph on n vertices has approximately 1/2n edges. In particular, we show that such a graph consists entirely of trees, unicyclic components, and bicyclic components with probability approaching √2/3 cosh √5/18 ≈ 0.9325 as n→∞. The limiting probability that it is consists of trees, unicyclic components, and at most one another component is approximately 0.9957; the limiting probability that it is planar lies between 0.987 and 0.9998. When a random graph evolves and the number of edges passes 1/2n, its components grow in cyclic complexity according to an interesting Markov process whose asymptotic structure is derived. The probability that there never is more than a single component with more edges than vertices, throughout the veolution, approaches 5 π/18 ≈ 0.8727. A “uniform” model of random graphs, which allows self-loops and multiple edges, is shown to lead to formulas that are substanitially simpler than the analogous formulas for the classical random graphs of Erdõs and Rényi. The notions of “excess” and “deficiency,” which are significant characteristics of the generating function as well as of the graphs themselves, lead to a mathematically attractive structural theory for the uniform model. A general approach to the study of stopping configurations makes it possible to sharpen previously obtained estimates in a uniform manner and often to obtain closed forms for the constants of interest. Empirical results are presented to complement the analysis, indicating the typical behavior when n is near 2oooO. © 1993 John Wiley & Sons, Inc.     

Oxidation of self-organized nonionic surfactants

Nonionic surfactants containing a polyoxyethylene headgroup are known to slowly undergo oxidative degradation when exposed to air. The oxidation, which starts by abstraction of a hydrogen atom from a methylene group in alpha-position to an ether oxygen, is accelerated by metal ions. Silver ion mediated oxidation of a technical grade surfactant of this type, Brij 30, was investigated in two types of self-assembled systems, a water-in-oil microemulsion and a liquid crystalline phase. It was found that in both systems the longer homologues, i.e., the surfactant homologues that carry a longer polyoxyethylene chain, decompose faster than the shorter homologues. This trend was found to be more pronounced when the surfactant is present in a liquid crystal than in a microemulsion. The difference is explained in terms of differences in accessibility of the polyoxyethylene chains to the silver ions.     

A proof of Parisi’s conjecture on the random assignment problem

An assignment problem is the optimization problem of finding, in an m by n matrix of nonnegative real numbers, k entries, no two in the same row or column, such that their sum is minimal. Such an optimization problem is called a random assignment problem if the matrix entries are random variables. We give a formula for the expected value of the optimal k-assignment in a matrix where some of the entries are zero, and all other entries are independent exponentially distributed random variables with mean 1. Thereby we prove the formula 1+1/4+1/9+...+1/k ² conjectured by G. Parisi for the case k=m=n, and the generalized conjecture of D. Coppersmith and G. B. Sorkin for arbitrary k, m and n. AcknowledgementWe thank Mireille Bousquet-Mélou and Gilles Schaeffer for introducing the problem to us. We also thank an anonymous referee for suggesting some improvements of the exposition.     

Highly diastereoselective hydrogenations leading to beta-hydroxy delta-lactones in hydroxy-protected form. A modified view of delta-lactone conformations

Enol MEM ethers 4 and 15 and the corresponding enol acetates were hydrogenated over Pd/C with very high (>99%) diastereoselectivity to saturated delta-lactones. A stereochemical generalization can be formulated thus: trans-5,6-disubstituted 1-oxa-3-cyclohexen-2-ones (e.g. 14 and 15) are hydrogenated over Pd with high selectivity from the side trans to the C(6)-substituent. A mechanistic rationalization of the stereochemical outcome in the Pd-catalyzed hydrogenation of this as well as other types of substituted alpha,beta-unsaturated delta-lactones is presented. An analysis of X-ray crystallographic data for 67 compounds demonstrated a great conformational diversity of the saturated delta-lactone ring. Besides, ab initio calculations (HF/6-31G) indicated a very high conformational mobility. Thus, the lowest calculated transition state for the conversion of the half-chair, most stable, conformer of delta-valerolactone to the boat-type conformer lies only 1.93 kcal/mol above the former. Beside these two conformers, also chair, envelope and skew conformations are accessible; all lie less than 2 kcal/mol above the half-chair. The previous conformational paradigm comprising only boat and half-chair types is incomplete.     

Colorimetrische pH-Bestimmung

Ohne Zusammenfassung     

Interactions between a lipase and charged surfactants--a comparison between bulk and interfaces

The interaction between a charged surfactant and a lipase has been investigated by several methods. Interactions in aqueous bulk phase was studied by NMR and by microcalorimetry. Surface tension and neutron reflectivity were used for studies at the air-water interface. Interactions at the interface between a hydrophobic solid surface and water was investigated by ellipsometry. The results obtained are as follows. The cationic surfactant, tetradecyltrimethylammonium bromide (iodide in the NMR experiments), showed strong interaction at the air-water and the hydrophobic solid-water interfaces but no clear indication of an interaction in bulk phase was seen. The anionic surfactant showed no interaction with the lipase neither at the interfaces, nor in bulk. The difference in behavior of the system cationic surfactant-lipase in bulk and at the interfaces may be due to the change in enzyme conformation that is known to occur at interfaces between water and an apolar phase.