Transition metal complexes of N,N-dimethylthreonine: Stability and UV/Vis spectra

Summary Acidity (dehydronation) constants of N,N-dimethylthreonine (DMT) and stability constants of its complexes with Cu⁺², Ni⁺², and Co⁺² were determined in aqueous solution by means of potentiometric titration. UV/Vis spectra were also taken during the titration. It is suggested thatDMT acts as a bidentate ligand toward copper(II) by engaging either (a) amino and carboxyl groups (in [Cu(DMT)] and [Cu(DMT)₂]), or, (b) upon dehydronation, amino and hydroxyl groups (in [Cu(DMT)H_–1], [Cu(DMT)₂H_–1], and [Cu(DMT)₂H_–2]). It is suggested that the coordination in threoninato andallo-threoninato complexes is similar to that described under (a).Based upon Master of Science thesis submitted to the University of Zagreb, Croatia byB. Blagovi     

Measure of the multiple self-intersection set of a markov process

Let X(t), t ≧ 0, be a Markov process in R^m with homogeneous transition density p(t; x, y). For a closed bounded set B ? R^m, X is said to have a self-intersection of order r ≧ 2 in B if there are distinct points t₁ < … < t_r such that X(t₁) ∈ B and X(t_j) = X(t¹), for j = 2,…, r. The focus of this work is the Hausdorff measure, suitably defined, of the set of such r-tuples. The main result is that under general conditions on p(t; x, y) as well as the specific condition there is a measure function M(t), defined in terms of the integral above, such that the corresponding Hausdorff measure of self-intersection set is positive, with positive probability. The results are applied to Lévy and diffusion processes, and are shown to extend recent results in this area.     

Estimation of spectra of individual species in a multisolute solution

Spectra of a series of solutions containing different concentrations of four solutes were simulated, assuming either normal or non-normal distribution of experimental errors. These synthetic data were then analyzed by linear least-squares procedures in order to estimate the spectra of individual solutes. Analysis of regression residuals and the estimated spectra showed that a correct set of statistical weights can be found by an iterative procedure, if the qualitative form of the weighting function is known in advance. When ever a least-squares estimation was successful, the estimates were practically unbiased and the moments of the distribution of regression residuals were close to their expectances. However, the distribution moments of the regression estimates were found to be far from normal in all cases, although the estimates were not necessarily biased.     

Numerical evaluation of complex stability constants from polarographic data for quasi-reversible processes

Stability constants of copper(II) butyrate complexes were determined by polarography. Numerical treatment of polarographic data for quasi-reversible electrode processes was developed and yielded good estimates of reversible E_{$\text{1}\text{2}$} values. An improved three-electrode polarographic apparatus was constructed based on operational amplifiers.     

Ammonia/desorption chemical ionization mass spectrometry of some cyclopentane iridoid glucosides

The ammonia/desorption chemical ionization (DCI) mass spectra of nine cyclopentane iridoid glucosides were measured. The dependences cf the intensities of different peaks on the structures and stereochemistries of the compounds investigated is discussed.     

Hydrogen Bonding and Solvent Effects on Complexation of Alkali Metal Cations by Lower Rim Calix[4]arene Tetra(O-[N-acetyl-D-phenylglycine methyl ester]) Derivative

Complexation of alkali metal cations with 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis(O-methyl-D-α-phenylglycylcarbonylmethoxy)calix[4]arene (L) was studied by means of spectrophotometric, conductometric and potentiometric titrations at 25 °C. The solvent effect on the binding ability of L was examined by using two solvents with different affinities for hydrogen bonding, viz. methanol and acetonitrile. Despite the presence of intramolecular NH···O=C hydrogen bonds in L, which need to be disrupted to allow metal ion binding, this calix[4]arene amino acid derivative was shown to be an efficient binder for smaller Li⁺ and Na⁺ cations in acetonitrile (lg K _LiL  > 5, lg K _NaL  = 7.66), moderately efficient for K⁺ (lg K _KL  = 4.62), whereas larger Rb⁺ and Cs⁺ did not fit in its hydrophilic cavity. The complex stabilities in methanol were significantly lower (lg K _NaL  =  4.45, lg K _KL  = 2.48). That could be explained by different solvation of the cations and by competition between the cations and methanol molecules (via hydrogen bonds) for amide carbonyl oxygens. The influence of cation solvation on complex stability was most pronounced in the case of Li⁺ for which, contrary to the quite stable LiL ⁺ complex in acetonitrile, no complexation was observed in methanol under the conditions used.     

Total synthesis and structural confirmation of ent-galbanic acid and marneral

By capitalizing on a highly selective Claisen rearrangement, ent-galbanic acid 1 and (+)-marneral 2 have been synthesized. The relative configurations of (+)- 1 and (+)- 2 were unambiguously established by X-ray crystallographic analysis of the precursors 11a and 20, with the absolute configuration ensuing from their derivation from R-pulegone. In this way, the controversial issue of the configuration of galbanic acid was unequivocally settled.     

On the graph of a function in many variables over a finite field

Some improved bounds on the number of directions not determined by a point set in the affine space AG(k, q) are presented. More precisely, if there are more than p ^e (q − 1) directions not determined by a set of q ^k-1 points then every hyperplane meets in 0 modulo p ^e+1 points. This bound is shown to be tight in the case p ^e = q ^s and when q = p ^es sets of q ^k-1 points that do not meet every hyperplane in 0 modulo p ^e+1 points and have a little less than p ^e (q − 1) non-determined directions are constructed. The author acknowledges the support of the Ramon y Cajal programme and the project MTM2005-08990-C02-01 of the Spanish Ministry of Science and Education and the project 2005SGR00256 of the Catalan Research Council.     

A rigidity theorem for holomorphic generators on the Hilbert ball

We present a rigidity property of holomorphic generators on the open unit ball of a Hilbert space . Namely, if is the generator of a one-parameter continuous semigroup on such that for some boundary point , the admissible limit - , then vanishes identically on .