Synthesis of four diastereomeric 3,5-dialkoxy-2,4-dimethylalkanals by a simple extension of the non-aldol aldol process to bis(propionates)

[formula: see text] The synthesis of all four diastereomers of bis(propionates), 3,5-dialkoxy-2,4-dimethylalkanals, by non-aldol aldol chemistry is described. The epoxy alcohols (3, 4) were converted into the mesylates (9, 11) which were cleanly rearranged to the desired 3,5-bis(oxygenated)-2,4-dimethylalkanals (10, 12) in high yield. The epoxy mesylates (13, 16) gave the desired products (14, 17) in good yield on treatment with TMSOTf and a hindered base.     

Determination of Trace Molybdenum in Biological Matrices by Neutron Activation Analysis

Based on consecutive extractions using bismuth diethyldithiocarbamate and thallium diethyldithiocarbamate as reagents, molybdenum was selectively and highly enriched from biological matrices, and then subjected to neutron activation analysis. Most of interfering elements, e.g., Na, K, Br, P, Fe, U, etc. were simultaneouly removed and the preconcentrated samples always showed only the r rays from molybdenum after neutron bombardment. Thus, molybdenum in the biological matrices could be accurately determined.     

Competitive binding of a Tris run buffer with chiral crown ether in chiral capillary electrophoresis

In capillary electrophoresis of primary amine racemates using (+)-(18-crown-6)-tetracarboxylic acid (18C6H4) as a chiral selector, chiral recognition emanates from the differences in the complex formation between 18C6H4 and the two protonated amine enantiomers. The presence of buffer constituents such as tris(hydroxymethyl)aminomethane (Tris) or Na+, capable of forming complexes with 18C6H4, is thus detrimental to the chiral separation of primary amines. Such a competitive binding of buffer constituents was studied by comparing the electrophoretic mobilities of racemic analytes obtained in Tris/citric acid and triethylamine/citric acid buffers. We developed a simple fitting method to determine the competitive binding constant and applied it to the Tris buffer system. The competitive binding constant of Tris with 18C6H4 obtained at pH 3.0 was 27 +/- 4.     

The Vroman effect: a molecular level description of fibrinogen displacement

The molecular level details of the displacement of surface adsorbed fibrinogen from silica substrates were studied by atomic force microscopy, immunochemical assays, fluorescence microscopy, and vibrational sum frequency spectroscopy. The results showed that human plasma fibrinogen (HPF) can be readily displaced from the interface by other plasma proteins near neutral pH because the positively charged alpha C domains on HPF sit between the rest of the macromolecule and the underlying surface. The alpha C domains make weak electrostatic contact with the substrate, which is manifest by a high degree of alignment of Lys and Arg residues. Upon cycling through acidic pH, however, the alpha C domains are irreversibly removed from this position and the rest of the macromolecule is free to engage in stronger hydrogen bonding, van der Waals, and hydrophobic interactions with the surface. This results in a 170-fold decrease in the rate at which HPF can be displaced from the interface by other proteins in human plasma.     

Synthese von 2-methylalanin-peptiden,die pH-Abhängiggkeit ihrer 13C-NMR-spektren und eine neue methode zur auswertung über CS-diagramme

The uncommon amino-acid 2-methylalanine (α-aminoisobutyric acid, Aib) was investigated by ¹³C-NMR. The chemical shifts of amino- or carboxy-protected derivatives of Aib and of protected oligopeptides are discussed with respect to neighbouring groups and amino acids. The pH-dependence of the ¹³C-NMR spectra of Aib, Aib-Ala, Ala-Aib, Aib-Ala-Aib and Aib-Ala-Aib-Ala-Aib was studied. Using these examples, a new and advantageous method is demonstrated for the first time for the evalutions of NMR titration curves, which uses so-called chemical shift diagrams (CS diagrams).     

Investigations on the location and construction of a low background gamma-spectrometer

The underground radiation conditions in the mining district of Freiberg and in a rock salt environment of the Werra district were investigated. In a salt mine a very low natural activity level can be found. For selection of proper shielding materials a low-level -spectrometer and an optimum sample geometry must be used. The photopeak differences between sample and blank are small in most cases. Considerable differences can be found in the continuous background below 0.7 MeV.     

Surface-initiated growth of poly d(A-T) by Taq DNA polymerase

In this paper, we report surface-initiated d(A-T) polymerization by Taq DNA polymerase as a method for constructing DNA-tethered surfaces using an enzyme. The enzymatic polymerization was conducted successfully via two steps: tethering of oligo d(A-T)s onto the surface presenting carboxylic acids by amide coupling and surface-initiated polymerization using Taq DNA polymerase. In this enzymatic polymerization process, the design and construction of carboxylic acid-presenting surfaces were found to be an important factor: DNA growth did not occur on the gold surface coated only with the self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHDA), but effectively proceeded on the surfaces presenting mixed SAMs of MHDA and 1-pentadecanethiol. The coupling of oligo d(A-T)s and the subsequent DNA polymerization reaction were characterized by polarized infrared external reflectance spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy.     

Syntheses of 1beta-methylcarbapenems bearing 5-methyl-4-hydroxypyrrolidinone

A new series of 1beta-methylcarbapenems 1a-d bearing 5-methyl-4-mercaptopyrrolidinone rings has been prepared and evaluated for in vitro antibacterial activity and pharmacokinetic parameters. Most compounds showed excellent antibacterial activity and high stability to dehydropeptidase-1. We have synthesized optically active 5-methyl-4-hydroxypyrrolidinones from enantiomerically pure aziridine esters.     

Hyperconjugative vs. d orbital effects in unsaturated silanes : I. The energy levels in para-group IV-substituted anilines

The energy levels of a series of para substituted N,N-dimethylanilines p-MH_nMe_3?n C₆H₄NMe₂ (n = 0?3, M = C or Si) for the ground and lower lying excited states have been determined in acetonitrile solution. The levels for the carbon compounds are all slightly destailized relative to N,N-dimethylaniline and the effects are rather insensitive to n. The stabilizations produced by silicon substituents on all levels are markedly affected by silicon's substituents, showing increasing perturbations with increasing n. It is concluded that variations in the interaction of the σ^* system of the silyl substituent with the aniline π system, and not d orbital interactions, account for the trends observed.