CHIROPTICAL PROPERTIES OF 1-DEOXY-1-THIOGALACTOPYRANOSIDES

Abstract

Continuing our studies of optically active sulfides we have investigated flexible systems incorporating the 1.3-O,S-chromophore, e.q., alkyl α-and B-D-thiogalactopyranosides and their tetraacetates. Although most substances were known from the literature, constitutional, configurational, and conformational assignments had hardly ever been proved rigorously; we therefore had to provide a firm basis by a systematic analysis of the ¹H and ¹³C NMR spectra of thioglycosides, the complexity of the carbohydrate signals necessitating high field studies. The compounds were thus, in the end, correlated with the natural thiogalactoside lincomycin, whose structure including its absolute configuration is known from X-ray investigations. CD curves have been measured at various temperatures in the range of 185–300 nm on a commercial spectropolarimeter equipped with a data processor and connected to a table calculator and plotter, directly furnishing data suitable for, e.g., Kronig-Kramers type transformations or curve analysis and displaying the results. These CD data were correlated with the UV spectra and the ORD curves of the substrates. Typically, the UV curves are devoid of detail except in the case of the acetates, where a shoulder in the region of the n→π? transition is discernible. In the ORD, the Cotton effects (CE) are largely suppressed by the background contribution of the “invisible giant” in the far UV. In the thiogalactopyranosides all accessible Cotton effects are associated with electron transitions within the sulfur or possibly the coupled O-C-S chromophore, whereas a relatively small negative, composite CE is contributed by the acetate carbonyl groups in the acetates.     

Solvatochromic Determination of Second-order Polarizabilities of Chromophore-functionalized Dextran and Amylose Derivatives

Linear dextran and helix amylose were covalently bonded with nonlinear optical (NLO) chromophores. The influence of the conformation of the polymer matrix on the NLO behavior of the supramolecular structure has been studied. The second order hyperpolarizability depends not only on the secondary structure of the biopolymer, but also on the position of the chromophore towards the polymeric backbone. Functionalization of NLO-phores with biopolymers led to increased thermo- and photostability.     

Avoiding problems with hydrogen misplacement in reporting crystal structures

Intermolecular hydrogen bonding is an integral part of many crystal structures. Hydrogen bonding sometimes results in one‐, two‐ or three‐dimensional supramolecular assemblies, a common feature of which is positional disorder of H atoms related to space‐group symmetry. Yet some reported structures fail to include all possible donor–acceptor close contacts, or to seek H‐atom electron densities associated with apparent D—H...A trios, while some H‐atom positions violate principles of chemistry or crystal physics. Modern diffraction equipment and sophisticated computing systems provide high‐quality data; thus, failure to characterize and report fully an accurate, complete and physically correct hydrogen‐bonding model should not be acceptable. We illustrate the relevant issues with three published examples in the hope of slowing the proliferation of these problems, with the scientifically desirable goal of improving the accuracy of crystallographic models while also providing improved search keys for information retrieval.     

Sorption of certain isatins on various sorbents under RP-HPLC conditions

The results from chromatographic analysis of biologically active isatin derivatives on hyper-crosslinked polystyrene (HCLPS) and silica gel modified by octadecyl groups (SilC₁₈) are presented. The constants of distribution of sorbates between a mobile phase and the investigated sorbents (K _x ) and the changes in the standard differential molar Gibbs energies of adsorption $(\Delta _a \bar G^\circ )$ are calculated, along with the chromatographic retention-physicochemical property of sorbate dependences. It is found that the equations describing these dependences have high forecasting ability with respect to the values of retention factors of the investigated sorbates.     

Synthesis of the Aliphatic Subunit of the Macrolide LL‐Z 1640‐2 via Vasella Ring Opening of a 6‐Iodo‐4‐deoxy‐D‐mannose

The synthesis of the aliphatic subunit 9 of the macrolide LL‐Z1640‐2 (I), starting from a 4‐deoxy‐D‐mannose derivative 2a, is described. The procedure includes the first successful application of a Vasella ring opening reaction for a 4‐deoxypyranoside. Nucleophilic addition of an alkynyllithium reagent to the aldehyde 4 led to the propargylic alcohol 7, which was converted to the advanced building block 9 in two further steps.     

Thermal stability of the extraction system “TODGA in Isopar M with n-decanol” at above atmospheric pressure

Journal of Thermal Analysis and Calorimetry - The gas evolution dynamics has been studied during thermal oxidation of 0.15 and 0.2 mol L?1 solutions of...     

Mechanism of current flow in alloyed ohmic In/GaAs contacts

A mechanism of current flow in an alloyed ohmic In contact to low-doped gallium arsenide (n = 4 × 10¹⁵ cm^?3) is studied. From the temperature dependence of the contact resistance per unit surface area, it is found that the basic mechanism of current flow is thermionic emission through a potential barrier 0.03 eV in height.     

Ultrabroadband continuum amplification in the near infrared using BiB3O6 nonlinear crystals pumped at 800 nm

Ultrabroadband parametric amplification of a white-light continuum in the near IR (approximately 100 THz, 1.2-2.4 microm) is demonstrated in BiB3O6 pumped by 45 fs long pulses at 800 nm at a repetition rate of 1 kHz. The energy obtained with a 5 mm thick crystal reached 50 microJ, corresponding to external conversion efficiency of 20%.     

Silver as a capturing material for iodine released from lead–bismuth eutectic in various conditions

Journal of Radioanalytical and Nuclear Chemistry - The usage of silver as a filtering material for removal of iodine from the gas phase of a lead–bismuth eutectic based nuclear reactor was...