Configurationally and conformationally homogeneous cyclic n-aryl sulfimides—IV : Synthesis,configuration and stereochemistry of the rearrangement of 1,3-di-thiane-1-N-p-chlorophenylimides

1,3-Dithiane-1-N-p-chlorophenylimides (1,4-9) were prepared and their configuration and conformation was determined by ¹H and ¹³C NMR. The compounds were rearranged to the corresponding 2-(2'-amino-5'-chlorophenyl)-1, 3-dithianes (1U,4U,9U). The rearrangement reactions took place with ?95% stereospecifity. The mechanism of the reaction was investigated with the aid of analogs specifically deuterated at C-2.     

Retention behavior of humic substances in reversed phase HPLC

Recovery as well as appearance and abundance (in percent) of different fractions of humic substances are found to depend on injected sample amounts in reversed phase HPLC. Sample amounts have been varied both by varying sample concentration and sample volume. In case of lowest amounts injected only two fractions were obtained for a commercial humic acid sodium salt, i.e. one for excluded molecules and one for hydrophobic components. The abundance of excluded molecules decreases upon increasing amounts injected. Another three fractions are obtained upon increasing amount injected: a hydrophilic fraction and two hydrophobic ones. This behavior is explained by auxiliary equilibria between excluded components and humic molecules previously adsorbed on the stationary phase.     

A general formalism of deriving the pair potential of polymer chains for arbitrary interaction potentials between isolated chain segments at and close to the theta-point

A formalism has been worked out which allows to transform any non-punctiform segment-segment potential of isolated polymer segments ε of fairly short-ranged character into the pair-potentialU operating between linear polymer chains with a certain reference to the arguments as they have been originally put forward byFlory andKrigbaum. Although no restrictions are made in the derivation as to the repulsive or attractive contribution of the segment-segment potential ε because of some known general deficiencies of theFlory-Krigbaum treatment for exclusively repulsive interaction, the resulting equations are primarily intended to describe the thermodynamic situation at and close to the θ-point where repulsion and attraction—though working at different ranges of segment separation—cancel. As the equation derived is somewhat complicated two different approximate forms have been developed: The first one is based on aTaylor series expansion retaining terms up to the fourth order which allows to characterizeU by the second and the fourth moment of the pair segment-segment distribution function, β and γ (β being the so-called binary cluster integral of segment-segment interaction, which is considered to be zero for θ-conditions). In this caseU may be represented by an expression of the general form $$U/kT = A(1 - BR^2 )\exp \{ - bR^2 \} .$$ The second method is based on a separate integration over the repulsive and attractive ranges of ε giving the repulsive (U ₊) and the attractive (U _?) part ofU finally after some approximations leading to an equation of the general form $$U/kT = (U_ + + U_ - )/kT = A_1 \exp \{ - b_1 R^2 \} - A_2 \exp \{ - b_2 R^2 \} .$$ In both cases the knowledge of the exact form of ε is dispensable, only β and γ—or for the second case their repulsive (β₊ and γ₊) and attractive (β_? and γ_?) parts have to be known. It is shown that the approximations are in excellent accordance with the exact form so that they may be conveniently used to describe pair potentials of polymer chains and to analyze pair potentials of segment-segment interactions under the limitations and conditions indicated.     

Ab initio calculations of electron-spin magnetic moments for Li,Be and B hydrides inX 2∑+ states

Electron-spin magnetic moments, in the form ofg-shifts, have been computed at the ROHF level for theX ²∑⁺ states of LiH⁺, BeH²⁺, LiH^?, BeH and BH⁺. A perturbative approach, complete to second-order in appropriate Breit-Pauli operators, has been used. Retention of two-centre integrals has proven vital. First-order terms are important, especially in describing the negativeg _∥ shifts observed experimentally in²∑⁺ molecules. The relativistic mass correction dominates in first-order, except for LiH^? where the two-electron spin-Zeeman gauge correction supersedes. Second-order terms contribute negatively, and only to the Δg _⊥ component. Along the isoelectronic series LiH^? → BeH → BH⁺, the magnitude of Δg _⊥ increases due to the dependence of spin-orbit coupling on nuclear charge. The relation ofg-shifts to electronic structure and bonding is explored.     

IDENTIFICATION OF THE PROTON ACCEPTOR OF SCHIFF BASE DEPROTONATION IN BACTERIORHODOPSIN: A FOURIER-TRANSFORM-INFRARED STUDY OF THE MUTANT ASP85 → GLU IN ITS NATURAL LIPID ENVIRONMENT

Abstract— In order to assign the proton acceptor for Schiff base deprotonation in bacteriorhodopsin to a specific Asp residue, the photoreaction of the Asp85 → Glu mutant, as expressed in Halobacterium sp . GRB, was investigated by static low-temperature and time-resolved infrared difference spec-troscopy. Measurements were also performed on the mutant protein labeled with [4-¹³C]Asp which allowed discrimination between Asp and Glu residues. 14,15-di¹³C-retinal was incorporated to distinguish amide-II absorbance changes from changes of the ethylenic mode of the chromophore. In agreement with earlier UV-VIS measurements, our data show that from both the 540 and 610 nm species present in a pH-dependent equilibrium, intermediates similar to K and L can be formed. The 14 ms time-resolved spectrum of the 540 nm species shows that a glutamic acid becomes protonated in the M-like intermediate, whereas the comparable difference spectrum of the 610 nm species demonstrates that in the initial state a glutamic acid is already protonated. In conjunction with earlier observations of protonation of an Asp residue in wild-type M, the data provide direct evidence that the proton acceptor in the deprotonation reaction of the Schiff base is Asp85.     

Surface Modification of Ultra-high Molecular Weight Polyethylene Membranes Using Underwater Plasma Polymerization

Ultra-high molecular weight polyethylene membranes were modified and subsequently polymer coated using the underwater plasma produced by glow discharge electrolysis. This plasma pretreatment generated various O-functional groups among them OH groups have dominated. This modified inner (pore) surface of membranes showed complete wetting and strong adhesion to a hydrogel copolymerized by glow discharge electrolysis also. The deposited hydrogel consists of plasma polymerized acrylic acid crosslinked by copolymerization with the bifunctional N,N′-methylenebis(acrylamide). Tuning the hydrogel hydrophilicity and bio-compatibility poly(ethylene glycol) was chemically inserted into the copolymer. Such saturated polymer could only be inserted on a non-classic way by (partial) fragmentation and recombination thus demonstrating the exotic properties of the underwater plasma. The modification of membrane was achieved by squeezing the reactive plasma solution into the pores by plasma-induced shock waves and supported by intense stirring. The deposited copolymer hydrogel has filled all pores also in the inner of membrane as shown by scanning electron microscopy of cross-sections. The copolymer shows the characteristic units of acrylic acid and ethylene glycol as demonstrated by infrared spectroscopy. A minimum loss in carboxylic groups of acrylic acid during the plasma polymerization process was confirmed by X-ray photoelectron spectroscopy. Additional cell adhesion tests on copolymer coated polyethylene using IEC-6 cells demonstrated the bio-compatibility of the plasma-deposited hydrogel.