pH-dependent transitions in xanthorhodopsin

Xanthorhodopsin (XR), the light-driven proton pump of the halophilic eubacterium Salinibacter ruber, exhibits substantial homology to bacteriorhodopsin (BR) of archaea and proteorhodopsin (PR) of marine bacteria, but unlike them contains a light-harvesting carotenoid antenna, salinixanthin, as well as retinal. We report here the pH-dependent properties of XR. The pKa of the retinal Schiff base is as high as in BR, i.e. > or =12.4. Deprotonation of the Schiff base and the ensuing alkaline denaturation cause large changes in the absorption bands of the carotenoid antenna, which lose intensity and become broader, making the spectrum similar to that of salinixanthin not bound to XR. A small redshift of the retinal chromophore band and increase of its extinction, as well as the pH-dependent amplitude of the M intermediate indicate that in detergent-solubilized XR the pKa of the Schiff base counterion and proton acceptor is about 6 (compared to 2.6 in BR, and 7.5 in PR). The protonation of the counterion is accompanied by a small blueshift of the carotenoid absorption bands. The pigment is stable in the dark upon acidification to pH 2. At pH < 2 a transition to a blueshifted species absorbing around 440 nm occurs, accompanied by loss of resolution of the carotenoid absorption bands. At pH < 3 illumination of XR with continuous light causes accumulation of long-lived photoproduct(s) with an absorption maximum around 400 nm. The photocycle of XR was examined between pH 4 and 10 in solubilized samples. The pH dependence of recovery of the initial state slows at both acid and alkaline pH, with pKas of 6.0 and 9.3. The decrease in the rates with pKa 6.0 is apparently caused by protonation of the counterion and proton acceptor, and that at high pH reflects the pKa of the internal proton donor, Glu94, at the times in the photocycle when this group equilibrates with the bulk.     

Preparation and investigation of LC packing made by microwave‐assisted solid‐phase synthesis

The preparation of the so‐called bonded phase liquid chromatographic packings is usually carried out by heating the silica, the silane, a catalyst, or a scavenger in an appropriate solvent (often toluene.) Due to the longtime of boiling, the procedure is time and energy consuming, and solvent intensive. The goal of this work is to present a simple, environment‐friendly preparation method with reduced solvent consumption to synthetize RP liquid chromatographic stationary phases. The effects of reaction conditions (amount of reagents, composition of the reagent, microwave energy, reaction time, reproducibility of the synthesis) are discussed. Pore structure, surface coverage, the change of the pore structure and surface coverage upon reaction are demonstrated, the efficiency of the column (van Deemter plot for different solutes) is presented. A variety of applications (aromatic hydrocarbons, halobenzenes, bioactive peptides, resveratrol from red wine) demonstrates the separation power of the new phase.     

Thermal stability of organoclays with mono- and di-alkyl cationic surfactants

In this study, mono- and di-alkyl cationic surfactants were used to prepare organoclays through ion exchange and the prepared organoclays were characterised by X-ray diffraction (XRD) and thermogravimetric analysis (TG). Larger basal spacings were observed in the interlayer of the organoclays intercalated with DDDMA than organoclays intercalated with DDTMA. The DTG curves identify the thermal stability of organoclays intercalated with two different types of surfactants (DDTMA and DDDMA) and the different arrangements of the surfactant molecules intercalated in the montmorillonite. Both organoclays intercalated with organic surfactant molecules proved to be thermally stable at high temperature. This study provides an understanding of the structure and properties of organoclays, which will enhance the potential applications of organoclays in environmental remediation.     

A Ramsey-Type Result for Convex Sets

Given a family of n convex compact sets in the plane, one canalways choose n of them which are either pairwise disjoint orpairwise intersecting. On the other hand, there exists a familyof n segments in the plane such that the maximum size of a subfamilywith pairwise disjoint or pairwise intersecting elements inn^log2/log5 n^0·431.     

Die Geometrie des aktivierten Komplexes der thermischen und ladungsinduzierten aromatischen para → ortho - Claisen-Umlagerung

Pure 10β-(trans-2′-butenyl)-17β-hydroxy-estra-1,4-dien-3-one ( 6 ), 10-(trans-2′-butenyl)-2-oxo-Δ^1(9),3(4)-hexahydronaphthalene ( 13 ), trans-2′-butenyl 17β-hydroxy-3-estra-1,3,5-(10)-trienyl ether ( 12 ) and trans-2′-butenyl 5,6,7,8-tetrahydro-2-naphthyl ether ( 14 ) were prepared by direct C- and O-alkylation, respectively, of the corresponding phenols (cf. [3] [10]), namely estra-3, 17β-diol and 5,6,7,8-tetrahydro-2-naphthol. The Claisen rearrangement of the ether 14 (200°, 12 h) yielded 53% 1-(1′-methylallyl)- and 34% 3-(1′-methylallyl)-5,6,7,8-tetrahydro-2-naphthol ( 15 and 16 , respectively), whereas in the thermal (120°, 14 h) and in the acid-catalysed (boron trifluoride in ether, 20°, 20 min) reaction of the corresponding dienone 13 nearly equal amounts of 15 (53–54%) and 16 (46%) were formed by thermal and charge-induced aromatic [3s, 3s]-sigmatropic rearrangements [2]. The steroid dienone 6 , on heating at 120°, was rearranged by [3s, 3s]-sigmatropic processes to form 52% of 2-(1′-methylallyl)- and 48% of 4′-(1′-methylallyl)-3, 17β-dihydroxy-estra-1,3,5,(10)-triene ( 7 and 8 , respectively). The steroid phenols 7 and 8 were carefully separated; subsequent hydrogenation (Raney-Ni in alcohol) and ozonolysis yielded 2-methylbutyric acid ( 9 ): from 7 , S-(+)- 9 , and from 8 , R-(?)- 9 , obtained in 88,5 and 88,0% optical purity (cf. [4a]). This means (cf. scheme 2 and Table 2) that both phenols are formed to the extent of at least 94% via a chair-like activated complex, and of at most 6% via a both-like activated complex (ΔΔG = 2.15 kcal/mol). Similarly, the boron trifluoride-induced rearrangement of 6 (born trifluoride in ether, 0°, 45 min) yielded 7 and 8 , from which S-(+)- 9 and R-(?)- 9 were respectively obtained in 89% and 98% optical purity. For these induced rearrangements this corresponds to at least 94,5 and 99%, respectively, of the chair-like, and to only 5.5 and 1% of the boat-like activated complex (ΔΔG = 1.5–2.5 kcal/mol). These results demonstrate that the activated complexes of both [3s,3s]-sigmatropic processes, i.e. the pure thermal reaction at 120° and the charge-induced reaction occurring at 0°, must be very similar. Thus, the boron trifluoride accelerates the Cope-like reactions 6 → 7 + 8 , but does not influence the geometries of their transition states. The Claisen rearrangement of the steroid ether 12 (200°, 15 h), yielding 7 and 8 , was not influenced by the chiral steroid skeleton, because no optical induction was observed (both phenols, 7 and 8 , yielded on degradation racemic 2-methylbutyric acid (9)).     

Whole cell immobilised biosensors for toxicity assessment of a wastewater treatment plant treating phenolics-containing waste

Wastewater treatment plants dealing with industrial wastes are often susceptible to overload of toxic influent that can partially or completely destroy treatment for extended periods. An obvious candidate for monitoring toxicity in such wastewater systems is bioluminescent bacteria. However, the natural bioluminescent bacteria can be particularly sensitive to some industrial wastes and therefore their response to normal operational conditions does not reflect the status of the microbial community responsible for treatment. Moreover, the salt dependence of the marine bioluminescent bacteria, and the temperature sensitivity of some strains, further complicate their use. Here we describe the construction of whole cell genetically modified bioluminescent biosensors and their immobilisation for use in monitoring the toxicity of a complex industrial wastewater containing phenolic materials. A hand-held luminometer was designed for laboratory or field use, and the immobilisation system designed with several things in mind: the geometry of the instrument; the need for containment of GM bacteria; the maximisation of the bioavailability of the wastewater to the biosensor. The performance of a candidate GM sensor was compared with Vibrio fischeri in liquid culture and after immobilisation in thin films of poly(vinyl alcohol) (PVA) cryogels. The biosensors were tested against pure phenol and 3-chlorophenol as a reference toxic chemical known to be much more toxic to bacteria than phenol. The biosensors were then tested with the phenolics-containing industrial wastewater. The immobilisation system proved to operate predictably with pure toxicants, and was able to discriminate toxicity of various zones within the wastewater treatment plant.     

3-Alkyl-1-benzoxepin-5-on-Derivate und 2-Alkyl-1, 4-naphthochinone aus 2-Acylaryl-propargyläthern

3-Alkyl-1-benzoxepin-5-one derivatives and 2-alkyl-1,4-naphtoquinones from 2-acylaryl propargyl ethers. It was found that 3-alkyl-1-benzoxepin-5(2H)-ones of type B can be synthesized by treating 2-acylaryl propargyl ethers of type A with sodium methylsulfinyl methide (NaMSM, dimesyl sodium) (Scheme 13). Oxepinone derivatives of type B undergo ring contraction with base (also NaMSM) to yield the quinol derivatives C which, oxidize (during work-up), if R² = H, to the 1,4-naphthoquinones D (Scheme 13). The propargyl ethers used are listed in Scheme 1. The naphthalene derivatives 1 and 3 give oxepinones (E- 9 and a mixture of 14/15 respectively), whereas the expected oxepinone from 2 is transformed directly into the quinone 11 (Scheme 2, 3 and 5). Isomerizations of 2-acetylphenyl propargyl ethers ( 4, 5 and 6 ) (Schemes 6, 7 and 8) are less successful because of side reactions. If however the acetyl group is replaced by a propionyl or substituted propionyl group (as in ethers 7 and 8 ) oxepinones are obtained again in good yield (Scheme 9). The mechanistic pathway for the transformation of naphthyl propargyl ethers (and phenyl derivatives) under influence of NaMSM is shown in Scheme 10. The base-catalysed conversion of 4-phenyl-l-benzoxepin-5(2H)-one,benzo[f]furo[2,3-c](10 H)-oxepin-4-oncsand 3-methoxy-G,11- dihydro-dibenzo[b, e]loxepin-11-oneinto thc corresponding quinones has been reported [13] [20] [21]. The conversion of 2-acylaryl propargyl others via the isolable benzoxepin-5-one derivativcs or directly into the specifically substituted 1,4-naphthoquinone derivatives is of synthetic interest.     

New implementation of a program to calculate correlated band structures of polymers: An application to the band structure of polyparaphenylene (PPP)

A new program has recently been implemented with the aim of extending quasi-particle (QP) band structure calculations to polymers with larger unit cells. The theoretical background is briefly reviewed and the new algorithm described, which has been optimized for machines with vector processors. To illustrate the usefulness of this technique, calculations have been performed on polyparaphenylene (PPP) using a double-zeta basis set. The calculated QP band gap between the valence and conduction bands is 2.3 eV, which compares favorably with the experimental value of 2.8 eV. The self-consistent field (SCF) result with the same double-zeta basis set is 8.7 eV. © 1994 by John Wiley & Sons, Inc.