Small peptides as modular catalysts for the direct asymmetric aldol reaction: ancient peptides with aldolase enzyme activity

Simple peptides and their analogues having a primary amino group as the catalytic residue mediate the direct asymmetric intermolecular aldol reaction with high stereoselectivity and furnish the corresponding aldol products with up to 99% ee; this intrinsic ability of highly modular peptides may explain the initial molecular evolution of aldolase enzymes.     

Bimolecular homolytic substitution (S(H)2) reactions with hydrogen atoms. time-resolved electron spin resonance detection in the pulse radiolysis of alpha-(methylthio)acetamide

Pulse radiolysis of aqueous solutions of alpha-(methylthio)acetamide produced unexpectedly large quantities of acetamide radicals that were identified by time-resolved electron spin resonance (TRESR) spectroscopy. The pH dependence of the TRESR-measured radical yields, results from selective scavenging reactions, and density functional theory predictions of the reaction thermochemistry prove that bimolecular homolytic substitution, S(H)2, of the acetamide radical fragment by a H atom is the most likely formation pathway.     

Oxazepines and thiazepines,XX: CD-spectra of optically active 2-phenyl-2,3-dihydro-1,5-benzothiazepin-4(5H)-ones and related 3-phenylthio-3-phenyl-propionic acid derivatives,and X-ray diffraction of one phenylethylamide

Summary The absolute configuration of (–)-(1R,3S)-4 has been determined by X-ray diffraction. The UV- and CD-spectra of the title compound8 and the intermediates for its synthesis are discussed. The stronger Cotton effects can be explained by application of the exciton theory to the observed CD-couplets. The CD of the lower homologue9 of known absolute configuration is in full agreement with that of homochirally analogue8.

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Oxazepine und Thiazepine, 20. Mitt.: CD-Spektren optisch aktiver 2-Phenyl-2,3-dihydro-1,5-benzothiazepin-4(5H)-one und verwandter 3-Phenylthio-3-phenyl-propionsäure-Derivate und Röntgenstrukturanalyse eines Phenylethylamids

Zusammenfassung Die absolute Konfiguration von (–)-(1R,3S)-4 wurde durch Röntgenbeugung bestimmt. UV- und CD-Spektren der Titelverbindung8 und der Zwischenprodukte für ihre Synthese werden diskutiert. Die stärkeren Cottoneffekte können durch Anwendung der Excitontheorie auf die erhaltenen CD-Couplets erklärt werden. Der CD des niederen Homologen9 bekannter absoluter Konfiguration steht in voller Übereinstimmung mit dem des homochiral analogen8.

     

Synthesis of the C20-C26 building block of halichondrins via a regiospecific and stereoselective S(N)2' reaction

[reaction: see text] A regiospecific and stereoselective S(N)2' reaction to convert the trisylate into the vinyl iodide is presented. The homoallylic alcohol is used to direct the delivery of LiCu(Me)(2).     

Chromatographic behaviour of selected steroids and their inclusion complexes with beta-cyclodextrin on octadecylsilica stationary phases with different carbon loads

Retention and separation studies of selected estrogens, progestogens and their inclusion complexes with beta-cyclodextrin were conducted using two C18 HPLC columns with different carbon loads. The difference in carbon load between investigated octadecylsilica packing materials was about 50%. The mobile phases were composed of a 30% v/v acetonitrile-water mixture without and with addition of beta-cyclodextrin at a concentration of 12 mM. The experimental data revealed that retention of the steroids was significantly reduced on the column with the lower carbon load. Moreover, it was found that this column offers better separation power and shorter analysis time at the temperatures studied. However, the calculated values of the retention factor ratios (k0(mMCD))/k(12mMCD)) of the steroids were similar for both columns investigated. This observation suggests that the stationary phase structure appears to have little effect on the formation of host-guest complexes if the complexation process is localised to the chromatographic mobile phase. From a practical point of view, when the mobile phase is modified with beta-cyclodextrin, the separation of the steroids is strongly influenced by temperature. The best chromatographic conditions were determined for the separation of multicomponent samples on the column with lower carbon load. A possible retention mechanism for components of interest in the presence of macrocyclic additives is discussed.     

Unexpected Rearrangement of Diethyl (±)(S,S)-1,2-epoxy-2-Phenylpentylphosphonate by NH 3(aqu.) : An Easy Entry to Ethyl 1-Formyl-1-Phenylbutylphosphonate

A simple reaction of diethyl ( - )(S,S)-1,2-epoxy-2-phenylpentylphosphonate with 28% NH 3(aqu.) in MeOH led to the ethyl 1-formyl-1-phenylbutylphosphonate in excellent yield. The procedure consists simply in stirring the substrate and 28% NH 3(aqu.) in MeOH, at 40;C.     

Interferences elimination in ion chromatography by inclusion of the interfering ion into the mobile phase—Analysis of fluoride in chloride rich dietary samples

New approach to the chloride interferences elimination by addition of the interfering ion to the mobile phase is proposed and evaluated. Different eluents for the non-suppressed ion chromatographic analysis of fluorides in chlorides rich samples were tested and compared with eluent recommended by the column manufacturer. The limit of detection, linearity range and resistance to matrix effects caused by chlorides were the comparison criteria. The applicability of the selected eluent was demonstrated through the analysis of the edible salts and various tea samples. The employment of the proposed eluent shorten the time of the analysis since the only required preparation steps for edible salts were the dissolution and appropriate dilution of the samples. The recovery test was employed to verify the obtained results.     

AgI-Ag2O-V2O5 glasses as ion-to-electron transducers for the construction of all-solid-state microelectrodes

A method for the fabrication of ion-selective all-solid-state microelectrodes is presented. The ion-to-electron transduction process takes place into the transducer material. In this approach, AgI-Ag₂O-V₂O₅ glasses, which exhibit ionic and electrical conductivity are applied as ion-to-electron transducers of polymeric membrane microelectrodes. All-solid-state electrodes based on potassium-sensitive poly(vinyl chloride) membranes, deposited directly on the surface of glass composites, exhibited theoretical responses. Their selectivity and durability were comparable to planar microelectrodes containing an internal electrolyte immobilized in the intermediate hydrogel layer. The only disadvantage of the proposed structures was their limited reproducibility. Moreover, it was found that the unmodified AgI-Ag₂O-V₂O₅ glasses can be applied as ion-sensitive membrane of solid-state microelectrodes for the determination of Ag⁺ and I⁻ ions.     

Foreword to the memorial issue for Professor Roberto Marassi

Journal of Solid State Electrochemistry -