Multi-analyte HPLC–DAD Method for Concurrent Analysis of Six Antimicrobials and Three Proton Pump Inhibitors Frequently used in Management of Helicobacter pylori Infection: Application to Simulated Intestinal Fluid Samples

Chromatographia - The present work deals with the optimization, validation and application of a versatile HPLC–DAD method for concurrent estimation of nine antimicrobials and proton pump...     

Site-to-site peptide transport on a molecular platform using a small-molecule robotic arm

Peptides attached to a cysteine hydrazide ‘transporter module’ are transported selectively in either direction between two chemically similar sites on a molecular platform, enabled by the discovery of new operating methods for a molecular transporter that functions through ratcheting. Substrate repositioning is achieved using a small-molecule robotic arm controlled by a protonation-mediated rotary switch and attachment/release dynamic covalent chemistry. A polar solvent mixtures were found to favour Z to E isomerization of the doubly-protonated switch, transporting cargo in one direction (arbitrarily defined as ‘forward’) in up to 85% yield, while polar solvent mixtures were unexpectedly found to favour E to Z isomerization enabling transport in the reverse (‘backward’) direction in >98% yield. Transport of the substrates proceeded in a matter of hours (compared to 6 days even for simple cargoes with the original system) without the peptides at any time dissociating from the machine nor exchanging with others in the bulk. Under the new operating conditions, key intermediates of the switch are sufficiently stabilized within the macrocycle formed between switch, arm, substrate and platform that they can be identified and structurally characterized by ¹H NMR. The size of the peptide cargo has no significant effect on the rate or efficiency of transport in either direction. The new operating conditions allow detailed physical organic chemistry of the ratcheted transport mechanism to be uncovered, improve efficiency, and enable the transport of more complex cargoes than was previously possible.

Peptides are transported in either direction between chemically similar sites on a molecular platform, substrate repositioning is achieved using a cysteine hydrazide transporter module and a small-molecule robotic arm controlled by a rotary switch.     

Highly selective asymmetric acetate aldol reactions of an N-acetyl thiazolidinethione reagent

[reaction: see text] A highly diastereoselective acetate aldol reaction that uses a tert-leucine-derived thiazolidinethione auxiliary and dichlorophenylborane has been developed. The reaction proceeds in excellent yields and with high diastereoselectivities (drs range from 9.5:1 to >100:1).     

Synthesis and Properties of Mononuclear and Homobinuclear Chelates of Mn(II), Co(II), Ni(II), and Cu(II) with Phthalein Purple

Mono- and homobinuclear complexes of Mn(II), Co(II), Ni(II), and Cu(II) with phthalein purple are prepared and characterized by elemental analysis, thermal studies (TGA and DTA), spectral methods (IR, UV/Vis, and ESR), magnetic moment determination, and electrochemical reduction (DC polarography at DME and CV at HMDE). Thermal degradation of the complexes was studied by TGA and DTA where some thermodynamic parameters were determined. The mode of bonding and geometry of the complexes were determined from the spectral studies. Magnetic moment values showed some antiferromagnetism in the homobinuclear complexes. The reduction of the metal ions proceeds to the metallic state along an irreversible process.     

UV-vis, IR and 1H NMR spectroscopic studies of some mono- and bis-azo-compounds based on 2,7-dihydroxynaphthalene and aniline derivatives

The absorption spectra of mono- and bis-azo-derivatives obtained by coupling the diazonium salts of aromatic amines and 2,7-dihydroxynaphthalene have been studied in six organic solvents. The different absorption bands have been assigned and the effect of solvents on the charge transfer band is also discussed. The diagnostic IR spectral bands and 1H NMR signals are assigned and discussed in relation to molecular structure. Also, semi-empirical molecular orbital calculations using the atom superposition and electron delocalization molecular orbital (ASED-MO) theory have been performed to investigate the molecular and electronic structures of these compounds. According to these calculations, an intramolecular hydrogen bonding is essential for stabilization of such molecules.     

On the structure of nonarchimedean exponential fields I

Given an ordered fieldK, we compute the natural valuation and skeleton of the ordered multiplicative group (K ^>0, ·, 1, <) in terms of those of the ordered additive group (K,+,0,<). We use this computation to provide necessary and sufficient conditions on the value groupv(K) and residue field , for theL -equivalence of the above mentioned groups. We then apply the results to exponential fields, and describev(K) in that case. Finally, ifK is countable or a power series field, we derive necessary and sufficient conditions onv(K) and forK to be exponential. In the countable case, we get a structure theorem forv(K).This paper represents some results of the author's doctoral thesisThis paper was written while the author was supported by a research grant from the University of Heidelberg     

A Convenient Regiospecific Synthesis of New Conjugated Tetrazole Derivatives via the Reaction of Dienones with the Tetrachlorosilane-Sodium Azide Reagent and their NMR Structural Assignment

Summary. Several new 1-aryl-, aralkyl-, and heteroaryl-5-(4-phenylbuta-1,3-dienyl)tetrazole derivatives and annulated tetrazole derivatives were efficiently and regiospecifically prepared in nearly quantitative yield via a facile one step reaction of dienones with a combination of tetrachlorosilane and sodium azide in acetonitrile under mild conditions. A complete structure assignment of three representative examples of the tetrazoles was achieved by advanced 2D NMR measurements including COSY, TOCSY, HSQC, HMBC, NOESY, and ROESY experiments.Received March 17, 2003; accepted March 18, 2003 Published online July 28, 2003     

A Convenient Regiospecific Synthesis of New Conjugated Tetrazole Derivatives via the Reaction of Dienones with the Tetrachlorosilane-Sodium Azide Reagent and their NMR Structural Assignment

Several new 1-aryl-, aralkyl-, and heteroaryl-5-(4-phenylbuta-1,3-dienyl)tetrazole derivatives and annulated tetrazole derivatives were efficiently and regiospecifically prepared in nearly quantitative yield via a facile one step reaction of dienones with a combination of tetrachlorosilane and sodium azide in acetonitrile under mild conditions. A complete structure assignment of three representative examples of the tetrazoles was achieved by advanced 2D NMR measurements including COSY, TOCSY, HSQC, HMBC, NOESY, and ROESY experiments.     

The3 A 2g →3 T 1g(F) transition in the spectrum of some oxygen-ligated octahedral nickel(II) species

Summary In sodium phosphate glasses, nickel(II) is octahedrally coordinated by the oxygens of the phosphates with ₀ = 7600 cm^–1 and B = 920 cm^–1. Contrary to the case of many other oxygen-coordinated systems including [Ni(H₂O)₆]²⁺ and low alkali borate glasses, the second spin-allowed transition to³ T _1g(F) appears as a single-peaked band well-separated from the spinforbidden transition to¹ E _g(D). Variation of the glass composition does not change the main features of the spectrum. Dissolving the glasses in water results in a shift of all the bands to higher energies with the second spin-allowed band becoming triple-peaked. This supports Liehr and Ballhausen's explanation of the structure of this band.Part of a thesis submitted by T. Genena in partial fulfillment of the M.Sc. degree in Solid State Science, 1985.