Adsorption characteristics of tripodal thiol-functionalized porphyrins on gold

X-ray photoelectron and Fourier transform infrared spectroscopy studies are reported for self-assembled monolayers (SAMs) of two tripodal thiol-functionalized metalloporphyrins (Zn and Cu) and three benchmark tripods on gold substrates. The tripodal unit common to all five molecules is 1-(phenyl)-1,1,1-tris(4-mercaptomethylphenyl)methane (Tpd). Both porphyrins contain S-acetyl-protected thiols and are linked to the 4-position of the phenyl ring of Tpd via a phenylethyne group. The benchmark molecules include (1) two tripods containing a bromine atom at the 4-position of the apical phenyl ring, one a free thiol and the other its S-acetyl-protected analogue, and (2) a S-acetyl-protected tripod containing a phenylethyne unit at the 4-position of the apical phenyl group. Together, the spectroscopic studies reveal that none of the five tripodal molecules bond to the gold surface via all three sulfur atoms. Instead, the average number of bound thiols ranges from 1.5 to 2, with the porphyrinic molecules generally falling at the middle to upper end of the range and the smallest benchmark tripods falling at the lower end. Similar surface binding is found for the S-acetyl-protected and free benchmark tripods, indicating that the presence of the protecting group does not influence binding. Furthermore, the surface binding characteristics of the SAMs are not sensitive to deposition conditions such as solvent type, deposition time, or temperature of the solution.     

Linear two-step gradient counter-current chromatography analysis based on a recursive solution of an equilibrium stage model

The implementation of gradients in continuously operated chromatographic counter-current processes has recently attracted considerable interest as a method to improve the performance of this effective separation method. If liquid mobile phases are applied it is advantageous to set the solvent strength in the desorbent stream higher than that in the feed stream. As a consequence. the components to be separated are more retained in the adsorption zones and more easily eluted in the desorption zones. Due to the additional degrees of freedom the design and the optimization of such a two-step gradient counter-current process is difficult. In this paper a steady state equilibrium stage model is used to simulate the process under linear conditions. A simple solution of the underlying model equations is presented capable to describe efficiently the unit for large stage numbers typically encountered in chromatographic columns. Due to the rapidity of the algorithm developed a broad range of operating conditions can be evaluated systematically for different types of gradients. The impact of (a) the functional dependence of the adsorption equilibrium constants on the solvent composition, (b) the number of equilibrium stages and (c) the specification of purity requirements is illustrated and discussed based on results of parametric calculations. The results achieved emphasize the potential of two-step gradient counter-current chromatography.     

Structure determination of diacholestanes by means of 13C-NMR and 1H-NMR spectroscopy

A full analysis of the ¹³C-NMR spectra of five C6-functionalized diacholestenes is reported using SFORD, PRS and LIS techniques. Good agreement was obtained between spectral results and data calculated for a theoretical model.The structure of the two C20 epimeric diacholest-13(17)-enes, as well as of their epoxidation products, was established by means of ¹³C and ¹H-NMR analysis.     

Synthesis of 1,2-Dihydropyridines, 2,3-Dihydro-4(1H)-pyridinone,and 1,2,3,4-Tetrahydropyridines via N-Acyl N,O-Hemiacetal Formation

New procedures are described for the synthesis of α,β-ethylenic and acetylenic aldehydes from 2-butene- and 2-butyne-1,4-diol, respectively (see Scheme 1). These are applied to the preparation of a particular δ-acetylamino-α,β-ethylenic aldehyde ((E)- 5 ) as well as of its acetylenic analogue 15 . On heating in the presence of a silyl enol ether, the former undergoes a complete dehydrative cyclization affording the N-acetyl-1,2-dihydropyridine 19 . The addition of HCl to aldehyde (E)- 5 results in the production of the 4-chloro-1,2,3,4-tetrahydropyridine 22 which is hydrolyzed to the corresponding alcohol 23 on silica gel. Similarly, the addition of HCl or HBr to the δ-acetyl-amino-α,β-acetylenic aldehyde 15 leads to the previously unknown 4-halo-1,2-dihydropyridines 26 ; these are easily hydrolyzed to the 2,3-dihydro-4(1H)-pyridinone 27 . The ring-forming process involves a N-acyl N,O-hemiacetal as intermediate which is eventually dehydrated.     

Anesthetics as chemical tools to study the structure and function of nicotinic acetylcholine receptors

The nicotinic acetylcholine receptor (AChR) is the archetype of the Cys-loop ligand-gated ion channel receptor superfamily. Noncompetitive antagonists inhibit the AChR without interacting directly with agonist sites. Among noncompetitive antagonists, general and local anesthetics have been used for decades to study the structure and function of muscle- as well as neuronal-type AChRs. In this review, we address and update all information regarding the characterization of binding sites and the mechanism of action for n-alkanols, barbiturates, inhalational and dissociative general anesthetics, as well as for tertiary and quaternary local anesthetics. The experimental evidence outlined in this review suggest that: (1) several neuronal-type AChRs might be targets for the pharmacological action of distinct anesthetics; (2) the molecular components of a specific anesthetic locus on a certain receptor type are different from the structural determinants of the site for the same anesthetic on a different receptor type; (3) there are unique binding sites for distinct anesthetics in the same receptor; (4) the affinity of a specific anesthetic depends on the AChR conformational state; (5) anesthetics may inhibit AChRs by different mechanisms including open-channel-blocking, augmenting the desensitization process, and/or inactivating the opening of resting receptors; and (6) some anesthetics may potentiate AChR activity.     

Halochrome Molekeln 4. Mitteilung. Chromogene Verbindungen durch Cyclisierung von [2-(Benzothiazol-2-yl)amino-4-(diäthylamino)phenyl]heteroaryliumsalzen: Synthese und acidobasisches Verhalten

Halochromic Molecules. Chromogenic Compounds by Cyclization of [2-(Benzothiazol-2-yl)amino-4-(diethylamino)phenyl]heteroarylium Salts: Synthesis and Acidobasic Behaviour Coloured [2-(Benzothiazol-2-yl)amino-4-(diethylamino)phenyl]heteroarylium salts are deprotonated to colourless spiro-compounds. The preparation of these products is described and their structure is explained by ¹H-NMR and UV/VIS spectroscopy. An investigation of the halochromic properties is carried out by spectro-photometric determination of ε_pH*- and εH₀*-curves in buffered MeOH/H₂O solutions. pK*-Values are determined, and the complex protonation equilibria are discussed. One of the heteroarylium salts does not form a spiro-compound by deprotonation, but it is stabilized by a σ-bond resonance.     

Atmospheric pressure photoionization applied to quantitation of cyproterone acetate in human plasma

Cyproterone acetate [6-chloro-1beta,2beta-dihydro-17alpha-hydroxy- 3'H-cyclopropa(1,2)-pregna-1,4,6-triene-3,20-dione acetate] is a powerful antiandrogen used in the treatment of women suffering from disorders associated with androgenization such as hirsutism and acne. A fast, sensitive, and robustness method is developed for the determination and quantitation of cyproterone acetate in human blood plasma by liquid chromatography coupled with tandem mass spectrometry. Cyproterone acetate is extracted from 0.2 mL human plasma by liquid-liquid extraction. The method has a chromatographic run of 4.5 min, using a C18 analytical column (100- yen 2.1-mm i.d.), and the linear calibration curve over the range is linear from 1 to 500 ng/mL (r2 > 0.994). The between-run precision, based on the relative standard deviation replicate quality controls, is 96.2% (3 ng/mL), 97.5% (120 ng/mL), and 99.1% (400 ng/mL). The between-run accuracy was +/- 2.7%, 3.1%, and 4.8% for the previously mentioned concentrations, respectively. The method is employed in a bioequivalence study of two tablet formulations of cyproterone acetate (100 mg).     

Über die Zusammensetzung des Pyrolysates von Weihrauch “Aden”, dem Gummiharz vonBoswellia carteri Birdw., 3. Mitt.

1,2,4-Trihydroxy-p-menthane (1) was isolated from the pyrolytic products of incense Aden (gum resin ofBoswellia carteri Birdw.) The relative and absolute configuration of1 was established on the basis of spectral and chemical evidences and also confirmed independently by partial synthesis.

2. Mitt.:Pailer, M. Scheidl, O., Gutwillinger, H., Klein, E., Obermann, H., Mh. Chem.112, 595 (1981).