An improved nicotinic pharmacophore and a stereoselective CoMFA-model for nicotinic agonists acting at the central nicotinic acetylcholine receptors labelled by [3H]-N-methylcarbamylcholine

A study of a series of compounds with agonistic effect at the alpha4beta2 nicotinic acetylcholine receptors resulted in an improved pharmacophore model as well as a CoMFA model. The pharmacophore was composed of three pharmacophoric elements: (1) a site point (a) corresponding to a protonated nitrogen atom, (2) a site point (b) corresponding to an electronegative atom capable of forming a hydrogen bond, and (3) the centre of a heteroaromatic ring or a C=O bond (c). The pharmacophoric elements were related by the following parameters: (a-b) 7.3-8.0 A, (a-c) 6.5-7.4 A, and the angle between the two distance vectors (delta bac) 30.4-35.8 degrees. In addition to this, a stereoselective CoMFA model was developed, which showed good predictability even for compound classes not present in the training set.     

The determination of trace amounts of tin by flow-injection hydride generation atomic-absorption spectrometry with on-line ion-exchange separation and preconcentration

A hydride generation atomic-absorption spectrometric (AAS) method with flow-injection (FI), aimed at developing a practical routine assay for the determination of tin in food digests, is described. In order to modify the sample matrix and to achieve optimized and reproducible conditions for the hydride generation reaction, the analyte is initially converted into its chlorostannate-complex thereby allowing it to be separated and preconcentrated on-line on an incorporated micro-column packed with a strongly basic anion exchanger and subsequently to be eluted by diluted nitric acid under strictly controlled conditions. Optimum acidic conditions for the FI hydride generation AAS system was found to be 0.01-0.05M nitric acid. At a consumption of 2.7-ml sample volume, aspirated by time-based injection, the procedure resulted in an enrichment factor of 3.5 and yielded a detection limit of 0.08 microg/l. (3sigma) at a sampling frequency of 72/hr. The precision was 2.5% rsd at the 10 microg/l. level. Potential interferents, such as Ni(II), Co(II), Zn(II) and Fe(III) could, at a Sn level of 10 microg/l., be tolerated at an excess of 1000 times without impairing the assay, while a 100-1000-fold excess of Cu(II) decreased the signal by 10-15%. Recoveries in the range 94-102% were obtained for canned food sample digests spiked with 10 microg/l. Sn.     

UVA PHOTOLYSIS USING THE PROTEIN-BOUND SENSITIZERS PRESENT IN HUMAN LENS

Abstract —This research was undertaken to demonstrate that the protein-bound chromophores in aged human lens can act as sensitizers for protein damage by UVA light. The water-insoluble (WI) proteins from pooled human and bovine lenses were solubilized by sonication in water and illuminated with UV light similar in output to that transmitted by the cornea. Analysis of the irradiated proteins showed a linear decrease in sulfiydryl groups with a 30% loss after 2 h. No loss was seen when native a-crystallin was irradiated under the same conditions. A 25% loss of histidine residues was also observed with the human lens WI fraction, and sodium dodecyl sulfate polyacrylamide gels indicated considerable protein cross-linking. Similar photodamage was seen with a WI fraction from old bovine lenses. While the data show the presence of UVA sensitizers, some histidine destruction and protein cross-linking were also obtained with a-crystallin and with lysozyme, which argue that part of the histidine loss in the human WISS was likely due to tryptophan acting as a sensitizer.
A preparation of human WI proteins was irradiated with a total of 200 J/cm² of absorbed light at 10 nm intervals from 290 to 400 nm. Photodamage of cysteine SH groups (35%) and methionine (28Y0) was maximum at 330 nm and diminished linearly at longer wavelengths. The major loss of tryptophan (80%) occurred at 290 nm, but destruction was observed throughout the UVA range. Tyrosine was 35% destroyed at 290 nm but decreased sharply to only 50 at 330 nm. A constant loss of histidine (20%) was seen at all wavelengths from 290 to 360 nm, with some loss (7–8%) even at 400 nm. These action spectra show that the human lens WI fraction contains a collection of protein-bound UVA sensitizers that can cause protein photodamage similar to that seen in cataractous lenses.     

Local field theory of the dual string

We develop a (classical) local field theory which contains as a special solution the (classical) dual string recently discussed by Goddard, Goldstone, Rebbi and Thorn. The basic field is a gauge field F_μν(x), and the Lagrangian is given by $\text{(}\text{?1}\text{2α'}\text{)√F}{}^2$. We treat the case of closed strings (corresponding to the Shapiro-Virasoro model) where F_μν can be expressed in terms of potentials A_μ. Quantization of F_μν is briefly discussed, but a more thorough discussion is postponed.     

Maintaining the Regular Ultra Passum Law in data envelopment analysis

The variable returns to scale data envelopment analysis (DEA) model is developed with a maintained hypothesis of convexity in input–output space. This hypothesis is not consistent with standard microeconomic production theory that posits an S-shape for the production frontier, i.e. for production technologies that obey the Regular Ultra Passum Law. Consequently, measures of technical efficiency assuming convexity are biased downward. In this paper, we provide a more general DEA model that allows the S-shape.     

Kinematics of periodic structures in SU(N) gauge theories

We study periodicity by use of the holonomy group. For a general field configuration, which spans the whole SU(N) group, we show that periodicity of gauge-invariant quantities implies that either the flux is quantized or that there is no flux at all. Finally we show that in a special gauge, the quantized 't Hooft flux can be expressed as a line integral over one of the components of the vector potential. The other components then have “Higgs-like” zeros, with winding numbers related to the 't Hooft flux.     

A dual quark prison

Using semi-classical arguments it is pointed out that the closed dual string, which arises in the strong coupling limit of gauge field theories, has the possibility of imprisoning quarks.