Soft agonist receptor interactions: Theoretical and experimental simulation of the active site of the receptor of sweet molecules

The structure-activity relationship of sweet molecules is chosen as an example to illustrate a mechanistic approach of soft agonist-receptor interactions. It is shown that an essentially geometric model of the receptor site can explain the activity of most sweet molecules, both rigid and flexible. The relevant conformations of flexible molecules in solution are extracted from a combination of NMR data and of energy calculations. A possible experimental simulation of the receptor environment in solution is illustrated by the complex of a dipeptide sweetener with a crown-ether.     

Behavior of 3,6-Bis(vinylsulfonyl)-1,2,4,5-tetrafluorobenzene in Homolytic Addition of Dialkyl Phosphites

Reaction of 3,6-bis(vinylsulfonyl)-1,2,4,5-tetrafluorobenzene with dialkyl phosphites at thermal initiation (70°C) gives rise to 3,6-bis(dialkoxyphosphonoethylsulfonyl)-1,2,4,5-tetrafluorobenzenes in up to 45% yield. The formation of diethoxyphosphonyl radicals in the course of the reaction was observed with the use of ESR method applying spin trapping by 2-methyl-2-nitrosopropane. The use as initiator of the azo-bis-isobutyronitrile increased the yield of diadducts to 60%.     

An investigation of catalytic activity in mixed metal oxide nanophase materials

We present preliminary evidence for catalytic activity by unsupported mixed metal oxide nanocrystalline materials. The results of this study show that a nanophase form of Li-MgO has begun to exhibit catalytic activity by 300 °C. This is at least 200 degrees below the temperature at which conventional Li-MgO catalysts exhibit comparable activity. Furthermore, at higher temperatures, the same nanophase composition shows enhanced activities and somewhat improved hydrocarbon selectivities over conventional Li-MgO catalysts.     

Hopanoids of methylotropic acetobacteria

Squalene, 35-methoxyho-6-ene-32R,33R,34S-triol, hop-22(29)-ene, and hopan-22-ol have been isolated fromAcetobacter sp. VSB 917. The structures of the substances isolated and of the 35-methoxyhop-6-ene-32R,33R,34S-triol triacetate obtained have been established by IR, mass, and¹H and¹³C NMR spectroscopies.Vitaminy Scientific-Production Association, Moscow. Translated from Khimiya Prirodnykh Soedinenii, Nos. 3,4, pp. 367–372, May–August, 1992.     

Determination of platinum and gold in biological materials by neutron activation analysis

A procedure for platinum and gold determination utilizing, neutron activation combined with radiochemical separation, has been developed. The reaction¹⁹⁸Pt (n, )¹⁹⁹ is used for Pt determination. Four procedures for gold separation are examined: (1) adsorption on untreated polyurethane foam (UPF). (2) extraction with dibutyl sulphide. (3) reduction of gold to elementary state in conc. H₂SO₄, and extraction of gold as diethyldithiocarbamate complex. The extraction with Cu(DDC)₂ is chosen as the most suitable process and applied to platinum and gold determinations in Bowen's Kale and mice organs, previously treated with Biocisplatinum^® specimens.     

Assembly of the inorganic double helix Mg6(Et2NCO2)12 by fixation of carbon dioxide: crystal and solution structure

The homoleptic magnesium carbamato complex Mg6(Et2NCO2)12, 1 (Et2NCO2- = diethylcarbamato anion), was prepared by the reaction of dibutylmagnesium with diethylamine, followed by carboxylation using gaseous carbon dioxide. Crystallographic characterization demonstrated that 1 has the standard M6(R2NCO2)12 structure and is a double helix of MgO(x)(x = 5, 6) coordination polyhedra with Delta or Lambda stereochemistry arising from the configuration around the six-coordinate Mg2+ cations. It crystallized in the orthorhombic space group Ccca with two molecules of Delta1 and two of Lambda1 per unit cell (a = 21.548 A, b = 25.094 A, c = 15.4485(11) A, alpha = beta = gamma = 90 degrees ). Extensive solution characterization of 1 by 1-dimensional proton and 13C NMR spectroscopy and by two-dimensional 1H-[13C] NMR correlation techniques verified that the helical structure is maintained in solution. Moreover, these measurements indicated that the intramolecular dynamics of 1 relating to motions of the ethyl groups was substantially hindered in solution. Correlation of the crystallographic and NMR structural studies indicated that this arises from a combination of hindered rotation about the carbamato C-N bond and efficient packing of the ethyl groups around the Mg6O24 core. The result is an inverted-micelle-like structure for 1 in which the hydrophobic ethyl groups form a sheath largely restricting access to the hydrophilic Mg6O24 core.     

Organic Synthesis and Technetium-99m Labeling of Some Amino-Phenol Ligands

We reported the synthesis and labeling of one tetradentate and two pentadentate amino-phenol ligands with technetium-99m by the direct pertechnetate addition and by ligand exchange methods. Labeling by direct pertechnetate addition was attended by adding pertechnetate eluate to the ethanolic solution of the amino-phenol ligands at pH 9. Stannous chloride dihydrate was used as reducing agent. Exchange studies were carried out via the use of the following ^99mTc-chelates: ^99mTc-DTPA, ^99mTc-gluconate, ^99mTc-tartrate and ^99mTc-citrate complexes. Ligand exchange method was achieved by incubation the ligand solutions with ^99mTc-co-ligands complexes in 0.05M bicarbonate buffer pH 9. At this pH value the ^99mTc-co-ligands dissociated and the more stable new ^99mTc-ligands were formed with high radiochemical yield 95%. The radiochemical yield of ^99mTc-labeled amino-phenol ligands were estimated by solvent extraction, electrophoresis and HPLC methods. The produced technetium-99m amino-phenol complexes were neutral, lipophilic and stable during the period of 24 hours.     

Peloruside A: a potent cytotoxic macrolide isolated from the new zealand marine sponge Mycale sp

A novel, polyoxygenated, pyranose ring containing 16-membered macrolide peloruside A (1) exhibiting cytotoxic activity in the nanomolar range was isolated from the New Zealand marine sponge Mycale sp. The structure of 1 and relative stereochemistry of the 10 stereogenic centers were determined on a 3 mg sample using a variety of spectroscopic methods. Compound 1 was isolated along with the previously reported cytotoxins mycalamide A (2) and pateamine (3) from a single specimen of this sponge.     

The Mukaiyama-Michael reaction of N-acyl-2,3-dihydro-4-pyridones: regio- and stereoselective synthesis of cis-2,6-disubstituted 1,2,5,6-tetrahydropyridines

[formula: see text] A convenient regio- and stereoselective preparation of 1,2,5,6-tetrahydropyridines of the type 1 has been developed, starting from readily available N-acyl-2,3-dihydro-4-pyridones 2.     

The possibility of different time scales in the dynamics of pore imbibition

To model the imbibition of liquids into porous solids, use is often made of the Lucas-Washburn equation, which relates the distance of penetration of a liquid at a given time to the pore radius, the viscosity and surface tension of the liquid, and the effective contact angle between the liquid and the solid. In this paper, we extend previous large-scale molecular dynamics simulations to show how this tool can be used to study the details of liquid imbibition, including the impact of the contact angle on the dynamics of penetration and the evolution of the internal flow field. In particular, we show that the asymptotic behavior of the contact angle versus time for a completely wetting liquid is given by approximately t(-1/4).