Synthesis and the crystal structure of [Hg6As4](InCl6)Cl: influence of covalent and electrostatic factors on the supramolecular structure

A new inorganic supramolecular complex [Hg₆As₄](InCl₆)Cl was synthesized. The complex crystallizes in the cubic space group Pa3 with the unit cell parameter a = 12.109(1) and Z = 4. The crystal structure of the complex is based on the ³[Hg₆As₄]⁴⁺ three-dimensional cationic host framework. The guest InCl₆ ^3– and Cl^– anions are located in the cavities of the framework. The host—guest interactions were examined by quantum-chemical calculations of the equilibrium geometry of the InCl₆ ^3– anion and analysis of the periodic zero-potential surface of the supramolecular complex. It was demonstrated that the electrostatic factors dominate over the covalent factors in the organization of the supramolecular structure of [Hg₆As₄](InCl₆)Cl.     

Synthesis of covalent probes for the radiolabeling of the cannabinoid receptor

The main psychoactive constituent of marijuana, (-)-Delta(9)-tetrahydrocannabinol, produces most of its physiological effects by interacting with the CB1 cannabinoid receptor, a membrane protein belonging to the large superfamily of G-protein coupled receptors. The 3-D structure of the receptor binding site is of value in the design of novel medications for a variety of therapeutic indications. To obtain information on the amino acid residues associated with this binding site, we have designed and synthesized a cannabinergic CB1 ligand prototype carrying an electrophilic isothiocyanato group capable of reacting covalently with amino acid residues bearing thiol or unprotonated amino groups. The ligand also incorporates an iodide atom, which can serve as a high-activity radiolabel. The key step in our synthesis involves a rapid intramolecular Diels-Alder reaction of a transiently formed o-quinone methide, which proceeds stereospecifically with the formation of the tricyclic cannabinoid template. Introduction of the iodo group is the last step in the sequence and is compatible with the use of (125)I-radiolabel.     

Theoretical study of the solvation of fluorine and chlorine anions by water

The solvation of fluoride and chloride anions (F(-) and Cl(-), respectively) by water has been studied using effective fragment potentials (EFPs) for the water molecules and ab initio quantum mechanics for the anions. In particular, the number of water molecules required to fully surround each anion has been investigated. Monte Carlo calculations have been used in an attempt to find the solvated system X(-)(H(2)O)(n) (X = F, Cl) with the lowest energy for each value of n. It is predicted that 18 water molecules are required to form a complete solvation shell around a Cl(-) anion, where "complete solvation" is interpreted as an ion that is completely surrounded by solvent molecules. Although fewer water molecules may fully solvate the Cl(-) anion, such structures are higher in energy than partially solvated molecules, up to n > or = 18. Calculations on the F(-) anion suggest that 15 water molecules are required for a complete solvation shell. The EFP predictions are in good agreement with the relative energies predicted by ab initio energy calculations at the EFP geometries.     

Femtosecond infrared study of the dynamics of solvation and solvent caging.

The ultrafast reaction dynamics following 295-nm photodissociation of Re2CO10 were studied experimentally with 300-fs time resolution in the reactive, strongly coordinating CCl4 solution and in the inert, weakly coordinating hexane solution. Density-functional theoretical (DFT) and ab initio calculations were used to further characterize the transient intermediates seen in the experiments. It was found that the quantum yield of the Re-Re bond dissociation is governed by geminate recombination on two time scales in CCl4, approximately 50 and approximately 500 ps. The recombination dynamics are discussed in terms of solvent caging in which the geminate Re(CO)5 pair has a low probability to escape the first solvent shell in the first few picoseconds after femtosecond photolysis. The other photofragmentation channel resulted in the equatorially solvated dirhenium nonacarbonyl eq-Re2(CO)9(solvent). Theoretical calculations indicated that a structural reorganization energy cost on the order of 6-7 kcal/mol might be required for the unsolvated nonacarbonyl to coordinate to a solvent molecule. These results suggest that for Re(CO)5 the solvent can be treated as a viscous continuum, whereas for the Re2(CO)9 the solvent is best described in molecular terms.     

An NMR and solvation study of rotational isomerism in epihalohydrins

The ¹H NMR spectra of epifluoro, chloro- and bromohydrin have been analysed in a number of solvents of varying polarity. Ab initio and molecular mechanism calculations together with solvation theory allowed an analysis of the observed solvent dependence of the proton couplings in terms of the anti and gauche rotamers only, the syn rotamer being of very small population: The Ga che-anti energy difference in the vapour is 0.1, 0.5 and 0.7 kcal mol^-1 for the three compounds respectively, though these relative energies may be reversed in solutions in which the gauche form is relatively more stabilized. The trans-oriented vicinal coupling has values of 7.3, 8.4 and 9.1 Hz for F, Cl, and Br respectively. Only one long-range coupling showed a pronounced orientation dependence, due to an approximately planar zizag orientation in the gauche rotamer.     

Two-dimensional covalent organic framework nanosheets: Synthesis and energy-related applications

Two-dimensional(2D) covalent organic framework nanosheets(CONs) are attracting increasing research attention because of their unique properties derived from their ultrathin thickness, high surface-tovolume atomic ratio, and extremely large surface area. 2D CONs can provide high transport pathways for charge carriers(e.g., electrons, holes and ions) through either the conjugated skeletons or the open channels. Therefore, they have shown great potential in energy related applications. In this revi...     

Synthesis and study of L-arabinopyranosides of 5- and 6-nitroindoles

Condensation of 5- or 6-nitroindoline with L-arabinose gave 1--L-arabinopyranosyl-5 (or 6)-nitroindolines, which, after acetylation, dehydrogenation, and removal of the protective groups, are converted to 1--L-arabinopyranosyl-5(or 6)-nitroindoles and then to the corresponding amino derivatives. 1--L-Arabinopyranosyl-6-nitro-3-bromo-(iodo)indoles were obtained. The selective 2-O- and 3-O-deacetylation of 1-(2, 3, 4-tri-O-acetyl)--L-arabinopyranosyl-6-nitroindole was accomplished.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 224–229, February, 1979.     

Synthesis and biological study of 6‐polyhydroxyalkylpteridines

6‐Polyhydroxyalkylpteridines are synthesised by oxidation of the corresponding pyrano[3,2‐g]pteridines, the latter ones having been obtained by condensation between 5,6‐diaminopyrimidines 1a,b and phenylhydra‐zones 2a‐e . The relative configuration at the chiral centers of the pyrano[3,2‐g]pteridines has been determined by nmr study and X‐ray analysis. The anti‐AIDS activity of several of these compounds has been tested.     

Femtosecond spectroscopic study of the solvation of amphiphilic molecules by water

We use polarization-resolved mid-infrared pump-probe spectroscopy to study the aqueous solvation of proline and N-methylacetamide. These molecules serve as models to study the solvation of proteins. We monitor the orientational dynamics of partly deuterated water molecules (HDO) that are present at a low concentration in the water. We find that the OD vibration of HDO relaxes via an intermediate level, that is characterized by a hydrogen-bond that is stronger than in the ground state. With increasing concentration the lifetime of the excited state increases from 1.8 ps to 2.4 ps and the lifetime of the intermediate level from 0.6 ps to 1.0 ps. Regarding the orientational dynamics we observe biexponential behavior, which finds its origin in the presence of two classes of water molecules. There is a fraction of water molecules that has bulk-like orientational dynamics (τ_rot = 2.5 ps) and a fraction of immobilized water molecules (τ_rot > 10 ps). The relative abundance of the two fractions is determined by the nature and concentration of the solute. We find that the hydrophobic solute groups are responsible for the immobilization of water molecules. Every methyl group causes the immobilization of approximately 4 water OH groups. The hydrophilic solute groups, on the other hand, do not hinder the reorientation and the water molecules solvating them reorient with the same rate as in the bulk liquid.     

Molecular dynamics study of the solvation of calcium carbonate in water

We performed molecular dynamics simulations of diluted solutions of calcium carbonate in water. To this end, we combined and tested previous polarizable models. The carbonate anion forms long-living hydrogen bonds with water and shows an amphiphilic character, in which the water molecules are expelled in a region close to its C(3) symmetry axis. The calcium cation forms a strongly bound ion pair with the carbonate. The first hydration shell around the CaCO(3) pair is found to be very similar to the location of the water molecules surrounding CaCO(3) in ikaite, the hydrated mineral.     

Theoretical study of the solvation of nitrogen. Two different approaches

Two different approaches were used for a theoretical study of the solvation of N₂, with HF, H₂O, NH₃, CH₄ as solvents. In the first approach, the contour maps of orientationally optimized interaction energy between N₂ and one solvent molecule were computed by fast semiempirical methods (Extended Hückel and CNDO/2) in order to find a reliable but not too expensive calculation method for solvation models. In the case of the N₂-H₂O system, anab initio map was also evaluated for comparison. The second approach is based on the building up of clusters with one molecule of N₂ surrounded by a number (2 to 8) of solvent molecules and finding the structure of such clusters by energy minimization. From the structures obtained it results that they are determined mainly by steric factors, so that clusters optimized by means of different methods are similar, despite the remarkable differences in the maps.     

Synthesis and study of the reactions of 2,5- and 1,2,5-substituted 6-aminoindoles

It has been shown that nitration with a KNO₃ + H₂SO₄ mixture of 2,5-dimethyl- and 5-methyl-2-phenylindoles proceeds strictly selectively with the formation of 6-nitro derivatives, by reduction of which the corresponding aminoindoles were synthesized. It was established that the condensation of the aminoindoles obtained with β-diketones leads initially to enamino ketones, which in the presence of various acidic reagents are not subject to cyclization, i.e. may not be used for the synthesis of the corresponding pyrroloquinolines.     

Free energy of solvation of simple ions: molecular-dynamics study of solvation of Cl- and Na+ in the ice/water interface

Molecular-dynamics simulations of Cl(-) and Na(+) ions are performed to calculate ionic solvation free energies in both bulk simple point-charge/extended water and ice 1 h at several different temperatures, and at the basal ice 1 h/water interface. For the interface we calculate the free energy of "transfer" of the ions across the ice/water interface. For the ions in bulk water in the NPT ensemble at 298 K and 1 atm, results are found to be in good agreement with experiments, and with other simulation results. Simulations performed in the NVT ensemble are shown to give equivalent solvation free energies, and this ensemble is used for the interfacial simulations. Solvation free energies of Cl(-) and Na(+) ions in ice at 150 K are found to be approximately 30 and approximately 20 kcal mol(-1), respectively, less favorable than for water at room temperature. Near the melting point of the model the solvation of the ions in water is the same (within statistical error) as that measured at room temperature, and in the ice is equivalent and approximately 10 kcal mol(-1) less favorable than the liquid. The free energy of transfer for each ion across ice/water interface is calculated and is in good agreement with the bulk observations for the Cl(-) ion. However, for the model of Na(+) the long-range electrostatic contribution to the free energy was more negative in the ice than the liquid, in contrast with the results observed in the bulk calculations.     

Conformational equilibria in halocyclohexanones,an NMR and solvation study

The conformational equilibrium in 2-chloro cyclohexanone is measured in thirteen solvents from the 220 MHz¹H NMR spectrum using the C₂-H couplings and chemical shifts and the cis and trans 4-t-butyl-2-chlorocyclohexanones as reference compounds. ΔG_ea varies from 1.04 $\text{kcal}\text{mole}$ in n-pentane to ?0.58 $\text{kcal}\text{mole}$ in DMSO. The large concentration dependence of the NMR parameters in non-polar solvents noted previously is confirmed.Generalised reaction-field theory is used to calculate this solvent dependence, using a refined model of the geometry and dipole moments of the conformers.The cyclohexanone ring is considerably flatter than that of cyclohexane and this has an appreciable effect on the resultant dipole moments. Use of this geometry and CO and C-Cl bond moments which reproduce the observed dipole moments of the t-butyl compounds together with the generalised reaction field theory gives calculated solvation energies in good agreement with the observed data and hence allows the prediction of the vapour state energy difference.The model is applied to a variety of halo-ketones and gives both a reasonable explanation of the observed solvent dependencies and also the vapour state energy differences.The vapour state conformer energies are compared with the corresponding values for the halocyclohexanes and illustrate the large polar and steric effects due to the introduction of the CO group.     

Experimental and thermodynamic study of solubility,partition and solvation of climbazole

Journal of Thermal Analysis and Calorimetry - The equilibrium solubility of climbazole (CLZ), an antifungal drug, was determined in buffers (pH 2.0; 7.4), hexane and 1-octanol within the...