Carlos Jaime

Molecular dynamics simulation studies of liquid acetonitrile: New six-site model

Molecular dynamics (MD) simulations are carried out for liquid acetonitrile using a new six‐site model for the solvent molecules. The recent force field of Cornell et al. ( J Am Chem Soc, 1995, 117, 5179) was used under the RESP approach to obtain the atomic charges. A new flexible all‐atom solvent model was achieved whose density, heat of vaporization, and isothermal compressibility values are in good agreement with available experimental data, especially for a generic force field. Radial distribution functions are calculated and discussed to study the liquid structure in detail.

β-Cyclodextrin inclusion complex with adamantane intermolecular 1H{1H} NOE determinations and molecular mechanics calculations

Abstract NOE experiments on the β-cyclodextrin (CD) /adamantane complex unequivocally demonstrate that the guest is inside the host cavity. Molecular mechanics calculations indicate the absence of preference by the guest for one single orientation. The host/guest supermolecule has been fully optimized and results show that adamantane is in the narrower half of the β-CD torus.

Empirical force field calculations (MM2-V4) on biphenyl and 2,2'-bipyridine

Abstract The experimental rotational barriers of biphenyl, 1 , (6.0 and 6.5 kJ mol −1 ) and the ab initio calculated conformational behaviour of 2,2′-bipyridine, 2 , (29.3, 21.7, 27.6 and 0.0 kJ mol −1 ), as well as their geometry, have been correctly reproduced by Empirical Force Field calculations using a modified MM2 program (MM2-V4) containing the fourth term in the torsional potential function ( 1 : 5.52 and 6.60 kJ mol −1 ; 2 : 29.7, 25.0, 26.9 and 0.0 kJ mol −1 ).

β-cyclodextrin bimodal complexes with n-alkylbenzenes and n-alkylcyclohexanes A molecular mechanics study

Abstract The bimodal complexation of phenyl- and cyclohexyl-alkanes in β-cyclodextrin has been studied by means of molecular mechanics calculations using Allingers MM3 force field. The host shows a computed preference for including the phenyl ring when alkyl chains contain less than five carbon atoms; the computed geometry always locates the phenyl ring at the primary hydroxyl group zone (narrower rim). In contrast, the cyclohexyl ring is computed to be either at the narrower or at the wider part of the host cavity. A good qualitative correlation between computed and experimental dissociation constants for related compounds have been obtained.

The CSIC Reaction on Substrates Derived From Aldehydes

Abstract The Carbanion-mediated Sulfonate (Sulfonamide) Intramolecular Cyclization reaction (CSIC reaction) on conveniently functionalized cyanoalkylsulfonates and cyanoalkylsulfonamides derived from aldehydes is possible and gives the new heterocyclic ring systems 5-alkyl-4-amino-5 H -1,2-oxathiole 2,2-dioxide and 3-alkyl-5 H -4-amino-5-cyano-5 H -2,3-dihydroisothiazole 1,1-dioxide in good yield.

Preparation of enantiomers of 9-(1-amino-2,2-dimethylpropyl)-9,10-dihydroanthracene. Conformational study and their behaviour as chiral solvating agents

Abstract Homochiral forms of 9-(1-amino-2,2-dimethylpropyl)-9,10-dihydroanthracene were prepared by hydrolysis of crystallised diastereomeric salts of mandelic acid. The activity as chiral solvating agent was tested in the presence of several alcohols and acids. A boat conformation of the central ring was demonstrated by NMR studies and MM3 calculations.

Synthesis and structure of new hosts related to 9,9′-bianthryl

The molecular structures of 10,10′-biacridinyl-9,9′-dione (5), 9-(10′-bromo-9′-anthryl)carbazole (9) and 9,9′-bicarbazyl (12) have been solved by X-ray crystallography. Proton and carbon-13 NMR studies of these and related compounds, show that in solution their conformations are also ‘scissor-like’. AM1 semi-empirical calculations provide a rationale for the geometries of these compounds.

HOST/GUEST INTERACTIONS AND NMR SPECTROSCOPY. A COMPUTER PROGRAM FOR ASSOCIATION CONSTANT DETERMINATION

A computer program is presented for the computation of association constants for host/guest compounds based on experimental data obtained from the NMR spectra of samples with different host/guest ratios of known concentration.

Cyclo-bis-intercalands with acridine subunits linked by rigid spacers

Abstract The tweezer 1 and macrocyclic 2 compounds containing two acridine subunits have been synthesized. A structural study by spectroscopic and molecular mechanics methods is reported. The in vitro cytotoxicity of compounds 1, 2, 4 and 6 has been evaluated.

α- and β-cyclodextrin complexes with n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates. A molecular mechanics study of 1:1 and 1:2 associations

Abstract Molecular mechanics (MM) methods were employed to evaluate stabilization upon formation of inclusion compounds between two different guest molecules and α- and β-cyclodextrins (CDs) for two different stoichiometries 1:1 and 1:2. The two guest molecules studied were n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates with variety of chain lengths. The computed stability for the inclusion compounds between α-CDs and n-alkyl carboxylic acids reproduced experimental data reported in the literature. The transition between 1:1/1:2 complexes occurred at an alkyl chain length of nC=9. It was previously demonstrated by diffusion coefficients measures that a stable 1:2 stoichiometry inclusion compound could be formed between n-alkyl p-hydroxy benzoates and α-CD for the chain length nC>4. The computed results reproduced the experimental ones. The combination between OPLS and GB/SA resulted in better agreements with experiments than those obtained with MM2 and MM3.