A 2:1 Receptor/C60 Complex as a Nanosized Universal Joint

Buckycatcher II, a C₅₁H₂₄ hydrocarbon with two corannulene pincers on a dibenzonorbornadiene tether, exhibits an affinity toward C₆₀ in organic solvents that is dramatically higher than the original buckycatcher C₆₀H₂₈ and other corannulene‐based molecular receptors for fullerenes. In addition to the formation of an usual 1:1 C₆₀@catcher inclusion complex, a trimeric C₆₀@(catcher)₂ assembly is detected in solutions and in the solid state. X‐ray structure determination reveals a remarkable “universal joint” solvent‐free crystal arrangement of the trimer, with a single fullerene cage wrapped by four corannulene subunits of two cooperating catcher receptors.     

Infrared spectra and structure of substituted unsaturated carbonyl compounds: XVII. Enamino ketone and aldehyde quaternary ammonium salts

The β-trialkylammonium chloride derivatives of several α,β-unsaturated carbonyl compounds have been shown by infrared spectra to exist in the s-cis and s-trans rotational forms. The equilibrium between these two forms shifts towards the s-cis with the increasing steric requirements of the alkyl substituent linked to carbonyl. The CO and CC stretching frequencies are shifted to higher values as compared with other types of α,β-unsaturated ketones.     

Preparation of New Dialkyl Benzene-, Biphenyl-, and Naphthalene-bis(α-oxoethanedithioates)

Novel arene-bis- and -tris(α-oxoethanedithioate) esters of the benzene, the biphenyl, and, in particular, the naphthalene series were prepared by reaction of the corresponding diazoacetyl or bromoacetyl derivatives with elemental sulfur in the presence of triethylamine in dry DMF, and subsequent direct alkylation of the produced dithiocarboxylate anions. The thiolation reaction of the diazoketones was significantly promoted by the addition of anhydrous calcium chloride (calcium chloride–activated thiolation, or CAT). Certain carbonyl-activated methylene and methyl compounds exhibiting no bromo or diazo substituents could be also transformed into dithioesters by the CAT reaction. The structure of three dithioesters was corroborated by X-ray structural analyses.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Reduced–size polarized basis sets for calculations of molecular electric properties. III. Second–row atoms

Reduced–size polarized (ZmPolX) basis sets are developed for the second–row atoms X = Si, P, S, and Cl. The generation of these basis sets follows from a simple physical model of the polarization effect of the external electric field which leads to highly compact polarization functions to be added to the chosen initial basis set. The performance of the ZmPolX sets has been investigated in calculations of molecular dipole moments and polarizabilities. Only a small deterioration of the quality of the calculated molecular electric properties has been found. Simultaneously the size of the present reduced–size ZmPolX basis sets is about one-third smaller than that of the usual polarized (PolX) sets. This reduction considerably widens the range of applications of the ZmPolX sets in calculations of molecular dipole moments, dipole polarizabilities, and related properties.     

Evidence for two forms, double hydrogen tunneling, and proximity of excited states in bridge-substituted porphycenes: supersonic jet studies

Laser-induced fluorescence and dispersed fluorescence spectra measured in supersonic jets for 9,10,19,20-tetra-n-methylporphycene and 9,10,19,20-tetra-n-propylporphycene reveal, for both compounds, the presence of two different species which are assigned to trans and cis tautomeric forms. Doublet splitting of lines is observed, disappearing upon deuteration of the inner nitrogen atoms. This finding is interpreted as an indication of double hydrogen tunneling. The values of tunneling splitting are obtained for both ground and lowest singlet excited states. The splitting is similar for cis and trans forms, and the barrier for tautomerization is larger in the excited state. Due to the coupling of hydrogen motion with rotation of alkyl substituents, tautomerization occurs in an asymmetric double minimum potential, with the ordering of energy minima reversed upon excitation. The second singlet excited state is found to lie very close to S(1), thus facilitating an efficient radiationless depopulation.     

Relationships between LC retention, octanol-water partition coefficient, and fungistatic properties of 2-(2,4-dihydroxyphenyl)benzothiazoles

The retention behavior of newly synthesized compounds with antimycotic activity from the 2-(2,4-dihydroxyphenyl)benzothiazole group by high-performance liquid chromatography has been investigated. RP-18 stationary phase and methanol-acetate buffer aqueous mobile phases at pH 4 and 7.4 have been used. In the case of the mobile phase at pH 7.4, higher concentrations of water can be applied than at pH 4. The studied compounds showed regular retention behavior, their log k values decreasing linearly with an increasing concentration of methanol in the mobile phase. On the basis of these relationships, the lipophilicity (log kw), specific hydrophobic surface area (S), and isocratic chromatographic hydrophobicity index (psi0) were determined. Similar log kw values and sensitivity to changes in the structure of compounds studied for both mobile phases have been found. Moderate correlations between the chromatographic parameters and the calculated octanol-water log P values were found. Finally, the lipophilicity parameters were compared with the fungistatic properties of compounds expressed by log MIC (minimum inhibitory concentration) values to find quantitative structure activity relationship equations.     

Protein structure prediction: combining de novo modeling with sparse experimental data

Routine structure prediction of new folds is still a challenging task for computational biology. The challenge is not only in the proper determination of overall fold but also in building models of acceptable resolution, useful for modeling the drug interactions and protein-protein complexes. In this work we propose and test a comprehensive approach to protein structure modeling supported by sparse, and relatively easy to obtain, experimental data. We focus on chemical shift-based restraints from NMR, although other sparse restraints could be easily included. In particular, we demonstrate that combining the typical NMR software with artificial intelligence-based prediction of secondary structure enhances significantly the accuracy of the restraints for molecular modeling. The computational procedure is based on the reduced representation approach implemented in the CABS modeling software, which proved to be a versatile tool for protein structure prediction during the CASP (CASP stands for critical assessment of techniques for protein structure prediction) experiments (see http://predictioncenter/CASP6/org). The method is successfully tested on a small set of representative globular proteins of different size and topology, including the two CASP6 targets, for which the required NMR data already exist. The method is implemented in a semi-automated pipeline applicable to a large scale structural annotation of genomic data. Here, we limit the computations to relatively small set. This enabled, without a loss of generality, a detailed discussion of various factors determining accuracy of the proposed approach to the protein structure prediction.     

Effects of surface nonuniformity and molecular association on mechanism of butanol adsorption from solution

The paper presents the results of calorimetric measurements and surface excess adsorption isotherms for n-butanol adsorption from n-hexane on a series of controlled porosity glasses characterized by different mean pore diameters. It is demonstrated that, in the region of very low alcohol concentration in solution, the heat of adsorption exhibits sharp maximum, independently of the pore diameter of adsorbent. This rather puzzling result is explained by the heterogeneity of the surface and the effects of molecular association of alcohol molecules in the solution. A simple theoretical model that supports our predictions is presented.     

Electroweak properties of nucleons in the MIT bag model with approximate chiral symmetry

Zeitschrift für Physik C Particles and Fields - Corrections to magnetic moments, axial coupling constantg A and root mean square charge radii of nucleons, resulting from specific quark-pion...