Comparison of Crystal Structures of New Racemic Chiral Compounds Showing and Not Showing the Phenomenon of Preferential Enrichment

Abstract

The crystal structures of (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]ethyl] trimethylammonium p-chlorobenzenesulfonate [(±)-NCMe₃] and its terminal methoxy derivative, (±)-NCMe₃-OMe, are compared. The former racemate exhibited the phenomenon of Preferential Enrichment, whereas the latter failed to do so. Crystal data, (±)-NCMe₃: CuKα radiation, space group P 1, Z = 2, a = 9.848(5), b = 14.823(3), c = 9.147(1) Å, α = 97.81(1), β = 92.68(3), γ = 105.92(2)°, D _calc = 1.355 g/cm³, R = 0.056 for 3213 observed reflections; (±)-NCMe₃-OMe: CuKα radiation, space group P 1, Z = 2, a = 11.350(1), b = 14.568(2), c = 8.2981(4) Å, α = 94.346(7), β = 112.376(5), γ = 78.622(9)°, D _calc = 1.343 g/cm³, R = 0.069 for 1519 observed reflections.     

Living Carbocationic Polymerization of Styrene in the Presence of Proton Trap

Abstract

The living polymerization of styrene was achieved with the 2,4,4-trimethyl-2-pentyl chloride/TiCl₄/MeCl:methylcyclohexane 40:60 v:v/?80°C polymerization system in the presence of di-tert-butylpyridine in concentrations comparable to the concentration of protic impurities. It was determined that the living nature of the polymerization is not due to carbocation stabilization. The polymerization is second order in TiCl₄. Side reactions, namely polymerization by direct initiation and intermolecular alkylation, are operational, and a careful selection of experimental conditions is necessary to minimize their effect and obtain apparently living behavior. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when the conversion reaches close to 100%.     

Improving molecular docking through eHiTS’ tunable scoring function

We present three complementary approaches for score-tuning that improve docking performance in pose prediction, virtual screening and binding affinity assessment. The methodology utilizes experimental data to customize the scoring function for the system of interest considering the specific docking scenario. The tuning approach, which has been implemented as an automated utility in eHiTS, is introduced as a solution to one of the conundrums of the molecular docking paradigm, namely, the lack of a universally well performing scoring function. The accuracy of scoring functions has been shown to be generally system-dependent, and particularly lacking for binding energy and bio-activity predictions. In the proposed approach, pose and energy predictions are enhanced by adjusting the relative weights of the eHiTS energy terms to improve score-RMSD or score-affinity correlations. In a virtual screening context ligand-based similarity is used to rescale the docking score such that better enrichment factors are achieved. We discuss the algorithmic details of the methods, and demonstrate the effects of score tuning on a variety of targets, including CDK2, BACE1 and neuraminidase, as well as on the popular benchmarks—the Directory of Useful Decoys and the PDBBind database.     

The role of defects in chemical sensing properties of carbon nanotube films

The electrical resistance of 24 different carbon nanotube (CNT) thin film samples in blowing ambient air and 10 different analyte vapor environments was measured. The effects of the CNT growth method, different chemical treatments, ball milling, sample preparation conditions and Ar⁺-ion irradiation are compared. Significant differences in the response signal curves as a function of time in the case of the studied sensor/vapor combinations show the important role of the defect structure and attached functional groups in the chemical sensing properties of CNTs.     

Modeling high density microholographic data storage: Using linear, quadratic, thresholding and hard clipping material characteristics

Crosstalk related raw signal-to-noise ratio (SNR) and bit error rate (BER) of high density bitwise microholographic data storage is investigated by numerical modeling. Scattering and diffraction of light is calculated in non-paraxial scalar approximation. A multiple thin slice implementation of the perturbative volume integral equation is used, which can be easily parallelized. The effect of bit and track spacing, and the different local characteristics of the holographic recording material on the SNR, BER and diffraction efficiency are investigated. The results show that these lateral spacing parameters have much more effect on crosstalk noise than the number of layers. Using two-photon, thresholding or hard clipping materials generates less crosstalk noise at the same data density than a linear material, and the dynamic range of these materials can be used more effectively resulting in higher single microhologram diffraction efficiencies.     

Synthesis of Silolide Dianions via Reduction of Dichlorosiloles: Important Role of the Solvent

The reduction of 1,1-dichloro-2,5-bistrimethylsilyl-3,4-diphenylsilole to silolide dianion by alkali metals was investigated. As previously demonstrated, the outcome of the reaction depends strongly on the applied alkali metal, solvent, reaction conditions, and substituent pattern. We showed that lithium is a powerful reducing agent in THF or DME solvents, the reaction is even faster than the same reaction with sodium. The X-ray structures of the corresponding dilithio and disodium silolide dianion were investigated, interestingly recrystallization of the dilithio salt results in a coordination polymer. In order to support the synthetic work DFT calculations were performed.     

Stereostructure of 8-chloro-5,6-di(methoxycarbonyl)-4,7-dimethyl-2-ethoxy-2-phosphabicyclo[2.2.2]octa-5,7-diene 2-oxide

The first X-ray structure of a phosphabicyclooctadiene, together with the NMR and mass spectral characterization of its isomers, is reported. © John Wiley & Sons, Inc.