The Cyclohexasilanes Si6H11X and Si6Me11X with X=F,Cl, Br and I: A Quantum Chemical and Raman Spectroscopic Investigation of a Multiple Conformer Problem

The conformers of the monohalocyclohexasilanes, Si₆H₁₁X (X=F, Cl, Br or I) and the haloundecamethylcyclohexasilanes, Si₆Me₁₁X (X=F, Cl, Br or I) are investigated by DFT calculations employing the B3LYP density functional and 6‐31+G* basis sets for elements up to the third row, and SDD basis sets for heavier elements. Five minima are found for Si₆H₁₁X—the axial and equatorial chair conformers, with the substituent X either in an axial or equatorial position—and another three twisted structures. The equatorial chair conformer is the global minimum for the X=Cl, Br and I, the axial chair for X=F. The barrier for the ring inversion is ～13 kJ mol^?1 for all four compounds. Five minima closely related to those of Si₆H₁₁X are found for Si₆Me₁₁X. Again, the equatorial chair is the global minimum for X=Cl, Br and I, and the axial chair for X=F. Additionally, two symmetrical boat conformers are found as local minima on the potential energy surfaces for X=F, Cl and Br, but not for X=I. The barrier for the ring inversion is ～14–16 kJ mol^?1 for all compounds. The conformational equilibria for Si₆Me₁₁X in toluene solution are investigated using temperature dependent Raman spectroscopy. The wavenumber range of the stretching vibrations of the heavy atoms X and Si from 270–370 cm^?1 is analyzed. Using the van′t Hoff relationship, the enthalpy differences between axial and equatorial chair conformers (H_ax?H_eq.) are 1.1 kJ mol^?1 for X=F, and 1.8 to 2.8 kJ mol^?1 for X=Cl, Br and I. Due to rapid interconversion, only a single Raman band originating from the “averaged” twist and boat conformers could be observed. Generally, reasonable agreement between the calculated relative energies and the experimentally determined values is found.     

Bildung siliciumorganischer Verbindungen. 94. Die Kristallstruktur des Hexaphenyltrisilacyclohexans Si3C39H36

Formation of Organosilicon Compounds. 94. Crystal Structure of Hexaphenyltrisilacyclohexane Si₃C₃₉H₃₆ 1.1.3.3.5.5-Hexaphenyl-1.3.5-trisilacyclohexane crystallizes monoclinically in the space group P2₁/n (No. 14) with a = 1718.3 pm, b = 1769.2 pm, c = 1091.4 pm, β = 90.72° and Z = 4 molecules per unit cell. The trisilacyclohexane sceleton is present in a flattened twist boat conformation with mean bond angles of 110.0° at the Si atoms and 117.9° at the C atoms, respectively. The mean bond lengths are d(Si? C) = 187.1 pm in the six membered ring and 187.9 pm to the substituents.     

Acylation of α-(N-carbamoyl)alkylcuprates and alkyl- or aryl(halo)cuprates

α-(N-Carbamoyl)alkylcuprates [R₂CuLi·LiX or RCuXLi (X=CN, Cl)] when prepared from THF soluble CuX·2LiCl (X=Cl, CN) undergo a reliable and generally high yield reaction with aroyl, alkanoyl, and alkenoyl chlorides to provide a rapid and efficient synthesis of α-carbamoyl ketones. Cuprates prepared from acyclic, cyclic, and a functionalized carbamate can be utilized. Although yields are a function of cuprate reagent and substrate structure, nearly quantitative yields can be obtained with reagents generated from 2RLi+CuCN·2LiCl. The use of reagents generated from CuCl·2LiCl are more efficient in the α-(N-carbamoyl)alkyl ligand, although yields are slightly lower. Acylation of alkyl(chloro)cuprates generated from one equivalent of CuCl·2LiCl and organolithium or Grignard reagents provides an efficient and high yield procedure for ketone synthesis.     

Biocompatible polymers for antibody support on gold surfaces

The elimination or minimization of non-specific protein adsorption from serum is critical for the use of surface plasmon resonance (SPR) sensors for in vitro and in vivo analysis of complex biological solutions. The ultimate goals in this application are to minimize non-specific adsorption of protein and to maximize analyte signal. A reduction of the non-specific protein adsorption from serum of up to 73% compared to carboxymethylated-dextran 500 kDa (CM-dextran) was achieved following a survey of eight biocompatible polymers and 10 molecular weights of CM-dextran. These coatings minimize non-specific adsorption on the sensor while also serving as immobilization matrices for antibody fixation to the probes. Polymers including polysaccharides: CM-dextrans, CM-hyaluronic acid, hyaluronic acid, and alginic acid were investigated. Humic acid, polylactic acid, polyacrylic acid, orthopyridyldisuldfide–polyethyleneglycol–N-hydroxysuccinimide (OPSS–PEG–NHS), and a synthesized polymer; polymethacrylic-acid-co-vinyl-acetate (PMAVA) were also used. The non-specific protein adsorption reduction was measured over a 14 day period at 0 °C for each polymer. Calibration curves using some of these polymers were constructed to show the performance and low detection limit possibilities of these new antibody supports. For many of the polymers, this is the first demonstration of employment as an antibody support for an optical or surface active sensor. CM-dextran is the polymer offering the largest signal for the antigen detection. However, the biocompatible polymers demonstrate a greater stability to non-specific binding in serum. These biocompatible polymers offer different alternatives for CM-dextran.     

An efficient synthesis of the novel triazoloquinazoline adenosine antagonist,CGS 15943

An efficient synthesis of the novel triazoloquinazoline adenosine antagonist, CGS 15943, is reported in five steps in approximately 50% overall yield. A key reaction in the synthetic sequence is the double cyclization of an N-(substituted-2-cyanophenyl)carbamate with a carboxylic acid hydrazide to afford a [1,2,4]triazolo-[1,5-c]quinazolin-5(6H)-one in high yield without either a Dimroth or “translocative” rearrangement occurring. Another key reaction is the condensation of a 2-(1H-1,2,4-triazol-5-yl)benzenamine with cyanamide under acidic conditions to prepare a guanidine.     

H2/CO2 separations in multicomponent metal-adeninate MOFs with multiple chemically distinct pore environments

Metal–organic frameworks constructed from multiple (≥3) components often exhibit dramatically increased structural complexity compared to their 2 component (1 metal, 1 linker) counterparts, such as multiple chemically unique pore environments and a plurality of diverse molecular diffusion pathways. This inherent complexity can be advantageous for gas separation applications. Here, we report two isoreticular multicomponent MOFs, bMOF-200 (4 components; Cu, Zn, adeninate, pyrazolate) and bMOF-201 (3 components; Zn, adeninate, pyrazolate). We describe their structures, which contain 3 unique interconnected pore environments, and we use Kohn–Sham density functional theory (DFT) along with the climbing image nudged elastic band (CI-NEB) method to predict potential H₂/CO₂ separation ability of bMOF-200. We examine the H₂/CO₂ separation performance using both column breakthrough and membrane permeation studies. bMOF-200 membranes exhibit a H₂/CO₂ separation factor of 7.9. The pore space of bMOF-201 is significantly different than bMOF-200, and one molecular diffusion pathway is occluded by coordinating charge-balancing formate and acetate anions. A consequence of this structural difference is reduced permeability to both H₂ and CO₂ and a significantly improved H₂/CO₂ separation factor of 22.2 compared to bMOF-200, which makes bMOF-201 membranes competitive with some of the best performing MOF membranes in terms of H₂/CO₂ separations.

Tailorable multicomponent MOFs and MOF membranes for efficient H₂/CO₂ separation.     

Organocatalytic asymmetric alpha-bromination of aldehydes and ketones

The first organocatalytic enantioselective alpha-bromination of aldehydes and ketones is presented; a C2-symmetric diphenylpyrrolidine catalyst afforded the alpha-brominated aldehydes in good yields and up to 96% ee, while ketones were alpha-brominated by a C2-symmetric imidazolidine in up to 94% ee; furthermore, the organocatalytic enantioselective alpha-iodination of aldehydes is also demonstrated to proceed with up to 89% ee.     

4‐(Trifluoromethyl)benzonitrile

4‐(Tri­fluoro­methyl)­benzo­nitrile, C₈H₄F₃N, at 123 K contains mol­ecules linked together through one C—H?F bond and two C—H?N hydrogen bonds into sheets that are further crosslinked to form a dense two‐dimensional network without π?π ring interactions. The aromatic ring is slightly deformed due to the two para‐related electronegative groups.