Fourier transform microwave spectroscopy of HSiBr: exploring the Si-Br bond through quadrupole hyperfine coupling

The 1(01)-0(00) (9-10 GHz) and 2(02)-1(01) (18-19 GHz) rotational transitions of HSi 79Br and HSi 81Br have been measured in a pulsed discharge jet expansion to an experimental uncertainty of approximately 1 kHz using Fourier transform microwave spectroscopy. The data have yielded an effective rotational constant, the centrifugal distortion constant Dj, the bromine nuclear quadrupole coupling constants, and the bromine nuclear spin-molecular rotation interaction parameter for both isotopomers. The derived parameters have been compared to their values calculated ab initio, and the nuclear quadrupole coupling tensor has been used to investigate the Si-Br bond, giving a sigma bond ionic character of 0.60, a pi bond character of 0.22, and a total Si-Br ionic character of 0.38. These bond characteristics have been compared to trends in other halosilylenes, silanes, and the analogous carbenes.     

Deciphering the Selectivity of Bombyx mori Pheromone Binding Protein for Bombykol over Bombykal: A Theoretical Approach

In this article we report calculations dedicated to estimate the selectivity of the Bombyx mori pheromone binding protein towards the two closely related pheromonal components Bombykol and Bombykal. The selectivity is quantified by the binding free‐energy difference, obtained either by the thermodynamic integration or by the MM‐GBSA approach. In the latter, the selectivity is decomposed on a per‐residue basis, which identifies the residues considered crucial for the selectivity of the protein for Bombykol over Bombykal. A discussion on the role of Bombyx mori pheromone binding protein is provided on the basis of these results.     

Diffusion-based deprotection in mesoporous materials: a strategy for differential functionalization of porous silica particles

A monodisperse, spherical mesoporous silica (Acid-Prepared Mesoporous Spheres, APMS) was prepared and then functionalized with two types of Fmoc (9-fluorenylmethyloxycarbonyl) terminated silanes with variable chain lengths. N2 physisorption experiments indicated that, under some conditions, the pores of the solid were completely filled by the Fmoc-protected organosilanes. These blocked pores were then "reopened" by the cleavage of Fmoc groups with a piperidine solution. In contrast to the solution reaction, this deprotection reaction was much slower within the pores. The rate of deprotection was followed by UV/visible spectroscopy, and a plot of Fmoc released versus time showed a sigmoidal shape. An empirical model was applied to the data, which indicated that the reaction was influenced by the concentration and temperature of the piperidine solution as well as the number of Fmoc moieties within the pores. Using this information, we show that the location of the deprotection reaction in the pores of the silica can be empirically controlled. Our work provides a method by which the surface of the porous silica can be functionalized in a well-defined manner. This method can be used to produce materials for catalysis or drug delivery.     

Molecularly ordered inorganic frameworks in layered silicate surfactant mesophases.

Self-assembled lamellar silica-surfactant mesophase composites have been prepared with crystal-like ordering in the silica frameworks using a variety of cationic surfactant species under hydrothermal conditions. These materials represent the first mesoscopically ordered composites that have been directly synthesized with structure-directing surfactants yielding highly ordered inorganic frameworks. One-dimensional solid-state 29Si NMR spectra, X-ray diffraction patterns, and infrared spectra show the progression of molecular organization in the self-assembled mesophases from structures with initially amorphous silica networks into sheets with very high degrees of molecular order. The silicate sheets appear to be two-dimensional crystals, whose structures and rates of formation depend strongly on the charge density of the cationic surfactant headgroups. Two-dimensional solid-state heteronuclear and homonuclear NMR measurements show the molecular proximities of the silica framework sites to the structure-directing surfactant molecules and establish local Si-O-Si bonding connectivities in these materials.     

A study of the influence of impurities when discriminating between the terminal and penultimate copolymerization models

We investigate the effect of the presence of reactive impurities during copolymerization on mathematical model discrimination and determine if impurities adversely affect the model discrimination process, depending on the criteria and response(s) used. Nonlinear mechanistic process models are employed in a multiresponse statistical discrimination scenario. The investigation also considers, via several case studies, the extremely interesting question of whether impurity effects could lead to incorrect choices about the copolymerization mechanism itself (terminal versus penultimate model). The answers to the above questions are that reactive impurities do affect the model discrimination process and, what is more, they may mislead researchers as to the choice of the copolymerization mechanism. The latter unexpected result is further illustrated with experimental data from the literature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2319–2332, 2000     

Generating Encoded Compound Libraries for Fabricating Microarrays as a High-Throughput Protein Ligand Discovery Platform

We demonstrate an effective method for generating libraries of encoded compounds for fabricating large compound microarrays on solid supports. This method is based on one-bead, one-compound synthesis and employs a novel trilayer bead-partition scheme that ensures sufficient quantity of synthesized compounds releasable from each bead for compound microarray fabrication in high-throughput protein–ligand discovery assays.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Oxidation of a mustard gas analogue using an aldehyde/O2 system catalyzed by V-doped mesoporous silica

Vanadium-doped mesoporous silica was shown to be an effective heterogeneous catalyst for the oxidation of a mustard gas analogue, 2-chloroethyl ethyl sulfide (CEES), in the presence of an aldehyde and molecular oxygen. The oxidation was shown to involve a radical mechanism, which was indicated by the appearance of an induction period when the reaction occurred in the presence of a free radical scavenger. The reaction was initially selective for the oxidation of CEES to the sulfoxide, CEESO, although oxidation of the sulfoxide to the sulfone occurred once all the CEES had been oxidized. Chemical analysis indicated that V species did not leach from the silica support when the reaction was performed in the fluorinated solvent HFE-7100.     

Synthesis, Characterization, and Catalytic Properties of a Microporous/Mesoporous Material, MMM-1

A microporous-mesoporous material composed of MCM-41 and MFI was produced by a two-step synthetic process. The solid, called “MMM-1,” was characterized by X-ray diffraction (XRD), N₂ physisorption, and transmission electron microscopy (TEM). At early stages of crystallization at 170°C, MCM-41 was formed exclusively, while at heating times longer than 96h MFI was formed. At intermediate times, MMM-1 was formed with varying amounts of MFI depending on the crystallization time. XRD revealed that the material could be severely oriented by sample preparation, which was consistent with an unusual ribbon-like morphology observed in TEM. This morphology was not seen for either pure MCM-41 or MFI. The N₂ physisorption isotherm for MMM-1 showed two distinct regions of capillary condensation, with H2 hysteresis. Synthesis and subsequent use of Al-MMM-1 in the isomerization of m-xylene and comparison to Al-MCM-41 and Al-MFI showed that although the latter material had a higher total conversion, Al-MMM-1 had a higher selectivity for p-xylene. Al-MMM-1 had a much higher selectivity and conversion than Al-MCM-41, which makes it promising for use in future catalytic applications.     

Effect of fluorescently labeling protein probes on kinetics of protein-ligand reactions

We studied the effect of fluorescently labeling proteins on protein-ligand reactions. Unlabeled ligands (streptavidin-binding peptides and rabbit immunoglobulin G (IgG) as antigen targets) are immobilized on epoxy-functionalized glass slides. Unlabeled and Cy3-labeled protein probes from the same batch (streptavidin and goat antibodies) subsequently react with the surface-immobilized targets. By monitoring in situ the surface mass density change using an oblique-incidence reflectivity difference scanning microscope (a label-free detector), we measured k(on) and k(off) for streptavidin-peptide reactions and antibody-antigen reaction. We found that (1) equilibrium dissociation constants, defined as K(D) = k(off)/k(on), for streptavidin-peptide reactions increases by a factor of 3-4 when the solution-phase streptavidin is labeled with Cy3 dye and (2) K(D) for reactions of solution-phase goat anti-rabbit antibodies with rabbit IgG targets also change significantly when the goat antibodies are labeled with Cy3 dye.