Transition metal-promoted reactions : VII. Novel reactions of acid chlorides with pentacarbonyliron in aromatic solvents

Upon treatment with Fe(CO)₅ in an aromatic hydrocarbon solvent aromatic acid chlorides gave an mixture of triarlmethane and tetraarylethane. The reaction may proceed via benzaldehyde and diarylmethanol intermediates. A free radical mechanism is proposed.     

Vibrational spectral studies of ion-ion and ion-solvent interactions. II. Zinc nitrate in water/dioxane mixtures

Raman and infrared spectral data have been collected forp-dioxane and solvated and bound nitrate ions for Zn(NO₃)₂/p-dioxane/water systems. It is concluded that Zn²⁺ is preferentially solvated by water and that this aquation is also responsible for a lower concentration of ion pairs than is found for methanol/Zn(NO₃)₂ solutions for which the dielectric constant of the bulk solvent is similar. Values of K₁ (M^–1), the association constant for Zn(NO₃)⁺, are 0.22±0.02 (2/1 solvent,D=12.6) and 0.071±0.01 (4/1 solvent,D=33.0). The log K₁ against 1/D plot is not linear.     

Weakly coordinating nature of a carborane cage bearing different halogen atoms. Synthesis and structural characterization of icosahedral mixed halocarborane anions, 1-H-CB11Y5X6- (X, Y = Cl, Br, I)

Mixed halocarborane anions, 1-H-CB11Y5X6- (X, Y = Cl, Br, I), have been prepared by treatment of [Me3NH][1-H-CB11H5X6] (X = Cl, Br, I) with proper halogenating reagents at 180-220 degrees C in a sealed tube in high yield. These new anions are fully characterized by 1H, 13C, and 11B NMR, IR, and negative-ion MALDI MS spectroscopy. Some are further confirmed by single-crystal X-ray analyses. The weakly coordinating nature of these anions is probed by 29Si chemical shifts of the resulting Pri3Si(1-H-CB11Y5X6) compounds. The results suggest that the coordinating ability of these anions is mainly dependent on the substituents at 7-12 positions (namely, X atoms), and the contribution from the upper belt substituents Y is relatively small. These suggestions are consistent with the results obtained from the structural study of silver salts of mixed halo- and perhalocarborane anions.     

Vibrational spectral studies of ion-ion and ion-solvent interactions. I. Zinc nitrate in water

Raman and infrared line parameters of Zn(NO₃)₂-H₂O systems ranging from dilute solutions (25°C) to ionic liquids of low water content (75°C) are reported. At 25°C the solutions contain a very low concentration of inner sphere [Zn(ONO₂)(H₂O)₅]⁺, outer sphere [Zn(H₂O)₆]²⁺[NO₃]^–, Zn(H₂O) ₆ ²⁺ , and NO ₃ ^– (aq.). In the ionic liquids the ion triplet also exists. Manifestations of a change from the octahedral coordination of zinc to tetrahedral coordination when the water content is very low include the appearance of a 285 cm^–1 band from the zinc nitrate bond and a shift to higher frequencies of the band from zinc-water.     

Microwave drying of granules containing a moisture-sensitive drug: a promising alternative to fluid bed and hot air oven drying

The impact of microwave drying and binders (copolyvidone and povidone) on the degradation of acetylsalicylic acid (ASA) and physical properties of granules were compared with conventional drying methods. Moist granules containing ASA were prepared using a high shear granulator and dried with hot air oven, fluid bed or microwave (static or dynamic bed) dryers. Percent ASA degradation, size and size distribution, friability and flow properties of the granules were determined. Granules dried with the dynamic bed microwave dryer showed the least amount of ASA degradation, followed by fluid bed dryer, static bed microwave oven and hot air oven. The use of microwave drying with a static granular bed adversely affected ASA degradation and drying capability. Dynamic bed microwave dryer had the highest drying capability followed by fluid bed, static bed microwave dryer and conventional hot air oven. The intensity of microwave did not affect ASA degradation, size distribution, friability and flow properties of the granules. Mixing/agitating of granules during drying affected the granular physical properties studied. Copolyvidone resulted in lower amount of granular residual moisture content and ASA degradation on storage than povidone, especially for static bed microwave drying. In conclusion, microwave drying technology has been shown to be a promising alternative for drying granules containing a moisture-sensitive drug.     

Synthesis and application of mono-6-ammonium-6-deoxy-beta-cyclodextrin chloride as chiral selector for capillary electrophoresis

A facile synthetic approach for mono-6-amino-6-deoxy-beta-cyclodextrin (beta-CD-NH2) was proposed. Its hydroxy chloride salt, mono-6-ammonium-6-deoxy-beta-cyclodextrin chloride (beta-CD-NH3Cl) was further prepared and used for the enantioseparation of various anionic and ampholytic analytes by capillary electrophoresis (CE). The effect of background electrolyte (BGE) pH and selector concentration on the enantioseparation was studied. Results showed that beta-CD-NH3Cl displayed powerful chiral resolution ability towards anionic analytes. In addition, baseline separation of a standard mixture consisting of eight acids was achieved within 35 min.     

Evaluating protein attraction and adhesion to biomaterials with the atomic force microscope

Failure of implanted biomaterials is commonly due to nonspecific protein adsorption, which in turn causes adverse reactions such as the formation of fibrous capsules, blood clots, or bacterial biofilm infections. Current research efforts have focused on modifying the biomaterial interface to control protein reactions. Designing biomaterial interfaces at the molecular level, however, requires an experimental technique that provides detailed, dynamic information on the forces involved in protein adhesion. The goal of this study was to develop an atomic force microscope (AFM)-based technique to evaluate protein adhesion on biomaterial surfaces. In this study, the AFM was used to evaluate (i) protein-protein, (ii) protein-substrate, and (iii) protein-dextran interactions. The AFM was first used to measure the pull-off forces between bovine serum albumin (BSA) tips/BSA surfaces and BSA tips/anti-BSA surfaces. Results from these protein-protein studies were consistent with the literature. More importantly, the successful measurement of antibody-antigen binding interactions demonstrates that both the BSA and anti-BSA proteins retain their folded conformation and remain functional following our immobilization protocol. The AFM was also used to quantify the physiochemical interactions of proteins during adhesion to various self-assembled monolayers (SAMs) and dextran-coated substrates representative of potential biomaterial interface modifications. Dextran, which renders surfaces very hydrophilic, was the only surface coating that BSA protein did not adhere to. Hydrophobic interactions were not found to play a significant role in BSA adhesion. Therefore, the dextran molecules may resist protein adhesion by repulsive steric effects or hydration pressure. Moreover, the AFM-based methodology provides dynamic, quantitative information about protein adhesion at the nanoscale level.     

One‐Electron Oxidation of [M(PtBu3)2] (M=Pd,Pt): Isolation of Monomeric [Pd(PtBu3)2]+ and Redox‐Promoted C−H Bond Cyclometalation

Oxidation of zero‐valent phosphine complexes [M(P^tBu₃)₂] (M=Pd, Pt) has been investigated in 1,2‐difluorobenzene solution using cyclic voltammetry and subsequently using the ferrocenium cation as a chemical redox agent. In the case of palladium, a mononuclear paramagnetic Pd^I derivative was readily isolated from solution and fully characterized (EPR, X‐ray crystallography). While in situ electrochemical measurements are consistent with initial one‐electron oxidation, the heavier congener undergoes C?H bond cyclometalation and ultimately affords the 14 valence‐electron Pt^II complex [Pt(κ²_PC‐P^tBu₂CMe₂CH₂)(P^tBu₃)]⁺ with concomitant formation of [Pt(P^tBu₃)₂H]⁺.     

Redox Reorganization: Aluminium Promoted 1,5-Hydride Shifts Allow the Controlled Synthesis of Multisubstituted Cyclohexenes

An efficient synthesis of cyclohexenes has been achieved from easily accessible tetrahydropyrans via a tandem 1,5-hydride shift–aldol condensation. We discovered that readily available aluminium reagents, e.g. Al₂O₃ or Al(O^tBu)₃ are essential for this process, promoting the 1,5-hydride shift with complete regio- and enantiospecificity (in stark contrast to results obtained under basic conditions). The mild conditions, coupled with multiple methods available to access the tetrahydropyran starting materials makes this a versatile method with exceptional functional group tolerance. A wide range of cyclohexenes (>40 examples) have been prepared, many in enantiopure form, showing our ability to selectively install a substituent at each position around the newly forged cyclohexene ring. Experimental and computational studies revealed that aluminium serves a dual role in facilitating the hydride shift, activating both the alkoxide nucleophile and the electrophilic carbonyl group.