Condensed-phase effects on the structural properties of C6H5CN-BF3 and (CH3)3CCN-BF3: IR spectra, crystallography, and computations

Condensed-phase effects on the structure and bonding of C(6)H(5)CN-BF(3) and (CH(3))(3)CCN-BF(3) are illustrated by a variety of results, and these are compared to analogous data for the closely related complex CH(3)CN-BF(3). For the most part, the structural properties of C(6)H(5)CN-BF(3) and (CH(3))(3)CCN-BF(3) are quite similar, not only in the gas phase but also in the solid state and in argon matrices. However, the structures do change significantly from medium to medium, and these changes are reflected in the data presented below. Specifically, the measured crystallographic structure of C(6)H(5)CN-BF(3) (s) has a B-N distance that is 0.17 A shorter than that in the equilibrium gas-phase structure obtained via B3LYP calculations. Notable differences between calculated gas-phase frequencies and measured solid-state frequencies for both C(6)H(5)CN-BF(3) and (CH(3))(3)CCN-BF(3) were also observed, and in the case of (CH(3))(3)CCN-BF(3), these data implicate a comparable difference between solid-state and gas-phase structure, even in the absence of crystallographic results. Frequencies measured in argon matrices were found to be quite similar for both complexes and also very near those measured previously for CH(3)CN-BF(3), suggesting that all three complexes adopt similar structures in solid argon. For C(6)H(5)CN-BF(3) and (CH(3))(3)CCN-BF(3), matrix IR frequencies differ only slightly from the computed gas-phase values, but do suggest a slight compression of the B-N bond. Ultimately, it appears that the varying degree to which these systems respond to condensed phases stems from subtle differences in the gas-phase species, which are highlighted through an examination of B-N distance potentials from B3LYP calculations. The larger organic substituents appear to stabilize the potential near 1.8 A, so that the structures are more localized in that region prior to any condensed-phase interactions. As a result, the condensed-phase effects on the structural properties of C(6)H(5)CN-BF(3) and (CH(3))(3)CCN-BF(3) are much less pronounced than those for CH(3)CN-BF(3).     

Microanalytical high-performance liquid chromatographic assay for cefpirome in human milk and urine.

To permit the characterization of cefpirome disposition in lactating females, a previously published high-performance liquid chromatographic (HPLC) method for determining the drug in serum was adapted for use with milk and urine. This automated, microanalytical technique requires 50 microliters of biological matrix, which is subjected to an isopropanol extraction. Chromatography was accomplished using a microbore HPLC system, a reversed-phase C18 column and a mobile phase of 0.3% triethylamine in water (pH 5.1). Cefpirome and the internal standard (beta-hydroxypropyltheophylline) were monitored using UV detection at 240 nm and had retention times of 2.84 and 5.05 min, respectively. The method was linear up to 500 mg/l for both matrices and had a limit of detection of 0.6 mg/l. The interday variation (relative standard deviation) at concentrations of 5.0, 50.0 and 500.0 mg/l was consistently less than 5% in both urine and breast milk. The method was found to be free from interference by other commonly administered medications and readily adaptable for use in clinical investigations. The ease of sample preparation, small sample volume requirement, short chromatographic time, apparent lack of interferences, analytical sensitivity and high precision and accuracy make this method ideal for use in pharmacokinetic investigations involving the determination of cefpirome in human milk and urine.     

Extraction and pre-concentration of organometallic species from environmental samples

Methods of extraction, clean-up and preconcentration normally reserved for organic trace analysis are considered with a view to applying such techniques to the developing field of organometallic speciation. The overview covers the main compartments of the natural environment; water, soil and sediment, plant and animal tissue.     

Method for separation and determination of lactone and hydroxy acid forms of a new HMG CoA reductase inhibitor (RG 12561) in plasma

The new drug RG 12561 (I) is a lactone that is undergoing clinical evaluation for its cholesterol lowering effect based on potent HMG CoA reductase inhibitory activity displayed by its open hydroxy acid form. To determine the dispositional characteristics of the drug, a method was developed for determination of the two forms in plasma. A 0.25-ml aliquot of plasma was deproteinized with 0.5 ml of methanol, and the lactone was extracted with hexane-ethyl acetate (75:25, v/v). The methanolic plasma was then acidified followed by extraction of the hydroxy acid with hexane-ethyl acetate. The extracts were dried, reconstituted and analyzed by isocratic, reversed-phase high-performance liquid chromatography using ultraviolet absorbance at 254 nm. The separations were performed utilizing a C18 column with mobile phase consisting of acetonitrile, 2-propanol and 0.1 M acetate buffer (pH 5), the proportions of which differed depending on the form of drug analyzed. The method was found to be selective and a quantitation limit of 50 ng/ml was established. Validation studies demonstrated that the method was sufficiently accurate and precise for determining disposition of the drug in the dog.     

Observation of high enantioselectivity for the gas phase hydrogenation of methyl pyruvate using supported Pt catalysts pre-modified with cinchonidine

Pt supported on alpha-Al2O3, gamma-Al2O3 and SiO2 pre-modified with cinchonidine gives over 50% ee in the hydrogenation of methyl pyruvate to methyl lactate using gas phase reactants at 40 degrees C giving the first clear observation of high enantioselection at the gas/solid interface.     

Preparation and Characterization of Halogen-Boron-Phosphorus Compounds. X-ray Crystal Structures of X(3)B.P(SiMe(3))(3) and [X(2)BP(SiMe(3))(2)](2) (X = Cl, Br)

The 1:1 mole ratio reactions of boron trihalides (BX(3)) with tris(trimethylsilyl)phosphine [P(SiMe(3))(3)] produced 1:1 Lewis acid/base adducts [X(3)B.P(SiMe(3))(3), X = Cl (1), Br (2), I (5)]. Analogous 1:1 mole ratio reactions of these boron trihalides with lithium bis(trimethylsilyl)phosphide [LiP(SiMe(3))(2)] produced dimeric boron-phosphorus ring compounds {[X(2)BP(SiMe(3))(2)](2), X = Br (3), Cl (4)}. X-ray crystallographic studies were successfully conducted on compounds 1-4. Compound 1 crystallized in the orthorhombic space group Pbca, with a = 13.420(3) ?, b = 17.044(5) ?, c = 21.731(7) ?, V = 4970.6(25) ?(3), and D(calc) = 1.229 g cm(-3) for Z = 8; the B-P bond length was 2.022(9) ?, Compound 2 crystallized in the orthorhombic space group Pbca, with a = 13.581(6) ?, b = 17.106(7) ?, c = 22.021(9) ?, V = 5116(4) ?(3), and D(calc) = 1.540 g cm(-3) for Z = 8; the B-P bond length was 2.00(2) ?. Compound 3 crystallized in the monoclinic space group P2(1)/n, with a = 9.063(5) ?, b = 16.391(8) ?, c = 9.331(4) ?, V = 1379.2(12) ?(3), and D(calc) = 1.676 g cm(-3) for Z = 2; the B-P bond length was 2.023(10) ?. Compound 4 crystallized in the monoclinic space group P2(1)/n, with a = 9.143(5) ?, b = 16.021(8) ?, c = 9.170(4) ?, V = 1342.2(11) ?(3), and D(calc) = 1.282 g cm(-3) for Z = 2; the B-P bond length was 2.025(3) ?. Thermal decomposition studies were performed on compounds 1-4, yielding colored powders with boron:phosphorus ratios greater than 1:1 and significant C and H contamination indicated by elemental analyses.     

Non-statistical effects for inelastic proton amplitudes in49V

The magnitudes and relative signs of inelastic proton-channel amplitudes have been measured for 71 3/2^? resonances in⁴⁹V. The measured quantitiesγ _c ² ,γ _c′ ² , andγ _c γ _c′ provide distributions of reduced widths, distribution of the relative sign between reduced width amplitudes, and correlations between reduced widthsρ(γ _c ² ,γ _c′ ² ) and between amplitudesρ(γ _c ,γ _c′ ). A variety of non-statistical effects are observed, including one case in which the effect occurs only in the signs, and not in the magnitudes of the amplitudes.