Analysis of binary mixtures of flufenamic, meclofenamic and mefenamic acids by derivative synchronous fluorescence spectrometry

Second-derivative synchronous fluorescence spectrometry was used to develop a simple, rapid and sensitive spectrofluorimetric method for the determination of binary mixtures of the nonsteroidal antiinflammatory drugs flufenamic (FFA), meclofenamic (MCFA) and mefenamic (MFA) acids in serum and pharmaceutical formulations. The method is based on the intrinsic fluorescence of these compounds in chloroform. A Deltalambda=105 nm was used for the resolution of FFA-MFA and MFA-MCFA mixtures, whereas the FFA-MCFA mixture was determined at Deltalambda=40 nm. Serum samples are treated with trichloroacetic acid to remove the proteins, and the analytes are extracted in chloroform prior to determination. Pharmaceutical preparations were analysed without prior separation steps.     

Application of photochemical inhibition in flow injection systems: Determination of epinephrine and L-dopa

An automated procedure for the photochemical determination of epinephrine and L-dopa has been developed. It is based on the strong inhibition by these catecholamines on the photochemical reaction between phloxin and ethylenediaminetetraacetic. The proposed flow-injection method allows the fluorimetric determination of epinephrine in the range 1.9-26.4 mug/ml and of L-dopa in the range of 1.5-12.7 mug/ml, with a sampling frequency of 35 samples/hr. The method was applied successfully to the determination of body catecholamines in pharmaceutical preparations.     

Interactions of cationic porphyrins with double-stranded oligodeoxynucleotides: a study by electrospray ionisation mass spectrometry

Electrospray ionisation mass spectrometry (ESI-MS), electrospray ionisation tandem mass spectrometry (ESI-MS/MS) and Ultraviolet-visible (UV-vis) spectroscopy were used to investigate the non-covalent interactions between small oligonucleotide duplexes with the GC motif and a group of cationic meso(N-methylpyridynium-4-yl)porphyrins (four free bases with one to four positive charges, and the zinc complex of the tetracationic free base).The results obtained point to outside binding of the porphyrins, with the binding strength increasing with the number of positive charges. Fragmentations involving losses from both chains were observed for the porphyrins with N-methylpyridinium-4-yl groups in opposite meso positions.     

Domain-specific incorporation of noninvasive optical probes into recombinant proteins

An integrated approach is described that allows the domain-specific incorporation of optical probes into large recombinant proteins. The strategy is the combination of two existing techniques, expressed protein ligation (EPL) and in vivo amino acid replacement of tryptophans with tryptophan (Trp) analogues. The Src homology 3 (SH3) domain from the c-Crk-I adaptor protein has been labeled with a Trp analogue, 7-azatryptophan (7AW), using Escherichia coli Trp auxotrophs. Structural, biochemical, and thermodynamic studies show that incorporation of 7AW does not significantly perturb the structure or function of the isolated domain. Ligation of the 7AW-labeled SH3 domain to the c-Crk-I Src homology 2 (SH2) domain, via EPL, generated the multidomain protein, c-Crk-I, with a domain-specific label. Studies of this labeled protein show that the biochemical and thermodynamic properties of the SH3 domain do not change within the context of a larger multidomain protein. The technology described here is likely to be a useful tool in enhancing our understanding of the behavior of modular domains in their natural context, within multidomain proteins.     

Stacking and separation of enantiomers by acetonitrile-salt mixtures in micellar electrokinetic chromatography

The feasibility of employing the "acetonitrile stacking" method in micellar electrokinetic chromatography (MEKC) for the on-line preconcentration and separation of enantiomers is demonstrated for the first time. The effects of various experimental parameters on the stacking and separation of three different pairs of optical isomers, i.e., two substituted naphthyl enantiomers and one dansylated-DL-amino acid, were examined. In particular, the effectiveness of the addition of acetonitrile and salt in the sample matrix to induce narrowing of the analyte bands was investigated in the presence of sodium cholate as the chiral surfactant micelle in the separation buffer. For example, it was found that the presence of both acetonitrile and 1% NaCl in the sample matrix (volume ratio = 2:1) led to a significant improvement of the peak height and resolution for the MEKC separation of a pair of R(-)/S(+)-1,1'-binaphthyl diyl hydrogen phosphate enantiomers when the injection sample size was relatively large (e.g., 12% capillary volume). Furthermore, the feasibility of combining salting-out solvent extraction (off-line) and acetonitrile stacking (on-line) as a novel approach for sample preconcentration in capillary electrophoresis was also demonstrated.     

Periodic trends in indirect nuclear spin-spin coupling tensors: relativistic density functional calculations for interhalogen diatomics

There have been significant advances in the calculation and interpretation of indirect nuclear spin-spin coupling (J) tensors during the past few years; however, much work remains to be done, especially for molecules containing heavy atoms where relativistic effects may play an important role. Many J tensors cannot be explained based solely on a nonrelativistic Fermi-contact mechanism. In the present work, the relativistic zeroth-order regular approximation density-functional (ZORA-DFT) implementation for the calculation of J has been applied to the complete series of homonuclear and heteronuclear diatomic halogen molecules: F(2), Cl(2), Br(2), I(2), At(2), ClF, BrF, IF, ClBr, ClI, and BrI. For all of these compounds, the reduced isotropic coupling constant (K(iso)) is positive and the reduced anisotropic coupling constant (DeltaK) is negative. With the exception of molecular fluorine, the magnitudes of K(iso) and DeltaK are shown to increase linearly with the product of the atomic numbers of the coupled nuclei. ZORA-DFT calculations of J for F(2) and ClF are in excellent agreement with the results obtained from multiconfigurational self-consistent-field calculations. The relative importance of the various coupling mechanisms is approximately constant for all of the compounds, with the paramagnetic spin-orbit term being the dominant contributor to K(iso), at approximately 70-80%. Available experimental stimulated resonant Raman spectroscopy data are exploited to extract the complete J((127)I,(127)I) tensor for iodine in two rotational states. The dependence of K(iso) and DeltaK on bond length and rovibrational state is investigated by using calculated results in combination with available experimental data. In addition to providing new insights into periodic trends for J coupling tensors, this work further demonstrates the utility of the ZORA-DFT method and emphasizes the necessity of spin-orbit relativistic corrections for J calculations involving heavy nuclei.     

The Amber biomolecular simulation programs

We describe the development, current features, and some directions for future development of the Amber package of computer programs. This package evolved from a program that was constructed in the late 1970s to do Assisted Model Building with Energy Refinement, and now contains a group of programs embodying a number of powerful tools of modern computational chemistry, focused on molecular dynamics and free energy calculations of proteins, nucleic acids, and carbohydrates.     

An extremely bent cyanide bridge in crystals of [(CN)3Pt(mu-CN)Cu(NH3)4]. Influence of electrostatic forces on the nature and geometry of bridging cyanides in the solid state

The dinuclear heterometallic complex [(CN)3Pt(mu-CN)Cu(NH3)4] has been obtained in the solid state, and its structure has been determined by X-ray diffraction techniques at two temperatures (102 and 233 K). C4H12CuN8Pt crystallizes in the orthorhombic system, with a = 14.554(3) A, b = 7.1901(12) A, c = 10.369(2) A, and V = 1085.1(3) A3 at 102 K (a = 14.5091(10) A, b = 7.2739(4) A, c = 10.4570(7) A, and V = 1103.61(12) A3 at 233 K), in space group Pnma, with Z = 4. The Pt and Cu atoms are linked by a CN bridge that presents a very bent C identical to N-Cu angle (120.1(6) degrees at 102 K). The C identical to N and N-Cu distances at 102 K are 1.147(10) and 2.394(7) A, respectively. [(CN)3Pt(mu-CN)Cu(NH3)4] is embedded in an extensive electrostatic net formed by (N)H...N(C) interactions which, it is concluded, play an important role in the extreme deviation from linearity observed for the C identical to N-Cu angle.