Determination of Clobazam, Clorazepate, Flurazepam and Flunitrazepam in pharmaceutical preparations

The separation of four benzodiazepines (Flurazepam, Flunitrazepam, Clobazam and Clorazepate) in pharmaceutical products by micellar electrokinetic chromatography (MEKC) is described. It was carried out at 25 degrees C and 25 kV by using a 57 cm (50 cm to the detector)x75 mum i.d. fused silica capillary and a 15 mM borate buffer (pH 9.2), 35 mM sodium dodecylsulfate (SDS) and 35 mM sodium deoxycholate water solution. Under these conditions, the analysis was performed in 8 min with acceptable limits of quantification (between 3 and 5 mg l(-1)). The method has been applied for quantifying these benzodiazepines in serum and different commercial formulations with recoveries near 100%.     

Carbon fiber cylindrical microelectrode-based detector for the determination of antithyroid drugs

An amperometric flow-injection method for the determination of antithyroid drugs such as 6-methyl-2-thiouracil (MTU) using a carbon fiber cylindrical microelectrode-based detector is reported. A home-made flow-cell specially adapted for working with cylindrical microelectrodes ranging between 4 and 10 mm in length was used for this purpose. Methanol containing 0.05 mol l(-1) tetrabutylammonium perchlorate as the supporting electrolyte was employed, and a potential of +1.6 V was selected for the amperometric detection of MTU. No cleaning or electrode surface regeneration of the fiber was necessary during the whole working day. A limit of detection of 2.6x10(-7) mol l(-1) (37 mug MTU l(-1)) was achieved. The method was applied to the determination of MTU in spiked feed samples (peas and corn flour), at the 142 mug g(-1) level. The procedure involved the extraction of the drug in methanol, a clean-up step using Florisil cartridges and the use of the standard additions method. Recoveries of 81+/-6 and 85+/-8% were obtained for peas and corn flour, respectively.     

Evaluating the significance threshold in robustness testing. A critical discussion on the influence of time in molecular fluorescence spectrometry

Robustness experiments are performed in analytical chemistry to assess the behaviour of an analytical procedure under conditions slightly different from those of the experimental optimum. This work presents a study of robustness applied to a previously proposed fluorescent methodology using two replicated 2(7-4) saturated fractional factorial designs. A comparison is established between three different ways to test the significance of the effects of the variables involved on the response signal. Critical discussions about the most appropriate threshold to be introduced when testing for significance of the factors and the influence of the time necessary to carry out the experiments are included.     

Magnetism in polyoxometalates: anisotropic exchange interactions in the Co3II moiety of [Co3W(D2O)2(ZnW9O34)2](12-)--A magnetic and inelastic neutron scattering study

The ground-state properties of a Co3II moiety encapsulated in a polyoxometalate anion were investigated by combining measurements of specific heat, magnetic susceptibility, and low-temperature magnetization with a detailed inelastic neutron scattering (INS) study on a fully deuterated polycrystalline sample of Na12[Co3W(D2O)2(ZnW9O34)2].40D2O (Co3). The ferromagnetic Co3O14 cluster core consists of three octahedrally oxo-coordinated CoII ions. According to the single-ion anisotropy and spin-orbit coupling of the octahedral CoII ions, the appropriate exchange Hamiltonian to describe the ground-state properties of the Co3 spin cluster is anisotropic and is expressed as H = -2 sigma a = x,y,z (Ja12 S1a S2a + Ja23 S2a S3a), where Ja are the components of the exchange interactions between the CoII ions. To reproduce the INS data, different orientations of the two anisotropic J tensors must be considered, and the following conditions had to be introduced: Jx12 = Jy23, Jy12 = Jx23, Jz12 = Jz23. This result was correlated with the molecular symmetry of the complex. The following set of parameters was obtained: Jx12 = Jy23 = 1.37, Jy12 = Jx23 = 0.218, and Jz12 = Jz23 = 1.24 meV. This set also reproduces in a satisfactory manner the specific heat, susceptibility, and magnetization properties of Co3.     

Second-generation mimics of ganglioside GM1 oligosaccharide: a three-dimensional view of their interactions with bacterial enterotoxins by NMR and computational methods

As a step to delineate a strategy of ligand design for cholera toxin (CT), NMR studies were performed on several mimics of the GM1 ganglioside oligosaccharide. The conformation of these analogues was investigated first in solution and then upon binding to cholera toxin by transferred nuclear Overhauser effect (TR-NOE) measurements. It was demonstrated that CT selects a conformation similar to the global minima of the free saccharides from the ensemble of presented conformations. No evidence of major conformational distortions was obtained, but one or two of the available conformers of the hydroxyacid side chain appear to be selected in the bound state. The NMR data were interpreted with the aid of computer models, generated and analyzed by using a combination of different approaches (MacroModels' MC/EM and MC/SD, Autodock, and GRID). Analysis of the NMR data supported by computational studies allowed us to interpret the experimental observations and to derive workable models of the ligand:toxin complexes. These models suggest that the higher affinity of the (R)-lactic acid derivative 3 may stem from lipophilic interactions with a hydrophobic area in the toxin binding site located in the vicinity of the sialic acid side chain binding region of the CT:GM1 complex, and formed by the side chain of Ile-58 and Lys-34. Thus, the models obtained have allowed us to make useful design suggestions for the improvement of ligand affinity.     

Structural and energetic aspects of the protonation of phenol,catechol, resorcinol,and hydroquinone

The various protonated forms of phenol (1), catechol (2), resorcinol (3), and hydroquinone (4) were explored by ab initio quantum chemical calculations at the MP2/6-31G(d) and B3LYP/6-31G(d) levels. Proton affinities (PA) of 1-4 were calculated by the combined G2(MP2,SVP) method, and their gas-phase basicities were estimated after calculation of the change in entropy on protonation. These theoretical data were compared with the corresponding experimental values determined in a high-pressure mass spectrometer. This comparison confirmed that phenols are essentially carbon bases and that protonation generally occurs in a position para to the hydroxyl group. Resorcinol is the most effective base (PA = 856 kJ mol-1) due to the participation of both oxygen atoms in the stabilization of the protonated form. Since protonation is accompanied by a freezing of the two internal rotations, a significant decrease in entropy is observed. The basicity of catechol (PA = 823 kJ mol-1) is due to the existence of an intramolecular hydrogen bond, which is strengthened upon protonation. The lower basicity of hydroquinone (PA = 808 kJ mol-1) is a consequence of the fact that protonation necessarily occurs in a position ortho to the hydroxyl group. When the previously published data are reconsidered and a corrected protonation entropy is used, a proton affinity value of 820 kJ mol-1 is obtained for phenol.     

Interligand interactions controlling the mu-N7,N9-metal bonding of adenine (AdeH) to the N-benzyliminodiacetato(2-) copper(II) chelate and promoting the N9 versus N3 tautomeric proton transfer: molecular and crystal structure of [Cu2(NBzIDA)(2)(H2O)(2)(mu-N7,N9-Ade(N3)H)].(3)H2O

The reaction in water of the N-benzyliminodiacetate-copper(II) chelate ([Cu(NBzIDA)]) and the adenine:thymine base pair complex (AdeH:ThyH) with a Cu/NBzIDA/AdeH/ThyH molar ratio of 2:2:1:1 yields [Cu(2)(NBzIDA)(2)(H(2)O)(2)(mu-N7,N9-Ade(N3)H)].3H(2)O and free ThyH. The compound has been studied by thermal, spectral, and X-ray diffraction methods. In the asymmetric dinuclear complex units both Cu(II) atoms exhibit a square pyramidal coordination, where the four closest donors are supplied by NBzIDA in a mer-tridentate conformation and the N7 or N9 donors of AdeH, which is protonated at N3. The mu-N7,N9 bridge represents a new coordination mode for nonsubstituted AdeH, except for some adeninate(1-)-[methylmercury(II)] derivatives studied earlier. The dinuclear complex is stabilized by the Cu-N7 and Cu-N9 bonds and N6-H(exocyclic)...O(carboxyl) and N3-H(heterocyclic)...O(carboxyl) interligand interactions, respectively. The structure of the new compound differs from that of the mononuclear compound [Cu(NBzIDA)(Ade(N9)H)(H(2)O)].H(2)O, in which the unusual Cu-N3(AdeH) bond is stabilized by a N9-H...O(carboxyl) interligand interaction and where alternating benzyl-AdeH intermolecular pi,pi-stacking interactions produce infinite stacked chains. The possibility for ThyH to be involved in the molecular recognition between [Cu(NBzIDA)] and the AdeH:ThyH base pair is proposed.     

High yield synthesis and reactivity of a phosphinidene bridged dimolybdenum complex

Protonation of [Mo2Cp2(mu-H)(mu-PHR*)(CO)4] (Cp = eta5-C5H5, R* = 2,4,6-C6H2tBu3) with HBF4.OEt2 gives the hydridophosphinidene complex [Mo2Cp2(mu-H)(mu-PR*)(CO)4]BF4, which is easily deprotonated with H2O to give the known phosphinidene complex [Mo2Cp2(mu-PR*)(CO)4] in 95% yield. Reaction of the latter with I2 gives the unsaturated phosphinidene complex [Mo2Cp2I2(mu-PR*)(CO)2], which exhibits an intermetallic distance of 2.960(2) A. Irradiation of solutions of [Mo2Cp2(mu-PR*)(CO)4] with UV light gives a mixture of the triply bonded [Mo2Cp2(mu-PR*)(mu-CO)2] and the hydridophosphido derivative [Mo2Cp2(mu-H){mu-P(CH2CMe2)C6H2tBu2}(CO)4] as major species. The latter complex results from an intramolecular C-H bond cleavage from a tBu group and has been characterized by spectroscopy and an X-ray study. Irradiation in the presence of HCC(p-tol) results in the insertion of the alkyne into the Mo-P bond to give [Mo2Cp2{mu-eta1:eta2,kappa-C(p-tol)CHPR*}(CO)4] structurally characterized through an X-ray study.     

Gas chromatography/mass spectrometric study of non-commercial C-4-substituted 1,4-dihydropyridines and their oxidized derivatives

A gas chromatography/mass spectrometry (GC/MS) method for the qualitative and quantitative determination of the calcium-channel antagonists C-4-substituted 1,4-dihydropyridines, and their corresponding N-ethyl derivatives, is presented. Also, the electrochemical oxidation and the reactivity of the compounds with alkyl radicals derived from 2,2'-azobis-(2-amidinopropane) were monitored by GC/MS. Mass spectral fragmentation patterns for the C-4-substituted 1,4-dihydropy-ridine parent drugs were significantly different from those of their oxidation products, generated either by electrochemical oxidation or by reaction with alkyl radicals. However, for N-ethyl-1,4-dihydropyridine compounds it was not possible to detect the final products (pyridinium salts) using these experimental conditions.