Surface‐enhanced Raman scattering and density functional theory studies of bis(4‐aminophenyl)sulfone

Raman and surface‐enhanced Raman scattering (SERS) spectra of dapsone by using colloidal silver nanoparticles have been recorded. Density functional theory was used for the optimization of ground state geometries and simulation of the vibrational spectrum of this molecule. The SERS spectrum with a large silver cluster as a model metallic surface was simulated for the first time. Taking into account the experimental and calculated Raman as well as the SERS normal modes and the corresponding assignments, along with the modeling of the free dapsone and the one in the presence of the colloidal silver nanoparticles, the importance of the sulfone group on the SERS effect in dapsone was inferred. Copyright © 2009 John Wiley & Sons, Ltd.     

Highly sensitive and rapid determination of tacrolimus in peripheral blood mononuclear cells by liquid chromatography–tandem mass spectrometry

After solid organ transplantation, tacrolimus is given to prevent rejection. Therapeutic drug monitoring is used to reach target concentrations of tacrolimus in whole blood. Because the site of action of tacrolimus is the lymphocyte, and tacrolimus binds ~80% to erythrocytes, the intracellular tacrolimus concentration in lymphocytes is possibly more relevant. For this purpose, we aimed to develop, improve and validate a UPLC–MS/MS method to measure tacrolimus concentrations in isolated peripheral blood mononuclear cells (PBMCs). PBMCs were isolated using a Ficoll separation technique, followed by a washing step using red blood cell lysis. A cell suspension of 50 μL containing 1 million PBMCs was used in combination with MagSiMUS‐TDM^PREP. To each sample we added 30 μL lysis buffer, 20 μL reconstitution buffer containing ¹³C²H₄‐tacrolimus as internal standard, 40 μL MagSiMUS‐TDM^PREP Type I Particle Mix and 175 μL Organic Precipitation Reagent VI for methanol‐based protein precipitation. A 10 μL aliquot of the supernatant was injected into the UPLC–MS/MS system. The method was validated, resulting in high sensitivity and specificity. The method was linear (r² = 0.997) over the range 5.0–1250 pg/1 × 10⁶ PBMCs. The inaccuracy was <5% and the imprecision was <15%. The washing steps following Ficoll isolation could be performed at either room temperature or on ice, with no effect of the temperature on the results. A method for the analysis of tacrolimus concentrations in PBMCs was developed and successfully validated. Further research will be performed to investigate the correlation between concentrations in PBMCs and clinical outcome.     

Crossed-beam study of Co+(3F4)+propane: experiment and density functional theory

A pulsed beam of Co+(3F4) crosses a pulsed beam of C3H8 or C3D8 gas under single collision conditions at collision energies of 0.01 eV and 0.21 eV. After a variable time delay t(ext) = 1-8 micros a fast high voltage pulse extracts product ions into a field-free flight tube for mass analysis. Consistent with earlier work, we observe prompt CoC3H6+ +H2 elimination products in 3:1 excess over CoC2H4+ +CH4 products at 0.21 eV on a 2-10 micros time scale. Long-lived CoC3H8+ complexes fragment predominantly back to Co+ +C3H8 reactants and to H2 elimination products on a 6-24 micros time scale. Density functional theory (B3LYP) calculations provide energies, geometries, and harmonic vibrational frequencies at key stationary points for use in a statistical rate model of the reaction. By adjusting two key multicenter transition state (MCTS) energies downward by 4-7 kcal mol(-1), we obtain good agreement with our decay time results and with the cross section versus collision energy of Armentrout and co-workers from 0.1-1.0 eV. B3LYP theory succeeds in finding relative energies of the MCTSs leading to CH4 and H2 in the proper order to explain the different product branching ratio for Co+ (which favors H2 over CH4) compared with its nearest neighbors Fe+ and Ni+ (which favor CH4 over H2).     

Preparation, characterization and thermolysis of metal nitrate complexes with 4,4’-bipyridine

Two bis(bipyridine) polymeric metal nitrate complexes with 4,4’-bipyridine of simple formula like [M(bipy)₂](NO₃)2⋅xH₂O (where M=Co, Ni and Cu; x=4, 2 and 0, respectively) have been prepared and characterized. Their thermal decomposition has been undertaken using simultaneous TG-DTG-DTA and DSC in nitrogen atmosphere and non-isothermal TG in air atmosphere. Isothermal TG has been performed at decomposition temperature range of the complexes to evaluate the kinetics of decomposition by applying model-fitting as well as isoconversional method. Possible mechanistic pathways have also been proposed for the thermolysis. Ignition delay measurements have been carried out to investigate the response of these complexes under the condition of rapid heating.     

Parahydrogen induced polarization of barbituric acid derivatives: 1H hyperpolarization studies

Homogeneous hydrogenation of barbituric acid derivatives with parahydrogen yields a substantial increase of the (1)H NMR signals of the reaction products. These physiologically relevant compounds were hydrogenated at both ambient and elevated temperatures and pressures using a standard cationic rhodium catalyst. The resulting nonthermal nuclear spin polarization (hyperpolarization) is limited by the spin-lattice relaxation time T(1) of the corresponding nuclei in the products, being shorter than the time constant of the hydrogenation. The signal-to-noise ratio of the NMR spectra could be further increased upon signal averaging the antiphase PHIP signals of 25 successive scans following 30 degrees pulse experiments and a delay of 10 s.     

Cyclobutadiene dianion derivatives – Planar 4c,6e or three-dimensional 6c,6e aromaticity?

The spatial magnetic properties (Through Space NMR Shieldings – TSNMRS) of two cyclobutadiene derivatives (2 and 5) and of a number of cyclobutadiene dianion derivatives (3, 4 and 6–8) have been calculated by the GIAO perturbation method employing the Nucleus-Independent Chemical Shift (NICS) concept of P. v. Ragué Schleyer, and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various size and direction. TSNMRS values can be successfully employed to quantify and visualize the (anti)aromaticity of the compounds studied and to discuss the influence of Li⁺ complexation to cyclobutadiene dianion (4a, 7 and 8) on planar 4c,6e or three-dimensional 6c,6e aromaticity.     

Synthesis, EPR spectrum and X-ray structure of tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κS,S′)platinate(III)

The new salt, tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κ²S,S′)platinate(III), [NBu₄][Pt(C₆H₄S₂)₂] (1), has been synthesized in ethanol/water, and fully characterized by single crystal X-ray structure determination. The central platinum in the complex ion [Pt(bdt)₂]⁻ is tetracoordinated by the S atoms of the bdt²⁻ ligands (bdt²⁻ is benzene-1,2-dithiolate) in a square-planar geometry. The well-resolved frozen solution EPR spectrum exhibits rhombic symmetry. The room temperature effective magnetic moment (μ_eff = 1.80 Bohr magneton) is in line with this spectrum and strongly supports the Pt(III) oxidation state in 1. This observation is in excellent agreement with previous results reported on closely related Ni(III), Pd(III) and Pt(III) species.     

In situ NMR observation of mono- and binuclear rhodium dihydride complexes using parahydrogen-induced polarization

Starting from the binuclear complex [RhCl(NBD)]2 (NBD = 2,5-norbornadiene) in the presence of the phosphines L = PMe3, PMe2Ph, PMePh2, PEt3, PEt2Ph, PEtPh2, or P(n-butyl)3, various mononuclear dihydrides of the type Rh(H)2CIL3, i.e., those of the homogeneous hydrogenation catalysts RhCIL3, have been obtained upon addition of parahydrogen, and their 1H NMR spectra have been investigated using parahydrogen-induced polarization (PHIP). Furthermore, the two binuclear complexes (H)(Cl)Rh(PMe3)2(mu-Cl)(mu-H)Rh(PMe3) and (H)(Cl)Rh(PMe2Ph)2(mu-Cl)(mu-H)Rh(PMe2Ph) have been detected and characterized by means of this in situ NMR method. Analogous complexes with trifluoroacetate instead of chloride, i.e., Rh(H)2(CF3COO)L3, have been generated in situ starting from Rh(NBD)(acac) in the presence of trifluoroacetic acid in combination with the phosphines L = PPh3, PEt2Ph, PEt3, and P(n-butyl)3, and their 1H NMR parameters have been determined.     

Simplex optimisation of conditions for the determination of antimony in environmental samples by using electrothermal atomic absorption spectrometry

Analysis of the total antimony in plant material was unsuccessful using the electrothermal atomic absorption spectrometry (ETAAS) conditions recommended by the instrument manufacturer. For this reason, an optimisation procedure utilising the Plackett-Burman method, simplex optimisation and visualisation of the generated response surface via principal components analysis, was carried out. The Plackett-Burman method was used to eliminate four of the initial variables chosen. Four variables (atomisation temperature, atomisation time, ash temperature and modifier concentration) were subsequently optimised using the composite modified simplex method and the results were visualised as a contour diagram, after reduction to two principal components. The optimised conditions were used for the analysis of both an acid digested pine needle standard reference material (NIST 1575) and a pond weed sample, collected from a contaminated site at Yellowknife Bay, Yellowknife, NWT, Canada. The total concentration of antimony present in the pine needles was statistically indistinguishable from the non-certified value, as was the value for the pond weed sample, compared with a value determined by neutron activation analysis (NAA). The results for the analysis of the pond weed sample by ETAAS agreed with those obtained from a subsequent analysis by inductively coupled plasma-mass spectrometry.