Computerized separation of chromatographically unresolved peaks

A computerized peak deconvolution software and mass spectra were successfully applied for the deconvolution of overlapped peak cluster in the chromatogram obtained separating the complex mixture of pesticides by retention time locking gas chromatography-mass spectroscopy. The method based on the unique fragment ions in the spectra can be used for deconvolution of peak clusters if mass spectra of overlapped peaks differ. This method allows determining actual retention times of overlapped peaks. Peak areas found by this method however, cannot be used naturally for the quantitative purposes as the abundance of fragment ions used for this deconvolution procedure can dramatically differ. Computer assisted deconvolution of peaks in the peak clusters gives more realistic peak area ratios as at this method it is supposed equal response for all peaks overlapped in a cluster.     

(Fluoren-9-ylidene)methanedithiolato complexes of platinum: synthesis, reactivity, and luminescence

Platinum(II) complexes with (fluoren-9-ylidene)methanedithiolato and its 2,7-di-tert-butyl- and 2,7-dimethoxy-substituted analogues were obtained by reacting different chloroplatinum(II) precursors with the piperidinium dithioates (pipH)[(2,7-R2C12H6)CHCS2] [R = H (1a), t-Bu (1b), or OMe (1c)] in the presence of piperidine. The anionic complexes Q2[Pt{S(2)C=C(C12H6R(2)-2,7)}2] [R = H, (Pr(4)N)(2)2a; R = t-Bu, (Pr4N)(2)2b, (Et4N)(2)2b; R = OMe, (Pr4N)(2)2c] were prepared from PtCl(2), piperidine, the corresponding QCl salt, and 1a-c in molar ratio 1:2:2:2. In the absence of QCl, the complexes (pipH)(2)2b and [Pt(pip)(4)]2b were isolated depending on the PtCl(2):pip molar ratio. The neutral complexes [Pt{S2C=C(C12H6R(2)-2,7)L(2)] [L = PPh(3), R = H (3a), t-Bu (3b), OMe (3c); L = PEt(3), R = H (4a), t-Bu (4b), OMe (4c); L(2) = dbbpy, R = H (5a), t-Bu (5b), OMe (5c) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridyl)] were similarly prepared from the corresponding precursors [PtCl2L2] and 1a-c in the presence of piperidine. Oxidation of Q(2)2b with [FeCp2]PF6 afforded the mixed Pt(II)-Pt(IV) complex Q2[Pt2{S2C=C[C12H6(t-Bu)(2)-2,7]}4] (Q(2)6, Q = Et4N+, Pr4N+). The protonation of (Pr4N)(2)2b with 2 equiv of triflic acid gave the neutral dithioato complex [Pt2{S2CCH[C12H6(t-Bu)(2)-2,7]}4] (7). The same reaction in 1:1 molar ratio gave the mixed dithiolato/dithioato complex Pr4N[Pt{S2C=C[C12H6(t-Bu)(2)-2,7]}{S2CCH[C12H6(t-Bu)(2)-2,7]}] (Pr(4)N8) while the corresponding DMANH+ salt was obtained by treating 7 with 2 equiv of 1,8-bis(dimethylamino)naphthalene (DMAN). The crystal structures of 3b and 5c.CH2Cl2 have been solved by X-ray crystallography. All the platinum complexes are photoluminescent at 77 K in CH2Cl2 or KBr matrix, except for Q(2)6. Compounds 5a-c and Q8 show room-temperature luminescence in fluid solution. The electronic absorption and emission spectra of the dithiolato complexes reveal charge-transfer absorption and emission energies which are significantly lower than those of analogous platinum complexes with previously described 1,1-ethylenedithiolato ligands and in most cases compare well to those of 1,2-dithiolene complexes.     

Synthesis, crystal structure, spectroscopic and electrochemical characterization of the dinuclear complex {tetra-μ-[(±)-2-(p-methoxyphenoxy)-propionato-O,O′]bis(aqua)dicopper(II)}

Structural, electrochemical and spectroscopic data of a new dinuclear copper(II) complex with (±)-2-(p-methoxyphenoxy)propionic acid are reported. The complex {tetra-μ-[(±)-2-(p-methoxyphenoxy)propionato-O,O′]-bis(aqua)dicopper(II)} crystallizes in the monoclinic system, space group P2₁/n with a = 14.149(1) ?, b = 7.495(1) ?, c = 19.827(1) ?, β = 90.62(1) and Z = 4. X-ray diffraction data show that the two copper(II) ions are held together through four carboxylate bridges, coordinated as equatorial ligands in square pyramidal geometry. The coordination sphere around each copper ion is completed by two water molecules as axial ligands. Thermogravimetric data are consistent with such results. The ligand has an “L” type shape due to the angle formed by the β-carbon of the propionic chain and the linked p-methoxyphenoxy group. This conformation contributes to the occurrence of a peculiar structure of the complex. The complex retains its dinuclear nature when dissolved in acetonitrile, but it decomposes into the corresponding mononuclear species if dissolved in ethanol, according to the EPR measurements. Further, cyclic voltammograms of the complex in acetonitrile show that the dinuclear species maintains the same structure, in agreement with the EPR data in this solvent. The voltammogram shows two irreversible reduction waves at E _pc = −0.73 and −1.04 V vs. Ag/AgCl assigned to the Cu(II)/Cu(I) and Cu(I)/Cu° redox couples, respectively, and two successive oxidation waves at E _pa =− 0.01 and +1.41 V vs. Ag/AgCl, assigned to the Cu°/Cu(I) and Cu(I)/Cu(II) redox couples, respectively, in addition to the oxidation waves of the carboxylate ligand.     

Water-soluble ruthenium(II) catalysts [RuCl2(eta6-arene)[P(CH2OH)3]] for isomerization of allylic alcohols and alkyne hydration

The novel water-soluble ruthenium(II) complexes [RuCl(2)(eta(6)-arene)[P(CH(2)OH)(3)]]2a-c and [RuCl(eta(6)-arene)[P(CH(2)OH)(3)](2)][Cl]3a-c have been prepared in high yields by reaction of dimers [[Ru(eta(6)-arene)(micro-Cl)Cl](2)](arene = C(6)H(6)1a, p-cymene 1b, C(6)Me(6)1c) with two or four equivalents of P(CH(2)OH)(3), respectively. Complexes 2/3a-c are active catalysts in the redox isomerization of several allylic alcohols into the corresponding saturated carbonyl compounds under water/n-heptane biphasic conditions. Among them, the neutral derivatives [RuCl(2)(eta(6)-C(6)H(6))[P(CH(2)OH)(3)]]2a and [RuCl(2)(eta(6)-p-cymene)[P(CH(2)OH)(3)]]2b show the highest activities (TOF values up to 600 h(-1); TON values up to 782). Complexes 2/3a-c also catalyze the hydration of terminal alkynes.     

Square-Planar Nickel(II) O,O′-Dialkyldithiophosphato Complexes with Triphenylphosphine of the Type [NiX(S2P{OR}2)(PPh3)] (X = Cl,Br, I and NCS)

A series of new [NiX(S₂P{O-c-Hex}₂)(PPh₃)](X = Cl^–, Br^–, I^– and NCS^–)(1)–(4) and [Ni(NCS)(S₂P{OR}₂)(PPh₃)][R =n-Pr (5), i-Pr (6)] complexes has been synthesized and characterized by elemental analyses, f.i.r., i.r., u.v.–vis., ¹H-, ¹³C{¹H}- and ³¹P{¹H}-n.m.r. spectra, magnetochemical and conductivity measurements. A single crystal X-ray analysis of [Ni(NCS)(S₂P{O-n-Pr}₂)(PPh₃)](5) reveals the molecular structure of the complex and confirms a square-planar geometry around the central atom of nickel with the NCS anion coordinated via the nitrogen atom.     

Structural Study of Alkaline 1-Phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate Salts: An Example of Periodicity in Alkaline Cations

The alkaline 1-phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate salts, M[C₆H₅N₄CS] (M = Li ( 1 ), Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 )) were obtained and characterized by means of mass spectrometry (FAB⁺) and NMR (¹H; ¹³C) spectroscopy. The structures of Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 ) compounds were determined by X-ray diffraction methods. The ligand shows a rich variety of coordination patterns with the alkaline cations. The formation of a four-membered ring MSCN in the compounds with heavier alkali cations (K, Rb and Cs) is shown. In all the cations the coordination number around it increases with the ionic radius. Compounds with Cs⁺ and Rb⁺ exhibited the formation of Cs-C and Rb-C interactions with the phenyl group.     

Direct capillary electrophoretic determination of three chemotherapeutic drugs in human urine

Summary Capillary zone electrophoresis (CZE) has been used for direct determination of 6-thioguanine, methotrexate, and 5-fluorouracil in human urine, by use of a fused-silica capillary (60.2 cm×75 μm i.d.). Separation was performed after hydrodynamic injection for 7 s; the separation potential and capillary temperature were 25 kV and 35°C, respectively. A 45mm borate buffer solution (pH 9.2) was used as separation electrolyte. Under these conditions the analysis takes approximately 10 min and interday precision of migration times and corrected peak areas is satisfactory. A linear response over the concentration range 3.0–20.0 mg L¹ was observed for the three chemotherapeutic drugs in diluted human urine. Detection limits (s/n=3) for 6-thioguanine and methotrexate were approximately 1.60 mg L¹ in diluted human urine; that for fluorouracil was 2.60 mg L¹. A 2-ml volume of human urine was diluted with 2-mL of water and introduced directly into the electrophoresis system. CZE was shown to be a good method with regard to simplicity, satisfactory precision, and sensitivity. This method resulted in especially excellent recoveries for determination of methotrexate in all the different urine samples analysed (n=10).     

A chemometric study of the simultaneous determination of calcium and magnesium in natural waters

A method for the simultaneous spectrophotometric determination of calcium and magnesium in mineral waters with an FIA system is tested. The method is based on the reaction between the analytes and arsenazo(III) at pH 8.5. The calculations of the amounts of both analytes in the samples are carried out with the H-point standard addition method (HPSAM) for ternary mixtures, and with a partial least squares (PLS) model after a proper variable selection. The results obtained for the determination of calcium were comparable using both methods. The employment of the HPSAM brings to our attention the influence of the calcium concentration in the sample to the development of the reaction between magnesium and arsenazo(III). HPSAM also permits to estimate the concentration of magnesium in the samples.     

C36 fullerenes and quasi-fullerenes: computational search through 598 cages

C₃₆ is computed at the SAM1 level and partially also at the HF/4-31G and B3LYP/6-31G^* levels. Altogether 598 cages are generated by a topological Stone–Wales treatment. Three cages contribute by more than 10% to the high-temperature equilibrium isomeric mixture – two conventional fullerenes with D_2d and C_2v symmetries and a C_s quasi-fullerene containing one four-membered ring.     

Heat-induced conformational transition of cytochrome c observed by temperature gradient gel electrophoresis at acidic pH

Temperature-gradient gel electrophoresis (TGGE) has been used to study the thermal unfolding of ferricytochrome c in low and high concentrations of acetic acid. It has been observed that the mobility of cytochrome c is a linear function of temperature when the system is characterized by a homogeneous population of conformation-state, single molecular species. Within the transition temperature range, the mobility clearly displays the characteristic sigmoidal shape describing the transitions of protein unfolding. The data obtained by TGGE were used to estimate the apparent thermodynamic parameters (enthalpy change deltaHvh and transition temperature Tm), associated with the transition of unfolding. The accuracy of the apparent thermodynamic parameters obtained by this method agrees within error limits with the values obtained by direct calorimetric measurements using differential scanning calorimetry (DSC).