Stereodynamics of 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane: experimental and theoretical analysis

Dynamic NMR of 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane reveals two dynamic processes: ring inversion leading to equilibrium between two degenerate rotamers of C_s symmetry (ΔG^≠ = 13.5 kcal/mol), and rotation about the S-N bond leading to equilibrium between the C_s (more stable) and C_3v (2.12 kcal/mol less stable) rotamers (ΔG^≠ = 13.0 kcal/mol).     

Computational study of keto–enol equilibria of tropolone in gas and aqueous solution phase

Density functional theory calculations employing the B3LYP exchange-correlation functional, as well as Hartree–Fock computations, were performed on 2-hydroxy-2,4,6-cycloheptatrien-1-one (tropolone) and 3,5- and 3,6-cycloheptadiene-1,2-dione in gas and aqueous solution phases in order to determine the equilibrium constant for keto to enol interconversion of the isomers of C₇H₆O₂. Two standard basis sets were used throughout, namely 6-311++G^∗∗ and aug-cc-pVDZ. Solvent effects were modelled using two different self-consistent reaction field approaches – the Onsager dipole and the polarizable continuum models (PCM). In addition, the G3 method was used for calculations on species in the gas phase. Molecular geometries were fully optimized at each model chemistry, and it was found that the two keto isomers are always higher in energy than the enol form. From the results of B3LYP/6-311++G^∗∗ calculations of the difference in Gibbs free energy in the gas phase and using PCM, the relative pK values for the 2-hydroxy-2,4,6-cycloheptatrien-1-one ? 3,5- and 3,6-cycloheptadiene-1,2-dione system are 13.75 (g), 15.78 (g) and 13.05 (aq) and 13.45 (aq), respectively. That equilibrium is tilted almost exclusively in the direction of tropolone is due to resonance stabilization of the enol as a result of aromaticity, and is most easily understood on the basis of elementary Hückel theory.     

Solid-state cis-trans isomerization reaction of (η-MeC5H4)W(CO)2P(OPr)3I

cis-(η⁵-MeC₅H₄)W(CO)₂P(OⁱPr)₃I (1) was converted to the trans isomer 2 in the solid state (90-110 °C). The reaction was monitored by heating 1 in NMR tubes for periods of time (2-60 min), cooling the tubes to room temperature and determining the conversion by solution ³¹P and ¹H NMR spectroscopy. The data were consistent with a first-order reaction and yielded an activation energy of 59 ± 3 kJ mol⁻¹. Comparative kinetic data were obtained from an in situ analysis of a powder-XRD study of 1. The powder-XRD study was conducted at 80-100 °C (10-60 min), yielding an activation energy of 52 ± 2 kJ mol⁻¹ (first-order reaction). The reaction could not be monitored by single crystal X-ray diffraction as the crystal disintegrated over time on heating. This disintegration process was monitored by optical microscopy and revealed that while the bulk crystal morphology was retained the crystal surface roughened with time. The compounds 1 and 2 were also structurally characterised by X-ray crystallographic techniques.     

Mineral content and botanical origin of Spanish honeys

Eleven elements (Zn, P, B, Mn, Mg, Cu, Ca, Ba, Sr, Na and K) were determined by inductively plasma coupled spectrometry in 40 honey samples from different places of Spain and four different botanical origins: Eucalyptus (Eucalyptus sp.), Heather (Erica sp.), Orange-blossom (Citrus sinensis) and Rosemary (Rosmarinus officinalis). K, Ca and P show the higher levels with average concentrations ranged between 434.1-1935 mg kg⁻¹ for K; 42.59-341.0 mg kg⁻¹ for Ca and 51.17-154.3 mg kg⁻¹ for P. Levels of Cu (0.531-2.117 mg kg⁻¹), Ba (0.106-1.264 mg kg⁻¹) and Sr (0.257-1.462 mg kg⁻¹) are the lowest in all honey samples. Zn (1.332-7.825 mg kg⁻¹), Mn (0.133-9.471 mg kg⁻¹), Mg (13.26-74.38 mg kg⁻¹) and Na (11.69-218.5 mg kg⁻¹) concentrations were found strongly dependent on the kind of botanical origin.Results were submitted to pattern recognition procedures, unsupervised methods such as cluster and principal components analysis and supervised learning methods like linear discriminant analysis in order to evaluate the existence of data patterns and the possibility of differentiation of Spanish honeys from different botanical origins according to their mineral content. Cluster analysis shows four clusters corresponding to the four botanical origins of honey and PCA explained 71% of the variance with the first two PC variables. The best-grouped honeys were those from heather; eucalyptus honeys formed a more dispersed group and finally orange-blossom and rosemary honeys formed a less distinguishable group.     

A DFT study on pyridine-derived N-heterocyclic carbenes

To appreciate the chemistry of N-heterocyclic carbenes (NHCs), eight carbenic tautomers of pyridine (azacyclohexadienylidenes) are studied at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G^∗ and B3LYP/6-311++G^∗∗//B3LYP/6-31+G^∗ levels of theory. Various thermodynamic parameters are calculated for these minima, along with a kinetic focus on carbene-pyridine tautomerization. Appropriate isodesmic reactions show stabilization energies of 2-azacyclohexa-3,5-dienylidene (1) and 4-azacyclohexa-2,5-dienylidene (6) as 119.4 and 104.1 kcal/mol, rather close to that of the synthesized 1,3-dimethylimidazol-2-ylidene (129.2 kcal/mol). Three different mechanisms are suggested for the tautomerizations including: [1,2]-H shift, [1,4]-H shift, and three sequential [1,2]-H shifts. The calculated energy barrier for [1,2]-H shift of 1 is 44.6 kcal/mol, while the first [1,2]-H shift for the proposed sequential mechanism of 6 requires 65.1 kcal/mol. Three preliminary minimum templates are introduced, which may possess the potential of synthetic consideration: 2,6-di(X)-3,5-dichloro-4-azacyclohexa-2,5-dienylidene for X=Mes, t-Bu, and Ad.     

Sorptive potential of sunflower stem for Cr(III) ions from aqueous solutions and its kinetic and thermodynamic profile

The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity X_m = 1.60 ± 0.23 mmol g⁻¹, β = −0.00654 ± 0.00017 kJ² mol⁻², mean free energy E = 8.74 ± 0.12 kJ mol⁻¹, Freundlich sorption capacity K_F = 0.24 ± 0.11 mol g⁻¹, 1/n = 0.90 ± 0.04 and of Langmuir constant K_L = 6800 ± 600 dm³ mol⁻¹ and C_m = 120 ± 18 μmol g⁻¹. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol⁻¹, ΔS = −64.0 ± 2.7 J mol⁻¹ K⁻¹ and ΔG_298k = −4.04 ± 0.09 kJ mol⁻¹. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed.     

The effect of spiroadamantane substitution on the conformational preferences of N-Me pyrrolidine and N-Me piperidine: a description based on dynamic NMR spectroscopy and ab initio correlated calculations

Dynamic NMR spectroscopy and ab initio correlated calculations revealed that the attachment of a spiroadamantane entity at the C-2 position of N-methylpyrrolidine or N-methylpiperidine induces a severe steric crowding around nitrogen, which changes the conformational space of the heterocycle resulting in: (a) the complete destabilization of the N-Me(eq) conformer in spiranic structures; in contrast the N-Me(eq) conformer corresponds to the global minimum in N-methylpyrrolidine or N-methylpiperidine. The spiroadamantane structure raises the energy of the equatorial conformer because of the severe van der Waals repulsion between the N-Me(eq) group and adamantane C-H bonds. (b) The interconversion between the only populated enantiomeric N-Me(ax) conformers ax→[eq]→ax′; the interconversion eq→ax between N-Me(eq) and N-Me(ax) conformers, which are both populated, is observed in N-methylpyrrolidine or N-methylpiperidine. (c) The raising of ring and nitrogen inversion barriers ax→ts by ∼4-6 kcal mol⁻¹. The dynamic NMR study provides evidence that the most important process required for the enantiomerization between the axial N-Me conformers in spiropiperidine 4 and spiropyrrolidine 5 are different, i.e., a nitrogen inversion in 5 (9.10 kcal mol⁻¹) and a ring inversion in 4 (15.2 kcal mol⁻¹). While an enantiomerization interconverts N-Me axial conformers in spiropiperidine 5 and spiropyrrolidine 4, substitution of the pyrrolidine ring of 5 with a C-Me group effects a diastereomerization between two N-Me axial conformers and reduces effectively the nitrogen inversion barrier according to the protonation experiments and the calculations. In general, all the calculations levels used, i.e., the MM3, B3LYP/6-31+G^∗∗ and MP2/6-311++G^∗∗//B3LYP/6-31+G^∗∗, predict correctly the different stability of the local minima; however only MP2/6-311++G^∗∗//B3LYP/6-31+G^∗∗ was found to be reliable for the calculation of the nitrogen inversion barriers.     

Redox-active metal(II) complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c. Part II. Metal(II) complexes of o-diphenol derivatives of thioglycolic acid

The synthesis and physico-chemical characterization of Fe(II) and Mn(II) complexes of 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid (HL^I) and 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfinyl]acetic acid (HL^II) were carried out. The investigation of the molecular and electronic structure of Cu(II), Ni(II), Zn(II), Fe(II) and Mn(II) complexes has been performed within the density functional theory (DFT) framework. The computed properties were compared to the experimental ones, and molecular structures of the compounds were proposed based on the array of spectral data and quantum chemical calculations. Antibacterial activity of the Fe(II) and Mn(II) complexes was evaluated in comparison with Cu(II), Co(II), Ni(II) and Zn(II) complexes and three standard antibiotics; it was found to follow the order: (1) Сu(L^I)₂ > Mn(L^I)₂ > HL^I > Ni(L^I)₂ > Zn(L^I)₂ > Fe(L^I)₂ > Co(H₂O)₂L^I; (2) Cu(L^II)₂ > Сo(L^II)₂ > Ni(L^II)₂ > Mn(H₂O)₂(L^II)₂ > Fe(L^II)₂ > HL^II > Zn(L^II)₂; their reducing ability (determined electrochemically) followed the same order. Spectrophotometric investigation was carried out in order to estimate the rate of the reduction of bovine heart сytochrome c with the ligands and their metal(II) complexes. The complexes Сu(L^I)₂, Mn(L^I)₂ and Co(L^II)₂ with the high reducing ability were found to be characterized by the highest rates of Cyt с reduction. NADPH:cytochrome P450-reductase had no substantial effect on the rate of сytochrome c reduction with HL^I and HL^II ligands.     

EPR study of mono-o-iminobenzosemiquinonato nickel(II) complexes with Ni-C σ-bond

New square-planar (Ph₃P)Ni^II(o-Tol)(ISQ-Prⁱ) (1), (Ph₃P)Ni^II(o-Tol)(ISQ-Me) (2), (Ph₃P)Ni^II(o-Tol)(ISQ-Bu^t) (3) nickel complexes (where ISQ-Prⁱ = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate, ISQ-Me = 4,6-di-tert-butyl-N-(2,6-di-methylphenyl)-o-iminobenzosemiquinonate, ISQ-Bu^t = 4,6-di-tert-butyl-N-(2,5-di-tert-butylphenyl)-o-iminobenzosemiquinonate, o-Tol = o-tolyl ligand) have been synthesized. Complexes contain σ-bound o-tolyl and neutral donor ligand Ph₃P. The sterical hindrances of N-aryl in o-iminobenzosemiquinonate ligands lead to the tetrahedral distortion of square-planar configurations of complexes as it was established using EPR spectroscopy.     

Amperometric choline biosensors prepared by layer-by-layer deposition of choline oxidase on the Prussian blue-modified platinum electrode

An amperometric choline biosensor was developed by immobilizing choline oxidase (ChOx) in a layer-by-layer (LBL) multilayer film on a platinum (Pt) electrode modified with Prussian blue (PB). 6-O-Ethoxytrimethylammoniochitosan chloride (EACC) was used to prepare the ChOx LBL films. The choline biosensor was used at 0.0 V versus Ag/AgCl to detect choline and exhibited good characteristics such as relative low detection limit (5 × 10⁻⁷ M), short response time (within 10 s), high sensitivity (88.6 μA mM⁻¹ cm⁻²) and a good selectivity. The results were explained based on the ultrathin nature of the LBL films and the low operating potential that could be due to the efficient catalytic reduction of H₂O₂ by PB. In addition, the effects of pH, temperature and applied potential on the amperometric response of choline biosensor were evaluated. The apparent Michaelis-Menten constant was found to be (0.083 ± 0.001) ×10⁻³ M. The biosensor showed excellent long-term storage stability, which originates from a strong adsorption of ChOx in the EACC multilayer film. When the present choline biosensor was applied to the analysis of phosphatidylcholine in serum samples, the measurement values agreed satisfactorily with those by a hospital method.     

Crystal and solution structures of di-n-butyltin(IV) complexes of 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol and benzoic acid derivatives: En route to elegant self-assembly via modulation of the tin coordination geometry

Reactions of ⁿBu₂SnCl(L¹) (1), where L¹ = acid residue of 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol, with various substituted benzoic acids in refluxing toluene, in the presence of triethylamine, yielded dimeric mixed ligand di-n-butyltin(IV) complexes of composition [ⁿBu₂Sn(L¹)(L^2-6)]₂ where L² = benzene carboxylate (2), L³ = 2-[(E)-2-(2-hydroxy-5-methylphenyl)-1-diazenyl]benzoate (3), L⁴ = 5-[(E)-2-(4-methylphenyl)-1-diazenyl]-2-hydroxybenzoate (4), L⁵ = 2-{(E)-4-hydroxy-3-[(E)-4-chlorophenyliminomethyl]-phenyldiazenyl}benzoate (5) and L⁶ = 2-[(E)-(3-formyl-4-hydroxyphenyl)-diazenyl]benzoate (6). All complexes (1-6) have been characterized by elemental analyses, IR, ¹H, ¹³C and ¹¹⁷Sn NMR and ¹¹⁹Sn Mössbauer spectroscopy and their structures were determined by X-ray crystallography, complemented by ¹¹⁷Sn CP-MAS NMR spectroscopy studies in the solid state. The crystal structure of 1 reveals a distorted trigonal bipyramidal coordination geometry around the Sn-atom where the Cl- and N-atoms of ligand L¹ occupy the axial positions. In complexes 2-5, the molecules are centrosymmetric dimers in which the Sn-atoms are connected by asymmetric μ-O bridges through the quinoline O-atom to give an Sn₂O₂ core. The differences in the Sn-O bond lengths within the bridge range from 0.28 to 0.48 Å, with the longer of the Sn-O distances being in the range 2.56-2.68 Å and the most symmetrical bridge being in 5. The carboxylate group is almost symmetrically bidentate coordinated to the tin atom in 5 (Sn-O distances of 2.327(2) and 2.441(2) Å), unlike the other complexes in which the distance of the carboxylate carbonyl O-atom from the tin atom is in the range 2.92-3.03 Å. The structure of 5 displays a more regular pentagonal bipyramidal coordination geometry about each tin atom than in 2-4. In contrast, the centrosymmetric dimeric structure of 6 involves asymmetric carboxylate bridges, resulting in a different Sn₂C₂O₄ motif. The Sn-O bond lengths in the bridge differ by about 0.6 Å, with the longer distance involving the carboxylate carbonyl O-atom (2.683(2) and 2.798(2) Å for two molecules in the asymmetric unit). The carboxylate carbonyl O-atom has a second, even longer intramolecular contact to the Sn-atom to which the carboxylate group is primarily coordinated, with these Sn?O distances being as high as 3.085(2) and 2.898(2) Å. If the secondary interactions are considered, all the di-n-butyltin(IV) complexes (2-6) display a distorted pentagonal bipyramidal arrangement about each tin atom in which the n-butyl groups occupy the axial positions.     

New effective reagent [Cp2ZrH2 · ClAlEt2]2 for alkene hydrometallation

New bimetallic complex [Cp₂ZrH₂ · ClAlEt₂]₂ (1) was synthesized, and its reactivity in hydrometallation reaction with the following alkenes was studied: hept-1-ene, okt-1-ene, α-methylstyrene, (1S)-β-pinene, (+)-camphene. Complex 1 shows the highest reactivity among the other known Al,Zr-bimetallic complexes: [Cp₂ZrH₂ · ClAlBuⁱ₂]₂ (2), [Cp₂ZrH₂ · AlEt₃]₂ (3), [Cp₂ZrH₂ · AlBuⁱ₃]₂ (4) and [Cp₂ZrH₂ · HAlBuⁱ₂] (5) as well as organoaluminium compounds (OAC): ⁱBu₂AlH, ⁱBu₃Al and ⁱBu₂AlCl in presence of Zr catalysts. Chlorine containing complexes 1 and 2 appear to be more effective in alkene hydrometallation, and relative hydrometallation rates are (1S)-β-pinene ? (+)-camphene < α-methylstyrene < oct-1-ene < hept-1-ene. Hydrometallation of (1S)-β-pinene and its subsequent oxidation with I₂ run with high diastereoselectivity and yield trans-myrtanol. However, the diastereoselectivity of (+)-camphene hydrometallation is less than that for (1S)-β-pinene, and the reaction gives predominately endo-camphanol.     

Experimental and theoretical study of N-(2-hydroxyethyl)morpholine betaine

N-(2-hydroxyethyl)morpholine betaine (HEMB) has been characterized by a single crystal X-ray analysis, FTIR spectroscopy and DFT calculations. The crystals are monoclinic, space group P2₁/c with a=10.273(2), b=9.360(2), c=9.447(2) Å and β=104.72(3)Å. Two molecules of HEMB form a centrosymmetric dimer (X2) connected by a pair of hydrogen bonds between the CH₂CH₂OH and COO⁻ groups, with the O?O distance of 2.672(2) Å. The morpholine ring adopts a chair conformation with the CH₂CH₂OH group in the axial and the CH₂COO⁻ group in the equatorial position. The structures of the dimer, B2, and two monomers, B1a and B1b, have been optimized by the B3LYP approach using the 6-31G(d,p) basis set. The computed structure of B2, agrees well with the experimental X2. From two stable monomeric conformers the more favored is B1a, with the intramolecular hydrogen bond with the O-H?O distance of 2.566 Å. The effects of hydrogen bonding and electrostatic interactions on the conformation of the molecules investigated have been discussed. The FTIR spectrum shows a broad absorption in the 3300-2600 cm⁻¹ region, typical of moderate O-H?O hydrogen bonds.     

Mn(II)-sodium dodecyl sulphate complex mimic enzyme-catalyzed fluorescence quenching of Pyronine B by hydrogen peroxide

Mn(II)-sodium dodecyl sulphate complex (Mn(II)-SDS) is used to mimic the active group of peroxidase. The catalytic characteristic of this mimic enzyme catalyst in the oxidation reaction of fluorescence substrate, tetraethyldiaminoxanthyl chloride (Pyronine B (PB)), with hydrogen peroxide has been studied. The experimental results show that Mn(II)-SDS complex has similar catalytic activity that of peroxidase. The steady-state catalytic rate depends upon mimic enzyme and substrate concentrations, and the Michaelis-Menten parameters K_m, V_max and K_cat are 7.6×10⁻⁶ M, 7.9×10⁻⁷ M s⁻¹ and 7.9 s⁻¹, respectively. The catalytic activity of Mn(II)-SDS complex is compared with those of HRP and Hemin. Though the catalytic activity of Mn(II)-SDS complex is 15.9% of that of HRP, it can catalyze the oxidation reaction of PB with hydrogen peroxide lead to fluorescence quenching of PB. Under optimum conditions, linear relationship between fluorescence quenching F₀/F and concentration of H₂O₂ is in the range of (0.0-3.6) × 10⁻⁷ M. The detection limit is determined to be 3.0×10⁻⁹ M. By coupling this mimic catalytic reaction with the catalytic reaction of glucose oxidase (GOD), glucose can be detected. Linear relationship between F₀/F and concentration of glucose is in the range of (0.0-1.4) × 10⁻⁷ M. The detection limit is determined to be 4.2×10⁻⁹ M. This method is applied to the determination of glucose in human serum and the results are in good agreement with the phenol-4-aminoantipyrine (4-AAP).     

Dual-color upconversion fluorescence and aptamer-functionalized magnetic nanoparticles-based bioassay for the simultaneous detection of Salmonella Typhimurium and Staphylococcus aureus

A sensitive luminescent bioassay for the simultaneous detection of Salmonella Typhimurium and Staphylococcus aureus was developed using aptamer-conjugated magnetic nanoparticles (MNPs) for both recognition and concentration elements and using upconversion nanoparticles (UCNPs) as highly sensitive dual-color labels. The bioassay system was fabricated by immobilizing aptamer 1 and aptamer 2 onto the surface of MNPs, which were employed to capture and concentrate S. Typhimurium and S. aureus. NaY_0.78F₄:Yb_0.2,Tm_0.02 UCNPs modified aptamer 1 and NaY_0.28F₄:Yb_0.70,Er_0.02 UCNPs modified aptamer 2 further were bond onto the captured bacteria surface to form sandwich-type complexes. Under optimal conditions, the correlation between the concentration of S. Typhimurium and the luminescent signal was found to be linear within the range of 10¹–10⁵ cfu mL⁻¹ (R² = 0.9964), and the signal was in the range of 10¹–10⁵ cfu mL⁻¹ (R² = 0.9936) for S. aureus. The limits of detection of the developed method were found to be 5 and 8 cfu mL⁻¹ for S. Typhimurium and S. aureus, respectively. The ability of the bioassay to detect S. Typhimurium and S. aureus in real water samples was also investigated, and the results were compared to the experimental results from the plate-counting methods. Improved by the magnetic separation and concentration effect of MNPs, the high sensitivity of UCNPs, and the different emission lines of Yb/Er- and Yb/Tm-doped NaYF₄ UCNPs excited by a 980 nm laser, the present method performs with both high sensitivity and selectivity for the two different types of bacteria.     

Redox-active metal(II) complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c

The synthesis and physico-chemical characterization of Fe(II) and Mn(II) complexes of 4,6-di-tert-butyl-3[(2-hydroxyethyl)sulphanyl]-1,2-dihydroxybenzene (HL^I) and 2-amino-4,6-di-tert-butylphenol (HL^II) were carried out. Antibacterial activity of the Co(II), Fe(II) and Mn(II) complexes was evaluated in comparison with Cu(II) complexes and three common antibiotics; it was found to follow the order: (1) Сu(L^I)₂ > Сo(L^I)₂ > Fe(L^I)₂ ? Mn(L^I)₂ > HL^I; (2) Сu(L^II)₂ > Сo(L^II)₂ > HL^II > Fe(L^II)₂ ? Mn(L^II)₂; and their reducing ability (determined electrochemically) followed the same order. Spectrophotometric investigation was carried out in order to estimate the rate of the reduction of bovine heart сytochrome c with the ligands and their metal(II) complexes. NADPH:cytochrome P450-reductase was found to increase the rate of сytochrome c reduction with HL^I and HL^II ligands, while adrenodoxin in couple with NAD(P)H: adrenodoxin reductase had no substantial effect thereon. It was shown that the reduction of сytochrome c with these compounds cannot be related solely to the facility of their oxidation оr ionization.     

Sc(III) porphyrins. The molecular structure of two Sc(III) porphyrins and a re-evaluation of the parameters for the molecular mechanics modelling of Sc(III) porphyrins

The crystal structures of two new Sc(III) porphyrins, [Sc(TPP)Cl]·2.5(1-chloronaphthalene), (5,10,15,20-tetraphenylporphyrin)-chloro-scandium(III)·2.5(1-chloronaphthalene) solvate, (Mo Kα, 0.71073 Å, triclinic system  = 9.9530(2) Å, b = 15.4040(3) Å, c = 17.7770(3) Å, α = 86.5190(10)°, β = 89.7680(10)°, γ = 86.9720(10)°, 13101 independent reflections, R₁ = 0.0712) and the dimeric [μ₂-(OH)₂(Sc(TPP))₂], bis-(μ-hydroxo)-(5,10,15,20-tetraphenylporphyrin) scandium(III) (Mo Kα, 0.71073 Å, monoclinic system C2, a = 24.2555(16) Å, b = 11.1598(7) Å, c = 25.6468(17) Å, β = 91.980(2)°, 13084 independent reflections, R₁ = 0.0485) are reported. In [Sc(TPP)Cl] the metal is five-coordinate and the porphyrin is domed with the metal displaced by 0.63 Å from the mean porphyrin towards the axial Cl⁻ ligand. The average Sc-N bond length is 2.143(3) Å, which is shorter than the average bond length of previously reported structures. Two of the phenyl rings are nearly orthogonal to the porphyrin core and the other two are significantly tilted because of contacts with 1-chloronaphthalene solvent molecules, and the phenyl rings of neighbouring porphyrins. In [μ₂-(OH)₂(Sc(TPP))₂] both porphyrins are domed, with the metal displaced from the mean porphyrin plane towards the bridging hydroxo ligands. The average Sc-N bond length is 2.197(12) Å, which is in the upper range of Sc-N bond lengths in known Sc(III) porphyrins but not dissimilar to the average Sc-N bond lengths in another other bis-μ₂-hydroxo Sc(III) porphyrin, [μ₂-(OH)₂(Sc(OEP))₂]. One porphyrin is rotated relative to the upper porphyrin by 25° due to steric contacts between the phenyl substituents. We have used these new structures to re-evaluated our previously reported molecular mechanics force field parameters for modelling Sc(III) porphyrins using the MM2 force field; the training set was augmented from two to seven structures by using all available Sc(III) porphyrin structures and the two new structures. The modelling reproduces the porphyrin core very accurately; bond lengths are reproduced to within 0.01 Å, bond angles to within 0.5° and torsional angles to within 2°. The optimum parameters for modelling the Sc(III)-N bond lengths, determined by finding the minimum difference between the crystallographic and modelling mean bond lengths with the aid of artificial neural network architectures, were found to be 0.90 ± 0.03 mdyn Å⁻¹ for the bond force constant and2.005 ± 0.005 Å for the strain-free bond length. Modelling the seven Sc(III) porphyrins with the new parameters gives an average Sc-N bond length of 2.182 ± 0.018 Å, indistinguishable from the crystallographic mean of 2.181 ± 0.024 Å.     

Magnetic single-component molecular conductors exhibiting strong π-d interactions

Single-component molecular conductors [M(tmdt)₂] (tmdt = trimethylenetetrathiafulvalenedithiolate; M = Ni, Au, Pt, Cu), exhibit a variety of electromagnetic properties, which originate from the differences of the metal’s d-orbitals role in the band structure formation. The [Au(tmdt)₂] crystal undergoes an antiferromagnetic transition at 110 K, while maintaining a metallic state at lower temperatures. The Au analog has a high magnetic transition temperature as compared to traditional magnetic molecular conductors due to the strong three-dimensional (3-D) structure and the contribution of the metal d-orbitals. The single-component molecular conductor, [Cu(tmdt)₂], with π- and d-like frontier orbitals is isostructural with other metallic [M(tmdt)₂] systems (M = Ni, Pt, Au). The Cu(tmdt)₂ molecule is planar, which strikingly contrasts the tetrahedral coordination of Cu(dmdt)₂ (dmdt = dimethyltetrathiafulvalenedithiolate) with similarly extended TTF type ligands. Interestingly, unlike other [M(tmdt)₂] with metallic behavior, [Cu(tmdt)₂] shows semiconducting behavior at room temperature (σ(RT) = ∼7 S cm⁻¹). The RT conductivity increased linearly with increased pressure to 110 S cm⁻¹ at 15 kbar despite the compressed pellet sample. The magnetic susceptibility indicates one-dimensional (1-D) Heisenberg behavior with J = 117 cm⁻¹ and shows antiferromagnetic ordering at 13 K. The [Cu(tmdt)₂] is a new multi-frontier π-d system, which introduces a d(σ)-type frontier orbital around the Fermi level of the π-like metal bands.     

Label-free electrochemical impedance detection of kinase and phosphatase activities using carbon nanofiber nanoelectrode arrays

We demonstrate the feasibility of a label-free electrochemical method to detect the kinetics of phosphorylation and dephosphorylation of surface-attached peptides catalyzed by kinase and phosphatase, respectively. The peptides with a sequence specific to c-Src tyrosine kinase and protein tyrosine phosphatase 1B (PTP1B) were first validated with ELISA-based protein tyrosine kinase assay and then functionalized on vertically aligned carbon nanofiber (VACNF) nanoelectrode arrays (NEAs). Real-time electrochemical impedance spectroscopy (REIS) measurements showed reversible impedance changes upon the addition of c-Src kinase and PTP1B phosphatase. Only a small and unreliable impedance variation was observed during the peptide phosphorylation, but a large and fast impedance decrease was observed during the peptide dephosphorylation at different PTP1B concentrations. The REIS data of dephosphorylation displayed a well-defined exponential decay following the Michaelis–Menten heterogeneous enzymatic model with a specific constant, k_cat/K_m, of (2.1 ± 0.1) × 10⁷ M⁻¹ s⁻¹. Consistent values of the specific constant was measured at PTP1B concentration varying from 1.2 to 2.4 nM with the corresponding electrochemical signal decay constant varying from 38.5 to 19.1 s. This electrochemical method can be potentially used as a label-free method for profiling enzyme activities in fast reactions.     

Rapid determination of acetaminophen and p-aminophenol in pharmaceutical formulations using miniaturized capillary electrophoresis with amperometric detection

Capability of fast analysis of a novel miniaturized capillary electrophoresis with carbon disk electrode amperometric detection (mini-CE-AD) system was demonstrated by determining acetaminophen and p-aminophenol in dosage forms. Factors influencing the separation and detection processes were examined and optimized. Under the optimum conditions, the end-capillary 300 μm carbon disc electrode amperometric detector offered favorable signal-to-noise characteristics at a relatively low potential (+600 mV versus Ag/AgCl) for detecting acetaminophen and p-aminophenol. Two analytes can been separated within 150 s in a 8.5 cm length capillary at a separation voltage of 2000 V using a Na₂B₄O₇-KH₂PO₄ running buffer (pH 7.2). Acetaminophen and p-aminophenol could be detected down to the 1.4 × 10⁻⁶-5.9 × 10⁻⁷ mol L⁻¹ level with linearity up to the 1.0 × 10⁻³ mol L⁻¹ level examined. The inter-day repeatability for analytes in peak current (R.S.D. ≤ 2.3%) and migration times (R.S.D. ≤ 1.3%) were excellent. The proposed mini-CE-AD system should find a wide range of analytical applications in pharmaceutical formulations as an alternative to conventional CE and μ-CE.