Geometric analysis of a two-body problem with quick loss of mass

Nonlinear Dynamics - We consider a two-body problem with quick loss of mass which was formulated by Verhulst (Verhulst in J Inst Math Appl 18: 87–98, 1976). The corresponding dynamical system...     

New coordination modes of iminodiacetamide type ligands in palladium(II) complexes: crystallographic and DFT studies

The reactions of N-alkyliminodiacetamide derivatives, namely N-ethyliminodiacetamide (CH₃CH₂N(CH₂CONH₂)₂; Etimda) and N-isopropyliminodiacetamide (CH₃)₂CHN(CH₂CONH₂)₂; i-Primda), with sodium tetrachloropalladate(II) in aqueous solutions were investigated. Three new palladium(II) complexes, [Pd(Etimda_?H)₂]?2H₂O (1), [Pd(i-Primda_?H)₂]?2H₂O (2) and [PdCl₂(i-Primda)] (3), were obtained and characterized by X-ray structural analysis, infrared spectroscopy and thermal analysis (TGA). The square planar coordination environments around the palladium(II) ions in complexes 1 and 2 consist of two N,N′-bidentate N-alkyliminodiacetamidato ligands, with imino N atoms in trans-position. The complex 3 also exhibits a square planar coordination environment around Pd(II), but with two chloride ions and one neutral N-isopropyliminodiacetamide ligand bound in an N,O′-bidentate coordination mode. The described coordination modes, as well as the presence of deprotonated amide groups in ligands in 1 and 2, are found for the first time in palladium(II) complexes with iminodiacetamide type ligands. The molecular geometries and infrared spectra of these three complexes were also modelled using DFT calculations, at the BP86-D3/def2-TZVPP/PCM level of theory. The RMSD values suggest a good agreement of the calculated and experimental geometries. A QTAIM analysis suggests a qualitative correlation between bond lengths and energy densities, also supported by an NBO analysis. The dimer interaction energy between complex units was estimated at about ?15 kcal/mol for all complexes.     

Proton exit channels in bovine cytochrome c oxidase

Cytochrome c oxidase (CcO) is the terminal transmembrane enzyme of the respiratory electron transport chain in aerobic cells. It catalyzes the reduction of oxygen to water and utilizes the free energy of the reduction reaction for proton pumping, a process which results in a membrane electrochemical proton gradient. Although the structure of the enzyme has been solved for several organisms, the molecular mechanism of proton pumping and proton exit pathways remain unknown. In our previous work, the continuum electrostatic calculations were employed to evaluate the electrostatic potential, energies, and protonation state of bovine cytochrome c oxidase for different redox states of the enzyme. A possible mechanism of oxygen reduction and proton pumping via His291 was proposed. In this paper, using electrostatic calculations, we examine the proton exit pathways in the enzyme. By monitoring the changes of the protonation states, proton affinities, and energies of electrostatic interactions between the titratable groups in different redox states of CcO, we identified the clusters of strongly interacting residues. Using these data, we detected four possible proton exit points on the periplasmic side of the membrane (Lys171B/Asp173B, His24B/Asp25B, Asp51, and Asp300). We then were able to trace the proton exit pathways and to evaluate the energy profiles along the paths. On the basis of energetic considerations and the conservation of the residues in a protein sequence, the most likely exit pathway is one via the Lys171B/Asp173B site. The obtained results are fully consistent with our His291 model of proton pumping, and provide a rationale for the absence of proton leaking in CcO between the pumping strokes.     

1:1 and 1:2 Complexes of Mercury(II) Halides with 1,3-Thiazolidine-2-thione. Spectral, Thermal, and Crystal Structure Studies

The series of compounds of the general formulae HgX₂(tzdtH) and HgX₂(tzdtH)₂ (X = Cl, Br, I; tzdtH = 1,3-thiazolidine-2-thione) have been prepared, as well as Hg(tzdt)₂. IR, ¹H, and ¹³C NMR spectral data of the complexes indicate thione donation, which is confirmed by the crystal structure analyses of [HgBr₂(tzdtH)]₂, [HgI₂(tzdtH)]₂, and HgI₂(tzdtH)₂. The structures of [HgBr₂(tzdtH)]₂ and [HgI₂(tzdtH)]₂ consist of centrosymmetric doubly bridged dimers, but they are not isostructural. The asymmetry in the HgX₂Hg bridge is more pronounced in the bromo than in the iodo derivative [S–Hg–X(terminal) is 138.19(9)° for X = Br and 123.49(10)° for X = I], which is accompanied by the stronger Hg–S covalent bond in the bromo than in the iodo complex [2.435(4) vs. 2.510(3) Å]. The Hg–X(bridging) (X = Br, I) bond distances are shorter than the sum of van der Waals radii for mercury and X. Dimeric centrosymmetric complex units are held together only by van der Waals forces in [HgI₂(tzdtH)]₂, while in [HgBr₂(tzdtH)]₂ there is an intramolecular hydrogen bond of N–H Br type (3.34(1) Å). HgI₂(tzdtH)₂ exists as a mononuclear tetrahedral complex with two long Hg–S [2.672(1) Å] and two short Hg–I bond distances [2.688(1) Å] related by a twofold axis. The molecules of HgI₂(tzdtH)₂ are linked into infinite chains along the c axis by intermolecular N–H S [3.38(1) Å] hydrogen bonds.     

catena-Poly­[[(2-methyl-1,3-benzo­thia­zole-N)­mercury(II)]-di-μ-chloro]

The reaction of 2-methyl-1,3-benzo­thia­zole (mebta) with mercury(II) chloride in methanol in a 1:1 molar ratio resulted in the formation of single crystals of the title compound, [HgCl₂(C₈H₇NS)]_n. The mol­ecules exist as continuous chlorine-bridged chains in which Hg atoms lie in distorted trigonal bipyramidal environments. The equatorial positions are occupied by an N atom from the ligand [2.236 (8) Å] and two Cl atoms [2.428 (3) and 2.459 (3) Å]. The two axial Hg—Cl contacts to two neighbouring mol­ecules [2.874 (3) and 2.964 (3) Å] are significantly shorter than the sum of the respective van der Waals radii, and form close to linear Cl—Hg—Cl sequences [177.80 (7)°].     

Modification of surface morphology and lattice order in nanocrystalline ZnO thin films prepared by spin-coating sol–gel method

Journal of Sol-Gel Science and Technology - Halloysite Nanotubes (HNTs) with large surface/volume ratio and rich reactive groups are incorporated into Fe-based MOF aerogel to develop MOF(Fe)/HNTs...     

Factorial Design in Optimization of Chromatographic Separation of Ramipril and Its Impurities

In this paper optimization of chromatographic retention of ramipril and its five impurities employing factorial design is presented. On the basis of preliminary experiments three factors were chosen as inputs (acetonitrile content, pH of the mobile phase and buffer concentration) and retention factor as output. As optimal full factorial design 2³ was chosen, factors were examined at two different levels “low” and “high”. Three replications at zero level were added in order to check linearity and complete statistical tests. Relationship between inputs and output is presented in form of second order interaction model. Adequacy of model was explained using analysis of variance. After analysis of results optimal chromatographic conditions were set. Separations were conducted on a C₁₈ column with a mixture of acetonitrile and water phase (TEA in potassium dihydrogen phosphate) in ratio 23:77 v/v. Finally, the LC method was validated and applied for quality control analysis of commercially available tablets. The proposed method is simpler and faster as compared to existing official methods and therefore more adequate for routine control of ramipril during shelf life. Also a general approach which includes factorial design in method optimization offers a possibility for predicting and following the chromatographic behavior of such complex mixtures.     

Promotional effect of Snad on the ethanol oxidation at Pt3Sn/C catalyst

Oxidation of ethanol was studied at Sn_ad modified and unmodified Pt₃Sn/C and Pt/C catalysts. Pt₃Sn/C and Pt/C catalysts were characterized by XRD. Potentiodynamic and chronoamperometric measurements were used to establish catalytic activity and stability. High activity achieved at Sn_ad modified Pt₃Sn/C catalyst has not been observed at any bimetallic catalyst so far. Promotional effect of Sn_ad on the ethanol oxidation was related to the enhancement of CO oxidation rate in bifunctional mechanism. It was shown that electrodeposited Sn exhibited different effect on the catalytic activity compared to Sn in alloy.