Sulfur K-edge XAS and DFT studies on NiII complexes with oxidized thiolate ligands: implications for the roles of oxidized thiolates in the active sites of Fe and Co nitrile hydratase

S K-edge X-ray absorption spectroscopy data on a series of NiII complexes with thiolate (RS-) and oxidized thiolate (RSO2-) ligands are used to quantify Ni-S bond covalency and its change upon ligand oxidation. Analyses of these results using geometry-optimized density functional theory (DFT) calculations suggest that the Ni-S sigma bonds do not weaken on ligand oxidation. Molecular orbital analysis indicates that these oxidized thiolate ligands use filled high-lying S-O pi* orbitals for strong sigma donation. However, the RSO2- ligands are poor pi donors, as the orbital required for pi interaction is used in the S-O sigma-bond formation. The oxidation of the thiolate reduces the repulsion between electrons in the filled Ni t2 orbital and the thiolate out-of-plane pi-donor orbital leading to shorter Ni-S bond length relative to that of the thiolate donor. The insights obtained from these results are relevant to the active sites of Fe- and Co-type nitrile hydratases (Nhase) that also have oxidized thiolate ligands. DFT calculations on models of the active site indicate that whereas the oxidation of these thiolates has a major effect in the axial ligand-binding affinity of the Fe-type Nhase (where there is both sigma and pi donation from the S ligands), it has only a limited effect on the sixth-ligand-binding affinity of the Co-type Nhases (where there is only sigma donation). These oxidized residues may also play a role in substrate binding and proton shuttling at the active site.     

(e,2e) Spectroscopy of methane

Measurements are reported on the spectroscopy of methane using the symmetric (e,2e) technique at energies of 600 eV and 1200 eV. The angular correlations of the states with separation energies of 14.2 and 23.1 eV have been measured and compared with the orbital wavefunctions of Snyder and Basch and with some earlier data at 400eV. The angular correlation of the configuration interaction state at 31 eV shows that this state definetely results from the removal of an electron in the 2a₁ orbital. Other structure at high separation energy is also identified with this orbital. Relative strengths of the It₂ and 2a₁ states are compared and found to be in agreement with the theory at 1200eV.     

The adiabatic‐to‐diabatic transformation angle and the berry phase for coupled jahn–teller/renner–teller systems: The F + H2 as a case study

The approach to calculate improved, two‐state, adiabatic‐to‐diabatic transformation angles (also known as mixing angles), presented before (see Das et al., J Chem Phys 2010, 133, 084107), was used here while studying the F + H₂ system. However, this study is characterized by two new features: (a) it is the first of its kind in which is studied the interplay between Renner–Teller (RT) and Jahn–Teller (JT) nonadiabatic coupling terms (NACT); (b) it is the first of its kind in which is reported the effect of an upper singular RT‐NACT on a lower two‐state (JT) mixing angle. The fact that the upper NACT is singular (it is shown to be a quasi‐Dirac δ‐function) enables a semi‐analytical solution for this perturbed mixing angle. The present treatment, performed for the F + H₂ system, revealed the existence of a novel parameter, η, the Jahn–Renner coupling parameter (JRCP), which yields, in an unambiguous way, the right intensity of the RT coupling (as resembled, in this case, by the quasi‐Dirac δ‐function) responsible for the fact that the final end‐of‐the contour angle (identified with the Berry phase) is properly quantized. This study implies that the numerical value of this parameter is a pure number (independent of the molecular system): η = $ 2\sqrt 2 /\pi $ (= 0.9003) and that there is a good possibility that this value is a novel characteristic molecular constant for a certain class of tri‐atomic systems. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Bioleaching of Nickel and Cobalt from Lateritic Chromite Overburden Using the Culture Filtrate of Aspergillus niger

Extraction of metals (Ni, Co) from chromite overburden of Sukinda mines of Orissa, India, with the culture filtrate of Aspergillus niger was studied. Results showed that the amounts of metals leached varied directly with reaction temperature and period of fermentation. The culture filtrate was analyzed for citric and oxalic acids, and contained only oxalic acid—the concentration of which increased with time. Although this acid played the major role in leaching of metals, other unidentified metabolites present in the culture filtrate influenced the dissolution of the metals significantly. Maximum recovery of metals from raw and roasted ore samples was achieved at 80 °C with the 21-day culture filtrate containing the highest amount of oxalic acid. Under identical experimental conditions, much higher amounts of the metals were leached from roasted ore. Microstructures of the ore particles were studied by scanning electron microscopy and transmission electron microscopy; the bonding behaviors of metal compounds were identified by Fourier transform infrared spectroscopy which showed that the metals were leached after chelation with oxalic acid.     

Intra-annular cyclophane diamines as proton sponges: a computational study

Gas-phase proton affinities of cyclophanes containing intra-annular amino groups were calculated using density functional theory (DFT) at the B3LYP/6-31+G^∗∗//B3LYP/6-31G^∗ level. They are higher in magnitude as those for proton sponges such as 1,8-bisaminonaphthalene, however, they are slightly weaker bases than 1,8-bis(dimethylamino)naphthalene. The high basicity of the cyclophane diamines is attributed mainly to their structural flexibility, which allows them to maximize the hydrogen bond strength in the cations by achieving N-H?N linearity, while strain relief upon protonation is less important. Another contributing factor is the stabilizing interaction of the added proton with adjacent phenyl π systems of the cyclophanes. Barriers for proton transfer between the nitrogen atoms of the diamine cations are also reported.     

Optimal non-linear dimension reduction scheme for classical molecular dynamics

The optimal creation of a reduced space that effectively captures the long timescale dynamics of a non-linear molecular system over a range of frequencies is described. The technique builds on a previously developed subspace method based on linear constant projective transformation of the original full space. The present work attempts to propose transformation that are spatially dependent thereby leading to an effective subspace for better representing the dynamics of interests. The algorithm seeks out an optimal transformation consistent with desired low frequency motion in a rather general way. The method is demonstrated for a six-dimensional nonlinear system reduced to two-dimensions. Superior performance is found in evaluating ensemble-averaged classical dynamical properties.     

Partial Molar Volumes and Partial Molar Adiabatic Compressibilities of Fe(III) Tetrafluoroborate Complexes with DMSO, Pyridine, and Pyridine Derivatives

The apparent and limiting apparent molar volumes of dilute aqueous solutions of KBF₄, and the complexes [Fe(DMSO)₆](BF₄)₃, [Fe(Py)₄(H₂O)₂](BF₄)₃, [Fe(4-Mepy)₂(H₂O)₂](BF₄)₃, and [Fe(4-Etpy)₂(H₂O)₂](BF₄)₃ were determined from density data measured at 5, 15, and 25°C. The apparent and limiting apparent molar adiabatic compressibilities of these complexes were determined from ultrasonic sound velocities measured at the same temperatures in dilute aqueous solutions. The volume change associated with complex formation is discussed in terms of the nature of the coordinate bond and also the role of the central metal atom and ligands in the solvation behavior of these complexes.     

Catalysis by ionic liquid: a simple, green and efficient procedure for the Michael addition of thiols and thiophosphate to conjugated alkenes in ionic liquid, [pmIm]Br

A room temperature ionic liquid, 1-pentyl-3-methylimidazolium bromide, [pmIm]Br efficiently catalyzes Michael addition of thiols and diethyl dithiophosphate to a variety of conjugated alkenes such as α,β-unsaturated carbonyl compounds, carboxylic esters, nitriles and chalcones without requiring any other organic solvent and catalyst. The ionic liquid can be recycled for subsequent reactions without any appreciable loss of efficiency.     

Kinematical separation of α-n final-state interaction at 50 MeV incident energy

A kinematically complete experiment has been performed to study the α-n final-state interaction (FSI) in the α + d ↦α + p + n break-up reaction at 50 MeV incident energy for the alpha-particles. For this, we have chosen four pairs of correlation angles for the outgoing alpha and protons. These are ( θ_α = 18^°, θ_p = 42^°), ( θ_α = 20^°, θ_p = 45^°), ( θ_α = 22^°, θ_p = 42^°) and ( θ_α = 22^°, θ_p = 47^°), selected kinematically where the allowed phase spaces are in favor of the α-n final-state interaction. Our experimental data show strong α-n FSI in all the selected configurations. Also, the FSI is found to be stronger at the lower alpha-particle energy when two FSI peaks appear in the same configuration. Received: 17 June 2002 / Accepted: 3 October 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: dey_s2001@yahoo.com; Present address: 445 Waupelani Drive, Apt. F3, State College, PA 16801, USA. Communicated by M. Gar?on     

Ultrafast photoinduced electron transfer in the micelle and the gel phase of a PEO-PPO-PEO triblock copolymer

Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to coumarin dyes is studied in the micelle and the gel phase of a triblock copolymer, (PEO)(20)-(PPO)(70)-(PEO)(20) (Pluronic P123) by picosecond and femtosecond emission spectroscopies. The rate of PET in a P123 micelle and gel is found to be nonexponential and faster than the slow components of solvation dynamics. In a P123 micelle and gel, PET occurs on multiple time scales ranging from a subpicosecond time scale to a few nanoseconds. In the gel phase, the highest rate constant (9.3 x 10(9) M(-1) s(-1)) of ET for C152 is about two times higher than that (3.8 x 10(9) M(-1) s(-1)) observed in micelle phase. The ultrafast components of electron transfer (ET) exhibits a bell shaped dependence with the free energy change which is similar to the Marcus inversion. Possible reasons for slower PET in P123 micelle compared to other micelles and relative to P123 gel are discussed.