Effect of sol-gel confinement on the structural dynamics of the enzyme bovine Cu,Zn superoxide dismutase

Immobilization of proteins in sol-gel glasses has allowed the development of a new generation of robust and sensitive analytical devices as well as contributes to the investigation of the effect of molecular confinement on the structure of proteins. The immobilized protein usually preserves its structural integrity and functionality, while interactions with the matrix and its surface seem to contribute to alter its dynamics and stability. With the aim of better understanding the nature of such interactions, we have encapsulated the enzyme bovine Cu,Zn superoxide dismutase (BSOD), negatively charged at physiological pH, in a sol-gel matrix and the photophysical properties of its single tyrosine have been determined using both steady-state and time-resolved fluorescence techniques. Fluorescence spectra, quenching experiments, fluorescence lifetimes, and anisotropy measurements indicate that immobilization does not lead to any major conformational change, at least in the region of protein where the tyrosine residue is located. In addition, fluorescence anisotropy decays recorded above and below the isoelectric point of the protein indicate that, at neutral pH, well above its isoelectric point, the entrapped BSOD freely rotates within the matrix pore, but showing a different rotational behavior as compared with that in the bulk aqueous solution. However, below the isoelectric point, the global motion of the protein is totally hindered upon entrapment. Electrostatic interactions with the gel matrix, changes in water viscosity, and protein-to-pore size ratio are discussed as possible factors responsible for this behavior.     

Hartogs Extension Theorem for Functions with Values in Complex Clifford Algebras

A regular extension phenomenon of functions defined on Euclidean space with values in a Clifford algebra was studied by Le Hung Son in the 90’s using methods of Clifford analysis, a function theory which, is centred around the notion of a monogenic function, i.e. a null solution of the firstorder, vector-valued Dirac operator in . The isotonic Clifford analysis is a refinement of the latter, which arises for even dimension. As such it also may be regarded as an elegant generalization to complex Clifford algebra-valued functions of both holomorphic functions of several complex variables and two-sided biregular function theories. The aim of this article is to present a Hartogs theorem on isotonic extendability of functions on a suitable domain of . As an application, the extension problem for holomorphic functions and so for the two-sided biregular ones is discussed.      

Correspondence of Ru(III) Ru(II) and Ru(IV) Ru(III) mixed valent states in a small dinuclear complex

The diruthenium(III) compound [(μ-oxa){Ru(acac)(2)}(2)] [1, oxa(2-) =oxamidato(2-), acac(-) =2,4-pentanedionato] exhibits an S=1 ground state with antiferromagnetic spin-spin coupling (J=-40 cm(-1)). The molecular structure in the crystal of 1?2 C(7)H(8) revealed an intramolecular metal-metal distance of 5.433 ? and a notable asymmetry within the bridging ligand. Cyclic voltammetry and spectroelectrochemistry (EPR, UV/Vis/NIR) of the two-step reduction and of the two-step oxidation (irreversible second step) produced monocation and monoanion intermediates (K(c) =10(5.9)) with broad NIR absorption bands (ε ca. 2000 M(-1)cm(-1)) and maxima at 1800 (1(-)) and 1500 nm (1(+)). TD-DFT calculations support a Ru(III)Ru(II) formulation for 1(-) with a doublet ground state. The 1(+) ion (Ru(IV)Ru(III)) was calculated with an S=3/2 ground state and the doublet state higher in energy (ΔE=694.6 cm(-1)). The Mulliken spin density calculations showed little participation of the ligand bridge in the spin accommodation for all paramagnetic species [(μ-oxa){Ru(acac)(2)}(2)](n), n=+1, 0, -1, and, accordingly, the NIR absorptions were identified as metal-to-metal (intervalence) charge transfers. Whereas only one such NIR band was observed for the Ru(III)Ru(II) (4d(5)/4d(6)) system 1(-), the Ru(IV)Ru(III) (4d(4)/4d(5)) form 1(+) exhibited extended absorbance over the UV/Vis/NIR range.     

Synthesis and structural characterization of diorganotin dithiocarbamates from 4‐(ethylaminomethyl)pyridine

Three 4‐(ethylaminodithiocarbamate) methylpyridine diorganotin derivatives were prepared using a one‐pot synthetic procedure from 4‐(ethylaminomethyl)pyridine, carbon disulfide, KOH as a base, and the corresponding diorganotin dichloride (R = Me, nBu, Ph). All three compounds were successfully characterized in solution (¹H, ¹³C, and ¹¹⁹Sn NMR) as well as in the solid state (IR, mass spectrometry, and X‐ray diffraction). In all three cases, an anisobidentate coordination mode was observed for the dithiocarbamate moiety to the tin atom, evidenced mainly by the different Sn S bond distances obtained from the X‐ray diffraction analysis. The organic groups attached to the tin atom have no influence on the reaction course, leading in each case to the formation of mononuclear complexes with the metal center in a hexacoordinated environment. Interestingly, in the solid state the methyl‐tin derivative showed Pyċn and SċSn intermolecular interactions, which were not observed in the two other complexes. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:422–428, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21032     

Obstructing extensions of the functor spec to noncommutative rings

This paper concerns contravariant functors from the category of rings to the category of sets whose restriction to the full subcategory of commutative rings is isomorphic to the prime spectrum functor Spec. The main result reveals a common characteristic of these functors: every such functor assigns the empty set to $\mathbb{M}_n (\mathbb{C})$ for n ? 3. The proof relies, in part, on the Kochen-Specker Theorem of quantum mechanics. The analogous result for noncommutative extensions of the Gel’fand spectrum functor for C*-algebras is also proved.     

Relation between single neuron and population spiking statistics and effects on network activity

To simplify theoretical analyses of neural networks, individual neurons are often modeled as Poisson processes. An implicit assumption is that even if the spiking activity of each neuron is non-Poissonian, the composite activity obtained by summing many spike trains limits to a Poisson process. Here, we show analytically and through simulations that this assumption is invalid. Moreover, we show with Fokker-Planck equations that the behavior of feedforward networks is reproduced accurately only if the tendency of neurons to fire periodically is incorporated by using colored noise whose autocorrelation has a negative component.     

Electrically controlled reflection and transmission of obliquely incident light by structurally chiral materials

The solution of a boundary-value problem for the reflection and transmission of obliquely incident plane waves due to a slab of a structurally chiral material (SCM) displaying the Pockels effect with a point group symmetry indicates the enhancement of circular Bragg phenomenon by the application of a dc voltage. The enhancement suggests that thinner SCMs can be used as devices such as polarization-rejection filters if the Pockels effect is exploited, for both normally and obliquely incident light.     

Simultaneous determination of tetracyclines in pharmaceuticals by CZE using experimental design

An optimized capillary zone electrophoresis (CZE) method for the analysis of tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC) and doxycycline (DXC) is described. Using fused-silica capillaries, the influence of the electrolyte composition, pH and concentration, as well as temperature and applied voltage were investigated. A factorial and central composite design was performed to optimize the method in a simple way. The optimal separation conditions were 50 mmol L⁻¹ sodium carbonate + 1 mmol L⁻¹ EDTA, pH 10; voltage 13 kV and temperature 23 °C. The method was validated for TC determination in pharmaceuticals through the following performance criteria: linearity and linear range, sensitivity, selectivity, intra-assay and inter-assay precision, detectability, accuracy and ruggedness. In comparison with the recommended HPLC method in the United States Pharmacopeia, this CZE-method exhibited the same performance as the official method, with the advantage that the same method could be used for the simultaneous determination of the different tetracyclines in pharmaceutical formulations.     

Controlling the electronic density of the [Ru2(DPhF)3(O2CR)] core to obtain one-dimensional compounds

The substitution of the acetate ligand in [Ru₂Cl(DPhF)₃(O₂CMe)] (DPhF⁻ = N,N′-diphenylformamidinate) by the pentafluorobenzoate group gives the complex [Ru₂Cl(DPhF)₃(O₂CC₆F₅)(OH₂)] (1), and the reaction of 1 with AgSO₃CF₃ leads to the compound [Ru₂(DPhF)₃(O₂CC₆F₅)(OH₂)₂]SO₃CF₃ (2). The low donor character of the pentafluorobenzoate ligand compared to the acetate group decreases the electron density of the Ru₂⁵⁺ unit which permits ligands to bond at both axial positions of the diruthenium moiety. The use of the [Au(CN)₂]⁻ group yields the new complex {[Ru₂(DPhF)₃(O₂CC₆F₅)][Au(CN)₂]} (3). Complexes 1–3 are characterized by elemental analysis, ¹⁹F{¹H} NMR, IR and electronic spectroscopy, mass spectrometry and variable-temperature magnetic measurements. The crystal structure of 2·H₂O is also reported. The magnetic properties of complex 1 is in accordance with the ground-state configuration σ²π⁴δ²(π*δ*)³. In contrast, the slope of representation of the magnetic moment towards temperature in complex 2 indicates a gradual transition from essentially high spin (S = 3/2) to low spin (S = 1/2) configuration.