Origin of the dynamic transition upon pressurization of crystalline proteins

We study the role of hydration water in the dynamic transition of low-hydrated proteins upon pressurization found recently (Meinhold, L.; Smith, J. C. Phys. Rev. E 2005, 72, 061908). Clustering and percolation of water in the hydration shells of protein molecules in crystalline Staphylococcal nuclease are analyzed at various pressures. The number of water molecules in the hydration shell increases and the hydrogen-bonded network of hydration water spans with increasing pressure. The dynamic transition of protein occurs when the spanning water network exists with the probability of about 50% and hydration water shows large density fluctuations. Formation of a spanning water network upon pressurization promotes protein dynamics as in the case of the dynamic transition with increasing hydration. Properties of hydration water in various thermodynamic states and their influence on biological function are discussed.     

Oscillation and nonoscillation of nonlinear second order difference equations

In this paper, we study oscillation and nonoscillation behaviour of the second order nonlinear difference equations of the form $$\Delta (r_n \psi (x_n )\Delta x_n ) + q_{n + 1} f(x_{n + 1} ) = 0, n \in N(n_o ),$$ and $$\Delta (r_n \psi (x_n )\Delta x_n ) + q_n f(n,x_n ) = 0, n \in N(n_o ),$$ whereN(n _o ) =n _o ,n _o + 1, …, (n _o is a fixed nonnegative integer number), Δx_n =x _n +1?x _n is the forward difference operator,x :N(n _o ) → ?,r :N(n _o ) → (0, ∞), Ψ : ? → (0, ∞),f is a real valued continuous function, andq _n is a sequence of real valued.     

Design of extractive distillation process with mixed entrainer

The separation of two systems containing minimum boiling azeotropes (acetone—methanol and tetrahydrofuran (THF)—water) was performed using extractive distillation with a heavy boiling mixed entrainer consisting of two compounds. The entrainer constituents did not form new azeotropes with each other and with the components of the original mixture. An analysis of the mixed entrainer influence on the vapor-liquid equilibrium (VLE) and relative volatility provides an understanding of the cases in which the separation by extractive distillation (ED) in the presence of the mixed entrainer revealed energy benefits over their individual constituents. New results for application of the mixed entrainer monoethanolamine (MEA)—ethylene glycol (EG) and dimethyl-sulphoxide (DMSO)—glycerol for the separation of THF—water and acetone—methanol, respectively, are presented for the first time. The individual selective agents were chosen from the efficient entrainers discussed in the literature. The calculations were performed using the platform Aspen Plus 7.3. Different extractive distillation flowsheets are provided for the zeotropic mixed agents, viz. with two or three columns. For the ED of the binary mixtures investigated, the structures of the different separation schemes, the operating parameters of the columns, and the energy consumptions are presented and compared. The application of the mixed entrainer MEA—EG fed into the ED column with pre-mixing can be recommended, providing up to 1.7 % of energy saving for acetone—methanol separation. In the case of THF—water, the mixed entrainer DMSO—glycerol provides 0.8 % of energy saving. The separate inputs of the individual constituents of the mixed entrainer led to a significant increase in the energy consumptions of the flowsheet because of the third regeneration column, hence this flowsheet cannot be recommended for use in the separation of both mixtures.     

Synthesis and multiparameter sensor properties of the crown‐containing thiophene derivatives

A novel ditopic receptor was constructed as a combination of bisthiophene with pyridinylvinyl and crown‐containing styryl fragments. In the receptor, the pyridine residue was able to coordinate Fe²⁺, Cd²⁺, and Mg²⁺ metal cations, whereas the oxocrown ether moiety bound with the alkaline earth metal (Mg²⁺, Ca²⁺, and Ba²⁺) cations. ¹H NMR, optical, electrochemical, and ESI‐MS results provided conclusive evidence of a complex formation through both the coordination centers of the molecule. The obtained results showed that cation complexation induces optical and electrochemical changes, particularly for each binding center. This type of multiparameter sensor provides interesting perspectives for the future design of unique sensors, promising different analytical techniques. Copyright © 2009 John Wiley & Sons, Ltd.     

Properties of spanning water networks at protein surfaces

The formation of a spanning two-dimensional hydrogen-bonded water network at the surface of proteins via a percolation transition enables their biological function. We show in detail how the spanning (percolating) water network appears at the surfaces of model hydrophilic spheres and at the surface of a single protein (lysozyme) molecule. We have found essential correlations of the linear extension, radius of gyration, and position of the center of mass of the largest water cluster with its size. The specific two-peak structure of the probability distribution of the largest cluster size allowed us to study various properties separately for spanning and nonspanning largest clusters. The radius of gyration of the spanning cluster always exceeds the radii of the spheres or the effective radius of the protein. Any spanning cluster envelops essentially more than half of the surface area. The temporal decay of the spanning networks shows a stretched exponential character. Their average lifetime at the percolation threshold is about the lifetime of a water-water hydrogen bond.     

Synthesis and characterization of polyamides obtained from tartaric acid and L-lysine

Two sets of AA · BB-type polyamides (PLyTA) were synthesized from natural compounds L-lysine and D- or L-tartaric acid via the active ester polycondensation method. The carboxyl and hydroxyl side groups were orthogonally protected as methyl ester and methyl ether, respectively. Direct reaction of methyl L-lysinate dihydrochloride with bis(pentachlorophenyl) di-O-methyl tartaric acid led to the aregic polyamide ar-PLyTA, whereas isoregic (ir-PLyTA) and syndioregic (sr-PLyTA) polyamides were obtained by polycondensation of specifically designed amide–aminoacid and amide–diamine monomeric precursors, respectively. These polyamides have intrinsic viscosities in the 0.50–0.76 dl g⁻¹ range, display optical activity, and are readily soluble in chloroform. They start to decompose well above 200 °C and display glass-transition temperatures at 100–105 °C. DSC and X-ray diffraction results indicated that these polyamides are not crystalline but they seem to adopt a partially ordered phase. No differences in properties other than optical rotation were observed between PLyTA made of D- and L-tartaric acid.     

How polar are ionic liquids? Determination of the static dielectric constant of an imidazolium-based ionic liquid by microwave dielectric spectroscopy

In a pilot study of the dielectric constant of room-temperature ionic liquids, we use dielectric spectroscopy in the megahertz/gigahertz regime to determine the complex dielectric function of five 1-alkyl-3-methylimidazolium salts, from which the static dielectric constant epsilon is obtained by zero-frequency extrapolation. The results classify the salts as moderately polar solvents. The observed epsilon-values at 298.15 K fall between 15.2 and 8.8, and epsilon decreases with increasing chain length of the alkyl residue of the cation. The anion sequence is trifluoromethylsulfonate > tetrafluoroborate approximately tetrafluorophosphate. The results indicate markedly lower polarities than found by spectroscopy with polarity-sensitive solvatochromic dyes.     

Determination of citrate in tablets and of oxytetracycline in serum using europium (III) luminescence

A direct method for the determination of citrate and oxytetracycline in samples containing complex matrices like tablets or serum has been developed using the luminescence of the ternary complex formed with Eu(III) ions. The triplet-state energy level of oxytetracycline (OxTc), the excitation maximum (412 nm) and the luminescence lifetime of Eu-OxTc (58 μs) were determined. A 17-fold luminescence enhancement at 615 nm occurs upon addition of citrate within a short 5-min incubation time at neutral pH. This is accompanied by a threefold increase of the luminescence decay time. The optimal conditions for determination of OxTc are equal concentrations of Eu (III) and citrate (C = 1 · 10^− 4 mol L^− 1) and pH 7.2. For determination of citrate, the optimal concentrations of Eu(III) and OxTc are 1 : 0.5 (C_Eu = 1 · 10^− 4 mol L^− 1, C_OxTc = 5 · 10^− 5 mol L^− 1) at pH 7.2. The linear range for determination of OxTc in serum is 0.25-250 μg mL^− 1, and for citrate in tablets from 0.5 to 10.0 μg mL^− 1 (2.3 · 10^− 6- 4 · 10^− 5 mol L^− 1). The detection limit was 0.1 μg mL^− 1 for OxTc and 0.2 μg mL^− 1 (1 · 10^-6 mol L^− 1) for citrate, respectively. A comparison of the new method with other methods for determination of citrate is given.     

Pressure-tuning of magnetism and linkage isomerism in iron(II) hexacyanochromate

A pressure-induced linkage isomerization of the cyanide anion has been observed in single crystals of a chromium(III)-iron(II) Prussian blue analogue of formula K0.4Fe4[Cr(CN)6]2.8 square1.2.16H2O (1). Upon application of pressure in the 0-1200 MPa range, the cyanide ligand rotates and becomes C-bonded to the iron(II) cations, leading to a stabilization of their diamagnetic low-spin states. The result is a decrease of magnetization and magnetic ordering temperatures from TC = 19 K at ambient pressure to 13 K at 1200 MPa. The initial magnetic properties can be restored on pressure release. The reversible movement of cyanide in the solid state can be exploited as a switch of the magnetic interaction at the molecular level.