Control Mechanism for Carbon‐Chain Length in Polyunsaturated Fatty‐Acid Synthases

Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are essential fatty acids. PUFA synthases are composed of three to four subunits and each create a specific PUFA without undesirable byproducts. However, detailed biosynthetic mechanisms for controlling final product profiles have been obscure. Here, the bacterial DHA and EPA synthases were carefully dissected by in vivo and in vitro experiments. In vitro analysis with two KS domains (KS_A and KS_C) and acyl‐acyl carrier protein (ACP) substrates showed that KS_A accepted short‐ to medium‐chain substrates while KS_C accepted medium‐ to long‐chain substrates. Unexpectedly, condensation from C₁₈ to C₂₀, the last elongation step in EPA biosynthesis, was catalyzed by KS_A domains in both EPA and DHA synthases. Conversely, condensation from C₂₀ to C₂₂, the last elongation step for DHA biosynthesis, was catalyzed by the KS_C domain in DHA synthase. KS_C domains therefore determine the chain lengths.     

On the spectral radius of the Jacobi iteration matrix for a rectangular region with two different media

The spectral radius of the Jacobi iteration matrix plays an important role to estimate the optimum relaxation factor, when the successive overrelaxation (SOR) method is used for solving a linear system. The specific systems are finite difference forms of the Laplace equation satisfied on a rectanglar region with two different media. Though the potential function for the inhomogeneous closed region is continuous, the first order derivative is not continuous. So this requires internal boundary conditions or interface conditions. In this paper, the spectral radius of the Jacobi iteration matrix for the inhomogeneous rectangular region is formulated and the approximation for the explicit formula, suitable for the computation of the spectral radius, is deduced. It is also found by the proposed formula that the spectral radius and the optimum relaxation factor rigorously depend on the inhomogeneity or the internal boundary conditions in the closed region, and especially vary with the position of the internal boundary. These findings are also confirmed by the numerical results of the power method.The stationary iterative method using the proposed formula for calculating estimates of the spectral radius of the Jacobi iteration matrix is compared with Carré's method, Kulstrud's method and the stationary iterative method using Frankel's theoretical formula, all for the case of some numerical models with two different media. According to the results our stationary iterative method gives the best results ffor the estimate of the spectral radius of the Jacobi iteration matrix, for the required number of iterations to calculate solutions, and for the accuracy of the solutions.As a numerical example the microstrip transmission line is taken, the propating mode of which can be approximated by a TEM mode. The cross section includes inhomogeneous media and a strip conductor. Upper and lower bounds of the spectral radius of the Jacobi iteration matrix are estimated. Our method using these estimates is also compared with the other methods. The upper bound of the spectral radius of the Jacobi iteration matrix for more general closed regions with two different media might be given by the proposed formula.     

Spin crossover phenomenon accompanying order-disorder phase transition in the ligand of [FeII(DAPP)(abpt)](ClO4)2 compound (DAPP = bis(3-aminopropyl)(2-pyridylmethyl)amine, abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) and its successive self-grinding effect

The spin crossover phenomenon of the recently described spin crossover complex [FeII(DAPP)(abpt)](ClO4)2 [DAPP = bis(3-aminopropyl)(2-pyridylmethyl)amine, abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole] accompanying an order-disorder phase transition of the ligand was investigated by adiabatic heat capacity calorimetry, far-IR, IR, and Raman spectroscopies, and normal vibrational mode calculation. A large heat capacity peak due to the spin crossover transition was observed at T(trs) = 185.61 K. The transition enthalpy and entropy amounted to Delta(trs)H = 15.44 kJ mol-1 and Delta(trs)S = 83.74 J K-1 mol-1, respectively. The transition entropy is larger than the expected value 60.66 J K-1 mol-1, which is contributed from the spin multiplicity (R ln 5; R: the gas constant), disordering of the carbon atom of the six-membered metallocycle in the DAPP ligand, and one of the two perchlorate anions (2R ln 2), and change of the normal vibrational modes between the high-spin (HS) and low-spin (LS) states (35.75 J K-1 mol-1). The remaining entropy would be ascribed to changes of the lattice vibrations and molecular librations between the HS and LS states. Furthermore, [Fe(DAPP)(abpt)](ClO4)2 crystals disintegrated and became smaller crystallites whenever they experienced the phase transition. This may be regarded as a successive self-grinding effect, evidenced by adiabatic calorimetry, DSC, magnetic susceptibility, and microscope observation. The relationship between the crystal size and the physical quantities is discussed.     

Macromolecular crowding effects on reactions of TePixD (Tll0078)

To reveal macromolecular crowding effects on a chemical reaction of a BLUF (sensors of blue light using FAD) protein (PixD from a thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 [TePixD, Tll0078]), the photoreaction was studied at various concentrations of the macromolecule Ficoll-70 by UV/Vis absorption spectroscopy and the pulsed laser-induced transient grating (TG) method. The absorption spectrum did not change with varying concentration of Ficoll-70. The crowding did not affect the quantum yield of the spectral red shift reaction, recovery rate of the product, rate constant of the volume change reaction and the magnitude of the volume change. However, the magnitude of the TG signal representing the diffusion-sensitive conformation change significantly increased on addition of Ficoll-70. This dependence was attributed to the crowding effect on the TePixD decamer-pentamer equilibrium in the solution. This result indicates that the TePixD reaction is more efficient in cellular than in in vitro conditions.     

Amino acid‐functionalized ethyl cellulose: Synthesis,characterization, and gas permeation properties

Amino acid esters of ethyl cellulose [R′ = H ( 1 ), CH₃ ( 2 ), CH₂CH(CH₃)₂ ( 3 ), CH₂CONH₂ ( 4 ), CH₂OCH₂C₆H₅ ( 5 , 5′ ), CH₂CH₂CH₂CH₂NHOCOC(CH₃)₃ ( 6 )] were synthesized in moderate to quantitative yields (30–99%) by the reaction of t‐butoxycarbonyl (t‐Boc)‐protected amino acids or an activated ester derivative with hydroxy groups of ethyl cellulose [EC; degree of substitution (DS_Et), 2.69]. The amino acid functionalities displaying varied chemical nature, shape, and bulk were used, and bulk of the substituent on the α‐carbon of amino acids was elucidated to be of vital significance for the observed degree of incorporation (DS_Est). ¹H NMR spectra were used to determine the degree of incorporation of amino acid moiety (DS_Est), and almost complete substitution of the hydroxy protons was revealed in 1 , 2 , and 5′ . The onset temperatures of weight loss of 1 – 6 were 198–218 °C, indicating fair thermal stability. The glass transition temperatures of the derivatized polymers were 30–40 °C lower than that of EC (T_g 131 °C; cf. T_g of 1 – 6 , 93.5–103 °C). Free‐standing membranes of EC and its amino acid esters ( 1 , 2 , 5 , 5′ , and 6 ) were fabricated, and enhanced permselectivity for CO₂/N₂ and CO₂/CH₄ gas pairs was discerned, when compared with EC. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3986–3993, 2010     

Comparison of properties of titanium aluminium nitride film produced by using two different types of Ti–Al target

This work aims to study the influence of two different types of Ti–Al target (sintered and melted) which have same nominal composition (50 at% Ti, 50 at% Al) on the properties of thin films coated by using arc ion plating (AIP) method. The hardness of the melted target was of higher value than that of the sintered target. The property of the film is related to the microstructure and phase analysis of both types of target that have quite different phases. Ti and Al metals were found as major phases and TiAl₂ as minor phase in the sintered target but only TiAl compound was found in the melted target. After film coating at the same operation parameters, it was found that although the phase structures of the sintered and melted targets were quite different, the coated thin films using these targets showed the same phase structure of Ti_0.5 Al_0.5 N. However, the microstructure of films coated by using the sintered target showed higher density of droplets and pores than those of film produced by using the melted target. As a result, the hardness and adhesion strength of thin film produced by using the melted target were slightly higher than those values of film produced by using the sintered target. Copyright © 2009 John Wiley & Sons, Ltd.     

Diffusion coefficients of C60 and C60- in benzonitrile and dichloromethane solutions containing tetrabutylammonium perchlorate, measured by potential-step chronoamperometry.

The diffusion coefficients of C(60) in dichloromethane and benzonitrile solutions containing 0.1 M tetrabutylammonium perchlorate were determined by single potential-step chronoamperometry at small disk electrodes. The diffusion coefficients of C(60) were obtained by curve fitting of the chronoamperograms to a theoretical equation by Shoup and Szabo. The values were (1.4 +/- 0.3) x 10(-9) and (4.1 +/- 0.3) x 10(-10) m(2) s(-1), respectively (the errors are 95% confidence limits). The diffusion coefficients of C(60)(-) in these solutions were measured by double potential-step chronoamperometry. The ratios of the diffusion coefficients of C(60) to those of C(60)(-) were obtained from theoretical curves of the ratios of the current at the second potential step to the current at the first one. The values of the ratios were 1.2 +/- 0.2 and 1.0 +/- 0.3, respectively.     

Successive phase transitions of <Emphasis Type="Italic">p</Emphasis>-methylbenzyl alcohol crystal studied by X-ray and adiabatic calorimetry

Summary Crystal structures of the room-temperature (RT) and low-temperature (LT) phases of p-methylbenzyl alcohol were reexamined by single-crystal X-ray diffraction method while paying special attention to detect structural disorder in the RT phase involved in successive structural phase transitions at 179 and 210 K. In the RT phase at 250 K, positional disorder of oxygen atoms was detected in contrast to the previous structure report. The structure of the LT phase coincided to the previous one. Heat capacities were measured by adiabatic calorimetry below 350 K, which covers the structural phase transitions and fusion at 331.87 K. The structural phase transitions were of first-order and required long time for completion. The combined magnitude of entropies of transition was ca. 5 J K^-1 mol^-1, a part of which can be ascribed to the positional disorder observed in the structure analysis. Standard thermodynamic functions are tabulated below 350 K.