A multipotential hydrolytic reactor using the yeast strainKluyveromyces marxianus

In previous publications, we described the continuous production of D-fructose from enzymatic hydrolysis of inulin with immobilized permeabiliized cells ofKluyveromyces marxianus and the increase of productivity obtained by using a mutant selected by NTG action on the wild-type strain. By improving reactor performance, it has been possible to reach 2000 g/L/d of liberated sugar from an inulin solution with the mutant strain.

In addition, it has been shown that the KF 28 mutant was an invertase and pectinase hyperproducer. These enzymatic activities are also secreted by the speciesKluyveromyces marxianus. Therefore, we investigated the possibility of using immobilized cells of this yeast as a multipotential hydrolysis reactor. A sucrose hydrolysis reactor and a pectin hydrolysis reactor were set up. It is shown here that the majority of the optimized parameters from the inulin hydrolysis reactor can be transported directly to the other reactors. However, some parameters have to be adapted, especially for pectin hydrolysis.

     

Hydrophobicity within the three-dimensional Mercedes-Benz model: potential of mean force

We use the three-dimensional Mercedes-Benz model for water and Monte Carlo simulations to study the structure and thermodynamics of the hydrophobic interaction. Radial distribution functions are used to classify different cases of the interaction, namely, contact configurations, solvent separated configurations, and desolvation configurations. The temperature dependence of these cases is shown to be in qualitative agreement with atomistic models of water. In particular, while the energy for the formation of contact configurations is favored by entropy, its strengthening with increasing temperature is accounted for by enthalpy. This is consistent with our simulated heat capacity. An important feature of the model is that it can be used to account for well-converged thermodynamics quantities, e.g., the heat capacity of transfer. Microscopic mechanisms for the temperature dependence of the hydrophobic interaction are discussed at the molecular level based on the conceptual simplicity of the model.     

Linear Conforming and Nonconforming Upwind Finite Elements for the Convection-Diffusion Equation

A conforming and a nonconforming method for the approximationof the stationary 2-D convection-diffusion equation at highP?clet number are presented. Convergence of order h is provedin a generic case and, for a particular choice of the upwindschemes, a discrete maximum principle is established under veryunrestrictive conditions on the mesh. Results of numerical computationsare produced to show the practical convergence of these methods.     

Measurement of ΔσL in pp scattering between 200 and 583 MeV

The main structure around m = 2.15 GeV first observed by the Argonne group in the spin-dependent total cross section Δσ_L is confirmed in the energy range available at SIN. A simultaneous study of the scattered particles at small angles has been carried out with success and gave the spin-correlation parameter A_00kk for the pp elastic scattering and for the reaction pp → π⁺d. The contribution of the 3-body reactions to this spin-dependent total cross section has been deduced and found to be lower than the contribution of the π⁺d reaction even at 583 MeV.     

13C NMR spectroscopic evidence for the existence of the monocation of pyropheophytin a

Pyropheophytin a, which is an unsymmetric porphyrin, has been titrated with trifluoroacetic acid (TFA) in tetrahydrofuran, the protonation reaction being followed by ¹³C NMR spectroscopy. TFA was added in small increments to a 0.28 M solution of pyropheophytin a in tetrahydrofuran, and the chemical shift changes of the macrocyclic carbons were determined as a function of the TFA increments. On the addition of TFA the signals of the α-carbons of ring II experienced a large upfield change, whereas the signals of all other macrocyclic carbons moved only slightly downfield or remained constant. These observations were interpreted as indicating the formation of a monocation in which the proton is attached to the nitrogen of ring II. The ¹³C protonation shifts of pyropheophytin a were compared with those previously reported for symmetric porphyrins. On the basis of this comparison, the basicity of the macrocyclic nitrogen atoms, the N–H tautomerism and the electron delocalization in structurally different porphyrin macrocycles are discussed.     

Carbon-13 NMR spectra of chlorophyll a,chlorophyll a′, pyrochlorophyll a and the corresponding pheophytins

The ¹³C NMR spectra of C-10 epimeric chlorophylls a and a′, pheophytins a and a′, pyrochlorophyll a and pyropheophytin a have been recorded and assigned by chemical shift comparison, by long-range selective ¹H decoupling experiments and by the examination of the fully coupled spectra. Various factors influencing the ¹³C chemical shifts of the chlorophyll derivatives, e.g. the coordination of magnesium to the chlorin nucleus, the effect of solvent and the steric strain at the periphery of the macrocycle, have been examined. The ¹³C NMR spectra of chlorophyll a measured in acetone-d₆ and tetrahydrofuran-d₈ (THF) were compared, and remarkable solvent effects on the ¹³C chemical shifts were observed. These effects were interpreted mostly in terms of specific chlorophyll-solvent interactions. Different electron donor and steric properties of acetone and THF were considered to cause conformational alterations in the macrocycle, induced by the ligation of the solvent molecule(s) to the axial position(s) of the central magnesium atom of chlorophyll a. These results show that ¹³C NMR spectroscopy is a method of high information value for investigations of the unique electron donor acceptor (EDA) properties of the chlorophylls. The structural differences between the C-10 epimeric chlorophylls and pheophytins were examined in terms of the substituent chemical shift (SCS) parameters for the C-10 methoxycarbonyl group. The analysis showed that the change from the (10R) to the 10(S) configuration induces conformational alterations in the whole macrocycle which are, however, most prominent in rings IV and V. Owing to the increased steric interaction (repulsion) between the bulky substituents at C-7 and C-10, the peripheral strain is larger in the (10S) form, and is relieved by more pronounced deviations of rings IV and V from the macrocyclic plane compared with the (10R) form. The examination of the SCS parameters also showed that the peripheral steric strain is dissipated to a larger extent over the entire macrocycle in the Mg-free derivatives. These results confirm the previous conclusions based on ¹H NMR and CD data. The possible function of chlorophyll a′ in photosynthesis is briefly discussed.     

Pressure viscosity behavior of various fluids

Abstract

Many works have been published on the pressure viscosity dependence of liquids. The difficulty to fit experimental results with a simple and universal law has been often put in evidence. According to our experimental results, we show that a power law is an acceptable alternative to the common Barus law.     

Gas-liquid phase separation in oppositely charged colloids: stability and interfacial tension

We study the phase behavior and the interfacial tension of the screened Coulomb (Yukawa) restricted primitive model (YRPM) of oppositely charged hard spheres with diameter sigma using Monte Carlo simulations. We determine the gas-liquid and gas-solid phase transitions using free energy calculations and grand-canonical Monte Carlo simulations for varying inverse Debye screening length kappa. We find that the gas-liquid phase separation is stable for kappasigma相似文献