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Optimization of the lignocellulosic bioconversion by cellulolytic enzymes requires good knowledge of reaction kinetics. In the present paper, the investigations of the kinetics have been performed on the fast-growing tree species of poplar, paulownia, willow and black locust, which were pretreated by steam explosion (SE), and bleached kraft pulp (BKP) made of a hardwood mixture. The applicability of different kinetic equations referring to diffusion, topochemical and other heterogeneous catalytic processes was examined, and it was found that the enzyme process is best described by the modified Prout-Tompkins topochemical equation. According to that kinetic model, the hydrolysis rate depends on the amount of the substrate left and the inhibition of the enzyme by the product formed and, moreover, on the combination of chemical interaction and diffusion processes. There is a compensation effect between activation energy and pre-exponential factor and there are correlations between rate constant, power factor, and wood density. The mechanisms of cellulase hydrolysis of BKP- and SE-treated fast-growing tree species are very similar. The results shows that the structural features of the lignocellulosic material are the controlling factor on the type of the kinetic mechanism. The obtained temperature-time dependence of degree of enzyme hydrolysis is useful for simulation and control of the process.

(1) Background: Hydrophobicity (or lipophilicity) is a limiting factor in the ability of molecules to pass through cell membranes and to perform their function. The ability to efficiently access cytosol is especially important when a synthetic compound has the potential to become a drug substance. D-Phe-Phe-Phe-D-Trp-Lys-Thr-Phe-Thr-NH2 (BIM-23052) is a linear analog of somatostatin with established in vitro GH-inhibitory activity in nanomolar (nm) concentrations and high affinity to different somatostatin receptors. (2) Methods: Series of analogs of BIM-23052 were synthesized where Phe residue(s) in the BIM-23052 molecule were replaced with Tyr using standard SPPS, Fmoc/t-Bu strategy. Analyses of target compounds were performed using HPLC/MS technique. Toxicity and antiproliferative activity were studied using in vitro NRU and MTT assays. The values of logP (partition coefficient in octanol/water) for BIM-23052 and its analogs were calculated. (3) Results: The obtained data show the best antiproliferative effect against studied cancer cells for compound D-Phe-Phe-Phe-D-Trp-Lys-Thr-Tyr7-Thr-NH2 (DD8), the most lipophilic compound according to the predicted logP values. (4) Conclusions: Multiple analyses of the obtained data reveal that compound D-Phe-Phe-Phe-D-Trp-Lys-Thr-Tyr7-Thr-NH2 (DD8) where one Phe is replaced by Tyr has the best combination of cytotoxicity, antiproliferative effect and hydrolytic stability.

Paulownia Tomentosa was pretreated by steam explosion. The cellulase complex NS 50013 and the β-glucosidase NS 50010 of Novozymes AS were used for the enzymatic conversion of cellulose to glucose. The kinetics of enzyme conversion was studied using the exponential kinetic equation valid for processes taking place at uniformly inhomogeneous surfaces. The kinetic coefficient of inhomogeneity accounts for the energy and entropy inhomogeneity of the system and depends on the temperature. It was established that both the activation energy and the pre-exponential factor increase simultaneously with increasing of conversion degree. A compensation effect between pre-exponential factor and activation energy was observed. The energetic hindrances established cannot be completely compensated by the positive effect of the pre-exponential factor increase. Hence, the activation energy has a determining influence on how quickly the rate of hydrolysis decreases.