Kinetic nature of the thermal destabilization of LHCII macroaggregates

The main light-harvesting chl a/b pigment-protein complex of photosystem II (LHCII) in isolated state forms macroaggregates with different ultrastructure and lipid content [I. Simidjiev, V. Barzda, L. Mustardy, G. Garab, Anal. Biochem. 250 (1997) 169-175]. The thermodynamic stability of highly delipidated tightly bound LHCII macroaggregates is studied by differential scanning calorimetry and fluorescence spectroscopy. The calorimetric profile of LHCII is asymmetric, the denaturation transition is taking place at around 72 degrees C. A shoulder, which overlaps with the main denaturation transition, appears around 58 degrees C. The denaturation temperature strongly depends on the scanning rate indicating the kinetic nature of the thermal destabilization of LHCII macroaggregates. The fluorescence data prove that the thermal denaturation of LHCII is an irreversible and kinetically controlled process.     

Kinetic parameters for solid-phase polycondensation of L-aspartic acid: Comparison of thermal gravimetric analysis and differential scanning calorimetry data

The computer simulation of the kinetic scheme advanced for the thermostimulated polycondensation of aspartic acid in the solid phase is performed. The scheme includes the autocatalytic growth of a polymeric chain followed by polymer dehydration. This process occurs simultaneously in two matrix zones with identical reaction products but different rate constants. Arrhenius parameters for each of the four chemical stages are defined via solution of the inverse kinetic problem. The functions obtained in the simulation almost coincide with kinetic curves obtained for three regimes of two thermochemical research methods: thermogravimetric analysis and differential scanning calorimetry. The parameters thus obtained can be described by the compensation-effect curve with a linear dependence between the logarithm of the pre-exponential factor and the activation energy. It was proposed that the bimolecular chain-growth reaction in one of the zones proceeds by the monomolecular mechanism.     

Aging-related changes in the calorimetric profile of red blood cells from women with miscarriages

The backward-facing step or the sudden expansion in internal flows is an important problem in different areas. In this study, a porous baffle is mounted on the opposite wall of a sudden expansion to enhance heat transfer near the step. Unlike the solid baffle, which is extensively studied in the literature, the porous baffle has a lower pressure drop, and its properties can be tuned to reach the optimal prospected performance. Effects of different porous baffle geometrical parameters including its normalized height (H_b?=?0.5, 1.0, 1.5, 1.75), width (W_b?=?0.5, 1, 1.5, 2.0, 2.5), porous baffle-step relative distance (D?=?1, 2, 3, 4), Darcy number (10^?2, 10^?3, 10^?4, 10^?6), and Reynolds number (100, 200, 300, 400, 500) on the heat transfer and pressure drop are investigated. The simulation indicates that higher Reynolds numbers enhance more the heat transfer (35% improvement at Re?=?500 with respect to 10% at Re?=?100). Also, longer baffles can lead to higher heat transfer rates (5% improvement in H_b?=?0.5 with respect to 32% at H_b?=?1.5).

     

Effect of ketoprofen-based ionic liquids on secondary structure and thermal stability of human serum albumin

Journal of Thermal Analysis and Calorimetry - This is the first study on the interactions of ionic liquids (ILs) composed of cations amino acid esters and anion ketoprofen (KETO) with human serum...     

Structural,Thermal, and Storage Stability of Rapana Thomasiana Hemocyanin in the Presence of Cholinium-Amino Acid-Based Ionic Liquids

Novel biocompatible compounds that stabilize proteins in solution are in demand for biomedical and/or biotechnological applications. Here, we evaluated the effect of six ionic liquids, containing mono- or dicholinium [Chol]_1or2 cation and anions of charged amino acids such as lysine [Lys], arginine [Arg], aspartic acid [Asp], or glutamic acid [Glu], on the structure, thermal, and storage stability of the Rapana thomasiana hemocyanin (RtH). RtH is a protein with huge biomedicinal potential due to its therapeutic, drug carrier, and adjuvant properties. Overall, the ionic liquids (ILs) induce changes in the secondary structure of RtH. However, the structure near the Cu-active site seems unaltered and the oxygen-binding capacity of the protein is preserved. The ILs showed weak antibacterial activity when tested against three Gram-negative and three Gram-positive bacterial strains. On the contrary, [Chol][Arg] and [Chol][Lys] exhibited high anti-biofilm activity against E. coli 25213 and S. aureus 29213 strains. In addition, the two ILs were able to protect RtH from chemical and microbiological degradation. Maintained or enhanced thermal stability of RtH was observed in the presence of all ILs tested, except for RtH-[Chol]₂[Glu].     

Rosmarinic acid-conjugated hemocyanins: synthesis and stability

Journal of Thermal Analysis and Calorimetry - Two oxygen-transporting proteins known for their immunostimulating and anticancer properties, namely hemocyanin from Helix lucorum (HlH) and hemocyanin...     

Investigation on chemical cross-linked collagen phosphoric acid hydrolysates with cyanuric chloride by differential scanning calorimetry

The process of cross-linking of collagen phosphoric acid hydrolysates (CH) with cyanuric chloride (CY) was studied by the increase in the denaturation temperature using differential scanning calorimetry (DSC). This measurement gave indications concerning the efficiency of the treatment, i.e., the extent of cross-linking of the collagen hydrolysates. The optimal conditions for cross-linking were determined: CH/CY in a ratio 1:1, reaction time 1 h at temperature 50 °C. At these conditions cross-linked structural units with higher thermal stability were formed.     

Solid-phase polycondensation of aspartic acid 1. Kinetics of the process as evidenced by TGA and DSC data

The TGA and DSC methods were used to investigate the process of thermostimulated polycondensation of aspartic acid, which was found to follow two parallel pathways. This apparently is due to the existence of two spatial regions, where the chemical transformation can take place. The first region (“potential”) already exists before the reaction begins, whereas the second (“dynamic”) is formed during the reaction progress. An autoaccelerated reaction is the first step in each of the pathways. The autoacceleration is likely to result from the reaction of the starting monomer with the reaction products. Some kinetic parameters were evaluated from experimental data. The rate constants of autocatalytic reactions in the two regions differ more than by an order of magnitude. This is the reason for very complex shape of the TGA and DSC isotherms. The kinetic curves in the differential forms have two maxima. The effective activation energy values for the reaction in the reaction regions considerably differ. According to the TGA and DSC data, they are 31.6/37.5 and 46.6/43.6 kcal mol^-1, respectively, for the approximate analytical and accurate computer methods of the experimental data processing. Excessively high values obtained for polycondensation suggest that the reaction proceeds in the solid phase.