Thermodynamic Tuning of Mg-Based Hydrogen Storage Alloys: A Review

Mg-based hydrides are one of the most promising hydrogen storage materials because of their relatively high storage capacity, abundance, and low cost. However, slow kinetics and stable thermodynamics hinder their practical application. In contrast to the substantial progress in the enhancement of the hydrogenation/dehydrogenation kinetics, thermodynamic tuning is still a great challenge for Mg-based alloys. At present, the main strategies to alter the thermodynamics of Mg/MgH₂ are alloying, nanostructuring, and changing the reaction pathway. Using these approaches, thermodynamic tuning has been achieved to some extent, but it is still far from that required for practical application. In this article, we summarize the advantages and disadvantages of these strategies. Based on the current progress, finding reversible systems with high hydrogen capacity and effectively tailored reaction enthalpy offers a promising route for tuning the thermodynamics of Mg-based hydrogen storage alloys.     

The role of water in computational and experimental derivation of binding thermodynamics in SH2 domains

We have studied the role of bound interface water molecules on the prediction of the thermodynamics of SH2 domain binding to tyrosyl phosphopeptides using a method based on accessible surface area buried upon association. We studied three phosphopeptide ligands, which have been shown by Lubman and Waksman (J Mol Biol;328:655, 2003) and Davidson et al. (JACS;124:205, 2002) to have similar binding free energies but very different thermodynamic signatures. The thermodynamic model is semiempirical and applies to the crystal structure of the SH2 domain-bound forms. We explored all possible combinations of bound interfacial waters. We show that the model does not predict the binding thermodynamics of either ligand. However, we identified the empirical formula describing the heat capacity change as the source of the problem. Indeed, systematic exploration of heat capacity change values between 0 and -300 cal/mol deg results in a sharp distribution of the number of ligand/SH2/water-subset structures that provide binding thermodynamics similar to experimental values. The heat capacity change values at which the distributions peak are different for each peptide. This prompted us to experimentally determine the heat capacity change for each of the peptides and we found them to coincide with the values of the peaks. The implications of such findings are discussed.     

Investigation of the Interpolymer Complex between Hydroxypropyl Cellulose and Maleic Acid‐Styrene Copolymer, 1

Summary: The hydrogen bonding‐interpolymer association of hydroxypropyl cellulose (HPC) with maleic acid‐styrene (MAc‐S) copolymer has been investigated in dilute aqueous solution by viscometry, turbidimetry and potentiometry. At a mixing ratio between MAc‐S and HPC of 10:90, the solution exhibits a phase separation upon heating, while for other mixing ratio no phase separation could be detected. The stability of the interpolymer complex (IPC) increases as the temperature rises. The stoichiometry of the IPC, in mole units, was estimated as being MAc‐S:HPC = 5:2. The thermodynamic functions (enthalpy and entropy) of the complexation process have been determined.

Dependence of IPC concentration in H₂O/MAc‐S/HPC system on the mole fraction of MAc‐S in polymer mixture at different temperatures.     

中药超分子“印迹模板”作用对成分簇动态性与稳态性变化规律的理论研究

中药药效成分是实现其功效的物质基础,受遗传、环境、人为加工等因素的影响,是随时随域随法变化的。中药超分子化学理论可为揭示多种中药成分中“变与不变”的规律提供依据。首先进行成分簇整合,根据中药成分在色谱柱上的印迹行为划分出“物质单元”,并建立中药成分簇网络动力学与热力学的研究方法,再采用线性和非线性拟合得回归方程,得到各物质单元的作用（活度）系数、作用贡献度、活度、化学势,最后按排序确定各物质单元的贡献大小。该法弱化了对具体成分的分析,强化了对整合成分簇的研究,为阐明中药药效物质基础及其多成分簇的作用机制提供新的研究方法和思路。     

纤维素酶辅助提取藕节多糖工艺优化及其动力学、热力学研究

目的优化纤维素酶辅助提取藕节多糖工艺,并研究其动力学、热力学。方法在单因素试验基础上,以加酶量、介质p H、酶解温度、酶解时间为影响因素,多糖得率为评价指标,Box-Behnken响应面法优化提取工艺。对提取期间的动力学、热力学进行分析。结果最佳条件为加酶量0.9%,介质p H 5.0,酶解温度47℃,酶解时间2.5 h,多糖得率为5.86%。加入纤维素酶后,多糖得率、提取速率常数(k)、表面扩散系数(Ds)提高。提取过程符合一级动力学模型,吸热熵增加,放热熵减小,为自发过程。结论该方法稳定可靠,可用于纤维素酶辅助提取藕节多糖。     

From sunscreens to medicines: Can a dissipation hypothesis explain the beneficial aspects of many plant compounds?

Medicine has utilised plant‐based treatments for millennia, but precisely how they work is unclear. One approach is to use a thermodynamic viewpoint that life arose by dissipating geothermal and/or solar potential. Hence, the ability to dissipate energy to maintain homeostasis is a fundamental principle in all life, which can be viewed as an accretion system where layers of complexity have built upon core abiotic molecules. Many of these compounds are chromophoric and are now involved in multiple pathways. Plants have further evolved a plethora of chromophoric compounds that can not only act as sunscreens and redox modifiers, but also have now become integrated into a generalised stress adaptive system. This could be an extension of the dissipative process. In animals, many of these compounds are hormetic, modulating mitochondria and calcium signalling. They can also display anti‐pathogen effects. They could therefore modulate bioenergetics across all life due to the conserved electron transport chain and proton gradient. In this review paper, we focus on well‐described medicinal compounds, such as salicylic acid and cannabidiol and suggest, at least in animals, their activity reflects their evolved function in plants in relation to stress adaptation, which itself evolved to maintain dissipative homeostasis.     

Stem–loop formation drives RNA folding in mechanical unzipping experiments

Accurate knowledge of RNA hybridization is essential for understanding RNA structure and function. Here we mechanically unzip and rezip a 2-kbp RNA hairpin and derive the 10 nearest-neighbor base pair (NNBP) RNA free energies in sodium and magnesium with 0.1 kcal/mol precision using optical tweezers. Notably, force–distance curves (FDCs) exhibit strong irreversible effects with hysteresis and several intermediates, precluding the extraction of the NNBP energies with currently available methods. The combination of a suitable RNA synthesis with a tailored pulling protocol allowed us to obtain the fully reversible FDCs necessary to derive the NNBP energies. We demonstrate the equivalence of sodium and magnesium free-energy salt corrections at the level of individual NNBP. To characterize the irreversibility of the unzipping–rezipping process, we introduce a barrier energy landscape of the stem–loop structures forming along the complementary strands, which compete against the formation of the native hairpin. This landscape correlates with the hysteresis observed along the FDCs. RNA sequence analysis shows that base stacking and base pairing stabilize the stem–loops that kinetically trap the long-lived intermediates observed in the FDC. Stem–loops formation appears as a general mechanism to explain a wide range of behaviors observed in RNA folding.

Unzipping experiments permit one to investigate the physico- chemical properties of nucleic acids, from the thermodynamics of duplex formation to the folding of secondary and tertiary structures. In particular, DNA hybridization finds diverse applications in the field of DNA nanotechnology, the construction of DNA origami, molecular robots, DNA walkers, switches, and nanomotors (1–5). In an unzipping experiment, the two strands of a duplex DNA or RNA molecule are mechanically pulled apart by exerting opposite forces on the two strands on one end. In this way, it is possible to measure a force–distance curve (FDC) that exhibits a sequence-dependent sawtooth pattern. DNA unzipping has been used to test the validity of the nearest-neighbor (NN) model (6–9) and to extract the 10 NN base pairs (NNBP) free-energy parameters at different salt conditions (10, 11). A precise knowledge of the NNBP energies might be also useful to unravel hidden energy codes in molecular evolution (12).Here we derive the 10 NNBP RNA energies from unzipping experiments carried out on a 2-kbp RNA hairpin in monovalent (sodium) and divalent (magnesium) salt conditions. The NN model has many parameters requiring a sufficiently long RNA hairpin to infer them from unzipping experiments reliably. Two are the main difficulties of these experiments: First, the molecular synthesis of a long (a few kilobases) RNA hairpin is challenging; second, the FDC along the RNA sequence alternates reversible unzipping regions with irreversible ones that exhibit hysteresis and multiple long-lived intermediates (13, 14). Compared to DNA, where unzipping is practically reversible, a similar derivation of the RNA energies from irreversible FDCs is not possible. Here we derive the full equilibrium FDC in RNA by the piecewise assembly of the reversible parts and the reconstructed equilibrium ones for the irreversible regions. These are obtained by repeatedly unzipping and rezipping the RNA hairpin in these irreversible regions and using statistical physics methods based on fluctuation theorems. This allows us to derive the NNBP energies for RNA in sodium and magnesium and compare them with the results reported by the literature (15–18). Moreover, we demonstrate the validity of an equivalence rule for the free-energy salt corrections between sodium and magnesium at the level of individual NNBP. We find that NNBP free-energy parameters for a given magnesium concentration are equal to those in 77(±49)-fold sodium. This result is compatible with the 100/1 rule of thumb by which the nonspecific RNA binding affinity of 10 mM Mg²⁺ approximately equals that of 1 M Na+ (19). We provide a solid verification of this phenomenological result by measuring the NNBP RNA energies in sodium and magnesium. We study the irreversibility and hysteresis in the FDCs and hypothesize that this is caused by the formation of stem–loop structures along the unpaired single strands. Remarkably, the hysteresis along the unzipping–rezipping pathway directly correlates with the barrier energy landscape defined by the stem–loops that are formed at the junction separating single strands and duplex. A sequence analysis of the irreversible regions of the 2-kbp RNA and experiments on specifically designed short-RNA sequences demonstrates that base stacking and base pairing within the single-stranded RNA (ssRNA) promote the formation of stem–loop RNA structures transiently stabilized at forces as high as 20 pN. The stem–loops mechanism explains the slow kinetics and multiple trapping conformations observed in RNA folding, with implications for the RNA folding problem (13, 20–23).     

热致相分离法制备聚苯硫醚多孔膜Ⅱ.聚苯硫醚和二苯砜体系

研究了聚苯硫醚／二苯酮体系的热力学相图，探讨了热致相分离法制备耐高温、耐溶剂的聚苯硫醚多孔膜的可能性，并就聚苯硫醚与二苯酮的组成比以及降温速率对多孔结构形成的影响规律进行了讨论。     

Conformational free energy of armadillo metmyoglobin

The conformational free energy of armadillo metmyoglobin was examined over a pH range of 4.4–8.0 and a guanidinium chloride concentration of 0–2.3 M. For isothermal unfolding at 25′ essentially the same value was obtained for the conformational free energy from all the data: 27 ± 2 kJ/mol. These data suggest that the armadillo has the least stable metmyoglobin of any mammal thus far examined. The cooperativity of the unfolding with respect to denaturant is considerably less than for other mammalian myoglobins. On unfolding only three to four side chains with a pK_A of 6 in the unfolded protein are protonated instead of the six found for horse and sperm whale myoglobins.     

Homolysis and Decomposition of Alkoxyamines Containing PROXYL and TEMPO Residues: A Comparison

Quantitative ESR and ¹H NMR spectroscopies have been used to study the homolysis and decomposition, respectively, of alkoxyamines derived from TEMPO and PROXYL nitroxides. It is shown that alkoxyamines substituted in the β position with a tert‐butoxy group have different activation parameters than those bearing a 1‐phenethyl fragment, however, there is compensation between transition state enthalpy and entropy, resulting in most cases in similar transition state free energies and homolysis kinetics. On the other hand, β‐substituted alkoxyamines show a much lower tendency to undergo decomposition, while species derived from TEMPO are more prone to decomposition than those from the substituted PROXYL derivative investigated. These findings are used to explain the observed differences in polymerisation behaviour of the various alkoxyamines.

Alkoxyamines used in the present study.