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991.
Membrane Binding and Insertion of a pHLIP Peptide Studied by All-Atom Molecular Dynamics Simulations
Yonghua Deng Zhenyu Qian Yin Luo Yun Zhang Yuguang Mu Guanghong Wei 《International journal of molecular sciences》2013,14(7):14532-14549
Recent experiments in function mechanism study reported that a pH low-insertion peptide (pHLIP) can insert into a zwitterionic palmitoyloleoylphosphatidylcholine (POPC) lipid bilayer at acidic pH while binding to the bilayer surface at basic pH. However, the atomic details of the pH-dependent interaction of pHLIP with a POPC bilayer are not well understood. In this study, we investigate the detailed interactions of pHLIP with a POPC bilayer at acidic and basic pH conditions as those used in function mechanism study, using all-atom molecular dynamics (MD) simulations. Simulations have been performed by employing the initial configurations, where pHLIP is placed in aqueous solution, parallel to bilayer surface (system S), partially-inserted (system P), or fully-inserted (system F) in POPC bilayers. On the basis of multiple 200-ns MD simulations, we found (1) pHLIP in system S can spontaneously insert into a POPC bilayer at acidic pH, while binding to the membrane surface at basic pH; (2) pHLIP in system P can insert deep into a POPC bilayer at acidic pH, while it has a tendency to exit, and stays at bilayer surface at basic pH; (3) pHLIP in system F keeps in an α-helical structure at acidic pH while partially unfolding at basic pH. This study provides at atomic-level the pH-induced insertion of pHLIP into POPC bilayer. 相似文献
992.
Ilaria Adamo Valeria Diella Alessandro Pavese Pietro Vignola Fernando Francescon 《Journal of the European Ceramic Society》2013,33(15-16):3387-3395
The system Na-feldspar (F) and kaolinite (K) was investigated at temperatures of interest in ceramic applications (1200–1280 °C) to study the effects of F/K ratios by weight and crystallinity degree of kaolinite on the final product, micro-structural features and mullite-glass Gibbs energy of formation (ΔGeff). Mullite and glass are the dominant phases; in general, the higher the temperature, the larger the former. An F/K increase promotes the formation of glass and secondary mullite, appearing along with the primary one. ΔGeff was modelled by α(T) × (F/K)2 + β(T) × F/K + γ(T), α, β and γ being linear functions of temperature whose coefficients were determined by fitting the ΔGeff-theoretical to the ΔGeff-obtained from the measured phase compositions. ΔGeff is less affected by temperature than by F/K, whose increase shifts equilibrium towards glass phases. The ΔGeff-curves for ordered and disordered kaolinite intersect one another at F/K ~0.5, a ratio close to that used in industrial practice. 相似文献
993.
Robert J. Buszek C. Michael Lindsay Jerry A. Boatz 《Propellants, Explosives, Pyrotechnics》2013,38(1):9-13
Ab initio electronic structure calculations at the MP2/cc‐pVTZ level predict the vibrational stability of the theoretical molecule tetrakis(nitratoxycarbon)methane, designated CLL‐1. The gas phase enthalpy of formation, predicted to be +1029.3 kJ mol−1 using the G3(MP2) method, and the estimated density of 1.87 g cm−3 are used to predict the explosive performance properties using the equilibrium thermochemical code CHEETAH. The predicted detonation velocity (8.61 km s−1) and pressure (33.1 GPa) are similar to those of RDX, but with a significantly higher detonation temperature (6740 K). Finally, the stability of this theoretical molecule is investigated by calculating the lowest energy unimolecular decomposition pathways of the HCO3N model compound as well as barriers to rearrangement upon interaction of two HCO3N molecules. 相似文献
994.
Zheng‐Jun Quan Wang‐Hua Hu Zhang Zhang Yu‐Xia Da Xiao‐Dong Jia Xi‐Cun Wang 《Advanced Synthesis \u0026amp; Catalysis》2013,355(5):891-900
The molecular iodine‐catalyzed three‐component reaction of amides or amide derivatives, paraformaldehyde and styrenes allows for the clean generation of allylamine derivatives in good yields and high regioselectivities. The reaction, forming water as the sole co‐product, is an experimentally easy to conduct transformation in the absence of transition metals under mild conditions. 相似文献
995.
Shao‐Yun Chen Chen‐Xi Yang Jian‐Ping Wu Gang Xu Li‐Rong Yang 《Advanced Synthesis \u0026amp; Catalysis》2013,355(16):3179-3190
To establish a system for the efficient one bacterial multi‐enzymatic biosynthesis of both (R)‐ and (S)‐β‐hydroxy nitriles, we co‐expressed alcohol dehydrogenases with opposite stereoselectivities, cofactor regeneration enzymes, and a halohydrin dehalogenase in Escherichia coli. By researching cofactor recycling and various co‐expression strategies and by selecting and engineering the halohydrin dehalogenase, we engineered two E. coli strains, which were subsequently used in a cascade of reactions to produce chiral β‐hydroxy nitriles with high enantiomeric excess directly from prochiral α‐halo ketones. Three valuable pharmaceutical intermediates were prepared by means of this catalytic system, and substrate conversion reached about >99%. More importantly, the system is of low cost because there is no need for expensive cofactors or for expression and purification of the component enzymes.
996.
The recovery or capture of one or more components from gas mixture by membrane separation has become a research focus in recent years. This study investigates the gas-membrane solution equilibrium, for which Henry’s law is not applicable if the gas phase is a mixture. This problem can be solved by using UNIQUAC model to calculate the activity coefficient of gas dissolved in the membrane. A method was proposed in this study to obtain the gas-membrane interaction parameter for UNIQUAC model. By the experiments of gas permeation through polydimethylsiloxane PDMS membrane, the solubility coefficients of some gases (N2, CO2, CH4) were measured. Through non-linear fitting UNIQUAC model to the experimental results from this study and in literature (H2, O2, C3H8), the gas-membrane interaction parameters for these gases were obtained. Based on these parameters, the activity coefficients of the dissolved gas were calculated by UNIQUAC model, and their values agree well with the experimental data. These results confirm the feasibility and effectiveness of the proposed method, which makes it possible to better predict gas-membrane solution equilibrium. 相似文献
997.
998.
去氢芳樟醇加氢在机械搅拌釜中进行,采用膜分离设备,实现了催化剂在反应系统中循环使用,大大提高了催化剂使用寿命:考察了反应温度、压力对加氢反应结果的影响;提出了反应终点预测方法. 相似文献
999.
1000.
Ramamourthy Gopal Jong Kook Lee Jun Ho Lee Young Gwon Kim Gwang Chae Oh Chang Ho Seo Yoonkyung Park 《International journal of molecular sciences》2013,14(1):2190-2202
In a previous study, we synthesized a series of peptides containing simple sequence repeats, (KW)n–NH2 (n = 2,3,4 and 5) and determined their antimicrobial and hemolytic activities, as well as their mechanism of antimicrobial action. However, (KW)5 showed undesirable cytotoxicity against RBC cells. In order to identify the mechanisms behind the hemolytic and cytotoxic activities of (KW)5, we measured the ability of these peptides to induce aggregation of liposomes. In addition, their binding and permeation activities were assessed by Trp fluorescence, calcein leakage and circular dichrorism using artificial phospholipids that mimic eukaryotic liposomes, including phosphatidylcholine (PC), PC/sphingomyelin (SM) (2:1, w/w) and PC/cholesterol (CH) (2:1, w/w). Experiments confirmed that only (KW)5 induced aggregation of all liposomes; it formed much larger aggregates with PC:CH (2:1, w/w) than with PC or PC:SM (2:1, w/w). Longer peptide (KW)5, but not (KW)3 or (KW)4, strongly bound and partially inserted into PC:CH compared to PC or PC:SM (2:1, w/w). Calcein release experiments showed that (KW)5 induced calcein leakage from the eukaryotic membrane. Greater calcein leakage was induced by (KW)5 from PC:CH than from PC:SM (2:1, w/w) or PC, whereas (KW)4 did not induce calcein leakage from any of the liposomes. Circular dichroism measurements indicated that (KW)5 showed higher conformational transition compared to (KW)4 due to peptide-liposome interactions. Taken together, our results suggest that (KW)5 reasonably mediates the aggregation and permeabilization of eukaryotic membranes, which could in turn explain why (KW)5 displays efficient hemolytic activity. 相似文献