等温滴定量热法和荧光滴定法研究十二烷基硫酸钠与纤维素酶的结合

用等温滴定量热法和荧光滴定法研究了阴离子型去垢剂十二烷基硫酸钠（SDS ）与绿色木霉纤维素酶相互作用的热力学，SDS结合纤维素酶的亲和力较弱，为较 小的放热反应，并伴随着一定程度的熵增，为焓和熵共同驱动的反应，而且存在着 显著的焓-熵补偿作用。该结合过程的摩尔恒压热容为较大的负值（-186 J·mol~ (-1)·K~(-1)），这表明疏水相互作用是形成复合物的主要作用力，SDS的加入使 纤维素酶的内源荧光发生猝灭，同时导致该蛋白荧光光谱最大发射峰位的红移和酶 活力的部分丧失，这表明SDS与纤维素酶的相互作用既包含结合反应也包含SDS诱导 该蛋白部分去折叠的过程。     

Isothermal Titration Calorimetry Study of a Bistable Supramolecular System: Reversible Complexation of Cryptand[2.2.2] with Potassium Ions

Isothermal titration calorimetry (ITC) is used to investigate the thermodynamics of the complexation of potassium ions by 1,10‐diaza‐4,7,13,16,21,24‐hexaoxabicyclo[8.8.8]hexacosane (cryptand[2.2.2]) in aqueous solution. By changing the pH of the solution it was possible to trigger the reversible complexation/decomplexation of the cryptand in consecutive in situ experiments and to assess for the first time the use of ITC to monitor the thermodynamics of a bistable system.     

表面活性剂分子间弱相互作用的直接能量表征——高灵敏等温滴定量热法

分子间弱相互作用热力学研究的直接实验方法就是利用量热手段测定相互作用的能量参数. 本文对TAM III-ITC 纳焦级量热计进行了电标定实验和标准反应热测量, 结果显示本量热计的精密度为±0.09%; 量热用基准物质三羟甲基氨基甲烷(Tris)与盐酸的反应热((-47.48±0.12) kJ·mol^-1)与文献值一致. 采用此量热计,对典型的头-尾链型阳离子表面活性剂十二烷基三甲基溴化铵(DTAB)测量得到了与文献报导值很好吻合的临界胶束浓度(cmc)和胶束化焓, 而且对具有亲水-疏水面式刚性结构的生物表面活性剂胆酸钠(NaC)也获得了可靠的结果. 进一步地, 对于相反电荷的混合表面活性剂体系(DTAB/NaC), 分别研究了在富NaC区和富DTAB区体系混合胶束的形成. 结果说明DTAB/NaC混合表面活性剂体系在富NaC区有较强的协同效应, 而在富DTAB区的协同效应较弱. 本文结合电导率测定结果, 对DTAB/NaC混合体系在水溶液中的分子自组装热力学行为进行了有价值的讨论.     

Complexation of Phenol and Thiophenol by Amine N‐Oxides: Isothermal Titration Calorimetry and ab Initio Calculations

To develop a new solvent‐impregnated resin (SIR) system for removal of phenols from water, the complex formation of dimethyldodecylamine N‐oxide (DMDAO), trioctylamine N‐oxide (TOAO), and tris(2‐ethylhexyl)amine N‐oxide (TEHAO) with phenol (PhOH) and thiophenol (PhSH) is studied. To this end we use isothermal titration calorimetry (ITC) and quantum chemical modeling (on B3LYP/6‐311G(d,p)‐optimized geometries: B3LYP/6‐311+G(d,p), B3LYP/6‐311++G(2d,2p), MP2/6‐311+G(d,p), and spin component scaled (SCS) MP2/6‐311+G(d,p); M06‐2X/6‐311+G(d,p)//M06‐2X/6‐311G(d,p), MP2 with an extrapolation to the complete basis set limit (MP2/CBS), as well as CBS‐Q). The complexes are analyzed in terms of structural (e.g., bond lengths) and electronic elements (e.g., charges). Furthermore, complexation and solvent effects (in benzene, toluene, and mesitylene) are investigated by ITC measurements, yielding binding constants K, enthalpies ΔH⁰, Gibbs fre energies ΔG⁰, and entropies ΔS⁰ of complex formation, and stoichiometry N. The ITC measurements revealed strong 1:1 complex formation between both DMDAO–PhOH and TOAO–PhOH. The binding constant (K=1.7–5.7×10⁴ M ^?1) drops markedly when water‐saturated toluene was used (K=5.8×10³ M ^?1), and π–π interaction with the solvent is shown to be relevant. Quantum mechanical modeling confirms formation of stable 1:1 complexes with linear hydrogen bonds that weaken on attachment of electron‐withdrawing groups to the amine N‐oxide moiety. Modeling also showed that complexes with PhSH are much weaker than those with PhOH, and in fact too weak for ITC determination. CBS‐Q incorrectly predicts equal or even higher binding enthalpies for PhSH than for PhOH, which invalidates it as a benchmark for other calculations. Data from the straightforward SCS‐MP2 method without counterpoise correction show very good agreement with the MP2/CBS values.     

Evaluating Tannins and Flavonoids from Traditionally Used Medicinal Plants with Biofilm Inhibitory Effects against MRGN E. coli

In the search for alternative treatment options for infections with multi-resistant germs, traditionally used medicinal plants are currently being examined more intensively. In this study, the antimicrobial and anti-biofilm activities of 14 herbal drugs were investigated. Nine of the tested drugs were traditionally used in Europe for treatment of local infections. For comparison, another five drugs monographed in the European Pharmacopoeia were used. Additionally, the total tannin and flavonoid contents of all tested drugs were analyzed. HPLC fingerprints were recorded to obtain further insights into the components of the extracts. The aim of the study was to identify herbal drugs that might be useable for treatment of infectious diseases, even with multidrug resistant E. coli, and to correlate the antimicrobial activity with the total content of tannins and flavonoids. The agar diffusion test and anti-biofilm assay were used to evaluate the antimicrobial potential of different extracts from the plants. Colorimetric methods (from European Pharmacopeia) were used for determination of total tannins and flavonoids. The direct antimicrobial activity of most of the tested extracts was low to moderate. The anti-biofilm activity was found to be down to 10 µg mL⁻¹ for some extracts. Tannin contents between 2.2% and 10.4% of dry weight and total flavonoid contents between 0.1% and 1.6% were found. Correlation analysis indicates that the antimicrobial and the anti-biofilm activity is significantly (p < 0.05) dependent on tannin content, but not on flavonoid content. The data analysis revealed that tannin-rich herbal drugs inhibit pathogens in different ways. Thus, some of the tested herbal drugs might be useable for local infections with multi-resistant biofilm-forming pathogens. For some of the tested drugs, this is the first report about anti-biofilm activity, as well as total tannin and flavonoid content.     

链式与面式两种不对称疏水结构表面活性剂之间的相互作用热力学

本文通过等温滴定量热法(ITC)、电导法和浊度法研究了阴离子生物表面活性剂脱氧胆酸钠(NaDC)及其与相反电荷的十二烷基三甲基溴化铵(DTAB)在水溶液中的自组装热力学.ITC结果支持了NaDC在水溶液中先生成预胶束再形成稳定胶束的分步聚集模型,由此得到了NaDC的预胶束和胶束化过程的一系列热力学参数,并讨论了它们形成的热力学机理.进一步研究了具有头-尾链式和疏水-亲水刚性面式非对称结构的DTAB/NaDC混合体系的聚集热力学行为,得到了富NaDC临界混合胶束浓度(cmcmix)、富DTAB临界胶束浓度(CM)及对应过程的转变焓.结果表明,NaDC面式结构与DTAB链式结构的对称性差异以及相反电荷的相互作用,导致混合体系有别于单一表面活性剂或头-尾链式结构的混合体系的聚集行为.混合溶液的聚集行为受控于表面活性剂浓度和摩尔分数的变化.富NaDC胶束化过程为熵驱动,而富DTAB的两种胶束形态转变过程为熵焓共同驱动的热力学机理.这些结果对于从热力学角度认识胆汁酸盐的自组装机理以及与传统的头-尾链式结构的表面活性剂相互作用机理和相行为有重要的意义.     

Ferrocene conjugates with mannose: synthesis and influence of ferrocene aglycon on mannose‐mediated adhesion of Escherichia coli

Bacterial adhesion, mediated through interaction of bacterial lectins with carbohydrate structures presented on the surface of the host cells, is a prerequisite for infection. Anti‐adhesion therapy, based on the inhibition of lectins by suitable carbohydrates, has been considered as a weapon for the combat of microbial diseases. Structural alteration of aglycon portions of mannose derivatives strongly influences their inhibitory potency toward type 1 fimbriated Escherichia coli. Thus several conjugates of mannose‐containing ferrocene aglycon moieties were synthesized and tested. The novel ferrocene conjugates 10, 12 and 14 were obtained by esterification of O‐mannosylated propionic acid 1 with ferrocene alcohols R‐Fn‐(CH₂)_n‐OH (Fn = 1,1'‐ferrocenylene; 2, n = 1, R = COOMe; 7, n = 1, R = NHBoc; 8, n = 2, R = H) in the presence of Boc₂O/DMAP with subsequent debenzylation of the intermediate O‐protected esters. Performed hemagglutination inhibitory tests showed that the examined bioorganometallics exhibit better inhibitory activity than known inhibitor methyl α‐d ‐mannoside. Thus ferrocene–mannose conjugate 14 with the dimethylene spacer between ferrocene core and chiral linker displayed the best inhibitory efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

On the conformational stability and dimerization of phosphotransferase enzyme I from Escherichia coli

The activity of enzyme I (EI), the first protein in the bacterial PEP:sugar phosphotransferase system, is regulated by a monomer–dimer equilibrium where a Mg²⁺-dependent autophosphorylation by PEP requires the homodimer. Using inactive EI(H189A), in which alanine is substituted for the active-site His189, substrate binding effects can be separated from those of phosphorylation. Whereas 1 mM PEP (with 2 mM Mg²⁺) strongly promotes dimerization of EI(H189A) at pH 7.5 and 20 °C, 5 mM pyruvate (with 2 mM Mg²⁺) has the opposite effect. A correlation between the coupling of N- and C-terminal domain unfolding, measured by differential scanning calorimetry, and the dimerization constant for EI, determined by sedimentation equilibrium, is observed. That is, when the coupling between N- and C-terminal domain unfolding produced by 0.2 or 1.0 mM PEP and 2 mM Mg²⁺ is inhibited by 5 mM pyruvate, the dimerization constant for EI(H189A) decreases from >10⁸ to <5 × 10⁵ or 3 × 10⁷ M⁻¹, respectively. With 2 mM Mg²⁺ at 15–25 °C and pH 7.5, PEP has been found to bind to one site/monomer of EI(H189A) with K_A′10⁶ M⁻¹ (ΔG′=−33.7±0.2 kJ mol⁻¹ and ΔH=+16.3 kJ mol⁻¹ at 20 °C with ΔC_p=−1.4 kJ K⁻¹ mol⁻¹). The binding of PEP to EI(H189A) is synergistic with that of Mg²⁺. Thus, physiological concentrations of PEP and Mg²⁺ increase, whereas pyruvate and Mg²⁺ decrease the amount of dimeric, active, dephospho-enzyme I.