A Study of the Hydration of Lime-Pozzolan Binders

DTA/TG and TG/DTG thermal studies and XRD investigations were carried out on pastes of lime-pozzolan binders to examine the relative hydration process. The binders were prepared with two natural pozzolans and hydrated lime, mixed together in different proportions. The main hydrated phases formed in the pastes are calcium silicate hydrate (CSH) and mono-carboaluminate. The growth of CSH was greater for the paste of the pozzolan richer in reactive constituents. For pastes with a higher lime/pozzolan ratio, a slowing of the formation of CSH was observed, while the formation of monocarboaluminate was more intense. The calcium hydroxide contents of the pastes obtained by thermogravimetric analysis made it possible to determine the pozzolanic activities of the two pozzolans under examination. The mortars for the various lime-pozzolan binders displayed characteristic hardening. This revised version was published online in July 2006 with corrections to the Cover Date.     

Configurational analysis of the natural product passifloricin A by quantum mechanical C NMR GIAO chemical shift calculations

Quantum chemical calculations at mPW1PW91 level, with full geometry optimization, using the 6-31g(d) basis set, and GIAO (gauge including atomic orbitals) ¹³C NMR chemical shifts using the 6-31g(d,p) basis set, are here utilized as a support to define the configurational features of the natural product passifloricin A, whose previously proposed relative configuration has been recently shown, by synthetic studies, to be incorrect. This study suggests that the relative stereostructure for passifloricin A corresponds to the δ-lactone of the (5R,7R,9S,11R)-tetrahydroxyhexacos-2-enoic acid.     

Towards the synthesis of [15]-membered stevastelins through the 2,3-epoxy analogues

A synthetic approach to the [15]-membered stevastelins, a novel class of immunosuppressant agents, is reported based on a macrolactamization route to the 2,3-epoxy derivative 6. The synthesis of this compound was achieved via a stereoselective epoxidation of the allylic alcohol 13, followed by a coupling reaction with a variety of peptide derivatives to give the epoxy peptides 7-10. After an extensive study of cyclizations with these precursors, the best result was achieved with the macrolactamization of 8 in the presence of DEPC, to obtain the epoxy cyclic depsipeptide 6 in 42% yield. From this product, an epoxy analogue of stevastelin B, compound 27, was prepared. Finally, the synthesis of the natural product was attempted through the opening of the oxirane ring contained in 6 and 26, with a variety of methyl cuprate reagents, but without success.     

Thermodynamics of formation of nitrogen bases and d-ribose from mineral substances in light of the problem of origination of simplest elements of living matter

The paper represents a further development of our hydrate hypothesis of simplest living matter origination (SLMO) from inorganic and simplest organic mineral substances. It is supposed that the sources of SLMO are simplest aliphatic hydrocarbons, niters, and phosphates. Thermodynamic calculations demonstrating a principal possibility for simultaneous syntheses of different nitrogen bases, d-ribose, and desoxy-d-ribose from these source substances are presented. The most probable principal mechanism of SLMO and the principal conditions necessary for realization of the proposed chemism of SLMO in the framework of the proposed mechanism are considered. A principal means for testing the hypothesis is proposed.     

The α-β inversion in submilligram particles of natural quartz

The bacground to the supposed development of the ‘Beilby layer’ on fine-grinding quartz is briefly reviewed. It is shown, using single crucible thermal analysis and sub-milligram DTA, that grinding quartz can cause a dispersion of the α-β inversion over a temperature range of several degrees; this is a crystallographic effect rather than an impurity effect. The sub-milligram DTA apparatus used is described and some thermal effects, such as impurity zoning, are illustrated.     

Protein-reactive natural products

Researchers in the post-genome era are confronted with the daunting task of assigning structure and function to tens of thousands of encoded proteins. To realize this goal, new technologies are emerging for the analysis of protein function on a global scale, such as activity-based protein profiling (ABPP), which aims to develop active site-directed chemical probes for enzyme analysis in whole proteomes. For the pursuit of such chemical proteomic technologies, it is helpful to derive inspiration from protein-reactive natural products. Natural products use a remarkably diverse set of mechanisms to covalently modify enzymes from distinct mechanistic classes, thus providing a wellspring of chemical concepts that can be exploited for the design of active-site-directed proteomic probes. Herein, we highlight several examples of protein-reactive natural products and illustrate how their mechanisms of action have influenced and continue to shape the progression of chemical proteomic technologies like ABPP.     

Theoretical study of 3d‐metal mononitrides using DFT method

3d‐Metal mononitrides are studied using the density functional theory method. The lowest spin state for these dimers is obtained using the B3LYP hybrid functional with the 6‐311+G* basis set. The equilibrium geometries, vibrational frequencies, binding energies, Mulliken, and natural orbital population analysis charges, natural orbital electronic configuration, electron affinity, and ionization potential are obtained. Mulliken as well as natural orbital population analysis charges indicate that for all dimers, in cations most of the positive charge localized on the transition metal atom where in anions most of the negative charge localized on nitrogen atom. The binding energies for 3d‐metal mononitrides are higher than those for monocarbides and monoxides. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

A New Model for the Genesis of Natural Gases--Multi-source Overlap, Multi-stage Continuity, Type Controlled by Main Source and Nomenclature by Main Stage (Ⅰ)--Multi-source Overlap and Type Controlled by Main Source

Based on the geochemical studies of natural gases in the past ten years in China, the authors have proposed a new model for their genesis--multi-source overlap, multi-stage continuity, main source-controlling type and nomenclature by the main stage.Multi-source refers to a diversity of material sources involved in the formation of natural gases, including abiogenic and biogenic material sources. In regard to biogenic sources, either oil-generating or coal-generating organic matter would produce gaseous hydrocarbon reservoirs of commercial importance. Generally, natural gases originating from these sources can overlap to form gas reservoirs. Under specific circumstances mantle-source abiogenic gases could overlap biogenic gases to form gas reservoirs. In nature, natural gases predominated by gaseous hydrocarbons may be formed from a single end-member source. However, multi-source overlap is more typical of the genesis of natural gases.     

DFT study and vibrational spectra of the phoshorus-containing G0 generation dendrimer

The Raman (10–3500 cm⁻¹) and infrared (150–3500 cm⁻¹) spectra have been recorded for tris(4-oxibenzaldehyde)thiophosphate. This compound includes structural parts of elementoorganic dendrimers: a core and terminal aldehyde groups. The structural optimization and normal mode analysis are performed for elementoorganic dendrimer on the basis of the ab initio density functional theory. It is found that the dendrimer exist in a single stable conformation with planar C₆H₄CHO fragments. Our calculations show that conformer with one trans and two gauche 4-oxibenzaldehyde groups is realized. All these observations suggest that steric congestion does not disturb the construction of dendrimers even for the highest generations, and that terminal groups are readily available for further reactions. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied dendrimers.     

C30卡宾三叶结分子结构与稳定性的理论研究

三叶结分子是最简单的非平凡纽结分子, C₃₀卡宾三叶结分子是由一条闭合的(C≡C—)₁₅ sp杂化碳链组成的, 是具有D₃对称性的拓扑手性分子. 本文用密度泛函方法[DFT/RB3LYP/6-31G(D)]对分子结构和光谱性质进行了研究, 在优化构型的基础上通过自然键轨道(NBO)方法和轨道能级研究了它的共轭性、成键情况和稳定性, 并与平面型C₃₀卡宾环分子进行了比较. 计算结果表明三叶结分子的三叶弧上形成了非平面的C≡C共轭和扭曲的内螺旋结构, 交叉处具有弱成键作用, 且分子轨道也发生了扭曲; 三叶结分子比卡宾环的共轭性和赝Jahn-Teller效应都明显小, 而总能量高. 因此, 分子打结是一个能量升高的过程.