Explicit and implicit multi‐center integrations

We present truncated expansions of multicenter one‐electron nuclear attraction and two‐electron repulsion integrals over localized basis functions in terms of one‐ and two‐center integrals of “Coulomb,” “exchange,” and “hybrid” type. Two variants are discussed: the “Explicit Multi‐center Integrations” and the “Implicit Multi‐Center Integrations” (abbreviated as “EMCI” and “IMCI”, respectively). While EMCI also deals with individual integrals, the IMCI option is the more appealing one: it enables us to evaluate the entire matrix elements of “Restricted Hartree–Fock”‐type in a very effective and chemically meaningful way. Due to the diatomic nature of our expansions, integrations over “Slater‐Type Orbitals” become well‐feasible, too. © 2012 Wiley Periodicals, Inc.     

Quantification of water soluble vitamins in six date palm (Phoenix dactylifera L.) cultivar's fruits growing in Dubai,United Arab Emirates,through high performance liquid chromatography

In present investigation, a comparative analysis of water soluble vitamins viz., B1 (thiamine HCl), B2 (riboflavin), B3 (nicotinamide), B5 (pantothenic acid), B6 (pyridoxine HCl), B9 (folic acid), B12 (cyanocobalamin) was carried out in fruits (immature, semimature and mature) of six date palm (Phoenix dactylifera L.) cultivars (“Barhee”, “Khalasah”, “Muzati”, “Shishi”, “Zart”, “Zardai”) growing in United Arab Emirates (UAE) by high performance liquid chromatograph (HPLC). The fruits were collected at three developing stages (immature, semimature and mature). Quantitative analysis of water soluble vitamins yield showed a significant variation within the different cultivars and the developing stages of date palm fruit. Vitamin B1, B3, B5, B6 were maximum (μg/100 g f.w.) in “Shishi”, “Zardai”, “Shishi” and “Muzati” at their matured stage, however, vitamin B2, B9, B12 were detected in immature fruit of “Khalasah”, “Khalasah” and “Shishi” cultivars. The vitamin production in fruits of different date palm cultivars was, therefore, developing stage specific and cultivar dependent. The present study showed that the date palm fruit could be used for human consumption with value addition of water soluble vitamins at their specific developmental stages.     

基于模型建构的“初中化学用语”教学*——从知识传递走向深度学习

通过化学用语认识模型的建构,彰显其教学功能价值,为内隐的“心智模型”与外显的“符号模型”之间建立可能的联系和发展。运用“联想与建构”“迁移与体验”“本质与变化”等教学策略,实现化学用语的教学从内容传递走向深度学习。     

用“表面离子”法制备组分可控的LB膜超分子体系

综述了LB膜超分子体系中“表面离子”法的概念及其与传统的“亚相离子”法的区别. 分别以钌螯合物(Ru(ph2phen)32＋)和金属β-二酮螯合物为例,详细描述这两类不同的“表面离子”在水面上的成膜作用机理,并举例说明“表面离子”法在铺展膜和LB膜中,功能分子二维密度和凝聚态结构精确可调,并对“表面离子”法在多功能分子体系中的应用作了详细描述.     

Separation and Identification of Glycosaminoglycans

The term “mucopolysaccharides” was originally introduced by Meyer to describe “hexosamine-containing heteropolysaccharides of animal origin occurring in a pure state or as protein salts”. Many of the names originally assigned to the mucopolysaccharides have since been revised in an effort to systematize the nomenclature (Table 1). Jeanloz² in 1960 proposed the term “glycosaminoglycuronoglycans” in place of mucopolysaccharides as in most cases they are composed of amino sugars (glycosamino-) and uronic acids (glycurono-) joined in long chains(-glycans). For the sake of simplicity, the term “glycosaminoglycans” is getting acceptance in place of the rather lengthy term “glycosaminoglycuronoglycans” as well as the old and perhaps more familiar term “mucopolysaccharides”. As a matter of convenience, the term “polysaccharides” will be frequently used here, instead of glycosaminoglycans.     

Acoustique d'un fluide au voisinage du point d'ébullition

In a previous paper (Boutin and Auriault 1993) the homogenization technique of multiscale expansions was used for investigating how acoustic waves may propagate in a bubbly fluid at finite concentration. Three different equivalent macroscopic behaviours where derived, for “large”, “medium” and “small” bubble systems, respectively. In the present paper, we extend the analysis by taking into consideration possible phase change effects. We show that phase change effects are negligible in the case of “large” bubbles, whereas they strongly modify the “medium” bubble system behaviour by decreasing the bulk modulus of several orders of magnitude. For “small” bubbles, capillary effects are dominating.     

CCK1受体的同源模拟和分子对接研究

采用同源建模法对CCK1受体的三维结构进行了模拟,并采用分子动力学方法对模型进行修正和优化,再采用与训练集激动剂和拮抗剂分子对接的方法分别得到激动状态和拮抗状态CCK1受体的三维结构模型。得到的模型使用DOCK对接软件对训练集中的分子进行对接,所得结果与其实际活性拟合度较好,说明我们建立的激动和拮抗状态下的CCK1受体的三维结构模型比较合理,可以作为化合物虚拟筛选的模型对新化合物进行虚拟筛选。     

Stereochemistry and dynamic behavior of some synthetic “angular” profisetinidin tetraflavanoid derivatives

The structure and stereochemistry of four synthetic “angular” tetraflavanoid-condensed tannin derivatives are examined by high-resolution variable temperature ¹H NMR. spectroscopy, and hence correlated with their dynamic behavior. Three “angular” oligomers exist as stable rotational isomers at ambient temperatures, thus contrasting with the mobility about their interflavanoid bonds of most natural profisetinidin “trimeric” and “tetrameric” homologs. A “linear” tetraflavanoid analog results from one of these regioselectively controlled condensations.     

Metallocene catalysts for the polymerization and copolymerization of α‐olefins: a research collaboration project report

Results obtained during the tenure of a BMBF‐supported collaborative research project, comprising the parts “Exploration of new ansa‐metallocene complexes”, “Commercially applicable metallocene syntheses”, “Metallocene catalysts on solid supports” and “Improved control of the polymerization process”, are reported in condensed form.     

Quadratisch,praktisch, natürlich?

In 2013 the consumer group Stiftung Warentest conducted tests on nut containing chocolates and detected piperonal (heliotropine) in Ritter‐Sport's “Voll‐Nuss” (whole hazelnut). Stiftung Warentest concluded that piperonal could not be obtained naturally and that Ritter‐Sport misled consumers by falsely labelling it as “natural flavor.” Ritter said the allegations were “baseless” and went to court. During the court case, Ritter's flavor supplier Symrise AG guaranteed that the “natural” piperonal was manufactured “naturally” according to the European flavor regulations. Ritter‐Sport had “won” the “German chocolate battle.” Although the full manufacturing process has not been revealed during the court case, there are many hints in the scientific and patent literature that piperonal can be indeed produced naturally in accordance with the European flavor regulations.     

Experimental Tests of Parity Violation at Helical Polysilylene Level

The author would like to announce the following corrections: On page 671, right column, line 2, the sentence should read “For a certain polysilylene, ΔE_ST is reported to be 0.32 eV”. The insets in Figure 3d should read “S‐1” and “R‐1” instead of “S‐1L” and “R‐1L” . In the reference section, [34] reads correctly “Y. Ishimaru, S. Sumida, T. Iida, Chem. Commun. 1997 , 2187‐‐2188”.     

Bioactive principles in exudate gel from the leaf of Aloe fleurentiniorum,traditionally used as folkloric medicine by local people of Aridah and Fayfa mountains,Saudi Arabia

Aloe fleurentiniorum is a desert plant that is occasionally used to treat wounds by local people of Aridah and Fayfa mountains in Saudi Arabia. However, medicinal value of the plant has not been scientifically established. The purpose of this study was to determine the bioactive phytocomponents contained in the exudate gel (EG) from the leaves of Aloe fleurentiniorum using GC–MS and FT-IR studies, as well as antibacterial assays. Medicinally important bioactive compounds were identified using GC–MS analysis. The bioactive compounds are “pregn-5-ene-3α,20-diol”, “16α-methyl-pregnane-11,20-dione”, “3-hydroxy-(3α,5α)-, ursodeoxycholic acid”, “1-heptatriacotanol”, “allopregnane-7α,11α-diol-3,20-dione”, “D-arabino-hexopyranoside”, “2-octadecenoic acid methyl ester”, “D-ribo-hexose,2,6-dideoxy-3-O-methyl glucosamine”, “N-acetyl-N-benzoyl-alpha-D-glucopyranoside”, “nonyl 1-thio pregnenolone”, “5-cholestene-3-ol, 24-methyl-cholestanol”, and “D-allose hexadecanoic acid methyl ester”. Furthermore, specific groups and their respective chemical compounds were identified via FT-IR spectroscopy studies. The FT-IR spectroscopy of EG showed various functional groups at 3354, 2945, 2832, 2523, 2046, 1707, 1451, 1108, 1031, 880, 737 and 610 cm⁻¹. The FT-IR peaks revealed the likely presence of various compounds such as glycosides, flavonoids, steroids, saponins, flavonoids, amino sugars, cutin and isothiocyanate. Moreover, EG produced a wide range of antibacterial effects on some screened human pathogenic bacteria.     

Remarques sur les définitions des acides et des bases

In the present state of knowledge it is not possible to account for the reactions used in analytical chemistry by setting up a single table of the “acids” and “bases” defined according to LEWIS.The most general definition which can be usefully adopted involves taking into account the exchange of “particles” (electrons, protons, ions, molecules) in the reactions. It follows from this that there arc as many types of reactions as there are “particles”.In accordance with the brönsted theory, in the case where the “particle” exchanged is the proton, an acid-base reaction is involved.     

Characterization of precursors of p-tert-butylcalix[6]arene synthesis. Mechanism of formation of p-tert-butylcalix[6]arene

Abstract

Gutsche has proposed the existence of “hemicalixarenes” and “pseudocalixarenes” to explain the formation of calixarenes. The characterization and the quantitative determination of molecules present during the reaction, described in “Organic Synthesis”, have permitted us to determine the immediate precursors of p-tert-butylcalix[6]arene. The calix[6]arene could be due to cyclization of linear species named “pseudocalixarenes” and not due to duplication of molecules named “hemicalixarenes”.     

What's Hot,What's Not: The Trends of the Past 20 Years in the Chemistry of Odorants

This review is the sequel to the 2000 report on the recent advances in the chemistry of odorants and it summarizes the developments in fragrance chemistry over the past 20 years. Following the olfactory spectrum set out in that report, trendsetting so‐called captive odorants (patent‐protected ingredients unavailable to the market) are presented according to the main odor families: “fruity”, “marine”, “green”, “floral”, “spicy”, “woody”, “amber”, and “musky”. The design of odorants, their chemical synthesis, and their use in modern perfumery are illustrated with prominent examples. Featured are new fruity odorants that provide signature in the top note, as well as precursor technology. In the green domain, focus is on leafy notes and green pear. New benzodioxepines and benzodioxoles have modernized the marine family and required a revision of the existing olfactophore models. The replacement of Lilial and Lyral kept the industry busy in the floral domain with a plethora of new “muguets”. There was continued activity in the domain of rose odorants, especially in the area of rose ketones. Biotechnology became significant, for example, with Clearwood and Ambrofix, and the principal odorants of vetiver oil in the woody family have been found. Fourth and fifth families of musk odorants were also discovered and populated. Thus, new avenues for further explorations into fragrance chemistry have been opened.     

On the “Wolfsberg–Helmholz Conjecture” of “Extended‐Hückel Theory”

After having reviewed some pioneer integral approximations closely related to Rüdenberg's expansions of one‐ and two‐electron orbital products, we apply the previously described “Implicit Multi‐Center Integration” techniques on Roothaan's “restricted” Fock‐matrix components over standard atomic orbital bases. The resulting compact forms are very similar to the well‐known “Wolfsberg–Helmholz Conjecture” of “Extended‐Hückel Theory,” which relates the various off‐diagonal matrix elements of “restricted” Fock‐type to their corresponding diagonal counterparts. In this way, a “nonempirical Extended‐Hückel Theory” can be created. © 2012 Wiley Periodicals, Inc.     

Do Anti‐Bredt Natural Products Exist? Olefin Strain Energy as a Predictor of Isolability

Bredt’s rule holds a special place in the realm of physical organic chemistry, but its application to natural products chemistry—the field in which the rule was originally formulated—is not well defined. Herein, the use of olefin strain (OS) energy as a readily calculated predictor of the stability of natural products containing a bridgehead alkene is introduced. Schleyer first used OS energies to classify parent bridgehead alkenes into “isolable”, “observable”, and “unstable” classes. OS calculations on natural products, using contemporary forcefield methods, unequivocally predict all structurally verified bridgehead alkene natural products to be “isolable”. Thus, when one assigns the structure of a putative bridgehead alkene natural product, an OS in the “observable” or “unstable” ranges is a red flag for error.