Monepaloside K,a New Triterpenoid Saponin from Morina nepalensis var.alba Hand.—Mazz.

One new triterpenoid saponin,monepaloside K(1) was isolated from the water-soluble part of the whole plant of a famous Tibetan medicinal herb,morina neplaensis var. alba Hand.-Mazz.Its structure was determined to be 3-O-α-L-arabinopyranosyl-(1→3)-β-D-xylopyranosyl siaresinolic acid on the basis of spectroscopic evidences,especially 2D NMR techniques.     

S. Wageh a,*, Ahmed A. Al‐Ghamdi a,Rashida Jafer a,Xin Li b,#, Peng Zhang c

太阳能是最丰富的清洁和可再生能源,光催化技术在太阳能利用中具有很大潜力,这有赖于高效半导体光催化剂的设计制备.然而,单一光催化剂效率很低,主要是光生电子和空穴的强库伦吸引力导致它们快速复合.此外,单一光催化剂也很难同时具有宽光谱吸收和足够的氧化还原能力.为了解决这一问题,构建异质结光催化剂成为一种有效途径,因为它可以实现光生电子和空穴在空间上的有效分离.针对传统的II型和Z型异质结在动力学和热力学方面的缺陷, 2019年由武汉理工大学余家国教授团队提出梯形异质这一新型异质结概念.对于II型异质结,热力学和动力学分析表明光生载流子的转移机理不正确.热力学和动力学分析表明光生载流子的转移机理不正确.而Z型异质结系统主要包括传统、全固态和直接Z型异质结三种类型.对于前两种异质结,它们的界面电子转移存在理论问题.传统Z型异质结利用氧化还原电对,而电子受体和给体更容易从与其具有较大的电势差的半导体接受或给予电子.全固态Z型异质结利用导体,比如导电金属或碳材料,取代氧化还原电对,从而使其应用范围由液态扩展到固态.然而通过进一步分析,它的电荷传输也有漏洞.首先,界面的肖特基势垒抑制电荷持续传输,此外,全固态Z型异质结中的导体与传统Z型中氧化还原电对的作用如出一辙.因此,传统Z型的问题在这里也依旧存在.总的来说, II型、传统和全固态Z型都面临相同的问题,就是光生电子和空穴拥有较弱的还原和氧化能力,而S型异质结则与它们截然不同.该异质结由氧化型和还原型光催化剂组成,内建电场、能带弯曲和库仑力三大作用促使氧化型的光生电子与还原型的光生空穴复合,同时阻止氧化型的光生空穴与还原型的光生电子转移.最终,电子和空穴分别具有高的还原和氧化能力.由于其优越性, S型异质结在各种光催化应用中引起了广泛的兴趣,包括产氢、二氧化碳还原、污染物降解和灭菌等领域.而S型异质结机理可以用X射线光电子能谱、电子顺磁共振和原子力显微镜进行表征.S型异质结崭露头角,未来发展可期.     

Alkaloids ofArundo donax. IV. donaxanine — a new pyrrolidine alkaloid fromArundo donax

The new pyrrolidone alkaloid donaxanine, C₁₂H₁₄N₂O₂, has been isolated from Arundo donax. Its structure has been shown by chemical transformations and a study of its IR, mass, and PMR spectra as spiro[(N-methylpyrrolidin-2-one)-3,4-(3,1-benzoxazine).Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 728–730, September–October, 1995. Original article submitted June 5, 1995.     

N-glycosides. 9. Reaction of 3,5-O-isopropylidenexylofuranosylamine with β-isothiocyanatoaldehydes. Synthesis of new cyclonucleosides with a hexahydropyrimidine aglycone

The reaction of 3,5-O-isopropylidenexylofuranosylamine p-toluenesulfonate with -isothiocyanatoaldehydes in the presence of triethylamine gives 4,2-anhydro-4-hydroxy-3-(3,5-O-isopropylidene--D-xylofuranosyl)hexahydropyrimidine-2-thiones. The structure of these compounds and their deblocking products was studied by IR, UV, PMR, and ORD spectroscopy and mass spectrometry.For Communication 8, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1252–1258, September, 1993.     

When Is a Bond Broken? The Polarizability Perspective.

The question of when a chemical bond can be said to be broken is of fundamental chemical interest but has not been widely studied. Herein we propose that the maxima of static polarizability along bond dissociation coordinates naturally define cutoff points for bond rupture, as they represent the onset of localization of shared electron density into constituent fragments. Examples of computed polarizability maxima over the course of bond cleavage in main-group and transition metal compounds are provided, across covalent, dative and charge-shift bonds. The behavior along reaction paths is also considered. Overall, the static polarizability is found to be a sensitive reporter of electronic structure reorganization associated with bond stretching, and thus can serve as a metric for describing bond cleavage (or diagnose the absence of a chemical bond).     

Pterisemipol, a novel sesquiterpenoid from Pteris semipinnata L.

A novel sesquiterpenoid,pterisemipol,was isolated from Pteris semipinnata L.Its skeleton,namely pterisane,was considered to be rearranged from protoilludane and its structure was elucidated on the basis of spectroscopic analysis.     

Hydrocarbon dispersion of nanospherical silica by a sol–gel process. 1. Tetraethoxysilane homopolymerization

This study focused on the preparation of a hydrocarbon dispersion of nanospherical silica using tetraethoxysilane homopolymerization by a sol–gel process catalyzed by NH₄OH in ethanol. The silica surface was rendered hydrophobic by the introduction of trimethylchlorosilane or trimethylethoxysilane as a terminator. Organophilic particles with diameters in the range 10–130 nm were obtained under controlled conditions. Nevertheless, the organophilic fraction dispersed in hexane was not greater than 62%. The homopolymerization reaction time was directly related to the particle size and, in some cases, its insolubility. High terminator concentration and low termination temperature favored the increase in the number of organophilic particles. The chlorine-containing terminator was more efficient in promoting the production of hydrocarbon hydrophobic nanospheres. Received: 21 February 2000/Accepted: 21 June 2000     

The heterometric micro-analysis of cobalt with α-nitroso - β-naphthol. a general study.

1. The reaction between cobaltous or cobaltic and α-nitroso-β-naphthol was extensively studied heterometrically both in water and in alcoholic solutions. The influence of complexing agents and of the acidity on the precipitation of cobalt-α-nitroso-β-naphthol was investigated. In all cases the molar ratios : [Co] [αβ] at the end of the precipitation were established and the possible compounds which were obtained were discussed. 2. Micro-analytical heterometric methods are given for the determination of cobalt or α-nitroso-β-naphthol. The determination can be carried out with precision even in concentrations as low as 0.0001M Co. Conversely, very dilute alcoholic solutions of α-nitroso-β-naphthol may be titrated with precision with a dilute solution of cobalt nitrate. 0.2–0.5 mg cobalt in 20 ml solution are required for the analysis. The error lies between zero and 3%.     

Sebiferone,a New Triterpenoid from Stem Bark of Sapium sebiferum （L.）Roxb.

From the stem bark of Sapium sebiferum a new triterpenoid,anmed sebiferone (1),was isolated.The structure of the new compound was clucidated as 3β-acetoxy-D-friedoolen-14-en-1-one-28-oic acid on the basis of spectral and chemical methods.     

The hydroperoxysulfonium ylide. An aberration or a ubiquitous intermediate?

An intramolecular isotope effect has been measured for the reaction of singlet oxygen with 2,2,8,8-tetradeuterio-1,5-dithiacyclooctane, 4d₄. The magnitude of the isotope effect, 1.21±0.09, provides verification of removal of an α-hydrogen during the product determining step to form a hydroperoxysulfonium ylide and ultimately the sulfoxide product. The absence of any special structural features in 4d₄ to enhance the propensity of hydrogen removal is used to suggest that the hydroperoxysulfonium ylide is a ubiquitous intermediate in the reactions of sulfides with singlet oxygen.     

Bericht über die DECHEMA-Jahrestagung 1963 vom 25. bis 26. April im Saal des Palmengartens zu Frankfurt a. M

Ohne Zusammenfassung     

Fusarielin E, a new antifungal antibiotic from Fusarium sp.

A new antifungal antibiotic,fusarielin E,was isolated from the marine-derived fungus Fusarium sp.Its structure was established on the basis of various NMR spectroscopic analyses and HR-FAB-MS.Fusarielin E displayed significant biological activity against Pyricularia oryzae.