Model studies for the synthesis of the antibiotic lactonamycin and the discovery of new reactions and mechanisms for the construction of substituted heterocycles

A new and highly efficient route for the construction of a model for the synthesis of lactonamycin 1 is reported. The chemistry has been utilised for the synthesis of heterocyclic rings, and new reactions for the synthesis of dienes and alkynes are reported.     

Separated internal force constants for the ethylene and ethane molecules and their use for calculation of the force field for the propylene molecule

We consider the question of separation of linear combinations of force constants for ethylene and ethane. Introduction of a perturbation into the matrix of the kinematic coefficients allows us to solve the inverted vibrational problem using the matrix method of successive approximations without eliminating dependent coordinates. Such an approach makes it possible to obtain a sufficient system of equations for determining the separated internal force constants. The separated internal force constants determined for ethylene and ethane are used to calculate the force field for propylene. The calculated separated internal force constants for propylene reproduce its vibrational spectrum and the spectrum or propylene-d₆ with average deviation from experimental frequencies of 8 cm^–1. The numerical influence coefficients for stretching vibrations of the C-H bond are linearly related to the lengths of these bonds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 118–122, Janauary–February, 1986.     

蟹,虾壳微观形貌与结构研究

用Ｘ射线衍射与扫描电镜研究了蟹壳，虾壳的形貌与微观结构，蟹壳中以方解石晶型存在的碳酸钙分布在网状结构的有机质中，网孔的尺寸约５～２５μｍ有机基质脱去蛋白后留下的甲壳质呈片层状结构，它的重复距离为０．９６ｎｍ。     

An algorithm for the uniform sampling of iso-energy surfaces and for the calculation of microcanonical averages

In this article an algorithm is proposed to efficiently perform the uniform sampling of an iso-energy surface corresponding to a fixed potential energy U of a molecular system, and for calculating averages of certain quantities over microstates having this energy (microcanonical averages). The developed sampling technique is based upon the combination of a recently proposed method for performing constant potential energy molecular dynamics simulations [Rapallo, A. J Chem Phys 2004, 121, 4033] with well-established thermostatting techniques used in the framework of standard molecular dynamics simulations, such as the Andersen thermostat, and the Nose-Hoover chain thermostat. The proposed strategy leads to very accurate and drift-free potential energy conservation during the whole sampling process, and, very important, specially when dealing with high-dimensional or complicated potential functions, it does not require the calculation of the potential energy function hessian. The technique proved to be very reliable for sampling both low- and high-dimensional surfaces.     

A new approach for the ortho-substitution of anilines and for the synthesis of indolines

Intermolecular radical addition of a xanthate to a vinyl sulfanilide is followed by ring closure to the aromatic ring to give a dihydrobenzoisothiazole dioxide structure, which upon heating loses sulfur dioxide to give a 2-substituted aniline; in some examples, the presence of DBU during heating induces the formation of an indoline.     

开环葫芦脲在水中对芳烃和芳醛的增溶和对腙大环形成的促进作用

利用核磁实验,研究了并入四个磺酸根或羧酸根的高水溶性开环葫芦脲对疏水性芳烃和芳醛的水相增溶作用.并入四个磺酸根的开环葫芦脲acCB-1能显著提高包括三联苯、4,4’-二甲基联苯和联苯-4,4’-二甲醛在内的芳烃和芳醛的水溶性,其中4,4’-二甲基联苯的溶解度可以提高到8.9mmol/L,联苯-4,4’-二甲醛的溶解度可以提高到11.2mmol/L.并入四个羧酸根的acCB-2可以把五氟甲苯和六氟苯在水中的溶解度提高到5.6和3.0 mmol/L. acCB-1还可以通过增溶芳香醛,促进其与酰肼反应形成腙.这一促进作用可以进一步应用于促进两个芳香二醛和一个芳香二酰肼在水中的反应,制备常规条件下不能形成的两个芳香腙大环.     

Theoretical models for the conformations and the protonation of triacetonamine

Summary In this paper we propose theoretical models for the conformations of triacetonamine and protonated triacetonamine (Vincubine, an anticancer chemotherapeutic agent) developed by quantum and molecular mechanics techniques. We discuss the theoretical factors which are involved in the stabilization of the conformations calculated by the MNDO, MM2 and COPEANE methods and show the relative percent abundance of each molecular shape. Graphic representations of the conformers are depicted.     

吸热型碳氢燃料裂解引发剂筛选及引发机理分析

筛选可溶性添加剂替代多相催化剂, 达到促进吸热型碳氢燃料裂解、提高燃料热沉以及燃烧性能的目的. 采用考察裂解气相产物气体流量的方法进行实验. 测试了10种添加剂在500～650 ℃范围内对正庚烷裂解效果的影响. 研究发现, 三乙胺、2,6-二叔丁基对甲酚(BHT)可促进正庚烷裂解, 其它添加剂均无显著效果. 在550 ℃时, 当三乙胺质量分数达到6%时, 实验总气体收率比计算总气体收率增加80%以上. 机理研究表明, 三乙胺的引发剂基团来源于C—N键的断裂. BHT的结构、性状与前者显著不同, 在550 ℃时, 当BHT质量分数为3.4%时体系的气体收率较之纯正庚烷裂解气体收率增加80%以上, BHT的引发基团主要是连接于叔丁基上的甲基发生脱离的结果     

Chemical and physical analysis for the improvement of the dry mounting method for fragile documents

Paper lamination is a widely used method to consolidate fragile documents. Previous studies have presented a new method of lamination that allows the consolidation of documents before undertaking aqueous treatments. In this method a thin Japanese paper coated with an acrylic resin is applied on the fragile document by means of a heated press. In this work we optimised the preparation of the lamination sheets as well as the working procedures, and we were able to establish that our laboratory-made specimens are chemically stable, easily reversible and permeable to aqueous solutions. The latest property is of particular importance, since it allows a subsequent aqueous deacidification even for fragile documents. The laminated paper documents were further analysed by means of colorimetry and FTIR spectroscopy before and after accelerated ageing as well as by determination of the alkali reserve left on the coated paper, in order to compare our lamination method with other commercially available lamination sheets.     

Conditions for the formation of superconductive polymers and possibilities for their realization

General principles of the creation of superconductivity at the polymers are considered. It is shown that high temperature superconductivity may be produced only at really one-dimensional conducting materials. It is also shown that conjugated polymers cannot have onedimensional conductivity. The new class of nonconjugated polar elastomers is proposed as a perspective one for the creation of high temperature superconductive structures–superpolarons–which appear as a result of internal selfionization of the polymer matrix and a consequent selforganization of free polarons. The practical methods of the formation of superpolarons are shown for the films of oxidized atactice polypropylene. Evidences are given which show the existence of superconductive structures in oxidized polypropylene at room temperature.     

Electrospray mass spectrometry for the analysis of opioid peptides and for the quantification of endogenous methionine enkephalin and β-endorphin

Electrospray ionization mass spectrometry was used to characterize several different neuropeptides, whose molecular weights ranged from 555 to 3463 Da, and to quantify endogenous methionine enkephalin (ME) and β -endorphin (β E) extracted from a human pituitary gland. Methionine enkephalin and leucine enkephalin both yield only an [M + H] + ion with electrospray mass spectrometry; the other peptides produce a series of multiply charged even-electron molecular ions of the general nature [M + nH]ⁿ+ in proportion to the number of basic amino acid units present, with no evidence of fragmentation. The electrospray mass spectra are characterized by low background noise. The quantiftcation of ME is based on a comliarison of the ion current due to the [M + H] + ion of native and of a deuterated ME ([²H₅ s?⁴Phe]?ME) internal standard. The calibration curve is linear in the range of ca. 1-35 pmol synthetic ME. The amounts of ME determined in three separate human pituitary extracts were 9.1, 8.2, and 4.7 pmol/mg protein. The corresponding amount of ME in a canine pituitary was 39.8 pmol/mg protein. To quantify β E, the ion current due to the [M + 5H]⁵ + ion was monitored and compared to an external calibration curve obtained by analyzing solutions of synthetic β E in the range 5 μmol-50 pmol. The analysis of a human pituitary yielded 660 fmol β E/mg protein.     

Reasons for the decomposition of the fungicide thiram during preparation of fruit and vegetable samples and consequences for residue analysis

The concentration of thiram in aqueous solution decreases by 50-75% within 20 min in the presence of cut pieces of apple, cucumber or celeriac with a section surface area of 160 cm2 each. The decomposition rate is predominantly influenced by the section surface area of the cut fruit and vegetable samples. Denaturing reaction conditions (exchange of the solvent water by methanol; boiling of sample material) will significantly slow down the decomposition rate. It was concluded that the thiram decomposition had been caused by enzymes on the section surface of the fruit and vegetable samples. For a specific determination of thiram, a simple rinsing of the intact fruit and vegetable material was appropriate as extraction method. For the screening of thiram residues, the often used Keppel method, which determines CS2 from thiram or dithiocarbamates seems to be applicable even if samples had been coarsely cut, since decomposition of the CS2-forming intermediates is slower than the breakdown of thiram itself. Therefore, specific determination of thiram is necessary only, if maximum residue limits for dithiocarbamates are not adhered to.     

Reasons for the decomposition of the fungicide thiram during preparation of fruit and vegetable samples and consequences for residue analysis

The concentration of thiram in aqueous solution decreases by 50–75% within 20 min in the presence of cut pieces of apple, cucumber or celeriac with a section surface area of 160 cm² each. The decomposition rate is predominantly influenced by the section surface area of the cut fruit and vegetable samples. Denaturing reaction conditions (exchange of the solvent water by methanol; boiling of sample material) will significantly slow down the decomposition rate. It was concluded that the thiram decomposition had been caused by enzymes on the section surface of the fruit and vegetable samples. For a specific determination of thiram, a simple rinsing of the intact fruit and vegetable material was appropriate as extraction method. For the screening of thiram residues, the often used Keppel method, which determines CS₂ from thiram or dithiocarbamates seems to be applicable even if samples had been coarsely cut, since decomposition of the CS₂-forming intermediates is slower than the breakdown of thiram itself. Therefore, specific determination of thiram is necessary only, if maximum residue limits for dithiocarbamates are not adhered to.     

Symmetry coupling coefficients for point groups and the importance of Racah's Lemma for the standardization of phase

Useful approaches to the calculation of symmetry coupling coefficients _{1 1 2}/₂|b are reviewed. Since a common phase factor always remains undetermined for each trio of ₁, ₂, and, a unique standardization of phase is proposed by the requirement, in Racah's lemma, (j _{1 1} a ₁,j _{2 2} a ₂|j ab) 0and real. In conjunction with the basis relations and the phase convention for Wigner coefficients, a novel method is suggested for the calculation of symmetry coupling coefficients in the group G from those in the subgroupG SU(2) orR ₃. The results apply in full generality to any point groupG, single or double group.