A computer system for structural identification of organic compounds from 13C NMR data

A computerised library search system for ¹³C NMR data is described. Given the spectral data of an unknown compound, the system will retrieve from the library those reference compounds exhibiting similar spectra. For comparison the spectral data are converted into a binary code, designed to reflect the underlying structure rather than exact values for chemical shifts. Thus, the ability of the system to retrieve compounds similar to the unknown (as opposed to identical) is greatly enhanced. A sophisticated search strategy adapting itself automatically to the problem at hand makes the system highly efficient.     

New liquid crystalline di- and tetra-acrylates for network formation

New liquid crystalline diacrylates and tetra-acrylates containing four to six aromatic rings were synthesized and characterized, and their mesophase behaviour was investigated. They are designed to be used in combination with chiral molecules to form cholesteric mesophases which can be crosslinked by photopolymerization. The acrylates presented exhibit broad mesophase ranges since mesogenic moieties longer than three are employed. Most diacrylates show no isotropization, due to premature thermal polymerization above 180°C. Additionally, liquid crystalline dipropionates were synthesized as reference compounds which cannot be crosslinked, and selected examples of these exhibit isotropization temperatures as high as 238°C prior to thermal degradation. Substituents at the mesogenic moiety have a great influence on the mesophase characteristics. Bulky substituents such as the tert-butyl group, induce a nematic mesophase, whereas compounds with small substituents (e.g. OCH3) or unsubstituted molecules also exhibit smectic phases. Tetra-acrylates with unsubstituted and substituted mesogenic units feature nematic mesophases only as a result of the additional spacers attached. Here isotropization was observed without polymerization at temperatures around 120-160°C.     

Pyroxene‐type compounds NaM3+Ge2O6, with M = Ga,Mn, Sc and In

The four title compounds, namely sodium gallium germanate, NaGaGe₂O₆, sodium manganese vanadate germanate, NaMnV_0.1Ge_1.9O₆, sodium scandium germanate, NaScGe₂O₆, and sodium indium germanate, NaInGe₂O₆, adopt the high‐temperature structure of the pyroxene‐type chain germanates, with monoclinic symmetry and space group C2/c. The lattice parameters, the individual and average bond lengths involving M1, and the distortion parameters scale well with the ionic radius of the M1 cation. NaGaGe₂O₆ has more distorted M1 sites and more extended tetrahedral chains than NaInGe₂O₆, in which a high degree of kinking is required to maintain the connection between the octahedral and tetrahedral building units of the pyroxene structure. An exceptional case is NaMnGe₂O₆, in which the strong Jahn–Teller effect of Mn³⁺ results in more distorted octahedral sites than expected according to linear extrapolation from the other NaM³⁺Ge₂O₆ pyroxenes. In contrast with the literature, minor incorporations of V⁵⁺ in the tetrahedral site and a corresponding reduction of Mn³⁺ to Mn²⁺ in the octahedral sites in the present sample lower the Jahn–Teller distortion and stabilize the Mn‐bearing pyroxene, even allowing its synthesis at ambient pressure.     

Ein neues Reagens auf Caffein

Ohne Zusammenfassung     

Ueber Aequivalentverh?ltnisse der Eiweissk?rper

Ohne Zusammenfassung     

Preparative separation of flavonoid glycosides in leaves extract of Ampelopsis grossedentata using high-speed counter-current chromatography

Preparative separation of flavonoid glycosides in leaves extract of Ampelopsis grossedentata was conducted using high-speed counter-current chromatograph (HSCCC) with a solvent system composed of n-hexane-ethyl acetate-methanol-water (1:6:1.5:7.5, v/v). In a single operation, 28 mg of 5,7-dihydroxy-3',4'-trihydroxyflavone-3-O-6'-rhamnose and 18 mg of 5,7-dihydroxy-3',4'-dihydroxyflavone-3-O-6'-rhamnose was obtained from 150 mg of the extract. The chemical structure of the two compounds was elucidated by electrospray ionization (EIS) MS and NMR.     

Determination of Li, Na, Mg, K, Ca and Fe with ICP-MS using cold plasma conditions

Some important analytes in ICP-MS are interfered by plasma argon or argon species, such as ArO⁺ and ⁵⁶Fe, ⁴⁰Ar and K or Ca. One approach to overcome this interference is the use of reduced forward power and a metal shield inserted between torch and load coil. These so called cold plasma conditions reduce the background caused by argon species and the formerly interfered analytes can be easily detected in the ng/g-range. Other elements in the lower mass region also profit from these conditions even when they are not interfered in normal plasma mode. The limits of detection are improved due to reduced background noise level and enhanced ion transmission. On the other hand, the reduced power fed to the plasma lowers the analytical performance and makes it susceptible to matrix effects. Elements of higher mass generally show higher detection limits compared to normal plasma mode.     

Random Walks with Stochastically Bounded Increments: Renewal Theory

Summary. This paper develops renewal theory for a rather general class of random walks S_N including linear submartingales with positive drift. The basic assumption on S_N is that their conditional increment distribution functions with respect to some filtration ?_? are bounded from above and below by integrable distribution functions. Under a further mean stability condition these random walks turn out to be natural candidates for satisfying Blackwell-type renewal theorems. In a companion paper [2], certain uniform lower and upper drift bounds for S_N, describing its average growth on finite remote time intervals, have been introduced and shown to be equal in case the afore-mentioned mean stability condition holds true. With the help of these bounds we give lower and upper estimates for H * U(B), where U denotes the renewal measure of S_N, H a suitable delay distribution and B a Borel subset of IR. This is then further utilized in combination with a coupling argument to prove the principal result, namely an extension of Blackwell's renewal theorem to random walks of the previous type whose conditional increment distribution additionally contain a subsequence with a common component in a certain sense. A number of examples are also presented.