29Si N.M.R. investigations of polysiloxanes

A number of side chain liquid crystal polysiloxanes prepared from both homo-and co-polymeric backbones have been studied by ²⁹Si N.M.R. and the chemical shifts assigned. Partly mesogenated poly(hydrogenmethylsiloxanes) have been similarly studied and chemical shift assignments made for sequence distributions. The data should prove helpful in studies of compositional variation in preparations of side chain copolymeric polysiloxanes.     

Pyrylocyanines. 29. tert-Butyl-substituted benzopyrylocyanines

2-tert-Butyl-4-methyl- and 2-methyl-4-tert-butylbenzopyrylium salts, as well as the sulfitr analog of the latter, were synthesized. Polymethine dyes with symmetrical and unsymmetrical structures were obtained from these salts. The factors that affect the color are analyzed.See [1] for Communication 28.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 339–344, March, 1992.     

New analogues of brefeldin A from sediment-derived fungus Penicillium sp. DT-F29

Four new analogues of brefeldin A named 7, 7-dimethoxybrefeldin C (3), 6β-hydroxybrefeldin C (4), 4-epi-15-epi-brefeldin A (5), 4-epi-8α-hydroxy-15-epi-brefeldin C (6), together with four known analogues (1, 7?9) were isolated from a fermentation of the sediment-derived fungus Penicillium sp. DT-F29. The structures of these compounds were elucidated on the basis of extensive spectroscopic and chemical methods. In the bioactivity assays, only compounds 1 and 8 showed significant inhibitory activities against human lung adenocarcinoma cell. In addition, compound 1 was first reported for the potent ability to reactivate latent HIV with EC₅₀ value of 0.03 μM.     

Thermodynamics of Mercurous Acetate from E M. F. Measurements

Measurements of the e.m. f.'s of the cell, have been made over a temperature range from 15° to 40°C. The standard e.m.f. of the Hg/Hg₂Ac₂(s), Ac^? electrode was given by E⁰=?0.8640+1.832×10_×3T?21.84×10_?7T₂. The thermodynamic properties of the reaction, Hg₂Ac₂(s)+2Cl^?=Hg₂Cl₂(s)+2Ac_? and those for the formation of Hg₂Ac₂(s) at 25°C were Computed.     

Pyrroles from ketoximes and acetylene. 29. Synthesis of alkylpyrroles from dialkylketoximes and dichloroethane by reaction with KOH-DMSO

Treatment of dialkylketoximes with dichloroethane and KOH-DMSO results in the formation of alkylpyrroles in 31–61% yields. In addition, the corresponding 1-vinylpyrroles are formed simultaneously in yields up to 18%. The corresponding 1,2-bis(alkylideneiminoxy)ethanes are obtained as side products in the reaction; they result from nucleophilic displacement of chlorine atoms by oximate anions.For Communication No. 28, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 59–62, January, 1985.     

Studies on pyrazines. 29 . High regioselective synthesis of chloropyrazines from 3-substituted pyrazine 1-oxides

Reaction of 3-methoxy- or 3-chloropyrazine 1-oxides with refluxing phosphoryl chloride in the presence of amine led to a high regioselective formation of 3-substituted 2-chloropyrazines. In contrast, the use of chloroacetyl chloride instead of phosphoryl chloride enabled different regioselectivity to yield 6-substituted 2-chloropyrazines, particularly 3-methoxycarbonylpyrazine 1-oxide was almost exclusively converted into methyl 6-chloropyrazinecarboxylate under the conditions without the amine.     

Methane production from synthesis gas using a mixed culture ofR. rubrum M. barkeri,and M. formicicum

The components of synthesis gas, CO, H₂, and CO₂, may be converted into CH₄ biologically through either acetate or H₂/CO₂ as intermediates. Of these two routes, conversion through H₂/CO₂ is preferred. This paper presents results of mixed-culture studies employing the photosynthetic bacteriumR. rubrum for converting CO to CO₂ and H₂ by the water gas shift reaction and two methanogens,M. formicicum andM. barkeri, for converting CO₂ and H₂ into CH₄. Results are presented for triculture operation in two types of reactors, the packed bubble column and the trickle-bed reactor.     

Lignins Isolated via Catalyst-Free Organosolv Pulping from Miscanthus x giganteus,M. sinensis,M. robustus and M. nagara: A Comparative Study

As a low-input crop, Miscanthus offers numerous advantages that, in addition to agricultural applications, permits its exploitation for energy, fuel, and material production. Depending on the Miscanthus genotype, season, and harvest time as well as plant component (leaf versus stem), correlations between structure and properties of the corresponding isolated lignins differ. Here, a comparative study is presented between lignins isolated from M. x giganteus, M. sinensis, M. robustus and M. nagara using a catalyst-free organosolv pulping process. The lignins from different plant constituents are also compared regarding their similarities and differences regarding monolignol ratio and important linkages. Results showed that the plant genotype has the weakest influence on monolignol content and interunit linkages. In contrast, structural differences are more significant among lignins of different harvest time and/or season. Analyses were performed using fast and simple methods such as nuclear magnetic resonance (NMR) spectroscopy. Data was assigned to four different linkages (A: β-O-4 linkage, B: phenylcoumaran, C: resinol, D: β-unsaturated ester). In conclusion, A content is particularly high in leaf-derived lignins at just under 70% and significantly lower in stem and mixture lignins at around 60% and almost 65%. The second most common linkage pattern is D in all isolated lignins, the proportion of which is also strongly dependent on the crop portion. Both stem and mixture lignins, have a relatively high share of approximately 20% or more (maximum is M. sinensis Sin2 with over 30%). In the leaf-derived lignins, the proportions are significantly lower on average. Stem samples should be chosen if the highest possible lignin content is desired, specifically from the M. x giganteus genotype, which revealed lignin contents up to 27%. Due to the better frost resistance and higher stem stability, M. nagara offers some advantages compared to M. x giganteus. Miscanthus crops are shown to be very attractive lignocellulose feedstock (LCF) for second generation biorefineries and lignin generation in Europe.     

Crystal structure of acetyl 29-methyl-29-methylidene-D:C-friedoolean-8-en-3beta-ol.

Acetyl 29-methyl-29-methylidene-D:C-friedoolean-8-en-3beta-o1 (2), derived from bryonolic acid (D:C-friedoolean-8-en-3beta-ol-29-oic acid) (1), was crystallographically analyzed. Rings A-E of 2 adopted chair, half-chair, half-chair, boat (with bow and stern at C-13 and C-16), boat (with bow and stem at C-19 and C-22) conformations, respectively. Good agreement was found between the structures from X-ray crystallography and that from MM2 calculations.     

29Si chemical shift anisotropies in calcium silicates from high-field 29Si MAS NMR spectroscopy

29Si chemical shift anisotropy (CSA) data have been determined from (29)Si MAS NMR spectra recorded at 14.1 T for a number of synthetic calcium silicates and calcium silicate hydrates. These are beta- and gamma-Ca(2)SiO(4), Ca(3)SiO(4)Cl(2), alpha-dicalcium silicate hydrate (alpha-Ca(2)(SiO(3)OH)OH), rankinite (Ca(3)Si(2)O(7)), cuspidine (Ca(4)Si(2)O(7)F(2)), wollastonite (beta-Ca(3)Si(3)O(9)), pseudowollastonite (alpha-Ca(3)Si(3)O(9)), scawtite (Ca(7)(Si(6)O(18))CO(3).2H(2)O), hillebrandite (Ca(2)SiO(3)(OH)(2)), and xonotlite (Ca(6)Si(6)O(17)(OH)(2)). The (29)Si MAS NMR spectra of rankinite and wollastonite clearly resolve manifolds of spinning sidebands from two and three Si sites, respectively, allowing the CSA parameters to be obtained with high precision for each site. For the (29)Si Q(1) sites in rankinite and cuspidine, the CSA asymmetry parameters (eta(sigma) approximately 0.6) contrast the general expectation that sorosilicates should possess small eta(sigma) values as a result of the nearly axially symmetric environments of the SiO(4) tetrahedra. The (29)Si CSA parameters provide an improved insight into the electronic and geometric environments for the SiO(4) tetrahedra as compared to the values solely for the isotropic chemical shift. It is shown that the shift anisotropy (delta(sigma)) and the CSA asymmetry parameter (eta(sigma)) allow a clear distinction of the different types of condensation of SiO(4) tetrahedra in calcium silicates. This relationship may in general be valid for neso-, soro-, and inosilicates. The CSA data determined in this work may form a valuable basis for (29)Si MAS NMR studies of the structures for tobermorites and calcium silicate hydrate phases resulting from hydration of Portland cements.     

Two New C29 Sterols from Clerodendrum colebrookianum

Clerodendrum. colebrookianum Walp. is a traditional Chinese medicine, it possesses thefunctions of "expelling toxin by cooling, cooling blood to induce diuresis and purgingheat"', and has been used as a remedy for hypertension in india2. The chemicalinvestigation of this plant has been reported previously'-'. In continuation of our studieson the constituents of the plant, we examined the steroid constitllents of the title speciesand isolated two new C,, sterols, colebrin A (l) and colebrin B…