Polymers from intermediates obtained from hydrogen cyanide

The recent demonstration of an easy synthesis of diiminosuccinonitrile (DISN) from hydrogen cyanide and cyanogen, the reduction of DISN to diaminomaleonitrile (DAMN), and the use of these compounds to form difunctional heterocycles has made several new polyamide intermediates accessible. The 1- and 2-methyl-1,2,3-triazole-4,5-dicarbonyl chlorides have been polymerized interfacially to form high-melting polyamides of good heat stability. Interfacial polymerization of 1-methylimidazole-4,5-dicarbonyl chloride and trans-2,5-dimethylpiperazine has given a polyamide that is water-soluble. The 2,6- and 2,3-pyrazinedicarbonyl chlorides have been similarly converted to high-melting polyamides. 2,6-Dicyano-3,5-dipiperazinylpyrazine has been prepared from tetracyanopyrazine and piperazine and reacted with toluene diisocyanate to form a strong, stiff polyurea. Polyamides were also made from 2,3-diaminoquinoxaline, 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, and DAMN.     

Synthesis of isoxazolines from nitrile N-oxides generated from nitroalkenes

In this review, information on the production of isoxazolines and condensed isoxazoline systems by the intramolecular 1,3-bipolar cycloaddition of unsaturated nitrile N-oxides generated in situ from nonconjugated nitroalkenes is generalized and systematized. The isoxazoline derivatives formed as the result of these reactions are promising synthons in the synthesis of various natural compounds and their analogues.Krakow Polytechnic Institute, Poland. Translated from Khimiya Prirodnykh Soedinenii, Nos. 3,4, pp. 291–305, May–August, 1992.     

Studies on Natural Products from Cuban Plants. Alkaloids from Tabernaemontana citrifolia

A detailed study of the alkaloids from Tabernaemontana citrifolia, a species growing in Cuba is presented. Thirteen alkaloids were isolated and characterized. One of these, (?)-19-oxovoacristine ( 7 ), is a new compound isolated for the first lime from a natural source.     

tert-butylcarbene from 1,1-diiodoneopentane

When 1,1-diiodoneopentane is passed through a hot tube containing methyllithium-coated Pyrex chips, 1,1-dimethylcyclopropane and 2-methyl-2-butene are produced in near quantitative yield. The ratio of products indicates that the intermediate carbene is the same as is produced from thermal or photosensitized decomposition of tert-butyldiazomethane but different from that formed by direct irradiation of the diazo compound.     

Precipitation from homogeneous solution of cations released from ETDA complexes

The suitability of EDTA complexes for use in precipitation of certain cations from homogeneous solution under various experimental conditions can be predicted from a knowledge of the solubility product of the compound to be precipitated and the complex stability constant. A brief review of previous work in the field of masking effectiveness is given. An examination of factors influencing precipitation has been carried out. It is shown that a simple ratio can be used for predicting the likelihood of precipitation at various pH values and that more rigorous theoretical approaches are not necessarily more advantageous.     

Non-atomic absorption from matrix salts volatilized from graphite atomizers in atomic absorption spectrometry

The non-atomic absorption signals obtained from alkali halides atomized from three types of graphite atomizer are examined. The wavelength dependence of the signals identifies the absorption as that of charge-transfer transitions of the alkali halide molecules. The contribution of light scattering to the total non-atomic absorption signal is shown to be of small significance; the observed light-scattering is not Rayleigh scattering. The temperature dependence of the loss of sodium chloride from a rod atomizer is studied experimentally and compared with calculated vaporization rates based on the kinetic theory of gases.     

Spiro-cyclopropanation from oxoallylsilanes

A novel highly stereoselective spiro-cyclopropanation reaction from oxoallylsilanes is described. Oxoallylsilanes are readily obtained by silylcupration of allene followed by conjugate addition to enones. The former oxoallylsilanes undergo a tandem cyclization-cyclopropanation reaction when treated with CH2I2/Me3Al, leading to hydroxylated polycyclic systems bearing the spiro-cyclopropane moiety. The scope of the process is studied, and a feasible pathway is discussed.     

Metabolites from fungi 15. New isocoumarins from an endophytic fungus isolated from the Canadian thistle Cirsium arvense

One known (1) and five new polyketide metabolites (2-6) were isolated from the culture extract of an endophytic fungus, Mycelia sterila, from the Canadian thistle Cirsium arvense. Compounds 1-4 are members of the isocoumarin family, whereas metabolite 5 is a dihydrobenzofuran and 6 has an open chain structure. All compounds have an unusual methyl group at the aromatic ring that does not fit into the usual polyketide pattern.     

Bioactive peptides from libraries

New ligands for a variety of biological targets can be selected from biological or synthetic combinatorial peptide libraries. The use of different libraries to select novel peptides with potential therapeutic applications is reviewed. The possible combination of molecular diversity provided by combinatorial libraries and a rational approach derived from computational modeling is also considered. Advantages and disadvantages of different approaches are compared. Possible strategies to bypass loss of peptide bioactivity in the transition from ligand selection to in vivo use are discussed.     

Upconversion luminescence from CdSe nanoparticles

Efficient upconversion luminescence has been observed from CdSe nanoparticles ranging in size from 2.5 to 6 nm. The upconversion luminescence exhibits a near-quadratic laser power dependence. Emissions from both excitons and trap states are observed in the upconversion and photoluminescence spectra, and in the upconversion luminescence the emission from the trap states is enhanced relative to the trap-state emission in the photoluminescence. The upconversion decay lifetimes are slightly longer than the photoluminescence decay lifetimes. Time-resolved spectral measurements indicate that this is due to the involvement of long decay components from surface or trap states. Both the photoluminescence and upconversion luminescence decrease in intensity with increasing temperature due mainly to thermal quenching. All the observations indicate that trap states work as emitters rather than as intermediate states for upconversion luminescence and that two-photon absorption is the likely excitation mechanism.     

Photoemission from solid neon

The photoelectric yield of solid Ne has been studied for photon energies between 15 and 30 eV. Strong photoemission from the valence band sets in at 21.4 ± 0.1 eV. The value of the electron affinity derived from this is discussed. A surface resonance for Ne atoms adsorbed on gold is observed at 17.1 eV.     

Pyrolytic hydrocarbon growth from cyclopentadiene

Aromatic hydrocarbon growth from cyclopentadiene (CPD) was studied using a laminar flow reactor operating in the temperature range 550-950 °C without oxygen. Benzene, indene, and naphthalene were the major products, which is in agreement with the previous computational studies on the reaction pathways from CPD. A crossover of indene and naphthalene yields around 775 °C was also observed, which further supports the results of the computational studies. Although the specific intermediates in the proposed pathways from CPD were not detected, the high selectivity of products and the observation of other methylindene and dihydronaphthalene intermediates suggest that the recombination of two CPDs via radical-molecule and/or radical-radical pathways to form indene and naphthalene is the dominant formation pathway. In addition to the products from the CPD-CPD reactions, the products from the reactions of CPD with indene, naphthalene, and acenaphthylene were also observed, which demonstrate the importance of CPD in carbon growth.     

Bioethanol Production from Glucose by Thermophilic Microbes from Ciater Hot Springs

Bioethanol has been considered as one of the alternative energy resources for fossil fuel substitute. Second generation of bioethanol production usually uses lignocellulosic material as its raw material which conducted at high temperature range (70-80^oC). In this case the thermophilic microbe is needed for fermentation process in order to minimize the use of energy. This paper will discuss the results of the study on bioethanol production from glucose by using thermophilic microbes isolated from local source namely from Ciater hot springs in Subang District, Indonesia. In this study six thermophilic isolates (C1, C2, C3, C4, C5 and C6) were tested their capability in producing ethanol in the fermentation medium containing 5% glucose substrate for 5 days incubation. To determine the activity of isolates in ferment substrate is done by measuring the concentration of glucose and ethanol produced using a spectrophotometer. Isolates tested (C1,C2,C3,C4 and C5) could reduce glucose concentration from 1.1up to 1.7% in the fermentation medium. The ethanol produced was tested qualitatively by reacting the samples with K₂Cr₂O₇inacidic conditions by observing its color change from yellow-orange to green-blue. The presence of ethanol indicatedby the decrease of OD's sample. This study showed that all isolates have the ability to produce ethanol. However, there are 2 isolates potentially produce ethanol that isolates C3 and C5 are characterized by low absorbance after adding potassium dichromate (K₂Cr₂O₇).     

Waste and fuels from waste

Thermogravimetric studies provide the basis for qualification of materials and suitability of biomass fuels and fuels formed from waste to convert them into fuel gas generated in the generator process. The paper presents the results of the analysis of thermal decomposition (thermogravimetric research) of fuel from waste, sewage sludge and wastes from the agro-food: potato pulp and rapeseed meal. Studies have shown how some biofuels and fuel formed from waste reach the semi-coke and coke structure, which is important later, in modeling industry degassing process. The most effective seems to be using rapeseed meal in generator process, since the thermal decomposition occurs in the form of transformation in the temperature range 200?C500?°C. On the basis of quantity analysis of gaseous transformation products from the above mentioned transformations, the calorific value of after process gases has been calculated. The highest calorific value is represented by a gas resulting from rapeseed meal pyrolysis ~10,040?kJ/Nm³. The solid residue obtained by dry decomposition of potato pulp has the highest energy value when compared with products from other fuels.     

Stereocomplex Formation from Enantiomeric Polyamides Derived from Tartaric Acid

Summary: The formation of stereocomplexes from the pair of enantiomorphs of the chiral polyamide poly(hexamethylene di‐O‐methyl tartaramide) was investigated for a variety of experimental conditions. DSC and X‐ray diffraction data evidenced that efficiency in enantiomeric association is highly sensitive to the procedure used for preparing the complex. A comparative isothermal crystallization study revealed that the stereocomplex crystallized from the melt at a rate lower than the enantiomerically pure components. The radial growth of individual spherulites was also delayed in the crystallization of the complex. No evidence of stereocoupling was detected for other poly(alkylene di‐O‐methyl tartaramide)s with the alkylene unit length different from six. It was concluded that molecular interlocking of hydrogen bonds in the enantiomeric pair is highly selective in this family of polymers.

Spherulitic growth at 200 °C from the melt.     

Electron scattering from tetrafluoroethylene

We report experimental results for electron scattering from tetrafluoroethylene, C2F4, obtained from measurements in two laboratories. An extensive set of differential, integral, and momentum transfer cross sections is provided for elastic scattering for incident electron energies from 1 to 100 eV and inelastic (vibrational excitation) scattering for incident electron energies at 3, 6, 7.5, 8, and 15 eV, and for scattering angles ranging from 10 degrees to 130 degrees. To highlight the role of intermediate negative ions (resonances) in the scattering process we have also measured excitation functions for elastic scattering and vibrational excitation of the ground electronic state of C2F4 for incident energies between 1.5 and 20 eV. Our results are compared with recent theoretical calculations and a limited number of other experimental results.     

Accuracy profiles from uncertainty measurements

Accuracy profiles of chemical assays are introduced and derived from the uncertainty of the analytical result. The calculation of accuracy profiles is based on the estimation of the measurement uncertainty of the analytical assay from validation data. For the sake of illustration, a case study dealing with the spectrofluorimetric determination of quinine in tonic water is explained in detail.     

Anion-exchange separation of cobalt from nickel

An anion-exchange method has been developed for the separation of cobalt from nickel, based on the observation that from a malonic acid solution containing sodium nitrite, cobalt is preferentially adsorbed by the exchanger but nickel passes through. The cobalt is eluted with 2M ammonium chloride in dilute ammonia solution. Prom an ammonium malonate solution containing chloride and nitrate, cobalt is quantitatively electro-deposited on a platinum cathode to give a bright, adherent deposit. Nickel is deposited from a solution of similar composition.     

Molecular conformations from distance matrices

Two algorithms are introduced that show exceptional promise in finding molecular conformations using distance geometry on nuclear magnetic resonance data. The first algorithm is a gradient version of the majorization algorithm from multidimensional scaling. The main contribution is a large decrease in CPU time. The second algorithm is an iterative algorithm between possible conformations obtained from the first algorithm and permissible data points near the configuration. These ideas are similar to alternating least squares or alternating projections on convex sets. The iterations significantly improve the conformation from the first algorithm when applied to the small peptide E. coli STh enterotoxin. © 1993 John Wiley & Sons, Inc.     

Tafel slopes from first principles

Tafel slopes for multistep electrochemical reactions are derived from first principles. The derivation takes place in two stages. First, Dirac’s perturbation theory is used to solve the Schrödinger equation. Second, current–voltage curves are obtained by integrating the single-state results over the full density of states in electrolyte solutions. Thermal equilibrium is assumed throughout. Somewhat surprisingly, it is found that the symmetry factor that appears in the Butler–Volmer equation is different from the symmetry factor that appears in electron transfer theory, and a conversion formula is given. Finally, the Tafel slopes are compiled in a convenient look-up table.