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951.
Filtering, drying and aging of crystalline solids can affect crystalline phase(s) and therefore ex situ X-ray diffraction is not necessarily indicative of the in situ crystalline components. This paper examines some of the factors affecting the crystallised phase of aluminium hydroxides in highly caustic solutions. Caustic aluminate solutions were prepared using several different methodologies. Where solutions were prepared from aluminium metal, gibbsite and bayerite were observed to be the crystallisation products. Where gibbsite was used as the aluminium source in the liquors, the crystallised phase was found to be a function of solution conditioning. Solutions prepared at 100°C and at atmospheric pressure crystallised to form only gibbsite. These same solutions subsequently heated to 160°C for 16 h crystallised as gibbsite and bayerite. It has been concluded from these results that the caustic aluminate solutions made using gibbsite were not dissolved on the molecular scale (although optically clear) if the solutions were heated to only 100°C. Further heating at elevated temperatures completed the dissolution process so that the species in solution were similar to those found in solutions made from aluminium metal. Solutions seeded with either bayerite or gibbsite crystallised to form only gibbsite. Only crystallisation in the bulk solution and not on the seed surfaces was recorded. In some cases seeding altered the expected crystallisation products, i.e. from gibbsite and bayerite to only gibbsite. 相似文献
952.
Gabriele Bocelli Andrea Cantoni Franca Bigi Giovanni Sartori 《Journal of chemical crystallography》1992,22(6):691-694
The structure of the compound obtained by reaction of AlCl3-promotedm-xilene with 2,6-pyridine dicarbonyldichloride in dichloromethane has been investigated by X-ray diffraction methods. The compound is monoclinic, space groupP21/c,a=13.907(2),b=17.247(3),c=12.042(2) Å,=109.75(4)°. The structure was solved by direct methods and refined by full matrix least-squares to a finalR=6.37 for 3718 independent observed reflections [I>2(I)]. The structure of the compound enables an understanding of the chemical pathway of the synthesis process. 相似文献
953.
Jeffrey?E.?Fiscus Neil?Pschirer Rachael?E.?Hipp Andrea?M.?Goforth Craig?Chapman Sandra?Shotwell Ralph?C.?Layland Mark?D.?Smith Uwe?H.?F.?Bunz Hans-Conrad?zur?LoyeEmail author 《Journal of chemical crystallography》2005,35(2):125-134
Using the new ligand, 2,2-bis-(4-pyridylethynyl)tolane we have synthesized five new coordination polymers: HgBr2[2,2-bis-(4-pyridylethynyl)tolane] (1), HgI2[2,2-bis-(4-pyridylethynyl)tolane] (2), Ni(acetylacetonate)2[2,2-bis-(4-pyridylethynyl)tolane] (3), Zn(acetylacetonate)2[2,2-bis-(4-pyridylethynyl)tolane] (4), and Cu(hexafluoro acetylacetonate)2[2,2-bis-(4-pyridylethynyl)tolane]CHCl3 (5). 2,2-Bis-(4-pyridyl ethynyl)tolane is a rigid ligand with a Z-shape that promotes the formation of zig-zag chains. Compounds 1– 5 were characterized by single crystal X-ray diffraction; and compounds 1– 3 were additionally characterized by IR, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic space group C2/c with a = 29.761(3) Å, b = 5.0531(5) Å, c = 16.7823(15) Å, = 104.090(2), V = 2447.9(4) Å3, Z = 4. Each mercury is bound to two tolane ligands and two bromine anions, resulting in a tetrahedral coordination environment. Compound 2 crystallizes in the monoclinic space group P2/c, with a = 20.3061(17) Å, b = 5.6303(5) Å, c = 24.5459(19) Å, = 110.338(2), V = 2631.4(4) Å3, Z = 4. Here also, each mercury is bound to two tolane ligands and two iodine anions in a tetrahedral coordination environment. The ligand orientation differs in compounds 1 and 2 being trans oriented in 1 and cis oriented in 2. Compound 3 crystallizes in the monoclinic space group P21/c with a = 14.5947(14) Å, b = 6.3082(6) Å, c = 18.3939(18) Å, = 112.112(2), V = 1568.9(3) Å3, Z = 2. Each nickel is bound to two tolane ligands and two bidentate AcAc anions, resulting in an octahedral coordination environment. Compound 4, which is isostructural with 3, also crystallizes in the monoclinic space group P21/c with a = 14.6990(9) Å, b = 6.2724(4) Å, c = 18.6433(11) Å, = 112.8610(10), V = 1583.86(17) Å3, Z = 2. Compound 5 crystallizes in the triclinic space group P-1 with a = 6.5487(4) Å, b = 11.6471(7) Å, c = 14.3225(9) Å, = 70.1360(10), = 89.3990(10), = 88.7680(10), V = 1027.18(11) Å3, Z = 1. Each copper in 5 is bound to two tolane ligands and two bidentate hfAcAc anions, resulting in an octahedral coordination environment identical to that found in 3 and 4. 相似文献
954.
Gabriele Bocelli Andrea Cantoni Elisabetta Giorgini Giorgio Tosi 《Journal of chemical crystallography》1990,20(5):419-423
A series of complexes between 1-oxide quinolines and 7,7,8,8-tetracyanoquinodimethane has been synthesized and one of them has been analyzed by x-ray diffraction methods. Crystals of the title compound are monoclinic (C15H11NO·C12H4N4), space groupP21/n,a=44.525(4),b=7.326(2),c=6.531(2) Å,=90.23(3)°. The structure was solved by direct methods and refined by block-matrix least-squares to giveR=0.047 for 1865 reflections above 2(I). Molecular dimensions, interplanar distances, empirical method and IR spectra suggest a -* interaction with very low charge-transfer in the complex. 相似文献
955.
3-Aryl-3-hydroxy-1-methylazetidine-2-thiones react with HCl in DMSO to give 3-methyl-5-aryloxazole-2-thiones. Substituent effects correlate with rate effects on hydrolyses of acetals of benzaldehyde. An (17)O labeling experiment indicates that the oxygen atom of the product is derived from the hydroxyl group. Trifluoroacetic anhydride/DMSO in CH2Cl2 can also promote the reaction. Mechanisms involving a Grob-type fragmentation of an activated substrate, followed by recyclization, or a cyclopropylcarbinyl type of rearrangement can account for this oxidative rearrangement. 相似文献
956.
Lait LA Rutledge LR Millen AL Wetmore SD 《The journal of physical chemistry. B》2008,112(39):12526-12536
The structural and binding properties of the natural and x- and y-pyrimidines were compared using computational methods. Our calculations show that although the x-pyrimidines favor different orientations about the glycosidic bond compared to the natural pyrimidines, which could have implications for the formation and resulting stability of xDNA duplexes and jeopardize the selectivity of expanded nucleobases, y-pyrimidines have rotational profiles more similar to the natural bases. Increasing the pyrimidine size using a benzene spacer leads to relatively minor changes in the hydrogen-bond strength of isolated Watson-Crick base pairs. However, differences in the anomeric carbon distances in pairs composed of x- or y-pyrimidines suggest yDNA may yield a more optimal expanded structure. By stacking two monomers via their centers of mass, we find that the expanded nucleobases stack much stronger than the natural bases. Additionally, although replacing xT by yT changes the stacking energy by less than 5 kJ mol (-1), replacing xC by yC significantly strengthens complexes with the natural nucleobases (by up to 30%). Calculations on larger duplex models composed of four nucleobases reveal that x- and y-pyrimidines can increase duplex stability of natural helices by strengthening both the intra and interstrand stacking interactions. Furthermore, when the total stability (sum of all hydrogen-bonding and (intrastrand and interstrand) stacking interactions) of the larger models is considered, y-pyrimidines lead to more stable complexes than x-pyrimidines for all but three duplex sequences. Thus, through analysis of a variety of properties, our calculations suggest that the location of the benzene spacer affects the properties of expanded nucleobases and the stability of expanded duplexes, and therefore should be carefully considered when designing future expanded analogues. 相似文献
957.
The synthesis of five natural products (3, 6, 7, 10, and 14), isolated from the Indian neem tree Azadirachta indica, is reported from a common intermediate (2). The judicious choice of transacetalization conditions allows efficient access to both the azadirachtinin (9 and 10) and the azadirachtin (3, 6, 7, and 14) skeletons. 相似文献
958.
Becker K Da Como E Feldmann J Scheliga F Csanyi ET Tretiak S Lupton JM 《The journal of physical chemistry. B》2008,112(16):4859-4864
Single oligo(phenylene-vinylene) molecules constitute model systems of chromophores in disordered conjugated polymers and can elucidate how the actual conformation of an individual chromophore, rather than that of an overall polymer chain, controls its photophysics. Single oligomers and polymer chains display the same range of spectral properties. Even heptamers support pi-electron conjugation across approximately 80 degrees curvature, as revealed by the polarization anisotropy in excitation and supported by quantum chemical calculations. As the chain becomes more deformed, the spectral linewidth at low temperatures, often interpreted as a sign of aggregation, increases up to 30-fold due to a reduction in photophysical stability of the molecule and an increase in random spectral fluctuations. The conclusions aid the interpretation of results from single-chain Stark spectroscopy in which large static dipoles were only observed in the case of narrow transition lines. These narrow transitions originate from extended chromophores in which the dipoles induced by backbone substituents do not cancel out. Chromophores in conjugated polymers are often thought of as individual linear transition dipoles, the sum of which make up the polymer's optical properties. Our results demonstrate that, at least for phenylene-vinylenes, it is the actual shape of the individual chromophore rather than the overall chromophoric arrangement and form of the polymer chain that dominates the spectroscopic properties. 相似文献
959.
Comandini P Blanda G Cardinali A Cerretani L Bendini A Caboni MF 《Journal of separation science》2008,31(18):3257-3264
Anthocyanins, the major colourants of strawberries, are polar pigments that are positively charged at low pH. Herein, we have assessed a new analytical method for the separation of anthocyanins using CZE. Acidic buffer solutions (pH <2) were employed in order to maintain pigments in the cation flavylium form and achieve high molar absorptivity at 510 nm. These spectral properties enabled us to identify strawberry anthocyanins in a preliminary stage by detection in the visible range, although the method was optimised at 280 nm to obtain the best S/N. The effects of buffer composition highlighted the necessity of adding an organic modifier to the running buffer to obtain a suitable separation. The electrophoretic method permitted the separation of the three main anthocyanins of strawberry extracts, namely pelargonidin 3-glucoside (Pg-glu), pelargonidin 3-rutinoside and cyanidin 3-glucoside. The electrophoretic results, expressed as retention time and separation efficiency of the major anthocyanin (Pg-glu), were compared to those achieved in HPLC, the analytical technique traditionally used for the investigation of anthocyanins in vegetable matrix. The content of Pg-glu in strawberries (cv. Camarosa), calculated with HPCE and HPLC methods, resulted respectively in 11.41 mg/L and 11.37 mg/L. 相似文献
960.
Roda B Reschiglian P Zattoni A Tazzari PL Buzzi M Ricci F Bontadini A 《Analytical and bioanalytical chemistry》2008,392(1-2):137-145
Interest in biological studies on various cell types for many biomedical applications, from research to patient treatments, is constantly increasing. The ability to discriminate (sort) and/or quantify distinct subpopulations of cells has become increasingly important. For instance, not only detection but also the highest depletion of neoplastic cells from normal cells is an important requisite in the autologous transplantation of lymphocytes for blood cancer treatments. In this work, gravitational field-flow fractionation (GrFFF) is shown to be effective for sorting a heterogeneous mixture of human, living lymphocytes constituted of neoplastic B cells from a Burkitt lymphoma cell line and healthy T and B lymphocytes from blood samples. GrFFF does not require the use of fluorescent immunotags for sorting cells, and the sorted cells can be collected for their further characterization. Flow cytometry was used to assess the viability of the cells collected, and to evaluate the cell fractionation achieved. A low amount of neoplastic B lymphocytes (less than 2%) was found in a specific fraction obtained by GrFFF. The high depletion from neoplastic cells (more than 98%) was confirmed by a clonogenicity test. 相似文献