Stability of lyophobic sols

The coagulation of positively charged sol of hydrous ferric oxide of different average sizes for potassium sulphate has been studied in the presence of glucose and urea which stabilise the sol. The degree of stabilisation increases with the fineness of dispersed particles. It has been concluded that the adhesive tendency of the surface of dispersed particles decreases in the presence of said non-electrolytes leading to a decrease in the frequency of collisions resulting in stabilisation. The stability ratioW increases in the presence of glucose and urea for the same amount of the coagulant.

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Zusammenfassung Die Koagulation positiv geladener Sole von wäßrigem Ferrioxid verschiedener mittlerer Partikelgrößen mit Kaliumsulfat wird in Gegenwart von Glykose und Harnstoff, die beide das Sol stabilisieren, untersucht. Der Grad der Stabilisierung hängt von der Teilchengröße ab. Es wird geschlossen, daß die Adhäsionstendenz der Oberflächen der dispergierten Partikel in Gegenwart besagter Nichtelektrolyte abnimmt und so zur Abnahme der Kollisionshäufigkeit und damit zur Stabilisierung führt. Das StabilisierungsverhältnisW wächst in Anwesenheit von Glykose und Harnstoff für gleiche Beträge des Koagulators.

     

Using fluorescence resonance energy transfer to measure distances along individual DNA molecules: corrections due to nonideal transfer

Single molecule fluorescence resonance energy transfer has been extensively used to measure distance changes and kinetics in various biomolecular systems. However, due to complications involving multiple de-excitation pathways of the dyes, the absolute inter-dye distance information has seldom been recovered. To circumvent this we directly probe the relative variations in the quantum yield of individual fluorophores. B-DNA was used as a scaffold to position the donor (Cy3 or TMR) at precise distances from the acceptor (Cy5) within the Forster radius. We found that the variation in the Cy3 quantum yield is approximately 5 times larger than that of TMR. By taking into account the molecule-to-molecule variability in the acceptor/donor quantum yield ratio, the apparent fluorescence resonance energy transfer efficiencies were scaled to yield the theoretical values. We obtained very good agreement with a physical model that predicts distances along B-DNA.     

A density-functional calculation of dynamic dipole polarizabilities of noble gas atoms

Using a very simple trial function and unperturbed electron densities calculated by a new procedure, the frequency-dependent dipole polarizability () of Ne, Ar, Kr and Xe has been calculated in the range 0 0.45 a.u., by a Karplus-Kolker-type variation-perturbation method. Results progressively worsen for larger systems so that, for Xe, (0) is only 75% of the experimental value. Probable reasons for this are discussed.     

Ionic Interactions of Calcium Sulfate Dihydrate in Aqueous Sodium Chloride Solutions: Solubilities,Densities, Viscosities,Electrical Conductivities,and Surface Tensions at 35 <Superscript>∘</Superscript>C

The thermodynamic, volumetric, transport, and surface properties, solubilities, densities, viscosities, electrical conductivities, and surface tensions of calcium sulfate dihydrate in aqueous sodium chloride solutions have been measured at 35 C, with a view to determine the ionic interactions that occur in these solutions. The experimental density values have been used to calculate the mean apparent molar volumes of the ternary mixtures. Viscosity values have been analyzed using different empirical equations and the experimental values of the viscosity were combined with conductivity to yield the Walden product. Molar surface energies have been computed using experimental surface tension data. The experimental data have been fitted to polynomial equations by a least-squares analysis to obtain the coefficients and their standard errors. Results have been examined in the light of structure making or structure breaking effects of the various ions present in the solutions.     

Enantioselective total synthesis of (+)-amphidinolide t1

An enantioselective first total syntheis of amphidinolide T1 (1) is described. Amphidinolide T1 (1), a 19-membered macrolide isolated from Amphidinium sp., has shown potent antitumor properties against a variety of NCI tumor cell lines. The synthesis is convergent and involves the assembly of C1-C10 segment 2 and C11-C21 segment 3 by an oxocarbenium ion-mediated alkylation and Yamaguchi macrolactonization sequence. The synthesis of fragment 2 involves an efficient cross metathesis and hydrogenation sequence between the terminal olefins of 5 and 6 to form the C4-C5 carbon-carbon bond. Enol ether 4 is designed to be the surrogate of fragment 3 where the sensitive C16-exo-methylene and the C13-hydroxyl group were protected as the bromoether derivative during the Lewis acid-catalyzed alkylation process. Both stereocenters in fragment 5 as well as the C2 and C3 stereocenters in fragment 4 are accessed by a highly diastereoselective ester-derived titanium enolate-mediated syn-aldol reaction. The bromoether derivative 24 was unraveled at the final stage of the synthesis, providing (+)-amphidinolide T1.     

Total synthesis of antitumor depsipeptide (-)-doliculide

[reaction: see text] (-)-Doliculide, a potent antitumor agent, is synthesized stereoselectively in a convergent manner. The key strategy involves a stereoselective synthesis of the polyketide unit and synthesis of the D-tyrosine derivative, followed by assembly of the fragments by an esterification and cycloamidation reaction sequence. The synthesis of the polyketide fragment was achieved by an iterative asymmetric synthesis to install stereoselectively both 1,3-dimethyl groups and the 1,3-diol unit by utilizing asymmetric cyclopropanations and Sharpless asymmetric epoxidations as the key steps.     

Radiometric study on bioaccumulation of gold by an alkaloid extracted from fruits of <Emphasis Type="Italic">Piper nigrum</Emphasis>

Piperine, an alkaloid derived from the fruits of Piper nigrum, has been tested as an extracting bioreagent for gold. It has been observed that piperine as well as the fruits of Piper nigrum itself can act as an efficient exchanger for gold both in trace and macro scale. The accumulation of gold by these bioreagents is highly pH dependent.     

Photopolymerization of methyl methacrylate using a combination of rhodamine 6G and benzoyl peroxide as photoinitiator in nonaqueous media

Photopolymerization of methyl methacrylate (MMA) in visible light was studied at 40°C using Rhodamine 6G—Benzoyl peroxide combination as photoinitiator. The photopolymerization proceeds by a free radical mechanism and the radical generation process occurs by an initial complexation reaction between the initiator components. Kinetic data indicated a lower-order dependence of R_p on initiator concentrations (initiator exponent < 0.5). Initiator-dependent chain termination was significant along with the bimolecular mode of chain termination.     

A new class of linear tetrapyrroles: acetylenic 10,10a-didehydro-10a-homobilirubins

Novel bilirubin analogues with dipyrrinones conjoined to an acetylene rather than a methylene group were synthesized and examined spectroscopically. Despite the increased separation of the dipyrrinones forced by replacing a -CH(2)- by a -C(triple bond)C- unit, molecular dynamics calculations show that, like bilirubin, they may still engage in intramolecular hydrogen bonding to carboxylic acid groups when the propionic acid chains are slightly lengthened, e.g., butanoic acids. Unlike bilirubin, however, which is bent in the middle and has a ridge-tile shape, the acetylene orients the attached dipyrrinones along a linear path, and intramolecular hydrogen bonding preserves a twisted linear molecular shape. The extended planes of the dipyrrinones intersect along the -C(triple bond)C- axis at an angle of 136 degrees for the conformation stabilized by intramolecular hydrogen bonding in the bis-butyric acid rubin (1b). With shorter acid chains (propionic), only one CO(2)H can engage an opposing dipyrrinone in intramolecular hydrogen bonding, and in this energy-minimum conformation of the linear pigment 1a, the intersection of the extended planes of the dipyrrinones has an angle of 171 degrees. Spectroscopic evidence for such linearized and twisted structures was found in the pigments' NMR spectral data and their exciton UV-vis and induced circular dichroism spectra.     

Synthesis,characterisation and solid state thermal behaviour of nickel(II) diamine complexes

Summary [NiL₂X₂] (L =N,N-dimethyl-1,2-ethanediamine; X = Cl^–, CF₃CO ₂ ^– , CC1₃CO ₂ ^– and CBr₃CO ₂ ^– ), [NiL₂C₂O₄] · H₂O and [NiL₂X₂] · 2 H₂O (X = Br^–, 0.5 SO ₄ ^2– and 0.5 SeO ₄ ^– ) have been synthesised and their thermal studies carried out. Thermally induced phase transition phenomena are noticed in [NiL₂X₂] (X = CF₃CO ₂ ^– and CCl₃CO ₂ ^– ) and their probable mechanisms are described. [NiL₂X₂] (X = Br^–, 0.5 SO ₄ ^2– and 0.5 SeO ₄ ^2– ) and [NiLX₂] (X = Cl^–, 0.5 C₂O ₄ ^2– and 0.5 SO ₄ ^2– ) have been prepared by solid state pyrolysis from the respective parent diamine complexes. [NiL₂X₂] have been made in solid state by temperature arrest technique from [NiL₂(CX₃CO₂)₂] (X = Cl^– and Br^–).