Thin layer chromatographic studies of anils II. Separation,identification and determination

Thin layer chromatographic behaviour of ten anils was studied on silica gel adsorbent mixed with starch binder with ten solvent systems. Simultaneous separation, identification and determination of ternary mixtures of isomers was stressed. TheR _F increasing order was found to be dependent on the solvent and independent of the degree of saturation of the chamber. The correlations ofR _F with _max and (C=O) of isomers were established and used in their identification. Six anils were separated in methanol—benzene (11).     

Preparation and thermal stability of trioxalatocobaltates of bivalent metals KM2+ [Co(C2O4)3]·xH2O

Trioxalatocobaltates of bivalent metals KM²⁺[Co(C₂O₄)₃]·x H₂O, with M²⁺ = Ba, Sr, Ca and Pb, have been prepared, characterized and their thermal behaviour studied. The compounds decompose to yield potassium carbonate, bivalent metal carbonate or oxide and cobalt oxide as final products. The formation of the final products of decomposition is influenced by the surrounding atmosphere. Bivalent metal cobaltites of the types KM²⁺CoO₃ and M²⁺CoO_3—x are not identified among the final products of decomposition. The study brings out the importance of the decomposition mode of the precursor in producing the desired end products.     

ULTRAVIOLET ACTION SPECTRA FOR PHOTOBIOLOGICAL EFFECTS IN CULTURED HUMAN LENS EPITHELIAL CELLS

Abstract— The action spectrum for cell killing by UV radiation in human lens epithelial (HLE) cells is not known. Here we report the action spectrum in the 297–365 nm region in cultured HLE cells with an extended lifespan (HLE B-3 cells) and define their usefulness as a model system for photobiological studies. Cells were irradiated with monochromatic radiation at 297, 302, 313, 325, 334 and 365 nm. Cell survival was determined using a clonogenic assay. Analysis of survival curves showed that radiation at 297 nm was six times more effective in cell killing than 302 nm radiation; 297 nm radiation was more than 260, 590, 1400 and 3000 times as effective in cell killing as 313, 325, 334 and 365 nm radiation, respectively. The action spectrum was similar in shape to that for other human epithelial cell lines and rabbit lens epithelial cells. The effect of UV radiation on crystallin synthesis was also determined at different wavelengths. To determine whether exposure to UV radiation affects the synthesis of β-crystallin, cells were exposed to sublethal fluences of UV radiation at 302 and 313 nm, labeled with [³⁵S]methionine and the newly synthesized βY-crystallin was analyzed by immunoprecipitation and western blotting using an antibody to β-crystallin. The results show a decrease in crystallin synthesis in HLE cells irradiated at 302 and 313 nm at fluences causing low cytotoxicity. The effect of radiation on membrane perturbation was determined by measuring enhancement of synthesis of prostaglandin E₂ (PGE₂). Synthesis of PGE₂ occurs at all UV wavelengths tested in the 297–365 nm region. The slope of the PGE₂ response curves was higher than that of cell killing curves in cultured HLE cells. These data show that cultured HLE cells with extended lifespan are a suitable system for investigating photobiological responses of cells to UV radiation.     

Towards the total synthesis of amphidinolide E: an enantioselective synthesis of C12-C29 fragment

An enantioselective synthesis of the C12-C29 fragment of amphidinolide E is described. Key transformations include an intramolecular mercuriocyclization reaction, stereoselective introduction of methyl group at the C2 position, and Stille coupling for the introduction of the diene side chain.     

The Spectrophotometric Determination of Gallium (III) with Glycine Thymol Blue

The reaction between gallium (III) and glycine thymol blue has been studied spectrophoptometrically in order to establish the optimum conditions for determining traces of gallium. The gallium (III) glycine thymol blue complex has an absorption maximum at 560 nm against a reagent blank and is stable between pH 4.0 and 5.5. The complex has a composition 1 : 2 and a formation constant of 6.4×10⁷ under the conditions studied. Beer's law is obeyed upto 126 μg of gallium. The net molar absorptivity has been found to be 11,000. The present method is very sensitive and rapid. Anions such as citrate and tartrate inhibit the colour development of the complex.     

Spin density distributions in some fluorinated radical cations

A theoretical study of π-electron spin density distributions has been made for a series of fluoro-substituted hydrocarbon radical cations using unrestricted Hartree-Fock theory. Although some of the predicted proton splittings are not in very good agreement with experiment, the overall agreement with experiment can be passed as fairly satisfactory considering the approximate nature of the theory used. The experimental fluorine splittings can be well predicted by using a one-parameter relationship between the isotropic fluorine splitting (a_F) and the π-electron spin density (ρ_CC) on the attached carbon. It has been further shown that both ρ_CC and the proportionality constant (Q_eff) in the linear relation, are fairly insensitive to the parameter choice.     

Self-assembly with degenerate prototropy

This work describes a rational approach for addressing the prototropy-related problems in heterocycle-based self-assembling systems by the use of degenerate prototropy. As a proof of principle, the utility of degenerate prototropy is demonstrated herein by developing heterocycle-based AADD-type self-assembling modules that exist as "single set of protameric pair (duplex)" in both solution and solid states. These self-assembling modules are quickly accessible in good yield by reacting 2-amino-5,5-disubstituted-1H-pyrimidine-4,6-diones, available in one step by the condensation of alpha,alpha-dialkyl malonates and free guanidine, with isocyanates. Evidence from NMR spectroscopy, ESI mass spectrometry, and single-crystal X-ray diffraction studies confirmed the formation of molecular duplexes. The effect of electronic repulsion in duplex formation is also investigated. Their ready synthetic accessibility, remarkably high propensity to crystal formation, and the novel property of degenerate prototropy would make these novel self-assembling molecules promising candidates for many proposed applications.     

Condensed cyclic and bridged-ring systems. VII. Acid-catalysed cyclisation of methyl substituted benzylcyclohexanols. Factors influencing the nature of cyclisation products

The gross structures of the cyclised products from the acid-catalysed cyclisations of 2-benzyl-1, 3-dimethylcyclohexanol (6) and 1-benzyl-3, 5-dimethylcyclohexanol (11) revealing the influence of the structure of the benzylcyclohexanol derivative, and of the cyclisation reagent, have been evaluated. Polyphosphoric acid and aluminium chloride catalysed cyclisations of (6) result in the formation of predominantly 1, 4a-dimethyl-1, 2, 3, 4, 4a, 9a-hexahydrofluorene (7) and 4, 9-dimethyl-7, 8-benzobicyclo [3.3.1] non-7-ene (9) respectively. Under the same conditions, (11) produced cyclised products consisting mostly the benzobicyclo [3.3.1] non-7-ene derivative (12), characterised through 1,3-dimethyl-7,8-benzobicyclo [3.3.1] non-6-oxo-7-ene (14) by oxidation with chromium trioxide. Phosphorus pentoxide induced cyclisation of (6), followed by oxidation gave a mixture of the bridged-ring ketone (10) and the 9-oxohydrofluorene (8) in a ratio ofca. 3 : 2, whereas 2-benzyl-5-methylcyclohexanol (19) resulted in mostly 2-methyl-7,8-benzobicyclo [3.3.1] non-6-oxo-7-ene (19).     

CONFORMATIONAL CHANGES OF BOVINE LENS CRYSTALLINS IN A PHOTODYNAMIC SYSTEM

Abstract— Conformational changes of bovine lens crystallins in a photodynamic system generating singlet oxygen, have been investigated. The formation of intersubunit crosslinks was observed in all three classes (α-, β and γ-) of crystallins by irradiation in the presence of the photosensitizer methylene blue. Near-UV circular dichroism (CD) spectra of the crystallins were significantly altered by irradiation under these conditions, indicating changes in tertiary structure but the far-UV CD remained unchanged suggesting that the secondary structure ((β-sheet conformation) remains unchanged. Significant changes in the absorption and fluorescence spectra were also observed. Measurement of total sulfhydryl content showed a decrease of 27%, 50% and 37% for α-, β- and γ-crystallins respectively, after irradiation. Fluorescence lifetime measurements of N-iodoacetyl-N'-(5-sulfo-l-naphthyl)ethylenediamine-labeled crystallins showed a significant decrease of the lifetime of the major decay components of the label bound to sulfhydryl groups of α- and γ-crystallins, but showed no change in the microenvironment of the sulfhydryl groups of β-crystallin. The results are consistent with the microenvironments of the tryptophan and sulfhydryl groups predicted from sequence studies.     

The effect of pressure on the dissociation constant of hydrofluoric acid and the association constant of the NaF ion pair at 25°C

The effect of pressure on the dissociation constant of hydrofluoric acid was determined by using the indicator technique at 25°C at an ionic strength of 0.1m over a pressure range of 1 to 2000 atm. A value of 3.14 for pK _a ^* at I =0 was obtained by extrapolation to zero ionic strength at 1 atm. The pressure dependence yielded a partial molar volume change of –9.6 cm³-mol^–1 and a compressibility change of — 35×10^–3 cm³-mol^–1 –atm^–1 for the dissociation. The dependence of ionic strength on the association constant K _A ^* of NaF was studied at 25°C and 1 atm. Extrapolation to I=0 yielded a pK _A ^* of –0.78. The pressure dependence of K _A ^* gave a change of volume of 3.26 cm³-mol^–1 and a change in compressibility of 6×10^–3 cm³-mol^–1-atm^–1 for the formation of the ion pair.