Effect of platinum on the photophysical properties of a series of phenyl-ethynyl oligomers

In this work we detail the photophysical properties of a series of butadiynes having the formula H-(C6H4-C[triple bond]C)n-(C[triple bond]C-C6H4)n-H, n=1-3 and ligands H-(C6H4-C[triple bond]C)n-H, n=1-3 and compare these to previous work done on a complimentary series of platinum-containing complexes having the formula trans-Pt[(PC4H9)3]2[(C[triple bond]-C6H4)n-H]2, n=1-3. We are interested in understanding the role of the platinum in the photophysical properties. We found that there is conjugation through the platinum in the singlet states, but the triplet states show more complex behavior. The T1 exciton, having metal-to-ligand charge-transfer character, is most likely confined to one ligand but the Tn exciton appears to have ligand-to-metal charge-transfer character. The platinum effect was largest when n=1. When n=2-3, the S0-S1,S1-S0,T1-S0, and T1-Tn spectral properties of the platinum complex are less influenced by the metal, becoming equivalent to those of the corresponding butadiynes. When n=1, platinum decreases the triplet state lifetime, but its effect diminishes as n increases to 2.     

Sodium-lead alloy in the decomposition of organic samples for the detection of heteroelements

The decomposition of organic samples using open-tube fusion with sodium-lead alloy was demonstrated to be safe, complete, and controlled, in most cases. The detection of heteroelements in the fusion mixture of common organic samples was successful with samples of 10 to 20 mg. Detection of chlorine and nitrogen by classical methods in “difficult” compounds was secured, and the detection of fluorine in the fusion mixture of fluorocompounds extended the use of the alloy into this area. The use of the pyrazolone color reaction in the detection of nitrogen allowed the detection of more minute amounts of nitrogen than was previously detected using Prussian blue formation. The detection limits for heteroelements in organic samples were in the low microgram region. The application of sodium-lead alloy in quantitative work was briefly studied and will be considered in greater detail in the future.     

An unreported bis-abeo cembrane-type diterpenoid with antioxidative and anti-lipoxygenase activities from the muricid gastropod mollusc Chicoreus ramosus

Abstract

The chemical analyses of ethyl acetate-methanol (EtOAc-MeOH) extract of muricid gastropod mollusk, Chicoreus ramosus from the southeastern coast of Indian peninsular led to the identification of unprecedented cembrane-type diterpenoid, which was characterized as (3E, 6E, 10E)-8a-butoxy-17(15→14), 20(12→11)-bis-abeo-cembra-3,6,10,14(17),15-pentaene (1). The structure of the studied cembrane was unambiguously assigned through the extensive spectroscopic experimentations. The antioxidant potentials of the bis-abeo cembrane as determined by in vitro 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis-3-ethylbenzothiozoline-6-sulfonic acid diammonium salt radical quenching potentials were greater (IC₅₀?<?0.40?mg/mL) related to α-tocopherol (IC₅₀?>?0.60?mg/mL). The pro-inflammatory anti-5-lipoxygenase potential of studied cembrane was higher (IC₅₀?<?0.80?mg/mL) related to those demonstrated by ibuprofen and sodium salicylate (IC₅₀?>?0.90?mg/mL).     

Chiral photochemistry within zeolites

Chiral induction of chemical reactions continues to be one of the main concerns of chemists. While basic rules of chiral induction of thermal reactions have been reasonably established, the same is not true of photochemical reactions. Short excited state lifetime and low activation energies for reactions in the excited state(s) leave very little room for manipulating the diastereomeric transition states. Yet impressive chiral induction of photochemical reactions in the solid state has been achieved. On the other hand, chiral induction of photoreactions of organic molecules in solution continues to be inefficient at ambient conditions. We are exploring the possibility of employing zeolites as a media for achieving chiral induction during photoreactions. The motivating force for such an attempt is the fact that chiral chemistry in the solid state is not completely general due to the fact that not all molecules crystallize. To achieve chiral induction one needs a chiral perturber. Zeolites are not chiral and therefore the perturber is added to the medium. Thus the medium for a photoreaction is a chirally modified zeolite. Of the several reactions investigated, results on photoelectrocylization of tropolone alkyl ethers are discussed at length. The confined space offered by the zeolite supercage forces a reactant and the chiral inductor to interact intimately to yield enantiomerically enriched product. Due to the transitory nature of the reaction cavity in solution such close interactions are less likely in isotropic solvent media. The examples discussed herein show negligible chiral induction in solution, whereas in a zeolite one obtains induction as high as 90%.     

Adsorption of a double-chain surfactant on an oxide

Adsorption of surfactants on solids is affected by the intermolecular packing in the adsorbed layer besides the driving forces. The adsorption behavior of a double-chain surfactant on silica is studied here along with that of the single-chain one. Comparison of adsorption of these two surfactants is warranted since while the single-chain surfactants form spherical micelles, the double-chain ones form bilayered vesicles in solution. While the adsorption of the single-chain surfactant reaches the plateau in a wide concentration range, the adsorption of the double-chain one increases sharply in a concentration range 10⁻⁵ mol/L up to the plateau. The single chain is found to form 1.5 monolayers under saturation coverage suggesting adsorption with reverse orientation at high concentration. In contrast, the adsorption of the double-chain surfactant under saturation coverage is equivalent to a 0.9 monolayer. Fluorescence tests revealed the hydrophobicity change of the surface with increase in adsorption. However, the hydrophobicity tests show the solid surface to be hydrophilic in this range; the double-chain surfactant is proposed to form a partial bilayer.     

Introduction of vinyl and hydroxymethyl functionalities at C-4 of glucose-derived substrates: synthesis of spirocyclic, bicyclic, and tricyclic nucleosides

Installing hydroxymethyl and hydroxyethyl substitutions at C-4 through vinylation and hydroboration-oxidation reactions of the C-4 bis-hydroxymethyl derivative of d-glucose based substrate, and inserting heteroatoms thereafter permitted formation of N-, O-, or S-heterocycles leading to [4,5]- or [5,5]-spirocycles and a bicyclo[3.3.0]octane product. Some of the spirocycles were converted to spironucleosides under Vorbruggen glycosidation reaction conditions. Similarly, the bicyclic product was elaborated to the corresponding bicyclic nucleoside as well as an unexpected tricyclic nucleoside.     

A new mixed ligand coordination polymer of Mn(II): structural aspect and cryomagnetic study

A new 1-D polymeric chain complex [Mn(pydc)(1,10-phen)]_n· nH₂O (pydc = pyridine-2,3-dicarboxylate, 1,10-phen = 1,10-phenanthroline) has been synthesised and characterised by elemental analysis, FT-IR spectrum, thermal analysis and variable temperature magnetic susceptibility studies. Single crystal X-ray diffraction study reveals that the central Mn(II) ion is in a distorted octahedral coordination geometry, and is coordinated to pydc and 1,10-phen. The complex shows interesting hydrogen bond modes involving the dicarboxylates and lattice water molecules. The presence of weak antiferromagnetic coupling with J = −0.72 cm⁻¹ for the complex has been concluded from the cryomagnetic susceptibility studies.     

Long-range radical cation migration in DNA: investigation of the mechanism

During the past decade, long-range radical cation migration in DNA has been an area of extensive experimental and theoretical examination. The motivations for the vigorous investigation of this topic are its potential to yield a deeper understanding of the processes that cause oxidative damage of genomic DNA and the potential for use of DNA architectures in molecular electronics. This investigation has revealed the mechanisms of charge transport and the limitations of DNA as a functional element in devices. In this article we discuss various aspects of the radical cation migration process and present the plausible mechanism by which this process occurs.