Intramolecularly Sensitized Precipitons

This dissertation describes the first intramolecularly activated precipitons. The isomerization process is induced by intramolecular triplet energy transfer from a covalently attached sensitizer. The intramolecular sensitization leads to a more rapid isomerization than can be achieved by intermolecular sensitization at accessible concentrations. Two different types of intramolecularly sensitized precipitons were investigated. The first precipiton receives intramolecular sensitization from a covalently attached metal complex (Ru(bpy)3Cl2). It was used in a model study for the sequestration of metal contaminants. The second precipiton receives intramolecular sensitization from a covalently attached organic compound (benzil). The preparation, photophysical properties, and photoisomerization kinetics of these precipitons, as well as the precipitation event, are discussed

INTRAMOLECULARLY SENSITIZED PRECIPITONS: APPLICATION TO METAL SEQUESTRATION

It has been demonstrated previously that precipitons can be successfully utilized in the area of chemical synthesis. Herein, we describe the properties of precipitons attached to metal complexes. Our preliminary studies show that the rate of an intermolecularly sensitized precipiton obeys first-order kinetics. A microcrystal suspension forms during the reaction, and we are interested in learning more about this process. To demonstrate intramolecular energy transfer, two new precipitons were designed, synthesized, and characterized. They represented two types of triplet energy transfer: Forster and Dexter. The Forster precipiton (10 uM solution) reached a photostationary state within two minutes when irradiated with visible light. In contrast, intermolecular sensitization (10 uM precipiton + 10 uM Ru(bpy)3Cl2) proceeded approximately ten times more slowly. What we have learned will be useful for metal sequestration applications

Chalcogen Bonding “2S–2N Squares” versus Competing Interactions: Exploring the Recognition Properties of Sulfur

ISSN:0947-6539ISSN:1521-376

Control of stilbene conformation and fluorescence in self-assembled capsules

The extensively studied trans-stilbene molecule is known to give only weak fluorescence in solution and inside loosely-fitting synthetic capsules. However, trans-stilbene has been recently studied in the context of antibody interiors, where binding results in strong blue fluorescence. The present research was undertaken to understand the spatial factors that influence stilbene fluorescence. trans-Stilbene was encapsulated in the snug, self-assembled complex 1.1 and exhibited fluorescence quenching due to the distortion of its ground-state geometry. When the complex is elongated by incorporating glycouril spacers, trans-stilbene is allowed to adapt a fully coplanar arrangement and fluorescence returns

Unraveling the Role of Alkyl F on CH−π Interactions and Uncovering the Tipping Point for Fluorophobicity

Although fluorine often plays an influential role in molecular recognition, little is known about the effect of aliphatic fluorine on the CH−π interaction in solution. A series of molecular balances were synthesized that contain fluorinated and nonfluorinated alkyl groups. Our findings indicate that fluorine’s polarizing ability does enhance CH−π binding and depends on molecular orientation. Surprisingly, when the terminal end of the alkyl group is completely fluorinated, the balance tips toward fluorophobicity and assumes an unusual constrained conformation

Unraveling the Role of Alkyl F on CH−π Interactions and Uncovering the Tipping Point for Fluorophobicity

Although fluorine often plays an influential role in molecular recognition, little is known about the effect of aliphatic fluorine on the CH−π interaction in solution. A series of molecular balances were synthesized that contain fluorinated and nonfluorinated alkyl groups. Our findings indicate that fluorine’s polarizing ability does enhance CH−π binding and depends on molecular orientation. Surprisingly, when the terminal end of the alkyl group is completely fluorinated, the balance tips toward fluorophobicity and assumes an unusual constrained conformation

New insights from Thailand into the maternal genetic history of Mainland Southeast Asia

Tai-Kadai (TK) is one of the major language families in Mainland Southeast Asia (MSEA), with a concentration in the area of Thailand and Laos. Our previous study of 1234 mtDNA genome sequences supported a demic diffusion scenario in the spread of TK languages from southern China to Laos as well as northern and northeastern Thailand. Here we add an additional 560 mtDNA genomes from 22 groups, with a focus on the TK-speaking central Thai people and the Sino-Tibetan speaking Karen. We find extensive diversity, including 62 haplogroups not reported previously from this region. Demic diffusion is still a preferable scenario for central Thais, emphasizing the expansion of TK people through MSEA, although there is also some support for gene flow between central Thai and native Austroasiatic speaking Mon and Khmer. We also tested competing models concerning the genetic relationships of groups from the major MSEA languages, and found support for an ancestral relationship of TK and Austronesian-speaking groups