Molecular and cluster anions have been investigated using a newly built tandem time-of-flight mass spectrometer combined with photoelectron imaging system. Solvation particularly hydration is shown not only to stabilize metastable anions such as CO₂⁻ in their ground state and impede autodetachment but also to alter the dynamics in the excited states. For instance, the 355 nm photoelectron image of mass-selected CO₂⁻(H₂O)(m) evolves from anisotropic to isotropic as m increases indicating excited state decay via electron autodetachment. Dissociation channels open at m=2 at 266 nm, resulting in O−(H₂O)m-k and CO₂⁻(H₂O)(m-k) products, the later becoming dominant as m increases. The photoelectron imaging of (CS₂)₂⁻ has revealed the coexistence of four electronic isomers: CS₂⁻•CS₂ [C(s)(₂A′)] and three covalent C₂S₄⁻ [C₂ᵥ(²B₁), D(2h)(²B(3g)), and D(2d)( ²A₁)] structures. Water-mediated intermolecular interactions have been shown to facilitate the formation of the global minimum C₂ᵥ(²B₁) structure rather than the less stable local minima C(s)(₂A′) and D(2d)(²A₁) structures that are favored in the dry source condition. In the (CS2)(n)⁻, n ≥ 3 and (CS₂)₂⁻ (H₂O)(m), m > 0 clusters, the population of the C₂ᵥ(²B₁) structure diminishes drastically due to more favorable solvent interactions with the CS2 − monomercore. Photoexcitation of the (CS₂)₂⁻ also results in the formation of CS₂⁻ and C₂S₂⁻ at 532 nm, and C₂S₂⁻, CS₂⁻, CS₃⁻, S₂⁻, and S⁻ at 355 and 266 nm. The relative yields of C₂S₂⁻ is significantly higher when (CS₂)₂⁻ is formed under wet source condition suggesting C₂ᵥ(²B₁) structure as the origin of C₂S₂⁻. An abrupt decrease in the relative yield of C₂S₂⁻ is observed upon adding CS₂ or H₂O to (CS₂)₂⁻. The CS₂⁻ based clusters are the likely origin of the S− photoproduct, while CS₃⁻ is formed through the secondary S⁻+CS₂ reaction. Novel anions (CS₂O₂⁻ and CS₃O⁻) are observed in the CS₂+O₂+e⁻ reaction. The photoelectron imaging and photodissociation results of these and other anionic products are presented. In addition, CS₂⁻•O₂ ion-neutral complex is formed depending on the conditions in the ion source. Despite the positive electron affinity of O₂, no clear signature of O₂⁻•CS₂ ion-neutral complex is seen in the photoelectron image. CO₃⁻ ion is also formed abundantly as a result of CS₂+CO₂+O₂+e⁻ reaction.

An integrated graph-theoretic and geometric approach to the analysis of aqueous solvation of atomic ions is presented. This analysis makes use of a novel data-mining tool, moleculaRnetworks, to process data from molecular dynamics simulations. The workings and structure of this tool are discussed, along with the development and testing of its PageRank algorithm-based rapid solvation polyhedra classifier. The ability to classify instantaneous solvation polyhedra enables a finely detailed understanding of shell structure-behavior relationships, as water molecules simultaneously rearrange about ions, exchange with the bulk, and rearrange their hydrogen-bond network. The application of the tool to cation systems, including lithium, sodium, potassium, magnesium, calcium, and lanthanum, yields new insight into the mechanisms of water exchange about these ions. It is shown that in order for exchange events to occur, the solvation shell must "preorganize" to admit or expel a molecule of water: this preorganization is reflected in the mechanistic preference for each ion. The application of the tool to anion systems, including fluoride, chloride, and bromide, reveals that these ions have an extended effect on the reorientation ability of water molecules beyond their first solvation shell. Finally, when both ions are present, as in the potential of mean force simulation between lanthanum and chloride, structural rearrangements can be seen as the ions break through the barrier to form the contact ion pair. Taken together, these results show the utility of the moleculaRnetworks tool in broadening our understanding of aqueous ion solvation.

No description available.

Spectrofluorometric probe methods are developed and examined regarding their ability to model preferential solvation around probe molecules in binary solvents. The first method assumes that each fluorophore is solvated by only one type of solvent molecule and that each fluorophore contributes to the emission intensity. Expressions for this model are illustrated using fluorescence behavior of pyrene, benzo[e]pyrene, benzo[ghi]perylene, and coronene dissolved in binary n-heptane + 1,4-dioxane and n-heptane + tetrahydrofuran mixtures. The second method treats the solvational sphere as a binary solvent microsphere, with the fluorophore's energy in both the ground and the excited states mathematically expressed using the "nearly ideal binary solvent" (NIBS) model. Expressions derived from this model are illustrated using fluorescence behavior of 9,9'-bianthracene and 9,9*-bianthracene-10-carboxaldehyde in binary toluene + acetonitrile and dibutyl ether + acetonitrile.

O grupo amida é encontrado em biomoléculas como as proteínas, ácidos nucleícos, bem como em polímeros sintéticos. A molécula mais simples que contém o grupamento amida é a formamida. Um grande número de estudos sobre essa molécula tem sido realizados no vácuo, no estado líquido e em solventes utilizando-se as mais diferentes técnicas experimentais e computacionais, mas ainda restam questões fundamentais sobre a sua estrutura eletrônica e solvatação. O conhecimento preciso da ressonância e das barreiras conformacionais desse composto é de fundamental importância para uma compreensão do comportamento conformacional de biomoléculas e polímeros sintéticos. Uma compreensão detalhada das interações dessa molécula com água é igualmente importante, pois o grupamento amida é um dos principais sítios de hidratação de proteínas. Este trabalho teve o objetivo de se estudar as interações existentes entre a formamida e água, nas formas de mínima energia e nos estados de transição do grupo amida, e as alterações na estrutura eletrônica da formamida. Constatou-se a existência de grandes diferenças entre a estrutura eletrônica da formamida na sua forma mais estável e a dos estados de transição da rotação do grupo amida. Através do método NBO (Natural Bond Orbitals), verificou-se uma diminuição nos efeitos de ressonância nos estados de transição provocada pela diminuição da interação entre o par de elétrons isolados do nitrogênio e o orbital 'pi' antiligante do grupo carbonila (nN→'pi'*CO). A hidratação provocou alterações na estrutura eletrônica da formamida planar e dos estados de transição. As interações intermoleculares entre formamida e água foram intensas, sobretudo nos casos em que o solvente interagiu simultaneamente com os grupos carbonila e amida. Nos estados de transição, a interação entre o par de elétrons isolado do nitrogênio da amida e a molécula de água se torna importante. As energias das ligações de hidrogênio entre a formamida e as moléculas de água são, de um modo geral, estabilizadoras das supermoléculas. Pode-se verificar que há cooperatividade apenas nas energias e não em outras propriedades. Com o auxílio das análises NBO (Natural Bond Orbitals) e NRT (Natural Resonance Theory), verificou-se um aumento da ressonância da formamida planar com a adição sucessiva de moléculas de água. Tal observação pode sugerir que as ligações de hidrogênio entre formamida e água possuem algum caráter covalente. O estudo da solvatação da formamida utilizando o modelo discreto/contínuo demonstrou que as moléculas de água explícitas exercem larga influência na energia livre de solvatação. Constatou-se a preferência pela solvatação no oxigênio do grupo carbonila e a validade do modelo discreto/contínuo. / The amide group is found in biomolecules such as proteins, nucleic acids, as well as synthetic polymers. The simplest molecule that contains the amide group is formamide. A large number of studies have been made on vacuum, liquid state and on various solvents, using the most different computational and experimental techniques, but there are many fundamental questions to be answered about its electronic structure and solvation. The precise knowledge about resonance and conformational barriers of this compound is of fundamental importance for the understanding of conformational behavior of biomolecules and synthetic polymers. A detailed understanding about the interactions of this molecule with water is equally important, for the amide group is one of the major sites of solvation in proteins. This work has the objective of studying the interactions of formamide and water, on the minimum energy conformation and the transition conformations of the amide group and the electronic structure of formamide. It has been found the existence of great differences between the electronic structure of formamide on its more stable conformation and the conformational transition states of the amide group rotation. Using the Natural Bond Orbital (NBO) analysis, a decrease of resonance effects on the transitions states was verified, due to the loss of interaction between the electrons of the nitrogen lone pair and the carbonyl 'pi' anti-bonding orbital (nN→'pi'*CO). The solvation of formamide has changed the electronic structure of planar formamide and the conformational transition states. The intermolecular interactions between planar formamide and water are very strong, specially when the solvent molecules interact simultaneously with the carbonyl and amide groups. Regarding the conformational transition states, the interaction between the nitrogen lone pairs of amide and the water molecule is observed. The hydrogen bond energies of formamide and water stabilizes the supermolecules. It can be verified that there is cooperativity only with energies and not in other properties. Using the NBO and the Natural Resonance Theory (NRT) methods, an increase of resonance for the planar form with the successive addition of water molecules has been verified. This observation suggests that the hydrogen bonds between formamide and water have some covalent character. The solvation study of formamide using the discrete/continuous model shows that the explicit waters influence the free energy of solvation. A preference for the solvation of carbonyl oxygen and the validity of the discret/continuous model has been verified.

Fung Wai-man. / Thesis (M.Phil.)--Chinese University of Hong Kong. / Includes bibliographies.

Wong Shu Yan. / On t.p. "n" is subscript. / Thesis submitted in: January 2003. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 112-115). / Abstracts in English and Chinese. / TITLE PAGE --- p.i / THESIS EXAMINATION COMMITTEE --- p.ii / ABSTRACT (ENGLISH) --- p.iii / (CHINESE) --- p.v / ACKNOWLEDGEMENTS --- p.vii / TABLE OF CONTENTS --- p.viii / LIST OF FIGURES --- p.xi / LIST OF TABLES --- p.xiii / Chapter CHAPTER ONE --- Introduction / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Solvation of clusters --- p.2 / Chapter 1.3 --- Reaction of a sodium atom with water --- p.3 / Chapter 1.4 --- Reaction of a sodium cation with methanol --- p.8 / Chapter 1.5 --- Computational Method --- p.12 / Chapter 1.5.1 --- Born-Oppenheimer (BO) Approximation --- p.12 / Chapter 1.5.2 --- Self-Consistent Fields (SCF) ´ؤ Hartree-Fock (HF) --- p.14 / Chapter 1.5.2.1 --- Moller-Plesset (MP) Perturbation Theory --- p.15 / Chapter 1.5.2.2 --- Ab Initio Molecular Orbital (MO) Calculation --- p.16 / Chapter 1.5.2.3 --- Basis Set Superposition Errors --- p.17 / Chapter 1.5.3 --- Density Functional Theory (DFT) --- p.18 / Chapter 1.5.3.1 --- Generalized-Gradient Approximation (GGA) --- p.20 / Chapter 1.5.3.2 --- Plane-wave Basis Set --- p.21 / Chapter 1.5.3.3 --- Pseudopotential Approximation --- p.21 / Chapter 1.5.3.4 --- Ab Initio Molecular Dynamics (MD) Calculation --- p.23 / Chapter CHAPTER TWO --- Reaction Mechanism of the Hydrogen Elimination Reaction of Na(H20)n clusters for n = 1 - 6 / Chapter 2.1 --- Introduction --- p.25 / Chapter 2.2 --- Computation details --- p.26 / Chapter 2.3 --- Optimized Structure of Na(H20)n and H.. .Na0H(H20)n-1 --- p.27 / Chapter 2.3.1 --- Solvation structures with n = 1-3 --- p.27 / Chapter 2.3.2 --- Solvation structures with n= 4-6 --- p.34 / Chapter 2.3.3 --- Relative energy of isomers --- p.40 / Chapter 2.3.4 --- Energy barrier of hydrogen elimination reaction --- p.42 / Chapter 2.3.5 --- Natural population analysis --- p.42 / Chapter 2.4 --- "Reaction energy for hydrogen loss in Na(H20)n, n = 1 -6" --- p.46 / Chapter 2.5 --- Ionization potential energy --- p.47 / Chapter 2.6 --- Summary --- p.50 / Chapter CHAPTER THREE --- Reaction Mechanism of the Ether Elimination Reaction of Na+(CH3OH)n cluster ions / Chapter 3.1 --- Introduction --- p.52 / Chapter 3.2 --- Computational details --- p.53 / Chapter 3.3 --- Optimized Structure for Na+(CH3OH)n (n = 1) --- p.55 / Chapter 3.4 --- Optimized Structure forNa+(CH3OH)n (n = 2-5) --- p.59 / Chapter 3.4.1 --- Na+(CH3OH)2 --- p.59 / Chapter 3.4.2 --- Na+(CH3OH)3 --- p.67 / Chapter 3.4.3 --- Na+(CH3OH)n(n = 4 and 5) --- p.75 / Chapter 3.5 --- Mechanism of ether elimination reaction --- p.79 / Chapter 3.6 --- Ab initio molecular dynamics study on Na+(CH3OH)n (n =6 and 8) --- p.85 / Chapter 3.6.1 --- Solvation dynamics for Na+(CH3OH)6 --- p.85 / Chapter 3.6.1.1 --- Dynamical structural for Na+(CH3OH)6 --- p.86 / Chapter 3.6.1.2 --- "Optimized Structures for Na+(CH3OH)n, n =6" --- p.95 / Chapter 3.6.2 --- Solvation dynamics for Na+(CH3OH)8 --- p.98 / Chapter 3.6.2.1 --- Dynamical structural for Na+(CH3OH)8 --- p.99 / Chapter 3.6.2.2 --- "Optimized Structures for Na+(CH3OH)n, n =8" --- p.106 / Chapter 3.7 --- Summary --- p.109 / REFERENCES --- p.112

"November 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 206-213). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry. / Includes bibliographical references. Also available on the Internet.

Thesis (M.Sc.)--York University, 2004. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 100-103). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ99372