Alzheimer's disease (AD) is the major cause of dementia and is characterized by neuronal death and brain atrophy. The amyloid ß (Aß) peptide is tightly associated with neuronal dysfunction during AD, but the molecular mechanism underlying the neurotoxic effect of Aß is poorly understood. Extracellular fibrillar deposits (plaques) of Aß were initially believed to be the cause of AD, but currently there is overwhelming evidence that the prefibrillar Aß oligomers are the major toxic entities. Structural characterization of Aß oligomers and fibrils is important for understanding the structural features determining the toxic potency of the peptide. This project has studied the aggregation and accompanying structural transitions of Aß, a naturally occurring hypertoxic species, i.e. pyroglutamylated Aß, and their combination, using biophysical approaches (circular dichroism, fluorescence, infrared spectroscopy). In addition, aggregation and structure of overlapping peptide fragments have been studied to identify the specific stretch of Aß that serves as seeding region initiating the aggregation and fibril formation by the full-length Aß peptide. These studies elucidate the structural features of Aß responsible for the peptide's neurotoxic action

Tumor biologist have long appreciated that both cell to cell and cell to extracellular matrix (ECM) interactions are involved in the invasive and metastatic events that are characteristic of malignancy. Cancer cell attachment to and invasion of an ECM has been associated with metastatic potential of cell lines of the Dunning rat prostate model. It was postulated that differences observed in the metastatic potential of four Dunning cell lines may correlate with cell-matrix interactions. Four cell lines, highly metastatic ML, MLL, AT-3 and non-metastatic AT-1 were studied. The adhesive, invasive and chemoinvasive capability of each cell line was compared. Cell adhesion was examined by plating the cells on plastic dishes coated with various components of the ECM (fibronectin, laminin and collagen) as well as EHS Natrix (a natural ECM) . Invasion was determined by examining cells ability to traverse a matrigel barrier. Correlations were found between the cells' adhesive and invasive abilities in response to the ECM. These observations suggest that ECM components are highly involved in prostate cancer cell activities and loss may contribute to tumor progression and metastasis.

Single molecule nanopore spectroscopy is a label-free method for characterizing a wide variety of water-soluble molecules. Recently there have been efforts to expand nanopore sensing to new areas of study. Forensic investigators require an easy to deploy method to identify an unknown number of contributors in a solution. Currently there is no easily available method to distinguish between a single or multiple contributor solution of DNA before being processed by more advanced analytical techniques which has led to wasted time and resources increasing the backlog of samples waiting to be processed. In this work we present a new nanopore technique capable of distinguishing between single and multiple contributors with an easy to deploy infrared heating laser. Previous cluster-nanopore enhancement interaction studies, produced by this group, have found that polymers in the presence of a gold-nanopore complex spend longer periods of time inside the pore. This is of great interest to the nanopore sensing community because longer residence times enable more accurate statistics on single polymers. In order to understand why x some polymers see large enhancements in the residence times (i.e. 20x) while other polymers see much less enhancement (i.e. 3x) a more complete picture of the free energy components is required. By using a IR heating laser, we construct an Eyring transition graph to extract the enthalpic and entropic energy components to find entropy plays a more important role than previously thought when a polymer interacts with a the nanopore. For nanoconfined polymers, entropy plays an important role on how a polymer will interact with the cluster-nanopore structure which in turn may lead to an increase or decrease of the residence time enhancement factor. This work shows with the addition of an infrared laser heater to a nanopore system a new tool has been added to the field. The IR laser coupled to a nanopore system allows for precise adjustments to residence times of events and extracts the free energy components without the need to physically modify the nanopore.

The radiation-induced decomposition of glycine is studied using a combination of Near Edge X-ray Absorption Fine Structure (NEXAFS) measurements and density functional theory calculations. Principal Component Analysis was used to determine the number of distinct molecules that were needed to explain the observed changes in the measured spectra, and the emerging absorption features are assigned to various product molecules through comparison with simulated spectra of several model compounds. It is clear from the experiment that the major effect of soft X-ray irradiation is the fragmentation of the molecule, primarily at the carbonyl sites. Peptide formation is shown to occur under irradiation; a condensation reaction initiated by the removal of a carbonyl oxygen is the proposed mechanism. This study utilizes a novel approach to the study of radiation damage that can occur during measurements, and suggests that it may be possible to use simulated model spectra to correct for these effects in measured spectra.<p> A study of oligothiophene-based molecular semiconductor materials with potential applications in light-emitting and photovoltaic devices is undertaken. Angle-resolved NEXAFS measurements of the star-shaped 4(HPBT) molecules on an amorphous indium surface show a strong dichroic signal indicating a well-ordered, uniformly upright arrangement of planar molecules. The X-ray excited optical luminescence (XEOL) measurements showed several sharp features associated with vibronic splitting of the LUMO-HOMO luminescent transition. The HOMO-LUMO gap determined from the XEOL measurements is 2.28 eV; this value is in agreement with previously published optical measurements as well as with the value that is estimated from the combination of NEXAFS and X-ray emission spectroscopy (XES) measurements. Films formed from blended solutions of 4(HPBT) and the hole-transporting molecular semiconductor PCBM are shown to form a bilayer structure with the PCBM adjacent to the substrate. Annealing causes desorption of the 4(HPBT) from the surface.

The radiation-induced decomposition of glycine is studied using a combination of Near Edge X-ray Absorption Fine Structure (NEXAFS) measurements and density functional theory calculations. Principal Component Analysis was used to determine the number of distinct molecules that were needed to explain the observed changes in the measured spectra, and the emerging absorption features are assigned to various product molecules through comparison with simulated spectra of several model compounds. It is clear from the experiment that the major effect of soft X-ray irradiation is the fragmentation of the molecule, primarily at the carbonyl sites. Peptide formation is shown to occur under irradiation; a condensation reaction initiated by the removal of a carbonyl oxygen is the proposed mechanism. This study utilizes a novel approach to the study of radiation damage that can occur during measurements, and suggests that it may be possible to use simulated model spectra to correct for these effects in measured spectra.<p> A study of oligothiophene-based molecular semiconductor materials with potential applications in light-emitting and photovoltaic devices is undertaken. Angle-resolved NEXAFS measurements of the star-shaped 4(HPBT) molecules on an amorphous indium surface show a strong dichroic signal indicating a well-ordered, uniformly upright arrangement of planar molecules. The X-ray excited optical luminescence (XEOL) measurements showed several sharp features associated with vibronic splitting of the LUMO-HOMO luminescent transition. The HOMO-LUMO gap determined from the XEOL measurements is 2.28 eV; this value is in agreement with previously published optical measurements as well as with the value that is estimated from the combination of NEXAFS and X-ray emission spectroscopy (XES) measurements. Films formed from blended solutions of 4(HPBT) and the hole-transporting molecular semiconductor PCBM are shown to form a bilayer structure with the PCBM adjacent to the substrate. Annealing causes desorption of the 4(HPBT) from the surface.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-06, Section: B, page: 3952. Adviser: Mark J. Kushner. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

voir pp. 293-294 du pdf

Afin d'éviter l'apparition de traces de type tache de café, une stratégié consiste à hydrophiliser les surfaces en déposant une couche de polymère hydrophile. La question qui s'est alors posée est : que se passe-t-il lorsque l'on mouille cette surface avec de l'eau ? La surface ainsi hydrophilisée empèche-t-elle la formation de traces ? Pour répondre à ces questions, nous avons observé l'étalement de gouttes d'eau sur des films de polymère hydrophile. Nous avons alors constaté que la goutte s'étale d'autant mieux (angle de contact faible, rayon de goutte élevé) que la fraction d'eau dans le film de polymère est élevée. Ainsi, une préhydratation de la couche polymère aide à l'étalement de la goutte. Nous avons montré que l'absorption d'eau de la phase vapeur, issue du gradient d'humidité imposé par la goutte elle-même, est l'origine principale de la préhydratation de la couche de polymère. Cette préhydratation est d'autant plus efficace que la ligne de contact avance lentement. Nous avons modélisé qualitativement ce phénomène. Cependant, lorsque la ligne triple ralentit, il existe des transferts de matière autres que celui par la phase vapeur : la dissolution du polymère dans la goutte aux vitesses intermédiaires de la ligne triple et la diffusion de l'eau dans le film de polymère, devant la ligne de contact, aux très faibles vitesses. Ces deux transferts modifient également la dynamique de la ligne de contact. Nous avons estimé à l'aide d'arguments simples, les vitesses critiques en-dessous desquelles la dissolution du polymère dans la goutte, puis la diffusion de l'eau dans le film de polymère affectent l'angle de contact. Ces vitesses dépendent de différents paramètres dont l'épaisseur de la couche de polymère ou encore les coefficients de diffusion de l'eau dans le film de polymère ou du polymère dans l'eau. En variant la physico-chimie du polymère, nous avons observé deux comportements de la ligne de contact lors du séchage de la goutte d'eau : 1. la ligne recule et laisse un dépôt continu de type volcan (cas du polymère neutre) 2. la ligne est accrochée et un anneau de polymère de type tache de café se forme (cas des polymères chargés). Nous donnons des arguments qui laissent à penser que la forte pression osmotique due à la présence des charges confinées non écrantées sur le squelette du polymère est une des raisons possibles du blocage de la ligne de contact. En pratique, le fait que la préhydratation par la phase vapeur soit le mécanisme dominant pour l'étalement d'une goutte posée sur un film fin de polymère, signifie que pour que la ligne de contact avance le plus loin possible, il faut un polymère qui s'hydrate très facilement, donc très hygroscopique. On pourra alors choisir un polymère chargé déposé en une couche de faible épaisseur. Cependant, le choix d'un polymère chargé pour favoriser l'étalement provoque un blocage de la ligne triple non désiré en condition de séchage. L'ajout de sel permettrait alors une reculée à vitesse constante avec un dépôt de taille réduite.

<p> Advancements in science and technology increasingly involve systems operating at the nanoscale. Interfaces are often present in these systems. Nanoscopic interfaces are ubiquitous in biological systems, nanofluidic devices, and integrated circuits. Properties at the interface may be quite different from the bulk, and in fact a true bulk may not be present in these systems. At the nanoscale the ratio of interface to volume is large, and the interface may have the dominant role in determining system behavior. Interfacial characteristics and their connection to interfacial properties are the focus of my thesis. Using molecular simulations of model interfaces we characterize how properties like chemistry, composition, and topography affect such phenomena such as hydrophobicity, heat transfer, and momentum transport at the nanoscale. An interface is defined simply as where two materials meet and a change in some structure or order parameter is observed. In aqueous systems, the type studied here, these changes are relatively sharp and occur within a distance of nanometers. Water molecules near the interface are expected to display sensitivity to the underlying surface. Indeed, water near a hydrophobic surface is more deformable and has greater fluctuations. The hydrophobicity of chemically heterogeneous surfaces and proteins are characterized using these nanoscopic measures. We find the effect of mixing hydrophobic and hydrophobic head group chemistries is asymmetric, i.e., it is easier to make a hydrophobic surface hydrophilic than the reverse. The role of hydrogen bonding in hydrophobic and ion hydration is also characterized using a short range water model. Hydrophobic and ion hydration are reasonably captured with the short range water model. These studies show the importance of chemical composition and local hydrogen bonding in determining surface hydrophobicity. Interfaces also lead to anomalous behavior in heat and momentum transport. Interfaces disrupt local structure and create boundary resistances that manifest in temperature discontinuities and interfacial slip. We explore the effects of chemical heterogeneity, nanoscale surface roughness, and directionality on thermal conductance across model solid-water interfaces. Interfacial conductance is directly influenced by the coupling strength or wettability of the surface. For chemically mixed surfaces, interfacial conductance does not precisely match with wettability. Surface roughness in general enhances conductance, but the improvement cannot be completely attributed to increased solvent accessible surfaced area. Momentum transport displays similar discontinuities at aqueous interfaces. These effects can be reduced through the use of osmolytes. Collectively this work highlights the influence of interfaces on heat and momentum transport. Insights are provided for modifying interfacial behavior and altering the property of interest.</p>

Neste trabalho foi realizado um estudo vibracional por espectroscopia de absorção no infravermelho por transformada de Fourier e de espalhamento Raman, do sal Li2C5O5.2H2O, para obter uma atribuição vibracional completa, ainda inédita para o ânion croconato, por causa da mútua exclusão e da ocorrência de modos inativos no espectro Raman e no infravermelho. Para tanto, a estrutura cristalina do croconato de lítio foi determinada por difração de raio-X. Ela pertence ao sistema monoclínico, grupo de espaço C2/c (C2h6), com quatro unidades-fórmula por célula unitária e consiste de planos contendo unidades do ânion croconato quase paralelas, interconectadas entre si por moléculas de água e cátions lítio. Não se observou distorção da planaridade do anel e nem desvio da geometria pentagonal que pudessem resultar em significativo abaixamento da simetria molecular. Com as informações cristalográficas obtidas, foi utilizado o método das correlações e de grupo de fator para prever o número e espécies de simetria das bandas vibracionais deste composto no estado sólido. A molécula de água encontra-se distorcida e participa de uma ligação de hidrogênio assimétrica de intensidade média. A técnica de substituição isotópica de H2O por D2O foi utilizada para caracterizar os modos vibracionais externos e internos da água de cristalização, distinguindo-os dos modos internos do croconato, o mesmo sendo feito para o cátion lítio, através de seu isótopo 6Li, permitindo caracterizar seus modos translacionais. Também foram preparados os compostos anidros Li2C5O5 e 6Li2C5O5, para auxiliar a atribuição dos modos vibracionais da água. A análise das razões isotópicas obtidas permitiu observar que os modos externos da água e do cátion lítio encontram-se acoplados, conforme indica a comparação entre as razões isotópicas observadas e esperadas. Este desvio também indicou o acoplamento entre os três modos libracionais, fato que concorda com os dados cristalográfícos, pois a molécula de água está localizada em um sítio C1. Foram obtidos os espectros Raman polarizados de monocristais orientados de Li2C5O5.2H2O, inéditos para esta classe de substâncias. Estes resultados permitiram a atribuição dos modos vibracionais inativos, bem como dos modos ativos apenas no IV, agora permitidos no efeito Raman pelo efeito de campo de correlação. / In this work a detailed vibrational Fourier Transform Infrared and Raman Scattering spectroscopic studies were performed on lithium croconate dihydrate (Li2C5O5.2H2O) aiming to get a complete vibrational assignment, still inedit for this molecule, that was precluded by mutual exclusion and inactive modes. To acomplish this task, the crystal structure of this salt was determined by means of X-ray diffraction. It belongs to the monoclinic system, space-group C2/c (C2h6), consisting of planes containing almost parallel croconate units interconnected by water molecules and lithium ions, with four formula-units by unit cell. The croconate ion does not show a significant deviation from planarity or from pentagonal geometry. The crystallographic information made possible the aplication of the correlation and the factor group methods to get the number and symmety species of the vibrational bands for the compound in the solid state. The water molecule is distorted and is envolved in an assymetric hydrogen bonding of medium strenght. Isotopic substitution techniques were extensively used to assign water vibrational bands (internal and external), enhancing the distinction between them and that of the croconate ion. In the same way, translational modes due to lithium sites have been assigned. The anhidrous derivatives Li2C5O5 and 6Li2C5O5 were worth in the assignment of water bands. The isotopic ratios indicate that water librations and lithium translations are coupled , since they deviate from the values expected for pure motions. This deviation also indicates the coupling between the three librational water modes, what is expected since the water molecule is situated on a symmetry C1 site. By the first time the Raman polarized spectra of the oriented single crystals have been obtained for this class of substances. These results were helpfull in the assignment of the inactive modes, as weel as the infrared active ones, now made allowed in the Raman spectra by the correlation field effect.