Download or read book Vibrational Sum frequency Spectroscopic Investigations of the Orientation and Conformation of Amphiphiles at Oil water and Vapor water Interfaces written by Mark Richard Watry and published by . This book was released on 2002 with total page 396 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Vibrational Sum Frequency Spectroscopic Investigations of the Structure Hydrogen Bonding and Orientation of Water Molecules at the Liquid liquid Interface written by Lawrence Francis Scatena and published by . This book was released on 2001 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2003 with total page 664 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Vibrational Sum Frequency Spectroscopy of Osmolytes and Ions at Aqueous Interface written by Yi Liu and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Surfaces/interfaces are omnipresent in nature, ranging from physics and chemistry to biology and material sciences. To characterize the interfacial structures and understand the surface phenomena, many useful tools have been developed. Vibrational sum frequency generation (VSFG) spectroscopy has proven to be a powerful second-order non-linear optical technique for this purpose and is gaining more and more attention nowadays. With VSFG, two pulsed laser beams, one at infrared frequency and one at visible frequency, are incident on the surface and generate a new beam with a frequency equal to the sum of the IR and visible frequencies. When the IR frequency matches a surface vibrational mode frequency, this process would be resonantly enhanced. In this dissertation, this surface-sensitive technique was adopted to investigate several interfaces with special relevance to biology. The first topic of interest is the unusual orientation of a strong protein stabilizer, trimethylamine N-oxide (TMAO), at two aqueous/hydrophobic interfaces (air/water interface and OTS/water interface). By interpretation of the relative phase of VSFG spectra coupled with a numerical algorithm, the maximum entropy method (MEM) anaylysis of the molecular orientation, it is found that the methyl groups of TMAO prefer to point into the aqueous medium, while the oxide moieties (N+-O-) orient towards the hydrophobic air or OTS. This unusual orientation may be attributed to the more hydrophilic nature of methyl groups that is attached to a strong electron withdrawing atom such as a quaternary nitrogen. These results could help elucidate the stabilizing effect of TMAO on proteins the increased need to keep the methyl group hydrated would cause them to be excluded from protein interface and thereby lead to protein stabilization.The other major issue focused in this dissertation is based on the ion specific interactions at a charged interface, which plays a decisive role in various physico-chemical and biological processes. Binding affinity of different cations to monolayers of amphiphilic molecules (e.g. fatty acids, phospholipids) at the air/aqueous surfactant interfaces, may provide molecular level clues on various functions of cell membranes that are resembled by these amphiphilic molecules. Specifically, the binding events of several alkali cations to the hydrophilic carboxylate headgroups of long chain fatty acid, inferred from interfacial water structures, are thoroughly investigated by VSFG measurement. Results show that Li+ binds strongest to the negatively charged carboxylate groups, followed by Na+, then K+ although the difference is slight. The ranking of the alkali metal cations' binding abilities differs from the sequence predicted by the law of match water affinities (LMWA) and also varies with different headgroups in the model system, which may suggest the distinct solvation behaviors of these ions. Such findings should help to elucidate the molecular-level binding behavior to proteins in aqueous solutions.
Download or read book Vibrational Sum frequency Spectroscopy Investigations of Carboxylic Acid Based Surfactants and Polymers at the Oil water Interface written by Daniel Keith Beaman and published by . This book was released on 2010 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Vibrational Spectroscopy of Water Interfaces written by Quan Du and published by . This book was released on 1994 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Vibrational Sum Frequency Spectroscopy of Surfactants and Phospholipid Monolayers at Liquid Liquid Interfaces written by and published by . This book was released on 1998 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Work from our laboratory on vibrational sum frequency spectroscopic investigations of molecular ordering at the carbon tetrachloride-water interface is reviewed. Simple charged surfactants adsorbed at the liquid-liquid interface are seen to induce alignment of interfacial water molecules to a degree which is dependent on the induced surface potential. Saturation of water molecule alignment occurs at a surfactant surface concentration corresponding to a calculated surface potential of approximately 160 mV. In complementary studies, the relative degree of hydrocarbon chain ordering within monolayers of symmetric phosphatidylcholines of different chain lengths is inferred by the relative signal contributions of the methyl and methylene symmetric stretch modes. The degree of hydrocarbon chain disorder observed depends strongly on the method of monolayer preparation. By one method, a decrease in hydrocarbon chain order is seen with increasing chain length. Another method of monolayer formation yielded very well ordered hydrocarbon chains for the longest chain phosphatidylcholine studied, and showed much greater disorder in shorter chain species which was comparable to the other preparation method. These studies are a foundation for further work with this technique geared towards understanding molecular-level structural features in membrane-like assemblies and surface biochemical interactions of relevance to biomedical research.
Download or read book American Doctoral Dissertations written by and published by . This book was released on 2002 with total page 776 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Vibrational Sum Frequency Generation Studies of Aqueous and Biological Relevant Interfaces written by Ping Yuan Hsu and published by . This book was released on 2011 with total page 197 pages. Available in PDF, EPUB and Kindle. Book excerpt: The molecular structures of soft or fluid-like surfaces during contact in aqueous media play an important role in understanding adhesion and wetting between colloidal and biological interfaces. For example, it has been suggested that the presence of bound water (hydration layer) is crucial in controlling the fusion of lipid bilayers and the adsorption of proteins to bio-materials. Interfacial force measurements have revealed the importance of interfacial molecular structures on the viscosity, lubricity and adhesion acting between two surfaces. However, force measurements cannot provide direct information of the molecular structure after contact. Due to the limitations of experimental techniques, the understanding about the molecular structures of soft contact interfaces is limited. In this dissertation, we have developed an experimental approach to study the contact interface between a liquid and a solid substrate in an environment where they are surrounded by water. The surface sensitive infrared-visible sum frequency generation spectroscopy (SFG) provides information on the chemical groups, concentration and orientation of the molecules at the interface. We have studied the interface between hexadecane and sapphire surface using this technique. The adhesion between hexadecane droplets and the sapphire surface are determined by pH and the isoelectric point of sapphire substrate. Also, the SFG results suggest that the oil does not come in direct contact with the sapphire surface but is separated by a thin layer of water, even though the oil droplet sticks to the sapphire surface. The presence of the surfactant generates heterogeneous patchy contact between the oil and the sapphire, where the methyl groups of hexadecane are in direct contact with the surface hydroxyl groups of the sapphire surface. We have also used this design to study the contact interface between surfactant (stearyl trimethyl ammonium bromide, STAB) monolayers to mimic lipid bilayer contact. We have taken advantage of the adsorption of STAB on polystyrene and on hexadecane to create a contact interface with surfactant molecules on both sides. At conditions when both the surfaces were saturated with the surfactant molecules, it was impossible to drain the water away and the spectral signature of water did not change. This indicated that the double layer forces were strong enough to prevent any drainage of water at the fluid-like interface. In addition, the structure of water remained the same which is consistent with the expectations from force measurements that water structure is only affected under confinement and between two rigid and flat substrates. We also studied soft contact interface between elastomeric poly-dimethyl siloxane lenses and sapphire in water by using SFG. The confined spectra showed peaks related to PDMS as well as water, suggesting formation of water puddles in the contact area. The presence of the peak at 3690 cm-1 suggests the contact of surface hydroxyl groups with PDMS, supporting our hypothesis that the contact is heterogeneous. This heterogenous picture provides insight into the higher friction for a rubber sliding on sapphire surface in the presence of water. By using the established experimental protocols of SFG and the matrix free nanoassisted laser desorption-ionization (NALDI) mass spectroscopy, the actual adhesive contact interface between the soft gecko toe pad and the sapphire substrate was determined. A gecko's stickiness derives from van der Waals interactions between proteinaceous hairs called setae and the substrate. However, the molecular structure of the immediate contact at the adhesive interface is unknown. The SFG experiments demonstrate that there is a high representation of C-H bonds at the interface during gecko/sapphire contact, but the signatures of O-H bonding (e.g. water) and aromatic groups (e.g. amino acids/proteins) are entirely absent. Our discovery and analysis of gecko footprints have led to a surprising finding that geckos left behind a distinct trace of phospholipid molecules, a material that has never been considered in papers that deal with gecko adhesion. Particularly interesting ramifications include the previously unexplained sensitivity of gecko shear adhesion to variation in humidity, and the observation that setae show little if any wear. In the former case we find that an increase in the surface exposure of methylene groups is correlated with exposure of setae to water. In the latter case, it may be that sacrificial lipid-like molecules prevent damage to the rigid setae made of [Beta]-keratin. Our analysis of gecko footprints and the toe pad/substrate interface has significant consequences for models of gecko adhesion and by extension, the design of synthetic mimics.
Download or read book Sum Frequency Generation Vibrational Spectroscopy Studies on ModelPeptide Adsorption at the Hydrophobic Solid Water and HydrophilicSolid Water Interfaces written by and published by . This book was released on 2007 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sum frequency generation (SFG) vibrational spectroscopy has been used to study the interfacial structure of several polypeptides and amino acids adsorbed to hydrophobic and hydrophilic surfaces under a variety of experimental conditions. Peptide sequence, peptide chain length, peptide hydrophobicity, peptide side-chain type, surface hydrophobicity, and solution ionic strength all affect an adsorbed peptide's interfacial structure. Herein, it is demonstrated that with the choice of simple, model peptides and amino acids, surface specific SFG vibrational spectroscopy can be a powerful tool to elucidate the interfacial structure of these adsorbates. Herein, four experiments are described. In one, a series of isosequential amphiphilic peptides are synthesized and studied when adsorbed to both hydrophobic and hydrophilic surfaces. On hydrophobic surfaces of deuterated polystyrene, it was determined that the hydrophobic part of the peptide is ordered at the solid-liquid interface, while the hydrophilic part of the peptide appears to have a random orientation at this interface. On a hydrophilic surface of silica, it was determined that an ordered peptide was only observed if a peptide had stable secondary structure in solution. In another experiment, the interfacial structure of a model amphiphilic peptide was studied as a function of the ionic strength of the solution, a parameter that could change the peptide's secondary structure in solution. It was determined that on a hydrophobic surface, the peptide's interfacial structure was independent of its structure in solution. This was in contrast to the adsorbed structure on a hydrophilic surface, where the peptide's interfacial structure showed a strong dependence on its solution secondary structure. In a third experiment, the SFG spectra of lysine and proline amino acids on both hydrophobic and hydrophilic surfaces were obtained by using a different experimental geometry that increases the SFG signal. Upon comparison of these spectra to the SFG spectra of interfacial polylysine and polyproline it was determined that the interfacial structure of a peptide is strongly dependent on its chain length. Lastly, SFG spectroscopy has been extended to the Amide I vibrational mode of a peptide (which is sensitive to peptide secondary structure) by building a new optical parametric amplifier based on lithium thioindate. Evidence is presented that suggests that the interfacial secondary structure of a peptide can be perturbed by a surface.
Download or read book Vibrational Spectroscopy of Molecules at Liquid Liquid Interfaces written by and published by . This book was released on 1997 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: Measurement of the nonlinear vibrational spectrum of molecules at a liquid/liquid interface has recently been achieved by the use of total internal reflection sum frequency vibrational spectroscopy (TIR SFVS). This report describes this nonlinear optical technique and gives examples of the type of information which has been obtained about interfacial water and surfactants adsorbed at this interface. The surfactants examined include simple alkyl cationic and anionic surfactants commonly used in cleaning products, and phosphatidylcholines which comprise the major component of cell membranes. Studies of interfacial water involve comparative studies at air/water and oil/water interfaces, and the effect of adsorbed surfactant on the water structure and orientation at these two interfaces.
Download or read book Investigation of Immiscible Liquid liquid Interfaces with Second Harmonic Generation and Sum frequency Vibrational Spectroscopy written by John Charles Conboy and published by . This book was released on 1996 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Interfacial Water Organization and Ion Distributions Investigated with Vibrational Sum Frequency Spectroscopy written by Wei Hua and published by . This book was released on 2013 with total page 219 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Here, interface-specific nonlinear optical spectroscopies, conventional vibrational sum frequency generation (VSFG) and heterodyne-detected vibrational sum frequency generation (HD-VSFG), are employed to probe interfacial water molecules at the molecular level. HD-VSFG spectroscopy allows for direct interrogation of the average orientation of the transition dipole moment of interfacial water molecules that is intrinsically contained in the sign of the second-order nonlinear susceptibility, X(2). The water organization and ion distributions at air/aqueous interfaces of inorganic salt solutions are inferred from Im X(2) spectra obtained by HD-VSFG spectroscopy.
Download or read book Structures and Dynamics of Interfacial Water written by Fujie Tang and published by Springer. This book was released on 2019-06-20 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on the study of the interfacial water using molecular dynamics simulation and experimental sum frequency generation spectroscopy. It proposes a new definition of the free O-H groups at water-air interface and presents research on the structure and dynamics of these groups. Furthermore, it discusses the exponential decay nature of the orientation distribution of the free O-H groups of interfacial water and ascribes the origin of the down pointing free O-H groups to the presence of capillary waves on the surface. It also describes how, based on this new definition, a maximum surface H-bond density of around 200 K at ice surface was found, as the maximum results from two competing effects. Lastly, the book discusses the absorption of water molecules at the water–TiO2 interface. Providing insights into the combination of molecular dynamics simulation and experimental sum frequency generation spectroscopy, it is a valuable resource for researchers in the field.
Download or read book Studies of Water and Solvents at Liquid solid Interfaces by Sum Frequency Generation Vibrational Spectroscopy written by Zheng Yang and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Comparisons of The Structure of Water at Neat Oil Water and Air Water Interfaces as Determined by Vibrational Sum Frequency Generation written by and published by . This book was released on 1997 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have employed vibrational sum frequency generation (VSFG) to investigate the structure of water at neat oil/water and air/water interfaces through the OH stretching modes of the interfacial water molecules. We find that at the oil/water interface the prevailing structure of the water molecules is a tetrahedral arrangement much like the structure of ice while at the air/water interface we observe an equal distribution between an ice-like and a less ordered water like arrangement. The relationship between the structure of the interfacial water molecules and the properties of the other fluid (air or oil) is discussed in terms of hydrogen bonding at the interface. We also compare our results to previous VSFG studies at similar interfaces and find a difference in the spectra obtained from the oil/water interface.
Download or read book A Theoretical Description of the Vibrational Sum Frequency Generation Spectroscopy of Interfaces written by Angela S. Perry and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: Our work investigates theoretical approximations to the interface specific sum frequency generation (SFG) spectra at aqueous interfaces constructed using time correlation function (TCF) and instantaneous normal mode (INM) methods. Both approaches lead to signals in excellent agreement with experimental measurements. This work demonstrates how TCF and INM methods can be used in a complementary fashion to describe interfacial vibrational spectroscopy. Our approach is to compare TCF spectra with experiment to establish that our molecular dynamics (MD) methods can reliably describe the system of interest. We then employ INM methods to analyze the molecular and dynamical basis for the observed spectroscopy. We have been able to elucidate, on a molecularly detailed basis, a number of interfacial line shapes, most notably the origin of the complex O-H stretching SFG signal, and the identity of several intermolecular modes in the SFG spectra for the water/vapor interface.
