acase@tulane.edu / Deep-cavity cavitands are a class of molecules that can be used for multiple applications, including: regioselective reactions, catalysis, separations & selectivity, and kinetic protection. They have also proven useful as models for studying the Hofmeister and hydrophobic effects, in context. Herein, the synthesis of these molecules will be outlined, highlighting novel approaches for molecular diversity with the synthesis of inherently positively charged hosts, protic hosts, neutral and negatively charged hosts. The effect of structure modification to the rim of the hosts will be discussed with a supramolecular ion-responsive dimer-to-tetramer system. This system also demonstrates cation selectivity and the importance of discussing ion-ion and ion-hydrophobic interactions in context. Finally, two systems with octa-cationic hosts will be presented. The change of charge on the host has dramatic consequences to their assembly properties, with salting-in salts stabilizing them. / 1 / Matthew B Hillyer

Trimethylamine-N-oxide (TMAO) and guanidinium chloride (GdmCl) are both highly studied molecules in the field of protein folding/unfolding. Thermodynamic studies have shown that TMAO, an organic osmolyte, is a strong stabilizer of the protein folded state, while GdmCl is known to be one of the most effective protein denaturants. Although TMAO and GdmCl are well studied the mechanism by which they stabilize and denature proteins, respectively, is not well understood. In fact there are few studies looking at their effects on hydrophobic interactions. In this work we determine the effect of TMAO and GdmCl on hydrophobic interactions, by looking at the model system of phenyl and alkyl hydrophobic contact pairs. Contact pair formation is monitored through the use of fluorescence spectroscopy, i.e., measuring the intrinsic phenol fluorescence being quenched by carboxylate ions. Hydrophobic interactions are isolated from other interactions through a developed methodology. The results show that TMAO addition to the aqueous solvent destabilizes hydrophobic contact-pairs formed between phenol and carboxylate ions. The TMAO acts as a “denaturant” for hydrophobic interactions. For GdmCl the data shows that for small alkyl groups, acetate and propionate, hydrophobic contact-pairs are slightly stabilized or are not affected, respectively. For the larger alkyl groups GdmCl disrupts contact pair formation and destabilizes them. GdmCl’s effect on hydrophobic interactions shows a size dependence on carboxylate ion size, i.e., as carboxylate ion tail length increases the contact pair formed with phenol is destabilized to a greater degree.

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No description available.

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acase@tulane.edu / Self-assembly driven by the hydrophobic effect is the fascinating phenomenon by which non-polar moieties in aqueous solution form unique structures. Perhaps the best known of these assembly processes is the creation of a micelle in water, where hydrophobic tail groups are forced inward while hydrophilic head groups are attracted to aqueous solvent. Beyond micellization, the hydrophobic effect has a strong effect on supramolecular assemblies where guest and host are driven together through the hydrophobic effect. One such supramolecular host is the deep cavity cavitand Octa-Acid (OA), which can encapsulate a hydrophobic guest. This encapsulation has potential applications in drug delivery, chemical catalysis and smart material polymer hydrogel synthesis. Molecular Dynamics simulations (MD) of this system have also been shown to demonstrate the curious phenomenon of cononsolvency, where addition of organic co- solvent causes non-monotonic changes in thermodynamic trends. Cononsolvency has been studied most notably in the literature through examining poly(n- isopropylacrylamide) (PNIPAM), which features a coil-globule-coil transition as methanol is added to aqueous solution. While current research into cononsolvency centers on structural characteristics of the solute, this research focuses on cononsolvency driving effects of the solvent itself by focusing on attributes such as the speed of sound in mixed solutions, the partial molar volume of a co-solvent and the excess chemical potential of argon in solvent mixtures. A solvent-based approach to understanding cononsolvency can reveal trends applicable to all systems, not simply characteristics of one system at a time. Through this research, we uncover structural signatures correlating with cononsolvency. These new insights not only give a more thorough understanding of hydrophobic guest-host assembly, but into the hydrophobic effect and the nature of solvation. / 1 / Alexander Saltzman

The studies presented here use the B- to Z-DNA transition and Z-DNA crystallization as model systems to determine the contribution of solvent interactions to macromolecular structures. The substituent groups of naturally occurring and modified nucleotide bases affect the hydration and thus the stability of right-handed B-DNA and left-handed Z-DNA. The free energy for alternating pyrimidine-purine sequences in the B- and Z-conformations are quantitated as solvent free energies (SFE) from their solvent-accessible surfaces. The effect of methylation of the C5 carbon of pyrimidine bases on the stability of Z-DNA was analyzed in comparisons of d(TA) versus d(UA) dinucleotides. In the minor groove, the N2 amino group of purine bases was examined by comparing the stability of d(CG) versus d(CI), and d(TA) versus d(TA') dinucleotides as Z-DNA. These comparisons correctly accounted for the observed effects of the major and minor groove substituent groups on the relative stability of Z-DNA. These predictions were confirmed by comparing the amount of salt required to crystallize various hexanucleotides as Z-DNA. The relative contribution of solvent and steric interactions in DNA assembly were studied crystallographically using an asymmetric hexanucleotide which assumes two discrete and discernible orientations in the crystal lattice. How this sequence orients in the lattice is a direct measure of the DNA-DNA interactions at the surface of the crystal. These interaction free energies were directly correlated with differences in solvation for 5 sequences where there was effectively no differences in steric interactions for the two orientations. In the singular case where a large steric clash was expected, the orientation was in fact determined by this interaction. The comparisons indicate that both solvent and van der Waals interactions are significant in DNA assembly with van der Waa ls interactions dominating in situations with large steric interactions. The analyses of the B- to Z-DNA transition and Z-DNA crystallization based on SFEs support the significance of solvent interactions in determining the structure and assembly of macromolecules. / Graduation date: 1995

The adsorption equilibrium and kinetic behavior exhibited by β-lactoglobulin at silanized silicon surfaces of varying hydrophobicity were examined using ellipsometry. Adsorption equilibrium results were used to construct adsorption isotherms; the adsorbed mass of β-lactoglobulin was observed to increase with increasing surface hydrophobicity, within a defined range of hydrophobicity. Adsorption kinetics recorded for β-lactoglobulin on each surface were compared to the kinetic behavior predicted by a simple model for protein adsorption. The model described the data well in all cases, enabling interpretation of the kinetic behavior in terms of contact surface hydrophobicity influences on rate constants affecting protein attachment and unfolding at the interface. In particular, both experimental and simulation results seem to be in support of a hypothesis that rate constants defining protein arrival and conversion to an irreversibly adsorbed state increase with increasing surface hydrophobicity, while the rate constant defining desorption of protein from a reversibly adsorbed state decreases with increasing surface hydrophobicity. Contact surface hydrophobicity was quantified using contact angle analysis to determine the polar component of the work required to remove water from unit area of surface. Quantitative consideration of possible mass transfer influences on the observed adsorption rates supports the notion that the experiments were not conducted in a transport-limited regime; i.e., true kinetics were measured. / Graduation date: 1992

No description available.

Commercial food proteins were used in order to study the relationship between hydrophobicity and two functional properties: emulsification and foaming. Hydrophobicity determined by sodium dodecyl sulfate (SDS) binding method and the cis-parinaric acid (CPA) fluorescence probe method gave poor statistical correlation with foaming and emulsification. The SDS binding method gave higher hydrophobicity and higher correlation values with foaming and emulsifying, than the fluorescence probe CPA method. / Fourier Transform Infrared (FTIR) spectroscopy was used to study the secondary structures, of the commercial food proteins. Infrared spectra of the protein samples with or without denaturing agents (SDS, urea, and guanidine) in the region of the amide I and II bands were determined in deuterium oxide (D$ sb{2}$O) buffer. Fourier self-deconvolution was used to study infrared band positions. BSA was an $ alpha$-helix protein, and in the presence of SDS, due to protein unfolding, exhibited a random coil structure. By correlating their infrared spectra to predetermined peak positions in the protein samples, it was shown that the legume proteins contained $ beta$-structure, and as SDS was added, exhibited non-ordered structures. The spectra of gluten samples were obtained only in the presence of SDS, showing either random coil, or non-ordered structures.