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Phase behavior and microstructure of perfluoropolyether surfactants. NMR, SAXS, and Optical Microscopy Studies
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Three Component Ionic Microemulsions
No full textNecessary design features of microemulsions formed from cationic surfactant without any requirement for cosurfactant are illustrated by a study of microemulsions formed from didodecyldimethylammonium bromide in various oils. Ease of purification, preparation and manipulation give this and related systems a considerable advantage over conventional systems in enhancing our understanding of microemulsions and emulsion behavior.Angel, L.R.; Evans, D.F.; Ninham, B.. (1983). Three Component Ionic Microemulsions. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/1764
Hofmeister Effects in Enzymatic Activity, Colloid Stability and pH Measurements: Ion-Dependent Specificity of Intermolecular Forces
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Reply to "Comments on 'Hofmeister Series: Hydrolytic Activity of Aspergillus niger Lipase Depends on Specific Anion Effects
No full textThe impact of ionic solvation energy and water structure on forces
No full textThe structure of water in an interfacial region differs from bulk due to
surface-induced water ordering. The difference is seen both in the local
water density and in the water polarisability, particularly orientational
polarisability as water dipoles are oriented towards the interface. The
impact of this phenomenon in continuum models is to replace the
dielectric constant of the medium with a position-dependent spatial
dielectric function. The relationship that this kind of dielectric function
bears with the electrostatic potential is known in the Poisson equation.
But an additional effect of the spatially dependent dielectric function
on ionic solvation energies (including a change in the Born energy of
the ion) has not been widely recognised. The dielectric constant in an
interfacial region has been reported to fall to values around 5, far from
the bulk value of 78. The corresponding spatially-dependent ionic
solvation energy therefore introduces a strongly repulsive ion-surface
interaction which must be included as an additional “nonelectrostatic
potential” in the Boltzmann factor, determining ion concentrations
in a Poisson-Boltzmann model. Consequently a strongly repulsive
surface force—a primary hydration force—is obtained with a range
corresponding to the range of the surface-induced water ordering,
usually the thickness of several water layers
Hofmeister Effects in Enzymatic Activity: Weak and Strong Electrolyte Influences on the Activity of Candida rugosa Lipase
No full textThe effects of weak and strong electrolytes on the enzymatic activity of Candida rugosa lipase are explored. Weak electrolytes, used as buffers, set the pH, while strong electrolytes regulate the ionic strength. The interplay
between pH and ionic strength has been assumed to be the determinant of enzymatic activity. In experiments that probe activities by varying these parameters, there has been little attention focused on the role of specific
electrolyte effects. Here we show that both buffers and the choice of background electrolyte ion strongly affect the enzymatic activity of Candida rugosa lipase. The effects here shown are dramatic at high salt concentration; indeed, a 2 M concentration of NaSCN is able to fully inactivate the lipase. By contrast, Na2SO4 acts generally as an activator, whereas NaCl shows a quasi-neutral behavior. Such specific ion effects are well-known and are classified among the “Hofmeister effects”. However, there has been little awareness of them, or of their potential for optimization of activities in the enzyme community. Rather than the effects per se, the focus here is on their origin. New insights into mechanism are proposed
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