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Using a surface forces apparatus(SFA), we studied the forces associatedwith the reorientation of molecules of a common nematic thermotropicliquid crystal, 4′-n-pentyl-4-cyanobiphenyl(5CB), confined between two conducting (silver) surfaces and its opticalbehavior under the influence of electric fields with varying magnitudesand field directions. A transient attractive force was observed dueto partial reorientations of the liquid crystal molecules and theflow of free ions, in addition to a stronger constant capacitanceattraction between the silver surfaces. At the same time, the opticalproperties of the liquid crystals were observed perpendicular to thesilver surfaces. Observations of shifts and fluctuations of the extraordinarywave of the (multiple beam) interference fringes measure the refractiveindex of the director component parallel to the surface, which issensitive to tilt motion (or reorientation) of the liquid crystalmolecules that provided details of the anisotropic orientations ofthe molecules and domains. Any lateral differential refractive indexchange is easily observed by optical microscopy. The optical microscopeimaging showed that the changes in the optical properties are dueto convective flow at domain boundaries of the liquid crystal molecules(and possible free ions) between the two charged surfaces. At lowelectric fields, propagation of domain boundaries was observed, whileat higher electric fields, hexagonal patterns of flowing moleculeswere observed. The interplay of the force measurements and opticalobservations reveal a complex dynamic behavior of liquid crystalssubjected to varying electric fields in confined spaces. [ABSTRACT FROM AUTHOR]

The energetics of amyloid fibrillaraggregation of β-lactoglobulin(βLG) following incubation at high temperature and acid pH wasstudied by differential scanning calorimetry in the presence of Cu2+or Fe3+cations, and without any metal. Cu2+and metal-free protein solutions showed a distinct exothermicresponse that disappeared almost completely when the Fe3+molar concentration was ten times greater than the βLG concentration.Thioflavin T fluorescence studies in solution and atomic force microscopyanalysis of the deposit left on flat mica substrates by heat-incubatedβLG solutions correlated the absence of exothermic responseof Fe3+-βLG solutions with a lack of fibril production.In contrast, abundant fibril deposits were observed for Cu2+-βLG solutions, with a rich polymorphism of multistrand fibrillarstructures. Electron paramagnetic resonance revealed that Fe3+permanently binds to βLG in the aggregate state whereas Cu2+plays a catalytic role without binding to the protein. Wepropose that Fe3+inhibits fibril production after bindingto a key region of the protein sequence, possibly interfering withthe nucleation step of the fibrillation process and opening a nonfibrillaraggregation pathway. These findings suggest that transition metalions can be utilized to effectively modulate protein self-assemblyinto a variety of structures with distinct morphologies at the nanoscalelevel. [ABSTRACT FROM AUTHOR]