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The prion protein (PrPC) is a glycoprotein that in mammals, differently from avians, can lead to prion diseases, by misfolding into a -sheet-rich pathogenic isoform (PrPSc). Mammal and avian proteins show different N-terminal tandem repeats:  PHGGGWGQ and PHNPGY, both containing histidine, whereas tyrosine is included only in the primary sequence of the avian protein. Here, by means of potentiometric, circular dichroism (CD), and molecular dynamics (MD) studies at different pH values, we have investigated the conformation of the avian tetrahexarepeat (PHNPGY)4(TetraHexaPY) with both N- and C-termini blocked by acetylation and amidation, respectively. We have found, also with the help of a recently proposed protein chirality indicator (Pietropaolo, A.; Muccioli, L.; Berardi, R.; Zannoni, C. Proteins2008, 70, 667−677), a conformational dependence on the protonation states of histidine and tyrosine residues:  the turn formation is pH driven, and at physiological pH a pivotal role is played by the tyrosine OH groups which give rise to a very compact bent structure of backbone upon forming a hydrogen-bond network. [ABSTRACT FROM AUTHOR]

The origin of the alignment with respect to the director observed for solutes in a nematic host remains unclear, and various mechanisms ranging from steric repulsions to dispersive or electrostatic interactions have been invoked. Here we present atomistic molecular dynamics (MD) computer simulations of rigid solutes of small dimensions dissolved in a nematic liquid crystal solvent, 4-n-pentyl-4′cyanobiphenyl (5CB), that aim to quantitatively predict the orientational order. We have validated the results comparing the dipolar couplings obtained by atomistic simulation with their experimental NMR counterparts. To help assess the separate effect of the various types of anisotropic interactions on the orientational order of solutes, we have modeled solute molecules with their partial atomic charges present or absent (switching them to zero), finding that, at least for the cases studied, the alignment mechanism is largely dominated by steric and van der Waals dispersive forces rather than Coulomb ones. We have compared the anisotropic aligning potential with the predictions of the Maier–Saupe and surface tensor models and discussed their performance. [ABSTRACT FROM AUTHOR]

We present a joint molecular dynamics (MD)/kinetic Monte Carlo (KMC) study aimed at the atomistic description of charge transport in stacks of liquid-crystalline tetraalkoxy-substituted, metal-free phthalocyanines. The molecular dynamics simulations reproduce the major structural features of the mesophases, in particular, a phase transition around 340 K between the rectangular and hexagonal phases. Charge transport simulations based on a Monte Carlo algorithm show an increase by 2 orders of magnitude in the hole mobility when accounting for the rotational and translational dynamics. The results point to the formation of dynamical structural defects along the columns. [ABSTRACT FROM AUTHOR]

We have performed a detailed study of the order and dynamics of the commercially available BL038 liquid crystal (LC) inside nanosized (50−300 nm) droplets of a reflection-mode holographic-polymer dispersed liquid crystal (H-PDLC) device where LC nanodroplet layers and polymer layers are alternately arranged, forming a diffraction grating. We have determined the configuration of the LC local director and derived a model of the nanodroplet organization inside the layers. To achieve this, we have taken advantage of the high sensitivity of the ESR spin probe technique to study a series of temperatures ranging from the nematic to the isotropic phase of the LC. Using also additional information on the nanodroplet size and shape distribution provided by SEM images of the H-PDLC cross section, the observed director configuration has been modeled as a bidimensional distribution of elongated nanodroplets whose long axis is, on the average, parallel to the layers and whose internal director configuration is a uniaxial quasi-monodomain aligned along the nanodroplet long axis. Interestingly, at room temperature the molecules tend to keep their average orientation even when the layers are perpendicular to the magnetic field, suggesting that the molecular organization is dictated mainly by the confinement. This result might explain, at least in part, (i) the need for switching voltages significantly higher and (ii) the observed faster turn-off times in H-PDLCs compared to standard PDLC devices. [ABSTRACT FROM AUTHOR]