Enantiomeric interactions between liquid crystals and organized monolayers of tyrosine-containing dipeptides

We have examined the orientational ordering of nematic liquid crystals (LCs) supported on organized monolayers of dipeptides with the goal of understanding how peptide-based interfaces encode intermolecular interactions that are amplified into supramolecular ordering. By characterizing the orientations of nematic LCs (4-cyano-4'-pentylbiphenyl and TL205 (a mixture of mesogens containing cyclohexane-fluorinated biphenyls and fluorinated terphenyls)) on monolayers of l-cysteine-l-tyrosine, l-cysteine-l-phenylalanine, or l-cysteine-l-phosphotyrosine formed on crystallographically textured films of gold, we conclude that patterns of hydrogen bonds generated by the organized monolayers of dipeptides are transduced via macroscopic orientational ordering of the LCs. This conclusion is supported by the observation that the ordering exhibited by the achiral LCs is specific to the enantiomers used to form the dipeptide-based monolayers. The dominant role of the -OH group of tyrosine in dictating the patterns of hydrogen bonds that orient the LCs was also evidenced by the effects of phosphorylation of the tyrosine on the ordering of the LCs. Overall, these results reveal that crystallographic texturing of gold films can direct the formation of monolayers of dipeptides with long-range order, thus unmasking the influence of hydrogen bonding, chirality, and phosphorylation on the macroscopic orientational ordering of LCs supported on these surfaces. These results suggest new approaches based on supramolecular assembly for reporting the chemical functionality and stereochemistry of synthetic and biological peptide-based molecules displayed at surfaces.     

The Raman spectra of the KOH-doped ice polymorphs: V and VI

The effect on the Raman spectra of the proton ordering induced by KOH in the high pressure phases of ice, ice V and VI has been studied. Our previous Raman studies of ice V and ice VI (ref.1) showed spectroscopic evidence of partial proton ordering at low temperatures (below about 130 K) in ice V and a possible phase change in ice VI. These conclusions were made on the measurements of the lattice vibration region. The present results, based on the observation of the bands due to the uncoupled O-D stretching vibrations of KOH-doped ice V and, in particular, ice VI, show that some kind of proton ordering or partial proton ordering may be induced by the presence of KOH dopant in these two ices.A Lorentzian curve fit has been used to separate the main band from the side bands in the relatively complex structured band due to the uncoupled O-D stretching vibration in ice V and ice VI.     

Orientationally ordered layers of saturated hydrocarbons and their derivatives on quartz surfaces

The structure of the adjacent-to-wall layers of aliphatic hydrocarbons on quartz surface was investigated. Measurements of dichroism of the dyestuff molecules, or “guest” in the matrix of the basic substance, allowed establishing the presence of the orientational ordering in liquid layers at distances up to 200 nm. Additional measurements of the optical anisotropy (birefringence) in such layers have substantiated the existence of that ordering and its type. The structural characteristics of the adjacent-to-wall layers, such as thickness, type, and degree of the orientational ordering of molecules depend on the specific hydrocarbon used and the preparation (modification) of the surface of the solid substrate.     

Charge, orbital, and magnetic ordering in YBaFe2O5 from first-principles calculations

First principles calculations using the augmented plane wave plus local orbitals method, as implemented in the WIEN2k code, have been used to investigate the electronic and magnetic properties of YBaFe2O5, especially as regards the charge-orbital ordering. Although the total 3d charge disproportion is rather small, an orbital order parameter defined as the difference between t2g orbital occupations of Fe2+ and Fe3+ cations is large (0.73) and gives unambiguous evidence for charge and orbital ordering. Strong hybridization between O2p and Fe e g states results in the nearly complete loss of the separation between the total charges at the Fe2+ and Fe3+ atoms. Furthermore, the relationship between the orbital ordering and charge ordering is also discussed. The dxz orbital ordering is responsible for the stability of the G-type antiferromagnetic spin ordering and the charge ordering pattern.     

The location and ordering of fluoride ions in pure silica zeolites with framework types IFR and STF; implications for the mechanism of zeolite synthesis in fluoride media

Single-crystal X-ray diffraction studies carried out at a synchrotron radiation source have allowed the structure solution and location of fluoride ions inside as-made pure silica zeolites with the IFR and STF framework structures. The local environment of the fluoride has been identified, and unusual ordering of the fluoride ions has been discovered in both cases. The details of the crystal structures are used to suggest structural features that are important in determining the ordering of fluoride ions in zeolites. A mechanism for how the fluoride ordering occurs is suggested for IFR and STF based on the local structure of small cages that make up these zeolites, and the implications for the mechanism of crystal growth are discussed.     

Dynamic ordering transitions of liquid crystals driven by interfacial complexes formed between polyanions and amphiphilic polyamines

We report the design of an amphiphilic polyamine (polymer 1) based on poly(2-alkenyl azlactone) that strongly couples the formation of polyelectrolyte complexes at aqueous/liquid crystal (LC) interfaces to ordering transitions in the LC. We demonstrate that the addition of a strong anionic polyelectrolyte to aqueous solutions in contact with polymer 1-laden LC interfaces (prepared by Langmuir-Schaefer transfer of monolayers of polymer 1 onto micrometer-thick films of nematic LC) triggers ordering transitions in the LCs. We further demonstrate that changes in the ordering of the LCs (i) are driven by electrostatic interactions between the polyelectrolytes, (ii) involve multivalent interactions between the polyelectrolytes, and (iii) are triggered by reorganization of the hydrophobic side chains of amphiphilic polymer 1 upon formation of the interfacial complexes. The results presented in this paper lead us to conclude that ordering transitions in LCs can be used to provide insights into the structure and dynamics of interfacial complexes formed between polyelectrolytes.     

Nanoparticle assemblies as probes for self-assembled monolayer characterization: correlation between surface functionalization and agglomeration behavior

The ordering of dodecyl chains has been investigated in mixed monolayers of phosphonic acid capping agents on the surface of hydrothermally prepared zirconia nanocrystals. Methyl-, phenyl-, pyryl-, and tert-butylphosphonic acids have been used to investigate series with different mixing ratios with dodecylphosphonic acid as the cocapping agent for the mixed monolayer formation. Fourier transform infrared (FTIR) studies revealed that an increasing amount (different for each type) of coadsorbed capping agent reduces the ordering of the dodecyl chains significantly. Small-angle X-ray scattering (SAXS) verified that with increasing amount of cocapping agent the agglomeration of the particles decreases. The strong correlation of the agglomeration behavior with the ordering of the surface-bound alkyl chains leads to the conclusion that interparticle bilayers, formed via long alkyl chain packing, are responsible and can be controlled on a molecular level by coadsorbing various molecules. On the basis of this correlation, nanoparticles can be used as probes for self-assembled monolayer investigation by an indirect structural method (SAXS) and correlated with the routine spectroscopical method for the chemical analysis of surface groups (FTIR).     

Backbone and side-chain ordering in a small protein

We investigate the relation between backbone and side-chain ordering in a small protein. For this purpose, we have performed multicanonical simulations of the villin headpiece subdomain HP-36, an often used toy model in protein studies. Concepts of circular statistics are introduced to analyze side-chain fluctuations. In contrast to earlier studies on homopolypeptides [Wei et al., J. Phys. Chem. B 111, 4244 (2007)], we do not find collective effects leading to a separate transition. Rather, side-chain ordering is spread over a wide temperature range. Our results indicate a thermal hierarchy of ordering events, with side-chain ordering appearing at temperatures below the helix-coil transition but above the folding transition. We conjecture that this thermal hierarchy reflects an underlying temporal order, and that side-chain ordering facilitates the search for the correct backbone topology.     

Metal Ion Complexation: A Route to 2 D Templates?

The two-dimensional ordering of a number of 2,2'-bipyridine derivatives at the liquid/solid interface has been investigated by scanning tunneling microscopy. By appropriate functionalization of the bipyridine units, their intermolecular distance can be tuned, which has proved to be crucial for complexation with metal ions. The in situ addition of metal salts (Pd(2+), Cu(2+)), leading to the formation of metal-bipyridine complexes, has a dramatic influence on the two-dimensional ordering of the molecules and suggests that these complexes could be used as templates.     

Reversible photoinduced change in molecular ordering of diarylethene derivatives at a solution-HOPG interface

A diarylethene-pyrene diad and a diarylethene-pyrene-diarylethene triad were synthesized to investigate the photoinduced two-dimensional ordering change at a solution-HOPG interface. The molecular arrangements were detected by STM. The different photochromic isomers showed different orderings reflecting the differences in their molecular structures. For the diarylethene-pyrene-diarylethene triad, a new ordering appeared upon irradiation with UV light and returned to the original ordering upon subsequent irradiation with visible light. The new arrangement was assigned to the ordering of the closed-closed isomers based on the images of the isolated open- and closed-isomers. The relationship between the nature of the two-dimensional ordering and the molecular structure is discussed.     

Non-cylindrical symmetry of the ordering matrix of some spectroscopic probes in a lyotropic mesophase studied by 2H N.M.R. spectroscopy

Deuterium N.M.R. spectroscopy has been used to investigate the orientational ordering of perdeuteriated naphthalene and two perdeuteriated fluorescent probes (pyrene and perylene) dissolved in a discotic nematic micellar phase of potassium laurate/potassium chloride/decanol/water. The results show that the ordering tensors of these probes are not cylindrically symmetric.     

On the influence of data noise and uncertainty on ordering of objects,described by a multi‐indicator system. A set of pesticides as an exemplary case

A priori in partial ordering methodology the input data are understood as exact and true values, which is denoted as the “original data matrix”. As such even minor differences between values are regarded as real. However, in real life data are typically associated with a certain portion of noise or uncertainty. Hence, introducing noise may cause changes in the overall ordering of objects. The present paper deals with the effects of data noise or uncertainties on the partial ordering of a series of objects, a series of obsolete pesticides being used as an illustrative example. The approach is fuzzy like, and partially ordered sets are obtained as function of noise. A main focus of the work is to identify the range in terms of noise, where the original partial order is retained. We call this range the “stability range”. It is demonstrated that by increasing data noise the range where the “original partial order” is obtained decreases. The original partial order is based on the original data matrix. Further, it is found that significant changes in the partial ordering appear outside of this stability range. The possible relation between data noise and the stability range is discussed on an empirical basis. Copyright © 2015 John Wiley & Sons, Ltd.     

Chronological Change from Face‐On to Edge‐On Ordering of Zinc–Tetraphenylporphyrin at the Phenyloctane–Highly Oriented Pyrolytic Graphite Interface

The self‐assembled structure of alkoxy‐ and N‐alkylcarbamoyl‐substituted zinc–tetraphenylporphyrin at the liquid–highly oriented pyrolytic graphite (HOPG) interface was observed by using scanning tunneling microscopy. The alkoxy porphyrin showed a phase transition from face‐on to edge‐on ordering. The phase transition requires the close‐packed structure of alkoxy porphyrin. The chronological change of the ordering was traced to show the existence of several types of Ostwald ripening including two‐step phase transition from small edge‐on to face‐on and then further to edge‐on orderings. On the other hand, the N‐alkylcarbamoyl porphyrin showed persistent edge‐on ordering, and the ordering was analyzed by the Moiré pattern. Although the edge‐on ordering is observed only in the nonpolar solvent, the orderings have potential applications in the charge and energy transfer.     

Cluster chemistry in the solid state: Structured diffuse scattering,oxide/fluoride ordering and polar behaviour in transition metal oxyfluorides

Oxide/fluoride ordering in three families of ‘disordered’ transition metal oxyfluoride compounds is carefully investigated and used to obtain insight into why the constituent inherently acentric octahedral units do not usually order in a long range ordered polar sense. Observed highly structured diffuse intensity distributions are used in each case to analyze the local crystal chemistry and orientational ordering rules governing the way in which the dipole moments from the individual polar pseudo-octahedral units add together. The common local oxide/fluoride ordering rules, the consequences of these rules for polar behaviour on the local scale as well as the role of configurational entropy and energy minimization in suppressing long range polar order are highlighted.     

Diabatic ordering of vibrational normal modes in reaction valley studies

Diabatic ordering of the normal model of a reaction complex along the reaction path has several advantages with regard to adiabatic ordering. The method is based on rotations of the vibrational normal modes at one point, s, of the reaction path to maximize overlap with the vibrational modes at a neighboring point. Global rotations precede the rotations of degenerate modes so that changes in the direction of the reaction path and changes in the force constant matrix, which represent the two major effects for changes in mode ordering, can be separated. Overlap criteria identify resolved and unresolved avoided crossings of normal modes of the same symmetry. Diabatic mode ordering (DMO) can be used to resolve the latter by reducing the step size, thus guaranteeing correct ordering of normal modes in dependence of s. DMO is generally applicable to properties of the reaction complex that depend on s such as normal mode frequencies, orbital energies, the energy of excited states, etc. Additional applications are possible using a generalized reaction path vector, which may describe the change in atom masses, geometrical parameters, and/or the force constant matrix. In this way, the vibrational spectra of isotopomers can be investigated or the vibrational frequencies of different molecules correlated. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1282–1294, 1997     

Alignment of carbon nanotubes in nematic liquid crystals

The self-organizing properties of nematic liquid crystals can be used to align carbon nanotubes dispersed in them. Because the nanotubes are so much thinner than the elastic penetration length, the alignment is caused by the coupling of the unperturbed director field to the anisotropic interfacial tension of the nanotubes in the nematic host fluid. In order to relate the degree of alignment of the nanotubes to the properties of the nematic liquid crystal, we treat the two components on the same footing and combine Landau-de Gennes free energies for the thermotropic ordering of the liquid crystal and for the lyotropic nematic ordering of carbon nanotubes caused by their mutually excluded volumes. The phase ordering of the binary mixture is analyzed as a function of the volume fraction of the carbon nanotubes, the strength of the coupling and the temperature. We find that the degree of ordering of the nanorods is enslaved by the properties of the host liquid and that it can be tuned by raising or lowering the temperature or by increasing or decreasing their concentration. By comparing the theory to recent experiments, we find the anchoring energy of multiwalled carbon nanotubes to be in the range from 10(-10) to 10(-7) N m(-1).     

An X-ray diffraction study of aqueous solutions of lutetium trichloride

The X-ray diffraction analysis is used to study aqueous solutions of lutetium chloride in a wide concentration range under standard conditions. Small angle peaks on the functions of the X-ray scattering intensity and the maxima of radial distribution functions of the atomic-electron density are interpreted. It is found that highly concentrated solutions are characterized by a unique quasi-crystalline structure distinguished by short- and long-range ordering. Dilution of solutions results in that the own structure of the solvent starts to play the major role in the structure of the systems. It is established for the first time that small angle peaks on the scattering intensity functions are also manifested for diluted solutions, which indicates that long-range ordering is preserved in them.     

Ordering transitions triggered by specific binding of vesicles to protein-decorated interfaces of thermotropic liquid crystals

We report that specific binding of ligand-functionalized (biotinylated) phospholipid vesicles (diameter = 120 ± 19 nm) to a monolayer of proteins (streptavidin or anti-biotin antibody) adsorbed at an interface between an aqueous phase and an immiscible film of a thermotropic liquid crystal (LC) [nematic 4'-pentyl-4-cyanobiphenyl (5CB)] triggers a continuous orientational ordering transition (continuous change in the tilt) in the LC. Results presented in this paper indicate that, following the capture of the vesicles at the LC interface via the specific binding interaction, phospholipids are transferred from the vesicles onto the LC interface to form a monolayer, reorganizing and partially displacing proteins from the LC interface. The dynamics of this process are accelerated substantially by the specific binding event relative to a protein-decorated interface of a LC that does not bind the ligands presented by the vesicles. The observation of the continuous change in the ordering of the LC, when combined with other results presented in this paper, is significant, as it is consistent with the presence of suboptical domains of proteins and phospholipids on the LC interface. An additional significant hypothesis that emerges from the work reported in this paper is that the ordering transition of the LC is strongly influenced by the bound state of the protein adsorbed on the LC interface, as evidenced by the influence on the LC of (i) "crowding" of the protein within a monolayer formed at the LC interface and (ii) aging of the proteins on the LC interface. Overall, these results demonstrate that ordering transitions in LCs can be used to provide fundamental insights into the competitive adsorption of proteins and lipids at oil-water interfaces and that LC ordering transitions have the potential to be useful for reporting specific binding events involving vesicles and proteins.