Protein and solvent dynamics as studied by QENS and dielectric spectroscopy

We have investigated the dynamics of a protein (hemoglobin) in three different solvents by broadband dielectric spectroscopy and quasi-elastic neutron scattering (QENS). The solvents used were water, glycerol and methanol. From the dielectric measurements we were able to extract four relaxation processes, where the fastest process is due to solvent dynamics, and the three slower processes arise from protein motions of a different nature, and hence, visible on different time and temperature scales. The results from the mean square displacement (MSD) obtained by quasi-elastic neutron scattering indicate that the fast and local protein motions are strongly related (slaved) by the fastest and most local solvent motions in the case of water and glycerol. In contrast, for methanol we found the low temperature dynamics are dominated by the CH₃ group rotation, which does not promote any protein dynamics.     

The Electroluminescence Spectra of Light-Emitting Devices Based on Zinc Complexes of Amino-Substituted Ligands

Exciplex bands in the electroluminescence (EL) spectra of electroluminescent devices based on the new zinc complexes of amino-substituted benzothiazoles and in the photoluminescence (PL) spectra of the blends of a zinc complex and the triphenylamine derivative are studied. For the EL spectra, it is found that the relation between the exciplex bands and the intrinsic bands of the zinc complex emission depends on the thickness of layers in the EL devices and on the applied voltage. For the PL spectra of blends, this relation strongly depends on the concentration of components.     

The crystallization of lysozyme and thaumatin with ionic liquid

Three different ionic liquids (ILs) were used for the crystallization of lysozyme and thaumatin. It would be a promising solvent for applications in protein chemistry, due to its unusual features such as excellent solubility of inorganic and organic materials, enhancement of protein activity and stability, etc. Here, [BMIm][BF₄] was used as precipitants or union-precipitants in the experiments of thaumatin and lysozyme, respectively. And the experimental results indicated that the probability of single crystals appearance was significantly increased with the addition of [BMIm][BF₄].     

Neutron scattering perspectives for protein dynamics

After a double decade of intensive neutron scattering studies of the biological physics of protein dynamics on a few well-characterised model systems, the time has come to extend the method to address the vast biological diversity of proteins and their dynamics-function relationships. The time-scale and length-scale dependent mean square displacement and effective force constant, measured by neutron elastic intensity temperature scans, are proposed as relevant experimental parameters, and examples are given of their correlation with biological function. The parameters are directly calculable from molecular dynamics simulations, and their proposed deposit in an accessible data bank will greatly strengthen the links between experimental and theoretical approaches to protein dynamics.     

Is the rigid-body assumption reasonable?: Insights into the effects of dynamics on the electrostatic analysis of barnase-barstar

Electrostatically-driven association of proteins is important to many biological functions, and understanding which amino acid residues contribute to these interactions is crucial to protein design. Theoretical calculations that are used to elucidate the role of electrostatics in association are typically based on a single experimentally determined protein structure, while an underlying rigid-body assumption is adopted. The goal of this study was to investigate the role of conformational fluctuations on electrostatic interaction energies, as applied to the electrostatic analysis of barnase-barstar. For our calculations, we apply theoretical alanine-scan mutagenesis to introduce charge perturbations by replacing every ionizable residue with alanine, one at a time. Electrostatic clustering and free energy calculations based on the Poisson-Boltzmann method are used to evaluate the effects of each perturbation. Molecular dynamics simulations are performed for the barnase-barstar parent complex and seven experimental alanine mutations from the literature, in order to introduce relaxation before and after mutation. We discuss the effects of dynamics, in the form of pre- and post-mutation relaxation, on electrostatic clustering and free energies of association in light of experimental data. We also examine the utility of nine electrostatic similarity methods for clustering of barnase alanine-scan mutants. Our calculations suggest that the rigid-body assumption is reasonable for electrostatic calculations of barnase-barstar.     

Supersaturation patterns in counter-diffusion crystallisation methods followed by Mach–Zehnder interferometry

We present experimental observation of the spatio-temporal pattern of supersaturation in counter-diffusion methods. These complex patterns were recorded by dynamical interferometric analysis using a Mach–Zehnder configuration. Tetragonal hen egg white lysozyme crystals were grown inside APCF (advanced protein crystallisation facility) reactors. Salt and protein diffusion profiles were obtained independently by performing duplicated experiments with and without protein in the protein chamber; salt gradients were observed directly while protein concentration profiles are computed from the differences in refractive index between the two experiments. As expected from computer simulations, the time evolution of supersaturation shows a maximum about 45 h after activation (although this value can change as a function of the starting conditions and the geometry of the reactor). Nucleation takes place before this maximum supersaturation is reached. This explains the trend of the growth rate versus time curves for experiments performed within APCF reactors (both on ground and in space) and in capillaries by the gel acupuncture technique. By using very low concentration agarose gel in the protein chamber, sedimentation and buoyancy effects are eliminated so that the effects of gravity on fluid dynamics and hence on the spatio-temporal evolution of supersaturation can be assessed. These results confirm experimentally the predicted behaviour of counter-diffusion systems and support their use in growing large high-quality protein single crystals.     

Dynamic properties of solvent confined in silica gels studied by broadband dielectric spectroscopy

We report the results of a broadband (10⁻²–10⁷ Hz) dielectric spectroscopy study on a solvent system (glycerol–water solution) confined in a porous silica matrix. The dielectric relaxation of the system is studied as a function of both temperature (120–280 K) and solvent composition (0–36 glycerol molar percentage), at constant matrix composition. Our data show that glycerol–water systems confined inside silica gel are characterized by a very complex dynamics quite different from that observed in solution, thus indicating that confinement may deeply modify solvent dynamics. Indeed in addition to the relaxation processes similar to those occurring in bulk samples, new dielectric relaxations are detected: two non-collective relaxations, attributed to water molecules strongly interacting with pore surfaces and to the glycerol trapped within the matrix structure, respectively; a relaxation in the glycerol free sample (and in samples at very low glycerol content) almost coincident with that observed in other different confinement conditions and governed by geometrical confinement per se. Moreover, at high glycerol content we observe two non-Arrhenius processes at least 4 order of magnitude slower than solution-like main relaxation; at low glycerol content the two above relaxations merge and show a fragile to strong transition at about 200 K.     

Slowing down of water dynamics in disaccharide aqueous solutions

The dynamics of water in aqueous solutions of three homologous disaccharides, namely trehalose, maltose and sucrose, has been analyzed by means of molecular dynamics simulations in the 0-66 wt.% concentration range. The low-frequency vibrational densities of states (VDOS) of water were compared with the susceptibilities χ″ of 0-40 wt.% solutions of trehalose in D₂O obtained from complementary Raman scattering experiments. Both reveal that sugars significantly stiffen the local environments experienced by water. Accordingly, its translational diffusion coefficient decreases when the sugar concentration increases, as a result of an increase of water-water hydrogen bond lifetimes and of the corresponding activation energies. This induced slowing down of water dynamics, ascribed to the numerous hydrogen bonds that sugars form with water, is strongly amplified at concentrations above 40 wt.% by the percolation of the hydrogen bond network of sugars, and may partially explain their well-known stabilizing effect on proteins in aqueous solutions.     

Estimated effects of silicone glue on protein crystal growth

Silicone glue (modified silicone polymer) is widely used for both experiments involving inorganic crystal growth and those involving organic materials like proteins. This material is very useful for building a hand-made experiment setup or for fixing protein crystals to specific locations. Though silicone glue is regarded as harmful to proteins, no systematic verification was performed to investigate its impurity effects on protein crystal growth. We focused on and estimated the impurity effects of silicone glue on protein crystal growth.     

The role of primitive relaxation in the dynamics of aqueous mixtures, nano-confined water and hydrated proteins

The relaxation scenario in aqueous systems, such as mixtures of water with hydrophilic solutes, nano-confined water and hydrated biomolecules, has been shown to exhibit general features, in spite of the huge differences in structure, chemical composition and complexity. Dynamics, in all these systems, invariably shows at least two relaxations: (i) a slower process, related to cooperative and structural motions of water and solute molecules (in the case of mixtures) or related to interfacial processes in the case of confined water and (ii) a faster process, with non-cooperative character originating from water. The latter has properties including timescale and temperature dependence similar or related in all the aqueous systems. This water-specific relaxation can be identified as the primitive relaxation, or the Johari-Goldstein β-relaxation. The primitive process is the precursor of the many-body relaxation process which increases in length-scale with time until the terminal α-relaxation is reached.Using new experimental data (at atmospheric and high pressure) along with a revision of most of the recent literature on the dynamics of confined water and aqueous mixtures, we show that the two abovementioned relaxation processes are inter-related as evidenced by correlations in their properties. For instance, both relaxation time and dielectric strength of the water-specific relaxation exhibit a crossover from a stronger to a weaker dependence with decreasing T, at the temperature where the slow process attains a very long timescale (> 1 ks) and becomes structurally arrested, exactly analogous to that found for β-relaxation in van der Waals liquids. Moreover, the primitive relaxation of water is shown to play a pivotal role in determining the dynamics of hydrated biomolecules in general, including the “dynamic transition” observed by neutron scattering and Mössbauer spectroscopy. We show that the primitive relaxation of the solvent is responsible for the dynamic transition, even in the case that the solvent is not pure water or an aqueous mixture.     

The Nature of As-related Defects in Semi-Insulating GaAs Bulk Crystals

The behaviour of As-related defects in SI (semi-insulating) GaAs are studied from the viewpoint of the origination of As-related precipitates, generation and evolution of EL2 during postgrowth and the possible defect interactions involved EL2 variation under As overpressure annealing. The precipitates were identified as elemental As and As-rich GaAs polycrystalline grains and their features depend on the growth process. A defect interaction model has been proposed on the generation/annihilation of EL2 assigned as As_Ga V_As V_Ga complex respect to non-stoichiometry such as As_i V_Ga and V_As.     

A distribution kinetics model of self-assembly: Effects of coalescence and solvent evaporation

Self-assembly from a metastable state often occurs by nucleation accompanied by nanoparticle growth and eventually by Ostwald coarsening. By developing a population balance model for growth and coarsening, we here determine the dynamics of self-assembled cluster size distributions (CSDs) in two or three dimensions. The governing equations are solved numerically and the asymptotic coarsening stage reveals a power-law increase in average particle mass as the CSD evolves to a (minimum) polydispersity index of unity for both 2-D and 3-D phase transitions. By incorporating solvent evaporation to simulate drying-mediated self-assembly of nanoparticles, the model yields a temporal power law relationship with exponent 1/4 for the average 2-D domain radius, in agreement with experimentally observed behavior. The power law relationships can also be obtained by varying the coalescence rate and the power on mass in rate coefficient expressions.     

New Emitting Materials Based on HTL Moiety with High Hole Mobility for OLEDs

New green emitting compounds based on tris(N-methylindolo)benzene (NMT), anthracene and pyrene were synthesized. NMT-An and NMT-Py were used as an emitting layer in OLED device to examine emitting property. OLED device containing NMT-An emitting layer and conventional hole transporting layer (HTL) of NPB was found to exhibit better characteristics compared to NMT-Py. And that device showed maximum EL emission at 502 nm and 550 nm, CIE coordinates (0.38, 0.48), and a luminance efficiency of 2.06 cd/A. Also when NMT and NMT-An were used as a HTL instead of NPB, the device including NMT-An emitter showed 2.67 cd/A and 2.29 cd/A in luminance efficiency.     

A new approach to diffusion-like relaxation processes

We measured the time decay of the electric field in two dielectric non-crystalline solids and the data were analyzed in the framework of a new theoretical approach. It is observed that the application of this approach allows identifying different regimes in the relaxation process. At long times the dynamics end up by following a power law decay, which suggests the existence of a scale property in the interaction that defines the state of the materials and also the possibility of defining an invariant. We check the stability of this invariant under different time intervals, which means also a low dependence of it on noisy data.     

Secondary dielectric relaxation in decahydroisoquinoline–cyclohexane mixture

We report dielectric relaxation measurements of the mixture 25% w/w cyclohexane in decahydroisoquinoline. Cyclohexane is a non-polar liquid that acts as an external parameter influencing relaxation dynamics of pure decahydroisoquinoline. Two different secondary relaxation processes dominate the relaxation dynamics below the glass transition temperature, as previously observed in the pure decahydroisoquinoline. Based on the coupling model analysis we identified the fastest secondary process as the genuine secondary Johari Goldstein process, reflecting the motion of the whole molecule. On the other hand, the microscopic origin of the slowest secondary process still remains unknown.     

Comparison Study of Phenylquinoline-based Iridium(III) Complexes for Solution Processable Phosphorescent Organic Light-Emitting Diodes by PEDOT:PSS and Graphene Oxide as a Hole Transport Layer

Electroluminescent (EL) properties of Ir(III) complex, [(2,4-diphenylquinoli-ne)]₂Iridium picolinic acid N-oxide [(DPQ)₂Ir(pic-N-O)] were investigated using PEDOT:PSS and reduced graphene oxide (rGO) as a hole transport layer for solution processable phosphorescent organic light-emitting diodes (PhOLEDs). High performance solution-processable PhOLED with PEDOT:PSS and (DPQ)₂Ir(pic-N-O) (8 wt%) doped CBP:TPD:PBD (8:56:12) host emission layer were fabricated to give a high luminance efficiency (LE) of 26.9 cd/A, equivelent to an external quantum efficiency (EQE) of 14.2%. The corresponding PhOLED with rGO as a hole transport layer exhibited the maximum brightness and LE of 13540 cd/m² and 16.8 cd/A, respectively. The utilization of the solution processable rGO thin films as the hole transport layer offered the great potential to the fabrication of solution processable PhOLEDs.     

Electroluminescence in Amorphous Pyrazoline Films Under DC Fields

We have investigated the electroluminescence, EL, behavior in amorphous films of a pyrazoline derivative under dc fields. The current vs. voltage characteristics indicated a space charge limited current behavior with traps distributed exponentially within the forbidden energy gap. EL was detected in the current range of double carrier injection which ocurred after all traps in the sample were filled up. Spectral studies showed that the light emission zone was loalized around the cathode side of the pyrazoline film. The brightness, measured as a function of current, indicated the EL in the lower current density range to be dominated by delayed luminescence.     

Comparative crystal habit study of quartz and MPO4 isomorphous compounds (M = Al,Ga)

Comparative investigation of the crystal habit of -quartz and two quartz-like materials (AlPO₄ and GaPO₄) has been undertaken on the basis of the Bravais-Friedel-Donnay-Harker (BFDH) law and the Hartman-Perdock (PBCs) theory. Unlike to these predictions, very strong morphological differences are observed. The crystal habit changes can be expressed in terms of crystal structure distortions and extrinsic parameters such as: temperature, pressure, solvent and impurities of the crystal growth experiments. All these parameters are not independent from one another, so only a qualitative explanation can be given.     

Influence of homocysteine on the physical structure and molecular mobility of elastin network in cultured arteries

The thermal and dielectric properties of the elastin network were investigated in arteries cultured with physiological and pathological concentrations of homocysteine, an aminoacid responsible of histological impairments in human arteries. The glass transition of this amorphous protein was investigated by Differential Scanning Calorimetry (DSC). To explore the molecular dynamics of the elastin network in the nanometer range, we used Thermally Stimulated Currents (TSC), a dielectric technique running at low frequency and measuring the dipolar reorientations in proteins subjected to a static electrical field. Combining TSC and DSC experiments with determination of the activation parameters of relaxation times reveals the molecular mobility of the proteins. The major differences in the relaxation behavior of elastin between arteries cultured with physiological and pathological concentrations of homocysteine are discussed.