One More for Light-triggered Conformational Changes in Cryptochromes: CryP from Phaeodactylum tricornutum.

Cryptochromes are a ubiquitously occurring class of photoreceptors. Together with photolyases, they form the Photolyase Cryptochrome Superfamily (PCSf) by sharing a common protein architecture and binding mode of the FAD chromophore. Despite these similarities, PCSf members exert different functions. Photolyases repair UV-induced DNA damage by photocatalytically driven electron transfer between FADH¯ and the DNA lesion, whereas cryptochromes are light-dependent signaling molecules and trigger various biological processes by photoconversion of their FAD redox and charge states. Given that most cryptochromes possess a C-terminal extension (CTE) of varying length, the functions of their CTE have not yet been fully elucidated and are hence highly debated. In this study, the role of the CTE was investigated for a novel subclass of the PCSf, the CryP-like cryptochromes, by hydrogen/deuterium exchange and mass-spectrometric analysis. Striking differences in the relative deuterium uptake were observed in different redox states of CryP from the diatom Phaeodactylum tricornutum. Based on these measurements we propose a model for light-triggered conformational changes in CryP-like cryptochromes that differs from other known cryptochrome families like the insect or plant cryptochromes.

Coexistence of Two Electronic Nano-Phases on a CH3NH3PbI3-xClx Surface Observed in STM Measurements.

Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3NH3PbI3-xClx perovskite in cross-sectional geometry. Two electronic phases, 10-20 nm in size, with different electronic properties inside the CH3NH3PbI3-xClx perovskite layer are observed by the dI/dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. By comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at -2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).

Kinetically Enhanced Approach for Rapid and Tunable Self-Assembly of Rod-Coil Block Copolymers.

A facile approach is reported to process rod-coil block copolymers (BCPs) into highly ordered nanostructures in a rapid, low-energy process. By introducing a selective plasticizer into the rod-coil BCPs during annealing, both the annealing temperature and time to achieve thermodynamic equilibrium and highly ordered structures can be decreased. This process improvement is attributed to enhanced chain mobility, reduced rod-rod interaction, and decreased rod-coil interaction from the additive. The novel method is based on kinetically facilitating thermodynamic equilibrium. The process requires no modification of polymer structure, indicating that a wide variety of desired polymer functionalities can be designed into BCPs for specific applications.

Molecular structure effect of pyridine-based surface ligand on the performance of P3HT:TiO2 hybrid solar cell.

Colloid TiO(2) nanorods are used for solution-processable poly(3-hexyl thiophene): TiO(2) hybrid solar cell. The nanorods were covered by insulating ligand of oleic acid (OA) after sol-gel synthesis. Three more conducting pyridine type ligands: pyridine, 2,6-lutidine (Lut) and 4-tert-butylpyridine (tBP) were investigated respectively to replace OA. The power conversion efficiency (PCE) of the solar cell was increased because the electronic mobility of pyridine-type ligand-modified TiO(2) is higher than that of TiO(2)-OA. The enhancement of PCE is in the descending order of Lut > pyridine > tBP because of the effective replacement of OA by Lut. The PCE of solar cell can be further enhanced by ligand exchange of pyridine type ligand with conjugating molecule of 2-cyano-3-(5-(7-(thiophen-2-yl)-benzothiadiazol-4-yl) thiophen-2-yl) acrylic acid (W4) on TiO(2) nanorods because W4 has aligned bandgap with P3HT and TiO(2) to facilitate charge separation and transport. The electronic mobility of two-stage ligand exchanged TiO(2) is improved furthermore except Lut, because it adheres well and difficult to be replaced by W4. The amount of W4 on TiO(2)-tBP is 3 times more than that of TiO(2)-Lut (0.20 mol % vs. 0.06 mol %). Thus, the increased extent of PCE of solar cell is in the decreasing order of tBP > pyridine > Lut. The TiO(2)-tBP-W4 device has the best performance with 1.4 and 2.6 times more than TiO(2)-pyridine-W4 and TiO(2)-Lut-W4 devices, respectively. The pKa of the pyridine derivatives plays the major role to determine the ease of ligand exchange on TiO(2) which is the key factor mandating the PCE of P3HT:TiO(2) hybrid solar cell. The results of this study provide new insights of the significance of acid-base reaction on the TiO(2) surface for TiO(2)-based solar cells. The obtained knowledge can be extended to other hybrid solar cell systems.

Correlating interface heterostructure, charge recombination, and device efficiency of poly(3-hexyl thiophene)/TiO2 nanorod solar cell.

The charge recombination rate in poly(3-hexyl thiophene)/TiO(2) nanorod solar cells is demonstrated to correlate to the morphology of the bulk heterojunction (BHJ) and the interfacial properties between poly(3-hexyl thiophene) (P3HT) and TiO(2). The recombination resistance is obtained in P3HT/TiO(2) nanorod devices by impedance spectroscopy. Surface morphology and phase separation of the bulk heterojunction are characterized by atomic force microscopy (AFM). The surface charge of bulk heterojunction is investigated by Kelvin probe force microscopy (KPFM). Lower charge recombination rate and lifetime have been observed for the charge carriers in appropriate heterostructures of hybrid P3HT/TiO(2) nanorod processed via high boiling point solvent and made of high molecular weight P3HT. Additionally, through surface modification on TiO(2) nan,orod, decreased recombination rate and longer charge carrier lifetime are obtained owing to creation of a barrier between the donor phases (P3HT) and the acceptor phases (TiO(2)). The effect of the film morphology of hybrid and interfacial properties on charge carrier recombination finally leads to different outcome of photovoltaic I-V characteristics. The BHJ fabricated from dye-modified TiO(2) blended with P3HT exhibits 2.6 times increase in power conversion efficiency due to the decrease of recombination rate by almost 2 orders of magnitude as compared with the BHJ made with unmodified TiO(2). In addition, the interface heterostructure, charge lifetime, and device efficiency of P3HT/TiO(2) nanorod solar cells are correlated.

Effect of solvent quality on the conformations of a model comb polymer.

The effect of solvent quality on the equilibrium structure of a densely branched comb polymer is investigated based on the structure factor analyses by off-lattice Monte Carlo simulations. First, theta temperature (theta(infinity)) must be determined to identify the solvent condition. We locate the characteristic temperature theta(A)(N) at which the second virial coefficient vanishes and the transition temperature theta(R)(N) at which radius of gyration R(g) of the chain varies most rapidly with temperature, i.e., d(2)R(g)/dT(2)|(theta(R)) = 0. N represents the total number of monomers of a comb. As N --> infinity, theta(A) and theta(R) coincide to a point that is identified as the true theta temperature (theta(infinity)). The structure factors of the main chain, the side chain, and the whole polymer are calculated, respectively. It is found that at T = theta(infinity), the structural factors S(qR(g)) for the overall comb polymers match quite well with those of their Gaussian counterparts. When T< theta(infinity), the overall comb polymer assumes collapsed conformations, similar to a homogeneous sphere. However, the structure factor of the side chain indicates that it always remains in an expanded state regardless of the solvent condition. It is attributed to the strong interactions between side chains. The same effect leads to enhanced rigidity of the main chain in comparison to the linear chain, as clearly observed from the rescaled Kratky plot.