Site-specific nucleation and growth kinetics in hierarchical nanosyntheses of branched ZnO crystallites

Here we report a site-specific sequential nucleation and growth route to the systematic building of hierarchical, complex, and oriented ZnO micro/nanostructures in solution nanosynthesis. Structures and morphologies of the products were confirmed by results from X-ray diffraction and scanning electron microscopy studies. The organic structure-directing agents (SDAs), diaminopropane and citrate, are found to play different roles in controlling the evolution of these new morphologies. Through the selective adsorptions of SDAs on different crystal facets of the primary ZnO rods, we have alternated the hierarchical growth of secondary and tertiary new complex nanostructures. Roles of the SDA concentration, nucleation time, and growth kinetics in the solution hierarchical ZnO nanosyntheses have all been systematically investigated.     

A self-consistent density-functional approach to the structure of electric double layer: charge-asymmetric electrolytes

A self-consistent density-functional approach has been employed to study the structure of an electric double layer formed from a charge-asymmetric (2:l) electrolyte within the restricted primitive model which corresponds to charged hard sphere ions and a continuum solvent. The particle correlation due to hard-core exclusions is evaluated by making use of the universality of the density functionals and the correlation function of the uniform hard sphere fluid obtained through the integral equation theory with an accurate closure relation whereas mean spherical approximation is employed for the electrical contribution. Numerical results on the diffuse layer potential drop, ionic density profile, and the mean electrostatic potential near the electrode surface at several surface charge densities are found to be in quantitative agreement with the available simulation data.     

STRUCTURE AND STABILITY OF γ-CRYSTALLINS-IV. AGGREGATION AND STRUCTURAL DESTABILIZATION IN PHOTOSENSITIZED REACTIONS

Abstract— Unlike α- and β-, γ-crystallins become turbid upon irradiation with 300 nm or white light in the presence of photosensitizers, e.g., methylene blue (MB) or riboflavin (RF). These proteins, however, do not aggregate in the presence of guanidine hydrochloride. Turbidity formation is concentration-dependent. Except in RF-sensitized reactions, the onset and rate of turbidity formation are faster in γ-IV than in the other two crystallins. Labeling the thiol groups of the protein with iodoacetamide does not change the turbidity rate in case of irradiation with 300 nm light, but it does change it in case of RF- or MB-sensitized reaction. The order of rate constants of the decrease in tryptophan emission under aerobic conditions upon 300 nm irradiation and MB- and RF-sensitized reactions is γ-IV > γ-III > γ-II. The rate constants in the absence of air and in the presence of D₂O upon MB- and RF-sensitized reactions also indicate that the role of singlet oxygen is significant in the former reaction. We suggest that the photoinduced structural changes occur in two steps. In the first, photooxidation of tryptophan as well as cysteine residues (including the buried cysteines) occurs, leading to small conformational changes of the protein. Conformational changes of the protein, as evident from the near-UV CD and fluorescence lifetime measurements, subsequently result in aggregation of the protein. As suggested by X-ray analysis, the perturbation of the cys 78 and 32 by the active species of oxygen appears to be responsible for the destabilization of the protein structure, resulting in rapid aggregation of these crystallins.     

Zinc ionomer based on sulfonated maleated styrene-ethylene/butylene-styrene block copolymer

A new ionomer, containing both carboxylated and sufonated groups, was obtained by sulfonating a maleated styrene-ethylene/butylene-styrene (m-SEBS) block copolymer, followed by its neutralization with zinc acetate. Dielectric thermal analyses show that the incorporation of ionic groups in m-SEBS is responsible for the occurrence of the high temperature ionic relaxation in addition to the relaxations of the base polymer. Formation of the ionomer causes a significant improvement in stress-strain properties compared to the corresponding base polymer.     

Unraveling the Efficiency of Thioxanthone Based Triplet Sensitizers: A Detailed Theoretical Study

Photochemical activation by triplet photosensitizers is highly expedient for a green focus society. In this work, we have theoretically probed excited state characteristics of thioxanthone and its derivatives for their triplet harvesting efficiency using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Absorption and triplet energies corroborate well with the available experimental data. Our results predict that both the S₁ and T₁ states are π-π^* in nature, which renders a high oscillator strength for S₀ to S₁ transition. Major triplet exciton conversion occurs through intersystem crossing (ISC) channel between the S₁ (¹π-π^*) and high energy ³n- π^* state. Apart from that, there is both radiative and non-radiative channel from S₁ to S₀, which competes with the ISC channel and reduces the triplet harvesting efficiency. For thioxanthones with −OMe (Me=Methyl) or −F substitution at 2 or 2’ positions, the ISC channel is not energetically feasible, causing sluggish intersystem crossing quantum yield (Φ_ISC). For unsubstituted thioxanthone and for isopropyl substitution at 2’ position, the S₁-T₁ gap is slightly positive ( ), rendering a lower triplet harvesting efficiency. For systems with −OMe or −F substitution at 3 or 3’ position of thioxanthone, because of buried π state and high energy π^* state, the S₁-³nπ^* gap becomes negative. This leads to a high Φ_ISC (>0.9), which is key to being an effective photocatalyst.