Molecular beam resonant two-photon ionization study of caffeine and its hydrated clusters

We investigated electronically excited states of caffeine and its 1:1 complex with water by using resonant two-photon ionization (R2PI) and UV-UV hole-burning techniques. Strong vibronic coupling between a pair of close-lying pi-pi* and n-pi* transitions is proposed to be responsible for the broad spectral feature observed. By comparing the experimental results with those of theoretical calculations, both the O-bonded and N-bonded forms were suggested to be initially produced for the 1:1 complex. The electronic transitions of the O-bonded complex were blueshifted in the R2PI spectrum. For the N-bonded complex, the excited state undergoes an ultrafast decay process, followed by dissociation on a repulsive potential energy surface, which gives rise to a characteristically anomalous cluster distribution in nanosecond experiments.     

Anisotropic assembly of Ag nanoprisms

The Ag nanoprisms with controlled arrangements show distinct optical, crystallographic, and surface-enhanced Raman scattering properties depending on their orientation in the assemblies, demonstrating that the controlled assembly of anisotropic nanostructures can be utilized as a powerful tool for studying their physicochemical properties and for the creation of new classes of functional materials.     

Tuning Local Coordination Environments of Manganese Single-Atom Nanozymes with Multi-Enzyme Properties for Selective Colorimetric Biosensing

Single-atom nanozymes (SAzymes) are promising in next-generation nanozymes, nevertheless, how to rationally modulate the microenvironment of SAzymes with controllable multi-enzyme properties is still challenging. Herein, we systematically investigate the relationship between atomic configuration and multi-enzymatic performances. The constructed Mn_SA−N₃-coordinated SAzymes (Mn_SA−N₃−C) exhibits much more remarkable oxidase-, peroxidase-, and glutathione oxidase-like activities than that of Mn_SA−N₄−C. Based on experimental and theoretical results, these multi-enzyme-like behaviors are highly dependent on the coordination number of single atomic Mn sites by local charge polarization. As a consequence, a series of colorimetric biosensing platforms based on Mn_SA−N₃−C SAzymes is successfully built for specific recognition of biological molecules. These findings provide atomic-level insight into the microenvironment of nanozymes, promoting rational design of other demanding biocatalysts.     

Theoretical study of the substituent effects on the S-H bond dissociation energy and ionization energy of 3-pyridinethiol: Prediction of novel antioxidant

The S-H bond dissociation enthalpies [BDE(S-H)] of a set of 5-X- and 6-X-3-pyridinethiols (X = F, Cl, CH3, OCH3, NH2, N(CH3)2, CF3, CN, and NO2) have been computed using the density functional theory based (RO)B3LYP procedure with 6-311++G(2df,2p) basis set. The effects of substituents on the BDE(S-H), proton affinity of the pyridinethiol anion [PA(S-)] and ionization energy (IE) are analyzed and their correlations with Hammett's substituent constants are examined. Subsequently, a series of 6-substituted 3-pyridinethiols have been explored to find out their antioxidant potentials. Finally, a number of 3-pyridinethiol based compounds are theoretically proposed as novel antioxidants.     

A DFT study on the mechanism of hydrosilylation of unsaturated compounds with neutral hydrido(hydrosilylene)tungsten complex

Recently, Tobita et al. reported stoichiometric hydrosilylation reactions of acetone and acetonitrile with neutral hydrido(hydrosilylene)tungsten complexes Cp'(CO)2(H)W=Si(H)[C(SiMe(3))(3)] (Cp' = Cp*, C(5)Me(4)Et). The mechanisms of the hydrosilylation reactions of unsaturated compounds (ketone and nitrile) with the tungsten complexes have been investigated with the B(3)LYP density functional theory method. Four possible reaction mechanisms were studied. The results of the calculations indicate that the hydrosilylation of acetone proceeds via a metal hydride migration mechanism proposed by Tobita et al., while the hydrosilylation of nitrile occurs through a silyl migration mechanism, analogous to the modified Chalk-Harrod mechanism. The [2(sigma)+2(pi)] additions of various CX (CX = C=O or CN) multiple bonds with the Si-H bonds in the neutral complexes have very high barriers although similar additions were found feasible in other related cationic complexes. All the hydrosilylation reactions studied here give stable tungsten-silylene or tungsten-silyl products, which are not easily converted into the starting hydrido(hydrosilylene)tungsten complexes when reacting with a hydrosilane substrate molecule. Therefore, we predict that hydrosilylation of acetonitrile and acetone catalyzed by these tungsten complexes is difficult to achieve.     

Sulfur fixation on bagasse activated carbon by chemical treatment and its effect on acid dye adsorption

Heteroatoms are known to introduce specific surface functionalities that can enhance the adsorption properties of carbons. Sulfur fixation on bagasse-activated carbon was conducted by a low temperature chemical treatment with sulfuric acid followed by physical activation with CO₂ at 900?°C. The effect of sulfur fixation on the surface chemical properties of bagasse-activated carbons were investigated and on their subsequent acid dye removal (CIBA AB80) behavior. Surface chemical development were examined and followed using Fourier transform infrared spectroscopy (FTIR), heteroatom analysis and carbon surface acidity. Functional group stability with thermal treatment was also investigated. The textural properties of the activated carbons were characterized by nitrogen adsorption. Chemical pre-treatment and gasification was able to fix up to 0.2 wt% of sulfur on the activated carbon. Although the sulfur fixed by chemical treatment is low, this method introduced several advantages in comparison to fixation by thermal methods. The chemical method did not interfere with the textural development of the carbon, as found in thermal methods. In addition, the surface chemistry generated by these levels of sulfur groups was sufficient to increase the uptake of acid blue dyes by more than 700% based on adsorption capacities normalized by the surface area of the carbon.     

Prevention of UV radiation-induced premature skin aging in hairless mice by the novel compound Melanocin A

Repetitive exposure of the skin to UV radiation induces various harmful changes, such as thickening, wrinkle formation, inflammation and carcinogenesis. A variety of natural compounds and synthetic compounds have been studied to determine whether they can prevent UV-induced harmful effects. In this study, we investigated the effect of a novel compound, Melanocin A, which was isolated from Eupenicillium shearii F80695, on UV-induced premature skin aging. First, we studied the effect of Melanocin A on UV-induced matrix metalloproteinase (MMP)-9 expression in an immortalized human keratinocyte cell line, HaCaT, in vitro. Acute UV irradiation induced MMP-9 expression at both the mRNA and protein levels and Melanocin A suppressed this expression in a dose-dependent manner. We then investigated the effect of Melanocin A on UV-induced skin changes in hairless mice in vivo. Chronic exposure of hairless mouse dorsal skin to UV increased skin thickness and induced wrinkle formation and the gelatinase activities of MMP-2 and MMP-9. Moreover, Melanocin A significantly suppressed UV-induced morphologic skin changes and MMP-2 and MMP-9 expression. Taken together, these results show that Melanocin A can prevent the harmful effects of UV that lead to skin aging. Therefore, we suggest that Melanocin A should be viewed as a potential therapeutic agent for preventing and/or treating premature skin aging.     

Understanding the structural properties of a dendrimeric material directly from powder X-ray diffraction data

Complete structure determination of an early-generation dendrimeric material has been carried out directly from powder X-ray diffraction data, using the direct-space genetic algorithm technique for structure solution followed by Rietveld refinement. This work represents the first application of modern direct-space techniques for structure determination from powder X-ray diffraction data in the case of a dendrimeric material and paves the way for the future application of this approach to enable complete structure determination of other dendrimeric materials that cannot be prepared as single crystal samples suitable for single crystal X-ray diffraction studies.     

NMR and FT-IR Investigation of Spinel LiMn2O4 Cathode Prepared by the Tartaric Acid Gel Process

The structure of the lithium manganese tartrate precursor and the synthesis mechanism of LiMn₂O₄ were investigated by FT-IR, NMR, TG/DSC, and XRD in this study. The results of FT-IR and ⁷Li and ¹³C NMR measurements revealed that lithium ions bond with carboxylic acid ligands and the O–H stretching modes of tartaric acid. Manganese ion bonds only with carboxylic acid. Lithium and manganese ions were trapped homogeneously on an atomic scale throughout the precursor. Such a structure eliminates the need for long-range diffusion during the formation of lithium manganese oxides. Therefore, spinel LiMn₂O₄ was synthesized at temperatures as low as 300°C. In this work, the electrochemical properties of Li/Li_xMn₂O₄ were studied. It is clear that the discharge curves exhibit two pseudo plateaus as the LiMn₂O₄ is fired to higher temperatures. The discharge capacity of LiMn₂O₄ increases from 84 to 117 mAh/g as the calcination temperature increases from 300 to 500°C. The LiMn₂O₄ powders calcined at low temperatures with a high specific surface area and an average valence of manganese exhibit a better cycle life.     

Soluble and easily crystallized anthracene derivatives: precursors of solution-processable semiconducting molecules

New soluble anthracene derivatives containing thiophene and phenylenevinylene derivatives were synthesized via well-known synthetic routes. TIPS derivatives were added at the 9,10-positions of anthracene for the solubility and crystallinity. Both of the molecules were found to be promising for high charge mobility and stable organic semiconductors. The soluble anthracene core (TIPSAnt) is a potential precursor for the synthesis of novel semiconducting materials.