Time-resolved response of fluorescent alkali ion indicators and detection of short-lived intermediates upon binding to molecular cavities

Stopped-flow kinetic studies have been performed to determine the kinetic parameters of K⁺ binding to the fluorescent cryptand F222 and of Na⁺binding to F221 at pH 8.O. The results clearly indicate that a comparatively stable intermediate is formed before the rate-limiting binding step occurs with a rate constant around 30 s^–1 under the chosen experimental conditions. The conversion of the intermediate to the final cation complex is assigned to the final penetration of the already bound, but still partially solvated cation into the ligand's cavity. The main fluorescence intensity change found upon cation binding is attributed to the second reaction step, and not to the fast, initial binding reaction. The comparatively slow overall binding reaction is interpreted on the bases of a special solvate substitution mechanism which, in principle, can also account for the 1500 times slower binding of Ca 2⁺ to F221. With regard to time-resolved analytical Na⁺ and K⁺ determinations, the response times under the chosen conditions are around 20 ms. Differentiation between Na⁺ and Ca²⁺, for example, is possible with F221 on the basis of completely different response times.     

Comparisons between adsorption and diffusion of alkali,alkaline earth metal atoms on silicene and those on silicane:Insight from first-principles calculations

The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory.Silicane is staler against the metal adatoms than silicene.Hydrogenation makes the adsorption energies of various metal atoms considered in our calculations on silicane significantly lower than those on silicene.Similar diffusion energy barriers of alkali metal atoms on silicane and silicene could be observed.However,the diffusion energy barriers of alkali-earth metal atoms on silicane are essentially lower than those on silicene due to the small structural distortion and weak interaction between metal atoms and silicane substrate.Combining the adsorption energy with the diffusion energy barriers,it is found that the clustering would occur when depositing metal atoms on perfect hydrogenated silicene with relative high coverage.In order to avoid forming a metal cluster,we need to remove the hydrogen atoms from the silicane substrate to achieve the defective silicane.Our results are helpful for understanding the interaction between metal atoms and silicene-based two-dimensional materials.     

双氟取代苯和联苯类液晶化合物的量子化学研究

运用AM1和PM3两种SCF-MO方法,通过能量梯度全优化计算,给出了对一系列环上双氟取代苯、联苯液晶化合物的稳定几何构型、电子结构和分子基本性质(生成热、偶极矩、前沿分子轨道能级等)。联系有机结构理论进行了分析和讨论。初步阐明了其分子结构与介电各向异性之间的关系,为设计和开发新型液晶分子研究提供了有较大价值的线索。     

Internal charge distribution of iodine adatoms on silicon and silicon oxide investigated with alkali ion scattering

Time-of-flight spectra were collected for low energy ⁷Li⁺ and ²³Na⁺ ions backscattered from Si(1 1 1) surfaces covered with sub-monolayers of iodine. Li ions singly scattered from the iodine adatoms have consistently larger neutralization probabilities than those scattered from the silicon substrate, and the neutralization decreases with off-normal emission. This indicates that the internal charge distribution of the iodine adatoms is not uniform, presumably due to attraction of electron density to the positively charged bonding Si atom. Photoelectron spectroscopy shows that iodine adsorbed on pre-oxidized Si bonds through the oxygen atom, forming hypoiodite (-OI) moieties. The neutralization of ²³Na⁺ backscattered from such iodine adatoms is independent of the emission angle, indicating that there is less charge rearrangement than for iodine bonded directly to Si.     

离子注入和固相外延制备Si1-x-yGexCy半导体薄膜

用等离子体增强化学气相淀积(PECVD)生长了200nm的SiGe薄膜,然后将C离子注入SiGe层,经两步热退火处理制备了Si1-x-yGexCy三元合金半导体薄膜.应用卢瑟福背散射(RBS),傅里叶变换红外光谱(FTIR)和高分辨率x射线衍射(HRXRD)研究了薄膜的结构和外延特性.发现C原子基本处于替代位置,C原子的掺入缓解了SiGe层的压应变 关键词： Si1-x-yGexCy薄膜 离子注入 固相外延     

Experimental and theoretical studies on corals. I. Toward understanding the origin of color in precious red corals from Raman and IR spectroscopies and DFT calculations

An attempt to explain the origin of the vivid red color in precious pink and red corals was undertaken. Raman and IR spectroscopies were applied to characterize white, pink and red corals. The position of the Raman signal near 1500 cm⁻¹ of some corals and pearls was associated by several authors with the presence of the mixture of all‐trans‐polyenic pigments, containing 6–16 conjugated CC bonds or β‐carotenoids. This hypothesis was examined theoretically by performing extensive B3LYP‐DFT calculations of vibrational spectra of the model polyenic compounds. The B3LYP/6‐311++G** predicted positions of the dominating Raman mode depend on the number of CC units (Cn parameter) and can be accurately predicted for larger systems from a simple nonlinear fit. The DFT‐predicted Raman activities of these modes are extremely sensitive to Cn, and sharply increase with the number of double bonds. This implies a presence of only—two to three polyenes differing slightly in the number of CC units as the source of color in pink and red corals. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrochemical, theoretical and XPS studies of 2-mercapto-1-methylimidazole adsorption on carbon steel in 1 M HClO4

The inhibition of the corrosion of carbon steel in 1 M HClO₄ by 2-mercapto-1-methylimidazole (MMI) has been investigated in relation to the concentration of the inhibitor as well as the temperature using weight loss and electrochemical measurements. The effect of the temperature on the corrosion behaviour with addition of different concentrations of MMI was studied in the temperature range 30-60 °C. Polarization curves reveal that MMI is a mixed type inhibitor. The inhibition efficiency of MMI is temperature independent but increases with the inhibitor concentration. Changes in impedance parameters (charge transfer resistance, R_t, and double-layer capacitance, C_dl) were indicative of adsorption of MMI on the metal surface, leading to the formation of a protective film. Adsorption of MMI on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution and adsorption processes were also determined. The X-ray photoelectron spectroscopy (XPS) of the carbon steel indicated that MMI is chemically adsorbed on the steel surface. Moreover, the electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels and molecular orbital densities were calculated.     

Secondary ion mass spectrometry and X-ray photoelectron spectroscopy studies on TiO2 and nitrogen doped TiO2 thin films

Anatase phase TiO₂ and nitrogen (N) doped TiO₂ thin films were synthesized by an ultrasonic spray pyrolysis technique on c-Si (100) substrates in the temperature range 300-550 °C. The former used a precursor solution of titanium oxy acetylacetonate in methanol whereas the later used a titanium oxy acetylacetonate hexamine mixture in methanol. Homogeneity across the film’s thickness and the nature of the film-substrate interface were studied by dynamic depth profiling acquired using secondary ion mass spectrometry SIMS. The stoichiometry and bonding state of various species present in the films were studied using X-ray photoelectron spectroscopy (XPS). N-doping was confirmed by both SIMS and XPS. XPS studies revealed that the nitrogen content of the films synthesized at 300 °C (3.2%) is high compared to that of films made at 350 °C (1.3%).     

XRD studies,vibrational spectra,and molecular structure of 1H‐imidazo [4,5‐b]pyridine based on DFT quantum chemical calculations

The molecular structures and vibrational properties of 1H‐imidazo[4,5‐b]pyridine in its monomeric and dimeric forms are analyzed and compared to the experimental results derived from the X‐ray diffraction (XRD), infrared (IR), and Raman studies. The theoretical data are discussed on the basis of density functional theory (DFT) quantum chemical calculations using Lee–Yang–Parr correlation functional (B3LYP) and 6‐31G(d,p) basis. This compound crystallizes in orthorhombic structure, space group Pna2₁(C_2v⁹) and Z = 4. The planar conformation of the skeleton and presence of the N H···N hydrogen bond was found to be characteristic for the studied system. The temperature dependence of IR and Raman modes was studied in the range 4–294 K and 8–295 K, respectively. The normal modes, which are unique for the imidazopyridine derivatives are identified. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparative studies on reaction of bis(p‐nitrophenyl) phosphate and α‐nucleophiles in cationic micellar media

We studied the cleave of bis(p‐nitrophenyl) phosphate (BNPP) over a pH range of 7.0–12.0 in the presence of cationic micelles of cetyldiethylethanolammonium bromide, cetyldimethylethanolammonium bromide, cetylpyridinium bromide, cetyltrimethylammonium bromide, and cetylpyridinium chloride by using different α‐nucleophiles, viz acetohydroxamate, benzohydroxamate, salicylhydroxamate, butane‐2,3‐dione monooximate, and α‐benzoin oximate ions. With the use of α‐nucleophiles in cationic micellar media, the hydrolytic cleavage of BNPP was found to be approximately 10⁵‐fold faster than its spontaneous hydrolysis. All reactions followed pseudo‐first‐order kinetics. The effect of various concentrations of cationic micelles for the reaction of BNPP and α‐nucleophiles has been studied. The variation of k_obs values of the reactions depends on the micellar structure, that is, head groups, hydrophobic tail length, and counter ion. Copyright © 2012 John Wiley & Sons, Ltd.