Acid dissolution of willemite (Zn,Mn)2 SiO4) and hemimorphite (Zn4Si2O7(OH)2 H2O)

The influence of temperature, pH, acid type, and surface area on the kinetics of the acid dissolution of natural and synthetic willemites and natural hemimorphites has been investigated. Specific rate constants, based upon areas determined by krypton adsorption measurements, were estimated from the experimental data obtained. For both willemite and hemimorphite, the rates of dissolution in different acids are shown to be related to the relative strengths of zinc-acid anion complexes. The reactivity of willemite toward acids increases with increasing replacement of zinc by manganese. Mixed chemical/diffusion control is responsible for the observed rates of willemite dissolution under the conditions studied (HNO₃, HCl, HClO₄, H₃PO₄, H₂SO₄, pH 0.31 to 3.00,T 21 to 94 °C). Estimates of the relative contributions of chemical and diffusional resistances to the overall rate have been made for the dissolution of manganese-free willemite in sulfuric acid solutions. The experimentally measured rates have been demonstrated to be in reasonable agreement with predicted overall dissolution rates. Proposals are made regarding the nature of the diffusion and chemical steps involved in the dissolution process. Hemimorphite was found to be considerably more reactive than willemite and its dissolution is primarily diffusion controlled under the conditions studied (T 20 to 76 °C, pH 2 to 3.5). Formerly a Postgraduate Research Student, Department of Metallurgy and Materials Science, Royal School of Mines, Imperial College, London     

(ZrO2)0.96(Y2O3)0.03(Al2O3)0.01陶瓷的制备及性能研究

采用化学共沉淀法制备（ZrO2）0.96（Y2O3）0.03（Al2O3）0.01的粉末, 在不同的升温速率、不同的烧结时间和不同的烧结温度等烧结工艺下制备出（ZrO2）0.96（Y2O3）0.03（Al2O3）0.01三相体系复合陶瓷. 经研究发现, 在升温速率和降温速率均为5 ℃·min^-1 的烧结制度下, 1550 ℃烧结时, 可以得到抗弯强度达998 MPa, 抗热震次数达33次, 相对密度达96%和电性能较好的烧结体.     

Mag-Fura-2 (Furaptra) exhibits both low (microM) and high (nM) affinity for Ca2+

Based on studies using high-affinity Ca2+ probes (dissociation constant (Kd) = 0.15-0.3 microM), steady-state [Ca2+]in is believed to be in the nanomolar range in most cells. However, probes with lower affinity indicate that [Ca2+]in may increase to micromolar levels during activation of specific cell functions, e.g., contraction. These conclusions rely on accurate knowledge of the Kd of the dyes for Ca2+. Mag-Fura-2 (also known as Furaptra) is a low-affinity Ca2+ indicator (Kd ca. 50 microM) which has been used for such studies. In the present work, Mag-Fura-2 is shown to respond to changes in cytosolic Ca2+ in the submicromolar range. In vitro, and in situ titration of Mag-Fura-2 in A7r5 cells, demonstrate that Mag-Fura-2 exhibits both high- and low-affinity for Ca2+. Moreover, pH affects both high and low affinity Ca2+ binding site. Since Mag-Fura-2 has been used to study Ca2+ within specific subcellular compartments, the present observations indicate that knowledge of factors such as ambient pH of these compartments is required to accurately interpret Ca2+ responses. Furthermore, the sensitivity of Mag-Fura-2 at submicromolar levels must be considered for accurate determination of Ca2+ in specific compartments believed to exhibit high micromolar levels of Ca2+.     

Synthesis and biological investigations of 2-(tetrahydropyran-2'-yl) and 2-(tetrahydrofuran-2'-yl)benzimidazoles

A set of benzimidazole derivatives bearing on position 2 a tetrahydropyranyl or tetrahydrofuranyl residue was prepared and tested for antitumoral, anti HIV-1 and other pharmacological activities. While the anti-HIV activity was completely lacking, moderate antitumoral activity was found in a few compounds; particularly the 5,6-dichloro-2-(tetrahydropyran-2-yl)-benzimidazole (8) was able to inhibit the growth of 19 cell lines of humane tumors at near micromolar concentration. On the other hand compounds 4, 6-8 and 10 exhibited significant tracheal relaxant activity in vitro at concentration 3-10 micrograms/ml, thus resulting superior to theophylline and comparable to amrinone.