Ion association in calcium phosphate solutions at 37°C

Ion association in the system Ca(OH)₂–H₃PO₄–KCl–H₂O at 37°C has been studied potentiometrically over a range of pH from 3 to 9. The experimental conditions were optimized for the accurate determination of the association constants for the formation of the ion pairs CaH₂PO ₄ ⁺ , CaHPO₄ and CaPO ₄ ^– which were found to be 27.9±0.1, 591±2, and (1.35±0.02)×10⁶ L-mol^–1, respectively.     

Water in melts: Raman spectral investigation of the molten Ca(NO3)2·4H2O−KNO3 system

The Raman spectra of molten mixtures of Ca(NO₃)₂\4H₂O–KNO₃ have been examined, covering the concentration range of 0–70 mole% KNO₃. The frequencies in the spectra of the mixtures have been found to change slightly with concentration. Striking variations in the band shapes have been observed in the regions corresponding to the O–H stretching mode (2850–3850 cm^–1) and the v₄-NO ₃ ^– mode (700–750 cm^–). The results are discussed in terms of perturbed quasi-lattice structure for the melt, in which there could be a displacement of water molecules in the first coordination sphere around Ca²⁺ by the NO ₃ ^– ion.     

5-Hydroxytryptamino-induced calcium sparks in cultured rat stomach fundus smooth muscle cells

With the imaging fluorescence probe of Ca2+ (fluo-3) and a laser scanning confocal micro-scope, the spontaneous localized calcium release event was first discovered in resting rat cardiac myocytes by Cheng[1] in 1993. A mathematical simulation is developed with computer in order to reveal the effect, which is immediately suggested that these events are likely to reflect the local-ized release of Ca2+ from a small cluster of ryanodine-sensitive Ca2+ release channels in sar-coplasmic reticulum …     

Lipophilicity in PK design: methyl, ethyl, futile

Lipophilicity, often expressed as distribution coefficients (log D) in octanol/water, is an important physicochemical parameter influencing processes such as oral absorption, brain uptake and various pharmacokinetic (PK) properties. Increasing log D values increases oral absorption, plasma protein binding and volume of distribution. However, more lipophilic compounds also become more vulnerable to P450 metabolism, leading to higher clearance. Molecular size and hydrogen bonding capacity are two other properties often considered as important for membrane permeation and pharmacokinetics. Interrelationships among these physicochemical properties are discussed. Increasing size (molecular weight) often gives higher potency, but inevitably also leads to either higher lipophilicity, and hence poorer dissolution/solubility, or to more hydrogen bonding capacity, which limits oral absorption. Differences in optimal properties between gastrointestinal absorption and uptake into the brain are addressed. Special attention is given to the desired lipophilicity of CNS drugs. In examples using -blockers, Ca channel antagonists and peptidic renin inhibitors we will demonstrate how potency and pharmacokinetic properties need to be balanced.     

不同结构的磷酸盐对凝胶体系中草酸钙晶体物相和相组成的影响

泌尿系结石的形成是一种病理性生物矿化过程，不同地区的结石发病率在3％～15％之间。且50％(美国)至80％(中国)的人会复发。结石中约70％以上为草酸钙(CaC2O4)结石。CaC2O4结石的形成与其热力学(过饱和度)和动力学(成核、生长和聚集)因素有关。由于结石患者尿液和正常人尿液中     

尖吻蝮蛇毒抗凝血因子(ACF)含量和钙离子含量的定量测定及钙离子结合位点的初步研究

由紫外光谱法测定蛋白质浓度,用ICP测定Ca含量,从而确定一个ACF分子中含一个钙离子.ACF中分子中除一个高亲和性钙结合位点外,至少还有一个低亲和性钙结合位点,只有当过量钙离子存在时,才可能在低亲和性钙结合位点上进一步结合钙离子.Tb~(3+)具有比Ca~(2+)离子更强的键合ACF能力,能定量结合在ACF中的两个位点上,且能全部取代ACF中Ca~(2+).文中提及的金属离子对ACF的抗凝血活性没有显著的影响.     

游离氧化钙,氧化镁连续测定的电导法研究

研究了乙二醇对氧化钙，氧化镁的提取条件，利用乙二醇提取氧化钙后在催化剂存在下继续提取氧化镁，建立了电导法连续测定ＣａＯ，ＭｇＯ分析方法，可用于水泥熟料中游离氧化钙，氧化镁的测定。     

Encapsulation of Mithramycin in Liposomes in Response to a Transmembrane Gradient of Calcium Ions

The recent discovery that mithramycin(MTR) in aqueous solution forms a high affinity[Ca(MTR)4]2- complex led us to the idea thatCa2+-loaded liposomes might be able to accumulateMTR in their aqueous internal compartment. Wetherefore investigated the uptake of MTR into largeunilamellar vesicles (LUV) containing NaCl orCaCl2. Our data show that MTR was efficientlyaccumulated within LUV made fromdipalmitoylphosphatidylcholine and cholesterol, onlywhen the liposomes contained Ca2+ and wereresuspended in a Ca2+-free medium. A drugencapsulation efficiency as high as 60% was achieved,at a drug to lipid molar ratio of 1/18. The circulardichroism and fluorescence excitation spectra ofliposome-encapsulated MTR (LMTR) displayed strongsimilarities with those of the [Ca(MTR)4]2-complex. LMTR was found to be stable, when submittedto conditions that destabilized the[Ca(MTR)4]2- complex. Upon dilution andincubation for 24 h at 37 °C, MTR-containingliposomes did not release a significant amount of MTR.These properties were attributed to the formation ofa high affinity complex between MTR and Ca2+inthe aqueous compartment of liposomes.     

Sorption equilibrium of methanol on new composite sorbents “CaCl<Subscript>2</Subscript>/silica gel”

This paper presents experimental data on methanol sorption on new composite sorbents which consist of mesoporous silica gels and calcium chloride confined to their pores. Sorption isobars and XRD analysis showed the formation of a solid crystalline solvate CaCl₂⋅2MeOH at low methanol uptake, while at higher uptake the formation of the CaCl₂–methanol solution occurred. The solution confined to the silica pores showed the sorption properties similar to those of the CaCl₂–methanol bulk solution. Calorimetric and isosteric analyses showed that the heat of methanol sorption depends on the methanol uptake, ranging from 38±2 kJ/mol for the solution to 81±4 kJ/mol for the solid crystalline phase CaCl₂⋅2MeOH. The above mentioned characterizations allowed the evaluation of the methanol sorption and the energy storage capacities, clearly showing that the optimal applications of these new composite sorbents are the methanol removal from gaseous mixtures, heat storage and sorption cooling driven by low temperature heat.     

Influence of CaCO<Subscript>3</Subscript> nanoparticles shape on thermal and crystallization behavior of isotactic polypropylene based nanocomposites

Summary The influence of calcium carbonate nanoparticles with different shapes (spherical and elongated) on the thermal properties and crystallization behavior of isotactic polypropylene was investigated. CaCO₃ nanoparticles were covered by an appropriate coating agent to improve the interfacial adhesion between the filler and the polyolefin matrix. The nanocomposites were prepared by melt mixing and subsequent compression molding. A remarkable effect of CaCO₃ on the thermal properties of iPP was observed. Moreover, the analysis of crystallization kinetics showed that CaCO₃ nanopowder coated with PP-MA are efficient nucleating agents for iPP, and the overall crystallization rate results higher than plain iPP.