Enthalpie De Formation Et De Melange De Phosphoapatites Calco-Cadmiees Chlorees

Calcium–cadmium chlorapatites solid solutions with the general formula Ca_10–xCd_x(PO₄)₆Cl₂,1≤x≤10, were prepared by solid state reaction and characterized by X-ray diffraction, infrared spectroscopy and chemical analysis. Using an isoperibol calorimeter, their enthalpies of solution in 9 mass% nitric acid were measured. In order to determine the enthalpies of formation and enthalpies of mixing, thermochemical cycles were proposed and complementary experiences were performed. The results obtained show a decrease of the enthalpy of formation with the amount of cadmium introduced in the lattice. The variation of mixing enthalpy vs. x=Cd/(Cd+Ca) shows a maximum at about x=0,4. This could be explained by the existence of two cationic sites in the phosphoapatite structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

The properties and potential uses of cyclodextrin derivatives

The hydroxyl groups can be selectively substituted to control the solubility and the complex forming selectivity of the modified cyclodextrins (CDs). Among the methylated CDs only two well-defined compounds can be taken into consideration: dimethyl- and dimethyl-CD (DIMEB and TRIMEB). In an aqueous solution of DIMEB the solubility of rather insoluble compounds and drugs like steroids, vitamin D₃, lidocaine and hydrocortisone increases. In some cases their stability and bioavailability are also improved. On the other hand, the hydrolysis rate of carmofur, coumarins etc. is retarded by the methylated cyclodextrins with blocked hydroxyl groups. The drug solubilizing capacity of hydroxypropyl-CD (HPBCD) is in most cases lower than that of DIMEB. The degree of substitution (DS) shows no remarkable effect on the solubilizing properties of HPBCD in the case of indomethacin, Dipiridamole etc., but in the case of Tolnaftate the solubility was enhanced by increasing the DS, other examples are shown.     

1,1-Insertion of substituted alkynes into the Ir-O bond of η-carboxylato iridium complexes

Alkyl-carbonyl-iridium [Ir(CH₃)(CO)(η²-O₂CR′)(PPh₃)₂]⁺ (1, R′ = CH₃, Ph, p-C₆H₄CH₃) react with alkynes (RCCH; R = Ph, p-C₆H₄CH₃) in the presence of NEt₃ to give acyl-alkynyl-iridium Ir(C(O)CH₃)(-CCR)(η²-O₂CR′)(PPh₃)₂ (4) which further react with RCCH to give alkyl-carbonyl-cis-bis(alkynyl) iridium Ir(CH₃)(CO)(CCR)₂(PPh₃)₂ (5). cis-Bis(alkenyl)iridium complexes, Ir(-CHCH₂)₂(η²-O₂CCH₃)(PPh₃)₂ (6) and (η²-O₂CCH₃)(PPh₃)₂ (7) react with substituted alkynes RCCH (R = Ph, p-C₆H₄CH₃, cyclohex-1-enyl) to give cis-bis(alkynyl) Ir(CCR)₂(η²-O₂CCH₃)(PPh₃)₂ (9) that further react with RCCH to undergo the alkyne insertion reaction into the Ir-O bond to produce iridacycles containing vinyl acetate ligands, (-CCR)₂(PPh₃)₂ (8).     

Synthesis and complexing properties ofcis,cis-1,3,5-tri-[2-(diphenylphosphinyI)ethylamino]cyclohexane

A novel polydentate phosphorus-containing complexing agent,cis,cis-1,3,5-tri[2-(diphenyl-phosphinyl)ethylamino]cyclohexane, has been prepared on the basis ofcis,cis-1,3,5-triamino-cyclohexane. The method of potentiometric titration in an aqueous—organic medium (70% ethanol, ionic strength 0.01M LiNO₃, 298 K) has been used to study the acid-base and complexing properties of the title compound. The ligand thus prepared forms 11 complexes with Cu²⁺, Co²⁺, Zn²⁺, and Ni²⁺ cations; formation of hydroxocomplexes MOHL⁺ has been observed in the case of Zn²⁺ and Cd²⁺.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1276–1279, July, 1993.The authors are grateful to A. G. Matveeva for his assistante in discussing the results of this study and in preparing this paper.     

Molecular dynamics study of salt effects on micellization of N-dodecyl-N,N-dimethyl-3-ammonio-1-propane-sulfonate

In this paper, molecular dynamics simulation methods were used to investigate salt effects on micellization of N-Dodecyl-N,N-Dimethyl-3-Ammonio-1-Propane-sulfonate (SB12-3) in aqueous solution. It is proved that micelle shapes transform from spherical to prolate spherical shape after 30.0?ns simulation with different NaCl and CaCl₂ concentration. By comparison with the eccentricity value without salt addition, SB12-3 shows salt tolerance behaviors due to its unique “inner salt” structure of amphiphilic surfactant. Radial distribution function (RDF), hydrophobic groups solvent accessible surface area (SASA), hydrogen bond, and the deuterium order parameter (S_CD) are to elucidate salt effects on SB12-3 micelle formation. The radius of micelle is achieved by the related RDF value and in accordance with other researches. The addition of NaCl and CaCl₂ didn’t change the structure of micelle significantly and have little effects on the interactions between SB12-3 and water molecule. By comparison with the results without salt system, SASA of hydrophobic groups is almost the same, and SASA of hydrophilic groups and total molecule fluctuates only slightly. This further indicates that the surface of micelles is more hydrophilic due to the strong interactions between SB12-3 and water molecules. The existence of NaCl and CaCl₂ will enhance the hydrophilic interactions.     

A theoretical model for bubble formation during horizontal gas injection into liquid flow in vertical tubes

Bubble formation in flowing liquid is an important process for wastewater treatment, processing of molten metals, and biological processes. Based on a global balance of force on the bubble, this report describes a new theoretical model for bubble formation during horizontal gas injection into turbulent liquid flow in a vertical tube. This work highlights the importance of choosing the correct drag law in accordance with the bubble size. Five models for drag coefficient are compared, and of these, model III is recommended. Modified detachment criteria are applicable, depending on the liquid velocity. The new analytical model yields good predictions compared with experimental data. Based on the theoretical model, this study investigates the effects of the direction of liquid flow, liquid velocity, gas velocity, and orifice diameter on the bubble formation behavior.     

Decarboxylative Negishi Coupling of Redox‐Active Aliphatic Esters by Cobalt Catalysis

A cobalt‐catalyzed decarboxylative Negishi coupling reaction of redox‐active aliphatic esters with organozinc reagents was developed. The method enabled efficient alkyl–aryl, alkyl–alkenyl, and alkyl–alkynyl coupling reactions under mild reaction conditions with no external ligand or additive needed. The success of an in situ activation protocol and the facile synthesis of the drug molecule (±)‐preclamol highlight the synthetic potential of this method. Mechanistic studies indicated that a radical mechanism is involved.     

Stimulus‐Triggered Formation of an Anion–Cation Exciplex in Copper(I) Complexes as a Mechanism for Mechanochromic Phosphorescence

The investigation of the mechanisms of mechanochromic luminescence is of fundamental importance for the development of materials for photonic sensors, data storage, and luminescence switches. The structural origin of this phenomenon in phosphorescent molecular systems is rarely known and thus the formulation of structure–property relationships remains challenging. Changes in the M–M interactions have been proposed as the main mechanism with d¹⁰ coinage metal compounds. Herein, we describe a new mechanism—a mechanically induced reversible formation of a cation–anion exciplex based on Cu–F interactions—that leads to highly efficient mechanochromic phosphorescence and unusual large emission shifts from UV‐blue to yellow for Cu^I complexes. The low‐energy luminescence is thermo‐ and vaporesponsive, thus allowing the generation of white light as well as for recovering the original UV‐blue emission.     

Asymmetric Reductive Carbocyclization Using Engineered Ene Reductases

Ene reductases from the Old Yellow Enzyme (OYE) family reduce the C=C double bond in α,β‐unsaturated compounds bearing an electron‐withdrawing group, for example, a carbonyl group. This asymmetric reduction has been exploited for biocatalysis. Going beyond its canonical function, we show that members of this enzyme family can also catalyze the formation of C?C bonds. α,β‐Unsaturated aldehydes and ketones containing an additional electrophilic group undergo reductive cyclization. Mechanistically, the two‐electron‐reduced enzyme cofactor FMN delivers a hydride to generate an enolate intermediate, which reacts with the internal electrophile. Single‐site replacement of a crucial Tyr residue with a non‐protic Phe or Trp favored the cyclization over the natural reduction reaction. The new transformation enabled the enantioselective synthesis of chiral cyclopropanes in up to >99 % ee.     

C8N26H4: An Environmentally Friendly Primary Explosive with High Heat of Formation

The synthesis and characterization of the metal‐free polyazido compounds 3,6‐bis‐(2‐(4,6‐diazido‐1,3,5‐triazin‐2‐yl)‐hydrazinyl)‐1,2,4,5‐tetrazine ( 2 ) and 3,6‐bis‐(2‐(4,6‐diazido‐1,3,5‐triazin‐2‐yl)‐diazenyl)‐1,2,4,5‐tetrazine ( 4 ) are presented. Two compounds were characterized by NMR spectra, IR spectroscopy, mass spectrometry, and differential scanning calorimetry (DSC). Additionally, the structure of 2 was confirmed by single‐crystal X‐ray diffraction. Compounds 2 and 4 exhibit measured densities (1.755 g cm^?3 and 1.763 g cm^?3), good thermal stabilities (194 °C and 189 °C), high heat of formation (2114 kJ mol^?1 and 2820 kJ mol^?1), and excellent detonation performance (D, 8365 m s^?1 and 8602 m s^?1; P, 26.8 GPa and 29.4 GPa). Furthermore, compounds 2 and 4 have been tested for their priming ability to detonate RDX. The results indicate that the title compound 2 is a potential environmentally friendly alternative candidate to lead‐based primary explosives.