Synthesis and Characterization of Tetraosmium Carbonyl Complexes Containing a Bridging CO2 Ligand

Treatment of (thd)H (thd=2,2,6,6-tetramethyl-3,5-heptandionate) with excess Os₃(CO)₁₂ in an autoclave at 180°C gives the formation of a brown metal chain complex [Os₂(CO)₅(thd)₂]₂ (1) and a yellow CO₂ cluster complex [Os₄(-H)(-CO₂)(thd)(CO)₁₃] (2) in low yields. Complex 2 was fully identified by a combination of spectroscopic methods and X-ray diffraction study, showing a unique CO₂ ligand bridging a triosmium metal fragment, Os₃(-H)(CO)₁₀ and a monometallic osmium fragment, Os(CO)₃(thd). Upon treatment of 1 with Me₃NO at an elevated temperature, oxidation of the CO ligand occurred at the position trans to the unique CO₂ ligand on the Os(CO)₃(thd) fragment, giving the formation of a second CO₂ cluster [Os₄(-H)(-CO₂)(thd)(CO)₁₂(NCMe)] (3), which is stabilized by a weakly coordinated acetonitrile molecule.     

C(2×2)S/Fe(001)吸附体系的SCF-Xa-MS研究

采用SCF-X_α-MS方法, 对于C(2×2)S/Fe(001)吸附体系, 选择Fe_5S和Fe_9S两种原子簇模型, 研究了该吸附体系的电子结构、吸附成键特征及其相互作用图象。结果表明, S吸附于Fe(001)单晶表面具有较强的定域性质, S原子与底物Fe原子之间的吸附相互作用主要表现为S(3p)-Fe(4s,3d)之间的轨道相互作用。通过对表面吸附键长的优化, 其结果与X.S.Zhang等的ARPEFS的实验结果一致。     

Synthesis of mesoionic[1,2,3]triazolo[5,1-d][1,2,5]triazepines

Intramolecular cyclization of 1-amino-3-phenacyl-4-carbohydrazido-1,2,3-triazolium-5-olates has been shown to take place via selective interaction of the carbonyl group with the terminal amino function of the hydrazido group to form a 1,2,5-triazepine ring. Minor products, resulting from the interaction of the α-nitrogen atom of the hydrazido group with the carbonyl function, having a N-amino-pyridazine structure were also detected and isolated. A general method for the synthesis of novel mesoionic 2-amino-7-aryl-4-oxo-2,4,5,8-tetrahydro[1,2,3]triazolo[5,1-d][1,2,5]triazepin-9-ium-3-olates was developed.     

Ein neues Kupfercobaltboratoxid mit isolierten B2O5-Baugruppen: Cu2Co(B2O5)O

On a New Copper Cobalt Borate Oxide with Isolated B₂O₅ Units: Cu₂Co(B₂O₅)O Single crystals of a new compound with the empirical formula Cu₂CoB₂O₆ were obtained by using a B₂O₃ flux technique. X-ray single crystal technique led to a new structure type. Cu₂CoB₂O₆ crystallizes monoclinic, space group C-P2₁/c (No. 14); a = 3.2250(6); b = 14.847(1); c = 9.1171(6) Å; β = 93.67°; Z = 4. All metal sites are octahedrally coordinated and form a two dimensional framework consisting of edge sharing octahedra ribbons. In addition one observes isolated B₂O₅-units and oxygen which is not coordinated to boron. The far relation to the crystal structure of the mineral Warwickite is illustrated.     

Addition of diazocyclopropane generatedin situ to vinyl bromide and chemical transformations of the resulting 5-bromospiro(1-pyrazoline-3,1′-cyclopropane)

The reaction of diazocyclopropane generatedin situ with vinyl bromide occurs as regioselective 1,3-dipolar cycloaddition to give 5-bromospiro(1-pyrazoline-3,1′-cyclopropane) in ∼60% yield. Reactions of the latter with nucleophilic reagents, which can occur both with retention and opening of the cyclopropane ring, were studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 688–690, April 1998.     

Thermochemistry of interactions of Na+ with benzo-15-crown-5 ether in acetonitrile-water mixtures at 298.15 K

Enthalpies of dissolution of benzo-15-crown-5 ether (B15C5) in mixtures of acetonitrile with water and in solutions of NaI and NaBPh₄ (I=0.05 mol dm^–3) in these mixtures were measured at 298.15 K. From the obtained results and appropriate literature data, the thermodynamic functions of B15C5/Na⁺ complex formation in acetonitrile-water mixtures were determined. The enthalpies of transfer of the complex B15C5/Na⁺ from pure acetonitrile to the examined mixtures were calculated and are discussed.     

Binding Ensembles of p53-MDM2 Peptide Inhibitors by Combining Bayesian Inference and Atomistic Simulations

Designing peptide inhibitors of the p53-MDM2 interaction against cancer is of wide interest. Computational modeling and virtual screening are a well established step in the rational design of small molecules. But they face challenges for binding flexible peptide molecules that fold upon binding. We look at the ability of five different peptides, three of which are intrinsically disordered, to bind to MDM2 with a new Bayesian inference approach (MELD × MD). The method is able to capture the folding upon binding mechanism and differentiate binding preferences between the five peptides. Processing the ensembles with statistical mechanics tools depicts the most likely bound conformations and hints at differences in the binding mechanism. Finally, the study shows the importance of capturing two driving forces to binding in this system: the ability of peptides to adopt bound conformations (ΔGconformation) and the interaction between interface residues (ΔGinteraction).     

6-Arylamino-3-methyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines: Novel N-Arylamidine Structures

We propose a method for obtaining derivatives of 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine by alkylation of 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol by substituted -chloroacetanilides, followed by cyclization of the intermediate by phosphorus oxychloride.     

Theoretical study of ribonucleotide reductase mechanism-based inhibition by 2'-azido-2'-deoxyribonucleoside 5'-diphosphates

2'-azido-2'-deoxyribonucleoside 5'-diphosphates are mechanism-based inhibitors of Ribonucleotide Reductase. Considerable effort has been made to elucidate their mechanism of inhibition, which is still controversial and not fully understood. Previous studies have detected the formation of a radical intermediate when the inhibitors interact with the enzyme, and several authors have proposed possible structures for this radical. We have conducted a theoretical study of the possible reactions involved, which allowed us to identify the structure of the new radical among the several proposals. A new reactional path is also proposed that is the most kinetically favored to yield this radical and ultimately inactivate the enzyme. The energetic involved in this mechanism, both for radical formation and radical decay, as well as the calculated Hyperfine Coupling Constants for the radical intermediate, are in agreement with the correspondent experimental values. This mechanistic alternative is fully coherent with remaining experimental data.     

Comparative study on the synthesis, photoluminescence and application in InGaN-based light-emitting diodes of TAG:Ce phosphors

Cerium-doped terbium aluminum garnet phosphors, Tb₃Al₅O₁₂:Ce³⁺ (TAG:Ce³⁺), were prepared with different methods: co-precipitation (CP), half dry-half wet (HDHW), sol-combustion (SC) and Pechini method plus conventional solid state reaction (SS) method. Comparative study on the phase-formation, particle size, morphologies and luminescent characteristics of the phosphors synthesized with different methods was carried out by means of XRD, FE-SEM and photoluminescence (PL) analysis and SC method was confirmed by the comparison of the results to be an easy and an effective process for preparing efficient and nano-sized Tb₃Al₅O₁₂:Ce³⁺ phosphors. Various factors influencing particle size, morphology and PL of the phosphors, such as precursor preparation, reaction temperature and heating time, were also investigated. Light-emitting diodes (LEDs) were fabricated with each phosphor and a ∼460 nm emitting InGaN chip. The LEDs from SS, HDHW and CP exhibit strong white emission while those from SC and Pechini emit yellow, revealing that the emission characteristics of LEDs are influenced not only by the morphology and the particle size of the phosphors, but also by the preparing process of the phosphors.