Thin Layer Chromatography of Purines on Silica Gel G Impregnated with Transition Metal Ions; Assay of Caffeine and Theophylline in Pharmaceutical Formulations

This study was undertaken to develop thin layers of silica gel G impregnated with transition metal ions for separation, identification and estimation of purines. The influence of transition metal ions and eluting solvents on chromatographic behaviour (hR_f) has been studied. The method was applied for qualitative analysis of purines in the mixtures and quantitative analysis of purine bases in the mixture as well as in pharmaceutical formulations. The results were compared statistically with those obtained by official methods. The method is simple, reproducible, and accurate within 1.3 ± 0.6%.     

4-(6-甲基-2-苯并噻唑偶氮)间苯二酚作螯合剂反相HPLC分离测定V(V)、cu(Ⅱ)、co(Ⅱ)、Ni(Ⅱ)、cr(VI)

本文提出用4-(6-甲基-2-苯并噻唑偶氮)间苯二酚(MBTAR)为柱前衍生试剂,用含有15mmol/L TBA·Br,10mmool/L pH6.0 HAc-NaAc缓冲溶液的甲醇-水(75/25,V/V)混合溶液作流动相,在C_8柱上分离和测定了V(V)、Cu(Ⅱ)、Ni(Ⅱ)、co(Ⅱ)和Cr(Ⅵ)。当信噪比为3时,其检出限为0.15～6.1ppb。本法干扰少,分离时间短,应用于人发分析,结果令人满意。     

Tandem transmetallation and oxidative addition reactions of [Sn(R)2(Ph2PC6H4-2-S)2] with transition metal complexes of the Group 9

The reactions of [Sn(Ph)₂(Ph₂PC₆H₄-2-S)₂] with trans -[M(Cl)(CO)(PPh₃)₂] M=Ir, Rh afford the complexes [Rh(Ph₂PC₆H₄-2-S)₂(SnClPh₂)] (1) and [Ir(CO)(Ph₂PC₆H₄-2-S)₂(SnClPh₂)] (2) as final products of two processes, a transmetallation reaction and an oxidative addition process. The crystal structures of both complexes have been determined, showing the rhodium compound to be into a slightly distorted square base pyramidal geometry, while that of the iridium derivative can be described as a distorted octahedron.     

On the Coordination Properties of New Bicyclophosphite-Carbohydrates

Summary. The coordination behavior of newly developed bicyclophosphite ligands toward Mo(0), Rh(I), and Pt(II) was studied.Reactions at different ratios of metal to ligand were done. It was found that the ligands act as monodentate ones and form with hexacarbonylmolybdenum(0) complexes with the general formula Mo(CO)₅L by replacing only one carbonyl ligand. Coordination experiments toward acetylacetonatodicarbonylrhodium(I) resulted in the formation of undefined compounds. Toward dichlorocyclooctadienylplatinum(II) the monomeric phosphorus ligands act as monodentate ligands forming complexes of the general structure cis-PtCl₂L₂. All the synthesized platinum-complexes possess cis-configuration (proven by ³¹P NMR). The corresponding coordination compounds were isolated and characterized by elemental analyses and ¹H, ¹³C, and ³¹P NMR.     

过渡金属催化CO2/H2参与的羰基化研究进展

Ever-increasing energy demands due to rapid industrialization and urban population growth have drastically reduced petroleum reserves and increased greenhouse-gas production, and the latter has consequently contributed to climate change and environmental damage. Therefore, it is highly desirable to produce fuels and chemicals from non-petroleum feedstocks and to reduce the atmospheric concentrations of greenhouse gases. One solution has involved using carbon dioxide (CO₂), a main greenhouse gas, as a C1 feedstock for producing industrial fuels and chemicals. However, this requires high energy input from reductants or reactants with relatively high free energy (e.g., H₂ gas) because CO₂ is a highly oxidized, thermodynamically stable form of carbon. H₂ can be generated through water photolysis, making it an ideal reductant for hydrogenating CO₂ to CO. In situ generation of CO such as this has been developed for various carbonylation reactions that produce high value-added chemicals and avoid deriving CO from fossil fuels. This is beneficial because CO is toxic, and when extracted from fossil fuels it requires tedious separation and transportation. This combination of CO₂ and H₂ allows for functional molecules to be synthesized as entries into the chemical industry value chain and would generate a carbon footprint much lower than that of conventional petrochemical pathways. Based on this, CO₂/H₂ carbonylations using homogeneous transition metal-based catalysts have attracted increasing attention. Through this process, alkenes have been converted to alcohols, carboxylic acids, amines, and aldehydes. Heterogeneous catalysis has also provided an innovative approach for the carbonylation of alkenes with CO₂/H₂. Based on these alkene carbonylations, the scope of CO₂/H₂ carbonylations has been expanded to include aryl halides, methanol, and methanol derivatives, which give the corresponding aryl aldehyde, acetic acid, and ethanol products. These carbonylations revealed indirect CO₂-HCOOH-CO pathways and direct CO₂ insertion pathways. The use of this process is ever-increasing and has expanded the scope of CO₂ utilization to produce novel, high value-added or bulk chemicals, and has promoted sustainable chemistry. This review summarizes the recent advances in transition-metal-catalyzed carbonylations with CO₂/H₂ and discusses the perspectives and challenges of further research.     

Wasserfreie Selten-Erd-Acetate,M(CH3COO)3 (M = Sm?Lu,Y) mit Kettenstruktur. Kristallstrukturen von Lu(CH3COO)3 und Ho(CH3COO)3

Anhydrous Rare-Earth Acetates, M(CH₃COO)₃ (M = Sm? Lu, Y) with Chain Structures. Crystal Structures of Lu(CH₃COO)₃ and Ho(CH₃COO)₃ Single crystals of the anhydrous rare-earth acetates containing lutetium (type 1) and holmium (type 2) were obtained by crystallisation at 120°C from diluted acetic acid solutions of their oxides and cesium acetate. The crystal structures [Lu(CH₃COO)₃: orthorhombic, a = 825.85(8), b = 1 398.1(2), c = 823.9(1) pm, V_m = 143.24(3) cm³/mol, space group Ccm2₁ (No. 36), Z = 4, R = 0.035, R_w = 0.030; Ho(CH₃COO)₃: monoclinic, a = 1 109.1(3), b = 2 916.3(10), c = 786.8(2) pm, β = 131.90(1)°, V_m = 142.58(8) cm³/mol, space group C2/c (No. 15), Z = 8, R = 0.039, R_w = 0.039, R_w = 0.026] were determined from four-circle diffractometer data sets. The structures consist of one-dimensional infinite chains built up by bridging acetate ions. Ho³⁺ is coordinated by 8 oxygen atoms, whereas Lu³⁺ has only 7 nearest oxygen neighbours. The chains are stacked parallel to the [001] direction. Isotypic compounds with Tm? Lu (type 1) and Sm? Er, Y (type 2) were prepared as powders and characterized by X-ray powder patterns. Thermoanalytical investigations (DTA, Guinier-Simon technique) of all compounds have shown that there is a first-order phase transition at 180°C (type 2) and in the range of 230–255°C (type 1). The high-temperature phase crystallizes with the known Sc(CH₃COO)₃ structure (type 0) where the rare earth cations are surrounded by 6 oxygen atoms. In the case of the type 1 compounds the phase transition is reversible.     

Ab initio Hartree-Fock calculations of molecular X-ray intensities. Validity of one-center approximations

Ab initio Hartree-Fock calculations of relative X-ray transition probabilities for core hole states of N₂, CO, H₂O and NH₃ have been carried out and compared with the respective high-resolution soft X-ray spectra. The same one-determinental wavefunctions were employed for both initial and final states and the dependence of the X-ray transition moments on the choice of orbitals and of basis set parameters was investigated. In particular, orbitals optimized for a transition state were tested. The use of the one-center intensity model as a guide for the assignment of second row X-ray spectra was justified at bothab initio and semiempirical (CNDO) levels of approximation. The breakdown of the MO-picture for inner-valence electrons is demonstrated in the X-ray spectrum of N₂ and the analogy with the corresponding photoelectron bands is pointed out.     

Effects of （BCO）n Substituent on Claisen Rearrangement of Phenyl Allyl Ether

IntroductionClaisen rearrangement exhibits interesting featuresboth as a technique for organic synthesis and as an im-portant part of the shikimate biosynthetic pathway. Aseries of researches on the kinetic and thermodynamiccharacters of Claisen rearrange…     

Transition metal dichalcogenide thin films for solar hydrogen production

In the last three decades, transition metal dichalcogenides (TMDs) have been extensively studied for electronic, photonic, and energy applications. Different efforts are directed to find a holy grail of efficient and economically feasible materials that could be simple in production and available on a large scale. The interest in TMDs (MoS₂, WS₂, MoSe₂, WSe₂) stems from their suitable electronic structure for efficient solar light absorption and simple exfoliation technique of 2D crystallites due to the van der Waals bonding of these materials. This led to various designs and combinations of 2D single layers that could form heterojunctions and multijunctions for efficient light absorption, charge carrier generation/separation, and its transfer in optoelectronic and energy harvesting devices. Herein, TMD thin films are reviewed as photoelectrodes for solar hydrogen evolution and compared to that of other more developed materials.     

The band structures of some transition metals and their NaCl-type compounds

The band structures of Group IVB (Ti,Zr,Hf),VB (V,Nb,Ta) and VIB (Cr,Mo,W) transition metals and some of their carbides and nitrides (TiN,ZrN,HfN,VC,NbC,TaC,VN,NbN,TaN) with NaCl-type (Bl-type) structure have been calculated by using the tight-binding method within the Extended Hiickel approximation (EHT).The energy bands,densities of states and crystal orbital overlap populations are given.The relationship between the bonding properties and the superconducting transition temperatures (Tc) of them is discussed.The influences of various kinds of metallic atoms and changes of bond lengths on Tc are also discussed.