A facile and improved synthesis of tubercidin and certain related pyrrolo[2,3-d]pyrimidine nucleosides by the stereospecific sodium salt glycosylation procedure

A simple synthesis of tubercidin ( 1 ), 7-deazaguanosine ( 2 ) and 2′-deoxy-7-deazaguanosine ( 14 ) has been accomplished using the sodium salt glycosylation procedure. Reaction of the sodium salt of 4-chloro- and 2-amino-4-chloro-pyrrolo[2,3-d]pyrimidine, 3 and 4 , respectively, with 1-chloro-2,3-0-isopropylidene-5-0-(t-butyl)dimethylsilyl-α-D-ribofuranose ( 5 ) gave the corresponding protected nucleosides 6n and 7 with β-anomeric configuration. Deprotection of 6 provided 8 , which on heating with methanolic ammonia gave tubercidin ( 1 ) in excellent yield. Functional group transformation of 7 , followed by deisopropylidenation gave 2-aminotubercidin ( 10 ) and 2-amino-7-β-D-ribofuranosylpyrrolo[2,3-d]pyrimidine-4(3H)-thione ( 11 ). Treatment of 7 with 1N sodium methoxide followed by exposure to aqueous trifluoroacetic acid, and ether cleavage furnished 7-deazaguanosine ( 2 ). 2′-Deoxy-7-deazaguanosine ( 14 ) and 2′-deoxy-7-deaza-6-thioguano-sine ( 18 ) were also prepared by using similar sequence of reactions employing 4 and 1-chloro-2-deoxy-3,5-di-O-p-toluoyl-α-D-erythro-pentofuranose ( 15 ).     

Substituted derivatives of [Fe2(CO)9] and [Ru2(CO)9] and their susceptibility to electrophilic attack: X-ray crystal structure of [Fe2(μ-Br)(CO)4{μ-(C6H5O)2PN(C2H5)P(OC6H5)2}2]PF6

Bis- and, in particular, tetra-substituted ditertiary phosphine and diphosphazane derivatives of [Fe₂(CO)₉] and [Ru₂(CO)₉], readily synthesised by reaction of the appropriate bidentate ligand with [Fe₂(CO)₉] and [Ru₃(CO)₁₂], respectively, are very susceptible to electrophilic attack by reagents such as halogens and protons; the solid state structure of one of the products [Fe₂(μ-Br)(CO)₄ {μ-(PhO)₂PN(Et)P(OPh)₂}₂]PF₆ has been determined by X-ray crystallography.     

Separation of aromatic solvents from oil refinery reformates by a newly designed ionic liquid using gas chromatography with flame ionization detection

The aim of this study was to determine whether the new ionic liquid, N,N‐dimethyl‐2‐oxopyrrolidonium iodide, synthesized in our laboratory is a suitable solvent for the separation of aromatic components benzene, toluene, ethylbenzene, and xylenes from petroleum mixtures (reformates) in liquid–liquid extraction. In pursuance of the above aim, a method to extract all components of a mixture, containing four aromatic components simultaneously, was developed. A new ionic liquid and a previously used liquid were compared for their extraction abilities. These ionic liquids were, respectively, N,N‐dimethyl‐2‐oxopyrrolidinium iodide and 1‐ethyl‐3‐methyl imidazolium ethyl sulfate. The concentrations of each benzene, toluene, ethylbenzene, and xylenes component in the extract and raffinate phases were measured by gas chromatography with flame ionization detection as volume percent to determine the extraction ability of the ionic liquids. The results obtained for both the reformate samples and model mixtures indicated that the new ionic liquid was effective as an extracting solvent for the recovery of aromatic components from reformates. Also the analysis results, using gas chromatography with flame ionization detection, for the reformate samples were as good as the results obtained by a local oil refinery. The extraction results also show that the developed method is very suitable for the separation and analysis of aromatic components in reformates.     

Magnetohydrodynamic and heat transfer effects on the stagnation-point flow of an electrically conducting nanofluid past a porous vertical shrinking/stretching sheet in the presence of variable stream conditions

A steady two-dimensional magnetohydrodynamic stagnation-point flow of an electrically conducting fluid and heat transfer with thermal radiation of a nanofluid past a shrinking and stretching sheet is investigated numerically. The model used for the nanofluid incorporates the effects of the Brownian motion and thermophoresis. A similarity transformation is used to convert the governing nonlinear boundary-layer equations into coupled higher-order nonlinear ordinary differential equations. The result shows that the velocity, temperature, and concentration profiles are significantly influenced by the Brownian motion, heat radiation, and thermophoresis particle deposition.     

Laminar boundary layer flow of a nanofluid along a wedge in the presence of suction/injection

The behavior of an incompressible laminar boundary layer flow over a wedge in a nanofluid with suction or injection has been investigated. The model used for the nanofluid integrates the effects of the Brownian motion and thermophoresis parameters. The governing partial differential equations of this problem, subjected to their boundary conditions, are solved by the Runge-Kutta-Gill technique with the shooting method for finding the skin friction and the rate of heat and mass transfer. The result are presented in the form of velocity, temperature, and volume fraction profiles for different values of the suction/injection parameter, Brownian motion parameter, thermophoresis parameter, pressure gradient parameter, Prandtl number, and Lewis number. The conclusion is drawn that these parameters significantly affect the temperature and volume fraction profiles, but their influence on the velocity profile is comparatively smaller.     

Soret and dufour effects on MHD free convective heat and mass transfer with thermophoresis and chemical reaction over a porous stretching surface: Group theory transformation

The group theoretic method is applied for solving the problem of the combined influence of the thermal diffusion and diffusion thermoeffect on magnetohydrodynamic free convective heat and mass transfer over a porous stretching surface in the presence of thermophoresis particle deposition with variable stream conditions. The application of one-parameter groups reduces the number of independent variables by one; consequently, the system of governing partial differential equations with boundary conditions reduces to a system of ordinary differential equations with appropriate boundary conditions. The equations along with the boundary conditions are solved numerically by using the Runge-Kutta-Gill integration scheme with the shooting technique. The impact of the Soret and Dufour effects in the presence of thermophoresis particle deposition with a chemical reaction plays an important role on the flow field.     

Thermal Stratification Effects on Hiemenz Flow of Nanofluid Over a Porous Wedge Sheet in the Presence of Suction/Injection Due to Solar Energy: Lie Group Transformation

The objective of the present work is to investigate theoretically the Hiemenz flow and heat transfer of an incompressible viscous nanofluid past a porous wedge sheet in the presence of thermal stratification due to solar energy (incident radiation). The wall of the wedge is embedded in a uniform Darcian porous medium to allow for possible fluid wall suction or injection and has a power–law variation of the wall temperature. The partial differential equations governing the problem under consideration are transformed by a special form of Lie symmetry group transformations viz., one-parameter group of transformation into a system of ordinary differential equations which are solved numerically by Runge–Kutta–Gill-based shooting method. The conclusion is drawn that the flow field and temperature are significantly influenced by convective radiation, thermal stratification, buoyancy force, and porosity of the sheet.     

Local non-similarity solution to impact of chemical reaction on MHD mixed convection heat and mass transfer flow over porous wedge in the presence of suction / injection

Combined heat and mass transfer on free, forced, and mixed convection flow along a porous wedge with magnetic effect in the presence of chemical reaction is investigated. The flow field characteristics are analyzed by the Runge-Kutta-Gill scheme with the shooting method as well as the local non-similarity method up to the third level of truncation, which are used to reduce the governing partial differential equations into nine ordinary differential equations. The governing boundary layer equations are converted to a dimensionless form by Falkner-Skan transformations. Because of the effect of suction/injection on the wall of the wedge with buoyancy force and variable wall temperature, the flow field is locally non-similar. Numerical calculations up to the third order level of truncation are carried out as a special case for different values of dimensionless parameters. Effects of the magnetic field strength in the presence of chemical reaction with variable wall temperature and concentration on the dimensionless velocity, temperature and concentration profiles are shown graphically.     

Expanding the Potential of DNA for Binding and Catalysis: Highly Functionalized dUTP Derivatives That Are Substrates for Thermostable DNA Polymerases

The discovery of a simple structural motif allows for the enzymatic synthesis by polymerase chain reactions (PCR) of modified DNA (see reaction scheme) bearing side chains similar or even identical to those of several amino acids. Libraries of DNA functionalized with both cationic and anionic groups may now be readily prepared. R=I, HgCl; X=functional group.