Identification of butyryl derivatives of cyclic nucleotides by positive ion fast atom bombardment mass spectrometry and mass-analysed ion kinetic energy spectrometry

The syntheses of the dibutyryl derivatives of the 3′,5′-cyclic monophosphates of adenosine, guanosine and cytidine are described. The fast atom bombardment mass spectra of these compounds are discussed, together with the mass-analysed ion kinetic energy spectra of their protonated molecular ions and of diagnostic fragments. A protocol for the identification of the derivatives is reported which includes criteria for confirming retention of the cyclic phosphodiester moiety, substitution of both heterocyclic base and ribose ring, and butyrylation of the 2′-O-position. The origins of significant fragments in the spectra are discussed.     

Synthesis and characterization oftrans-dihalogeno(isonitrosoketonato) (isonitrosoketone)osmium(III)

Summary Reaction of [OsX₆]^2– (X = Cl or Br) with HK [HK = PhC(=O)C(=NOH)R; R=H, Me or Ph] yielded osmium(III) complexes of the type [OsX₂(K)(HK)]. The OsX₂ group wastrans and the hydrogen-bonded (K)(HK) moiety behaved as a planar tetradentate N₂O₂ chelator. The complexes were one-electron paramagnets and exhibited characteristic osmium(III) e.p.r. spectra. Several spin-allowed and spin-forbidden charge-transfer transitions were observed in the 200–1300 nm region.     

Novel solvent effects in the photopolymerization of methyl methacrylate by use of quinoline–bromine charge-transfer complex as photoinitiator

Photopolymerization of MMA was carried out at 40°C in diluted systems by use of quinolinebromine (Q–Br₂) charge-transfer complex as the initiator and chloroform, carbon tetrachloride, chlorobenzene, dioxane, THF, acetone, benzene, toluene, quinoline, and pyridine as solvents. The results showed variable monomer exponents ranging from 1 to 3. For chloroform, carbon tetrachloride, and chlorobenzene, the monomer exponent observed was unity; for other solvents used, the value of the same exponent was much higher (between 2 and 3). Initiation of polymerization is considered to take place through radicals generated in the polymerization systems by the photodecomposition of (Q–Br₂)–monomer complex (C) formed instantaneously in situ on addition of the Q–Br₂ complex in monomer. The kinetic feature of high monomer exponent is considered to be due to higher order of stabilization of the initiating complex (C) in presence of the respective solvents. In the presence of the retarding solvents, very low or zero initiator exponents were also observed, depending on the nature and concentration of the solvents used. The deviation from the square-root dependence of rate on initiator concentration becomes higher at high solvent and initiator concentrations in general. This novel deviation is explained on the basis of initiator termination, probably via degradative chain transfer involving the solvent-modified initiating complexes and the propagating radicals.     

A comparative Langmuir-Blodgett study on a set of covalently linked porphyrin-based amphiphiles: a detailed atomic force microscopic study

A set of covalently linked phenyl-amidophenyl-substituted porphyrin amphiphiles with n-C15H31 tails have been synthesized and completely characterized. These amphiphiles form good Langmuir-Blodgett (LB) films at the air/water interface. Mean molecular areas for the series were measured from the isotherms and found to increase as the number of aliphatic chains increased from one to four. No influence of the subphase pH was observed on the isotherms. LB films can be transferred successfully onto different solid surfaces. The LB films were characterized using tapping mode atomic force microscopy (AFM). Bis-, tris-, and tetra-substituted porphyrins were found to be fairly good film-forming amphiphiles, whereas irregular aggregates were seen in the case of the monosubstituted porphyrin amphiphile. Multilayers were also formed with tetra-substituted amphiphiles on mica. Detailed AFM studies of tetra-substituted amphiphiles have been carried out to investigate the effect of preparation procedure and solid substrates on film formation and transfer. The absorption and fluorescence spectra for the amphiphiles in solution and LB films deposited onto mica and glass were recorded, which demonstrated the successful transfer of LB films onto the substrates and provided more information about the arrangement of porphyrin molecules within the LB films. For comparison, self-assembled monolayers (SAMs) and the cast thin films of the amphiphiles were prepared and characterized.     

Activation of N2O reduction by the fully reduced micro4-sulfide bridged tetranuclear Cu Z cluster in nitrous oxide reductase

The tetranuclear CuZ cluster catalyzes the two-electron reduction of N2O to N2 and H2O in the enzyme nitrous oxide reductase. This study shows that the fully reduced 4CuI form of the cluster correlates with the catalytic activity of the enzyme. This is the first demonstration that the S = 1/2 form of CuZ can be further reduced. Complementary DFT calculations support the experimental findings and demonstrate that N2O binding in a bent mu-1,3-bridging mode to the 4CuI form is most efficient due to strong back-bonding from two reduced copper atoms. This back-donation activates N2O for electrophilic attack by a proton.     

Synthesis and crystal structure of bis(benzimidazolium) tetrahalocobaltate(II)

The crystal structures of benzimidazolium tetrahalocobaltates (HBz)₂[CoX₄] (X = Cl and Br) have been determined. The chloride salt is triclinic, P-1, with a = 7.670(3) Å, b = 8.307(3) Å, c = 15.730(2) Å, and = 87.37(3)°, = 84.99(3)°, = 67.72(2)°. The bromide salt is monoclinic, C2/c, with a = 15.568(2) Å, b = 8.063(3) Å, c = 5.762(2) Å and = 91.36(3)°. The structures of the two salts are closely related. Both the compounds contain isolated tetrahedral CoX₄ ^2– anions and benzimidazolium cations. In the chloride salt, three chloride ions are involved in strong hydrogen bonding while only two bromide ions participate in the bromide salt. The greater deviation from the ideal tetrahedral geometry in CoBr₄ ^2– can be related to the less extensive hydrogen-bonding network compared to the chloro complex.     

Studies on stable aqueous poly(o-toluidine) prepared with the use of a water soluble support polymer,polyacrylamide

Polymerization of o-methylaniline or o-toluidine (OT) was studied in aqueous acidic (HCl) medium with or without the use of the support of a water soluble polymer, polyacrylamide (PAAm). Poly(o- toluidine) (POT) produced with PAAm support was in the form of aqueous solution or dispersion that showed high stability and good processibility. High degree of dispersion or near solubility and storage stability of POT thus prepared are explained on the basis of establishment of hydrogen bonding between segments of POT being formed and the PAAm present in the medium thus resulting in a template effect. Studies by UV-visible spectroscopy and FTIR spectroscopy lend support to this view. POT-PAAm composites commonly show higher thermal stability than POT and the composites show DC-electrical conductivities in the range of 10⁻⁹–10⁻¹ S · cm⁻¹ depending on the POT content. Morphological analysis of the optically clear aqueous POT-PAAm solution by transmission electron microscopy (TEM) shows the presence of large clusters of PAAm-supported near-spherical POT nanoparticles in the aqueous PAAm solution. Scanning electron microscopic (SEM) analysis of isolated POT-PAAm composites shows a cocontinuous phase morphology without any trend of gross phase separation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3243–3256, 1999     

Synthetic and spectral studies of novel spiro {bicyclo[3,3,0]octene‐8,3′(2′H)‐indol}‐2′‐ones obtained from indol‐2,3‐diones

The present article reports our approach toward the synthesis of spiro compounds via indol‐2,3‐diones. Thus, reaction of indol‐2,3‐dione derivatives with a secondary cyclic amino acid, namely, (R)‐(−)‐thiazolidine‐4‐carboxylic acid, affords a thiazolo‐oxazolidinone as the main product. When the reaction is carried out in the presence of a dipolarophile, 1,3‐dipolar cycloaddition to the intermediate azomethine ylide leads to a novel spiro compound. The products have been characterized on the basis of spectral studies, and the geometry of the intermediate iminium compound has been optimized by use of the semiempirical molecular orbital method. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 381–384, 1999     

Universal density functional approach to the calculation of correlation energies of atoms

A new local density functional approach for the calculation of correlation energies of many-electron atomic systems is proposed by using the exact results for the correlation energy of a two-electron system bound by a harmonic oscillator external potential. This is motivated by the fact that the correlation energy is a universal functional of the electron density, and the form of this functional is independent of the external potential. The calculated numerical results for the correlation energies show very good agreement with the standard values reported in the literature. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 461–465, 1997     

A Simple Lithographic Approach for Preparing Patterned,Micron-Scale Corrals for Controlling Cell Growth

Hydrophobic n -alkanethiolate bottoms and walls consisting of hydrophilic three-layer poly(acrylic acid)/poly(ethylene glycol) nanocomposite polymers are used for making patterned corrals having lateral dimensions of 63 μm. Macrophage cells are confined within these corrals and are unable to grow over the corral walls (see picture).