Polymerization of 3‐ethynylthiophene with homogeneous and heterogeneous Rh catalysts

3‐Ethynylthiophene (3ETh) was polymerized with Rh(I) complexes: [Rh(cod)acac], [Rh(nbd)acac], [Rh(cod)Cl]₂, and [Rh(nbd)Cl]₂ (cod is η²:η²‐cycloocta‐1,5‐diene and nbd η²:η²‐norborna‐2,5‐diene), used as homogeneous catalysts and with the last two complexes anchored on mesoporous polybenzimidazole (PBI) beads: [Rh(cod)Cl]₂/PBI and [Rh(nbd)Cl]₂/PBI used as heterogeneous catalysts. All tested catalyst systems give high‐cis poly(3ETh). In situ NMR study of homogeneous polymerizations induced with [Rh(cod)acac] and [Rh(nbd)acac] complexes has revealed: (i) a transformation of acac ligands into free acetylacetone (Hacac) occurring since the early stage of polymerization, which suggests that this reaction is part of the initiation, (ii) that the initiation is rather slow in both of these polymerization systems, and (iii) a release of cod ligand from [Rh(cod)acac] complex but no release of nbd ligand from [Rh(nbd)acac] complex during the polymerization. The stability of diene ligand binding to Rh‐atom in [Rh(diene)acac] catalysts remarkably affects only the molecular weight but not the yield of poly(3ETh). The heterogeneous catalyst systems also provide high‐cis poly(3ETh), which is of very low contamination with catalyst residues since a leaching of anchored Rh complexes is negligible. The course of heterogeneous polymerizations is somewhat affected by limitations arising from the diffusion of monomer inside catalyst beads. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2776–2787, 2008     

A separable approximation to the two-body t-matrix for short-range central local potentials

The S-wave potential in momentum space, V₀(p, p′), corresponding to a local two-body central short-range potential may be expanded in separable form with the help of suitable quadrature formulae. With a two-term separable expansion for a variety of nuclear potentials, the resulting t-matrix is found to be in close agreement with the corresponding result with a six-term expansion for small values of p and p′ which are important in the calculation of the trinucleon binding energy.     

Synthesis and biological activity of phosphorylated compounds of 2‐substituted benzazoles

A series of organophosphorus derivatives have been synthesized by the reaction of phosphorylchloride with 2‐(2′‐hydroxyphenyl)benzimidazole and 2‐(2′‐hydroxynaphthyl)benzimidazole in the presence of KHCO₃ in dry THF in different molar ratios. Newly synthesized derivatives were tested for their insecticidal activity against Periplenata americana. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:246–249, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20533     

In silico structure-based design of a novel class of potent and selective small peptide inhibitor of Mycobacterium tuberculosis Dihydrofolate reductase,a potential target for anti-TB drug discovery

The worldwide TB structural genomics initiative has identified several new drug targets for Mycobacterium tuberculosis (M. tb). Dihydrofolate reductase (DHFR) catalyzes the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate that is essential for DNA synthesis. Inhibition of its activity leads to arrest of DNA synthesis and hence cell death. Thus, M. tb DHFR (mtDHFR) is an attractive novel drug target for developing anti-TB drugs. Structural comparison of mtDHFR and human DHFR (hDHFR) reveals key differences in the active sites. These differences can be exploited for the design of selective inhibitors for mtDHFR. Based on the recently determined high resolution crystal structure of mtDHFR complexed with known inhibitor methotrexate (MTX) and cofactor NADPH, a tri-peptide inhibitor has been identified using a structure-based drug design approach. Docking studies indicate that the designed tripeptide inhibitor has a high potency (K _d = 1.78 nM) and is a selective (approximately 120 fold over hDHFR) inhibitor for mtDHFR. Hence, the tripeptide is a suitable lead compound for the development of novel anti-TB drugs.     

Mononuclear and binuclear manganese(II) complexes with tridentate bis-benzimidazolyl ligands

Summary Manganese(II) complexes of bis(2-benzimidazolylmethyl) ether (DGB), bis(2-benzimidazolylmethyl) sulphide (TGB) and the n-butyl derivative of DGB (BDGB) were prepared and characterised. The solution e.p.r. spectrum of [Mn(TGB)Cl₂] in DMF at 143 K is commensurate with an axially distorted monomeric manganese(II) complex, room temperature magnetic moment (6.04 B.M.) per manganese(II) atom being in the range found for other d⁵ monomeric manganese(II) complexes. The solution e.p.r. spectrum of [Mn(BDGB)Cl₂]-2H₂O in DMF at 143 K indicates the presence of two equivalent manganese(II) ions coupled by an exchange interaction, fostered by bridging chlorides. Evidence for this is provided by a nearly isotropic 11 line hyperfine structure of ⁵⁵Mn, with a coupling constant 45 ± 5G. Contact-shifted ¹H n.m.r. data also supports an exchange coupled dimeric manganese complex. The room temperature magnetic moment, 5.64 B.M., per manganese(II) indicates quenching of the magnetic moment below that of monomeric manganese(II) ion. The [Mn(DGB)Cl₂]·H₂O complex exhibits a magnetic moment of 6.02 B.M. per manganese, indicating a monomeric manganese complex. E.p.r. data of the complex diluted in an analogous Zn-DGB complex (1∶20) correlates well for D = 0.22cm⁻¹ and λ ∼- 0.267. The [Mn(DGB)-(C1O₄)₂] and [Mn(BDGB)(ClO₄)₂] complexes, diluted in analogous Zn-DGB and Zn-BDGB complexes (1∶20), show a strong single e.p.r. line at g _eff ∼- 2. The complexes have low magnetic moments; 4.44 B.M./Mn and 4.39 B.M./Mn, at room temperature.     

Calculation of the minimum energy conformation of acetylcholine using a global optimization technique

The conformational energy of acetylcholine is minimized with respect to the distances between nonbonded atoms with the help of the Bremermann method of unconstrained global optimization. The set of distances for which the energy is the absolute minimum is then used to calculate the coordinates of all the atoms and hence the conformation of the molecule. The simplest type of potential function, namely the classical potential function is chosen for the calculation. The major advantages of this method are (i) that the starting point need not be close to the actual solution, (ii) that it gives the global minimum, irrespective of the starting point, (iii) that it is very general and can be used for any type of potential function, and (iv) that it does not require the computation of gradients. The results obtained are in very good agreement with those of other workers.     

Radial characteristics of radiation of high-frequency electrodeless lamps

The radial dependences of the radiative characteristics of high-frequency electrodeless lamps (HFELs) using as a working medium either a mixture of mercury and argon or helium have been investigated in experiments and numerical simulations. The intensities of the mercury line at a wavelength of 546.1 nm and the helium line at 587.6 nm have been measured. The measurements were conducted at different points lying on the central chord of the circular end of a cylindrical lamp. As the power of the pumping generator increases, a decrease in the radiation intensity near the axis of the discharge in a mercury vapor HFEL is observed, while, in the helium lamp, on the contrary, the intensity increases. On the basis of models of HFELs developed earlier, we have calculated the radial dependences of the radiation intensity of the mercury line at 546.1 nm and the helium line at 587.6 nm. A satisfactory agreement with the data of experimental measurements has been attained. A comparative analysis has been carried out, and an explanation has been proposed for the difference in the observed radial intensity profiles of these two lines.     

Study of the dependence of the radiative properties of high-frequency electrodeless lamps in an Hg-Ar mixture on the pressure of mercury vapor

The radiative characteristics of high-frequency electrodeless lamps in a mixture of mercury and argon have been studied theoretically and experimentally as functions of the cold spot temperature (the pressure of mercury vapor). The intensity of the mercury lines at 404.7, 435.8, and 546.1 nm, corresponding to the triplet transition (7³ S ₁-6³ P _0,1,2) in the visible spectral region, as well as the intensity of the UV resonance line (6³ P ₁-6¹ S ₀) at 253.7 nm, has been measured. A model describing the physical processes in the discharge plasma and including the kinetics of excited states of mercury and argon atoms has been suggested. The parameters of the discharge plasma and the electromagnetic field have been calculated self-consistently through the numerical solution of the system of equations of electron density and energy balance and population balance of excited levels of argon and mercury atoms, as well as the Maxwell equations. The model developed has allowed us to calculate the intensities of the mercury emission lines at 253.7, 404.7, 435.8, and 546.1 nm and to compare the results with experimental data. The relative intensities of the mercury spectral lines corresponding to the triplet transition 7³ S ₁-6³ P _0,1,2 have been calculated for the first time on the basis of a self-consistent model of the discharge.     

Ligand-free copper nanoparticle promoted N-arylation of azoles with aryl and heteroaryl iodides

A relatively mild, efficient, and inexpensive method for the nucleophilic aromatic substitution of the N–H heterocycles with various aryl and heteroaryl iodides using copper nanoparticles (Cu-NP) is reported. The coupling reaction has been successfully achieved with moderate to good yields.