Synthesis of poly(norbornene-g-ɛ-caprolactone) copolymers by sequential controlled ring opening polymerization

Summary Poly(norbornene-g-ɛ-caprolactone) copolymers have been prepared by the “grafting from” technique. Well controlled polynorbornene containing 5% acetate pendant groups has been firstly synthesized by ruthenium complex-mediated ring opening metathesis polymerization. The acetate groups have been derivatized into aluminum alkoxides by hydrolysis into alcohol followed by reaction of the alcohol with triethylaluminum. The two polymerization steps are under complete control, so that graft copolymers have been synthesized with a narrow molecular weight distribution and are free from any detectable traces of the parent homopolymers as stated by selective fractionation experiments. These original copolymers have been characterized by SEC, FTIR, ¹H NMR, DSC, TGA. Received: 28 January 1998/Revised version: 14 April 1998/Accepted: 14 April 1998     

Microstructure of bacterial poly(β-hydroxybutyrate-co-β-hydroxyvalerate) by FAB mass-spectrometry

Summary Bacterially synthesized Poly (-hydroxybutyrate-co--hydroxyvalerate), P(HB-co-HV), with different compositions were analyzed by NMR spectroscopy and HPLC-mass spectrometry. Partial methanolysis or partial ammonolysis of P(HB-co-HV) has been performed, the oligomers obtained were separated by high-performance liquid chromatography (HPLC) and identified by fast atom bombardment mass spectrometry, (FAB-MS). The normalized intensities of oligomer peaks provided an estimate of the copolymer composition and of the sequence distribution of monomeric units. The interpretation of the data indicated that the sequence distributions of all samples were statistically random (Bernoullian model), and permited the detection in one sample, of traces of pure poly(-hydroxybutyrate), (PHB).     

Binuclear rhodium(III) and iridium(III) monoselenocarboxylates: Synthesis,spectroscopy and structure of an ortho-metallated iridium complex featuring an IrCCC(μ-Se) chelate ring

Monoselenocarboxylate–bridged binuclear complexes of Rh^III and Ir^III, [(Cp1MCl)₂(μ-SeCOAr)₂] (1) (M = Rh or Ir; Cp1 = pentamethylcyclopentadienyl; Ar = Ph, C₆H₄Me–4), have been isolated either by the reaction between [Cp1₂M₂(μ-Cl)₂Cl₂] with KSeCOAr in acetonitrile or by treatment of [Cp1MCl(solvent)₂][PF₆] with KSeCOAr in acetone. The novel binuclear complexes, [Cp1IrCl(μ-SeCOAr)(κ²-SeCOC₆H₃R–)IrCp1] (2) (R = H or Me-4) with ortho-metallation at one of the iridium centres have been isolated following the use of excess AgPF₆. The single crystal structure of [Cp1IrCl(μ-SeCOC₆H₅)(κ²-SeCOC₆H₄–)IrCp1] (2a) exhibits two phenylcarboselenolate moieties situated in syn fashion with respect to the “Ir₂Se₂” plane, one of which leans towards the metal centre in order to undergo ortho-metallation after iridium–chlorine bond dissociation.     

Osmium(VIII) catalyzed oxidation of a sulfur containing amino acid—a kinetics and mechanistic approach

The kinetics of osmium (VIII) catalyzed oxidation of DL-methionine by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm^?3 was studied spectrophoto-metrically. The reaction between hexacyanoferrate(III) and DL-methionine in alkaline medium exhibits 2:1 stoichiometry (2HCF:DL-methionine). The reaction is of first order each in [HCF] and [Os(VIII)], less than unit order in [alkali] and zero order for [DL-methionine]. The decrease in dielectric constant of the medium increases the rate of the reaction. The added products have no effect on the rate of reaction. The main products were identified by spot test. A free radical mechanism has been proposed. In a prior equilibrium step Os(VIII) binds to OH^? species to form a hydroxide species and reacts with [Fe(CN)₆]^3? in slow step to form an intermediate species(C₁). This reacts with a molecule of DL-methionine in a fast step to give the sulfur radical cation of methionine and yields the sulfoxide product by reacting with another molecule of [Fe(CN)₆]^3?. The rate constant of the slow step of the mechanism is calculated. The activation parameters with respect to slow step of the mechanism are evaluated and discussed.     

Silarylene-containing poly(ether-amide)s obtained by Yamazaki–Higashi phosphorylation technique: use of bis(4-(4-aminophenoxy)phenyl)ethylmethyl silane

Aromatic poly(ether-amide)s (PEAs) based on -(R₁,R₂)diphenylsilane- and oxyether units were synthesized by direct polycondensation of a diamine and two dicarboxylic acids. For this, the diamine bis(4-(4-aminophenoxy)phenyl)ethylmethylsilane was obtained by reduction of the respective dinitro compound, which was synthesized by nucleophilic aromatic halogen displacement from 1-fluoro-4-nitrobenzene with bis(4-hydroxyphenyl)ethylmethylsilane in basic medium. New silicon-containing aromatic diamine and the PEAs were characterized by elemental analysis, FT-IR, ¹H, ¹³C and ²⁹Si NMR spectroscopy and the results were in agreement with the proposed structures. The incorporation of aliphatic units such as methyl and/or ethyl groups on the silicon atoms affected positively the solubility of the PEAs in organic polar solvents. When their thermal and optical properties were compared with two PEAs of similar structure, containing phenyl groups bonded to the silicon atoms, it was observed a decrease of the glass transition temperature and transmittance values, maintaining a high thermal resistance.     

Stereospecific formation of a ternary complex of (S)-α,β-fluoromethylene-dATP with DNA pol β

The influence of water: crystallization of (R/S)-α,β-CHF-dATP with the preorganized pol β-DNA complex shows that (S)-α,β-CHF-dATP is preferentially bound to the active site with the C=F fluorine proximal to a structural water bound to Asp276.     

Production of (S)-β-Nitro Alcohols by Enantioselective C−C Bond Cleavage with an R-Selective Hydroxynitrile Lyase

Hydroxynitrile lyase (HNL)-catalysed stereoselective synthesis of β-nitro alcohols from aldehydes and nitroalkanes is considered an efficient biocatalytic approach. However, only one S-selective HNL—Hevea brasiliensis (HbHNL)—exists that is appropriate for the synthesis of (S)-β-nitro alcohols from the corresponding aldehydes. Further, synthesis catalysed by HbHNL is limited by low specific activity and moderate yields. We have prepared a number of (S)-β-nitro alcohols, by kinetic resolution with the aid of an R-selective HNL from Arabidopsis thaliana (AtHNL). Optimization of the reaction conditions for AtHNL-catalysed stereoselective C−C bond cleavage of racemic 2-nitro-1-phenylethanol (NPE) produced (S)-NPE (together with benzaldehyde and nitromethane, largely from the R enantiomer) in up to 99 % ee and with 47 % conversion. This is the fastest HNL-catalysed route known so far for the synthesis of a series of (S)-β-nitro alcohols. This approach widens the application of AtHNL for the synthesis not only of (R)- but also of (S)-β-nitro alcohols from the appropriate substrates. Without the need for the discovery of a new enzyme, but rather by use of a retro-Henry approach, it was used to generate a number of (S)-β-nitro alcohols by taking advantage of the substrate selectivity of AtHNL.     

A luminescent 2,2′-bipyridyl tricarbonyl rhenium(I) complex containing a non-bridging dicyanamide ligand

fac-(bpy)Re(CO)₃CF₃SO₃ reacts with sodium dicyanamide in THF/MeOH/H₂O to give fac-(bpy)Re(CO)₃N(CN)₂ (1) in 81% yield. Complex 1 was characterized spectroscopically and electrochemically using NMR, IR, UV–Vis, fluorescence and cyclic voltammetry. Complex 1 crystallizes in the P2₁/c space group with a = 7.2004(3) Å, b = 12.9547(5) Å, c = 16.8523(6) Å, β = 101.989(1) °, and Z = 4. Photophysical measurements indicate the π-acceptor ability of N(CN)₂⁻ as equivalent to that of the 4-N,N-dimethylaminopyridine ligand. Strong luminescence is observed in solution at room temperature and in 4:1 ethanol:methanol matrices at 77 K attributed to the ³MLCT state.     

Cleavage of the C–N bond of a peptide group by a copper(II)-peroxide adduct with an η1-coordination mode

We have obtained clear evidence that a copper(II)-peroxide adduct with an η¹-coordination mode can cleave the C–N bond of a peptide group and hydroxylate the alkyl group nearby; this may provide helpful information for elucidation of the reaction mechanism of PAM, peptidylglycine α-amidating monooxygenase.     

The encapsulation of [Cu(en)2]2+ (en=ethylenediamine) by a novel three-dimensional CuII–MoIV bimetallic porous coordination polymer containing zigzag-ladder structure

The neutral three-dimensional cyano-bridged bimetallic coordination polymer, {[Cu(en)₂][Cu(en)][Mo(CN)₈]}_n·4nH₂O (en=ethylenediamine), has been synthesized and characterized. X-ray study shows that the asymmetric unit of the three-dimensional Cu(II)–Mo(IV) polymeric assembly consists of two half [Cu(en)₂]²⁺ cations, a [Cu(en)]²⁺ cation and a [Mo(CN)₈]⁴⁻ ion, together with four water molecules. The latter Cu site is coordinated by two N atoms from an en ligand and by three cyanides in a distorted square-pyramidal environment. The Cu(II) ions of the two [Cu(en)₂]²⁺ cations on the centers of inversion reside in an elongated octahedral geometry, and one of the [Cu(en)₂]²⁺ cations is encapsulated in a ‘box’ formed by two pairs of co-lateral Cu₂Mo₂(CN)₄ 12-membered macrocyclic units. The Mo(VI) atom is coordinated by eight cyanides in an irregular square antiprism. Five of these acting as bridging units connect the Mo and the three Cu atoms to form an infinite three-dimensional porous network containing a zigzag-ladder structure.     

Reaction Pathways for the Enzymatic Degradation of Poly(Ethylene Terephthalate): What Characterizes an Efficient PET-Hydrolase?

Bioprocessing of polyester waste has emerged as a promising tool in the quest for a cyclic plastic economy. One key step is the enzymatic breakdown of the polymer, and this entails a complicated pathway with substrates, intermediates, and products of variable size and solubility. We have elucidated this pathway for poly(ethylene terephthalate) (PET) and four enzymes. Specifically, we combined different kinetic measurements and a novel stochastic model and found that the ability to hydrolyze internal bonds in the polymer (endo-lytic activity) was a key parameter for overall enzyme performance. Endo-lytic activity promoted the release of soluble PET fragments with two or three aromatic rings, which, in turn, were broken down with remarkable efficiency (k_cat/K_M values of about 10⁵ M⁻¹s⁻¹) in the aqueous bulk. This meant that approximatly 70 % of the final, monoaromatic products were formed via soluble di- or tri-aromatic intermediates.     

First complex containing a Pd2(μ2-NCPh2)2 functional group

Synthesis of the azavinylidene-bridged compound anti-[{Pd(C₆F₅)(t-BuNC)(μ-NCPh₂)}₂] is described. The molecular structure reveals that the core of the molecule is formed by a Pd₂N₂ skeleton in a bent configuration.     

Strong and Specific Recognition of CAG/CTG Repeat DNA (5’-dWGCWGCW-3’) by a Cyclic Pyrrole-Imidazole Polyamide

Abnormally expanded CAG/CTG repeat DNA sequences lead to a variety of neurological diseases, such as Huntington's disease. Here, we synthesized a cyclic pyrrole-imidazole polyamide (cPIP), which can bind to the minor groove of the CAG/CTG DNA sequence. The double-stranded DNA melting temperature (T_m) and surface plasmon resonance assays revealed the high binding affinity of the cPIP. In addition, next-generation sequencing showed that the cPIP had high specificity for its target DNA sequence.     

Synthesis of amphiphilic macrocyclic graft copolymer consisting of a poly(ethylene oxide) ring and multi-poly(?-caprolactone) lateral chains

A series of amphiphilic macrocyclic graft copolymers composed of a hydrophilic poly(ethylene oxide) as ring and hydrophobic poly(?-caprolactone) as lateral chains with different grafting lengths and densities of side chains were prepared by a combination of anionic ring-opening polymerization and coordination-insertion ring-opening polymerization. The anionic ring-opening copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was carried out first using triethylene glycol and diphenylmethyl potassium (DPMK) as co-initiators, and a linear α,ω-dihydroxyl poly(ethylene oxide) with pendant protected hydroxymethyls (l-poly(EO-co-EEGE)) was obtained. The monomer reactivity ratios of these compounds are r_1(EO) = 1.20 ± 0.01 and r_2(EEGE) = 0.76 ± 0.02, respectively. Then the ring closure of l-poly(EO-co-EEGE) was achieved via an ether linkage by reaction with tosyl chloride (TsCl) in the presence of solid KOH. The crude cyclized product containing the linear chain-extended polymer was hydrolyzed in acidic conditions first and then purified by treating with α-CD. The pure cyclic copolymer of EO and glycidol (Gly) with multipendant hydroxymethyls [c-poly(EO-co-Gly)] as the macroinitiator was used further to initiate the ring-opening polymerization of ?-caprolactone (CL), and a series of amphiphilic macrocyclic graft copolymers c-PEO-g-PCL were obtained. The final products and intermediates were characterized by GPC, NMR and MALDI-TOF in detail.     

Biological effects of poly(ethylene glycol) on the microbial poly(β-hydroxyalkanoates) produced by pseudomonads microorganisms

Poly(ethylene glycol) of M_n 200 g/mol (PEG-200) was added to cultivation media of Pseudomonas oleovorans and Pseudomonas putida during fermentation. The carbon source and the medium used were sodium octanoate and medium E*, respectively. It was discovered that PEG-200 can control product molecular weight as well as cell productivity for both microorganisms. However, PEG-200 had no significant effect on the polymer compositions. The introduction of PEG-200 in the second-stage culture for 24 hr did not result in any notable cellular toxicity-measured in terms of colony forming unit/mL. Increasing the PEG-200 concentration to 8%, however, caused a decrease in the total polymer yield, the cell productivity as the well as M_n values. Gas chromatography analysis of products indicated that the major repeat units were β-hydroxycaproate, β-hydroxyoctanoate, and β-hydroxydeca noate. Thus, this work initiates new research opportunities for the control of product molecular weight for in-vivo microbial polymer synthetic reactions.     

Removal of Copper(II) from a Concentrated Sulphate Medium by Cloud Point Extraction Using an N,N′-Bis(salicylaldehyde)Ethylenediimine Di-Schiff Base Chelating Ligand

Various chelating ligands have been investigated for the cloud point extraction of several metal ions. However, limited studies on the use of the Schiff base ligands have been reported. In this work, cloud point extraction behavior of copper(II) with N,N′‐bis(salicylaldehyde)Ethylenediimine Schiff base chelating ligand, (H₂SALEN), was investigated in aqueous concentrated sulphate medium. The extraction process used is based on the formation of hydrophobic H₂SALEN–copper(II) complexes that are solubilized in the micellar phase of a non‐ionic surfactant, i.e. ethoxylated (9.5EO) tert‐butylphenol. The copper(II) complexes are then extracted into the surfactant‐rich phase above cloud point temperature. Different parameters affecting the extraction process of Cu(II), such as equilibrium pH, extractant concentration, and non‐ionic surfactant concentration were explored. The extraction of Cu(II) was studied in the pH range of 2–11. The results obtained showed that it was profoundly influenced by the pH of the aqueous medium. The concentration factor, C_f, of about 17 with extraction efficiency of E % ≈100 was achieved. The stoichiometry of the extracted complex of copper(II) was ascertained by the Yoe–Jones method to give a composition of 1:1 (Cu:H₂L). The optimum conditions of the extraction‐removal have been established as the following: (1) 1.86 × 10^?3 mol/L ligand; (2) 3 wt% surfactant; (3) pH of 8 (4) 0.5 mol/L Na₂SO₄ and (5) temperature of 60 °C.