Degrees of polymerization (DP) and DP distribution of cellouronic acids prepared from alkali-treated celluloses and ball-milled native celluloses by TEMPO-mediated oxidation

Various cellulose II samples, ball-milled native celluloses and ball-milled wood saw dust were subjected to 2,2,6,6-tetramethypyperidine-1-oxyl radical (TEMPO)-mediated oxidation to prepare cellouronic acid Na salts (CUAs). The TEMPO-oxidized products obtained were analyzed by ¹³C-NMR and size-exclusion chromatography (SEC). When the cellulose II samples with degrees of polymerization (DP) of 220–680 were used as the starting materials, the CUAs obtained had weight-average DP (DPw) values of only 38–79. Thus, significant depolymerization occurs on cellulose chains during the TEMPO-mediated oxidation. These DP values of CUAs correspond to the cellulose II crystal sizes along the chain direction in the original cellulose II samples, but not necessarily to their leveling-off DP values. CUAs can be obtained also from ball-milled native celluloses in good yields by TEMPO-mediated oxidation, although their DPw values are lower than about 80. On the other hand, CUA with DPw of about 170 was obtained from ball-milled wood saw dust.     

Analysis of the substituent distribution in the glucosyl units and along the polymer chain of hydroxypropylmethyl celluloses and statistical evaluation

Three hydroxypropylmethyl celluloses (HPMC 1, 2, 3; DS_Me=2.06, 1.99, 2.04; MS_HP=0.21, 0.19, 0.21) have been analyzed with respect to their methyl and hydroxypropyl pattern in the glucosyl units and along the polymer chain. The determination of the methyl pattern in the glycosyl unit was performed by GLC/MS after hydrolysis, reduction, and acetylation, while the distribution of hydroxypropyl residues in the monomers could be analyzed with higher sensitivity including a permethylation step prior to hydrolysis. To determine the distribution of the substituents along the polymer chain, a method developed for hydroxyethylmethyl cellulose (HEMC) was applied. This method comprises random partial acid hydrolysis after perdeuteromethylation and reductive amination with propylamine, followed by N- and O-alkylation, yielding completely alkylated and permanently charged oligosaccharide derivatives. These compounds could be quantitatively analyzed by means of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), since all discrimination effects related to the hydroxyalkyl groups are leveled off by the sample preparation procedure in combination with the choice of a MALDI-TOF instrument. Methyl data deviate to some extent from the random distribution calculated from the monomer composition, but in contrast to methyl cellulose (MC) or HEMC, it is not heterogeneous, but more regular. The distribution of HP groups is random within experimental error as has been found for HEMC as well.     

Studies of the compositions of Pd(II) hydrolysis products

The characterization of the clusters formed on alkaline hydrolysis of [PdCl₄]^2– was performed using¹⁷O,²³Na,³⁵Cl,¹³³Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)₂] _n ·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993.     

Interpretation of relaxation and swelling phenomena in lyocell regenerated cellulosic fibres and textiles associated with the uptake of solutions of sodium hydroxide

The uptake of solutions of sodium hydroxide by lyocell fibre results in a phenomenon in textiles described as swelling–shrinkage. The response of woven fabrics in a tensile stress–relaxation experiment shows two time-dependent processes, corresponding to different mechanisms of pressure development. Rapid diffusion has been assigned to osmotic swelling through the interconnected pore structure of the fibre (D = 6–15 × 10⁻¹² m²/s), which is influenced by the extent of ionization of hydroxyl groups at the pore surfaces. A ratio for the cellulose and water dissociation constants (K_cell/K_w) of 70 provides best agreement with experimental data. A second slower diffusion process (D = 2–10 × 10⁻¹⁴ m²/s) is assigned to transport through the cellulose polymer structure, associated with the Na-cellulose transition. This can be modeled assuming an ion-exchange equilibrium, where the cellulose gel converts reversibly between compact hydrogen and expanded sodium forms, with K = 1.04 × 10¹⁴, in favour of the hydrogen form. The model successfully predicts the concentration dependence of the transition and the movement to higher concentration with external constraint. The slow diffusion process only becomes apparent at high alkali concentrations, as the pores in the fibre collapse due to the expansion of the gel. Continued gel-diffusion is only possible through the polymer phase, which then dominates over fast pore-diffusion.     

Kinetics and Mechanism of Formation and Acid–Catalyzed Decomposition of the [Co(NH3)4CO3]+ Complex Cation in Aqueous Solution

It has been found that the kinetics of acid‐catalyzed hydrolysis of the [Co(NH₃)₄CO₃]⁺ cation follows the rate law –d ln [complex]/d t = k₁K[H⁺]/(1+K[H⁺]) (5 °C < T < 25 °C; 0.0543M < [HClO₄] < 2.7M and I = 1.0M (NaClO₄). The reaction course consists of a rapid pre‐equlibrium protonation followed by a rate determining ring opening process and the subsequent fast release of monodentate carbonato ligand. The changes of the absorbance for the acidic aqueous solution of the [Co(NH₃)₄CO₃]⁺ complex ion proceeded at relevant wavelength in the UV‐Vis region and time course of these changes were analysed according to a programme “Glint” for the consecutive first – order reaction with two experimental rate constants k_fast and k_slow. Finally, the aquation mechanism has been proposed and the effect of ligand coordination mode (bidentate carbonato anion) on complex reactivity has been discussed.     

Analytical Separation of Copper(II), Cobalt(II) and Nickel(II) Using Polymer Bound Anthrantic Acid

Abstract

The preferential complexing tendency of different nietal ions towards chelating agents anchored on a polymer has been used for separation of transition metals. the anthranilic acid group was anchored on the polymeric cellulose back-bone by successive coupling with trifunctional reagent cyanuric chloride, in diozane medium, at pH 7 and 9–10, respectively. This polymer bound chelating agent was used to separate copper(II), nickel(II) and cobalt(II) in the concentration range 1.0–0.1 mmol/L. the separation of a mixture of two components was quantitative using column chromatography.     

Immobilization of glucose oxidase with the blend of regenerated silk fibroin and poly(vinyl alcohol) and its application to a 1,1′- dimethylferrocene-mediating glucose sensor

The structure and properties of the blend of regenerated silk fibroin (RSF) and poly(vinyl alcohol) (PVA) were investigated. The two polymers in the blend are in the state of phase segregation. Infrared (IR) spectra indicate that the RSF in the blend maintains its intrinsic properties, thus, ethanol treatment can transfer silk I structure of RSF to silk II structure. The water absorption property and mechanical property of the blend are improved in comparison with those of RSF. The blend maintains the major merit of RSF, that is, it can immobilize glucose oxidase on the basis of the conformational transition from silk I structure to silk II structure. The properties of the immobilized enzyme are examined. Moreover, the second generation of glucose sensor based on the immobilized enzyme is fabricated and it has a variety of advantages including easy maintenance of enzyme, simplicity of construction, fast response time and high stability.     

Preparation and characterization of Cu(II)-N-salicylideneanthranilic acids,their reduction products and hydrolysis of the Schiff base

Copper (II) complexes ofN-salicylideneanthranilic acid (I) and its derivatives (II, III) as well as their NaBH₄ reduction products, namelyN-(2-hydroxybenzyl) anthranilic acids (IV–VI) have been prepared and their structures have been determined analytically. Tetracoordinated planar structures of the Cu(II) complexes of the Schiff bases and distorted tetrahedral structures of the Cu(II) complexes of compoundsV–VI have been elucidated by ESR and other spectral methods. During the preparation of the complex the hydrolysis of the Schiff base often takes place in the presence of water giving anthranilates and salicylaldehydates of metals to some extent along with the complexes of the Schiff base. The kinetic data for the hydrolysis ofN-salicylideneanthranilic acid (I) in methanol-water solution also are reported.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995.     

Interfacial structure and properties of polyurethane/poly(methylacrylate-co-styrene) coating to regenerated cellulose film

A semiinterpenetrating polymer network (IPN) containing 72 wt % polyurethane (PU) and 6 wt % poly(methylacrylate-co-styrene) [P(MA-St)] was coated onto surfaces of regenerated cellulose (RC) film, which was prepared by coagulating a cellulose cuoxam from bagasse pulp. The interfacial structures, bonding manner, and the strength of the coated film were studied by infrared (IR),¹³C nuclear magnetic resonance (NMR), differential thermal analysis (DTA), transmission electron microscopy (TEM), and electron probe microscopy analysis (EPMA). It was shown that the RC film coated with PU/P(MA-St) has strong interfacial interactions, where covalent and hydrogen bonds are formed across the interface between cellulose and the PU/P(MA-St) coating. The interfacial structure of the coated film is regarded as a shared PU network crosslinked simultaneously with P(MA-St) and cellulose film. The tensile strength, water resistivity, and optical transmission of the coated films were considerably higher than that of the uncoated films. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2495–2501, 1997     

The Crystal and Molecular Structures of Pb(II) Complexes with Furan-2-Carboxylate and Furan-3-Carboxylate Ligands

The crystals of Pb(II) 2-furancarboxylate (title compound I) contain tetrameric structural units Pb₄(2-FCA)₈(H₂O₂) in which four Pb(II) ions are bridged by carboxylate oxygen atoms forming a circular moiety. In addition, pairs of Pb(II) ions are bridged by carboxylate oxygen atoms inside this moiety. The molecular pattern observed in Pb(II) 3-furancarboxylate (title compound II) is polymeric. It consists of Pb(3-FCA)₂(H₂O) structural units bridged by carboxylate oxygen atoms donated by the furan-3-carboxylate (3-FCA) ligands which are bidentate, using both their carboxylate oxygen atoms for chelation. The coordination around Pb(II) ions is eightfold and ninefold including, apart from carboxylate oxygen atoms, a water oxygen atom and oxygen atoms donated by the furan rings of the ligand molecules. Hydrogen bonds with the water molecule as the donor operate between adjacent ligand molecules. The stereochemical activity of the lone 6s ² electron pair on the Pb(II) is observed in title compound II.     

Vinyl addition polymerization of norbornene with cationic (allyl)Ni catalysts: Mechanistic insights and characterization of first insertion products

Several cationic (allyl)Ni(II) complexes were synthesized and shown to be highly active for (2,3)‐vinyl addition polymerization of norbornene to yield polymers with low molecular weight distributions (MWDs) ranging from 1.4–1.9. In all cases slow initiation was followed by rapid propagation which prevents molecular weight control of the poly(norbornene). One of the intermediates in the polymerization process has been identified and characterized by NMR spectroscopy as the first insertion product resulting from the insertion of norbornene into the Ni? C allyl bond in cis‐exo fashion. This insertion product was synthesized independently and NMR studies showed that the first insertion of norbornene into the Ni? C allyl bond is a reversible process. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2560–2573, 2009     

Metathesis polymerization of norbornene and terminal acetylenes catalyzed by bis(acetonitrile) complexes of molybdenum and tungsten

The ring-opening metathesis polymerization (ROMP) of norbornene catalyzed by bis(acetonitrile) molybdenum and tungsten complexes, [M(η³-C₃H₅)Cl(CO)₂(NCMe)₂] (1-Mo: M = Mo, 1-W: M = W), which have two labile acetonitrile ligands, has been investigated. These complexes catalyzed the ROMP of norbornene as a single-component initiator. The highly cis-selective polymerization proceeded in a THF solution (95% for 1-Mo and 96% for 1-W), whereas polymerization in CH₂Cl₂ or toluene resulted in lower cis selectivity. The polymerization of terminal acetylenes using these complexes was also examined. The tungsten complex 1-W showed a high catalytic activity for the polymerization of terminal acetylenes, such as phenyl- and tert-butylacetylene. A highly active catalytic system for the ROMP of norbornene was achieved by the activation of the tungsten complex, 1-W, with one equivalent of phenylacetylene, giving poly(norbornene) with a high molecular weight (M_n = 391 × 10⁴) and a high cis selectivity (cis  89%).     

Updating Insights into the Catalytic Domain Properties of Plant Cellulose synthase (CesA) and Cellulose synthase-like (Csl) Proteins

The wall is the last frontier of a plant cell involved in modulating growth, development and defense against biotic stresses. Cellulose and additional polysaccharides of plant cell walls are the most abundant biopolymers on earth, having increased in economic value and thereby attracted significant interest in biotechnology. Cellulose biosynthesis constitutes a highly complicated process relying on the formation of cellulose synthase complexes. Cellulose synthase (CesA) and Cellulose synthase-like (Csl) genes encode enzymes that synthesize cellulose and most hemicellulosic polysaccharides. Arabidopsis and rice are invaluable genetic models and reliable representatives of land plants to comprehend cell wall synthesis. During the past two decades, enormous research progress has been made to understand the mechanisms of cellulose synthesis and construction of the plant cell wall. A plethora of cesa and csl mutants have been characterized, providing functional insights into individual protein isoforms. Recent structural studies have uncovered the mode of CesA assembly and the dynamics of cellulose production. Genetics and structural biology have generated new knowledge and have accelerated the pace of discovery in this field, ultimately opening perspectives towards cellulose synthesis manipulation. This review provides an overview of the major breakthroughs gathering previous and recent genetic and structural advancements, focusing on the function of CesA and Csl catalytic domain in plants.     

Synthesis and characterization of para-nitro substituted 2,6-bis(phenylimino)pyridyl Fe(II) and Co(II) complexes and their ethylene polymerization properties

Four iron(II) and cobalt(II) complexes ligated by 2,6-bis(4-nitro-2,6-R₂-phenylimino)pyridines, LMCl₂ (1: R = Me, M = Fe; 2: R = iPr, M = Fe; 3: R = Me, M = Co; 4: R = iPr, M = Co) have been synthesized and fully characterized, and their catalytic ethylene polymerization properties have been investigated. Among these complexes, the iron(II) pre-catalyst bearing the ortho-isopropyl groups (complex 2) exhibited higher activities and produced higher molecular weight polymers than the other complexes in the presence of methylaluminoxane (MAO). A comparison of 2 with the reference non-nitro-substituted catalyst (2,6-bis(2,6-diisopropylphenylimino)pyridyl)FeCl₂ (FeCat 5) revealed a modest increase of the catalytic activity and longer lifetime upon substitution of the para-positions with nitro groups (activity up to 6.0 × 10³ kg mol⁻¹ h⁻¹ bar⁻¹ for 2 and 4.8 × 10³ kg mol⁻¹ h⁻¹ bar⁻¹ for 5), converting ethylene to highly linear polyethylenes with a unimodal molecular weight distribution around 456.4 kg mol⁻¹. However, the iron(II) pre-catalyst 1 on changing from ortho-isopropyl to methyl groups displayed much lower activities (over an order of magnitude) than 2 under mild conditions. As expected, the cobalt analogues showed relatively low polymerization activities.     

Hydrolysis and DFT structural studies of dinuclear Zn(II) and Cu(II) macrocyclic complexes of m-12N3O-dimer and the effect of pH on their promoted HPNP hydrolysis rates

The synthesis of the ligand, m-12N₃O-dimer (1,3-bis(1-oxa-4,7,10-triazacyclododecan-7-yl)methyl)benzene, L), and the stability and hydrolysis constants of its dinuclear Zn(II) and Cu(II) complexes are reported, in addition to the effect of pH on HPNP (2-hydroxypropyl-4-nitrophenylphosphate) hydrolysis reaction rates promoted by these complexes. Various structural possibilities of the [Zn₂L] and [Cu₂L] hydrolytic species derived from solution equilibrium modeling are predicted from density functional theory (DFT) studies to correlate with the promoted HPNP hydrolysis reaction rates and to establish the structure–function–reactivity relationship. Upon deprotonation [Zn₂L(OH)]³⁺ tends to form a structure with a “closed-form” conformation where it is not possible for para-isomers. At pH >8, the formation of the closed-form [Zn₂L(OH)₂]²⁺ and [Zn₂L(μ-OH)(OH)₂]⁺ species led to faster promoted HPNP hydrolysis rates than the [Zn₂L(OH)]³⁺ species. On the other hand, the observed rates of the Cu₂L-promoted HPNP hydrolysis reaction were much slower than those of the [Zn₂L]-promoted ones due to formation of the inactive, di-μ-OH^? bridged closed-form [Cu₂L(μ-OH)₂]²⁺ structure at high pH. The effects of solvent molecules and the use of higher DFT computation levels, i.e., M06 and M06–2X, in conjunction with cc-pVDZ and cc-pVTZ basis sets on the DFT-predicted structures for both [Cu(12N₄)(H₂O)]²⁺ and [Zn(12N₃O)(H₂O)₂]²⁺ complexes were also evaluated and compared with those using the B3LYP/6–31G* method.     

Voltammetric Sensing of Amino Acids in the Presence of Cu(II) in Acidic and Alkaline Solutions

A number of amino acids have been determined at carbon film electrodes in the presence of copper. Strongly acidic, 0.1 M HCl, in the presence of 0.1 mM Cu(II), as well as alkaline, 0.1 M NaOH, solution permit successful measurement of individual amino acids, clearer separation between oxidation of Cu and Cu‐complexes occurring in alkaline solution. Electrochemical impedance showed that Cu(II) facilitates charge transfer, particularly in alkaline medium. Square wave voltammetry with preconcentration increased the response compared to linear sweep voltammetry. Protein hydrolysis rates were monitored through determination of amino acids produced by decomposition, injecting samples into alkaline electrolyte solution.