CL 6B Research Articles

Development of an effective method for purifying trypsin using a recombinant inhibitor

A trypsin affinity material was prepared by covalently immobilizing buckwheat trypsin inhibitor (BTI) on epichlorohydrin-activated cross-linked agarose gel (Selfinose CL 6 B). The optimal conditions for activating Selfinose CL 6 B were 15 % epichlorohydrin and 0.8 M NaOH at 40 °C for 2 h. The optimal pH for immobilizing BTI was 9.5. BTI-Sefinose CL 6 B showed a maximum adsorption capacity of 2.25 mg trypsin/(g support). The material also displayed good reusability, retaining over 90 % of its initial adsorption capacity after 30 cycles. High-purity trypsin was obtained from locust homogenate using BTI-Selfinose CL 6 B through one-step affinity chromatography. The molecular mass and Km value of locust trypsin were determined as 27 kDa and 0.241 mM using N-benzoyl-DL-arginine-nitroanilide as substrate. The optimal temperature and pH of trypsin activity were 55 °C and 9.0, respectively. The enzyme exhibited good stability in the temperature range of 30–50 °C and pH range of 4.0–10.0. BTI-Selfinose CL 6 B demonstrates potential application in the preparation of high-purity trypsin and the discovery of more novel trypsin from various species.

Rational design of biocatalysts based on covalent immobilization of acylase enzymes

Acylases catalyze the hydrolysis of amide bonds. Penicillin G acylase (PGA) is used for the semi-synthesis of penicillins and cephalosporins. Although protein immobilization increases enzyme stability, the design of immobilized systems is difficult and usually it is empirically performed. We describe a novel application of our strategy for the Rational Design of Immobilized Derivatives (RDID) to produce optimized acylase-based immobilized biocatalysts for enzymatic bioconversion. We studied the covalent immobilization of the porcine kidney aminoacylase-1 onto aldehyde-based supports. Predictions of the RDID1.0 software and the experimental results led to the selection of glyoxyl-Sepharose CL 4B support and pH 10.0. One of the predicted clusters of reactive amino groups generates an enzyme-support configuration with highly accessible active sites, contributing with 82% of the biocatalyst’s total activity. For Escherichia coli PGA, the predictions and experimental results show similar maximal amounts of immobilized protein and activity at pH 8.0 and 10.0 on glyoxyl-Sepharose CL 10B. However, thermal stability of the immobilized derivative is higher at pH 10.0 due to an elevated probability of multipoint covalent attachment. In this case, two clusters of amino groups are predicted to be relevant for PGA immobilization in catalytically competent configurations at pH 10.0, showing accessible active sites and contributing with 36% and 44% of the total activity, respectively. Our results support the usefulness of the RDID strategy to model different protein engineering approaches (site-directed mutagenesis or obtainment of fusion proteins) and select the most promising ones, saving time and laboratory work, since the in silico-designed modified proteins could have higher probabilities of success on bioconversion processes.

Halogenated Dihydropyrrol-2-One Molecules Inhibit Pyocyanin Biosynthesis by Blocking the Pseudomonas Quinolone Signaling System.

Quorum-sensing (QS) systems of Pseudomonas aeruginosa are involved in the control of biofilm formation and virulence factor production. The current study evaluated the ability of halogenated dihydropyrrol-2-ones (DHP) (Br (4a), Cl (4b), and F (4c)) and a non-halogenated version (4d) to inhibit the QS receptor proteins LasR and PqsR. The DHP molecules exhibited concentration-dependent inhibition of LasR and PqsR receptor proteins. For LasR, all compounds showed similar inhibition levels. However, compound 4a (Br) showed the highest decrease (two-fold) for PqsR, even at the lowest concentration (12.5 µg/mL). Inhibition of QS decreased pyocyanin production amongst P. aeruginosa PAO1, MH602, ATCC 25619, and two clinical isolates (DFU-53 and 364707). In the presence of DHP, P. aeruginosa ATCC 25619 showed the highest decrease in pyocyanin production, whereas clinical isolate DFU-53 showed the lowest decrease. All three halogenated DHPs also reduced biofilm formation by between 31 and 34%. The non-halogenated compound 4d exhibited complete inhibition of LasR and had some inhibition of PqsR, pyocyanin, and biofilm formation, but comparatively less than halogenated DHPs.

A new thermostable rhizopuspepsin: Purification and biochemical characterisation

The new thermostable fungal aspartic protease was produced through solid-state fermentation from Rhizopus azygosporus (MTCC 10195). The protease was purified by a three-tandem steps of ammonium sulfate precipitation (25−65 % saturation), ion exchange (DEAE sepharose CL 6B) chromatography, and gel filtration (Sephacryl S 200) chromatography. The optimum pH and temperature for protease activity were 4 and 52 ± 1.8 °C, respectively. The enzyme was unusually thermostable, as it retained 50 % of its activity beyond 85 °C after 20 min of incubation. The apparent molecular weight was 33.2 ± 2.3 kDa with a final specific activity of 86.6 U/mg. The enzyme was rich in β sheets (63 %) and was inhibited by pepstatin A, indicating that it is an aspartic protease. MS/MS analysis revealed the enzyme is an endopeptidase cleaving the C-terminus of Phe, Leu, Lys, Val, His, Glu, Met, and Tyr. Amino-terminal sequencing, coupled with in-gel trypsin digestion and MS analysis revealed that the enzyme was being reported for the first time with “experimental evidence at protein-level”.

Modeling and experimental validation of covalent immobilization of Trametes maxima laccase on glyoxyl and MANA-Sepharose CL 4B supports, for the use in bioconversion of residual colorants.

Our novel strategy for the rational design of immobilized derivatives (RDID) is directed to predict the behavior of the protein immobilized derivative before its synthesis, by the usage of mathematic algorithms and bioinformatics tools. However, this approach needs to be validated for each target enzyme. The objective of this work was to validate the RDID strategy for covalent immobilization of the enzyme laccase from Trametes maxima MUCL 44155 on glyoxyl- and monoaminoethyl-N-aminoethyl (MANA)-Sepharose CL 4B supports. Protein surface clusters, more probable configurations of the protein-supports systems at immobilization pHs, immobilized enzyme activity, and protein load were predicted by RDID1.0 software. Afterward, immobilization was performed and predictions were experimentally confirmed. As a result, the laccase-MANA-Sepharose CL 4B immobilized derivative is better than laccase-glyoxyl-Sepharose CL 4B in predicted immobilized derivative activity (63.6% vs. 29.5%). Activity prediction was confirmed by an experimentally expressed enzymatic activity of 68%, using 2,6-dimethoxyphenol as substrate. Experimental maximum protein load matches the estimated value (11.2±1.3 vs. 12.1protein mg/support mL). The laccase-MANA-Sepharose CL 4B biocatalyst has a high specificity for the acid blue 62 colorant. The results obtained in this work suggest the possibility of using this biocatalyst for wastewater treatment.

Evaluating the ion exchange chromatography for matrix-assisted PEGylation and purification of consensus interferon.

Scientists have implemented protein-PEGylation technology for boosting-up the pharmacokinetics and stability of recombinant therapeutic proteins. In the present study, (a) matrix-assisted PEGylation was compared with solution-phase PEGylation and (b) matrix-assisted PEGylation was performed with different ion exchange resins for impact of chromatography medium on yield and purity of PEGylated product. DEAE Sepharose CL 6B, DEAE Fracto gel, and Macro cap Q ion exchange chromatography medium were compared for on column PEGylation and purification of cIFN. A MSC-PEG of 12.0 KDa was selected. cIFN was bound to ion exchange medium, and PEG solution was passed through resin for 180 Min, and protein was eluted by sodium chloride linear gradient. Yield and purity for mono-PEGylated cIFN with Macro cap Q matrix was 75% and 99%, respectively, whereas for DEAE Sepharose was 45% and 60%. DEAE Fracto gelTM purity was 85% with 50% yield of mono-PEGylated cIFN. Further investigation of in vitro biological activities demonstrated that about 30% antiviral activity was reduced as compared to unmodified cIFN. However, thermal stability was significantly improved. The present study proved that matrix-assisted PEGylation can improve the yield and purity of mono-PEGylated product, and Macro Cap resin provided the highest yield of a homogeneous product. In present study, (a) matrix-assisted PEGylation was compared with solution-phase PEGylation and (b) matrix-assisted PEGylation was performed with different ion exchange resins for impact of chromatography medium on yield and purity of PEGylated product. Matrix-assisted PEGylation increases the yield of mono-PEGylated product and further Macro CapTM produced highest yield and purity of PEGylated cIFN.

Screening and Immobilization of Interfacial Esterases from Marine Invertebrates as Promising Biocatalyst Derivatives.

Interfacial esterases are useful enzymes in bioconversion and racemic mixture resolution processes. Marine invertebrates are few explored potential sources of these proteins. In this work, aqueous extracts of 41 species of marine invertebrates were screened for esterase, lipase, and phospholipase A activities, being all positive. Five extracts (Stichodactyla helianthus, Condylactis gigantea, Stylocheilus longicauda, Zoanthus pulchellus, and Plexaura homomalla) were selected for their activity values and immobilized on Octyl-Sepharose CL 4B support by interfacial adsorption. The selectivity of this immobilization method for interfacial esterases was evidenced by immobilization percentages ≥ 94% in almost all cases for lipase and phospholipase A activities. Six pharmaceutical-relevant esters (phenylethyl butyrate, ethyl-2-hydroxy-4-phenyl-butanoate, 2-oxyranylmethyl acetate (glycidol acetate), 7-aminocephalosporanic acid, methyl-prostaglandin F2α, and methyl-6-metoxy-α-methyl-2-naphtalen-acetate -naproxen methyl ester-) were bioconverted by at least three of these biocatalysts, with the lowest conversion percentage of 24%. In addition, three biocatalysts were used in the racemic mixture resolution of three previous compounds. The S. helianthus-derived biocatalyst showed the highest enantiomeric ratios for glycidol acetate (2.67, (S)-selective) and naproxen methyl ester (8.32, (R)-selective), and the immobilized extract of S. longicauda was the most resolutive toward the ethyl-2-hydroxy-4-phenyl-butanoate (8.13, (S)-selective). These results indicate the relevance of such marine interfacial esterases as immobilized biocatalysts for the pharmaceutical industry.

Purification and characterization of exo-β-1,4-glucosaminidase produced by chitosan-degrading fungus, Penicillium sp. IB-37-2A.

Chitosan-degrading fungal strain, Penicillium sp. IB-37-2A, produced mainly extracellular chitosanolytic enzymes under submerged agitating cultivation in presence of soluble chitosan or colloidal chitin as main carbon source. Significant N-acetyl-β-D-glucosaminidase activity (8-18 × 103 U·ml-1) was also detected in culture filtrate of the fungal strain. Alone major exo-chitosanase from culture filtrate of Penicillium sp. IB-37-2A was purified in 46-fold using ultrafiltration, affinity sorption on colloidal chitosan and hydrophobic chromatography on Phenyl-Sepharose CL 4B and characterized. Molecular weight of the exo-β-1.4-glucosaminidase is 41kDa according to SDS-PAGE. The purified enzyme has optima pH and temperature 4.0 and 50-55°C, respectively, pI 4.9; it is stable under pH 3.0-8.0 and 55°C. Activity of the enzyme is strongly inhibited by 1mM Hg2+ and Ag+, in less degree-10mM Cu2+, Zn2+, Ni+ and Fe2+, slightly activated-with 1mM Mg2+, 10mM Ca2+, tween-80 (10mM) and Triton X-100 (1mM). Viscosimetric assay confirmed reported earlier exo-splitting manner of the enzyme activity. Soluble chitosan (deacetylation degree (DD) 80-85%) is most rapidly hydrolyzed by the enzyme (Vmax = 7.635µM × min-1 × mg-1, KM ~ 0.83mg/ml). Purified exo-chitosanase also degraded laminarin, β-glucan, colloidal chitin and showed significant chitobiohydrolase activity (V ~ 50µM × ml-1 × min-1 for pNP-GlcNAc2) but no hydrolyzed CMC, cellulose, xylan and galactomannan. It is found that crude and partially purified exo-β-1.4-glucosaminidase inhibits in vitro the growth of some phytopathogenic fungi that is first report for antifungal activity of exo-chitosanase.

Unusual C-O bond cleavage of aromatic ethers in ruthenium complexes bearing a 2-alkoxypyridyl fragment.

Two tetradentate (NNOP) ruthenium products [{RO-C5H3N-C5H3N-CH(O)-C6H4-PPh2}Ru(CO)(PPh3)]Cl (1: R = Me; 3: R = Ph) were isolated by the reactions of the corresponding ligands with RuHCl(PPh3)3(CO). Complex 1 could also be transformed into 2 when heated in THF, through C-OMe bond cleavage. The mechanism of the unusual C-O cleavage in complex 1 was investigated, and the results indicate that it is an SN2 mechanism through the attack of trace amounts of neutral H2O. In contrast, in the presence of KOH, the reaction switches to an SNAr chemistry. The bidentate ruthenium isomers [{CH3O-C5H3N-C5H4N}RuH(CO)(PPh3)2]Cl (4a and 4b) could undergo similar C-O cleavage, affording product {O-C5H3N-C5H4N}RuH(CO)(PPh3)2 (5), which reacted with HCl to generate complex [{HO-C5H3N-C5H4N}RuH(CO)(PPh3)2]Cl (6). These complexes were tested as catalysts for β-alkylation of secondary alcohols with primary alcohols, and a series of β-alkylated 1-phenylethanol derivatives were isolated in high yields.

Amberlite IR-120 (H) mediated “on water” synthesis of fluorescent Ruthenium(II)-arene 8-hydroxyquinoline complexes for cancer therapy and live cell imaging

A series of Ruthenium-Quinolinol complexes (3a–d &4a–d) has been synthesized by employing a simple, efficient and environmental friendly condition. Catalytic role of Amberlite IRA-120(H) has been demonstrated. The structures of the new compounds were elucidated by the analysis of spectroscopic data. The stability of these complexes was measured by UV spectroscopy & time dependent NMR spectroscopy. These newly developed complexes were represented as potential anticancer agent against human breast carcinoma cell line (MCF-7), human Epitheloid Cervix Carcinoma (HeLa), human lung adenocarcinoma epithelial cell line (A549) and human colon cancer cell line (Caco-2). Most of the ruthenium complexes showed higher anticancer activity in MCF-7, HeLa and Caco-2 cell lines than cisplatin. A high selectivity (9–28 folds) was observed with these newly developed organoruthenium compounds in human cancer cell lines (MCF-7, HeLa and Caco-2) with respect to normal fibroblast cell line (MRC-5). Complex [(η6-hexamethylbenzene)RuCl(κ2-O,N-5-chloro-HyQ)]·Cl (4b), [(η6-hexamethylbenzene)RuCl(κ2-O,N-5,7-dibromo-HyQ)]·Cl (4c) and [(η6-hexamethylbenzene)RuCl(κ2-O,N-5-chloro-7-iodo-HyQ)]·Cl (4d) exhibited best cytotoxicity profiles in three reported human cancer cell lines (MCF-7, HeLa, Caco-2). Cellular imaging study was also performed with these newly developed organoruthenium compounds. Compound 4c might be utilized for cancer theranostic agents because of its significant quantum yield in water, high potency, selectivity and high cellular uptake in cancer cell lines.

Substituent Effects in the Cyclization of Yne-Diols Catalyzed by Gold Complexes Featuring L2/Z-Type Diphosphinoborane Ligands

Gold(I) complexes featuring Z-type ligands introducing electron-withdrawing groups (EWG), Au(DPBF)Cl (4a) and Au(DPBCl)Cl (4b) (DPB = diphosphine-boron), have been synthesized and structurally characterized. These studies suggest that increasing the electron-withdrawing properties of the boron phenyl substituent only results in minor structural changes of the gold complexes. These complexes can be converted into Au(DPBF)SbF6 and Au(DPBCl)SbF6 by treatment of 4a,b with AgSbF6. The cationic complexes show interesting catalytic properties and readily promote the cyclization of yne-diols into unprecedented dioxabicyclo[3.2.2] derivatives.

Hemocytes and hemocytic responses in the mole crab Emerita emeritus (Linnaeus 1767).

The mole crab, Emerita emeritus, collected from the sandy shores of a Chennai beach, was investigated for cellular immune responses based on the morphology and defensive reactions of the circulating haemocytes. Three haemocyte morphotypes were identified using light and electron microscopy, and separated in a discontinuous percoll gradient. A phagocytosis study using human B erythrocyte as a target cell under phase-contrast optics showed that granular and semi-granular haemocytes were phagocytic, and this response was enhanced by using serum (opsonin)-coated human B erythrocyte in unfractionated and fractionated haemocytes. Observation of TEM image of phagocytosis revealed that the initial recognition and binding of the target cell was restricted to granular and semigranular haemocytes, which were lacking with hyaline cells. However, the encapsulation of DEAE Sepharose CL 6B beads, either untreated or coated with serum (opsonin), was restricted to hyaline cells. This suggests the occurrence of two cell lines in haemocytes, based on the differences observed in the response of haemocytes to bind target cells for phagocytosis or encapsulation. The present study also differentiated the activation of PO in the plasma, serum, and haemocyte lysate supernatant (HLS).

Insights into Molecular Beryllium–Silicon Bonds

We present the synthesis of two silyl beryllium halides HypSiBeX∙(thf) (HypSi = Si(SiMe3)3, X = Cl 2a, I 4a) and the molecular structure of 2a as determined by single crystal X-ray diffraction. Compounds 2a and 4a were characterized via multi-nuclear NMR spectroscopy (1H, 9Be, 13C, 29Si), and the bonding situation was further investigated using quantum chemical calculations (with the addition of further halides X = F 1b, Cl 2b, Br 3b, I 4b). The nature of the beryllium silicon bond in the context of these compounds is highlighted and discussed.

Purification, characterization, and bioactivities of a polysaccharide from mycelial fermentation of Bjerkandera fumosa

In this work, a novel polysaccharide (named DBFM3) was isolated from mycelia of Bjerkandera fumosa by DEAE-32 and Sepharose CL–6B column chromatography. High-performance gel permeation chromatography showed that DBFM3 was homogeneous, with an average molecular weight of 1.8×105Da. Structural characteristics of the purified fraction were investigated by high-performance liquid chromatography (HPLC), FT-IR, and NMR. HPLC analysis indicated that DBFM3 was composed of mannose, galacturonic acid, and galactose at molar ratios of 1:18.16:0.702. Spectral analysis suggested that DBFM3 had (1→6), (1→3,6), (1→3) linkages and pyranose conformation. Antioxidant assay in vitro showed that DBFM3 exhibited 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radical scavenging activity, and has protective effect against DNA damage and damage to SH-SY5Y cells induced by H2O2. Immunological tests indicated that DBFM3 significantly increased lymphocyte proliferation in vitro. Furthermore, DBFM3 increased the proliferation of lymphocytes in the presence of concanavalin A or lipopolysaccharide as mitogen.

Purification, partial characterization and bioactivity of sulfated polysaccharides from Grateloupia livida

Purification, preliminary characterization and bioactivity of polysaccharides from Grateloupia livida (GL) were investigated. Three water-soluble sulfated polysaccharide fractions (GLP-1, GLP-2 and GLP-3) were isolated and purified from the edible and medicinal red seaweed, Grateloupia livida (Harv.) Yamada by DEAE Sepharose CL–6B and Sephadex G-100 column chromatography, and chemical characterization was performed by HPGPC, GC–MS, FT-IR and SEM. In addition, anticoagulant activities were determined by activated partial thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT) using normal human plasma in vitro. The antioxidant activities against DPPH and ABTS+ radicals were evaluated and compared. The molecular weights of GLP-1, GLP-2 and GLP-3 were 39.5, 60.4 and 3.36kDa, respectively. Monosaccharide analysis revealed that three polysaccharide fractions were homopolysaccharides and comprised of galactose only. Anticoagulant assays indicated that crude GLP, and purified GLP-1 and GLP-2 effectively prolonged APTT and TT, but not PT. All polysaccharide fractions exhibited significant in vitro antioxidant activities in a dose-dependent manner. GLP-2 showed consistently better anticoagulant and antioxidant activities compared with GLP, GLP-1 and GLP-3. These results demonstrate that sulfated polysaccharides isolated from Grateloupia livida can serve as readily available alternative natural sources of anticoagulant and antioxidant agents.

Assessment of the cytotoxic and genotoxic effects of TiO2 nanoparticles in A549 cells

The mole crab, Emerita emeritus, collected from the sandy shores of a Chennai beach, was investigated for cellular immune responses based on the morphology and defensive reactions of the circulating haemocytes. Three haemocyte morphotypes were identified using light and electron microscopy, and separated in a discontinuous percoll gradient. A phagocytosis study using human B erythrocyte as a target cell under phase-contrast optics showed that granular and semi-granular haemocytes were phagocytic, and this response was enhanced by using serum (opsonin)-coated human B erythrocyte in unfractionated and fractionated haemocytes. Observation of TEM image of phagocytosis revealed that the initial recognition and binding of the target cell was restricted to granular and semigranular haemocytes, which were lacking with hyaline cells. However, the encapsulation of DEAE Sepharose CL 6B beads, either untreated or coated with serum (opsonin), was restricted to hyaline cells. This suggests the occurrence of two cell lines in haemocytes, based on the differences observed in the response of haemocytes to bind target cells for phagocytosis or encapsulation. The present study also differentiated the activation of PO in the plasma, serum, and haemocyte lysate supernatant (HLS).

Half-Sandwich Silane σ-Complexes of Ruthenium Supported by NHC Carbene

Reactions of carbene complex [Cp(IPr)Ru(pyr)2][BF4] (6, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with excess acetonitrile and LiCl in THF afford complexes [Cp(IPr)Ru(NCCH3)2][PF6] (7) and Cp(IPr)RuCl (8), respectively. Complex 8 was characterized by NMR and X-ray diffraction analysis. Addition of hydrosilanes to 8 results in silane σ-complexes Cp(IPr)Ru(η2-HSiR3)Cl (4), which were characterized by NMR and X-ray studies of Cp(IPr)Ru(η2-HSiMeCl2)Cl (4b) and Cp(IPr)Ru(η2-H3SiPh)Cl (4d). The hydrogen–silicon coupling constants of complexes 4 show an unusual trend in that the J(H–Si) values increase from the less-chlorinated complex Cp(IPr)Ru(η2-HSiMe2Cl)Cl (4c) to the trichloro derivative Cp(IPr)Ru(η2-HSiCl3)Cl (4a). Reaction of Cp(IPr)RuCl (8) with two equivalents of HSiCl3 gave the ruthenate complex [IPrH]+[CpRuCl(H) (SiCl3)2]−, characterized by NMR and X-ray study. Addition of hydrosilanes to the cationic complex [Cp(IPr)Ru(NCCH3)2][BArF4] (9) furnished very unstable cationic silane σ-comple...

Immune indices and identical functions of two prophenoloxidases from the haemolymph of green tiger shrimp Penaeus semisulcatus and its antibiofilm activity.

In the present study, we purified two prophenoloxidases (proPO) from haemolymph of green tiger shrimp, Penaeus semisulcatus by gel fermentation chromatography using blue Sepharose matrix. The two purified prophenoloxidase macromolecules are of about 76 and 75kDa determined through SDS-PAGE and named as Penaeus semisulcatus prophenoloxidase I (PSproPO I) and Penaeus semisulcatus prophenoloxidase II (PSproPO II). It was further characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Circular Dichroism (CD) and High Performance Liquid Chromatography (HPLC) analysis. The purified PSproPO I and PSproPO II showed the strongest agglutination titre against human erythrocytes compared to goat RBC. The PSproPO I and PSproPO II showed phagocytic activity against yeast Saccharomyces cerevisiae and encapsulation activity against Sepharose CL 6B beads compared to CM Sepharose and Sodium alginate beads. The functional analysis of purified PSproPO I and PSproPO II showed enhanced PO activity when added with the triggering molecules such as pathogen associated molecular patterns (PAMPs), metals and chemicals. In addition, eluted fraction containing PSproPO I and PSproPO II showed antibiofilm activity against Gram positive and Gram negative bacteria. The above results concluded that no significant differences were found between the purified PSproPO I and PSproPO II immune indices and functions. This study might provide a sensitive platform to understand more about the critical roles of PSproPO I and PSproPO II in crustacean immune system.

Chemical composition and thermal properties of Chilean Araucaria araucana starch

Starch isolated from Chilean Araucaria araucana seed was characterized as a follow‐up on a previous study. The apparent amylose (AMM) content determined by potentiometric titration was 28%. The chain length distribution profile of amylopectin (AP) showed two peaks at polymerization degrees (DP) of 12 and 43–44. Around 51% of unit chains had DP in the range 13–24. The average DP of AP branch chains was 19.6%. The molecular weight distribution of A. araucana starch analyzed by Sepharose CL 2B is also reported. The ratio of blue value to total carbohydrates was 0.30 for the AP peak, which is characteristic of a low proportion of long lateral chains. The gelatinization temperature and enthalpy determined by DSC were 65.6°C and 14.5 J/g, respectively.

Synthesis and application of α-diimine Ni(II) and Pd(II) complexes with bulky steric groups to polymerization of ethylene and methyl methacrylate

A series of α-diimine Ni(II) and Pd(II) complexes containing bulky steric groups, {[(4-R-2,6-Ph2C6H2NC)2Nap]MX2} (Nap: 1,8-naphthdiyl, MX2=NiBr2, R=F (4a); R=Cl (4b); R=Me (4c); R=n-Bu (4d) and MX2=PdCl2, R=F (5a); R=Cl, (5b); R=Me (5c); R=n-Bu (5d)), {[4-F-2,6-Ph2C6H2NC(Me)]2PdCl2}(5e), were synthesized and characterized. The crystal structures of ligands 3d, 3e and complexes 4a, 4b, 5a, 5b, 5e were determined by X-ray crystallography. These complexes, when activated with diethylaluminum chloride (DEAC), were used to catalyze polymerization of ethylene and methyl methacrylate (MMA) under mild conditions. The introduction of an electron-withdrawing group to the ligand framework improves the catalytic activity significantly. The Ni(II) catalysts 4a–d exhibited high catalytic activity in the polymerization of ethylene (up to106g PE/(molNihbar)) and produced highly branched polyethylenes at high temperature. Interestingly, complex 4a could produce syndiotactic-rich PMMAs at low temperature (0°C, up to 77.2% of rr triads).