Gursharan Singh

Critical factors affecting laccase-mediated biobleaching of pulp in paper industry

Next to xylanases, laccases from fungi and alkali-tolerant bacteria are the most important biocatalysts that can be employed for eco-friendly biobleaching of hard and soft wood pulps in the paper industry. Laccases offer a potential alternative to conventional, environmental-polluting chlorine and chlorine-based bleaching and has no reductive effect on the final yield of pulp as compared to hemicellulases (xylanases and mannanases). In the last decade, reports on biobleaching with laccases are based on laboratory observations only. There are several critical challenges before this enzyme can be implemented for pulp bleaching at the industrial scale. This review discusses significant factors like redox potential, laccase mediator system (LMS)—synthetic or natural, pH, temperature, stability of enzyme, unwanted grafting reactions of laccase, and cost-intensive production at large scale which constitute a great hitch for the successful implementation of laccases at industrial level.

Xenobiotics enhance laccase activity in alkali-tolerant γ-proteobacterium JB

Various genotoxic textile dyes, xenobiotics, substrates (10 µM) and agrochemicals (100 µg/ml) were tested for enhancement of alkalophilic laccase activity in γ-proteobacterium JB. Neutral Red, Indigo Carmine, Naphthol Base Bordears and Sulphast Ruby dyes increased the activity by 3.7, 2.7, 2.6 and 2.3 fold respectively. Xenobiotics/substrates like p-toluidine, 8-hydroxyquinoline and anthracine increased it by 3.4, 2.8 and 2.3 fold respectively. Atrazine and trycyclozole pesticides enhanced the activity by 1.95 and 1.5 fold respectively.

Silyl-nitrogen compounds: I. Reactions of dilithium bis(trimethylsilyl)hydrazine with group IV halides

Abstract Dilithium 1,2-bis(trimethylsilyl)hydrazine ( 1 ) reacts with CCl 4 , Me 3 SiCCl 3 and CBr 4 to form predominantly bis(trimethylsilyl)aminocarbonimidic dichloride, bis(trimethylsilyl)aminoisocyanide and bis(trimethylsilyl)diazene, whereas similar reactions with HCCl 3 , HCI 3 , H 2 CCl 2 H 2 CI 2 , C 2 H 4 Cl 2 or C 2 H 2 Cl 4 lead to increasing amounts of bis(trimethylsilyl)hydrazine. In addition to the hydrazone, (Me 3 Si) 2 NNCH(Cl), the reaction of 1 with CHCl 3 forms a small amount of triazasilacyclopentane, (Me 3 Si) 2 NN CN(NHSiMe 3 SiMe 2 NHN SiMe 3 . In contrast, Me 2 SnCl 2 reacts with 1 to give tetraazadistannacyclohexane [Me 2 SnNSiMe 3 ) 2 ] 2 , whereas SnCl 4 , SnCl 2 and PbCl 2 act mainly as oxidants and Me 2 SiCl 2 forms polymers. Another product of the reaction of 1 with SnCl 2 or PbCl 2 is LiN(SiMe 3 ) 2 originating perhaps from LiNH(SiMe 3 ) or [LiNN(SiMe 3 ) 2 ] 2 .

Reactions of bis(trimethylsilyl)amine and -amide with MoOCl4

Oxo-Mo(VI) imido-chloride, [MoOCl2(NH)(Et2O)]n and nitrido-chloride, [Mo2O2Cl2(N)2(Et2O)]n have been synthesized by equimolar reactions of MoOCl4 with HN(SiMe3)2 and LiN(SiMe3)2, respectively. Higher molar reactions of HN(SiMe3)2 lead to imido-silylamido derivatives, [Mo2OCl3(NH)3(NHSiMe3)]n, whereas those of LiN(SiMe3)2 give silylimido bridged compounds, Mo4O4Cl4(NSiMe3)6 and Mo4O4(NSiMe3)8. Elemental analyses, redox titration, magnetic moment, molecular weight, molar conductance, infrared,1H-NMR and TG-DTG-DTA studies are reported.ZusammenfassungDurch equimolare Reaktionen von MoOCl4 mit HN(SiMe3)2 und LiN(SiMe3)2 wurden die Oxo-Mo(VI) Imido-chloride [MoOCl2(NH)(Et2O)]n und die Nitrido-chloride [Mo2O2Cl2(N)2(Et2O)]n dargestellt. Höhermolekulare Reaktionen von HN(SiMe3)2 führen zu Imido-silylamido Derivaten [Mo2OCl3(NH)3(NHSiMe3)]n, währenddessen die von LiN(SiMe3)2 silylimidoüberbrückte Verbindungen ergeben: Mo4O4Cl4(NSiMe3)6 und Mo4O4(NSiMe3)8. Die Strukturen sind mit Elementaranalysen, Redoxtitrationen, Messung der magnetischen Momente, Molekulargewichten, molarer Leitfähigkeit, Infrarot,1H-NMR und TG-DTG-DTA-Untersuchungen charakterisiert.

Enzymes: Applications in Pulp and Paper Industry

The pulp and paper production technology is highly diverse and provides numerous opportunities for the application of microbial enzymes in processes, such as biopulping, biobleaching, de-inking, pitch removal, fiber grafting, paper coloration, and bioremediation of effluents. Although many applications of enzymes in pulp and paper industry are still at the research and development stage, currently the most important application is eco-friendly biobleaching of hard and soft wood pulps. In most instances, the enzymes employed are xylanases, laccases, and rarely mannanases, which offer the potential alternative to conventional, environmental-polluting chlorine and chlorine-based bleaching. Many industries all over the world are evaluating the potential of these biocatalysts through routine trials at large scale delignification of pulps. On the other hand, pitch control by lipases (and recently by laccases) has also being widely adapted by several paper mills as a quality-enhancing step. Improved pulp drainage with enzymes is practiced routinely at several mills. But before the complete implementation of enzymes in papermaking industries, there are some critical challenges, especially for laccases regarding their low redox potential and dependency on cost-intensive mediators.