Formation Of Unwanted By-products Research Articles

Crystallization Assisted Dynamic Kinetic Resolution for the Synthesis of (R)-β-Methylphenethylamine.

This study explores a combination of the concept of enantioselective enzymatic synthesis of β-chiral amines through transamination with in situ product crystallization (ISPC) to overcome product inhibition. Using 2-phenylpropanal as a readily available and easily racemizing substrate of choice, (R)-β-methylphenethylamine ((R)-2-phenylpropan-1-amine) concentrations of up to 250 mM and enantiomeric excesses of up to 99 % are achieved when using a commercially available transaminase from Ruegeria pomeroyi in a fed-batch based dynamic kinetic resolution reaction on preparative scale. The source of substrate decomposition during the reaction is also investigated and the resulting unwanted byproduct formation is successfully reduced to insignificant levels.

High-Entropy Materials for Lithium Batteries

High-entropy materials (HEMs) constitute a revolutionary class of materials that have garnered significant attention in the field of materials science, exhibiting extraordinary properties in the realm of energy storage. These equimolar multielemental compounds have demonstrated increased charge capacities, enhanced ionic conductivities, and a prolonged cycle life, attributed to their structural stability. In the anode, transitioning from the traditional graphite (372 mAh g−1) to an HEM anode can increase capacity and enhance cycling stability. For cathodes, lithium iron phosphate (LFP) and nickel manganese cobalt (NMC) can be replaced with new cathodes made from HEMs, leading to greater energy storage. HEMs play a significant role in electrolytes, where they can be utilized as solid electrolytes, such as in ceramics and polymers, or as new high-entropy liquid electrolytes, resulting in longer cycling life, higher ionic conductivities, and stability over wide temperature ranges. The incorporation of HEMs in metal–air batteries offers methods to mitigate the formation of unwanted byproducts, such as Zn(OH)4 and Li2CO3, when used with atmospheric air, resulting in improved cycling life and electrochemical stability. This review examines the basic characteristics of HEMs, with a focus on the various applications of HEMs for use as different components in lithium-ion batteries. The electrochemical performance of these materials is examined, highlighting improvements such as specific capacity, stability, and a longer cycle life. The utilization of HEMs in new anodes, cathodes, separators, and electrolytes offers a promising path towards future energy storage solutions with higher energy densities, improved safety, and a longer cycling life.

An Overview of Preparation for Different Azo Compounds

Azo compounds are a class of organic materials that have the group R-N=N-R' where the substitution group R and R' are aromatic or heterocyclic sides. The azo compounds have a variety of applications including dyes, pigments, and pharmaceuticals. The preparation and characterization of different azo compounds is an important area of research in organic synthesis. The azo compound synthesis typically involves the diazotization process for coupling between an aromatic amine and another aromatic compound containing an activating group such as -OH, -NH2, or -NR2. The reaction conditions must be carefully controlled to prevent side reactions, such as the formation of unwanted byproducts. Once synthesized, azo compounds can be characterized using a variety of techniques including UV-Vis spectroscopy, NMR spectroscopy, and mass spectrometry. UV-Vis spectroscopy is a commonly used technique for characterizing azo compounds. The absorption spectrum of an azo compound typically exhibits a strong absorption band in the visible region due to the delocalized π-electrons in the azo group. While in FTIR, the loss of the amine peak and showing a weak peak at about 1550 cm−1forthe (N=N) group, indicates the presence of Azo. The preparation and characterization of different azo compounds is a significant field of research in organic chemistry, which are applied as acid and base indicators, food coloring, optical switches, liquid crystal and in medicine. By carefully controlling the synthesis conditions and using a variety of characterization techniques, researchers can gain a better understanding of the properties and applications of these compounds.

(Selective) Isolation of acetic acid and lactic acid from heterogeneous fermentation of xylose and glucose

The present study focuses on the isolation of acetic and lactic acid from a fermentation broth produced by heterofermentative microorganisms using glucose and xylose as substrate. Especially xylose fermentation to lactic acid leads to unwanted by-product formation of acetic acid. Reactive liquid-liquid extraction is an energy-efficient downstream process, where the use of green solvents such as d-limonene opens the way to a more sustainable production. To find the optimum solvent/reactive extractant pairing, the reactive extractants trioctylamine, trioctylphosphine oxide, Aliquat 336, and tributyl phosphate were used diluted in 1-octanol, 1-decanol, d-limonene or a deep eutectic solvent. The phosphine-based extractants proved to be most effective for both acids. In the first extraction step, 19% of acetic acid and only 3% of lactic acid are extracted with trioctylphosphine oxide/1-octanol when the xylose feed is used without pH adjustment. The pKa value of the acids is responsible for the difference in extraction efficiency leading to the proposal of a two-step extraction separating first acetic acid and after pH adjustment, lactic acid can be extracted. The combination of trioctylphosphine oxide diluted in d-limonene leads to a surprisingly high selectivity for lactic acid isolation in the second extraction step. The present study shows for the first time that green solvents lead to similar extraction efficiencies compared to conventional solvents such as 1-octanol. For back extraction n-heptane and p-cymene are used as disintegration agents and water as stripping phase; n-heptane results in a lactic acid back extraction efficiency of up to 82% and p-cymene up to 70%. This shows that also for the back extraction p-cymene as a green disintegration agent leads to similar results as fossil-based n-heptane.

Facile, versatile and stepwise synthesis of high-performance oligomer acceptors for stable organic solar cells.

Oligomer acceptors haverecently emerged aspromising photovoltaic materialsfor achieving high power conversion efficiency (PCE) and long-term stability in organic solar cells (OSCs). However, the limited availability of diverse acceptors, resulting from the sole synthetic approach, has hindered their potential for future industrialization.In this study, we present a facile and effective stepwise approach that utilizes two consecutive Stille coupling reactions for the synthesis of oligomer acceptors. To demonstrate the feasibility of the novel approach, we successfully synthesize a trimer acceptor, Tri-Y6-OD, and further systematically investigate the impact of oligomerization on device performance and stability. The result reveals that this approach has significant advantages compared to the conventional method, such as reduced formation of unwanted by-products and lower difficulties in purification. Remarkably, the OSC based on PM6:Tri-Y6-OD achieves an impressive PCE of 18.03% and maintains 80% of the initial PCE (T80) for 1523h under illumination, surpassing the performance of the corresponding small molecule acceptor Y6-OD-based device. Furthermore, the versatility of the synthetic strategy in obtaining diverse acceptors is further demonstrated. Overall, our findings provide afacile, versatile and stepwisewayfor synthesizingoligomeric acceptors, thereby facilitating the development of stable and efficient OSCs.

Study on by-products synthesis of powder coating polyester resin catalyzed by organotin

Abstract In the production of powder-coating polyester, a strong odor emanates from the water, prompting us to investigate its composition and origin. We studied the process of powder coating epoxy/polyester 50/50, which employs butyl tin tris (2-ethyl hexanoate) as a catalyst. The esterified water was extracted using ethyl acetate. It was analyzed via GC–MS to identify the side reactions and by-products that arise during the tin-catalyzed esterification process. Then we discussed their formation mechanism. Our results indicate that butyl tin tris (2-ethyl hexanoate) triggers side reactions such as cyclization and transesterification, leading to the production of by-products such as heterocyclic compounds (1,4-dioxane), anhydride compounds (propionic anhydride), and others. Notably, the unpleasant odor was found to be derived from propionic anhydride. These findings provide insights into the chemistry of tin-catalyzed esterification and highlight the importance of addressing the formation of unwanted by-products in the production of powder-coating polyester.

Carbon armor for zinc anodes: Mitigating dendrite formations and unwanted side reactions in zinc-ion batteries

BackgroundOwing to their high safety and abundance, zinc-ion batteries (ZIBs) have gained significant attention as promising energy-storage technologies. However, these energy storage systems continue to suffer from the formation of Zn dendrites, corrosion, and parasitic side reactions during battery cycling; this severely reduces their performance and lifespan. To address these issues, researchers have investigated carbon-based protection layers to prevent such hindrances at Zn anodes. MethodsIn this mini-review, we provide a comprehensive overview of the current state-of-the-art in the development of carbon-based protection layers for ZIBs to prevent dendrite formation, including conventional carbon materials, carbon nanotubes, MOF-derived carbon layers, graphdiyne layers, graphene, and fiber-like carbons. Moreover, we have summarized the recent progress in these approaches to suppress dendrite formation on Zn electrodes and the formation of unwanted by-products by creating carbon protection layers. Some of the limitations and challenges of current state-of-the-art methods, including their poor cycling retention and instability, are also discussed. Additionally, this study provides insights into the future direction of research in this area. Significant findingsIt was found that the use of carbon-based protection layers for Zn anodes is an effective strategy for preventing dendrite formation in ZIBs. We expect the findings of this review paper to provide a comprehensive understanding of the status and future prospects of carbon-based protection layers for Zn anodes, and hence, contribute to the development of next-generation ZIBs.

Techno-Economic Analysis of Interesterification for Biodiesel Production

Interesterification is an alternative reaction for the production of fatty acid alkyl esters from triglycerides, a pathway that avoids unwanted byproduct formation. In this work, the technical and economic feasibility of soybean oil interesterification for biodiesel production on a commercial scale is assessed. The interesterification kinetics of triolein (model soybean oil) and methyl acetate using ferric sulfate as a heterogeneous acid catalyst are experimentally determined, and the results are used to parameterize a kinetic model. Process simulations are developed using Aspen Plus V11 for acid and alkaline heterogeneously catalyzed interesterification plants at varying production rates and methyl acetate-to-oil molar ratios (MAOMRs). At all production capacities and MAOMRs tested, the acid-catalyzed processes are found to have more favorable process energy consumption and profitability metrics compared to the alkaline-catalyzed processes. The most economically promising design operates at a production capacity of 30,000 metric tons/yr and an MAOMR of 10:1 with a net present value of $34 million after 20 years and a biodiesel breakeven price of $0.78/kg. This case has a process energy demand of 35,000 MJ/h, resulting in a process energy ratio of 0.25. This work indicates that interesterification shows commercial viability and is a promising alternative to transesterification for biodiesel production.

Microwave catalytic conversion of acetylene for co-production of hydrogen and carbon nanotubes

Natural gas conversion to hydrogen and solid carbon can drastically reduce the carbon footprint. Microwave plasma pyrolysis is an emerging process for chemical industries to directly convert methane (CH4), the major component of natural gas, to hydrogen and carbon, which offers benefits such as fast process dynamics, flexibility, and high product yield. However, the formation of unwanted by-products, like acetylene (C2H2), will require extra cost for gas separation. Plasma pyrolysis of CH4 produces large amount of acetylene at downstream, which is currently used mainly for welding. To avoid gas separation and upgrade acetylene from the downstream of methane plasma reactor, a novel approach toward its transformation to carbon nanotubes (CNT) and pure hydrogen (H2) over Ni-based bimetallic catalyst driven by microwave irradiation has been reported in this work. The dominant gas product was hydrogen. Low concentrations of methane, ethane, and ethylene were observed in the product stream. Catalytic acetylene decomposition was carried out at 400 °C over Al2O3 supported Ni catalyst. The results showed that, at 400 °C, acetylene was dehydrogenated to CNT and hydrogen was the dominant gas in product stream over 10Ni-1Pd-Al2O3 catalyst. Characterizations of spent catalysts was conducted using Raman spectroscopy and transmission electron microscopy (TEM) to investigate the properties of carbon deposited over the catalyst during the catalytic acetylene decomposition. The results highlight that methane can be efficiently converted to hydrogen and CNT through 2-step process, microwave plasma and microwave catalytic conversion of intermediate acetylene, operated in a single reactor system driven by microwave.

Experimental study of the oxidative steam reforming of fuel grade bioethanol over Pt–Ni metallic foam structured catalysts

In this work, Pt–Ni/CeO2 catalysts have been used for the oxidative steam reforming of fuel grade bioethanol. To transfer the above formulation on structured carriers, due to the requirement of a washcoat (wc) deposition, it was mandatory to carry out a preliminary study on the catalysts in the form of powder. An initial experimental campaign was performed to optimise the ceria loading (between 25 and 45 wt%) as well as the Pt content (between 2 and 5 wt%): stability tests were carried out for 24 h at 500 °C, WHSV = 12.3 h−1, H2O/C2H5OH ratio of 4, O2/C2H5OH of 0.5. The highest activity, selectivity and durability was recorded over the 3Pt–10Ni/35CeO2/wc, which assured an ethanol conversion of almost 98% at the end of the test with a corresponding H2 yield of 50%. This interesting formulation was transferred on a Ni–Fe substrate, made of an open cell foam, which was tested under the same operative conditions described above: the structured catalyst, due to the very good heat management within the catalytic bed and the improved mass transport, displayed a more stable behaviour compared to the corresponding powder, even in the presence of the typical bioethanol impurities; moreover, the formation of unwanted by-products was negligible throughout the whole investigated interval.

Lowering the fresh water footprint of cooling towers: A treatment-train for the reuse of discharged water consisting of constructed wetlands, nanofiltration, electrochemical oxidation and reverse osmosis

The reuse instead of discharge of cooling tower water can significantly lower the industrial fresh water footprint. The reuse of cooling tower water requires the removal of different chemical fractions from the cooling tower water, such as dissolved minerals, phosphate, organic carbon and industrial chemicals. However, there is no stand-alone water treatment technology that can remove all these fractions simultaneously. Therefore, the aim of this study was to assess the removal of these fractions with an innovative pilot-scale technology train that was fed with real cooling tower water consisting of green and grey technologies: constructed wetlands, nanofiltration, electrochemical oxidation and reverse osmosis. In addition, attention was paid to the fate of emerging industrial contaminant benzotriazole, the performance of the nanofiltration membranes and potential production of unwanted by-products by electrochemical oxidation. The experiments showed that 1) The treatment-train was capable of reaching the desired water quality; 2) Benzotriazole was completely removed by the constructed wetlands that acted as pre-treatment before nanofiltration as a result of biodegradation; 3) the production of inorganic carbon species in the constructed wetlands resulted in increased fouling of the subsequent nanofiltration membranes; 4) these membranes mainly retained divalent ions and did not retain monovalent ions, which resulted in a permeate stream whose EC was too high for reuse applications and therefore required further treatment by reverse osmosis; 5) electrochemical oxidation of the nanofiltration concentrate was more efficient than direct electrochemical oxidation of cooling tower water in terms of degradation of recalcitrant humic acids. In addition, less unwanted chlorinated by-products were produced as a result of different ions ratios due to retention of ions by the nanofiltration membranes. Before the full-scale application of the studied treatment train for cooling tower water treatment, it is recommended to identify strategies to improve the water recovery, to include innovative new nanofiltration membranes that can make the use of reverse osmosis redundant and to adopt new insights in preventing unwanted by-product formation during electrochemical oxidation.

One-Pass Conversion of Benzene and Syngas to Alkylbenzenes by Cu-ZnO-Al2O3 and ZSM-5 Relay.

Alkylbenzenes have a wide range of uses and are the most demanded aromatic chemicals. The finite petroleum resources compels the development of production of alkylbenzenes by non-petroleum routes. One-pass selective conversion of benzene and syngas to alkylbenzenes is a promising alternative coal chemical engineering route, yet it still faces challenge to industrialized applications owing to low conversion of benzene and syngas. Here we presented a Cu–ZnO–Al2O3/ZSM-5 bifunctional catalyst which realizes one-pass conversion of benzene and syngas to alkylbenzenes with high efficiency. This bifunctional catalyst exhibited high benzene conversion (benzene conversion of 50.7%), CO conversion (CO conversion of 55.0%) and C7&C8 aromatics total yield (C7&C8 total yield of 45.0%). Characterizations and catalytic performance evaluations revealed that ZSM-5 with well-regulated acidity, as a vital part of this Cu–ZnO–Al2O3/ZSM-5 bifunctional catalyst, substantially contributed to its performance for the alkylbenzenes one-pass synthesis from benzene and syngas due to depress methanol-to-olefins (MTO) reaction. Furthermore, matching of the mass ratio of two active components in the dual-function catalyst and the temperature of methanol synthesis with benzene alkylation reactions can effectively depress the formation of unwanted by-products and guarantee the high performance of tandem reactions.Graphic Supplementary InformationThe online version contains supplementary material available at 10.1007/s10562-021-03617-5.

A Phosphotungstic Acid Catalyst for Depolymerization in Bulrush Lignin

Obtaining renewable fuels and chemicals from lignin is an important challenge in the use of biomass to achieve sustainability and energy goals. At present, acid-based catalysts for lignin depolymerization are considered to be a potential but challenging way to produce low-molecular-mass aromatic chemicals. The main concerns with the use of Lewis acids and zeolite catalysts are the corrosive nature of the acids, the possible formation of unwanted byproducts, and the possible formation of harsh reaction conditions. We achieved high-yield conversion using phosphotungstic acid (PTA) polyoxometalate catalysts in ethanol/water under different reaction conditions with little formation of bio-char. The monomeric products were mainly composed of various types of aromatic compounds. Our method does not require the use of precious metals and harsh reaction conditions—it only requires relatively mild reaction conditions and homogeneous catalysis—thereby greatly reducing operating costs and increasing the yields. Therefore, this PTA catalyst, which has excellent performance in bulrush lignin catalysis, would be a good alternative to the traditional catalysts used in lignin depolymerization and have wide application in biomass use.

Facile construction of a DNA tetrahedron in unconventional ladder-like arrangements at room temperature.

A DNA tetrahedron as the most classical and simplest three-dimensional DNA nanostructure has been widely utilized in biomedicine and biosensing. However, the existing assembly approaches usually require harsh thermal annealing conditions, involve the formation of unwanted by-products, and have poor size control. Herein, a facile strategy to fabricate a discrete DNA tetrahedron as a single, thermodynamically stable product in a quantitative yield at room temperature is reported. This system does not require a DNA trigger or thermal annealing treatment to initiate self-assembly. This DNA tetrahedron was made of three chemically ligated triangular-shaped DNAs in unconventional ladder-like arrangements, with measured heights of ∼4.16 ± 0.04 nm, showing extra protections for enzymatic degradation in biological environment. They show substantial cellular uptake in different cell lines via temperature, energy-dependent and clathrin-mediated endocytosis pathways. These characteristics allow our DNA tetrahedron to be used as vehicles for the delivery of very small and temperature-sensitive cargos. This novel assembly strategy developed for DNA tetrahedra could potentially be extended to other highly complex polyhedra; this indicated its generalizability.

Catalytic hydrotreating of jatropha oil into non-isomerized renewable diesel: Effect of catalyst type and process conditions

The selective production of renewable diesel through the hydrotreating of jatropha oil was investigated to determine the effects of the catalyst type (Ni-Mo and Co-Mo) and of the variables temperature (300–370 °C), pressure (5.0–9.0 MPa) and time (3–6 h). Reactions were carried out in a high-pressure reactor operated in semi-batch mode. The experiments also allowed to stablish the reaction pathway and to optimize the response variable (yield). A thorough characterization of the catalysts was carried out using the techniques XRF, TPR coupled to a mass spectrometer, CO-chemisorption, XRD, N2-sorptometry and TGA/DTA. Results indicate that temperatures as high as 370 °C should be avoided because they induce the formation of unwanted by-products by cracking or polymerization reactions, and NiMoS was more sensitive to this effect. At intermediate temperature (350 °C), both catalysts behaved nearly the same. However, at the lowest temperature (300 °C) NiMoS was clearly more active than CoMoS. Amongst all the characterizations performed to the catalysts, only the chemisorption analyses (TPR and CO-chemisorption) showed relevant differences. TPR analyses showed that the amount of stronger sulfided sites, the ones still present at the reaction temperature, were higher in NiMoS, compared to CoMoS. Besides, CO-chemisorption revealed that Ni-Mo had a metal dispersion 75% higher than Co-Mo. Hence, these two factors could be the responsible for the better performance of NiMoS over CoMoS. The main reaction pathway was the decarboxylation/decarbonylation route. A clear optimum value for the yield of 80% (97% of theoretical) could be obtained at 300 °C, 9.0 MPa and 6 h with NiMoS. The variable temperature had a negative effect on yield while pressure and time had a positive effect. NiMoS did not lose activity after five re-uses.

High-yield production of 1,3-propanediol from glycerol by metabolically engineered Klebsiella pneumoniae

BackgroundGlycerol is a major byproduct of the biodiesel industry and can be converted to 1,3-propanediol (1,3-PDO) by microorganisms through a two-step enzymatic reaction. The production of 1,3-PDO from glycerol using microorganisms is accompanied by formation of unwanted byproducts, including lactate and 2,3-butanediol, resulting in a low-conversion yield.ResultsKlebsiella pneumoniae was metabolically engineered to produce high-molar yield of 1,3-PDO from glycerol. First, the pathway genes for byproduct formation were deleted in K. pneumoniae. Then, glycerol assimilation pathways were eliminated and mannitol was co-fed to the medium. Finally, transcriptional regulation of the dha operon were genetically modified for enhancing 1,3-propanediol production. The batch fermentation of the engineered strain with co-feeding of a small amount of mannitol yielded 0.76 mol 1,3-PDO from 1 mol glycerol.ConclusionsKlebsiella pneumoniae is useful microorganism for producing 1,3-PDO from glycerol. Implemented engineering in this study successfully improved 1,3-PDO production yield, which is significantly higher than those reported in previous studies.

The Mechanism of Non-thermal Plasma Catalysis on Volatile Organic Compounds Removal

Non-thermal plasma (NTP) catalysis has attracted widespread attention in volatile organic compounds (VOCs). Combining NTP with heterogeneous catalyst has been proved to reduce the formation of unwanted by-products and improve the energy efficiency of the process. The mechanisms of interaction with plasma and catalyst and VOCs oxidation in plasma catalysis are particularly hot research topic. This paper reviewed the mechanism of non-thermal plasma catalysis on volatile organic compounds removal. In the first part, the interaction between plasma and catalyst is disscussed. And the different catalysis systems and discharge types are presented in the second part. In the third part, attention is given to the influence of critical parameters on the removal processes. Finally, based on a large number of literatures, an extended review is presented detailly on the treatment of VOCs with plasma-catalysis system including the oxidation pathways. Moreover, future works of this promising technology are discussed.

Novel protocol for highly efficient gas-phase chemical derivatization of surface amine groups using trifluoroacetic anhydride

In the current work, chemical derivatization of amine (NH2) groups with trifluoroacetic anhydride (TFAA) as an analytical method to improve the information scope of X-ray photoelectron spectroscopy (XPS) is investigated. TFAA is known to successfully label hydroxyl (OH) groups. With the introduction of a newly developed gas-phase derivatization protocol conducted at ambient pressure and using a catalyst also NH2 groups can now efficiently be labelled with a high yield and without the formation of unwanted by-products. By establishing a comprehensive and self-consistent database of reference binding energies for XPS a promising approach for distinguishing hydroxyl from amine groups is presented. The protocol was verified on different polymers, including poly(allylamine), poly(ethyleneimine), poly(vinylalcohol) and chitosan, the latter one containing both types of addressed chemical groups.

Homo- and heteropolymer self-assembly of recombinant trichocytic keratins.

In the past two decades, keratin biomaterials have shown impressive results as scaffolds for tissue engineering, wound healing, and nerve regeneration. In addition to its intrinsic biocompatibility, keratin interacts with specific cell receptors eliciting beneficial biochemical cues. However, during extraction from natural sources, such as hair and wool fibers, natural keratins are subject to extensive processing conditions that lead to formation of unwanted by-products. Additionally, natural keratins suffer from limited sequence tunability. Recombinant keratin proteins can overcome these drawbacks while maintaining the desired chemical and physical characteristics of natural keratins. Herein, we present the bacterial expression, purification, and solution characterization of human hair keratins K31 and K81. The obligate heterodimerization of the K31/K81 pair that results in formation of intermediate filaments is maintained in the recombinant proteins. Surprisingly, we have for the first time observed new zero- and one-dimensional nanostructures from homooligomerization of K81 and K31, respectively. Further analysis of the self-assembly mechanism highlights the importance of disulfide crosslinking in keratin self-assembly.

Evolving transpeptidase and hydrolytic variants of γ-glutamyl transpeptidase from Bacillus licheniformis by targeted mutations of conserved residue Arg109 and their biotechnological relevance

γ-Glutamyl transpeptidase (GGT) catalyzes the transfer of the γ-glutamyl moiety from donor compounds such as l-glutamine (Gln) and glutathione (GSH) to an acceptor. During the biosynthesis of various γ-glutamyl-containing compounds using GGT enzyme, auto-transpeptidation reaction leads to the formation of unwanted byproducts. Therefore, in order to alter the auto-transpeptidase activity of the GGT enzyme, the binding affinity of Gln should be modified. Structural studies of the Bacillus licheniformis GGT (BlGT) complexed with the glutamic acid has shown that glutamic acid has strong ionic interactions through its α-carboxlic group with the guanidine moiety of Arg109. This interaction appears to be an important contributor for the binding affinity of Gln. In view of this, six mutants of Bacillus licheniformis ER15 GGT (BlGGT) viz. Arg109Lys, Arg109Ser, Arg109Met, Arg109Leu, Arg109Glu and Arg109Phe were prepared. As seen from the structure of BlGT, the mutation of Arg109 to Lys109 may reduce the affinity for Gln to some extent, whereas the other mutations are expected to lower the affinity much more. Biophysical characterization and functional studies revealed that Arg109Lys mutant has increased transpeptidation activity and catalytic efficiency than the other mutants. The Arg109Lys mutant showed high conversion rates for l-theanine synthesis as well. Moreover, the Arg109Met mutant showed increased hydrolytic activity as it completely altered the binding of Gln at the active site. Also, the salt stability of the enzyme was significantly improved on replacing Arg109 by Met109 which is required for hydrolytic applications of GGTs in food industries.