Microbial production of nutraceuticals: Metabolic engineering interventions in phenolic compounds, poly unsaturated fatty acids and carotenoids synthesis

Nutraceuticals have attained substantial attention due to their health-boosting or disease-prevention characteristics. Growing awareness about the potential of nutraceuticals for the prevention and management of diseases affecting human has led to an increase in the market value of nutraceuticals in several billion dollars. Nevertheless, limitations in supply and isolation complications from plants, animals or fungi, limit the large-scale production of nutraceuticals. Microbial engineering at metabolic level has been proved as an environment friendly substitute for the chemical synthesis of nutraceuticals. Extensively used microbial systems such as E. coli and S. cerevisiae have been modified as versatile cell factories for the synthesis of diverse nutraceuticals. This review describes current interventions in metabolic engineering for synthesising some of the therapeutically important nutraceuticals (phenolic compounds, polyunsaturated fatty acids and carotenoids). We focus on the interventions in enhancing product yield through engineering at gene level or pathway level.

Ixora coccinea L. - A reliable source of nanocellulose for bio-adsorbent applications

Nanocellulose, a subset of nanomaterials made from cellulose, one of the world's most plentiful natural resources, has the potential to offer environmentally friendly, renewable, and sustainable building blocks with enhanced properties for a variety of applications in the nanotechnology field. This article describes the impact of glutaraldehyde (GA) on glycerol plasticized nanocellulose derived from I. coccinea L. plant root. Using a variety of characterization techniques, including Fourier Transform Infrared Spectroscopy (FTIR), X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM), AFM, tensile and Brunauer-Emmett-Teller (BET) analysis, the effect of GA on glycerol plasticized nano-cellulose was investigated. The tensile modulus of the GA-crosslinked, 2 % glycerol-plasticized nanocellulose scaffolds is higher (88.82 MPa) than that of the regular nanocellulose scaffolds (78.8 MPa). The scaffold Young's modulus has been increased to 86.3 MPa. The results of the BET study proved that the surface area of the GA crosslinked nano-cellulose scaffold improved to129.703 m²/g. The larger surface area in turn results in a greater number of contact sites between consecutive fibers. This enhances the utility of the scaffold as a bio-adsorbent for waste water treatment. The absorbance of textile black dye and methylene blue dye in sunlight using nanocellulose composites as photocatalyst revealed a significant decrease in dye concentration after each hour, demonstrating the composites' bio-adsorbent property. The non-toxic nature, inertness, increased crystallinity index values, and good mechanical qualities are other characteristics of the GA-treated nanocellulose encourages its uses as product packaging, bioengineering materials, tissue engineering, and insulation coatings.

Progress and challenges of Microwave-assisted pretreatment of lignocellulosic biomass from circular bioeconomy perspectives

The recent scenario has witnessed the augmenting demand for energy precursors primarily from renewable ways in respect of the natural environment. The high energy along with the cost-intensive nature of the conventional approaches directed the researchers to find out an effective and promising method that principally uses the microwave for the pretreatment. The formation of heat energy from electromagnetic energy through polar particle rotation would be noted to be the core principle of the aforesaid effective approach. The microwave treatments speed up the destruction of complex structure of the biomass by applying a specific range of heat over the polar parts in a selective manner in the aqueous medium. In this review, the implementation of microwave-assisted green approaches for modeling an integrated circular bioeconomic strategy to potentially use lignocellulosic biomass for bioproducts is discussed.

Sustainable valorization of sugarcane residues: Efficient deconstruction strategies for fuels and chemicals production

The global climate crisis and the ongoing increase in fossil-based fuels have led to an alternative solution of using biomass for fuel production. Sugarcane bagasse (SCB) is an agricultural residue with a global production of more than 100 million metric tons and it has various applications in a biorefinery concept. This review brings forth the composition, life cycle assessment, and various pretreatments for the deconstruction techniques of SCB for the production of valuable products. The ongoing research in the production of biofuels, biogas, and electricity utilizing the bagasse was elucidated. SCB is used in the production of carboxymethyl cellulose, pigment, lactic acid, levulinic acid, and xylooligosaccharides and it has prospective in meeting the demand for global energy and environmental sustainability.

Integrated biorefinery development for pomegranate peel: Prospects for the production of fuel, chemicals and bioactive molecules

Current experimental evidence has revealed that pomegranate peel is a significant source of essential bio compounds, and many of them can be transformed into valorized products. Pomegranate peel can also be used as feedstock to produce fuels and biochemicals. We herein review this pomegranate peel conversion technology and the prospective valorized product that can be synthesized from this frequently disposed fruit waste. The review also discusses its usage as a carbon substrate to synthesize bioactive compounds like phenolics, flavonoids and its use in enzyme biosynthesis. Based on reported experimental evidence, it is apparent that pomegranate peel has a large number of applications, and therefore, the development of an integrated biorefinery concept to use pomegranate peel will aid in effectively utilizing its significant advantages. The biorefinery method displays a promising approach for efficiently using pomegranate peel; nevertheless, further studies should be needed in this area.

Bioremediation of Endocrine Disrupting Chemicals- Advancements and Challenges

Endocrine Disrupting Chemicals (EDCs), major group of recalcitrant compounds, poses a serious threat to the health and future of millions of human beings, and other flora and fauna for years to come. A close analysis of various xenobiotics undermines the fact that EDC is structurally diverse chemical compounds generated as a part of anthropogenic advancements as well as part of their degradation. Regardless of such structural diversity, EDC is common in their ultimate drastic effect of impeding the proper functioning of the endocrinal system, basic physiologic systems, resulting in deregulated growth, malformations, and cancerous outcomes in animals as well as humans. The current review outlines an overview of various EDCs, their toxic effects on the ecosystem and its inhabitants. Conventional remediation methods such as physico-chemical methods and enzymatic approaches have been put into action as some form of mitigation measures. However, the last decade has seen the hunt for newer technologies and methodologies at an accelerated pace. Genetically engineered microbial degradation, gene editing strategies, metabolic and protein engineering, and in-silico predictive approaches - modern day's additions to our armamentarium in combating the EDCs are addressed. These additions have greater acceptance socially with lesser dissonance owing to reduced toxic by-products, lower health trepidations, better degradation, and ultimately the prevention of bioaccumulation. The positive impact of such new approaches on controlling the menace of EDCs has been outlaid. This review will shed light on sources of EDCs, their impact, significance, and the different remediation and bioremediation approaches, with a special emphasis on the recent trends and perspectives in using sustainable approaches for bioremediation of EDCs. Strict regulations to prevent the release of estrogenic chemicals to the ecosystem, adoption of combinatorial methods to remove EDC and prevalent use of bioremediation techniques should be followed in all future endeavors to combat EDC pollution. Moreover, the proper development, growth and functioning of future living forms relies on their non-exposure to EDCs, thus remediation of such chemicals present even in nano-concentrations should be addressed gravely.

Enhancement of mechanical and thermal properties of Ixora coccinea L. plant root derived nanocellulose using polyethylene glycol-glutaraldehyde system

Nanocellulose fibers are widely acknowledged as a more sustainable alternative to polyimide and polyethylene terephthalate-based plastic films derived from petrochemicals. Cellulose is also utilised in packaging, tissue engineering, electronic, optical, and sensor applications, pharmaceutical applications, cosmetic applications, insulation, water filtration, and hygiene applications, as well as vascular grafts. In the present study to improve the tensile and thermal properties of cellulose nanofibers, polyethylene glycol (PEG 600) with varying concentrations was produced by solvent casting and chemically crosslinked with glutaraldehyde (GA). The effects of various PEG 600 concentrations on nanofibers and the morphology of the resulting nanofibers were investigated. The effects of GA on PEG-nanocellulose morphology, average diameter, tensile strength, elongation, and thermal characteristics were investigated. Strong (GA)-based acetal linkages are used to substitute secondary hydrogen bonds in nanocellulose films. The 1% PEG 600 plasticized nanocellulose scaffolds cross-linked with GA showed a higher tensile modulus (93 MPa) than its GA untreated nanocellulose scaffolds (69 MPa). The Young's modulus of the scaffold is increased up to 83.62 MPa. The crystallinity index values of GA-treated scaffolds were increased, and the mechanical characteristics were greatly improved, according to Fourier transform infrared (FTIR) and XRD analysis on the films. The thermogravimetric analysis (TG/DTG/DSC) of the GA treated plasticized nanocellulose scaffold showed maximum decomposition temperature (T_max) at 360.01 °C.

Nanocellulose in tissue engineering and bioremediation: mechanism of action

Nanocellulose are nano-sized components which are biodegradable, biocompatible and renewable. It offers mechanical strength and chemical stability in plants and bacteria. The environmental contamination is reduced by employing various bioremediation techniques which usesmicroorganisms like algae, bacteria and fungi as bio-adsorbents. The bio adsorbent property of nanocellulose contribute more for the bioremediation methods and the detailed study of its mechanism and application is essential which is discussed here. The mechanism happening between the contaminant and nanocellulose adsorbent should be explored in detail in order to develop effective new bioremediation strategies. Nanocellulose structural functionalization helps to modify the nanocellulose structure based on which it can be utilized for specific functions. Exploring the mechanisms that contribute to the implementation of nanocellulose in tissue engineering helps for further developments and advancement in the biomedical application of nanocellulose. Not much studies are available that elucidate and study the basic steps involved in the biomedical and environmental usage of nanocellulose. This review has focussed on the basic mechanisms involved in the use of nanocellulose in tissue engineering and bioremediation processes.

Nanocellulose as green material for remediation of hazardous heavy metal contaminants

Heavy metal pollution generated by urban and industrial activities has become a major global concern due to its high toxicity, minimal biodegradability, and persistence in the food chain. These are the severe pollutants that have the potential to harm humans and the environment as a whole. Mercury, chromium, copper, zinc, cadmium, lead, and nickel are the most often discharged hazardous heavy metals. Nanocellulose, reminiscent of many other sustainable nanostructured materials, is gaining popularity for application in bioremediation technologies owing to its many unique features and potentials. The adsorption of heavy metals from wastewaters is greatly improved when cellulose dimension is reduced to nanometric levels. For instance, the adsorption efficiency of Cr³⁺ and Cr⁶⁺ is found to be 42.02% and 5.79% respectively using microcellulose, while nanocellulose adsorbed 62.40% of Cr³⁺ ions and 5.98% of Cr⁶⁺ ions from contaminated water. These nanomaterials are promising in terms of their ease and low cost of regeneration. This review addresses the relevance of nanocellulose as biosorbent, scaffold, and membrane in various heavy metal bioremediation, as well as provides insights into the challenges, future prospects, and updates. The methods of designing better nanocellulose biosorbents to improve adsorption efficiency according to contaminant types are focused.

The hazardous threat of Bisphenol A: Toxicity, detection and remediation

Bisphenol A (or BPA) is a toxic endocrine disrupting chemical that is released into the environment through modern manufacturing practices. BPA can disrupt the production, function and activity of endogenous hormones causing irregularity in the hypothalamus-pituitary-gonadal glands and also the pituitary-adrenal function. BPA has immuno-suppression activity and can downregulate T cells and antioxidant genes. The genotoxicity and cytotoxicity of BPA is paramount and therefore, there is an immediate need to properly detect and remediate its influence. In this review, we discuss the toxic effects of BPA on different metabolic systems in the human body, followed by its mechanism of action. Various novel detection techniques (LC-MS, GC-MS, capillary electrophoresis, immunoassay and sensors) involving a pretreatment step (liquid-liquid microextraction and molecularly imprinted solid-phase extraction) have also been detailed. Mechanisms of various remediation strategies, including biodegradation using native enzymes, membrane separation processes, photocatalytic oxidation, use of nanosorbents and thermal degradation has been detailed. An overview of the global regulations pertaining to BPA has been presented. More investigations are required on the efficiency of integrated remediation technologies rather than standalone methods for BPA removal. The effect of processing operations on BPA in food matrices is also warranted to restrict its transport into food products.

Engineering interventions in industrial filamentous fungal cell factories for biomass valorization

Filamentous fungi possess versatile capabilities for synthesizing a variety of valuable bio compounds, including enzymes, organic acids and small molecule secondary metabolites. The advancements of genetic and metabolic engineering techniques and the availability of sequenced genomes discovered their potential as expression hosts for recombinant protein production. Remarkably, plant-biomass degrading filamentous fungi show the unique capability to decompose lignocellulose, an extremely recalcitrant biopolymer. The basic biochemical approaches have motivated several industrial processes for lignocellulose biomass valorisation into fermentable sugars and other biochemical for biofuels, biomolecules, and biomaterials. The review gives insight into current trends in engineering filamentous fungi for enzymes, fuels, and chemicals from lignocellulose biomass. This review describes the variety of enzymes and compounds that filamentous fungi produce, engineering of filamentous fungi for biomass valorisation with a special focus on lignocellulolytic enzymes and other bulk chemicals.

Lignocellulose in future biorefineries: Strategies for cost-effective production of biomaterials and bioenergy

Lignocellulosic biomass has been emerging as a biorefinery precursor for variety of biofuels, platform chemicals and biomaterials because of its specific surface morphology, exceptional physical, chemical and biological characteristics. The selection of proper raw materials, integration of nano biotechnological aspects, and designing of viable processes are important to attain a cost-effective route for the development of valuable end products. Lignocellulose-based materials can prove to be outstanding in terms of techno-economic viability, as well as being environmentally friendly and reducing effluent load. This review should facilitate the identification of better lignocellulosic sources, advanced pretreatments, and production of value-added products in order to boost the future industries in a cleaner and safer way.

Microbial valorization of lignin: Prospects and challenges

Lignin is the world's second most prevalent biomaterial, but its effective value-added product valorization methods are still being developed. The most common preparation processes for converting lignin to platform chemicals and biofuels are fragmentation and depolymerization. Due to its structural diversity, fragmentation generally produces a variety of products, necessitating tedious separation and purifying methods to isolate the desired products. Bacterial-based techniques are commonly utilized for lignin fragmentation due to their high metabolitic activity. Recent advancements in lignin valorization utilizing bacteria, such as lignin decomposing microbes and major pathways involved that can breakdown lignin into various valuable products namely lipids, furfural, vanillin, polyhydroxybutyrate, poly lactic acid blends were discussed in this review. This review also covers the genetic and fermentation methodologies to enhance lignin decomposition, challenges and future trends of microbe based lignin valorization.

Bacterial nanocellulose: engineering, production, and applications

Bacterial nanocellulose (BNC) has been emerging as a biomaterial of considerable significance in a number of industrial sectors because of its remarkable physico-chemical and biological characteristics. High capital expenses, manufacturing costs, and a paucity of some well-scalable methods, all of which lead to low BNC output in commercial scale, are major barriers that must be addressed. Advances in production methods, including bioreactor technologies, static intermittent, and semi-continuous fed batch technologies, and innovative outlay substrates, may be able to overcome the challenges to BNC production at the industrial scale. The novelty of this review is that it highlights genetic modification possibilities in BNC production to overcome existing impediments and open up viable routes for large-scale production, suitable for real-world applications. This review focuses on various production routes of BNC, its properties, and applications, especially the major advancement in food, personal care, biomedical and electronic industries.

Probiotics and gut microbiome - Prospects and challenges in remediating heavy metal toxicity

The gut microbiome, often referred to as "super organ", comprises up to a hundred trillion microorganisms, and the species diversity may vary from person to person. They perform a decisive role in diverse biological functions related to metabolism, immunity and neurological responses. However, the microbiome is sensitive to environmental pollutants, especially heavy metals. There is continuous interaction between heavy metals and the microbiome. Heavy metal exposure retards the growth and changes the structure of the phyla involved in the gut microbiome. Meanwhile, the gut microbiome tries to detoxify the heavy metals by altering the physiological conditions, intestinal permeability, enhancing enzymes for metabolizing heavy metals. This review summarizes the effect of heavy metals in altering the gut microbiome, the mechanism by which gut microbiota detoxifies heavy metals, diseases developed due to heavy metal-induced dysbiosis of the gut microbiome, and the usage of probiotics along with advancements in developing improved recombinant probiotic strains for the remediation of heavy metal toxicity.

Nanobiocatalysts: Advancements and applications in enzyme technology

Nanobiocatalysts are one of the most promising biomaterials produced by synergistically integrating advanced biotechnology and nanotechnology. These have a lot of potential to improve enzyme stability, function, efficiencyand engineering performance in bioprocessing. Functional nanostructures have been used to create nanobiocatalystsbecause of their specific physicochemical characteristics and supramolecular nature. This review covers a wide range of nanobiocatalysts including polymeric, metallic, silica and carbon nanocarriers as well as their recent developments in controlling enzyme activity. The enormous potential of nanobiocatalysts in bioprocessing in designing effective laboratory trials forapplications in various fields such as food, pharmaceuticals, biofuel, and bioremediation is also discussed extensively.

Potential of nanocellulose for wastewater treatment

Wastewater management has significant interest worldwide to establish viable treatment techniques to ensure the availability of clean water. The specialities of nanocellulose for this particular application is due to their high aspect ratio and accessibility of plenty of -OH groups for binding with dyes, heavy metals and other pollutants. This review aggregates the application of nanocellulose for wastewater treatment particularly as adsorbents of dyes and heavy metals, and also as membranes for filtering various other contaminants including microbes. The membrane technologies are proven to be effective relating to their durability and separation effectiveness. The commercial scale application of nanocellulose based materials in water treatment processes depend on various factors like routes of synthesis, surface modifications, hydrophilic/hydrophobic, porosity, durability etc. The recent developments on production of novel adsorbents or membranes encourage the implementation of nanocellulose based cleaner technologies for wastewater treatment.

Advanced biomaterials for sustainable applications in the food industry: Updates and challenges

Maintaining the safety and quality of food are major concerns while developing biomaterial based food packaging. It offers a longer shelf-life as well as protection and quality control to the food based on international standards. Nano-biotechnology contributes to a far extent to make advanced packaging by developing multifunctional biomaterials for potential applications providing smarter materials to consumers. Applications of nano-biocomposites may thus help to deliver enhanced barrier, mechanical strength, antimicrobial and antioxidant properties to novel food packaging materials. Starch derived bioplastics, polylactic acid and polyhydroxybutyrate are examples of active bioplastics currently in the food packaging sector. This review discusses the various types of biomaterials that could be used to improve future smarter food packaging, as well as biomaterials' potential applications as food stabilizers, pathogen control agents, sensors, and edible packaging materials. The regulatory concerns related to the use of biomaterials in food packaging and commercially available biomaterials in different fields are also discussed. Development of novel biomaterials for different food packaging applications can therefore guarantee active food packaging in future.

Development of an eco-friendly biodegradable plastic from jack fruit peel cellulose with different plasticizers and Boswellia serrata as filler

Pure nanocellulose was extracted from agricultural waste material namely jackfruit (Artocarpus heterophyllus) peel through acid hydrolysis. The extraction method utilizes soapnut solution as an eco-friendly bleaching agent in order to avoid environment polluting chlorinated chemicals. Various thin films were prepared by solvent casting nanocellulose and different plasticizers namely glycerol, polyethylene glycol, polyvinyl alcohol, triethyl citrate along with novel filler, Boswellia serrata commonly known as frankincense. Thin films were characterized by FT-IR, XRD and the surface modifications were investigated using FESEM. The physical, mechanical, thermal properties and biodegradability of the film were also reported. The surface morphology was improved by different plasticizers and a self-assembly was obtained due to more stable hydrogen bonding between the nanocellulose, plasticizers and filler during the film formation. Thermal investigations of plasticizers/Boswellia serrata incorporated thin films revealed an increase in glass transition temperature of nanocellulose. Results indicate that these films are biodegradable and compostable in nature and could be used as substitute for petroleum derived plastics.

Metabolic circuits and gene regulators in polyhydroxyalkanoate producing organisms: Intervention strategies for enhanced production

Worldwide worries upsurge concerning environmental pollutions triggered by the accumulation of plastic wastes. Biopolymers are promising candidates for resolving these difficulties by replacing non-biodegradable plastics. Among biopolymers, polyhydroxyalkanoates (PHAs), are natural polymers that are synthesized and accumulated in a range of microorganisms, are considered as promising biopolymers since they have biocompatibility, biodegradability, and other physico-chemical properties comparable to those of synthetic plastics. Consequently, considerable research have been attempted to advance a better understanding of mechanisms related to the metabolic synthesis and characteristics of PHAs and to develop native and recombinant microorganisms that can proficiently produce PHAs comprising desired monomers with high titer and productivity for industrial applications. Recent developments in metabolic engineering and synthetic biology applied to enhance PHA synthesis include, promoter engineering, ribosome-binding site (RBS) engineering, development of synthetic constructs etc. This review gives a brief overview of metabolic routes and regulators of PHA production and its intervention strategies.

Design of novel enzyme biocatalysts for industrial bioprocess: Harnessing the power of protein engineering, high throughput screening and synthetic biology

Biocatalysts have wider applications in various industries. Biocatalysts are generating bigger attention among researchers due to their unique catalytic properties like activity, specificity and stability. However the industrial use of many enzymes is hindered by low catalytic efficiency and stability during industrial processes. Properties of enzymes can be altered by protein engineering. Protein engineers are increasingly study the structure-function characteristics, engineering attributes, design of computational tools for enzyme engineering, and functional screening processes to improve the design and applications of enzymes. The potent and innovative techniques of enzyme engineering deliver outstanding opportunities for tailoring industrially important enzymes for the versatile production of biochemicals. An overview of the current trends in enzyme engineering is explored with important representative examples.

Valorization of food and kitchen waste: An integrated strategy adopted for the production of poly-3-hydroxybutyrate, bioethanol, pectinase and 2, 3-butanediol

The present investigation gives an insight on the potential of food and kitchen waste as a suitable feed stock for the production of biopolymer, biofuels, enzymes and chemicals. Media engineering improved poly-3-hydroxybutyrate (PHB) production from 0.91 g/L to 5.132 g/L. There is a five-fold increase in PHB production. The food and kitchen waste was also evaluated for the production of bioethanol, 2, 3 - butanediol, and pectinase. Saccharomyces cerevisiae produced 0.316 g of bioethanol, Bacillus sonorensis MPTD1 produced 2.47 (µM/mL)/min of pectinase and Enterobacter cloacae SG1 produced 3 g/L of 2, 3-butanediol with a productivity of 0.03 g/L/h using food and kitchen waste as carbon source. Targeting on multiple value added products will improve the overall process economics.

Vibrational spectra, structural conformations, scaled quantum chemical calculations and NBO analysis of 3-acetyl-7-methoxycoumarin

The powder form NIR-FT Raman and FT-IR spectra of 3-acetyl-7-methoxycoumarin (3A7MC) have been recorded in the regions 4000-400 and 3500-100 cm(-1), respectively. The equilibrium geometry, vibrational frequencies, band intensities, NMR spectra, NBO analysis and UV-Vis spectral studies of the most stable conformer have been calculated by density functional B3LYP method with the 6-311G(d,p) basis set. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra, the calculated wavenumber and intensity of the vibrational bands and the potential energy distribution over the internal coordinates. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping the electron density isosurface with electrostatic potential surfaces (ESP). Natural bond orbital analysis has been carried out to understand the nature of different interactions responsible for the electron delocalization and the intramolecular charge transfer between the orbitals (n→π(∗), n→σ(∗), π→π(∗)).

Synthesis, growth and vibrational spectroscopic study of a novel coumarinoylthiazole

An efficient route was developed for the synthesis of novel 3-(2-morpholinyl-4-phenylthiazol-5-oyl)coumarin (MPTC). FT-IR spectrum of MPTC was recorded and analyzed. The crystal structure data are also described. The vibrational wavenumbers were computed theoretically using the Gaussian03 package of programs using HF/6-31G(d) and B3LYP/6-31G(d) levels of theory. The data obtained from vibrational wave number calculations are used to assign vibrational bands observed in the infrared spectra of MPTC. The first hyperpolarizability, infrared absorption band intensities and intensities of raman active bands are reported. The calculated first hyperpolarizability is comparable with the values reported for compounds of similar structure. The structural parameters of MPTC obtained from XRD studies are in agreement with the calculated values. The unit cell parameters of crystals of MPTC are: a=8.6017(10)Å, b=9.9735(5)Å, c=13.3870(13)Å, α=111.123(6)°, β=90.102(9)°, γ=110.246(6)°, and Z=2,1.397 Mg/m(3).

DFT-based molecular modeling, NBO analysis and vibrational spectroscopic study of 3-(bromoacetyl)coumarin

The NIR-FT Raman and FT-IR spectra of 3-(bromoacetyl)coumarin (BAC) molecule have been recorded and analyzed. Density functional theory (DFT) calculation of two BAC conformers has been performed to find the optimized structures and computed vibrational wavenumbers of the most stable one. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Characteristic vibrational bands of the pyrone ring and methylene and carbonyl groups have been identified. The lowering of HOMO-LUMO energy gap clearly explains the charge transfer interactions taking place within the molecule.

EFFECT OF BENZOTHIAZOLOYLTHIAZOLES AS SECONDARY ACCELERATORS IN THE SULFUR VULCANIZATION OF NATURAL RUBBER

The vulcanization of natural rubber and a blend of natural rubber and reclaimed rubber by using binary accelerator systems containing a novel series of benzothiazoloylthiazole as secondary accelerator (SA) has been studied. These secondary accelerators were synthesized by a green chemical method under solvent-free conditions, by the irradiation of microwaves (180 W). The synergistic effect of the SA with N-Cyclohexyl-2-benzothiazolsulfenamide as primary accelerator was studied at 150 °C. These binary systems were effective in reducing the cure time and improving the rheometric and mechanical properties. These SAs were found to be effective in reducing the cure time with a minimal amount of 0.5 phr, but commercially available SAs such as thioureas and tetramethylthiuram disulfide were reported to show reduction in cure time only by increasing the amount of SA. Mechanical properties such as hardness, abrasion loss, tensile strength, percentage strain at break, and modulus at different elongations 100, 200, and 300% were evaluated and found to be immensely improved. The improved mechanical properties were also shown to be at par with crosslink densities (1/2Mc) of different mixes.