Green Synthetic Process Research Articles

Structural and Functional Characterization of 4-Hydroxyphenylacetate 3-Hydroxylase from Escherichia coli.

The hydroxylation of phenols into polyphenols, which are valuable chemicals and pharmaceutical products, is a challenging reaction. The search for green synthetic processes has led to considering microorganisms and pure hydroxylases as catalysts for phenol hydroxylation. Herein, we report the structural and functional characterization of the flavin adenine dinucleotide (FAD)-dependent 4-hydroxyphenylacetate 3-monooxygenase from Escherichia coli, named HpaB. It is shown that this enzyme enjoys a relatively broad substrate specificity, which allows the conversion of a number of non-natural phenolic compounds, such as tyrosol, hydroxymandelic acid, coumaric acid, hydroxybenzoic acid and its methyl ester, and phenol, into the corresponding catechols. The reaction can be performed by using a simple chemical assay based on formate as the electron donor and the organometallic complex [Rh(bpy)Cp*(H2 O)]2+ (Cp*: 1,2,3,4,5-pentamethylcyclopentadiene, bpy: 2,2'-bipyridyl) as the catalyst for FAD reduction. The availability of a crystal structure of HpaB in complex with FAD at 1.8 Å resolution opens up the possibility of the rational tuning of the substrate specificity and activity of this interesting class of phenol hydroxylases.

Preparation of a Pt/Active Carbon Fiber Catalyst and Its Application in the Synthesis of p-Chloroaniline with Catalytic Hydrogenation.

In this study, a Pt loaded active carbon fiber (Pt/ACF) catalyst was prepared by immobilizing Pt nanoparticles on ACF. The catalyst accelerated hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CA) at lower temperature and atmospheric pressure, resulting in approximately 100% yield and selectivity. Several factors that affect p-CA yield were investigated. The nitro reduction rate reached 100% under the optimal reaction conditions, indicating excellent selectivity of the prepared catalyst. This process will overcome the environmental pollution problems associated with the traditional process, and is a green synthetic process.

Green Synthesis and Characterization of α-Fe2O3 Nanoparticles using Leaf Extract of Syzygium cumini and their Suitability for Adsorption of Cu(II) and Pb(II) Ions

In the present study, we have synthesized α-Fe2O3 nanoparticles by using the leaf extract of Syzygium cumini. The applying green synthetic process is very efficient, low cost and can be applicable in the large scale operations. The freshly synthesized dried nanoparticles were characterized by UV-visible, FT-IR, XRD and FESEM. The α-Fe2O3 (haematite) nanoparticles have now used as effective nano-adsorbents for the removal of Cu(II) and Pb(II) ions from synthetically prepared wastewater under batch conditions. The batch system included contact time, dosage, pH, concentration and temperature. The maximum adsorption efficiency was found at optimized conditions such as contact time 60 min, higher acidic pH 6, higher dosage of sorbent 1.0 g and lower metal ion concentration 10 mg/L. For Pb(II) ions, 59.79, 85.10, 51.39 and 36.81 % adsorption was found at contact time 60 minutes, pH 6, dosage 1 g and metal ion concentration 10 mg/L. Similarly, for Cu(II) ions at same conditions, the adsorption was found to be 49.88, 69.73, 53.77 and 20.68 %, respectively. The equilibrium data of adsorption have been tested by Langmuir, Freundlich and Temkin isotherm models. The adsorption data were best fitted to Langmuir isotherm model with the regression values R2 = 0.984 for Cu(II) ions and R2 = 0.9383 for Pb(II) ions. The adsorption capacity of α-Fe2O3 nanoparticles for Cu(II) and Pb(II) ions was found 7.535 and 6.480 mg/g, respectively.

Microbial synthesis of anti-tumor agent oxysophoridine through one step by filamentous fungus

Sophoridine and oxysophoridine are alkaloids extracted from Chinese traditional medicine with significant antitumor activities. Computer-aided design and preliminary structure-activity relationship studies showed that the biological activity of sophoridine can be improved after oxidation (oxysophoridine) while its toxicity significantly decreased. A new method to prepare oxysophoridine from natural product Sophoridine by biotransformation was established for the first time except for traditional extraction from plants and chemical synthesis. Positive biocatalytic reaction was detected by TLC. Structure of conversion product was elucidated based on NMR spectroscopy. Optimizations of reactions including substrate concentration, pH, conversion time and inoculation quantity were complemented which analyzed by LC-MS. Results showed that filamentous fungus Xylariales. sp F005 (CCTCC M2014660) has the capacity of synthetizing oxysophoridine from sophoridine in the selected 37 strains. The yield of oxysophoridine reached highest at conditions pH 6.0, the third day of conversion time, 5.0 mg substrate and 5% inoculums respectively. The method for preparing oxysophoridine catalyzed by enzymes with green and sustainable synthetic processes was developed.

Development and characterization of fully bio‐based polybenzoxazine‐silica hybrid composites for low‐k and flame‐retardant applications

In the present work, new classes of bio‐based polybenzoxazines were synthesized using eugenol as phenol source and furfurylamine and stearylamine as amine sources separately through solventless green synthetic process routes and were further reinforced with varying percentages (1, 3, 5, and 10 wt%) of silica (from rice husk) to attain hybrid composites. The molecular structure, cure behaviour, thermal stability, dielectric properties, and flame‐retardant behaviour of both benzoxazine monomers and benzoxazine composites were characterized using appropriate modern analytical techniques. The eugenol‐based benzoxazines synthesized using furfurylamine (FBz) and stearylamine (SBz) were cured at 223°C and 233°C, respectively. The differential scanning calorimetry (DSC) data reveal the glass transition temperatures (Tg) of FBz and SBz were 157°C and 132°C, respectively, and the maximum decomposition temperature (Tmax) as obtained from thermogravimetric analysis (TGA), were found to be 464°C and 398°C for FBz and SBz, respectively. The dielectric constants for FBz and SBz obtained at 1 MHz were 3.28 and 3.62, respectively. Furthermore, varying weight percentages (1, 3, 5, and 10 wt%) of 3‐mercaptopropyltrimethoxysilane (3‐MPTMS) functionalized bio‐silica reinforced the composite materials as evidenced by their improved thermal stability and lower dielectric constant. Data obtained from thermal and dielectric studies suggested that these polybenzoxazines could be used in the form of adhesives, sealants, and composites for high performance inter‐layer low‐k dielectric applications in microelectronics.

In situ synthesized lactobionic acid conjugated NMOFs, a smart material for imaging and targeted drug delivery in hepatocellular carcinoma

Development of multifunctional nanoscale materials for targeted drug delivery in liver tumor cells has been realized in this work. Recently, nanoscale metal organic frameworks (NMOFs) have been used as a potential drug carrier for its unique characteristic properties. Here we have demonstrated a single step approach for the fabrication of lactobionic acid (LA) modified NH2-MIL-53(Al) NMOFs via green synthetic process. The anticancer drug doxorubicin (DOX) is loaded for targeted delivery in hepatocellular carcinoma cell lines (HepG2). The LA-targeted NMOFs have no cytotoxicity in both normal and hepatocellular cell lines. Human hepatocellular carcinoma cell lines are enriched of asialoglycoprotein receptors and simultaneously LA has strong recognition ability towards this receptor. The MTT assay reveals the DOX loaded LA-embedded NMOFs show greater cytotoxicity towards HepG2 cell lines in compare to normal cell lines. The FACS study also indicates that DOX-loaded LA-targeted NMOFs show greater cell death than bare NMOFs. More importantly, the NH2-MIL-53 NMOFs possess inherent fluorescent property and also the fluorescence intensity remains unaltered after conjugation of LA. So, the developed LA-embedded multifunctional NMOFs have good therapeutic efficacy for cell imaging and targeted drug delivery.

Microwave, Ultrasound, and Mechanochemistry: Unconventional Tools that Are Used to Obtain “Smart” Catalysts for CO2 Hydrogenation

The most recent progress obtained through the precise use of enabling technologies, namely microwave, ultrasound, and mechanochemistry, described in the literature for obtaining improved performance catalysts (and photocatalysts) for CO2 hydrogenation, are reviewed. In particular, the main advantages (and drawbacks) found in using the proposed methodologies will be discussed and compared by focusing on catalyst design and optimization of clean and efficient (green) synthetic processes. The role of microwaves as a possible activation tool used to improve the reaction yield will also be considered.

Ionic Liquids for Clean Biocatalytic Processes

Background: Biocatalysis has many attractive features in the context of green chemistry, due to the high efficiency of chemical transformations and the renewable character of the enzymes used. Since the beginning of this century, ILs have emerged as exceptionally interesting non-aqueous reaction media for biotransformations because of their unique solvent properties, headed by their negligible vapour pressure and their exceptional ability to maintain enzymes in active and stable conformations. However, the goal of green chemistry is much more than simply replacing hazardous solvents with environmentally benign ones, and it is necessary to devise new clean methodologies that will fulfil the sustainable requirements for efficient transformations of substrates, product recovery and the reuse of all the elements of the reaction system. Results: The use biocatalyst in IL/scCO2 biphasic systems was the first approach forward to develop integral green chemical processes in non-aqueous environments. The combination of these sustainable tools provides synergies in both biocatalyst performance (i.e. improved activity and enantioselectivity, enhanced stability, etc.), and the genuine separation technologies of nearly pure products. Sponge-Like Ionic Liquids (SLILs) were recently reported as a new platform for green biocatalytic chemical processes using straightforward technologies. These SLILs are a new class of hydrophobic ILs based on cations with long alkyl side-chains (e.g. 1-octadecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, ([C18mim][NTf2], etc.), which behaves as a sponge-like system by switching from liquid to solid phase as the temperature changes. Thus, such ILs are able to dissolve (“soak up”) hydrophobic compounds as a liquid phase, and products can then be “wrung out” by centrifugation of the resulting solid phase after cooling. Based on this property, clean biocatalytic processes for the production of nearly pure compounds of high added value (e.g. geranyl acetate, anisyl acetate, biodiesel, monolaurin, etc.) can be easily designed by the coupling of both biotransformation and separation steps, in a sustainable approach of high potential for practical applications at industrial level. Conclusions: The use of biocatalytic approaches in green non-conventional reaction media holds much promise for the development of a sustainable chemical manufacturing industry. The combination of enzymes with multiphase neoteric systems (SLILs, ILs and/or scCO2) should be explored in the near future, as a clear strategy for developing integral new green multi-catalytic synthetic processes of industrial interest (e.g. pharmaceutical drugs). Keywords: Biocatalysis, clean processes, ionic liquids, sponge-like ionic liquids, green chemistry, terpene, biodiesel, anisyl acetate, lipases.

Biosynthesis of silver nanoparticles from Spirulina microalgae and its antibacterial activity.

The present work focuses on a low-cost, simple, and green synthesis of silver nanoparticles (AgNPs) by mixing AgNO3 solution with the extract of Spirulina platensis (SP) without any chemical reducing and/or capping agents. The green synthesis of AgNPs was confirmed by the color change from colorless to yellowish brown. The biosynthesis of AgNPs was further confirmed by UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), biological transmission electron microscopy (Bio-TEM), and energy dispersive X-ray analysis (EDX). The UV-vis spectroscopy results showed the surface plasmon resonance (SPR) of AgNPs around 450nm. Bio-TEM analysis revealed that the Ag nanoparticles were well dispersed with average range of 5-50nm. XRD results indicated that the green synthetic process produced face-centered cubic structure of AgNPs. FT-IR spectroscopy analysis showed that the bioactive molecules from the SP extract believed to be the responsible for the reduction of Ag ions. Furthermore, the synthesized AgNPs were evaluated against pathogens such as Staphylococcus sp. and Klebsiella sp. The AgNPs (1-4mM) extensively reduced the growth rate of the pathogens.

Ionic liquid-mediated deoxydehydration reactions: Green synthetic process for bio-based adipic acid

A novel recyclable Re-catalyzed deoxydehydration (DODH) reaction was developed with an ionic liquid (IL) as a reaction medium for an efficient synthesis of adipic acid (1), one of the commercially important dicarboxylic acids, from biomass galactaric acid. The carefully designed solubility of ILs allowed a homogeneous DODH reaction to produce muconate 3 in excellent yields, a key intermediate for 1. Use of the IL also enabled an efficient separation of the DODH product 3 from the reaction mixture by simple decantation. The recovered IL layer containing the expensive Re catalyst was reused up to four times, yielding 3 without much decrease in yields. The target compound 1 was also produced in an excellent yield with the catalytic hydrogenation of 3 followed by the acidic hydrolysis. Thus, the overall process for bio-based adipic acid would become much more cost-effective, eco-friendly, and industrially viable, which could be applied to various biomass conversions.

Contribution of microreactor technology and flow chemistry to the development of green and sustainable synthesis.

Microreactor technology and flow chemistry could play an important role in the development of green and sustainable synthetic processes. In this review, some recent relevant examples in the field of flash chemistry, catalysis, hazardous chemistry and continuous flow processing are described. Selected examples highlight the role that flow chemistry could play in the near future for a sustainable development.

Vapor phase solvents loaded in zeolite as the sustainable medium for the preparation of Cu-BTC and ZIF-8

Solvent-evaporated conversion (SEC) and steam-assisted conversion (SAC) have been developed to prepare the typical metal-organic frameworks (MOFs) Cu-BTC (HKUST-1) and ZIF-8 using a unique solvent recovery strategy using zeolite. As a green circulation medium, zeolite Na-4A loading and removal of solvent (H2O and EtOH) can transport solvent in the vapor phase and avoid solvent condensation, which was the defect in previous SAC syntheses of MOFs, and achieves efficient solvent recovery as well as being an economical and green synthetic process. Moreover, SEC and SAC processes exhibited different mechanisms during the multi-stage reaction and solid diffusion reaction, respectively and both can synthesize the desired products in 12h. These two methods for MOFs preparation were characterized in detail using XRD, SEM and N2 adsorption during the different growing stages. According to polar molecules (H2O and EtOH) steam-assisted in those synthesis, polar destruction molecules (H2O, NH3) adsorption and stability of Cu-BTC and ZIF-8 was investigated.

Controllable Biosynthesis and Properties of Gold Nanoplates Using Yeast Extract

Biosynthesis of gold nanostructures has drawn increasing concerns because of its green and sustainable synthetic process. However, biosynthesis of gold nanoplates is still a challenge because of the expensive source and difficulties of controllable formation of morphology and size. Herein, one-pot biosynthesis of gold nanoplates is proposed, in which cheap yeast was extracted as a green precursor. The morphologies and sizes of the gold nanostructures can be controlled via varying the pH value of the biomedium. In acid condition, gold nanoplates with side length from 1300 ± 200 to 300 ± 100 nm and height from 18 to 15 nm were obtained by increasing the pH value. Whereas, in neutral or basic condition, only gold nanoflowers and nanoparticles were obtained. It was determined that organic molecules, such as succinic acid, lactic acid, malic acid, and glutathione, which are generated in metabolism process, played important role in the reduction of gold ions. Besides, it was found that the gold nanoplates exhibited plasmonic property with prominent dipole infrared resonance in near-infrared region, indicating their potential in surface plasmon-enhanced applications, such as bioimaging and photothermal therapy.Graphical

Regio‐selective Reduction of Oxysophoridine by Microorganism Isolated from Soil

AbstractOxysophoridine (OSR), an alkaloid extracted from a traditional Chinese medicine, attracted more and more attention because of remarkable biological activities. Biocatalysis of OSR by 86 stains including soil microbes and endophytic fungi were investigated. Incubation of OSR with soil bacteria T003 identified as Escherichia coli could lead to only one reductive product with highly regio‐selectivity. The structural elucidations of transformation product were achieved mainly by the NMR spectroscopic methods and references. Effect of pH, substrate concentration, conversion time and strain concentration was studied, the optimization of reaction was analyzed by LC‐MS. The production of sophoridine (SR) from OSR was highest at pH 7.0, 36 h of incubation and in presence of 625 μg/mL substrate concentration, 50 μL/mL strain concentration respectively. Biocatalysis was considered the alternatives to preparation of sophoridine with green and sustainable synthetic processes except for less time‐consuming and more environmentally friendly.

Biocatalytic Synthesis of the Anti‐diabetes Agent‐corosolic Acid by Whole Cells of Microorganisms

AbstractDiabetes is one of the most prevalent and costly global diseases. For diabetes, frequent insulin treatment and synthetic drugs are very expensive and may cause unwanted side effects. Corosolic acid (CA), a natural product, was reported to be efficient in the treatment of diabetes, meanwhile without induction of anti‐insulin antibodies and obesity. The preparation of CA attracted many researchers in the world. This study investigated the biocatalytic synthesis method of CA from ursolic acid by Streptomyces griseus subsp. griseus 4.18. LCMS analysis demonstrated that 5 day, 125 μg/mL substrate, pH=9 and 10% strain concentration were the appropriate conditions. It is estimated that biocatalysis will contribute to the development of green and sustainable synthetic processes with less time‐consuming and more environmentally friendly.

Photocatalysis in dimethyl carbonate green solvent: degradation and partial oxidation of phenanthrene on supported TiO2

Dimethyl carbonate (DMC) is here proposed – for the first time – as a green organic solvent for photocatalytic synthesis. In this work, the photocatalytic partial oxidation of phenanthrene in dimethyl carbonate (DMC) by using anatase TiO2 as the photocatalyst is described as paradigmatic example of a green synthetic process starting from polycyclic aromatic hydrocarbons (PAHs). For comparison, the same reaction carried out also in ethanol, 1-propanol or 2-propanol is reported. The use of DMC as the solvent allowed us to achieve 19% and 23% selectivity towards 9-fluorenone and 6H-benzo[c]chromen-6-one, respectively. The proposed approach may represent both a new green synthetic process and an environmentally friendly route to degradation of PAHs.

Direct use of nanoparticles as a heterogeneous catalyst: Pd0-doped CoFe2O4 magnetic nanoparticles for Sonogashira coupling reaction

A magnetically separable nanocatalyst prepared by incorporating Pd nanoparticles onto CoFe2O4 magnetic nanoparticles was found to be very effective in catalyzing Sonogashira cross-coupling reactions. In this green synthetic process, it is not necessary to use an external linker to support the palladium nanoparticles onto the cobalt ferrite matrix. The catalyst is effective without the use of any ligand or copper additive. The reaction works smoothly in ethanol at 70 °C with both aryl iodides and bromides to produce corresponding product in high yield. After completion of the reaction, the catalyst could be easily separated using an external magnet and reused up to five catalytic cycles with sustained catalytic activity.

Facile single-step preparation of Pt/N-graphene catalysts with improved methanol electrooxidation activity

In this work, we describe a facile single-step approach for the simultaneous reduction of graphene oxide to graphene, functional doping of graphene with nitrogen, and loading of the doped graphene with well-dispersed platinum (Pt) nanoparticles using a solvent mixture of ethylene glycol and N-methyl-2-pyrrolidone. The as-prepared Pt/nitrogen-doped graphene (N-graphene) catalysts are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy while the electrocatalytic methanol oxidation properties of the catalysts are evaluated by cyclic voltammetry and chronoamperometry. Compared with an updoped Pt/graphene control catalyst, the Pt/N-graphene catalyst shows a narrower particle size distribution and improved catalytic performance. Considering the facile, green and effective single-step synthetic process for the Pt/N-graphene catalyst, the results are promising for the potential application of these materials in emerging fuel cell technologies.

Metal–Ligand Cooperation by Aromatization–Dearomatization: A New Paradigm in Bond Activation and “Green” Catalysis

In view of global concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh approaches to catalytic design are desirable. In recent years, complexes based on "cooperating" ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation. We have discovered a new mode of metal-ligand cooperation, involving aromatization-dearomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidation state, and so far the activation of H-H, C-H (sp(2) and sp(3)), O-H, and N-H bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process, which involves consecutive thermal liberation of H(2) and light-induced liberation of O(2), using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex. An acridine pincer complex displays unique "long-range" metal-ligand cooperation in the activation of H(2) and in reaction with ammonia. In this Account, we begin by providing an overview of the metal-ligand cooperation based on aromatization-dearomatization processes. We then describe a range of novel catalytic reactions that we developed guided by these new modes of metal-ligand cooperation. These reactions include the following: (1) acceptorless dehydrogenation of secondary alcohols to ketones, (2) acceptorless dehydrogenative coupling of alcohols to esters, (3) acylation of secondary alcohols by esters with dihydrogen liberation, (4) direct coupling of alcohols and amines to form amides and polyamides with liberation of dihydrogen, (5) coupling of esters and amines to form amides with H(2) liberation, (6) selective synthesis of imines from alcohols and amines, (6) facile catalytic hydrogenolysis of esters to alcohols, (7) hydrogenolysis of amides to alcohols and amines, (8) hydrogenation of ketones to secondary alcohols under mild hydrogen pressures, (9) direct conversion of alcohols to acetals and dihydrogen, and (10) selective synthesis of primary amines directly from alcohols and ammonia. These reactions are efficient, proceed under neutral conditions, and produce no waste, the only byproduct being molecular hydrogen and/or water, providing a foundation for new, highly atom economical, green synthetic processes.

Interactions of zeatin with gold ions and biomimetic formation of gold complexes and nanoparticles

We report here a simple one-pot synthesis for the preparation of gold nanoparticles biomimetically using zeatin nanostructures. Zeatin, a plant phytohormone was self-assembled into nanospheres. Those nanospheres transformed into nanoribbons over a period of time upon formation of zeatin–gold (III) complexes in the presence of hydrogen tetrachloroaurate. Further, upon heating, gold nanoparticles were formed due to mineralization in the presence of zeatin nanofibers. The effect of pH on the self-assembly of zeatin and the formation of gold nanoparticles, was investigated. We also compared the preparation of gold nanoparticles in the presence of zeatin nanoribbons, using a known reducing agent such as hydrazine, which resulted in loss of morphology control and alignment of the gold nanoparticles. Thus zeatin nanoribbons act as templates which allow for size as well as alignment control for the gold nanoparticles. The materials obtained were analyzed using FTIR, absorbance spectroscopy as well as by transmission electron microscopy, EDX, SEM and AFM. The method involved here is a mild, green-synthetic process, which could be used for facile preparation of morphology controlled gold nanoparticles and may open up new avenues for device fabrications for a wide range of applications, particularly in optoelectronics and sensors.