Highly Electrophilic Mononuclear Cationic Aluminium Alkoxide Complexes: Syntheses, Reactivity and Catalytic Applications.

Herein, we report the synthesis of ß-diketiminate-supported aluminium complexes bearing terminal alkoxide and mono-thiol functional groups: LAlOMe(Et) (2), LAlOtBu(Et) (3), and LAlSH(Et) (4), (L=[HC{C(Me)N-(2,6-iPr2 C6 H3 )}2 ]). Complexes 2 and 3 are further used as synthons to generate the fascinating cationic aluminium alkoxide complexes, [LAlOMe(µ-OMe)-Al(Et)L][EtB(C6 F5 )3 ] (5), [LAlOMe(OEt2 )][EtB(C6 F5 )3 ] (6), and [LAlOtBu(OEt2 )][EtB(C6 F5 )3 ] (8). These electrophilic cationic species are well characterized by spectroscopic and crystallographic techniques. The assessment of Lewis acidity by the Gutmann-Beckett method revealed superior Lewis acidity of the cations substituted with electron-demanding alkoxy groups in comparison to the known methyl analogue [LAlMe][B(C6 F5 )4 ]. This has been further endorsed by computational calculations to determine the NBO charges and hydride ion affinity for complexes 6 and 8. These complexes are also capable of activating triethylsilane in stoichiometric reactions. The applicability of these complexes has been realized in the hydrosilylation of ethers, carbonyls, and olefines. Additionally, the solid-state structure of a new THF stabilized aluminium halide cation [LAlCl(THF)][B(C6 F5 )4 ] (11) has also been reported.

Hydroboration of Imines and Alkynes Catalyzed by Electronically Unsaturated Aluminum Hydride and Methyl Aluminum Cations.

Aluminum hydride cations, [LAlH]+[HB(C6F5)3]- (1) and [LAlH]+[B(C6F5)4]- (2), and the methyl aluminum cation, [LAlMe]+[B(C6F5)4]- (3) (L = [{(2,6-iPr2C6H3N)P(Ph2)}2N]), due to their electronic and coordinative unsaturation at the Al center, exhibit high Lewis acidity and have been exploited for catalytic hydroboration (using HBpin/HBcat) of a variety of imines and alkynes. These catalysts, under mild reaction conditions, afford excellent yields of the respective products. Thorough mechanistic investigations have been performed using a series of stoichiometric experiments and successful isolation of the key intermediates was accomplished. The obtained results demonstrate the predominant Lewis acid activation mechanism over the pathways previously reported for covalent aluminum complexes catalyzed hydroboration of imines. The title cations form Lewis adducts with imines which are thoroughly characterized via multinuclear NMR measurements. For the hydroboration of alkynes, a detailed mechanistic study with the most efficient catalyst 2 supports the formation of a novel cationic aluminum alkenyl complex [LAl-C(Et)═CH(Et)]+[B(C6F5)4]- (7) via the hydroalumination reaction between the Al-H cation 2 and 3-hexyne. Similarly, hydroalumination of an unsymmetric internal alkyne 1-phenyl-1-propyne with 2 occurs regioselectively, leading to the formation of [LAl-C(Me)═CH(Ph)]+[B(C6F5)4]- (8). These unique cationic aluminum alkenyl complexes have been isolated and well characterized by multinuclear 1-D and 2-D NMR measurements. These alkenyl complexes further act as catalytically active species to carry forward the hydroboration reaction via the Lewis acid activation pathway.

An integration of algae-mediated wastewater treatment and resource recovery through anaerobic digestion.

Eutrophication is one of the major emerging challenges in aquatic environment. Industrial facilities, including food, textile, leather, and paper, generate a significant amount of wastewater during their manufacturing process. Discharge of nutrient-rich industrial effluent into aquatic systems causes eutrophication, eventually disturbs the aquatic system. On the other hand, algae provide a sustainable approach to treat wastewater, while the resultant biomass may be used to produce biofuel and other valuable products such as biofertilizers. This review aims to provide new insight into the application of algal bloom biomass for biogas and biofertilizer production. The literature review suggests that algae can treat all types of wastewater (high strength, low strength, and industrial). However, algal growth and remediation potential mainly depend on growth media composition and operation conditions such as light intensity, wavelength, light/dark cycle, temperature, pH, and mixing. Further, the open pond raceways are cost-effective compared to closed photobioreactors, thus commercially applied for biomass generation. Additionally, converting wastewater-grown algal biomass into methane-rich biogas through anaerobic digestion seems appealing. Environmental factors such as substrate, inoculum-to-substrate ratio, pH, temperature, organic loading rate, hydraulic retention time, and carbon/nitrogen ratio significantly impact the anaerobic digestion process and biogas production. Overall, further pilot-scale studies are required to warrant the real-world applicability of the closed-loop phycoremediation coupled biofuel production technology.

Hydrosilylation of Carbonyls Catalyzed by Hydridoborenium Borate Salts: Lewis Acid Activation and Anion Mediated Pathways.

The electronically unsaturated three-coordinated hydridoborenium cations [LBH]+[HB(C6F5)3]- (1) and [LBH]+[B(C6F5)4]- (2), supported by a bis(phosphinimino)amide ligand, were found to be excellent catalysts for hydrosilylation of a range of aliphatic and aromatic aldehydes and ketones under mild reaction conditions (L = [{(2,4,6-Me3C6H2N)P(Ph2)}2N]). The key steps of the catalytic cycle for hydrosilylation of PhCHO were monitored via in situ multinuclear NMR measurements for catalysts 1 and 2. The combined effect of carbonyl activation via the Lewis acidic hydridoborenium cation and the hydridic nature of the borate counteranion in 1 makes it a more efficient catalyst in comparison to that of carbonyl activation via the predominant Lewis acid activation pathway operating with catalyst 2. The catalytic cycle of 1 showed hydride transfer from the borate moiety [HB(C6F5)3]- to PhCHO in the first step, forming [PhCH2-O-B(C6F5)3]-, which subsequently underwent σ-bond metathesis with Et3SiH to form the product, PhCH2-O-SiEt3. Quantum chemical calculations also support the borate anion mediated mechanism with 1. In contrast, the reaction catalyzed by 2 proceeds predominantly via the Lewis acid activation of the carbonyl group involving [LB(H)←OC(H)Ph]+[B(C6F5)4]- as the transition state and [LBOCH2Ph]+[B(C6F5)4]- as the intermediate.

Electronically Unsaturated Three-Coordinate Aluminum Hydride and Organoaluminum Cations.

New three-coordinate and electronically unsaturated aluminum hydride [LAlH]+ [HB(C6 F5 )3 ]- (LH=[{(2,6-iPr2 C6 H3 N)P(Ph2 )}2 N]H) and aluminum methyl [LAlMe]+ [MeB(C6 F5 )3 ]- cations have been prepared. The quantitative estimation of Lewis acidity by Gutmann-Beckett method revealed [LAlH]+ [HB(C6 F5 )3 ]- to be better Lewis acid than B(C6 F5 )3 and AlCl3 making these compounds ideal catalysts for Lewis acid-mediated reactions. To highlight that the work is of fundamental importance, catalytic hydroboration of aliphatic and aromatic aldehydes and ketones have been demonstrated. Important steps of the catalytic cycle have been probed by using multinuclear NMR measurements, including successful characterization of the proposed aluminum benzyloxide cationic intermediate, [LAl-O-CH2 Ph]+ [HB(C6 F5 )3 ]- . The proposed catalytic cycle has been found to be consistent with experimental observations and computational studies clearly indicating the migration of hydride from cationic aluminum center to the carbonyl carbon is the rate-limiting step of the catalytic cycle.

Synthesis, pharmacological evaluation and molecular docking of pyranopyrazole-linked 1,4-dihydropyridines as potent positive inotropes.

1,4-Dihydropyridines are well-known calcium channel blockers, but variations in the substituents attached to the ring have resulted in their role reversal making them calcium channel activators in some cases. We describe the microwave-assisted eco-friendly approach for the synthesis of pyranopyrazole-1,4-dihydropyridines, a new class of 1,4-DHPs, under solvent-free conditions in good yield, and screen them for various in silico, in vitro and in vivo activities. The in vivo experimentation results show that the compounds possess positive inotropic effect, and the docking results validate their good binding with calcium channels. Compounds 7c, 7g and 7i appear to be the most effective positive inotropes, even at low doses, and bind with the calcium channels even more strongly than Bay K 8644, a well-known calcium channel activator. The chronotropic effect for the new compounds was also studied. The target and off-target affinity profiling supported the in vivo results and revealed that the hybridized pyranopyrazole dihydropyridine scaffold has delivered new moderate hits, to be optimized, for the cytochrome P450 3A4 enzymes, opening avenues for combined pharmacological activity through standard structural modification.

A rhodamine based fluorescent and colorimetric chemosensor for the detection of Cr3+ ions and its utility in a molecular logic gate.

A new rhodamine based fluorescent and colorimetric chemosensor S1 was synthesized for the selective recognition of Cr3+, a trivalent metal ion. The interaction of S1 toward different metal ions has been studied via fluorescence and UV-visible spectroscopy. The studies revealed that the fluorescence and colorimetric changes of chemosensor S1 are prominent for Cr3+ over other competitive metal ions. Moreover, the chemosensor S1 exhibits 1 : 1 complex formation with Cr3+ as apparent from the Job's plot and the Benesi-Hildebrand (B-H) plot. Density functional theory (DFT) studies also revealed that the Cr3+ ion is coordinated to three atoms of S1, which validates the formation of a complex between S1 and Cr3+. The limit of detection (LOD) of chemosensor S1 for Cr3+ was 0.21 µM. Furthermore, to explore the recyclability of S1, ethylenediaminetetraacetic acid (EDTA) was added to the S1-Cr3+ solution. On the addition of EDTA to the solution of S1-Cr3+, the reversibility of the complex was observed, and a colorimetric variation was also observed on the addition of Cr3+ and EDTA to S1 which mimics the "INHIBIT "molecular logic gate. Chemosensor S1 also demonstrated practical utility through detection of Cr3+ in the solid state.

Use of reverse osmosis reject from drinking water plant for microalgal biomass production.

The present study evaluates the use of reverse osmosis (RO) reject, termed as ROR, for microalgal biomass production. The supplementation of ROR from two different sources, namely domestic RO unit (ROR1) and commercial-scale RO plant (ROR2), showed a synergistic effect on the growth and biochemical composition of Chlorella pyrenoidosa. Among the tested ROR1 doses, the highest biomass production (1.27±0.06 g L-1) was observed with 25% ROR1 supplemented growth media. In contrast, the lipid content (28.85±3.13% of TS) in C. pyrenoidosa at 50% ROR1 dose was almost twice that in BG11 (positive control). Interestingly, the microalgae showed relatively higher biomass production (1.37±0.07 g L-1) and higher lipid content (33.23±3.92% of TS) when 50% ROR2 was used in growth media. At the same time, the estimated carbohydrate and protein contents were 28.41±0.73 and 29.75±0.31% of TS, respectively. Furthermore, the lipid productivity (28.98±2.79 mg L-1 d-1) was relatively higher than the nutrient media (12.35±1.34 mg L-1 d-1). The present findings revealed that the RO reject from drinking water purifiers can efficiently be utilized for lipid-rich microalgal biomass production. Hence, the dependency on freshwater resources for mass scale microalgae cultivation through recycling of RO reject can be reduced.

Enzymatic pretreatment of algal biomass has different optimal conditions for biogas and bioethanol routes.

Enzymatic pretreatment is emerging as an efficient tool for the extraction of biofuel precursors from algal biomass. However, yardsticks for end-use directed selection of optimal pretreatment conditions are not yet identified. The present study, for the first time, reveals different optimal conditions for algal biomass solubilization and sugar release. Algal biomass pretreatment optimization was carried out using the Taguchi method. Crude enzyme from Aspergillus fischeri was found effective for pretreatment of Chlorella pyrenoidosa. Maximum sugar yield (190 mg g-1 biomass) from algal biomass was observed at a substrate concentration of 4 g L-1, with a 5% enzyme load at temperature 60°C, pH 5.5, and shaking speed of 80 rpm. In contrast, maximum sCOD (1350 mg g-1 biomass) was obtained at 2 g L-1 substrate concentration with enzyme load of 20% v/v, at 60°C, pH 4, and shaking speed of 100 rpm. Hence, the first set of conditions would be more beneficial for bioethanol production. Whereas another set of conditions would improve the biofuel production that requires maximum solubilization of algal biomass, such as fermentative methane production. Overall, the present observations established that process conditions required for enzymatic pretreatment of algal biomass should be selected according to the desired biofuel type.