RESUMEN

We show that the ability of the ligand to reorganize the electric double layer (EDL) often dominates the electrocatalysis contrary to their inductive effect in the spectrochemical series, leading to counterintuitive electrocatalysis. With water oxidation and chlorine evolution as the probe reactions, the same catalytic entity with carboxy functionalized ligand exhibited surprisingly higher electrochemical activity in comparison to the aggressively electron-withdrawing nitro functionalized ligands, which is contrary to their actual location in the spectrochemical series. Spectroscopic and electrochemical analyses suggest the enrichment of catalytically active species in the carboxy substituted ligand via proton charge assembly in the EDL that in turn enhances the kinetics of the overall electrochemical process. This demonstration of less obvious ligands becoming indispensable in electrocatalysis suggests a blind designing of ligands solely based on their inductive effect should be reconsidered as it will prevent the utilization of the maximum potential of the molecule in electrocatalysis.

RESUMEN

Hydrohydrazination of terminal alkynes with hydrazides yielding hydrazones 5-14 were successfully catalyzed by a series of gold(I) acyclic aminooxy carbene complexes of the type [{(4-R2-2,6-t-Bu2-C6H2O)(N(R1)2)}methylidene]AuCl, where R2 = H, R1 = Me (1b); R2 = H, R1 = Cy (2b); R2 = t-Bu, R1 = Me (3b); R2 = t-Bu, R1 = Cy (4b). The mass spectrometric evidence corroborated the existence of the catalytically active solvent-coordinated [(AAOC)Au(CH3CN)]SbF6 (1-4)A species and the acetylene-bound [(AAOC)Au(HC≡CPhMe)]SbF6 (3B) species of the proposed catalysis cycle. The hydrohydrazination reaction was successfully employed in synthesizing several bioactive hydrazone compounds (15-18) with anticonvulsant properties using a representative precatalyst (2b). The DFT studies favored the 4-ethynyltoluene (HC≡CPhMe) coordination pathway over the p-toluenesulfonyl hydrazide (NH2NHSO2C6H4CH3) coordination pathway, and that proceeded by a crucial intermolecular hydrazide-assisted proton transfer step. The gold(I) complexes (1-4)b were synthesized from the {[(4-R2-2,6-t-Bu2-C6H2O)(N(R1)2)]CH}+OTf- (1-4)a by treatment with (Me2S)AuCl in the presence of NaH as a base. The reactivity studies of (1-4)b yielded the gold(III) [{(4-R2-2,6-t-Bu2-C6H2O)(N(R1)2)}methylidene]AuBr3 (1-4)c complexes upon reaction with molecular bromine and the gold(I) perfluorophenylthiolato derivatives, [{(4-R2-2,6-t-Bu2-C6H2O)(N(R1)2)}methylidene]AuSC6F5 (1-4)d, upon treatment with C6F5SH.

RESUMEN

Lead-free halide perovskites have gained immense popularity in photovoltaic and energy harvesting applications because of their excellent optical and electrical attributes with minimal toxicity. We synthesized composite films of lead-free Cs3Bi2Br9 perovskite embedded in the polyvinylidene fluoride (PVDF) matrix and have investigated their piezoelectric energy harvesting. Five PVDF@Cs3Bi2Br9 composite films were fabricated with varying wt% of the perovskite in the PVDF. The composite with a 4 wt% of the perovskite shows 85% activation of the electroactive ß-phase of PVDF. Additionally, this composite exhibits a maximum polarisation of ∼0.1 µC cm-2 and the best energy storage density of ∼0.8 mJ cm-3 at an applied field of ∼16 kV cm-1 among all the synthesized composites. A nanogenerator fabricated using 4 wt% loading in the composite film produced an instantaneous output voltage of ∼40 V, an instantaneous current of ∼4.1 µA, and a power density of ∼17.8 µW cm-2 across 10 MΩ resistance when repeatedly hammered by the human hand. The nanogenerator is further employed to light up several LEDs and to charge capacitors with a small active area demonstrating significant promise for prospective wearables and portable devices and paving the way for high-performance nanogenerators using lead-free halide perovskites. Density functional theory calculations were performed to understand the interaction of the electroactive phase of the PVDF with different perovskite surface terminations to unravel the various interaction mechanisms and their ensuing charge transfer properties.

RESUMEN

Heterocyclic polynuclear aromatic hydrocarbons (PAH) are characterized by higher aqueous solubility and enhanced bioavailability due to presence of nitrogen, sulfur or oxygen heteroatoms in their chemical structure and are referred to as nitrogen (PANH), sulfur (PASH) and oxygen (PAOH) heterocyclic PAHs, respectively. Inspite of their significant ecotoxicity and human health impacts, these compounds have not yet been included in the U.S. EPA's list of "priority PAH". The current paper presents a comprehensive review of the environmental fate, various detection techniques and toxicity of heterocyclic PAH compounds, highlighting their significant environmental impacts. Heterocyclic PAHs have been detected at 0.03 to 11,000 ng/L in various aquatic bodies and at 0.1 to 3210 ng/g in contaminated land. PANHs are the most polar heterocyclic PAHs, having aqueous solubility at least 10 to 10,000 times higher than PAH, PASH, and PAOH compounds, which make them more bioavailable. Aquatic fate of heterocyclic PAHs is dominated by volatilization and biodegradation processes for low molecular weight (MW) compounds and photochemical oxidation for high MW compounds. Sorption of heterocyclic PAHs on soil is governed by partitioning to soil organic carbon, cation exchange, and surface complexation mechanisms for PANHs and non-specific interactions, such as van der Waals forces with soil organic carbon for PASHs and PAOHs. Various chromatographic and spectroscopic techniques, such as HPLC and GC, NMR, and TLC have been employed to elucidate their distribution and fate in the environment. PANHs are also the most acutely toxic heterocyclic PAHs with EC50 values ranging from 0.001 to 1100 mg/L in various species of bacteria, algae, yeast, invertebrate, and fish. Heterocyclic PAHs also induce mutagenicity, genotoxicity, carcinogenicity, teratogenicity, and phototoxicity in various aquatic and benthic organisms and terrestrial animals. Compounds, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and some acridine derivatives are proven human carcinogens and several other heterocyclic PAHs are suspected human carcinogens.

Asunto(s)

RESUMEN

Double proton transfers (DPTs) are important for several physical processes, both in molecules and in the condensed phase. While these have been widely studied in biological systems, their study in crystalline environments is rare. In this work, using path integral molecular dynamics simulations, we have studied temperature dependent DPT in molecular crystals of terephthalic acid (TPA). In accordance with experimental reports, we find evidence for a double proton transfer induced order-to-disorder transition that is sensitive to the inclusion of nuclear quantum effects. Our simulations show that in addition to the presence of L and R tautomers of terepthalic acid, there are a small but non-negligible concentration of positive and negatively charged pairs of TPA molecules. At the onset of the transition at low temperatures, DPT likely occurs through a tunneling mechanism while at room temperature, likely involving the dominance of activated hopping. Through an analysis of the electronic structure of the system using Wannier functions, we show that the H atom shuttling between the donor and acceptor O atoms involves a proton.

RESUMEN

The coupling of aryl and aliphatic azides with isocyanides yielding carbodiimides (8-17) were efficiently catalyzed by well-defined structurally characterized trans-(MIC)PdI2(L) [MIC = 1-CH2Ph-3-Me-4-(CH2N(C6H4)2S)-1,2,3-triazol-5-ylidene, L = NC5H5 (4), MesNC (5)], trans-(MIC)2PdI2 (6), and cis-(MIC)Pd(PPh3)I2 (7) type palladium complexes, which incidentally mark the first instances of the use of mesoionic singlet palladium carbene complexes for the said application. As observed from the product yields, the catalytic activity varied in the order 4 > 5 ∼ 6 > 7 for these complexes. A detailed mechanistic studies indicated that the catalysis proceeded via a palladium(0) (4a-7 a) species. Using a representative palladium precatalyst (4), the azide-isocyanide coupling was successfully extended to synthesizing two different bioactive heteroannular benzoxazole (18-22) and benzimidazole (23-27) derivatives, thereby broadening the scope of the catalytic application.

RESUMEN

Metallophilic interactions were observed in four pairs of 12-membered metallamacrocyclic silver and gold complexes of imidazole-derived N-heterocyclic carbenes (NHCs), [1-(R1)-3-N-(2,6-di-(R2)-phenylacetamido)-imidazol-2-ylidene]2M2 [R1 = p-MeC6H4, R2 = Me, M = Ag (1b) and Au (1c); R1 = Me, R2 = i-Pr, M = Ag (2b) and Au (2c); R1 = Et, R2 = i-Pr, M = Ag (3b) and Au (3c)], and a 1,2,4-triazole-derived N-heterocyclic carbene (NHC), [1-(i-Pr)-4-N-(2,6-di-(i-Pr)-phenylacetamido)-1,2,4-triazol-2-ylidene]2M2 [M = Ag (4b) and Au (4c)]. The X-ray diffraction, photoluminescence, and computational studies indicate the presence of metallophilic interactions in these complexes, which are significantly influenced by the sterics and the electronics of the N-amido substituents of the NHC ligands. The argentophilic interaction in the silver 1b-4b complexes was stronger than the aurophilic interaction in the gold 1c-4c complexes, with the metallophilic interaction decreasing in the order 4b > 1b > 1c > 4c > 3b > 3c > 2b > 2c. The 1b-4b complexes were synthesized from the corresponding amido-functionalized imidazolium chloride 1a-3a and the 1,2,4-triazolium chloride 4a salts upon treatment with Ag2O. The reaction of 1b-4b complexes with (Me2S)AuCl gave the gold 1c-4c complexes.

RESUMEN

One-pot tandem dehydrogenative cross-coupling of primary and secondary alcohols was catalyzed by three ruthenium complexes [1-(R)-4-N-(furan-2-ylmethyl)acetamido-1,2,4-triazol-5-ylidene]Ru(p-cymene)Cl [R = Et (1b), i-Pr (2b), Bn (3b)], of amido-functionalized 1,2,4-triazole derived N-heterocyclic carbene (NHC) ligands. Density Functional Theory (DFT) calculations were employed for the ruthenium (1b) precatalyst to understand this reaction mechanism completely, and the mechanisms adapted are divided categorically into three steps (i) nucleophilic substitution of chloride ions by alcohols, (ii) dehydrogenation of primary and secondary alcohols, and (iii) olefin and ketone hydrogenation. Our mechanistic study reveals that the formation of a deprotonated Ru-alcoholate (A) or (E) intermediate is favorable compared to the protonated form (A') or (E') from (1b) by associative nucleophilic substitution. Though an ionic pathway that proceeds through (A') or (E'), has less barriers in the dehydrogenation and olefin/ketone hydrogenation steps than that of the neutral pathway, proceeding through (A) or (E), a steep energy barrier was observed in the first nucleophilic substitution step, prohibiting the reaction to proceed via the intermediate (A') or (E'). Thus, our thorough mechanistic study reveals that the reaction proceeds via deprotonated Ru-alcoholate (A) or (E) species. Furthermore, the 1,4 addition of an α,ß-unsaturated carbonyl compound is kinetically and thermodynamically favorable over the 1,2 addition, and the experiments support these observations. As a testimony towards practical application in synthesizing bio-active flavonoid based natural products, five different flavan derivatives (16-20), were synthesized by the dehydrogenative coupling reaction using the neutral ruthenium (1-3)b complexes.

RESUMEN

Abatement of CO, due to its poisonous nature, is an extensively researched topic. Oxidation to CO2 is one of the strategies deployed and finds application in automobiles and fuel cells. Gold nanoparticles on an oxide support is a pioneering catalyst in this field, but need improvement in cost, stability, and O2 activation. Doping with Cu can open up avenues for improvement in these attributes. In the present investigation, we have explored the possibility of using bimetallic AunCum (n + m = 4) clusters supported on Ti2CO2 MXene. We find that AuCu3 is the most stable cluster on the support. The complete CO oxidation cycle on this supported cluster proceeds through a mix of Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. Our calculations predict that the first cycle is expected to proceed only via the LH mechanism due to kinetic and thermodynamic limitations ascribed to ER and Mars van Krevelen (MvK) mechanisms, respectively. The second cycle, however, prefers ER over the LH mechanism. Overall, with the highest barrier of 0.56 eV, this low cost novel catalyst performs better in terms of stability and/or activity in comparison with many of the catalysts reported in the literature.

RESUMEN

Degradation of the mechanical properties of α-titanium, which is used to manufacture parts of jet engines, due to high-temperature oxidation is detrimental for the engine components. Therefore, to overcome this problem there are ongoing endeavors to develop novel oxidation-resistant titanium alloys and improve the properties of the existing ones. In an effort to understand the effect of alloying on oxidation of the α-Ti(0001) surface and to identify descriptors for rational design of oxidation-resistant alloys, in this work, using density functional theory-based calculations, we studied oxygen sorption and surface to subsurface diffusion on pure and alloyed α-Ti(0001) surfaces. Zr, Hf, Nb, and Mo from the d block and Al, Ga, Si, and Ge from the p block were used as alloying elements. We find that the alloying elements prefer to segregate on the surface compared to the subsurface layers. Our calculations show that the diffusion barrier correlates with the difference in the electronegativity between the alloying element and Ti. Elements which are more electropositive than Ti are found to hinder the oxygen dissolution in Ti and vice versa. We propose that the electronegativity difference can act as a good descriptor for choosing alloying elements. Our results are in reasonably good agreement with experimental reports on the growth of oxide layers on these alloyed Ti surfaces.

RESUMEN

Two different classes of ruthenium complexes, namely, [1-mesityl-3-(2,6-Me2-phenylacetamido)-imidazol-2-ylidene]Ru(p-cymene)Cl (1c) and {[1-(pyridin-2-ylmethyl)-3-(2,6-Me2-phenyl)-imidazol-2-ylidene]Ru(p-cymene)Cl}Cl (2c), successfully catalyzed the one-pot tandem alcohol-alcohol coupling reactions of a variety of secondary and primary alcohols, in moderate to good yields of ca. 63-89%. The mechanistic investigation performed on two representative catalytic substrates, 1-phenylethanol and benzyl alcohol using the neutral ruthenium (1c) complex showed that the catalysis proceeded via a partially reduced CC hydrogenated carbonyl species, [PhCOCH2CH2Ph] (3'), to the fully reduced CO and CC hydrogenated secondary alcohol, [PhCH(OH)CH2CH2Ph] (3). Furthermore, the time dependent study showed that the major product of the catalysis modulated between (3') and (3) during the catalysis run performed over an extended period of 120 hours. Finally, the practical utility of the alcohol-alcohol coupling reaction was demonstrated by preparing five different flavan derivatives (13-17) related to various bioactive flavonoid natural products, in a one-pot tandem fashion.

RESUMEN

Heterocyclic polynuclear aromatic hydrocarbons (PAHs) have been detected in all environmental matrices at few ppb to several ppm concentrations and they are characterized by high polarity. Some heterocyclic PAHs are mutagenic and carcinogenic to humans and various organisms. Despite being potent environmental pollutants, these compounds have received less attention. This paper focuses on the sources and occurrence of these compounds and their microbial degradation using diverse species of bacteria, fungi, and algae. Complete removal of 1.8 to 2614 mg/L of nitrogen heterocyclic PAH (PANH), 0.27 to 184 mg/L of sulfur heterocyclic PAH (PASH), and 0.6 to 120 mg/L of oxygen heterocyclic PAH (PAOH) compounds by various microbial species was observed between 3 h and 18 days, 8 h to 6 days, and 4 h to 250 h, respectively under aerobic condition. Strategies for enhancing the removal of heterocyclic PAHs from aquatic systems are also discussed along with the challenges.

Asunto(s)

RESUMEN

Bacterial growth and degradation experiments were conducted on carbazole (CBZ), fluorene (FLU) and dibenzothiophene (DBT) individually and in various mixture combinations using an efficient polynuclear aromatic hydrocarbon (PAH) degrading bacterial strain, Pseudomonas aeruginosa RS1. In single component systems, bacterial growth on CBZ (specific growth rate, µ = 0.99 day-1) was much higher compared to that on FLU (µ = 0.38 day-1) and DBT (µ = 0.33 day-1) and bacterial growth was inhibited in the presence of FLU and DBT in binary (µ = 0.64 day-1) and ternary (µ = 0.75 day-1) mixtures. Multisubstrate additive modelling indicated growth inhibition in all the systems. The degradation of the compounds was significantly inhibited in binary mixtures. While the degradation of the compounds in binary mixtures varied from 35 ± 4% to 73 ± 3%, their degradation varied from 61 ± 5% to 91 ± 4%, when applied as sole substrates and from 77 ± 3% to 96 ± 3%, when applied in a ternary mixture. Degradation experiments were also conducted in ternary mixtures using a 23 full factorial design and the results were examined using analysis of variance (ANOVA) and Tukey's honest significant difference (HSD) tests. At a low concentration of the heterocyclics, CBZ and DBT (5 mg L-1 each), the degradation of the PAH, FLU, was significantly enhanced (from 81 ± 1% to 93 ± 0.3%) when its concentration was increased from 5 to 30 mg L-1. The full factorial design can provide valuable insights into substrate interaction effects in mixtures.

Asunto(s)

RESUMEN

Thermoelectric materials are used for the conversion of waste heat to electrical energy. The transport coefficients that determine their thermoelectric properties depend on the band structure and the relaxation time of the charge carriers. Both of these are significantly affected by electron-phonon coupling. In this work, using a combination of density functional theory and semiclassical Boltzmann transport theory, we have studied the effect of electron-phonon coupling in monolayers of ZrS2, BiI3 and PbI2. Our results show that in these ionic materials charge carriers are primarily scattered by the optical modes that strongly couple with them. From our study it is conclusively shown that neglecting the contributions of optical modes to electron-phonon coupling in these low-dimensional ionic solids, as is usually done in the computation of relaxation time from deformation theory, results in severe overestimation of the relaxation time. In particular, neglecting the scattering of the optical phonons results in about two orders of magnitude overestimation of relaxation times in these materials. Moreover, we also find that the renormalization of the band structure not only results in the reduction of band gaps but also changes the band dispersion, which strongly affect different transport properties like the electrical conductivity and Seebeck coefficient. Amongst these three materials, we observe that carrier relaxation time due to electron-phonon scattering is reduced as the ionicity of the material decreases.

RESUMEN

The current study illustrates the growth kinetics of an efficient PAH and heterocyclic PAH degrading bacterial strain, Pseudomonas aeruginosa RS1 on fluorene (FLU) and dibenzothiophene (DBT) over the concentration 25-500 mg L-1 and their concomitant degradation kinetics. The specific growth rate (µ) was found to lie within the range of 0.32-0.57 day-1 for FLU and 0.24-0.45 day-1 for DBT. The specific substrate utilization rate (q) of FLU and DBT over the log growth phase was between 0.01 and 0.14 mg FLU mg VSS-1 day-1 for FLU and between 0.01 and 0.18 mg DBT mg VSS-1 day-1 for DBT, respectively. The µ and q values varied within a narrow range for both FLU and DBT and they did not follow any specific trend. Dissolution together with direct interfacial uptake was the possible uptake mechanism for both FLU and DBT. The q values over the log growth phase depicts the specific substrate transformation rates. Kirby-Bauer disc diffusion studies performed using an E. coli strain indicated accumulation of some toxic intermediates of FLU and DBT during their degradation. Decrease in TOC and toxicity towards the end of the degradation experiments indicates further utilization of the intermediates. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02742-7.

RESUMEN

In the current context of green mobility and sustainability, the use of new generation natural fillers, namely, α-cellulose, has gained significant recognition. The presence of hydroxyl groups on α-cellulose has generated immense eagerness to map its potency as filler in an elastomeric composite. In the present work, α-cellulose-emulsion-grade styrene butadiene rubber (E-SBR) composite is prepared by conventional rubber processing method by using variable proportions of α-cellulose (1 to 40 phr) to assess its reinforce ability. Rheological, physical, visco-elastic and dynamic-mechanical behavior have clearly established that 10 phr loading of α-cellulose can be considered as an optimized dosage in terms of performance parameters. Morphological characterization with the aid of scanning electron microscope (SEM) and transmission electron microscopy (TEM) also substantiated that composite with 10 phr loading of α-cellulose has achieved the morphological threshold. With this background, synthetic filler (silica) is substituted by green filler (α-cellulose) in an E-SBR-based composite. Characterization of the compound has clearly established the reinforcement ability of α-cellulose.

Asunto(s)

RESUMEN

Although bacterial degradation of polynuclear aromatic hydrocarbons (PAH) have been studied using various pure cultures, only a few studies have explored the degradation kinetics and uptake mechanism of nitrogen heterocyclic PAHs (PANH) with three or more rings. This work explored growth kinetics of a PAH degrading bacterial strain, Pseudomonas aeruginosa RS1 on carbazole (CBZ) and concomitant degradation kinetics of CBZ over the concentration range 25 to 500 mg/L. For CBZ acclimatized strain, the specific growth rate (µ) and specific CBZ uptake rate (q) varied from 0.96 ± 0.05 to 2 ± 0.15 day-1 and from 0.002 ± 0.001 to 0.02 ± 0.01 mg CBZ mg VSS-1 day-1, respectively. The Moser and Monod model provided best fits to the µ vs CBZ concentration and q vs CBZ concentration profiles, respectively. Biosurfactant activity did not play a role in CBZ uptake. However, elevation in cell surface hydrophobicity as revealed through the water contact angle values on bacterial cell mat indicated the possible role of direct interfacial uptake in facilitating CBZ uptake over and above uptake after dissolution. Elevated catechol 1,2-dioxygenase enzyme activity was observed during CBZ degradation. Interestingly, the specific activity of this enzyme was higher in the culture supernatant than in the cell extract. However, during CBZ degradation, accumulation of some toxic metabolites in the aqueous phase was revealed through increase in TOC of the aqueous phase and Kirby-Bauer disc diffusion study performed using a E. coli strain. Both aqueous phase TOC and toxicity decreased beyond the log growth phase indicating further utilization of the degradation intermediates.

Asunto(s)

RESUMEN

Atmospheric CO2 is one of the main components of the greenhouse effect. To overcome this problem there are ongoing efforts to convert CO2 to some other useful and harmless products. The capture, activation and dissociation of CO2 are the preliminary steps in this process. In an effort to understand the role of surface composition and structure in CO2 adsorption and dissociation, in this work, with the help of first principles density functional theory based calculations, we have studied the same on the {100} surface of cubic Ti2C and MXene (also the {0001} surface of trigonal Ti2C). Our results show that CO2 undergoes barrierless chemisorption on both of these surfaces with a preference towards {100} cubic Ti2C. We attribute the reason for this to a lower value of the work function of the {100} surface. Furthermore, on MXene, the barrier for CO2 dissociation is lower compared to that on the {100} surface. Coverage dependent CO2 chemisorption studies on these two surfaces show that on the Ti2C surface the CO2 molecules form clusters around the C-vacancies while on MXene they are uniformly spread on the surface.

RESUMEN

A 3 D intermetallic anti-perovskite carbide, Fe3 SnC, is reported as a Li-ion battery anode. Single-phase Fe3 SnC showed a reversible Li-ion capacity of 426 mAh g-1 that increased significantly (600 mAh g-1 ) upon its in situ synthesis by electrospinning and pyrolysis to render a conducting carbon nanofibre (CNF) based composite. Importantly, the Fe3 SnC@CNF composite showed excellent stability in up to 1000 cycles with a remarkable 96 % retention of capacity. The rate performance was equally impressive with a high capacity of 500 mAh g-1 delivered at a high current density of 2 A g-1 . An estimation of Li ion diffusion from the electrochemical impedance data showed a major enhancement of the rate by a factor of 2 in the case of Fe3 SnC@CNF compared to the single-phase Fe3 SnC sample. Post-cyclic characterisation revealed that the unit cell was retained despite a volume expansion upon the inclusion of four Li atoms per unit cell, as calculated from the capacity value. The cyclic voltammogram shows four distinctive peaks that could be identified as the sequential incorporation of up to four Li atoms. First-principles DFT calculations were performed to elucidate the favourable sites for the inclusion of 1-4 Li atoms inside the Fe3 SnC unit cell along with the associated strain.