The enhanced electrocatalytic performance of nanoscopic Cu6Pd12Fe12 heterometallic molecular box encaged cytochrome c.

Designing molecular cages for atomic/molecular scale guests is a special art used by material chemists to harvest the virtues of the otherwise vile idea known as "the cage". In recent years, there has been a notable surge in research investigations focused on the exploration and utilization of the distinct advantages offered by this art in the advancement of efficient and stable bio-electrocatalysts. This usually is achieved through encapsulation of biologically accessible redox proteins within specifically designed molecular cages and matrices. Herein, we present the first successful method for encaging cytochrome c (Cyt-c), a clinically significant enzyme system, inside coordination-driven self-assembled Cu6Pd12Fe12 heterometallic hexagonal molecular boxes (Cu-HMHMB), in order to create a Cyt-c@Cu-HMHMB composite. 1H NMR, FTIR, and UV-Vis spectroscopy, ICP-MS, TGA and voltammetric investigations carried out on the so-crafted Cyt-c@Cu-HMHMB bio-inorganic composite imply that the presented strategy ensures encaging of Cyt-c in a catalytically active, electrochemically stable and redox-accessible state inside the Cu-HMHMB. Cyt-c@Cu-HMHMB is demonstrated to exhibit excellent stability and electrocatalytic activity toward very selective, sensitive electrochemical sensing of nitrite exhibiting a limit of detection as low as 32 nanomolar and a sensitivity of 7.28 µA µM-1 cm-2. Importantly, Cyt-c@Cu-HMHMB is demonstrated to exhibit an excellent electrocatalytic performance toward the 4e pathway oxygen reduction reaction (ORR) with an onset potential of 0.322 V (vs. RHE) and a Tafel slope of 266 mV dec-1. Our findings demonstrate that Cu-HMHMB is an excellent matrix for Cyt-c encapsulation. We anticipate that the entrapment-based technique described here will be applicable to other enzyme systems and Cyt-c for various electrochemical and other applications.

Synthesis of Novel One-Walled meso-Phenylboronic Acid-Functionalized Calix[4]pyrrole: A Highly Sensitive Electrochemical Sensor for Dopamine.

Facile access to new one-walled meso-substituted phenylboronic acid-functionalized calix[4]pyrrole (C4P) has been revealed for the first time, starting from cost-effective and easily accessible materials. The structures of both the intermediate dipyrromethane (DPM) and the targeted functionalized C4P have been confirmed by means of 1H-NMR, 13C-NMR, IR, and HRMS spectral data. The voltammetric investigations of the functionalized C4P films cast over a glassy carbon electrode (C4P-GCE) clearly establish the redox stability and redox accessibility of the boronic acid functional moiety present in the C4P framework. We demonstrate that the presence of the unique boronic acid functionality in the C4P endows it with an excellent potential for the highly sensitive electrochemical sensing of the neurotransmitter dopamine (DA). A linear correlation between the strength of the Faradaic signals corresponding to the electro-oxidation of DA over C4P-GCE and the concentration of DA was observed in a concentration range as wide as 0.165-2.302 µM. The C4P-GCE has revealed exceptional stability and reproducibility in the electrochemical sensing of DA, with a nanomolar level limit of detection as low as 15 nM.

Eureka Moment: An Archimedean Alternative for the Determination of cmc of Surfactants via Weight Measurements.

Critical micelle concentration (cmc) is a key parameter of generally used surfactants, and many experimental techniques like tensiometry, conductivity, spectrophotometry, fluorometry, etc. for its determination have been reported. However, these contemporary methods for cmc determination are tedious, are time-consuming, are sensitive, and require sophisticated instrumentation. Herein, we demonstrate that the cmc of the surfactants can be estimated via monitoring the variation in the apparent weight of a density bottle floating in a surfactant solution as a function of surfactant concentration. The proposed method requires the use of a simple weighing balance; a cost-affordable instrument always available in scientific laboratories. The proposed method is simple to execute and does not require any complicated data analysis procedures. As an experimental proof attached to the claim, we demonstrate the estimation of the cmcs of all types of surfactants, viz., anionic, cationic, and nonionic, through the formulated method. The results obtained in terms of cmc values of the chosen surfactants closely match those reported through the use of different standardized protocols. The formulated experimental protocol is desirable in terms of the simplicity of the protocol, accuracy, and reproducibility of the results, and cost and accessibility of the required instrument. All these attributes of the presented protocol qualify it as an appropriate substitute to the modern techniques commonly used for the cmc determination.

Mechanistic insight into the electrocatalytic performance of reduced graphene oxide supported palladium, silver and palladium-silver nanodeposits toward electro-dehalogenation of halocarbons in room temperature ionic liquids.

Herein, we report the results from our extensive voltammetric investigations designed to explore, assess and explain the electrocatalytic performance of reduced graphene oxide supported metal nano-deposits toward the electro-dehalogenation of halocarbons in room temperature ionic liquids (RTILs). Specifically, we investigated the electro-reductive dechlorination of the model halocarbon, carbon tetrachloride over glassy carbon electrode (GCE) and palladium-graphene (Pd-Gr), silver-graphene (Ag-Gr) and palladium-silver-graphene (PdAg-Gr) nanocomposites in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]). Analysis of the voltammetric data in light of Marcus-Hush formulation reveals that the electro-reductive cleavage of the C-Cl bond of CCl4 over GCE in [BMIM][NTf2] follows a sticky dissociative electron transfer (SDET) pathway. The significantly stronger interaction energy between electrogenerated Cl- and CCl3˙ (radical) fragments in RTILs makes electroreduction of CCl4 in [BMIM][NTf2] much easier than in organic solvents. The activation-driving force relationship for electro-catalytic dechlorination of CCl4 over Pd-Gr was observed to follow a modified sticky dissociative electron transfer model wherein apart from the ion-radical interaction, the adsorptive interaction of chlorinated species with the electrocatalytic surface needs to be taken into consideration to account for the apparent activation energy-driving force dependence. Interestingly the activation energy-driving force relationships for the electroreduction of CCl4 over Ag-Gr and PdAg-Gr were observed to fit a modified stepwise ET (MSET) pathway. In the MSET pathway, the adsorption and the implied free energy change of the electroreducible halocarbon significantly alter the solvent re-organization energy and the inherent barrier for the heterogeneous ET process. The adsorptive interaction and hence the electrocatalytic performance of PdAg-Gr were observed to be more than that observed for Ag-Gr. This is attributed to the Ag to Pd charge transfer in the PdAg-Gr nanodeposits. Our results besides underlining the positive influence of RTILs in facilitating the electroreductive detoxification of halocarbons, very well establish the mechanistic basis for the electrocatalytic performance of graphene based nanodeposits toward electrodehalogenation of halocarbons.

Transforming micelles into mixed micelles: a promising approach to tune the catalytic performance of imidazolium-based surface active ionic liquids toward degradation of rhodamine B.

Herein, we demonstrate that the catalytic performance of imidazolium-based surface-active ionic liquid (SAIL) micelles can be significantly enhanced through the addition of an appropriate type and amount of intelligently conceived amphiphile to form mixed micelles. Specifically, we show that the catalytic performance of 1-dodecyl-3-methyl imidazolium chloride (DDMIMCl) micelles toward the reductive degradation of rhodamine B (RhB), a carcinogenic dye extensively used in multiple industrial applications, can be appreciably boosted through addition of Brij56, a nonionic surfactant. Detailed kinetic investigations on the catalytic performance of pre- and post-micellar concentrations of DDMIMCl and its mixed micelles with Brij56 over various mole fractions, toward the reductive degradation of RhB, are presented. The data analyzed in light of Berezin's kinetic model suggest that the addition of Brij56 to DDMIMCl micelles significantly enhances their catalytic performance. The catalytic activity exhibited by the DDMIMCl-Brij56 (XBrij56 = 0.2) mixed micellar system is better than that reported for many state-of-the-art nanoparticle/homogenous catalysts. The results explained in light of Berezin's kinetic model are well supported by physico-chemical studies like conductometry, fluorimetry and dynamic light scattering. The presented results anticipate stimulation of extensive research activity for exploiting the mixed micellization approach as a novel avenue for modulating the catalytic performance of SAILs.

Structural-functional integrity of lysozyme in imidazolium based surface active ionic liquids.

The present study was designed to explore the hydrophobicity and concentration dependence of imidazolium based surface active ionic liquids (SAILs) effects on the structural-functional integrity of proteins. Specifically, we investigated the impact of SAILs viz. 1-octyl-3-methylimidazolium dodecylbenzenesulfonate ([OMIM][DBS]) and 1-dodecyl-3-methylimidazolium dodecylbenzenesulfonate ([DDMIM][DBS]) on activity, structure and stability of lysozyme. Activity measurements revealed that, in contrast to [DDMIM][DBS] that renders lysozyme either feebly active or inactive, [OMIM][DBS] significantly enhances the lysozyme activity in the concentration range of critical aggregation concentrations (CAC) to Cs (SAIL saturation concentration of protein backbone) i.e., 0.5 mM-1.35 mM. Tensiometric results in agreement with turbidity measurements inferred significant composition and concentration dependence of the lysozyme-SAIL interactions. Spectroscopic investigations revealed that compared to destabilizing behaviour of [DDMIM][DBS], [OMIM][DBS] significantly enhances both conformational as well as thermal stability of lysozyme in the CAC to Cs concentration regime. Altogether, results obtained do indicate that [OMIM][DBS], in the concentration regime of CAC to Cs, serves as an efficient stabiliser with an ability to appreciably enhance the activity, thermal stability and overall conformational stability of lysozyme. We firmly believe that [OMIM][DBS], at least in the CAC to Cs concentration ranges, can be exploited as a promising stabiliser and activity enhancer for numerous industrially important enzymes.

Electrochemical reduction of CO2 to ethylene on Cu/Cu x O-GO composites in aqueous solution.

Here, we present fabrication of Graphene oxide (GO) supported Cu/Cu x O nano-electrodeposits which can efficiently and selectively electroreduce CO2 into ethylene with a faradaic efficiency (F.E) of 34% and a conversion rate of 194 mmol g-1 h-1 at -0.985 V vs. RHE. The effect of catalyst morphology, working electrode fabricational techniques, the extent of metal-GO interaction and the oxide content in Cu/Cu x O, was studied in detail so as to develop a protocol for the fabrication of an active, stable and selective catalyst for efficient electro-production of ethylene from CO2. Moreover, a detailed comparative study about the effect of the GO support, and the nature of the cathodic collection substrate used for the electro-deposition is presented.

PdAg Bimetallic Nanoalloy-Decorated Graphene: A Nanohybrid with Unprecedented Electrocatalytic, Catalytic, and Sensing Activities.

Recent reports about the promising and tunable electrocatalytic activity and stability of nanoalloys have stimulated an intense research activity toward the design and synthesis of homogeneously alloyed novel bimetallic nanoelectrocatalysts. We herein present a simple one-pot facile wet-chemical approach for the deposition of high-quality bimetallic palladium-silver (PdAg) homogeneous nanoalloy crystals on reduced graphene (Gr) oxide sheets. Morphological, structural, and chemical characterizations of the so-crafted nanohybrids establish a homogeneous distribution of 1:1 PdAg nanoalloy crystals supported over reduced graphene oxide (PdAg-Gr). The PdAg-Gr nanohybrids exhibit outstanding electrocatalytic, catalytic, and electroanalytical performances. The PdAg-Gr samples were found to exhibit exceptional durability when subjected to repeated potential cycles or long-term electrolysis. In the CVs recorded for fuel cell reactions, viz. methanol oxidation reaction and oxygen reduction reaction, and for detoxification of environmental pollutants, viz. electroreduction of methyl iodide and chloroacetonitrile over PdAg-Gr with potential sweep rate of 25 mVs-1, the peak potentials were observed to be just -0.221, -0.297, (vs Ag/AgCl, 3 M KCl) -1.508, and -1.189 V (vs Fc+/Fc), respectively. The potential of PdAg-Gr nanohybrid for simultaneous and sensitive electrochemical sensing and estimation of hydroxybenzene isomers with very low detection limits (0.05 µM for hydroquinone, 0.06 µM for catechol, 6.7 nM for 4-aminophenol, and 13.7 nM for 2-aminophenol) is demonstrated. Additionally, PdAg-Gr was observed to offer excellent solution-phase catalytic performance in bringing about the reduction of notorious environmental pollutant 4-nitrophenol to pharmaceutically important 4-aminophenol with an apparent rate constant ( kapp) of 3.106 × 10-2 s-1 and a normalized rate constant ( knor) of 6.21 × 102 s-1 g-1. The presented synthetic scheme besides being high yielding, low cost, and easy to carry out results in the production of PdAg-Gr nanohybrids with stability and activity significantly better than most of the nanomaterials purposefully designed and testified so far by various groups.

Towards Understanding the Solvent-Dynamic Control of the Transport and Heterogeneous Electron-Transfer Processes in Ionic Liquids.

The impact of temperature-induced changes in solvent dynamics on the diffusion coefficient and standard rate constant k0 for heterogeneous electron transfer (ET) of ethylferrocene (EFc) in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6 ]) is investigated. The results are analysed to understand the impact of solvent-dynamic control, solute-solvent interactions and solvent friction on the transport of redox probes and k0 . Concentration dependence of the diffusion coefficient of EFc in [BMIM][PF6 ] is observed. This is attributed to the solute-induced enhancement of the structural organisation of the ionic liquid (IL), which is supported by the concentration-dependent UV/Vis absorption and photoluminescence responses of EFc/[BMIM][PF6 ] solutions. Similar values of the activation energies for mass transport and ET and a linear relationship between the diffusion coefficient and the heterogeneous ET rate is observed. The ratio between the diffusion coefficient and the heterogeneous rate constant allows a characteristic length Ld , which is temperature-independent, to be introduced. The presented results clearly establish that mass transport and heterogeneous ET of redox probes are strongly correlated in ILs. It is proposed that the apparent kinetics of heterogeneous ET reactions in ILs can be explained in terms of their impact on thermal equilibration, energy dissipation and thermal excitation of redox-active probes.

Oxides in silver-graphene nanocomposites: electrochemical signatures and electrocatalytic implications.

Herein we report an electrochemical approach to establish the presence of silver oxides in silver-reduced graphene oxide (Ag-rGO) nanocomposites synthesised under alkaline conditions. The recorded electrochemical signatures, further supported and validated by UV-Vis spectroscopy, XRD and TEM analysis, clearly establish the presence of an oxide phase of silver in the nanodimensional silver present in Ag-rGO. The Ag-rGO was tested for its electrocatalytic and electrosensing activity for hydroquinone (H2Q) and ascorbic acid (AA). The presented results establish that the electrocatalytic and electrosensing potential of the Ag-rGO for H2Q and AA can be enhanced through electroreduction of the oxide phase of silver in these nanocomposites. Our results prove that the electrocatalytic and electroanalytic activities of electroreduced Ag-rGO for AA are better than most of the electrode materials reported so far in the literature.

Determination of cmc of imidazolium based surface active ionic liquids through probe-less UV-vis spectrophotometry.

In the first of its kind we herein report the results of our studies undertaken on the micellization behaviour of imidazolium based surface active ionic liquids (SAILs) to prove that their critical micelle concentration (cmc) can be estimated through ultraviolet-visible (UV-vis) spectroscopy without using any external probe. Tensiometric and spectrophotometric investigations of a series of freshly prepared SAILs viz. 1-octyl-3-methylimidazolium chloride ([OMIM][Cl]), 1-octyl-3-methylimidazolium dodecylsulphate ([OMIM][DS]), 1-octyl-3-methylimidazolium benzoate ([OMIM][Bz]), 1-octyl-3-methylimidazolium salicylate ([OMIM][Sc]), 1-octyl-3-methylimidazolium acetate ([OMIM][Ac]) are presented as a case study in support of the said claim. The cmcs estimated through spectrophotometric method were found to be close to the values estimated through tensiometry for the said SAILs. The cmcs for the investigated SAILS were found to vary in order of [OMIM][Cl]>[OMIM][Ac]>[OMIM][Bz]>[OMIM][Sc]>[OMIM][DS]. To the best of our knowledge the present communication will be the first report about the synthesis, characterization and micellization behaviour of [OMIM][Bz] and [OMIM][Sc].

Pseudo-indicator behaviour of platinum electrode explored for the potentiometric estimation of non-redox systems.

A pseudo-indicator electrode based potentiometric method for estimation of non-redox metal ions is presented. In the proposed method, nature and concentration specific impact of analyte over the redox potential of ideally polarisable Pt/pregenerated-redox-couple interface forms the basis of quantification. Utility of the method in estimation of six non-redox metal ions viz. Zn(2+), Cu(2+), Ni(2+), Cd(2+), Pb(2+), Al(3+) in the concentration range of 10(-1)-10(-3) moldm(-3), individually and as binary mixtures is also presented. Three types of potentiometric behaviours, which we ascribe to the nature specific thermodynamic and kinetic aspects of metal-EDTA binding, were observed. While Cu(2+), Ni(2+), Pb(2+) and Al(3+) were found to bind EDTA efficiently, without exchanging Fe(3+); Zn(2+) and Cd(2+) were observed to replace Fe(3+) from EDTA. In contrast, Ca(2+) and Mg(2+) were found to show no binding affinity to EDTA in the pH range employed in the present work. The proposed method was also used to explore the reversibility and the Nernestian behaviour of ferricyanide/ferrocyanide redox couple through spectroelectrochemical titration of Zn(2+) with ferrocyanide. The presented method is presaged to be a reliable and low cost future replacement for costly and delicate ion selective electrodes (ISE) in the estimation of non-redox species like Zn(2+), Cu(2+), etc.

Outer sphere electroreduction of CCl4 in 1-butyl-3-methylimmidazolium tetrafluoroborate: an example of solvent specific effect of ionic liquid.

Electrodics of CCl4 reduction in 1-butyl-3-methylimmidazolium tetrafluoroborate [BMIM][BF4] room temperature ionic liquid (RTIL) is reported. A convolutive analysis of the cyclic voltammograms suggests that CCl4 electroreduction follows stepwise (outer sphere) dissociative electron transfer pathway, rather than the sticky dissociative (inner sphere) electron transfer, as in the case of conventional organic solvents. This difference in the mechanism of electron transfer initiated bond cleavage is attributed to the solvent specific effects, namely, stabilization of CCl4*- intermediate radical anion in RTIL, which in turn decreases the electron transfer rate and thus the carbon-halogen bond cleavage rates. Electroreduction of CCl4 in RTIL through outer sphere electron transfer would be a promising pathway for its direct conversion to methane.