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Density functional theory calculations within the framework of generalized gradient approximation (GGA), meta-GGA, and local functionals were carried out to investigate the reactivity and catalytic activity of Ag n ( n = 15-20) clusters. Our results reveal that all the Ag n clusters in this size range, except Ag 20 , adsorb O 2 preferably in the bridged mode with enhanced binding energy as compared to the atop mode. The O 2 binding energies range from 0.77 to 0.29 in the bridged mode and from 0.36 to 0.15 eV in the atop mode of O 2 adsorption. The strong binding in the case of the bridged mode of O 2 adsorption is also reflected in the increase in O-O bond distance. Natural bond orbital charge analysis and vibrational frequency calculations reveal that enhanced charge transfer occurs to the O 2 molecule and there is significant red shift in the stretching frequency of O-O bond in the case of the bridged mode of O 2 adsorption on the clusters, thereby confirming the above results. Moreover, the simulated CO oxidation reaction pathways show that the oxidation of the CO molecule is highly facile on Ag 16 and Ag 18 clusters involving small kinetic barriers and higher heats toward CO 2 formation., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

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 ( k app ) of 3.106 × 10 -2 s -1 and a normalized rate constant ( k nor ) of 6.21 × 10 2 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.

The interaction of xanthine oxidase (XO), a key enzyme in purine metabolism, with cetyltrimethylammonium bromide (CTAB) and bis(cetyldimethylammonium)butane dibromide (C16C4C16Br2) has been studied using tensiometry, spectrofluorometry, spectrophotometry, and circular dichroism at pH 7.4 and 25 °C. The tensiometric profiles of CTAB and C16C4C16Br2 in the presence of XO exhibit a single break at a lower surfactant concentration termed as C1 compared to their CMC in the buffered solution and show the existence of interaction between the surfactants and the enzyme. The results of the multitechnique approach showed that, although both CTAB as well as C16C4C16Br2 interact with the XO, C16C4C16Br2 interacts more strongly than its conventional single chain counterpart. Fluorescence and absorption measurements revealed that, compared to CTAB, C16C4C16Br2 is more effective in unfolding the enzyme. Change in XO activity by the surfactants was in concurrence with the structural alterations monitored by circular dichroism and showed structural stabilization of XO at higher surfactant concentrations, consistent with the aggregation results. This stabilization has been explained in light of strong tendency of C16C4C16Br2 for micellar growth and membrane/water stabilization of proteins by membrane-like fragments provided by higher concentrations of C16C4C16Br2 . The results are related to the stronger electrostatic and hydrophobic forces in C16C4C16Br2, owing to the presence of two charged headgroups and two hydrophobic tails.

The interaction of bovine serum albumin (BSA) with cetyltrimethylammonium bromide (CTAB), C(16)C(4)C(16)Br(2), Brij58, and their binary mixtures has been studied using tensiometry, spectrofluorometry, and circular dichroism at physiological pH and 25 degrees C. The tensiometric profiles of CTAB and C(16)C(4)C(16)Br(2) in the presence of BSA exhibit a single break at a lower surfactant concentration termed as C(1) (concentration corresponding to saturation of the interface) compared to their critical micelle concentration (CMC) in the buffered solution. However, for Brij58, CTAB+Brij58, and C(16)C(4)C(16)Br(2)+Brij58, two breaks were observed, first at the critical aggregation concentration (CAC), corresponding to onset of interaction with BSA and the second at C(1) corresponding to saturation of the interface. The interaction of CTAB+Brij58 and C(16)C(4)C(16)Br(2)+Brij58 mixtures with the BSA solution is discussed in terms of competition between surfactant-surfactant and surfactant-BSA interactions. CTAB+Brij58 and C(16)C(4)C(16)Br(2)+Brij58 mixtures show nonideality with respect to mixed micelle formation, which is reflected in their interaction with the BSA. The interaction of CTAB+Brij58 with BSA decreases with increase in the mole fraction of CTAB in the mixture, whereas in C(16)C(4)C(16)Br(2)+Brij58 the reverse is the case. The results of the present study may prove fruitful in optimizing the properties of surfactant-protein mixtures relevant for many formulations.

Mixed surfactants may improve the performance of surfactant-enhanced solubilization of drugs and thus can serve as the tool for increased bioavalaibility, controlled drug release, and targeted delivery. Solubilization of Naproxen by micellar solutions at 25 degrees C using single and mixed surfactant systems was measured and compared. Solubilization capacity determined with spectrophotometry and tensiometry has been quantified in terms of molar solubilization ratio, micelle-water partition coefficient, and locus of solubilization. Cationic surfactants exhibited higher solubilization capacity than nonionics and anionics, the efficiency increasing with chain length. Mixing effect of surfactants on mixed micelle formation and solubilization efficiency has been discussed in light of regular solution approximation (RSA). Equimolar cationic-nonionic surfactant combinations showed better solubilization capacity than pure cationics or nonionics, which, in general, increased with increase in hydrophobic chain length. Equimolar cationic-nonionic-nonionic ternary surfactant systems exhibited intermediate solubilization efficiency between their single and binary counterparts. Use of RSA has been extended, with fair success, to predict the partition coefficient of ternary surfactant systems using data from binary mixtures. The theoretical micelle-water partition coefficients calculated from the geometric mean equation compared well with experimental values. Locus of solubilization of NAP in different micellar solutions was probed by UV-visible spectroscopy.

Water solubility enhancements of polycyclic aromatic hydrocarbons (PAHs), viz., naphthalene, anthracene and pyrene, by micellar solutions at 25 degrees C using two series of surfactants, each involving two cationic and one nonionic surfactant in their single as well as equimolar binary and ternary mixed states, were measured and compared. The first series was composed of three surfactants, benzylhexadecyldimethylammonium chloride (C16BzCl), hexadecyltrimethylammonium bromide (C16Br), and polyoxyethylene(20)mono-n-hexadecyl ether (Brij-58) with a 16-carbon (C16) hydrophobic chain; the second series consisted of dodecyltrimethylammonium bromide (C12Br), dodecylethyldimethylammonium bromide (C12EBr), and polyoxyethylene(4)mono-n-dodecyl ether (Brij-30) with a 12-carbon (C12) chain. Solubilization capacity has been quantified in terms of the molar solubilization ratio, the micelle-water partition coefficient, the first stepwise association constant between solubilizate monomer and vacant micelle, and the average number of solubilizate molecules per micelle, determined employing spectrophoto-, tensio-, and flourimetric techniques. Cationic surfactants exhibited lesser solubilization capacity than nonionics in each series of surfactants with higher efficiency in the C16 series compared to the C12 series. Increase in hydrophobicity of head groups of cationics by incorporation of ethyl or benzyl groups enhanced their solubilization capacity. The mixing effect of surfactants on mixed micelle formation and solubilization efficiency has been discussed in light of the regular solution approximation (RSA). Cationic-nonionic binary combinations showed better solubilization capacity than pure cationics, nonionics, or cationic-cationic mixtures, which, in general, showed increase with increased hydrophobicity of PAHs. Equimolar cationic-cationic-nonionic ternary surfactant systems showed lower solubilization efficiency than their binary cationic-nonionic counterparts but higher than cationic-cationic ones. In addition, use of RSA has been extended, with fair success, to predict partition coefficients of ternary surfactant systems using data of binary surfactants systems. Mixed surfactants may improve the performance of surfactant-enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus remediation cost.