Horses for courses: risk information and decision making in the regulation of nanomaterials

Despite the widespread commercial use of nanomaterials, regulators currently have a limited ability to characterize and manage risks. There is a paucity of data available on the current production and use of nanomaterials and extreme scientific uncertainty on most aspects of the risk assessment “causal chain.” Regulatory decisions will need to be made in the near-term in the absence formal quantitative risk assessments. The article draws on examples from three different regulatory contexts—baseline data monitoring efforts of the U.S. Environmental Protection Agency and California Department of Toxic Substances Control, prioritization of risk information in the context of environmental releases, and mitigation of occupational risks—to argue for the use of decision-analytic tools in lieu of formal risk assessment to help regulatory bodies. We advocate a “horses for courses” approach whereby existing analytical tools (such as risk ranking, multi-criteria decision analysis, and “control banding” approaches) might be adapted to regulators’ goals in particular decision contexts. While efforts to build new and modify existing tools are underway, they need greater support from funding and regulatory agencies because innovative approaches are needed for the “extreme” uncertainty problems that nanomaterials pose.     

Direct Allylation of In Situ Generated Aldehyde Acyl Anions by Synergistic NHC and Palladium Catalysis

The direct regioselective allylation of in situ generated aldehyde acyl anions has been achieved by synergistic NHC and Pd catalysis. It provides an efficient access to valuable β,γ‐unsaturated ketones under mild reaction conditions starting from easily accessible allylic carbonates and aldehydes without any preactivation. The synergistic catalysis method demonstrated herein adds a new dimension to the area of metal‐mediated C allylation.     

Intramolecular hydrogen bonding and cooperative interactions in carbohydrates via the molecular tailoring approach

In spite of many theoretical and experimental attempts for understanding intramolecular hydrogen bonding (H-bonding) in carbohydrates, a direct quantification of individual intramolecular H-bond energies and the cooperativity among the H-bonded networks has not been reported in the literature. The present work attempts, for the first time, a direct estimation of individual intramolecular O-H...O interaction energies in sugar molecules using the recently developed molecular tailoring approach (MTA). The estimated H-bond energies are in the range of 1.2-4.1 kcal mol(-1). It is seen that the OH...O equatorial-equatorial interaction energies lie between 1.8 and 2.5 kcal mol(-1), with axial-equatorial ones being stronger (2.0-3.5 kcal mol(-1)). The strongest bonds are nonvicinal axial-axial H-bonds (3.0-4.1 kcal mol(-1)). This trend in H-bond energies is in agreement with the earlier reports based on the water-water H-bond angle, solvent-accessible surface area (SASA), and (1)H NMR analysis. The contribution to the H-bond energy from the cooperativity is also estimated using MTA. This contribution is seen to be typically between 0.1 and 0.6 kcal mol(-1) when H-bonds are a part of a relatively weak equatorial-equatorial H-bond network and is much higher (0.5-1.1 kcal mol(-1)) when H-bonds participate in an axial-axial H-bond network.     

Two-step evaluation of binding energy and potential energy surface of van der Waals complexes

Evaluation of intermolecular distance and binding energy (BE) of van der Waals complex/cluster at ab initio level of theory is computationally demanding when many monomers are involved. Starting from MP2 energy, we reached a two-step evaluation method of BE of van der Waals complex/cluster through reasonable approximations; BE = BE(HF) + sum Mi> Mj{BE (Mi- Mj)(MP2 or MP2.5) - BE(Mi-Mj)(HF)} where HF represents the Hartree-Fock calculation, Mi, Mj, etc. are interacting monomers, and MP2.5 represents the arithmetic mean of MP2 and MP3. The first term is the usual BE of the complex/cluster evaluated at the HF level. The second term is the sum of the difference in two-body BE between the correlated and HF levels of theory. This equation was applied to various van der Waals complexes consisting of up-to-four monomers at MP2 and MP2.5 levels of theory. We found that this method is capable of providing precise estimate of the BE and reproducing well the potential energy surface of van der Waals complexes/clusters; the maximum error of the BE is less than 1 kcal/mol and 1% in most cases except for several limited cases. The origins of error in these cases are discussed in detail.     

Cation interdiffusion model for enhanced oxygen kinetics at oxide heterostructure interfaces

An interface between the perovskite La(0.8)Sr(0.2)CoO(3-δ) (LSC-113) and the K(2)NiF(4)-type (La(0.5)Sr(0.5))(2)CoO(4-δ) (LSC-214) heterostructure was recently shown to enhance oxygen surface exchange and the rate of the oxygen reduction reaction (ORR) by orders of magnitude compared to either the LSC-113 or LSC-214 phase alone. This result is of interest to develop better optimized materials for solid-state electrochemical devices, e.g. solid oxide fuel cells. The effect has been attributed to the interface itself, rather than changes in the bulk LSC-113 or LSC-214 phases. Using density functional theory (DFT)-based simulations, we demonstrate that there is a ～0.9 eV (～1.3 eV) energy gain for exchanging a Sr from LSC-113(25%Sr) (LSC-113(40%Sr)) with a La from LSC-214(50%Sr). These changes in energy create a large driving force for interdiffusion across the heterostructure interface from Sr into LSC-214 and La into LSC-113. We estimate that the Sr concentrations (in the LSC-214 phase) in a typical experimental temperature range of 500-600 °C and in equilibrium with LSC-113(25%Sr) and LSC-113(40%Sr), may be about 75% Sr and 90% Sr, respectively. Based on the bulk behavior of the LSC-214 phase (Vashook et al., Solid State Ionics, 2000, 138, 99-104), an Sr enrichment from x = 0.5 to x = 0.75 in (La(1-x)Sr(x))(2)CoO(4-δ) is expected to enhance the oxygen vacancy concentration by 2-2.5 orders of magnitude under typical experimental conditions. An increased vacancy concentration in LSC-214 near the interface can explain most of the enhanced oxygen kinetics observed up until now in these heterostructures.     

Development of New Synthetic Strategies,Tactics and their Applications

This account covers our work related to the development of various synthetic methodologies since 1994. We summarized our strategies and their application to design various functional molecules. In this regard, we also report the utility of our methodologies in others research work. These methods we report here are simple and efficient for the synthesis of a wide variety of intricate molecules such as heterocycles, polycycles, unusual α‐amino acids, star‐shaped molecules, and modified peptides. For this purpose, we used various transition metal‐based reagents and catalysts. Various popular reactions such as metathesis, Suzuki coupling, [2+2+2] cyclotrimerization were used to assemble these targets. Moreover, rongalite has been used to expand the Diels‐Alder chemistry.     

Theoretical prediction of Ni(I)-catalyst for hydrosilylation of pyridine and quinoline

Catalytic synthesis of dihydropyridine by transition-metal complex is one of the important research targets, recently. Density functional theory calculations here demonstrate that nickel(I) hydride complex (bpy)Ni^IH (bpy = 2,2′-bipyridine) 1 is a good catalyst for hydrosilylation of both quinoline and pyridine. Two pathways are possible; in path 1, substrate reacts with 1 to form stable intermediate Int1 . After that, N³─C¹ bond of substrate inserts into Ni─H bond of 1 via TS1 to afford N-coordinated 1,2-dihydroquinoline Int2 with the Gibbs activation energy (ΔG°^‡) of 21.8 kcal mol⁻¹. Then, Int2 reacts with hydrosilane to form hydrosilane σ-complex Int3 ; this is named path 1A. In the other route (path 1B), Int1 reacts with phenylsilane in a concerted manner via hydride-shuttle transition state TS2 to afford Int3 . In TS2 , Si atom takes hypervalent trigonal bipyramidal structure. Formation of hypervalent structure is crucial for stabilization of TS2 (ΔG°^‡ = 17.3 kcal mol⁻¹). The final step of path 1 is metathesis between Ni─N³ bond of Int3 and Si─H bond of PhSiH₃ to afford N-silylated 1,2-dihydroproduct and regenerate 1 (ΔG°^‡ = 4.5 kcal mol⁻¹). In path 2, 1 reacts with hydrosilane to form Int5 , which then forms adduct Int6 with substrate through Si–N interaction between substrate and PhSiH₃. Then, N-silylated 1,2-dihydroproduct is produced via hydride-shuttle transition state TS5 (ΔG°^‡ = 18.8 kcal mol⁻¹). The absence of N-coordination of substrate to Ni^I in TS5 is the reason why path 2 is less favorable than path 1B. Quinoline hydrosilylation occurs more easily than pyridine because quinoline has the lowest unoccupied molecular orbital at lower energy than that of pyridine. © 2019 Wiley Periodicals, Inc.     

Molecular electrostatic potentials of divalent carbon(0) compounds

The molecular electrostatic potentials of divalent carbon(0) and divalent carbon(ii) compounds are calculated and the results are compared with theoretically predicted proton affinities and complexation energies with BH(3).     

Experimental investigation on phosphate adsorption,mechanism and desorption properties of Mn-Zn-Ti oxide trimetal alloy nanocomposite

Recently composite metal oxides have gained significant attention to be used as adsorbent because of their synergetic effects. Particularly Manganese containing composite oxides are useful for removal of inorganic oxyacids such as phosphate or arsenate. In present study fabrication of Mn-Zn-Ti Oxide adsorbent for phosphate removal carried out via co precipitation method. Surface properties deduced by TEM, FESEM, EDAX and XRD, revealed nanosized composite material has a porous nature constitute of alloy type mixing of the metals. Size of the nanocomposite found to be as small as 6?nm. Adsorption capacity for phosphate estimated at different pH, time and adsorbent dose by batch mode. In addition desorption properties and thermodynamic study also carried out. Several isotherms and kinetic models applied to observe adsorption properties of the Mn-Zn-Ti Oxide nanocomposite. Adsorption capacity found to be 151?mg/g at pH 6, time 90?min, adsorbent dose 0.20?g/L and phosphate concentration of 200?mg/L. Adsorption data fitted to second order kinetics and Freundlich isotherm. Formation of complex between nanocomposite and phosphate predicted from FTIR and supported by pH kinetic and isotherm studies. Desorption and reusability found to be well maintained over five cycles.