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Chemical research on noble metal monolayer-protected clusters (MPCs) has typically focused on discovering new sizes and compositions. However, the discovery of the fundamental chemical principles that govern MPC reactions, which are required for the rational chemical transformation of MPCs, has received significantly less attention. Here, we study in detail the electronic nature of the mechanism of postsynthetic ligand exchange reactions using M4Ag44(p-MBA)30as a model system, where M is a monocationic counterion and p-MBA is para-mercaptobenzoic acid. The systematic exchange of aryl thiol ligands, with different electron-withdrawing and -donating substituents in different ring positions, was studied in detail by electrospray-ionization mass spectrometry measurements of equilibrium product distributions and density functional theory (DFT) calculations of fully ligand-exchanged clusters. We found that (i) these ligand exchange reactions are driven by the relative electrophilicity of the incoming ligands, (ii) the electrophilic driving force was stronger than modest steric effects, and (iii) site-specific substitution due to ligand shell bonding geometries was not observed, revealing certain limitations of rational synthesis. DFT calculations uncovered the complexity of the charge distributions on the clusters, contrasting with currently used simple heuristic models of charge withdrawal and calling attention to the subtlety and intricacy of the effects of charge redistribution upon substitution. By carefully and systematically establishing such basic chemical principles to build a catalog of MPC reactions, in analogy to organic chemistry, the rational synthesis of new MPC materials using MPCs as reagents in transformation reactions could become possible.

Using historical data from Nepal—one of the largest recipients of aid among South Asian countries—this paper investigates the link between foreign aid, growth, remittances and carbon dioxide (CO2) emissions. The investigation of this issue is particularly important, as policy makers in the least developed countries are increasingly concerned about growing reliance on energy imports, particularly fossil fuels, and increasing CO2 emissions. Mounting energy consumption has not only made their economies vulnerable to environmental disasters and increased health costs, but also to external shocks due to frequent fluctuations in international market prices for petroleum products. Since available studies are largely based on cross-sectional data—which lump together countries with different characteristics— empirical evidence is contradictory. In-depth case studies of countries with different backgrounds would certainly provide better insights into the link between aid, growth, remittances and CO2 emissions, and contribute to ongoing policy dialogue. Our empirical results, based on an in-depth case study of Nepal, suggest that more foreign aid and remittances reduce CO2 emissions, whereas financial development and higher income increase CO2 emissions. These findings point to the importance of market mechanisms for regulating financial development and higher income to control CO2 emissions, without undermining competitiveness.

Silver and gold molecular nanoparticles (mNPs) are a relatively new class of molecular materials of fundamental interest. They are high-nuclearity metal–organic compounds, with ligated metal cores, where the different character of bonding in the ligand shell and metal core gives rise to many of the unique properties of these materials. Research has primarily focused on gold mNPs, due to their good stability and the ease with which they may be synthesized and processed. To understand these materials as a general class, however, it will be necessary to broaden research efforts to other metals. Gold and silver are isoelectronic and have the same atomic radius, making the comparison of gold and silver mNPs attractive. The optical and chemical differences of the two metals provide useful contrasts, however, as well as a means to access a wider range of properties.

The synthesis of gold and silver nanoparticles was evaluated using green chemistry metrics, with an emphasis on process mass intensity (PMI). Opportunities for improving synthetic methods were identified based on these metrics. Solvent usage was identified as the biggest challenge among nanoparticle syntheses, including those otherwise deemed as green, with PMIs that were typically in the thousands. The synthesis of ligated metal nanoparticles by arrested precipitation was identified as the best opportunity for making impactful improvements, since they are the most industrially relevant but the least green. Although this review focuses on gold and silver nanoparticles, much of the discussion also pertains to inorganic nanomaterials synthesis in general.

Metal heteroatom substitution in molecular nanoparticles offers a unique opportunity to study alloying with an unprecedented level of detail and control, which may be important for applications in optics, electronics, medicine, and catalysis. Many examples of single- or few-heteroatom substitutions exist in molecular nanoparticles, but true alloys with compositions varying over a wide range of substitutions are rare. Here, we study M4AuxAg44–x(p-MBA)30alloy nanoparticles as a model system, where M is a countercation and p-MBA is a p-mercaptobenzoic acid ligand, and where 0 ≤ x≤ 12 represents the full range of possible compositions, all of which are stable in solution. Synthetic reactions produced M4AuxAg44–x(p-MBA)30alloy nanoparticle products whose compositions were found to be a complex function of the reaction mixture composition. Postsynthetic reactions showed that oxidation of M4AuxAg44–x(p-MBA)30nanoparticles was slowed in a monotonic fashion by the addition of gold atoms. Density functional theory provided insights into the variation in the chemistry, electronic structure, and reactivity of M4AuxAg(44–x)(p-MBA)30nanoparticle alloys as a function of composition and showed that the stabilization mechanism was the result of the electrophilicity of the gold atoms, which polarized the metal core. An oxidation reaction mechanism was proposed based on these experimental and computational results, which involved the octahedrally located silver atoms.

Nanoparticles rival pharmaceuticals in synthetic inefficiency, in particular as measured by process mass intensity, with by far the largest contribution to waste being from solvents. We have therefore developed a greener method of synthesizing silver nanoparticles using a paste format instead of a metal salt solution. The paste-based synthesis requires 87% less solvent yet still produces exclusively Na4Ag44(p-MBA)30nanoparticles, without size sorting, with 89% yield. By using a stoichiometric silver-thiolate polymer as a precursor to intimately mix the metal atoms and ligands, and by using a small amount of liquid to form a paste to promote mass transport, the heterogeneity and kinetics problems that are associated with entirely solid-state syntheses were avoided. Because the nanoparticle product was also a paste, solvent use for postprocessing was minimized. Use of the silver-thiolate polymer can also reduce health risks associated with hazardous free thiols in conventional solution-phase syntheses. Using this strategy, the process mass intensity was reduced from ∼1800 for the solution-phase reaction to ∼200 and ∼100 for the paste-based reaction with and without protonation of the ligands, respectively.

M4Ag44(p-MBA)30molecular nanoparticles, where M is an alkali metal, have recently been shown to have exceptional stability, which confers unique traits to this molecule. In particular, the synthesis is straightforward, produces a truly single-sized molecular product, and has a quantitative yield. Here we describe in detail the results of experimental and theoretical studies on the synthesis, structure, stability, and electronic and optical properties of M4Ag44(p-MBA)30, including ESI-MS, NMR, optical absorption, IR, TGA, and other measurements as well as DFT and TDDFT calculations. This work deepens our understanding of this important Ag molecule, which should facilitate its use in a wide range of fundamental studies and applications.

Using the cointegration technique, this paper examines the revenue and expenditure behaviour of the Nepalese government in the presence of foreign aid for the period 1975–2002. The results show that aid positively affects both development and non-development expenditure in the long run. However, the long-run relationship between aid and non-development expenditure is found to be stronger than that between aid and development expenditure. Since aid is generally given for development expenditure, these results indicate the possibility of diversion of aid to non-development expenditure. Thus, the long-run relationship between aid and non-development expenditure may indicate aid fungibility. On the other hand, no evidence is found in favour of the hypothesis that aid availability makes the government lazy in terms of domestic revenue mobilisation.