Macromolecular soft templates for synthesis and self-assembly of functional nanomaterials

Nanostructured composite materials made of organic matrices and inorganic nanoparticles (NPs) represent the new paradigm of functional hybrid materials. This dissertation is focused on the synthesis and self-assembly of NPs within organic matrices which act as templates, targeting the formation of use-inspired structures. Particularly, self-assembly of macromolecules such as proteins and polymers, and polymer-functionalized NPs is utilized to create ordered assemblies of NPs. Inspired by the formation of chains of magnetic NPs in a group of bacteria referred to as Magnetotactic bacteria, we used Mms6, a biomineralization protein, as a template towards the formation of self-assembled arrays of magnetic NPs. Surface sensitive techniques such as atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy, show the formation of these arrays on solid substrates. An alternative to the use of templates is to directly control the interactions between the NPs. In the presence of short dithiol tethers, gold nanoparticles crosslink covalently and form assemblies with short ranged FCC-like order. PEG functionalized nanoparticles, obtained by ligand exchange procedure, form a crystalline monolayer at the vapor-liquid interface in the presence of electrolytes in the suspension. In the presence of a complexing polymer (specifically, neutral PAA) the crystallinity of these monolayers decreases and NPs aggregate in the bulk. Analysis of these aggregates shows that in contrast to the covalent linkage, non-covalent interactions (hydrogen bonds and van der Waal\u27s forces, via inter-polymer complexes) between the poly(ethylene glycol) (PEG) functionalized NPs, lead to the formation of FCC superlattices of NPs. Theoretical considerations of the variation of inter-particle distances show the significance of van der Waal\u27s forces in these superlattices. Self-assembly processes used to create ordered assemblies of nanoparticles developed here are promising routes to fabricate functional nanomaterials such as metamaterials

Reduction of derived Hochschild functors over commutative algebras and schemes

We study functors underlying derived Hochschild cohomology, also called Shukla cohomology, of a commutative algebra S essentially of finite type and of finite flat dimension over a commutative noetherian ring K. We construct a complex of S-modules D, and natural reduction isomorphisms Ext^*_{S\otimes^L_{K}S}(S|K;M\otimes^L_{K}N) ~ Ext^*_S(RHom_S(M,D),N) for all complexes of S-modules N and all complexes M of finite flat dimension over K whose homology H(M) is finitely generated over S; such isomorphisms determine D up to derived isomorphism. Using Grothendieck duality theory we establish analogous isomorphisms for any essentially finite type flat maps f: X->Y of noetherian schemes, with f^!(O_Y) in place of D.Comment: 32 pages. Minor changes from previous version. To appear in the Advances in Mathematic

Air Quality, National Standards and Human Health in India (NIAS Policy Brief No. NIAS/NSE/EEC/U/PB/25/2021)

A clean air environment is prudent to healthy living. Studies related to the impact of ambient air pollution on public health are limited in India. Studies conducted by researchers at NIAS indicate that the natural baseline levels for Particulate Matter pollution in 10 megacities (with different climatological conditions) are significantly higher than the WHO’s Air Quality Guidelines levels. The exposure-response function cannot be universal due to the adaptive power of human beings. Therefore, coordinated national effort between MoES, MOEFCC, and ICMR is required to conduct scientific studies to determine the "exposure-response function" for Indians

Solvent Effects on Extractant Conformational Energetics in Liquid-Liquid Extraction: A Simulation Study of Molecular Solvents and Ionic Liquids

Extractant design in liquid-liquid extraction (LLE) is a research frontier of metal ion separations that typically focuses on the direct extractant-metal interactions. However, a more detailed understanding of energetic drivers of separations beyond primary metal coordination is often lacking, including the role of solvent in the extractant phase. In this work, we propose a new mechanism for enhancing metal-complexant energetics with nanostructured solvents. Using molecular dynamics simulations with umbrella sampling, we find that the organic solvent can reshape the energetics of the extractant's intramolecular conformational landscape. We calculate free energy profiles of different conformations of a representative bidentate extractant, n-octyl(phenyl)-N,N-diisobutyl carbamoyl methyl phosphinoxide (CMPO), in four different solvents: dodecane, tributyl phosphate (TBP), and dry and wet ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf_2N]). By promoting reorganization of the extractant molecule into its binding conformation, our findings reveal how particular solvents can ameliorate this unfavorable step of the metal separation process. In particular, the charge alternating nanodomains formed in ILs substantially reduce the free energy penalty associated with extractant reorganization. Importantly, using alchemical free energy calculations, we find that this stabilization persists even when we explicitly include the extracted cation. These findings provide insight into the energic drivers of metal ion separations and potentially suggest a new approach to designing effective separations using a molecular-level understanding of solvent effects

Interfacial Self-Assembly of Polyelectrolyte-Capped Gold Nanoparticles

We report on pH- and salt-responsive assembly of nanoparticles capped with polyelectrolytes at vapor–liquid interfaces. Two types of alkylthiol-terminated poly(acrylic acid) (PAAs, varying in length) are synthesized and used to functionalize gold nanoparticles (AuNPs) to mimic similar assembly effects of single-stranded DNA-capped AuNPs using synthetic polyelectrolytes. Using surface-sensitive X-ray scattering techniques, including grazing incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR), we demonstrate that PAA-AuNPs spontaneously migrate to the vapor–liquid interfaces and form Gibbs monolayers by decreasing the pH of the suspension. The Gibbs monoalyers show chainlike structures of monoparticle thickness. The pH-induced self-assembly is attributed to the protonation of carboxyl groups and to hydrogen bonding between the neighboring PAA-AuNPs. In addition, we show that adding MgCl2 to PAA-AuNP suspensions also induces adsorption at the interface and that the high affinity between magnesium ions and carboxyl groups leads to two- and three-dimensional clusters that yield partial surface coverage and poorer ordering of NPs at the interface. We also examine the assembly of PAA-AuNPs in the presence of a positively charged Langmuir monolayer that promotes the attraction of the negatively charged capped NPs by electrostatic forces. Our results show that synthetic polyelectrolyte-functionalized nanoparticles exhibit interfacial self-assembly behavior similar to that of DNA-functionalized nanoparticles, providing a pathway for nanoparticle assembly in general

Effect of (poly)electrolytes on the interfacial assembly of PEG functionalized gold nanoparticles

We report on the effect of interpolymer complexes (IPCs) of poly(acrylic acid) (PAA) with poly(ethylene glycol) functionalized Au nanoparticles (PEG-AuNPs) as they assemble at the vapor-liquid interface, using surface sensitive synchrotron X-ray scattering techniques. Depending on the suspension pH, PAA functions both as a weak polyelectrolyte and a hydrogen bond donor, and these two roles affect the interfacial assembly of PEG-AuNPs differently. Above its isoelectric point, we find that PAA leads to the formation of a PEG-AuNPs monolayer at the interface with hexagonal structure. In the presence of high concentration of HCl (i.e., below the isoelectric point), at which PAA forms IPCs with PEG, the hexagonal structure at the interface appears to deteriorate, concurrent with aggregation in the bulk. Thus, while electrolytic behavior of PAA induces interfacial assembly, hydrogen bonding behavior, as PAA becomes neutral, favors the formation of 3D assemblies. For comparison, we also report on the formation of PEG-AuNPs monolayers (in the absence of PAA) with strong electrolytes such as HCl, H2SO4 and NaOH that lead to a high degree of crystallinity

Ordered Networks of Gold Nanoparticles Crosslinked by Dithiol‐Oligomers

Controlled aggregation of nanoparticles into superlattices is a grand challenge in material science, where ligand based self‐assembly is the dominant route. Here, the self‐assembly of gold nanoparticles (AuNPs) that are crosslinked by water soluble oligo‐(ethylene glycol)‐dithiol (oEG‐dithiol) is reported and their 3D structure by small angle X‐ray scattering is determined. Surprisingly, a narrow region is found in the parameter space of dithiol linker‐length and nanoparticle size for which the crosslinked networks form short‐ranged FCC crystals. Using geometrical considerations and numerical simulations, the stability of the formed lattices is evaluated as a function of dithiol length and the number of connected nearest‐neighbors, and a phase diagram of superlattice formation is provided. Identifying the narrow parameter space that allows crystallization facilitates focused exploration of linker chemical composition and medium conditions such as thermal annealing, pH, and added solutes that may lead to superior and more robust crystals