Structural Variation in Homopolymers Bearing Zwitterionic and Ionic Liquid Pendants for Achieving Tunable Multi-Stimuli Responsiveness and Hierarchical Nanoaggregates

A series of monomers comprising units bearing both imidazolium bromide ionic liquid (IL) and zwitterionic imidazolium alkyl carboxylate moieties with different alkyl spacer groups are designed and synthesized. RAFT polymerization of these monomers produces a new class of ionic homopolymers, named poly­(zwitterionic ionic liquid)­s (PZILs), which behave like poly­(ionic liquid)­s as well as poly­(zwitterion)­s depending on the solution pH. Such PZILs exhibit an isoelectric point (pI) at pH 5.7, where they exist in their zwitterionic form, making them dual responsive to both pH and temperature. Above pH 5, the aqueous transparent solution of PZIL transforms into turbid suspension due to the formation of insoluble hierarchical nanoaggregates (NAs) of various morphologies such as small spheres, large spheres, flower-like, dendrite-shaped, and dendritic fibril-like depending upon the solution pH and PZILs’ structures. The dissolution of aggregates upon heating and reaggregation upon cooling suggests existence of reversible upper critical solution temperature (UCST)-type phase transition above pH 5. Below pH 5, owing to the presence of cationic IL moieties, aqueous PZIL solution exhibits transparent-to-turbid transition due to the formation of anion-induced NAs of various dendritic morphologies upon addition of various chaotropic anions within the Hofmeister series. Upon heating, this colloidal turbid suspension becomes transparent, showing a distinct UCST-type phase transition, and the process is reversible. It is easily possible to fine-tune the cloud point and morphologies of the NAs by changing various parameters such as molecular weight, concentrations, structure of PZILs, nature and concentration of anions, and solution pH

Poly(ionic liquid)-Promoted Solvent-Borne Efficient Exfoliation of MoS₂/MoSe₂ Nanosheets for Dual-Responsive Dispersion and Polymer Nanocomposites

Considering the great potential of layered transition-metal dichalcogenides in thin film photovoltaic, advanced composite materials, and biomedical applications, it is of high importance to have a highly efficient method for their generation in both aqueous and nonaqueous media. Here, we demonstrate a simple one-pot efficient exfoliation approach to prepare dispersion of single or few-layers MoS₂ nanosheets by quick sonication in the presence of cationic poly­(ionic liquids)­s (PILs) in both aqueous and nonaqueous media at room temperature. These PILs are synthesized by simple conventional free radical polymerization from designed ionic liquid monomers. This method is extendable for efficient generation of MoSe₂ nanosheets’ dispersion in these solvents. Owing to the solubility in both water and organic solvents, cationic PIL molecules serve the dual purpose of an exfoliating-cum-stabilizing agent. PIL-stabilized nanosheets’ dispersions are stable for more than two months at ambient temperature. The adsorption of PIL to the surface of MoS₂ nanosheet converts them to responsive toward ions and temperature in aqueous medium. Additionally, MoS₂–PIL nanosheets can easily be dispersed in water-soluble poly­(vinyl alcohol) and nonaqueous-soluble poly­(methyl methacrylate) matrices for making well-dispersed homogeneous nanocomposites and their dielectric properties are studied

Poly(ionic liquid)-Promoted Solvent-Borne Efficient Exfoliation of MoS₂/MoSe₂ Nanosheets for Dual-Responsive Dispersion and Polymer Nanocomposites

Considering the great potential of layered transition-metal dichalcogenides in thin film photovoltaic, advanced composite materials, and biomedical applications, it is of high importance to have a highly efficient method for their generation in both aqueous and nonaqueous media. Here, we demonstrate a simple one-pot efficient exfoliation approach to prepare dispersion of single or few-layers MoS₂ nanosheets by quick sonication in the presence of cationic poly­(ionic liquids)­s (PILs) in both aqueous and nonaqueous media at room temperature. These PILs are synthesized by simple conventional free radical polymerization from designed ionic liquid monomers. This method is extendable for efficient generation of MoSe₂ nanosheets’ dispersion in these solvents. Owing to the solubility in both water and organic solvents, cationic PIL molecules serve the dual purpose of an exfoliating-cum-stabilizing agent. PIL-stabilized nanosheets’ dispersions are stable for more than two months at ambient temperature. The adsorption of PIL to the surface of MoS₂ nanosheet converts them to responsive toward ions and temperature in aqueous medium. Additionally, MoS₂–PIL nanosheets can easily be dispersed in water-soluble poly­(vinyl alcohol) and nonaqueous-soluble poly­(methyl methacrylate) matrices for making well-dispersed homogeneous nanocomposites and their dielectric properties are studied

Structures and Electronic Properties of Heavier Congeners of Disk-Like Molecules: (Si, Ge) Sulflower and (Si, Ge) Olympicene

The ground-state structures, HOMO–LUMO gaps, singlet–triplet splitting, and the UV–vis absorption spectra for Si, Ge-substituted analogues of the recently synthesized disk-like π-conjugated molecules, like octathio[8]­circulene, popularly termed “sulflower”, and 2<i>H</i>-benzo­[<i>cd</i>]­pyrene, popularly termed “olympicene”, are studied using density functional theory. Unlike their pure organic counterparts, these molecules are found to be nonplanar with substantial puckering from the high symmetric structures. The origin of puckering is traced to pseudo Jahn–Teller (PJT) distortions due to favorable mixing of the occupied molecular orbitals (OMO) and unoccupied molecular orbitals (UMO). Even though the HOMO–LUMO and singlet–triplet gaps for these molecules are smaller than their organic counterparts, the reorganization energies (both hole, λ_h, and electron, λ_e) for the Si, Ge analogues of sulflower and olympicene are much higher. Therefore, these molecules are expected to be rather inefficient for field effect transistor (FET) device fabrication

Synthesis and Self-Aggregation of Poly(2-ethyl-2-oxazoline)-Based Photocleavable Block Copolymer: Micelle, Compound Micelle, Reverse Micelle, and Dye Encapsulation/Release

We report on the synthesis of photocleavable poly­(2-ethyl-2-oxazoline)-<i>block</i>-poly­(2-nitrobenzyl acrylate) (PEtOx-<i>b</i>-PNBA) block copolymers (BCPs) with varying compositions via combination of microwave-assisted cationic ring-opening polymerization (CROP) and atom transfer radical polymerization (ATRP) using α-bromoisobutyryl bromide as an orthogonal initiator. The amphiphilic nature of this BCP causes them to self-assemble into primary micelles in THF/H₂O, which further undergo secondary aggregation into nanostructured compound micelles as established through DLS, FESEM, and TEM. Upon UV irradiation (λ = 350 nm), the photocleavage of the PNBA block of the PEtOx-<i>b</i>-PNBA BCP takes place, and that leads to the formation of the doubly hydrophilic poly­(2-ethyl-2-oxazoline)-<i>b</i>-poly­(acrylic acid) (PEtOx-<i>b</i>-PAA) BCP causing the rupture of compound micelles as confirmed by spectroscopic and microscopic techniques. Encapsulation of a model hydrophobic guest molecule, nile red (NR), into the photocleavable BCP micellar core in aqueous solution and its UV-induced release is also investigated by fluorescence emission measurements. PEtOx-<i>b</i>-PNBA BCP amphiphiles are also shown to self-assemble into spherical nanostructures (∼90 nm) in dichloromethane as established by DLS and TEM analysis. These are referred to as reverse micelles and are able to encapsulate anionic hydrophilic dye, Eosin B, and facilitate its solubilization in organic media

Ionic Liquid Cross-Linked Multifunctional Cationic Polymer Nanobeads via Dispersion Polymerization: Applications in Anion Exchange, Templates for Palladium, and Fluorescent Carbon Nanoparticles

This report describes the design and synthesis of an ionic liquid by simple nucleophilic substitution reaction of 4-vinylbenzyl chloride and <i>N</i>-vinylimidazole. This ionic liquid is utilized as cross-linker for dispersion polymerization of acrylamide in the presence of poly­(vinyl methyl ether) (PVME) stabilizer, which produces water-friendly cationic cross-linked poly­(acrylamide) (CPAAm) beads. Morphology investigation reveals that these beads are nanosized and spherical and their size varies with the amount of cross-linker and PVME used. The ionic cross-linker imparts ionic nature in these beads, where anion is mobile and are eventually exchangeable. Consequently, anion exchange capacity is checked using an anionic dye Eosin B via UV–vis spectroscopy. Subsequently, the release of dye is monitored on addition of a pinch of sodium acetate. Analogous anion exchange with [PdCl₄]^2– results in the formation of palladium (Pd) nanoparticles (NPs) inside the cross-linked poly­(acrylamide) beads due to <i>in situ</i> reduction by imidazolium cation present in CPAAm. The carbonization of the CPAAm nanobeads produces nitrogen-doped carbon nanoparticles of comparable morphology and sizes. The resultant carbon nanoparticles emit blue fluorescence under irradiation of UV light. Similarly, Pd NPs embedded carbon nanoparticles are easily prepared by carbonization of the Pd NPs loaded CPAAm nanobeads

Dual-Stimuli-Responsive l‑Serine-Based Zwitterionic UCST-Type Polymer with Tunable Thermosensitivity

The synthesis of l-serine-based zwitterionic polymers, poly­(l-serinyl acrylate)­s (PSAs), of controllable molecular weights and low polydispersities via reversible addition–fragmentation chain transfer (RAFT) polymerization in water at 70 °C is described. The obtained homopolymer PSA exhibits dual responsiveness toward pH and temperature in aqueous solution. The PSA exhibits an isoelectric point near pH 2.85 where the PSA molecules exist in its zwitterionic form. In the pH range of 2.3–3.5, the aqueous PSA solution appears as a two-phase system due to the formation of insoluble aggregates through the intra- and intermolecular electrostatic interaction between the pendent ammonium and carboxylate groups of the neighboring zwitterionic PSA molecules. Furthermore, in this pH range, the two-phase PSA solution becomes one-phase upon heating, exhibiting distinct reversible upper critical solution temperature (UCST)-type phase transition. The cloud point (<i>T</i>_<i>p</i>) is found to increase with increasing molecular weights of PSAs. It is also observed that the <i>T</i>_<i>p</i> changes with changing the solution pH, exhibiting highest <i>T</i>_<i>p</i> near the isoelectric point of PSA. Addition of an electrolyte such as brine solution also affects the <i>T</i>_<i>p</i> of PSA solution following the antipolyelectrolyte effect. Finally, fluorescein isothiocyanate (FITC) tagged PSA with dual-responsiveness is prepared by the postmodification of pendent amino groups of PSA for futuristic applications in biosensors and bioimaging

Polymer-Assisted Chain-like Organization of CuNi Alloy Nanoparticles: Solvent-Adoptable Pseudohomogeneous Catalysts for Alkyne–Azide Click Reactions with Magnetic Recyclability

A solution-phase reduction method is undertaken to produce polymer magnetic bimetallic CuNi nanoalloy with chain-like structures, which are formed by the magnetic dipole-directed assembly of spherical alloy nanoparticles as confirmed from TEM analysis. Magnetic property measurement reveals paramagnetic nature of the alloy nanochain. These polymer-capped chain-like alloy nanoparticles are dispersible in water as well as in organic solvents that increase their ease of application as catalyst in both of these environments. The XPS and zeta potential analysis demonstrates the presence of Cu­(I) on the alloy particle surface and justifies their catalytic activity toward alkyne–azide click reactions. Consequently, the catalytic activity of the as-synthesized polymer CuNi alloy nanochain is investigated toward a wide variety of alkyne–azide click reactions at room temperature in water and in DMF. Depending upon the nature of the substrate and the surface stabilizing polymer on the nanocatalyst, a moderate to quantitative yield of the click-conjugated product is obtained. Additionally, the advantage of pseudohomogeneity of CuNi nanoalloy suspension is utilized to modify polymer end group with amino acid and peptide with ionic liquid via click reaction to create new bioconjugates. Moreover, the nanoalloy catalyst is magnetically recoverable and reusable up to three cycles of click reactions without losing much of its original activity

Solvent-Adoptable Polymer Ni/NiCo Alloy Nanochains: Highly Active and Versatile Catalysts for Various Organic Reactions in both Aqueous and Nonaqueous Media

The synthesis of solvent-adoptable monometallic Ni and NiCo alloy nanochains by a one-pot solution phase reduction method in the presence of poly­(4-vinylphenol) (PVPh) is demonstrated. The elemental compositions of the as-prepared alloys are determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS), which are matching well with the target compositions. The morphology analysis by TEM and FESEM confirms that the nanochains are made up of organized spherical monometallic Ni or bimetallic NiCo alloy nanoparticles (NPs). However, there is no nanochain formation when the alloy is prepared without the polymer PVPh. A possible mechanism for the formation of such NiCo alloy nanochains is discussed. The X-ray diffraction and selected area electron diffraction patterns reveal that the Ni/NiCo alloys are polycrystalline with fcc structure. The obtained Ni or NiCo alloy nanostructures are ferromagnetic with very high coercivity. The polymer Ni/NiCo alloy nanochains are dispersible in both water and organic media that makes them versatile enough to use as catalysts in the reactions carried out in both types of media. The catalytic activities of these Ni/NiCo alloy nanochains are extremely high in the borohydride reduction of <i>p</i>-nitrophenol in water. In organic solvents, these nanochains can act as efficient catalysts, under ligand-free condition, for the C–S cross-coupling reactions of various aryl iodides and aryl thiols for obtaining the corresponding cross-coupled products in good to excellent yield up to 96%. The NiCo nanochain also successfully catalyzes the C–O cross-coupling reaction in organic medium. A possible mechanism for NiCo alloy nanochain-catalyzed cross-coupling reaction is proposed

Mn(III) and Cu(II) complexes of 1-((3-(dimethylamino)propylimino)methyl) naphthalen-2-ol): Synthesis, characterization, catecholase and phenoxazinone synthase activity and DFT-TDDFT study

<p>Two new complexes, [MnL₂](ClO₄) (<b>1</b>) and [CuL₂] (<b>2</b>) (where LH = (E)-1-((3-(dimethylamino)propylimino)methyl)naphthalen-2-ol), have been synthesized and characterized by spectroscopic techniques and their molecular structures are established by single-crystal X-ray diffraction study. Complex <b>1</b> adopts an octahedral geometry around the central manganese atom which is in + 3 oxidation state, whereas in complex <b>2</b>, the Cu⁺² ion preferred a square pyramidal environment around it through the ligand donor atoms. Both complexes were tested for catecholase and phenoxazinone synthase activity. Complex <b>1</b> catalyzes the oxidation of 3,5-ditertiary-butyl catechol with a <i>k</i>_cat value of 6.8424 × 10² h⁻¹ in acetonitrile whereas the same for complex <b>2</b> is 3.7485 × 10² h⁻¹ in methanol. Phenoxazinone synthase activity was shown only by complex <b>2</b> having <i>k</i>_cat = 74.225 h⁻¹. Structures of both the title complexes have been optimized by means of DFT calculations. Experimental electronic spectra of the complexes have been corroborated by TDDFT analysis. Electrochemical investigations by means of cyclic voltammetry have been carried out to study the electron transfer processes in the complexes.</p