34 research outputs found
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 MoS<sub>2</sub>/MoSe<sub>2</sub> 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 MoS<sub>2</sub> 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 MoSe<sub>2</sub> 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 MoS<sub>2</sub> nanosheet converts them to responsive
toward ions and temperature in aqueous medium. Additionally, MoS<sub>2</sub>–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 MoS<sub>2</sub>/MoSe<sub>2</sub> 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 MoS<sub>2</sub> 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 MoSe<sub>2</sub> 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 MoS<sub>2</sub> nanosheet converts them to responsive
toward ions and temperature in aqueous medium. Additionally, MoS<sub>2</sub>–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<sub>h</sub>, and electron, λ<sub>e</sub>) 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/H<sub>2</sub>O, 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 [PdCl<sub>4</sub>]<sup>2–</sup> 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><sub><i>p</i></sub>) is found to
increase with increasing molecular weights of PSAs. It is also observed
that the <i>T</i><sub><i>p</i></sub> changes with
changing the solution pH, exhibiting highest <i>T</i><sub><i>p</i></sub> near the isoelectric point of PSA. Addition
of an electrolyte such as brine solution also affects the <i>T</i><sub><i>p</i></sub> 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, [MnL<sub>2</sub>](ClO<sub>4</sub>) (<b>1</b>) and [CuL<sub>2</sub>] (<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<sup>+2</sup> 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><sub>cat</sub> value of 6.8424 × 10<sup>2</sup> h<sup>−1</sup> in acetonitrile whereas the same for complex <b>2</b> is 3.7485 × 10<sup>2</sup> h<sup>−1</sup> in methanol. Phenoxazinone synthase activity was shown only by complex <b>2</b> having <i>k</i><sub>cat</sub> = 74.225 h<sup>−1</sup>. 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