Ph.D., IIT BOMBAY
Ion selectivity switching in bulk compared to air-water interface by an amphiphile,calixarene
Role of calixarene as a molecular as well as ionic receptor has been explored widely in the literature.It has been found that based on the conformation, solvent, medium etc. its selectivity and sensitivity may change.This particular nature of calixarene has been well used for stimuli responsive sensing properties. Our group has extensively worked towards the recognition properties of calixarenes both in its solution form as well as a self-assembled monolayer. Change in the selectivity in different mediums encouraged us to study more of the derivatives of calixarene in comparison in different environments.. The receptor molecule having similar binding core as explored earlier in our group has been used for metal ion recognition through absorption-emission and pressure-area isotherm studies. The variable nature of the interaction of receptor molecule with metal ions in random form (solution) was seen through spectroscopic studies (absorption, emission and ESI-MS titration) which showed greater sensitivity towards Fe3+. When interaction of receptor with metal ions was studied in its more oriented form using Langmuir-Blodgett trough, Al3+ was favoured over other metal ion used(Mg2+, Al3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+ ions). The monolayers were trasfered later onto H-terminated Si-wafer and well characterized (Brewster Angle Microscopy, Atomic Force Microscopy, X-ray Photoelectron Spectroscopy, contact angle). How the interface vs. bulk plays role in the interaction as well as sensitivity has been studied in the work. The result also shows that the receptor molecule is sensitive as well as selective towards Al3+ at the air-water interface where as binding constant calculation shows that in solution Fe3+ is favoured.It can be said that mainly electrostatic interaction plays leading role in the selectivity as well sensitivity.
Abstract: Gels are interesting soft materials owing to their functional properties leading to potential applications. This paper deals with the synthesis of monocholesteryl derivatized calixarene (G) and its instantaneous gelation at a minimum gelator concentration of 0.6% in 1:1 v/v THF/acetonitrile. The gel shows remarkable thermoreversibility by exhibiting Tgel→sol at ∼48 °C and is demonstrated for several cycles. The gel shows an organized network of nanobundles, while that of the sol shows spherical nanoaggregates in microscopy. A bundle with ∼12 nm diameter possessing hydrophobic pockets in itself is obtained from computationally modeled gel, and hence the gel is suitable for storage and release applications. The guest-entrapped gels exhibit the same microstructures as that observed with simple gels, while fluorescence spectra and molecular mechanics suggests that the drug molecules occupy the hydrophobic pockets. All the entrapped drug molecules are released into water, suggesting a complete recovery of the trapped species. The reusability of the gel for the storage and release of the drug into water is demonstrated for four consecutive cycles, and hence the gel formed from G acts as a functional material that finds application in drug delivery.
Pub.: 07 May '15, Pinned: 27 Jul '17
Abstract: This paper describes the detection of volatile organic compounds (VOCs) using an e-nose type integrated microfabricated sensor array, in which each resonator is coated with different supramolecular monolayers: p-tert-butyl calixarene (Calixarene), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (Porphyrin), β-cyclodextrin (β-CD), and cucurbituril (CB). Supramolecular monolayers fabricated by Langmuir-Blodgett techniques work as specific sensing interface for different VOCs recognition which increase the sensor selectivity. Microfabricated ultrahigh working frequency film bulk acoustic resonator (FBAR) transducers (4.4 GHz) enable their high sensitivity toward monolayer gas sensing which facilitate the analyses of VOCs adsorption isotherms and kinetics. Two affinity constants (K1, K2) are obtained for each VOC, which indicate the gas molecule adsorption happen inside and outside of the supramolecular cavities. Additional kinetic information on adsorption and desorption rate constants (ka, kd) are obtained as well from exponential fitting results. The five parameters, one from the conventional frequency shift signals of mass transducers and the other four from the indirect analyses of monolayer adsorption behaviors, thus enrich the sensing matrix (Δf, K1, K2, ka, kd) which can be used as multiparameter fingerprint patterns for highly selective detection and discrimination of VOCs.
Pub.: 01 Aug '15, Pinned: 27 Jul '17
Abstract: Supramolecular approach plays pivotal role in the construction of smart and functional materials due to the reversible nature of noncovalent interactions. In the present work, two compounds, cholesterol-functionalized calixpyrrole (CCP) and perylene bisimide diacid (PDA), were synthesized. Little fluorescence is observed in the ethanol solution of the mixture of CCP and PDA, while the solution turns fluorescent upon introduction of ammonia, which is attributed to the formation of a supramolecular ensemble, PDA/(CCP)2/NH3. The fluorescence emission of the as formed ensemble is sensitive to the presence of phenol, an electron-rich analyte. Interestingly, the sensing can also be observed in film state, and the relevant detection limit (DL) is lower than 1 ppb. Moreover, the sensing could also be performed in a visualized manner. Based upon the findings, a sensor device with instant response and good reversibility was developed. Further studies revealed that the as developed fluorescent ensemble is also sensitive to the presence of TNT, an electron-poor compound. The DL for this sensing is ~80 nM. To our knowledge, this is the first report that a fluorescent sensor could be used for phenol sensing in vapor state, and for sensing of both electron-rich and electron-poor analytes in solution state. It is believed that the present study presents a distinctive example that demonstrates how smart sensing is realized via combination of the host-guest chemistry of calixpyrrole and the aggregation and disaggregation property of PBI derivatives.
Pub.: 06 Oct '16, Pinned: 27 Jul '17
Abstract: Calixarene derivatives bearing carboxyl groups at the upper rim and alkyl groups at the lower rim were synthesized. Micrometer-size porous honeycomb-patterned thin films were prepared by evaporating chloroform solution of polystyrene containing the calixarene derivatives under high humidity. These films were coated on gold electrodes of QCM, and the high-frequency changes were observed to detect volatile organic compounds such as dichlorobenzene.
Pub.: 26 Mar '10, Pinned: 27 Jul '17
Abstract: The binding interactions between aqueous copper (Cu(2+)) and lithium (Li(+)) ions and Langmuir monolayers and Langmuir-Blodgett (LB) multilayers have been investigated by studying surface pressure-area (Pi-A) isotherms and surface potential-area (DeltaV-A) behavior in order to find the effective dipole moment, mu(perpendicular), of the calixarene molecules in the uncomplexed and complexed states. The orientation of both calixarenes, namely, 5,11,17,23-tetra-tert-butyl-25,27-diethoxycarbonyl methyleneoxy-26,28-dihydroxycalixarene and 5,17-(9H-fluoren-2-yl)methyleneamino)-11,23-di-tert-butyl-25,27-diethoxycarbonyl methyleneoxy-26,28-dihydroxycalixarene, is such that the plane of the calix ring is parallel with the plane of the water surface regardless of the ion content of the subphase. The Gibbs equation was used to interpret the adsorption of ions with both calixarenes as a function of the concentration. Effective dipole moments have been calculated from surface potential values using the Helmholtz equation. In this work, new LB films have been prepared employing two novel amphiphilic calixarene derivatives bearing different upper rim substituents. Thus, the effect of modifiying the upper rim has been observed. The results have shown that these calixarenes may be useful components of ion sensors.
Pub.: 27 Apr '10, Pinned: 27 Jul '17
Abstract: A homologous series of calixarene-, calixarene-, and calixarene-based surfactants, containing pendant trimethylammonium and n-hexadecyl groups, have been compared with respect to their ability (i) to undergo ionic cross-linking at the air/water interface, (ii) to incorporate poly(4-styrenesulfonate) (PSS) in Langmuir-Blodgett (LB) bilayers, and (iii) to act as barriers toward He, N(2), and CO(2) when assembled into cross-linked LB bilayers. As these calix[n]arenes increase in size, their ability to undergo ionic cross-linking has been found to increase, the thickness of corresponding glued LB bilayers has been found to decrease, and their barrier properties and permeation selectivities have been found to increase. The likely origin for these effects and the probable mechanism by which He, N(2), and CO(2) cross these ultrathin films are discussed.
Pub.: 30 Jul '10, Pinned: 27 Jul '17
Abstract: In this work, we have studied the interactions between the water-soluble p-sulfonatocalixarene and cationic surfactants octyltrimethylammonium bromide below the cmc and dodecyltrimethylammonium bromide above the cmc, by saturation transfer difference (STD) NMR spectroscopy. From the STD build-up curves, we have obtained the T1 independent cross relaxation rates, and the results show that the interactions established between the cationic headgroup of the surfactant and the OMe group of the macrocycle play an important role in the stabilization of the complex, both below and above the cmc.
Pub.: 28 Mar '12, Pinned: 27 Jul '17
Abstract: A covalently immobilized calixhydroquinone monolayer was used as the host matrix to synthesize metallic NPs using an in situ redox process. The characteristics of different metallic ions that affect the synthesis process were studied. Metallic ions with less charges, lower oxidation state in the reaction, and higher standard redox potential provided better yield. Bimetallic NPs with a core-shell structure were synthesized by a sequential deposition of different metals on the same monolayer. The process was applied to form a layer of immobilized NPs on flat and curved surfaces. The ability to synthesize and immobilize well-controlled NPs on different surfaces has promising applications in decoration of irregular surfaces of miniaturized, three-dimensional objects.
Pub.: 08 Oct '13, Pinned: 27 Jul '17
Abstract: The interactions of an amphiphilic calixarene, namely p-guanidino-dodecyloxy-calixarene, 1, self-assembled as Langmuir monolayers, with short double stranded DNA, were investigated by surface pressure-area (π-A) isotherms, surface ellipsometry and Brewster angle microscopy (BAM). Three DNA 30mers were used as models, poly(AT), poly(GC) and a random DNA sequence with 50% of G:C base pairs. The interactions of these model DNA duplexes with 1-based Langmuir monolayers were studied by measuring compression isotherms using increasing DNA concentrations (10(-6), 10(-5), 10(-4), and 5 × 10(-4) g L(-1)) in the aqueous subphase. The isotherms of 1 showed an expansion of the monolayer with, interestingly, significant differences depending on the duplex DNA sequence studied. Indeed, the interactions of 1-based monolayers with poly(AT) led to an expansion of the monolayer that was significantly more pronounced that for monolayers on subphases of poly(GC) and the random DNA sequence. The structure and thickness of 1-based Langmuir monolayers were investigated by BAM and surface ellipsometry that showed differences in thickness and structure between a monolayer formed on pure water or on a DNA subphase, with here again relevant dissimilarities depending on the DNA composition.
Pub.: 17 Jul '14, Pinned: 27 Jul '17
Abstract: The present work investigates the interaction of hexadecylbetainate chloride (C(16)BC), a glycine betaine-based ester with palmitoyl-oleoyl-phosphatidylcholine (POPC), sphingomyelin (SM), and cholesterol (CHOL), three biological relevant lipids present in the outer leaflet of the mammalian plasma membrane. The binding affinity and the mixing behavior between the lipids and C(16)BC are discussed based on experimental (isothermal titration calorimetry (ITC) and Langmuir film balance) and molecular modeling studies. The results show that the interaction between C(16)BC and each lipid is thermodynamically favorable and does not affect the integrity of the lipid vesicles. The primary adsorption of C(16)BC into the lipid film is mainly governed by a hydrophobic effect. Once C(16)BC is inserted in the lipid film, the polar component of the interaction energy between C(16)BC and the lipid becomes predominant. Presence of CHOL increases the affinity of C(16)BC for membrane. This result can be explained by the optimal matching between C(16)BC and CHOL within the film rather by a change of membrane fluidity due to the presence of CHOL. The interaction between C(16)BC and SM is also favorable and gives rise to highly stable monolayers probably due to hydrogen bonds between their hydrophilic groups. The interaction of C(16)BC with POPC is less favorable but does not destabilize the mixed monolayer from a thermodynamic point of view. Interestingly, for all the monolayers investigated, the exclusion surface pressures are above the presumed lateral pressure of the plasma membranes suggesting that C(16)BC would be able to penetrate into mammalian plasma membranes in vivo. These results may serve as a useful basis in understanding the interaction of C(16)BC with real membranes.
Pub.: 24 Jan '12, Pinned: 27 Jul '17
Abstract: A hybrid was at first synthesized by a postfunctionalization of an aminomethane trisalkoxo-functionalized Anderson-type polyoxometalate (POM) encapsulated by three tetrabutylammonium ions using a 3,5-bis(tetradecyloxy)benzoic acid by amidation. Then the three TBA(+) counter cations were programmatically replaced by protons (H(+)) following a molecule-to-amphiphile conversion. In this way one hybrid and three POM-containing hybrid amphiphiles (PCHAs) were acquired by adjusting the number (n) of TBA(+) ions and number (3 - n) of H(+) ions (n = 3, 2, 1, and 0). These compounds can be spread onto a water surface to form a Langmuir monolayer film at the air-water interface. Surface pressure-molecular area measurements exhibit the TBA(+) (H(+)) number playing an important role in the forming ability and stability of Langmuir monolayer films. Also, the Langmuir-Blodgett (LB) technique has been used to transfer the monolayer film onto solid supports to fabricate solid multilayer films. It was found that the PCHA with three H(+) ions had the best Langmuir film-forming ability and thus formed stable LB films with a two-dimensional ordered structure. Our findings are instructive in fabricating and using solid films of the amphiphiles with POM headgroups.
Pub.: 09 May '13, Pinned: 27 Jul '17
Abstract: The incorporation of chiral amphiphilic lanthanide-directed self-assembled Nd(III) complexes (Nd.13 and Nd.23) into stable Langmuir monolayers, and the subsequent Langmuir-Blodgett film formation of these, is described. The photophysical properties of the enantiomeric pair of ligands 1 and 2 in the presence of Nd(CF3SO3)3 were also investigated in CH3CN solutions using UV-vis, fluorescence, and lanthanide luminescence spectroscopies. Analysis of the resulting self-assembly processes revealed that two main species were formed in solution,1:1 and 1:3 Nd:L self-assembly complexes, with the latter being the dominant species upon the addition of 0.33 equivalents of Nd(III). Excited state lifetime measurements of Nd.13 and Nd.23 in CH3OH and CD3OD and CH3CN were also evaluated. The formation of the self-assembly in solution was also monitored by observing the changes in the circular dichroism (CD) spectra; and large differences were observed between the 1:3 and other stoichiometries in the spectra, allowing for correlation to be made with that seen in the emission studies of these systems. Surface pressure-area and surface pressure-time isotherms evidenced the formation of stable Langmuir monolayers of Nd.13 and Nd.23 at an air-water interface, and the deposition of these monolayers onto a quartz solid substrate (Langmuir-Blodgett films) gave rise to immobilized chiral monomolecular films which exhibited Nd(III) NIR luminescence upon excitation of the ligand chromophore, demonstrating efficient energy transfer to the Nd(III) excided state (sensitized) with concomitant emission centered at 800 and 1334 nm.
Pub.: 29 Aug '13, Pinned: 27 Jul '17
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