Deepthi S. Yarramala

Binding and Ratiometric Dual Ion Recognition of Zn2+ and Cu2+ by 1,3,5-Tris-amidoquinoline Conjugate of Calix[6]arene by Spectroscopy and Its Supramolecular Features by Microscopy

Lower rim amide linked 8-amino quinoline and 8-amino naphthalene moiety 1,3,5-triderivatives of calix[6]arene L1 and L2 have been synthesized and characterized. While the L1 acts as a receptor molecule, the L2 acts as a control molecule. The complexation between L1 and Cu(2+) or Zn(2+) was delineated by the absorption and electrospray ionization (ESI) MS spectra. The binding ability of these molecules toward biologically important metal ions was studied by fluorescence and absorption spectroscopy. The derivative L1 detects Zn(2+) by bringing ratiometric change in the fluorescence signals at 390 and 490 nm, but in the case of Cu(2+), it is only the fluorescence quenching of 390 nm band that is observed, while no new band is observed at 390 nm. The stoichiometry of both the complexes is 1:1 and was confirmed in both the cases by measuring the ESI mass spectra. The isotopic peak pattern observed in the ESI MS confirmed the presence of Zn(2+) or Cu(2+) present in the corresponding complex formed with L1. Among these two ions, the Cu(2+) exhibits higher sensitivity. The density-functional theory (DFT) studies revealed the conformational changes in the arms and also revealed the coordination features in the case of the metal complexes. The arm conformational changes upon Zn(2+) binding were supported by nuclear Overhauser effect spectrometry (NOESY) studies. The stronger binding of Cu(2+) over that of Zn(2+) observed from the absorption study was further supported by the complexational energies computed from the computational data. While the L1 exhibited spherical particles, upon complexation with Cu(2+), it exhibits chain like morphological features in scanning electron microscopy (SEM) but only small aggregates in the case of Zn(2+). Thus, even the microscopy data can differentiate the complex formed between L1 and Cu(2+) from that formed with Zn(2+).

Green synthesis, characterization and anticancer activity of luminescent gold nanoparticles capped with apo-α-lactalbumin

A green synthesis was developed in order to prepare protein coated gold nanoparticles using a metal free, α-helical protein, i.e., apo-α-LA, that acts as both the reducing as well as stabilizing agent to result in Au0 nanoparticles from Au3+ which are luminescent and hence can be used for biological imaging, including of cells. The nanoparticles, apo-α-LA-AuNPs, thus synthesized were characterized by multiple techniques, such as, analytical, spectral, microscopy and light scattering, in order to support the presence of NPs in terms of their size and shape, involvement of Au0 and the protein encapsulation and its structural changes upon coating. The 10–16 nm sized apo-α-LA-AuNPs were shown to be non-toxic to healthy cells as studied using normal mouse fibroblast cells (L929). Having found that these NPs are biocompatible and possess structurally altered apo-α-LA protein, the luminescent apo-α-LA-AuNPs were demonstrated to have cytotoxicity towards cancer cells as studied by cell viability tests as well as fluorescence microscopy. While these NPs kill ∼75% of MCF-7 cells, at the same concentration these are capable of killing only ∼30% of HeLa cells, thus exhibiting cell dependency. The present study clearly demonstrates the advantage of the luminescent apo-α-LA-AuNPs in their attack of cancer cells in general and selective killing of breast cancer cells in particular. Thus coating AuNPs with the protein apo-α-LA enhanced their anticancer activity several fold.

Differential Recognition of Anions with Selectivity towards F(-) by a Calix[6]arene-Thiourea Conjugate Investigated by Spectroscopy, Microscopy, and Computational Modeling by DFT.

Anion recognition studies were performed with triazole-appended thiourea conjugates of calix[6]arene (i.e., compound (6) L) by absorption and (1) H NMR spectroscopy by using nineteen different anions. The composition of the species of recognition was derived from ESI mass spectrometry. The absorption spectra of compound (6) L showed a new band at λ=455 nm in the presence of F(-) due to a charge transfer from the anion to the thiourea moiety and the absorbance increases almost linearly in the concentration range 5 to 200 μm. This is associated with a strong visual color change of the solution. Other anions, such as H2 PO4 (-) and HSO4 (-) , exhibit a redshift of the λ=345 nm band and the spectral changes are associated with the formation of an isosbestic point at λ=343 nm. (1) H NMR studies further confirm the binding of F(-) efficiently to the thiourea group among the halides by shifting the thiourea proton signals downfield followed by their disappearance after the addition of more than one equivalent of F(-) . The other anions also showed interactions with compound (6) L, however, their binding strength follows the order F(-) >CO3 (2-) >H2 PO4 (-) ≈CH3 COO(-) >HSO4 (-) . The NMR spectral changes clearly revealed the anion-binding region of the arms in case of all these anions. The anion binding to compound (6) L indeed stabilizes a flattened-cone conformation as deduced based on the calix-aromatic proton signals and was further confirmed by VT (1) H NMR experiments. The stabilization of the flattened-cone conformation was further augmented by the interaction of the butyl moiety of the nBu4 N(+) counterion. The structural features of the anion-bound species were demonstrated by DFT computations and the resultant structures carried the features that were predicted based on the (1) H NMR spectroscopic measurements. In addition, SEM images showed a marigold flower-type morphology for compound (6) L and this has been transformed into a chain-like structure of connected spherical particles in the presence of F(-) . The anion-induced microstructural features are reflective of the binding strength, size, and shape of the anions. The binding strengths of the anions by compound (6) L were further compared with that of compound (4) L, a calix[4]arene analogue of compound (6) L, in order to address the role of the number of arms built on the calixarene platform based on absorption spectroscopy, (1) H NMR spectroscopy, and DFT computations and it was found that compound (6) L is a better receptor for F(-) , which extends its interactions from all the three arms.

Differentiating Phosphates by an Mg2+ Complex of the Conjugate of Calix[4]arene via the Formation of Ternary Species and Causing Changes in the Aggregation: Spectroscopy, Microscopy, and Computational Modeling

A phenylene diimine capped conjugate of 1,3-calix[4]arene (L) was synthesized and characterized, and its Mg(2+) complex has been isolated and characterized. The chemo sensing ensemble of Mg(2+) bound L provides distinguishable features of response toward phosphates, viz., HPO4(2-), P2O7(4-), and AMP(2-) (Set A) and H2PO4(-), ATP(2-), and ADP(2-) (Set B). While the Set A shows the formation of ternary complex, the Set B does not exhibit any intermediate complex, but both show the release of Mg(2+) and L at different equivalents. The structures of {L + Mg(2+)} and its phosphate bound ternary complexes have been established by computational calculations, and the corresponding results agree well with the experimental ones. The microscopy studies show an aggregation-disaggregation phenomenon in the presence of different equivalents of phosphates in both of the sets. Using the fluorescence data, an INHIBIT logic gate has been built.

Versatile, Reversible, and Reusable Gel of a Monocholesteryl Conjugated Calix[4]arene as Functional Material to Store and Release Dyes and Drugs Including Doxorubicin, Curcumin, and Tocopherol

Gels are interesting soft materials owing to their functional properties leading to potential applications. This paper deals with the synthesis of monocholesteryl derivatized calix[4]arene (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.

Time- and concentration-dependent reactivity of Cys, Hcy, and GSH on the Diels-Alder-grafted 1,3,5-tris conjugate of calix[6]arene to bring selectivity for Cys: spectroscopy, microscopy, and its reactivity in cells.

Herein we report the synthesis and characterization of 7-oxanorbornadiene (OND)-appended 1,3,5-tris conjugate of calix[6]arene (L2). L2 has been shown to exhibit selective reactivity toward cysteine (Cys) over homocysteine (Hcy) and glutathione (GSH) under stoichiometric conditions. The selectivity of L2 is attributed to the steric crowding of three Diels-Alder centers possessing OND units present on the calix[6]arene platform, while a control molecular system possessing only one such unit without the calix[6]arene platform (L1) does not show any selectivity toward Cys. While L2 exhibited spherical particles, its reactivity with Cys resulted in flowerlike morphological features, as revealed by scanning electron microscopy. However, the reaction with GSH did not result in any such morphological features, a result that is in agreement with that observed from fluorescence studies in solution. L2 has been shown to react with Cys present in HeLa and Jurkat E6 cells by fluorescence microscopy.

Supramolecular Complexation of Biological Phosphates with an Acyclic Triazolium-Linked Anthracenyl-1,3-Diconjugate of Calix[4]Arene: Synthesis, Characterization, Spectroscopy, Microscopy, and Computational Studies

A triazolium-anthracenyl calix[4]arene conjugate (L) was synthesized by methylating the precursor triazole derivative and then characterized. The potential of the cationic L to differentiate nucleoside triphosphates (NTPs) from their mono- and diphosphates was demonstrated. Due to its unique combination of arms with the calix-platform, a fluorescence enhancement was observed for L with all the NTPs, whereas there is no report with such enhancement being exhibited in case of all the NTPs. This has been supported by the aggregation of L observed from microscopy. Selectivity of L towards NTPs over other phosphates was a result of specific weak interactions, namely, ion-ion, hydrogen bonding and π⋅⋅⋅π, present in the 1:2 complex of L and NTPs (based on ESI MS), which were absent in their congener-phosphates as delineated by NMR and computational studies. Thus, L stands as a unique receptor for NTPs.

Glyco-conjugate as selective switch-on molecule for Hg2+ in the presence of albumin proteins, blood serum milieu and on silica gel solid support

The glyco-conjugate, LS, its Hg2+ complex, and the LO were synthesized and characterized in their solid state by FTIR, diffuse reflectance, and powder XRD. The mercury complex shows dumbbell-like microstructures as a result of the metal ion-induced aggregation of the glyco-conjugate as studied based on scanning electron microscopy. The aggregation was also supported by atomic force microscopy. The Hg2+ was detected on LS-coated silica gel sheets by switch-on fluorescence, wherein, the enhancement in the fluorescence intensity varies linearly with the added Hg2+ in the concentration range 5–60 μM. The concentration-dependent variation was also detected on silica gel sheets by viewing their colour under 365 nm light. Hg2+ was detected by the LS-coated silica gel sheets by switch-on fluorescence even in the presence of blood serum. Thus, this method is extendable for the detection and quantification of Hg2+ present in blood and or in biological fluids using disposable silica gel sheets. The sensing of Hg2+ in HEPES buffer solution is well demonstrated in this paper using various techniques, such as fluorescence, absorption, visual color, ESI MS, and 1H NMR. In the buffer medium, the LS exhibit selective chromogenic as well as fluorogenic properties towards Hg2+ by showing ∼75-fold higher fluorescence emission intensity and the studies were further extended to show that none of the 13 ions studied compete for Hg2+. A minimum detection limit of 25 ± 4 ppb was shown by LS for Hg2+ in the buffer. All the experimental studies carried out support the formation of 2 : 1 complex between LS and Hg2+. At higher mole ratios of Hg2+, the same yields the oxo-product, viz., LO. The structure of the 2 : 1 complex was modeled by DFT using B3LYP/LANL2DZ.

Differential copper binding to alpha-synuclein and its disease-associated mutants affect the aggregation and amyloid formation

BACKGROUND Copper is an essential trace element required for the proper functioning of various enzymes present in the central nervous system. An imbalance in the copper homeostasis results in the pathology of various neurodegenerative disorders including Parkinsons Disease. Hence, residue specific interaction of Cu2+ to α-Syn along with the familial mutants H50Q and G51D needs to be studied in detail. METHODS We investigated the residue specific mapping of Cu2+ binding sites and binding strength using solution-state NMR and ITC respectively. The aggregation kinetics, secondary structural changes, and morphology of the formed fibrils in the presence and absence of Cu2+ were studied using fluorescence, CD, and AFM respectively. RESULTS Copper binding to α-Syn takes place at three different sites with a higher affinity for the region 48-53. While one of the sites got abolished in the case of H50Q, the mutant G51D showed a binding pattern similar to WT. The aggregation kinetics of these proteins in the presence of Cu2+ showed an enhanced rate of fibril formation with a pronounced effect for G51D. CONCLUSION Cu2+ binding results in the destabilization of long-range tertiary interactions in α-Syn leading to the exposure of highly amyloidogenic NAC region which results in the increased rate of fibril formation. Although the residues 48-53 have a stronger affinity for Cu2+ in case of WT and G51D, the binding is not responsible for enhancing the rate of fibril formation in case of H50Q. GENERAL SIGNIFICANCE These findings will help in the better understanding of Cu2+ catalyzed aggregation of synucleins.

Optimizing the electron-withdrawing character on benzenesulfonyl moiety attached to a glyco-conjugate to impart sensitive and selective sensing of cyanide in HEPES buffer and on cellulose paper and silica gel strips

Dansyl-derivatized, triazole-linked, glucopyranosyl conjugates, (5F)LOH, (2F)LOH, (1F)LOH, and (0F)LOH were synthesized and characterized. While the (5F)LOH acts as a molecular probe for CN(-), (2F)LOH, (1F)LOH, and (0F)LOH acts as control molecules. The reactivity of CN(-) toward (5F)LOH has been elicited through the changes observed in NMR, ESI MS, emission, and absorption spectroscopy. The conjugate (5F)LOH releases a fluorescent product upon reaction by CN(-) in aqueous acetonitrile medium by exhibiting an ∼125-fold fluorescence enhancement even in the presence of other anions. Fluorescence switch-on behavior has been clearly demonstrated on the basis of the nucleophilic substitution reaction of CN(-) on (5F)LOH. A minimum detection limit of (2.3 ± 0.3) × 10(-7) M (6 ± 1 ppb) was shown by (5F)LOH for CN(-) in solution. All the other anions studied showed no change in the fluorescence emission. The utility of (5F)LOH has been demonstrated by showing its reactivity toward CN(-) on a thin layer of silica gel as well as on Whatman No. 1 cellulose filter paper strips. The role of glucose moiety and the penta-fluorobenzenesulfonyl reactive center present in (5F)LOH in the selectivity of CN(-) over other anions has been demonstrated by fluorescence, absorption and thermodynamics study. Similar studies carried out with the control molecules showed no selectivity for CN(-). The mechanistic aspects of the reactivity of CN(-) toward (5F)LOH were supported by DFT computational study.