Jugun Prakash Chinta

Lower Rim 1,3-Diderivative of Calix[4]arene-Appended Salicylidene Imine (H2L): Experimental and Computational Studies of the Selective Recognition of H2L toward Zn2+ and Sensing Phosphate and Amino Acid by [ZnL]

A new 1,3-diderivative of calix[4]arene appended with hydroxymethyl salicylyl imine has been synthesized and its ion recognition toward biologically relevant M(n+) ions studied. The receptor H(2)L showed selectivity toward Zn(2+) by switch-on fluorescence among the 12 metal ions studied with a detection limit of 192 ppb. The interaction of Zn(2+) with H(2)L has been further supported by absorption studies, and the stoichiometry of the complex formed (1:1) has been established on the basis of absorption and ESI MS. Competitive ion titrations carried out reveal that the Zn(2+) can be detected even in the presence of other metal ions of bioimportance. The mode of interaction of Zn(2+) with conjugate has been established by a fleet of computational calculations carried out in a cascade manner, either on the ligand or on the complex, wherein the final optimizations were carried out by the density functional theory (DFT) and found that the Zn(2+) and Cd(2+) indeed bind differently. In situ prepared [ZnL] complex responds to both inorganic phosphate as well as AMP, ADP, and ATP with a minimum detection limit of 426 ppb wherein the Zn(2+) from the complex is detached and recomplexed by the added phosphate moiety. It has been possible to build an INHIBIT logic gate for the conjugate using Zn(2+) and HPO(4)(2-) as inputs by monitoring the fluorescence emission band at 444 nm as output. The amino acid sensing abilities of [ZnL] have been explored by fluorescence and absorbance spectroscopy where it showed selectivity toward Cys, Asp, and His through the formation of the Zn(2+) complex of these amino acids by chelating through their side chain moieties. Thus, while H(2)L is selective for Zn(2+) among a number of cations, the [ZnL] is selective toward phosphate among a number of anions and also toward Asp, Cys, and His among the naturally occurring amino acids.

Synthesis, characterization, plasmid cleavage and cytotoxicity of cancer cells by a copper(II) complex of anthracenyl-terpyridine

Metallo-organic compounds are interesting to study for their antitumor activity and related applications. This paper deals with the syntheses, characterization, structure determination of a copper complex of anthracenyl terpyridine (1) and its plasmid cleavage and cytotoxicity towards different cancer cell lines. The complex binds CT-DNA through partial intercalation mode. The plasmid cleavage studies carried out using pBR322 and pUC18 resulted in the formation of all the three forms of the plasmid DNA. Plasmid cleavage studies carried out with a non-redoxable Zn(2+) complex (2) supported the role of the redox activity of copper in 1. The complex 1 showed remarkable antiproliferative activity against cancer cell lines, viz., cervical (HeLa, SiHa, CaSki), breast (MCF-7), liver (HepG2) and lung (H1299). A considerable lowering was observed in the IC(50) values of HPV-infected (viz., HeLa, SiHa, CaSki) vs. non-HPV-infected cell lines (MCF-7, HepG2, H1299). Antiproliferative activity of 1 was found to be much higher than the carboplatin when treated with the same cell lines. Incubation of the cells with 1 results in granular structures only with the HPV-infected cells and not with others as studied by phase contrast and fluorescence microscopy. The lower IC(50) value observed in case of 1 with HPV-infected cell lines may be correlated with the involvement of HPV oncoprotein. The role of HPV has been further augmented by transfecting the MCF-7 cells (originally not possessing HPV copy) with e6 oncoprotein cDNA. To our knowledge this is the first copper complex that causes cell death by interacting with HPV oncoprotein followed by exhibition of remarkable antiproliferative activity.

1,3-Diamido-calix[4]arene Conjugates of Amino Acids: Recognition of -COOH Side Chain Present in Amino Acids, Peptides, and Proteins by Experimental and Computational Studies

Lower rim 1,3-diamido conjugates of calix[4]arene have been synthesized and characterized, and the structures of some of these have been established by single crystal XRD. The amido-calix conjugates possessing a terminal -COOH moiety have been shown to exhibit recognition toward guest molecules possessing -COOH moiety, viz., Asp, Glu, and reduced and oxidized glutathione (GSH, GSSG), by switch-on fluorescence in aqueous acetonitrile and methanol solutions when compared to the control molecules via forming a 1:1 complex. The complex formed has been shown by mass spectrometry, and the structural features of the complexes were derived on the basis of DFT computations. The association constants observed for the recognition of Asp/Glu by Phe-calix conjugate, viz., 532/676 M(-1), are higher than that reported for the recognition of Val, Leu, Phe, His, and Trp (16-63 M(-1)) by a water-soluble calixarene (Arena, G., et al. Tetrahedron Lett. 1999, 40, 1597). For this recognition, there should be a free -COOH moiety from the guest molecule. AFM, SEM, and DLS data exhibited spherical particles with a hundred-fold reduction in the size of the complexes when compared to the particles of the precursors. These spherical particles have been computationally modeled to possess hexameric species reminiscent of the hexameric micellar structures shown for a Ag(+) complex of a calix[6]arene reported in the literature (Houmadi, S., et al. Langmuir 2007, 23, 4849). Both AFM and TEM studies demonstrated the formation of nanospheres in the case of GSH-capped Ag nanoparticles in interaction with the amido-calix conjugate that possesses terminal -COOH moiety. The AFM studies demonstrated in this paper have been very well applied to albumin proteins to differentiate the aggregational behavior and nanostructural features exhibited by the complexes of proteins from those of the uncomplexed ones. To our knowledge, this is the first report wherein a amido-calix[4]arene conjugate and its amino acid/peptide/protein complexes have been differentiated on the basis of spectroscopy and microscopy studies followed by species modeling by computations.

Spectroscopy and microscopy studies of the recognition of amino acids and aggregation of proteins by Zn(II) complex of lower rim naphthylidene conjugate of calix[4]arene

A lower rim naphthylidene conjugate of calix[4]arene [L] has been synthesized and characterized, and the structure has been established on the basis of single crystal XRD. The L has been found to be selective toward Zn(2+), which induces appropriate changes in the arms of L so that the N(2)O(2) coordination results in the formation of a tetrahedral complex; namely, [ZnL]. [ZnL] recognizes Asp, Cys, His, and Glu from among the naturally occurring amino acids owing to the protonation and chelating ability of the amino acid and the pi-pi interaction ability of the side chain of the amino acid with [ZnL]. All of these features have been demonstrated on the basis of fluorescence, absorption, and lifetime measurements. The rechelation of Zn(2+) by the amino acid used in the titration has been demonstrated on the basis of ESI-MS studies in the case of Cys to result in a Zn(2+) complex having either 5- or 6-coordination. [ZnL] has also been shown to be selective toward glutathione and glutathione oxidized. The amino acids present in the proteins also interact with [ZnL], resulting in dechelation of [ZnL] as well as aggregation of the protein, as demonstrated on the basis of absorption and fluorescence spectroscopy and atomic force microscopy. The alpha-helical proteins (namely, albumins) exhibit greater conformational changes, as compared to the beta-sheet proteins (namely, lectins), as studied on the basis of CD spectroscopy. The aggregation of the proteins when treated with [ZnL] follows a trend: peanut agglutinin < bovine serum albumin < jacalin < human serum albumin. The present studies clearly demonstrated the recognition features of [ZnL] toward Asp, Cys, His, and Glu, and the peptides and proteins containing these by spectroscopy and microscopy studies.

Calix[4]arene-Based 1,3-Diconjugate of Salicylyl Imine Having Dibenzyl Amine Moiety (L): Synthesis, Characterization, Receptor Properties toward Fe2+, Cu2+, and Zn2+, Crystal Structures of Its Zn2+ and Cu2+ Complexes, and Selective Phosphate Sensing by the [ZnL]

A calix[4]arene conjugate bearing salicylyl imine having dibenzyl moiety (L) has been synthesized and characterized, and its ability to recognize three most important essential elements of human system, viz., iron, copper, and zinc, has been addressed by colorimetry and fluorescence techniques. L acts as a sensor for Cu(2+) and Fe(2+) by exhibiting visual color change and for Zn(2+) based on fluorescence spectroscopy. L shows a minimum detection limit of 3.96 ± 0.42 and 4.51 ± 0.53 ppm and 45 ± 4 ppb, respectively, toward Fe(2+), Cu(2+), and Zn(2+). The in situ prepared [ZnL] exhibits phosphate sensing among 14 anions studied with a detection limit of 247 ± 25 ppb. The complexes of Zn(2+), Cu(2+), and Fe(2+) of L have been synthesized and characterized by different techniques. The crystalline nature of the zinc and copper complexes and the noncrystalline nature of simple L and its iron complex have been demonstrated by powder XRD. The structures of Cu(2+) and Zn(2+) complexes have been established by single crystal XRD wherein these were found to be 1:1 monomeric and 2:2 dimeric, respectively, using N(2)O(2) as binding core. The geometries exhibited by the Zn(2+) and the Cu(2+) complexes were found to be distorted tetrahedral and distorted square planar, respectively. The iron complex of L exists in 1:1 stoichiometry as evident from the mass spectrometry and elemental analysis.

Recognition of Polycyclic Aromatic Hydrocarbons and Their Derivatives by the 1,3-Dinaphthalimide Conjugate of Calix[4]arene: Emission, Absorption, Crystal Structures, and Computational Studies

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants as well as well-known carcinogens. Therefore, it is important to develop an effective receptor for the detection and quantification of such molecules in solution. In view of this, a 1,3-dinaphthalimide derivative of calix[4]arene (L) has been synthesized and characterized, and the structure has been established by single crystal XRD. In the crystal lattice, intermolecular arm-to-arm π···π overlap dominates and thus L becomes a promising receptor for providing interactions with the aromatic species in solution, which can be monitored by following the changes that occur in its fluorescence and absorption spectra. On the basis of the solution studies carried out with about 17 derivatives of the aromatic guest molecular systems, it may be concluded that the changes that occur in the fluorescence intensity seem to be proportional to the number of aromatic rings present and thus proportional to the extent of π···π interaction present between the naphthalimide moieties and the aromatic portion of the guest molecule. Though the nonaromatic portion of the guest species affects the fluorescence quenching, the trend is still based on the number of rings present in these. Four guest aldehydes are bound to L with K(ass) of 2000-6000 M(-1) and their minimum detection limit is in the range of 8-35 μM. The crystal structure of a naphthaldehyde complex, L.2b, exhibits intermolecular arm-to-arm as well as arm-to-naphthaldehyde π···π interactions. Molecular dynamics studies of L carried out in the presence of aromatic aldehydes under vacuum as well as in acetonitrile resulted in exhibiting interactions observed in the solid state and hence the changes observed in the fluorescence and absorption spectra are attributable for such interactions. Complex formation has also been delineated through ESI MS studies. Thus L is a promising receptor that can recognize PAHs by providing spectral changes proportional to the aromatic conjugation of the guest and the extent of aromatic π···π interactions present between L and the guest.

Role of the conformational changes brought in the arms of the 1,3-di-capped conjugate of calix[4]arene (L) in turning on the fluorescence of L by Hg2+

A new 1,3-di-capped calix[4]arene conjugate of salicylidene (L) has been synthesized, characterized and the structure has been established by single crystal XRD. L shows selectivity towards Hg(2+) in ethanol by turn-on fluorescence among the biologically important metal ions studied. The species of recognition has been modeled by DFT computational calculations to result in conformational changes in the arms that support the turn-on fluorescence behaviour.

Triazole linked lower rim glycosyl appended 1,3-calix[4]arene conjugates: Synthesis, characterization, and their interaction with jacalin.

Triazole linked lower rim galactosyl and lactosyl appended calix[4]arene conjugates have been synthesized by 1,3 dipolar addition of glycosyl azide and calix[4]arene alkyne. All these conjugates were characterized by (1)H and (13)C NMR, IR and mass spectrometry. Interaction of amino acids with the galactosyl conjugate of calix[4]arene (5) was studied using absorption and (1)H NMR techniques. Absorption studies showed that Trp interacts with triazole ring of 5. This was further confirmed by (1)H NMR study which showed an upfield shift in the triazole proton of 5 upon titrating with Trp. The preliminary studies of interaction of these conjugates with Jacalin were demonstrated by fluorescence and circular dichroism (CD) spectroscopy techniques.

Carbon Nanotube and Semiconductor Nanorods Hybrids: Preparation, Characterization, and Evaluation of Photocurrent Generation

Carbon nanotubes (CNTs) and semiconductor nanocrystals (SCNCs) are known to be interesting donor-acceptor partners due to their unique optical and electronic properties. These exciting features have led to the development of novel composites based on these two nanomaterials and to their characterization for use in various applications, such as components in sensors, transistors, solar cells and biomedical devices. Two approaches based on covalent and noncovalent methods have been suggested for coupling the SCNCs to CNTs. Most covalent conjugation methods used so far were found to disrupt the electronic structure of the CNTs or interfere with charge transfer in the CNT-SCNC interface. Moreover, it offers random and poorly organized nanoparticle coatings. Therefore, noncovalent methods are considered to be ideal for better electronic coupling. However, a key common drawback of noncovalent methods is the lack of stability which hampers their applicability. In this article, a method has been developed to couple semiconductor seeded nanorods onto CNTs through π-π interactions. The CNTs and pyrene conjugated SCNC hybrid materials were characterized by both microscopic and spectroscopic techniques. Fluorescence and photocurrent measurements suggest the proposed pi-stacking approach results in a strong electronic coupling between the CNTs and the SCNCs leading to better photocurrent efficiency than that of a covalent conjugation method reported using similar SCNC material. Overall, the CNT-SCNC films reported in the present study open the scope for the fabrication of optoelectronic devices for various applications.

Synthesis, characterization and ion recognition studies of lower rim 1,3-di{rhodamine} conjugate of calix[4]arene

AbstractAn amido-linked rhodamine conjugate of calix[4]arene, L has been synthesized and characterized. Metal ion recognition properties of L have been studied by emission and absorption techniques with 14 different metal ions including the transition ones. Results show that, L exhibits ratiometric emission intensity towards Hg2+, Fe2+, Fe3+, Cu2+, Pb2+ and Zn2+. Composition of the complex formed in the solution has been found to be 1:2 (L:Mn + ), based on the Job’s plot. The L can also act as a chemosensor for Hg2+ through naked eye detection. Fluorescence quenching observed at 485 nm follows an order, Hg2+ > > Fe3+ ~ Cu2+ > Zn2+ > Pb2+ > Ca2+, while the enhancement observed at 580 nm follows, Hg2+ > > Fe2+ ~ Pb2+ > Zn2+. Mode of interaction of Mn +  with L is by the ring opening of spirolactam moiety. Graphical AbstractAn amido-linked rhodamine conjugate of calix[4]arene, L has been synthesized and characterized and was shown to exhibit ratiometric emission towards Hg2+, Fe2+, Fe3+, Cu2+, Pb2+ and Zn2+. L can act as a chemosensor for Hg2+ by showing a colour change and by forming a 1:2 L:Mn+ complex while opening the spirolactam moiety.