T. Govindaraju

Conformationally constrained (coumarin-triazolyl-bipyridyl) click fluoroionophore as a selective Al3+ sensor.

A conformationally constrained (coumarin-pyrrolidinyl-triazolyl-bipyridyl) fluoroionophore conjugate was synthesized through click chemistry. The fluoroionophore serves as a selective chemosensor for Al(3+) based on internal charge transfer. The coumarin-bipyridyl chemosensor exhibited a high association constant with submicromolar detection for the aluminum ion.

Visible-near-infrared and fluorescent copper sensors based on julolidine conjugates: selective detection and fluorescence imaging in living cells.

We present novel Schiff base ligands julolidine-carbonohydrazone 1 and julolidine-thiocarbonohydrazone 2 for selective detection of Cu(2+) in aqueous medium. The planar julolidine-based ligands can sense Cu(2+) colorimetrically with characteristic absorbance in the near-infrared (NIR, 700-1000 nm) region. Employing molecular probes 1 and 2 for detection of Cu(2+) not only allowed detection by the naked eye, but also detection of varying micromolar concentrations of Cu(2+) due to the appearance of distinct coloration. Moreover, Cu(2+) selectively quenches the fluorescence of julolidine-thiocarbonohydrazone 2 among all other metal ions, which increases the sensitivity of the probe. Furthermore, quenched fluorescence of the ligand 2 in the presence of Cu(2+) was restored by adjusting the complexation ability of the ligand. Hence, by treatment with ethylenediaminetetraacetic acid (EDTA), thus enabling reversibility and dual-check signaling, julolidine-thiocarbonohydrazone (2) can be used as a fluorescent molecular probe for the sensitive detection of Cu(2+) in biological systems. The ligands 1 and 2 can be utilized to monitor Cu(2+) in aqueous solution over a wide pH range. We have investigated the structural, electronic, and optical properties of the ligands using ab initio density functional theory (DFT) combined with time-dependent density functional theory (TDDFT) calculations. The observed absorption band in the NIR region is attributed to the formation of a charge-transfer complex between Cu(2+) and the ligand. The fluorescence-quenching behavior can be accounted for primarily due to the excited-state ligand 2 to metal (Cu(2+)) charge-transfer (LMCT) processes. Thus, experimentally observed characteristic NIR and fluorescence optical responses of the ligands upon binding to Cu(2+) are well supported by the theoretical calculations. Subsequently, we have employed julolidine-thiocarbonohydrazone 2 for reversible fluorescence sensing of intracellular Cu(2+) in cultured HEK293T cells.

Highly Selective Colorimetric Chemosensor for Co2

A new highly selective colorimetric chemosensor for Co(2+) was developed based on coumarin-conjugated thiocarbanohydrazone. The ligand senses Co(2+) in solution by changing its color from light yellow to deep pink. The sensor has been used in the development of practically viable colorimetric kits and as a staining agent for Co(2+) in microorganisms.

Reactive Probes for Ratiometric Detection of Co2+ and Cu+ Based on Excited-State Intramolecular Proton Transfer Mechanism

An excited-state intramolecular proton transfer (ESIPT) mechanism based two reactive probes HBTCo and HBTCu is reported for the selective detection of Co(2+) and Cu(+) respectively in a reducing aqueous environment. Co(2+) and Cu(+) mediated oxidative benzylic ether (C-O) bond cleavage offers ratiometric detection of these metal ions.

Two-dimensional nanoarchitectonics: organic and hybrid materials.

Programmed molecular assemblies with molecular-level precision have always intrigued mankind in the quest to master the art of molecular engineering. In this regard, our review seeks to highlight the state of the art in supramolecular engineering. Herein we describe two-dimensional (2D) nanoarchitectonics of organic and organic-inorganic based hybrid materials. Molecular systems ranging from simpler hydrogen bonding driven bis-acylurea and cyclic dipeptide derivatives to complex peptoids, arylenes, cucurbiturils, biphenyls, organosilicons and organometallics, which involve a delicate interplay of multiple noncovalent interactions are discussed. These specifically chosen examples illustrate the molecular design principles and synthetic protocols to realize 2D nanosheets. The description also emphasizes the wide variety of functional properties and technological implications of these 2D nanomaterials besides an outlook for future progress.

Amino acid derivatized arylenediimides: a versatile modular approach for functional molecular materials.

Natures elegant molecular designs and their assemblies with specific structure-property correlations have inspired researchers to design and develop bio-mimics for advanced functional applications. To realize such advanced molecular materials, naturally evolved amino acids are arguably the ideal auxiliaries due to their remarkable molecular/chiral recognition and distinctive sequence specific self-assembling properties. Over the years, this modular approach of derivatizing naphthalenediimides (NDIs) and perylenediimides (PDIs) with amino acids and peptides have resulted in several hitherto unknown molecular assemblies with phenomenal impact on their performance. Derivatization with versatile arylenediimides is especially interesting due to their wide spread applications in fields ranging from biomedicine to electronics. Herein some of these seminal reports of this rapidly emerging field and the design principles embraced are discussed.

Surface immobilization of biomolecules by click sulfonamide reaction.

Alkyne-modified biomolecules can be immobilized site- and chemoselectively on sulfonylazide slides under very mild conditions by means of the click sulfonamide reaction.

A probe for ratiometric near-infrared fluorescence and colorimetric hydrogen sulfide detection and imaging in live cells

A ratiometric, near-infrared (NIR), fluorescence and colorimetric probe DNPOCy for hydrogen sulfide (H2S) has been developed. The chemical basis for the operation of the probe is thiolysis of a dinitrophenyl ether, which liberates a cyanine dye chromophore. The probe exhibits a rapid response and high sensitivity to H2S in pure aqueous media, in the near infrared optical window. DNPOCy is highly selective for H2S over other biologically relevant species including biothiols. This probe can be conveniently used for monitoring H2S without the interference from pH dependent effects of physiological media. The practical utility of the probe was demonstrated by its application to the detection of H2S in live cells.

Chiral Transcription and Retentive Helical Memory: Probing Peptide Auxiliaries Appended with Naphthalenediimides for Their One-Dimensional Molecular Organization

Right or left paradox: Homochiral, heterochiral and achiral peptide auxiliaries appended with naphthalenediimide (NDI, see figure) were employed to demonstrate chiral transcription. We report an interesting phenomenon coined as retentive helical memory. Remarkably, NDI-peptide conjugates were tuned into hierarchical 1D molecular assemblies of opposite helicity in case of homochiral peptide auxiliaries.

Solvent‐Induced Helical Assembly and Reversible Chiroptical Switching of Chiral Cyclic‐Dipeptide‐Functionalized Naphthalenediimides

Understanding the roles of various parameters in orchestrating the preferential chiral molecular organization in supramolecular self-assembly processes is of great significance in designing novel molecular functional systems. Cyclic dipeptide (CDP) chiral auxiliary-functionalized naphthalenediimides (NCDPs 1-6) have been prepared and their chiral self-assembly properties have been investigated. Detailed photophysical and circular dichroism (CD) studies have unveiled the crucial role of the solvent in the chiral aggregation of these NCDPs. NCDPs 1-3 form supramolecular helical assemblies and exhibit remarkable chiroptical switching behaviour (M- to P-type) depending on the solvent composition of HFIP and DMSO. The strong influence of solvent composition on the supramolecular chirality of NCDPs has been further corroborated by concentration and solid-state thin-film CD studies. The chiroptical switching between supramolecular aggregates of opposite helicity (M and P) has been found to be reversible, and can be achieved through cycles of solvent removal and redissolution in solvent mixtures of specific composition. The control molecular systems (NCDPs 4-6), with an achiral or D-isomer second amino acid in the CDP auxiliary, did not show chiral aggregation properties. The substantial roles of hydrogen bonding and π-π interactions in the assembly of the NCDPs have been validated through nuclear magnetic resonance (NMR), photophysical, and computational studies. Quantum chemical calculations at the ab initio, semiempirical, and density functional theory levels have been performed on model systems to understand the stabilities of the right (P-) and left (M-) handed helical supramolecular assemblies and the nature of the intermolecular interactions. This study emphasizes the role of CDP chiral auxiliaries on the solvent-induced helical assembly and reversible chiroptical switching of naphthalenediimides.