Dhanya T. Jayaram

β-Cyclodextrin as a Photosensitizer Carrier: Effect on Photophysical Properties and Chemical Reactivity of Squaraine Dyes

With the objective of understanding the utility of β-cyclodextrin (β-CD) as a carrier system, we have investigated its interactions with a few near-infrared absorbing squaraine dyes (i.e., 1a,b and 2a,b) through absorption and steady-state and time-resolved fluorescence techniques. The addition of β-CD to the phloroglucinol dyes 1a,b resulted in a significant bathochromic shift in absorption, together with a ca. 1.5-2.5-fold enhancement in fluorescence intensity, whereas for the aniline-based dyes 2a,b, a hypsochromic shift in the absorption and a ca. 5-12-fold fluorescence enhancement were observed in a 10% (v/v) ethanol/water mixture. Benesi-Hildebrand analysis showed that both the dyes 1a,b and 2a,b form 2:1 stoichiometric complexes with β-CD. The complex formation was confirmed by competitive binding analysis employing adamantyl-1-carboxylic acid (ACA) and adamantyl-1-ammonium chloride (ADAC). The displacement of the dyes 1a,b and 2a,b from the [dye-β-CD] complex by ADAC and ACA unambiguously establishes the encapsulation of these dyes in the hydrophobic nanocavity of β-CD. Uniquely, the formation of the inclusion complexes with β-CD provides unusual protection from nucleophilic attack by aminothiols such as cysteine and glutathione for dyes 1a,b, whereas negligible protection was observed for dyes 2a,b. These results demonstrate the substituent-dependent encapsulation of potentially useful squaraine dyes in β-CD, thereby indicating its potential as a carrier system for the squaraine dyes 1a,b useful in photodynamic therapy.

In Vitro and in Vivo Demonstration of Photodynamic Activity and Cytoplasm Imaging through TPE Nanoparticles

We synthesized novel tetraphenylethene (TPE) conjugates, which undergo unique self-assembly to form spherical nanoparticles that exhibited aggregation induced emission (AIE) in the near-infrared region. These nanoparticles showed significant singlet oxygen generation efficiency, negligible dark toxicity, rapid cellular uptake, efficient localization in cytoplasm, and high in vitro photocytotoxicity as well as in vivo photodynamic activity against a human prostate tumor animal model. This study demonstrates, for the first time, the power of the self-assembled AIE active tetraphenylethene conjugates in aqueous media as a nanoplatform for future therapeutic applications.

Naphthalene Imide Conjugates: Formation of Supramolecular Assemblies, and the Encapsulation and Release of Dyes through DNA - Mediated Disassembly

We report the synthesis of two new amphiphilic conjugates 1 and 2 based on naphthalene di- and monoimide chromophores and the investigation of their photophysical, self-assembly and DNA-binding properties. These conjugates showed aqueous good solubility and exhibited strong interactions with DNA and polynucleotides such as poly(dG⋅dC)-poly(dG⋅dC) and poly(dA⋅dT)-poly(dA⋅dT). The interaction of these conjugates with DNA was evaluated by photo- and biophysical techniques. These studies revealed that the conjugates interact with DNA through intercalation with association constants in the order of 5-8×10(4)  M(-1) . Of these two conjugates, bolaamphiphile 1 exhibited a supramolecular assembly that formed vesicles with an approximate diameter of 220 nm in the aqueous medium at a critical aggregation concentration of 0.4 mM, which was confirmed by SEM and TEM. These vesicular structures showed a strong affinity for hydrophobic molecules such as Nile red through encapsulation. Uniquely, when exposed to DNA the vesicles disassembled, and therefore this transformation could be utilised for the encapsulation and release of hydrophobic molecules by employing DNA as a stimulus.

Selective recognition of cyanide ions by amphiphilic porphyrins in aqueous medium

Herein, we report the synthesis of two amphiphilic porphyrins having pyridinium moieties and their anion recognition properties in aqueous medium. The study of their interactions with various anions reveals that these porphyrins exhibit unique and selective interactions with CN- ions when compared to the other anions. The addition of CN- ions to an aqueous solution of the butyl porphyrin resulted in a hypochromicity of ca. 78% at 419 nm with a concomitant band formation at 449 nm in the absorption spectrum. Similarly, we observed ca. 82% quenching in the emission intensity by the addition of 12.5 M of CN- ions in the fluorescence spectrum of the porphyrin mediated through aggregation. The limit of detection of CN- ions was found to be ca. 49 ppb and the nature of interactions has been studied through various microscopic and spectroscopic techniques. These studies have confirmed 1,4-addition of CN- ions to the pyridinium moiety of the porphyrin system, which led to the aggregation induced self-assembly resulting in the sensitive detection of CN- ions through changes in absorbance and fluorescence intensity in aqueous medium.

Effective Amyloid Defibrillation by Polyhydroxyl-Substituted Squaraine Dyes

With an objective to develop β-amyloid destabilizing agents, we have investigated the interactions of a few water-soluble near-infrared (NIR)-absorbing squaraine dyes 1-3 with lysozyme and its amyloid aggregates through photophysical and biophysical techniques. These dyes exhibited strong interactions with lysozyme and β-amyloids in addition to serum albumins as evidenced by the absorption and emission changes. The interactions were found to be spontaneous with association constant values in the range of approximately 10(4)-10(5)  m(-1), as confirmed through half-reciprocal analysis and isothermal calorimetric measurements. Uniquely, such effective interactions of the dyes have led to the complete disassembly of the β-amyloid fibrillar structures to form spherical particles approximately 350 nm in size, as confirmed through photophysical, thioflavin assay, circular dichroism (CD), atomic force microscopy (AFM), TEM, and selected-area electron diffraction (SAED) techniques. These results demonstrate that the squaraine dyes 1-3 under investigation act as effective protein-labelling and destabilizing agents of the protein amyloidogenesis.

Photomorphogenesis of γ-globulin: effect on sequential ordering and knock out of gold nanoparticles array

Herein we describe the synthesis of monodisperse protein-gold nanoparticles (AuNPs), wherein γ-globulin, a blood plasma protein acts as a capping, reducing, as well as a templating agent. As analysed through various photophysical, biophysical and microscopic techniques such as TEM, AFM, C-AFM, SEM, DLS, OPM, CD, and FTIR, we observed that the initial photoactivation of γ-globulin at pH 12 for 3 h resulted in small protein fibres of ca. 20 ± 5 nm in size. Subsequently, these fibres found to assist in the alignment of the colloidal gold nanoparticles of average diameter of ca. 2–2.5 nm on the surface of protein. At this particular irradiation time, the nano-bioconjugate thus formed exhibited negligible surface plasmon resonance absorption but showed an intense photoluminescence at 680 nm. Further irradiation for 24 h, led to the formation of self-assembled long fibres of the protein of ca. 2 ± 0.5 μm in diameter and ca. 18 μm in length. Interestingly, such a morphological transformation resulted in the sequential knock out of the anchored gold nanoparticles resulting in the clustering of the nanoparticles of size ca. 5–6 nm and observation of surface plasmon resonance band at around 520 nm with the concomitant quenching of luminescence intensity at 680 nm. The observation of light triggered self-assembly of protein and its effect on ordering and knock out of metal nanoparticles offers an approach for the design of novel nano-biohybrid materials for medicinal and optoelectronic applications.

Synthesis and in vitro photobiological studies of porphyrin capped gold nanoparticles\(^{\S }\)

We describe the synthesis and characterization of a thiol-functionalized porphyrin derivative 2 and its gold nanoparticle conjugates. The porphyrin 2 exhibited its characteristic intense Soret absorption at 420 nm with a molar extinction coefficient value of 3.6×105M-1cm-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}

A Reversible Dual Mode Chemodosimeter for the Detection of Cyanide Ions in Natural Sources

3.6\times 10^{5}\, \hbox {M}^{-1}\, \hbox {cm}^{-1}