N. D. Pradeep Singh

Photodegradation of organic dyes in the presence of [Fe(III)-salen]Cl complex and H2O2 under visible light irradiation

Photodegradation of persistent organic dyes (Rhodamine B (RhB), Malachite Green Oxalate (MG) and Crystal Violet 10B (CV)) is studied with Fe(III)-salen complex (λ(max) 494 nm), and hydrogen peroxide under visible light irradiation (λ≥400 nm). The complete decolourization of the dyes (60 mg/L each) was achieved in the aqueous medium. The pseudo-first-order degradation rate constants of RhB, MG, CV were found to be 2.83×10(-3) s(-1), 1.57×10(-3) s(-1) and 1.34×10(-3) s(-1), respectively. The effect of various parameters like concentration of H(2)O(2), pH of the medium, and influence of electrolytes are investigated on the degradation of RhB. A modified benzoic acid hydroxylation method has been used to detect the active oxygen species (OH radicals) in this study. The hydroxyl radical production is increased with the increase in irradiation time. Interestingly, even an excess amount of scavenger could not arrest the degradation of the dyes. This may be due to the formation of some secondary oxidants. Here, active ferryl ion was identified as the secondary oxidant. Degradation products of the dye (RhB) were determined by GC-MS, and phthalic acid was identified as the major one. From the results, a possible photodegradation mechanism has been proposed.

Photoresponsive coumarin-tethered multifunctional magnetic nanoparticles for release of anticancer drug

Recently, photoresponsive nanoparticles have received significant attention because of their ability to provide spatial and temporal control over the drug release. In the present work, we report for the first time photoresponsive multifunctional magnetic nanoparticles (MNPs) fabricated using coumarin-based phototrigger and Fe/Si MNPs for controlled delivery of anticancer drug chlorambucil. Further, newly fabricated photoresponsive multifunctional MNPs were also explored for cell luminescence imaging. In vitro biological studies revealed that coumarin tethered Fe/Si MNPs of ~9 nm size efficiently delivered the anticancer drug chlorambucil into cancer cells and thereby improving the drug action to kill the cancer cells upon irradiation. Such multifunctional MNPs with strong fluorescence, good biocompatibility and efficient photocontrolled drug release ability will be of great benefit in the construction of light-activated multifunctional nano drug delivery systems.

Photoresponsive real time monitoring silicon quantum dots for regulated delivery of anticancer drugs

Recently, photoresponsive nanoparticles have been widely used to develop drug delivery systems (DDSs) wherein light is used as an external stimulus to trigger drug release in a spatially and temporally controlled fashion. Real time monitoring DDSs are also gaining much interest due to their capability of monitoring drug release in situ. In this context we designed a new photoresponsive real time monitoring nanoparticle based on photoluminescent silicon quantum dots (SiQDs) using the o-nitrobenzyl (ONB) derivative as a phototrigger for the controlled release of anticancer drug chlorambucil (Cbl). The strong fluorescence of SiQDs was initially quenched by ONB. Upon irradiation ONB triggered the release of the drug switching on the fluorescence of SiQDs to monitor the drug release. We reported a new and simple strategy to synthesise amine functionalised silicon quantum dots and covalently conjugated phototrigger ONB with caged anticancer drug Cbl onto it. Newly designed photoresponsive theranostic ONBCbl-SiQDs performed three important functions: (i) nanocarriers for drug delivery, (ii) controlled drug release under both one photon and two-photon excitation, and (iii) photoswitchable fluorescent nanoparticles for real-time monitoring of drug release based on the photoinduced electron transfer (PET) process. In vitro biological studies revealed the efficient cellular internalisation and cancer cell destruction ability of ONBCbl-SiQDs upon photoirradiation. ONBCbl-SiQDs exhibit a successful example of combining multiple functions into a single system for drug delivery systems.

Photocontrolled Nuclear-Targeted Drug Delivery by Single Component Photoresponsive Fluorescent Organic Nanoparticles of Acridin-9-Methanol

We report for the first time an organic nanoparticle based nuclear-targeted photoresponsive drug delivery system (DDS) for regulated anticancer drug release. Acridin-9-methanol fluorescent organic nanoparticles used in this DDS performed three important roles: (i) ″nuclear-targeted nanocarrier″ for drug delivery, (ii) ″phototrigger″ for regulated drug release, and (iii) fluorescent chromophore for cell imaging. In vitro biological studies reveal acridin-9-methanol nanoparticles of ~60 nm size to be very efficient in delivering the anticancer drug chlorambucil into the target nucleus, killing the cancer cells upon irradiation. Such targeted organic nanoparticles with good biocompatibility, cellular uptake property, and efficient photoregulated drug release ability will be of great benefit in the field of targeted intracellular controlled drug release.

Synthesis, photophysical and photochemical properties of photoacid generators based on N-hydroxyanthracene-1,9-dicarboxyimide and their application toward modification of silicon surfaces.

We have introduced a series of nonionic photoacid generators (PAGs) for carboxylic and sulfonic acids based on N-hydroxyanthracene-1,9-dicarboxyimide (HADI). The newly synthesized PAGs exhibited positive solvachromatic emission (λ(max)(hexane) 461 nm, λ(max)(ethanol) 505 nm) as a function of solvent polarity. Irradiation of PAGs in acetonitrile (ACN) using UV light above 410 nm resulted in the cleavage of weak N-O bonds, leading to the generation of carboxylic and sulfonic acids in good quantum and chemical yields. Mechanism for the homolytic N-O bond cleavage for acid generation was supported by time-dependent density functional theory (TD-DFT) calculations. More importantly, using the PAG monomer N-(p-vinylbenzenesulfonyloxy)anthracene-1,9-dicarboxyimide (VBSADI), we have synthesized N-(p-vinylbenzenesulfonyloxy)anthracene-1,9-dicarboxyimide-methyl methacrylate (VBSADI-MMA) and N-(p-vinylbenzenesulfonyloxy)anthracene-1,9-dicarboxyimide-ethyl acrylate (VBSADI-EA) copolymer through atom transfer radical polymerization (ATRP). Finally, we have also developed photoresponsive organosilicon surfaces using the aforementioned polymers.

Synthesis, photochemistry, DNA cleavage/binding and cytotoxic properties of fluorescent quinoxaline and quinoline hydroperoxides

Novel fluorescent quinoxaline and quinoline hydroperoxides were shown to perform dual role as both fluorophores for cell imaging and photoinduced DNA cleaving agents. Photophysical studies of newly synthesized quinoxaline and quinoline hydroperoxides showed that they all exhibited moderate to good fluorescence. Photolysis of quinoxaline and quinoline hydroperoxides in acetonitrile using UV light above 350nm resulted in the formation of corresponding ester compounds via γ-hydrogen abstraction by excited carbonyl chromophore. Single strand DNA cleavage was achieved on irradiation of newly synthesized hydroperoxides by UV light (⩾350nm). Both hydroxyl radicals and singlet oxygen were identified as reactive oxygen species (ROS) responsible for the DNA cleavage. Further, we showed quinoline hydroperoxide binds to ct-DNA via intercalative mode. In vitro biological studies revealed that quinoline hydroperoxide has good biocompatibility, cellular uptake property and cell imaging ability. Finally, we showed that quinoline hydroperoxide can permeate into cells efficiently and may cause cytotoxicity upon irradiation by UV light.

Development of 1-hydroxy-2(1H)-quinolone-based photoacid generators and photoresponsive polymer surfaces.

A new class of carboxylate and sulfonate esters of 1-hydroxy-2(1H)-quinolone has been demonstrated as nonionic photoacid generators (PAGs). Irradiation of carboxylates and sulfonates of 1-hydroxy-2(1H)-quinolone by UV light (λ≥310 nm) resulted in homolysis of weak N-O bond leading to efficient generation of carboxylic and sulfonic acids, respectively. The mechanism for the homolytic N-O bond cleavage was supported by time-dependent DFT calculations. Photoresponsive 1-(p-styrenesulfonyloxy)-2-quinolone-methyl methacrylate (SSQL-MMA) and 1-(p-styrenesulfonyloxy)-2-quinolone-lauryl acrylate (SSQL-LA) copolymers were synthesized from PAG monomer 1-(p-styrenesulfonyloxy)-2-quinolone, and subsequently controlled surface wettability was demonstrated for the above-mentioned photoresponsive polymers.

Microwave- and ultrasound-assisted oxidation of bio-active limonoids

Abstract Tetranortriterpenoids from Azadirachta indica A. Juss and Soymida febrifuga (Meliaceae), have been selectively oxidized to single major products which exhibit bioactivity higher than the parent compounds, comparable to that of azadirachtin A. The reaction proceeds to completion in less than 15 min and 1 min on being assisted by ultrasound and microwave irradiation, respectively.

Photooxidation of Cedrelone, a Tetranortriterpenoid from Toona ciliata¶

Abstract Cedrelone, a tetranortriterpenoid on photolysis by UV light yields a true photooxidation product 3 [14 β,15β,22β,23β-diepoxy-6-hydroxy-1,5,20(22)-meliatriene-2,7,21-trione] whose structure is well established by NMR studies and confirmed by X-ray crystallography, along with product 4 [14 β,15β-epoxy-6,23-dihydroxy-1,5,20(22)-meliatriene-2,7,21-trione]. Addition of rose bengal increases the rate of photooxidation whereas DABCO decreases rate of photolysis proving the involvement of singlet oxygen in the photooxygenation. Both the photoproducts exhibited antifeedant activity.

A targeted, image-guided and dually locked photoresponsive drug delivery system

We have developed a new targeted image-guided photoresponsive drug delivery system (DDS) based on a dual locking strategy. Excitation of the DDS by fluorescent light results in the first unlocking and activation of the drug, and allows real-time monitoring of the prodrug. Extended irradiation results in a second unlocking, giving drug release within cancer cells.