Sanghamitra Atta

Fluorescent caged compounds of 2,4-dichlorophenoxyacetic acid (2,4-d): photorelease technology for controlled release of 2,4-D.

A novel controlled-release formulation (CRF) of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was developed to reduce its negative environmental impacts by improving its herbicidal efficacy. The 2,4-D was chemically caged by coupling with photoremovable protecting groups (PRPGs) of coumarin derivatives. Photophysical studies of caged compounds showed that they all exhibited strong fluorescence properties. Controlled release of 2,4-D was achieved by irradiating the caged compounds using UV-vis light (310, 350, and 410 nm). The effect of various factors such as pH, solvent, and different substituents at the seventh position of coumarin moiety on the rate of photorelease was studied. The herbicidal activity of caged compounds and 4-(hydroxymethyl)-7-substituted coumarins was studied against Vigna radiata . The new formulation provided greater control over the release of 2,4-D by UV-vis light and also demonstrated the potential of the PRPGs not only to act as a delivery device but also to possess herbicidal activity after photorelease.

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.

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.

Photoresponsive polymers based on a coumarin moiety for the controlled release of pesticide 2,4-D

We report an excellent photoresponsive controlled release formulation based on a coumarin copolymer for pesticide 2,4-D. In the present work, acrylate and polyethylene glycol (PEG) based coumarin photoresponsive polymers were synthesised. The newly synthesised coumarin based polymers exhibited dual functionalities, namely as “fluorophores” and “phototriggers” for the controlled release of pesticide 2,4-D. The fluorescence properties of coumarin based polymers helped us to monitor the release of 2,4-D from the polymeric formulation. Release of the pesticide by coumarin based polymers was achieved on exposure to UV light. TGA results indicated that the coumarin polymer encapsulated pesticide has a good thermal stability compared to the free pesticide 2,4-D. A further leaching experiment also showed that the polymer encapsulated pesticide leaches slowly compared to the free pesticide 2,4-D. Bioassay studies in a plant suggest that the coumarin polymer encapsulated pesticide efficiently delivered 2,4-D inside the plant tissues (pumpkin plant Cucurbita maxima) improving its herbicidal activity. Our results indicated that use of a fluorescent coumarin polymer based delivery device for controlled release of pesticide by light holds great interest for field application.

Application of photoremovable protecting group for controlled release of plant growth regulators by sunlight.

We report a novel technique for controlled release of plant growth regulators (PGRs) by sunlight using photoremovable protecting group (PRPG) as a delivery device. In the present work, carboxyl-containing PGRs of the auxin group [indoleacetic acid (IAA) and naphthoxyacetic acid (NOAA)] were chemically caged using PRPGs of coumarin derivatives. Photophysical studies showed that caged PGRs exhibited good fluorescence properties. Irradiation of caged PGRs by sunlight in both aqueous ethanol and soil media resulted in controlled release of PGRs. The results of the bioactivity experiments indicated that caged PGRs showed better enhancement in the root and shoot length growth of Cicer arietinum compared to PGRs after 10days of sunlight exposure. Our results indicated that use of PRPG as a delivery device for controlled release of PGRs by sunlight in soil holds great interest for field application since it can overcome the rapid loss of PGRs in environmental conditions.

Nano-pesticide formulation based on fluorescent organic photoresponsive nanoparticles: for controlled release of 2,4-D and real time monitoring of morphological changes induced by 2,4-D in plant systems

In recent times, nano-pesticide formulations have gained great popularity since they enable effective usage of smaller quantities of the pesticides without creating much damage to the environment. The benefits of a nano-pesticide formulation can be further expanded by adding to its arsenal both tracking ability and precise control over the pesticide release. Recently, fluorescent photoresponsive nanocarriers have gained considerable momentum in the field of drug delivery since they can act as both a “fluorophore” for cell luminescence imaging and a “phototrigger” for regulated drug release by external light stimuli. Hence, we report for the first time a nano-pesticide formulation based on fluorescent photoresponsive organic nanoparticles of perylene-3-ylmethanol for regulated release of pesticide 2,4-dichlorophenoxyacetic acid (2,4-D). Further, the fluorescent nature of the photoresponsive organic nanoparticles was used to study the morphological changes induced by 2,4-D inside the plant system using confocal imaging studies. Additionally, the fluorescent colour change by photoresponsive organic nanoparticles before and after photorelease was exploited for real time monitoring of 2,4-D release inside the plants. Bioassay experiments revealed that nano-pesticide, Pe-2,4-D efficiently delivered 2,4-D inside the plant tissues improving its herbicidal activity. Such photoresponsive multifunctional nanocarriers with good fluorescence, cellular uptake property and efficient photoregulated release ability will be of great benefit in the construction of nano-pesticide formulations.

1-Acetylferroceneoxime-based photoacid generators: application towards sol–gel transformation and development of photoresponsive polymer for controlled wettability and patterned surfaces

A newsworthy class of carboxylate and sulfonate esters of 1-acetylferroceneoxime has been demonstrated as non-ionic photoacid generators (PAGs). PAGs based on 1-acetylferroceneoxime were synthesized in good yields by simple treatment of 1-acetylferroceneoxime with various carboxylic and sulfonyl chlorides. Newly developed PAGs of 1-acetylferroceneoxime showed good absorbance >350 nm. On irradiation using UV light (≥365 nm), carboxylates and sulfonates of 1-acetyl ferroceneoxime in aqueous acetonitrile solvent underwent efficient homolytic cleavage of N–O bond, resulting in the generation of carboxylic and sulphonic acids, respectively, with high chemical and good quantum yields. Further, we demonstrated the application of our newly developed 1-acetylferroceneoxime-based PAGs for gelation of biopolymer alginate on UV irradiation. More interestingly, we synthesized a ferroceneoxime bound photoresponsive polymer, 1-acetylferroceneoxime-polycaprolactone (AFO-PCL), and demonstrated its controlled surface wettability and generation of patterned surfaces.