Publications

MedChemComm, 2017, 8, 606-615

Carvedilol is a widely prescribed drug for the treatment of heart failure and the prevention of associated ventricular arrhythmias. It has also been reported to function as a biological antioxidant via hydrogen atom transfer from its carbazole N–H moiety to chain-propagating radicals. Metabolites of the drug include phenolic derivatives, such as 3-hydroxy-, 4′-hydroxy- and 5′-hydroxycarvedilol, which are also potential antioxidants. A comparison of the radical-inhibiting activities of the parent drug and the three metabolites was carried out in two separate assays. In the first, hydrogen atom transfer from these four compounds to the stable radical DPPH was measured by the decrease in the UV-visible absorption at 515 nm of the latter. The known radical inhibitors BHT, 4-hydroxycarbazole and α-tocopherol were employed as benchmarks in parallel experiments. In the second assay, inhibition of the photoinduced free-radical 1,2-addition of Se-phenyl p-toluenesel...

August 15, 2016

Photochem. Photobiol. Sci. 2016, 15, 1103. 

Many scientists probably consider dye aggregation in solution a curse. Here, the adjective “many” should be stressed, as some other researchers thrive on forcing dyes to aggregate in solution. This perspective paper is certainly not meant to be a comprehensive review on the topic. However, for people intrigued by this pervasive phenomenon, I will try to offer a general picture on the self-assembly of dyes into supramolecular aggregates by presenting and discussing key information on their thermodynamics, kinetics, and optical changes. More recent topics will be introduced, such as the impact of external stimuli on dye aggregation, with a particular focus on ion specific effects. Finally, aggregation-induced emission will also be examined.

J. Am. Chem. Soc. 2016, 138, 2762.

Herein, we synthesized a series of 10 core–shell silver–silica nanoparticles with a photosensitizer, Rose Bengal, tethered to their surface. Each nanoparticle possesses an identical silver core of about 67 nm, but presents a different silica shell thickness ranging from 5 to 100 nm. These hybrid plasmonic nanoparticles thus afford a plasmonic nanostructure platform with a source of singlet oxygen (1O2) at a well-defined distance from the metallic core. Via time-resolved and steady state spectroscopic techniques, we demonstrate the silver core exerts a dual role of enhancing both the production of 1O2, through enhanced absorption of light, and its radiative decay, which in turn boosts 1O2 phosphorescence emission to a greater extent. Furthermore, we show both the production and emission of 1O2 in vitro to be dependent on proximity to the plasmonic nanostructure. Our results clearly exhibit three distinct regimes as the plasmonic nanostructure moves apar...

Phys. Chem. Chem. Phys. 2015, 17, 20903. 

The synthesis of two neutral acridone derivatives was carried out to design media sensitive chromophores by taking advantage of intramolecular charge transfer (ICT) features. The molecules comprised two different donor–acceptor–donor triads, with absorption maxima at 425 nm and 520 nm, for the ketone and dicyanomethylene derivatives, respectively. The ketone variant exhibited fluorescence at room temperature, whereas the dicyanomethylene derivative was only emissive in frozen hexane. The ketone emission was highly solvatochromic, with Stokes shifts that ranged from 5000 cm−1 to 10000 cm−1. Electrochemically, both compounds displayed similar oxidation potentials at approximately 0.35 V versus ferrocene/ferrocenium, which was anticipated since both systems employ the same ethynylaniline donor portion of the molecule, whereas only the 9-dicyanomethylene derivative showed a reduction peak at −1.5 V vs. Fc/Fc+. Additional spectroelectro-chemical expe...

March 15, 2015

J. Photochem. Photobiol. A: Chemistry, 2015, 306, 1. (Cover Page)

Reactive oxygen species (ROS) originating from the metabolism of molecular oxygen are a double-edge sword. Their involvement in various diseases is well documented, while they also serve essential signaling functions. In order to shed light on their biochemical role, chemical tools have been designed for ROS detection and production. This featured article describes and illustrates different photochemical processes, which have been exploited to engineer new probes for the detection and the site-specific production of ROS.

Photochem. Photobiol. 2015, 91, 272. 

The nitrobenzofurazan (NBD) moiety has gained tremendous popularity over the last decades due to its fluorogenic nature. Indeed, upon interaction with aliphatic amines, it generates a stable fluorescent adduct, which has been used for protein and lipid labeling. In fact the 4-amino substituted NBD belongs to the broad family of intramolecular charge transfer molecules, with the amino group acting as an electron donor upon photoexcitation, and the nitro group as an electron acceptor. Although the singlet excited state of 4-amino NBD derivatives has been abundantly studied, investigation of its triplet manifold is scarce and even the absence of intersystem crossing for this type of molecules has been suggested. However, intramolecular charge transfer molecules are known to undergo intersystem crossing and high phosphorescence quantum yields have been reported in a nonpolar solvent. In the present paper, we have investigated the photophysical and photo...

Langmuir, 2014, 30, 9654. 

It is uncommon to read about cyanine dyes in the literature and not have their aggregation discussed. They are of high interest considering their propensity to undergo self-organization in aqueous solution, leading to interesting photophysical properties resulting from the formation of their dimers and higher ordered aggregates. Currently, the study of their aggregation is in high demand due to their diverse application range including dye-sensitized solar cells. However, their aggregation in high salt solutions is under studied, and the effect on aggregation in congruence with high ionic strength is often overlooked. In a previous study, our group established the role of specific ion effects and in particular the necessity of matching water affinity to induce aggregation of a cationic cyanine dye, thiazole orange. In order to advance the understanding of this topic, we present in this article the diverse aggregation of cyanine dyes, as a single monovalent sal...

October 21, 2013

Photochem. Photobiol. 2013, 90, 85. 

Studies involving metal enhancement effects have gained popularity, and enhancement of fluorescence due to the close proximity of a dye molecule to a metal nanoparticle is well documented. Although enhancement of singlet oxygen production by metal has been reported, studies are relatively scarce and so far only stationary silver island films have been proven to be adequate to do so. Herein, we describe the synthesis and characterization of core-shell nanoparticles on which a photosensitizer acting as source of singlet oxygen has been covalently attached to the nanoparticle surface. As a proof of concept, silver nanoparticles with a diameter around 68nm were chosen as the metallic core, and were coated by a silica shell of about 22nm in thickness. The silica shell plays a dual role as a spacer and a medium onto which the photosensitizer, rose bengal (RB), has been covalently attached. These novel core-shell nanoparticles allow for the amplification of...

November 12, 2012

Langmuir, 2012, 28, 16524. 

Understanding the role played by external factors on the organization of molecules has the potential to contribute greatly to fundamental research and applications in fields as diverse as nanotechnology, medicine, material chemistry, etc. Countless studies involve the organization of small organic molecules in environments rich in ionic species, yet their participation in molecular organization is often overlooked. Herein, we critically assess the organization in aqueous solution of the cationic cyanine dye, thiazole orange, in the presence of different monovalent sodium salts. Our findings clearly indicate that not all ions are identical with regards to the organization of thiazole orange molecules and specific ions effects are at play. The conventional Debye and Huckel model is not sufficient to explain our results, and the participation of ionic species in molecular organization is explained in terms of the recent theory of water matching affinity. Herein,...

J. Nanopart. Res. 2012, 14, 1099. 

Herein, we present a unique approach to easily achieve redox-active nanosized organic particles in aqueous environment using a strategy based on ion association between large organic ions, namely tetraphenylborate anions and thiazole orange cations. The anionic tetraphenylborate associates tightly with the cationic redox-active thiazole orange producing a well-defined meta-stable organic nanoscale particle (73 +/- 20 nm). These redox-active nanosized organic particles can act as seed sites for metal reductions and as a proof-of-concept, they were used to reduce gold(III) to gold nanoparticles in a neutral, aqueous environment at room temperature.

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