Heavy metal ions are of great concern, not only among the scientific community, especially chemists, biologists, and environmentalists, but increasingly among the general population, who are aware of the some of the disadvantages associated with them. In spite of the fact that some heavy metal ions play important roles in living systems, they are very toxic and hence capable of causing serious environmental and health problems.1-6 Some heavy metal ions, such as Fe(III), Zn(II), Cu(II), Co(II), Mn(II), and Mo(VI), are essential for the maintenance of human metabolism. However, high concentrations of these ions can lead to many adverse health effects.1,2,7-20 It is also a fact that others such as Hg(II), Cd(II), Pb(II), and As(III) are among the most toxic ions known that lack any vital or beneficial effects. Accumulation of these over time in the bodies of humans and animals can lead to serious debilitating illnesses.2,21-30 Therefore, the development of increasingly selective and sensitive methods for the determination of heavy metal ions is currently receiving considerable attention.7,23,31-36 Several methods, including atomic absorption spectroscopy, inductively coupled plasma atomic emission spectrometry, electrochemical sensoring, and the use of piezoelectric quartz crystals make it possible to detect low limits.37-40 However, these methods require expensive equipment and involve time-consuming and laborious procedures that can be carried out only by trained professionals. Alternatively, analytical techniques based on fluorescence detection are very popular because fluorescence measurements are usually very sensitive (parts per billion/trillion), easy to perform, and inexpensive.23,37,41-45 Furthermore, the photophysical properties of a fluorophore can be easily tuned using a range of routes: charge transfer, electron transfer, energy transfer, the influence of the heavy metal ions, and the destabilization of nonemissive n-π* excited states.5 Consequently, a large number of papers involving fluorescent chemosensors (see definition in section 2) have been published. In general to date, fluorescent chemosensors for anions and cations have proven popular, but those for many heavy metal ions such as Hg(II), Pb(II), Cu(II), Fe(III), and Ag(I) present challenges because these ions often act as fluorescence quenchers. Cu(II) is a typical ion that causes the chemosensor to decrease fluorescent emissions due to quenching of the fluorescence by mechanisms inherent to the paramagnetic species.46-48 Such decreased emissions are impractical for analytical purposes because of their low signal outputs upon complexation. In addition, temporal separation of spectrally similar complexes by time-resolved fluorimetry is subsequently prevented.49 Compared to the relatively well-developed fluorescent chemosensors, fluorescent chemodosimeters (see definition in section 2) have recently emerged as a research area of * Corresponding author. E-mail: jongskim@korea.ac.kr. † Hue University. ‡ Korea University. Duong Tuan Quang was born in 1970 in Thanhhoa, Vietnam, and graduated from Hue University in 1992, where he obtained his M.S. degree two years later and began his career as a lecturer in Chemistry soon afterwards. He received his Ph.D. degree in 2003 from Institute of Chemistry, Vietnamese Academy of Science and Technology. In 2006, he worked as a postdoctoral fellow in Professor Jong Seung Kim’s laboratory, Dankook University, Seoul, Korea. He was promoted as an associate professor in 2009 and went to Korea University as a research professor in 2010. His main task involved the development of chromogenic and fluorogenic molecular sensors to detect specific cations and anions. Chem. Rev. 2010, 110, 6280–6301 6280

Fluoro- and Chromogenic Chemodosimeters for Heavy Metal Ion Detection in Solution and Biospecimens

Curcumin, a pigment from turmeric, is one of the very few promising natural products that has been extensively investigated by researchers from both the biological and chemical point of view. While there are several reviews on the biological and pharmacological effects of curcumin, chemistry reviews are comparatively scarcer. In this article, an overview of different aspects of the unique chemistry research on curcumin will be discussed. These include methods for the extraction from turmeric, laboratory synthesis methods, chemical and photochemical degradation and the chemistry behind its metabolism. Additionally other chemical reactions that have biological relevance like nucleophilic addition reactions, and metal chelation will be discussed. Recent advances in the preparation of new curcumin nanoconjugates with metal and metal oxide nanoparticles will also be mentioned. Directions for future investigations to be undertaken in the chemistry of curcumin have also been suggested.

/pdf/the-chemistry-of-curcumin-from-extraction-to-therapeutic-3i2ua7g7ok.pdf

The Chemistry of Curcumin: From Extraction to Therapeutic Agent

Investigation of adsorption and inhibitive effect of 2-mercaptothiazoline on corrosion of mild steel in hydrochloric acid media

Melatonin (N-acetyl-5-methoxytryptamine), an indoleamine produced in many organs including the pineal gland, was initially characterized as a hormone primarily involved in circadian regulation of physiological and neuroendocrine function. Subsequent studies found that melatonin and its metabolic derivatives possess strong free radical scavenging properties. These metabolites are potent antioxidants against both ROS (reactive oxygen species) and RNS (reactive nitrogen species). The mechanisms by which melatonin and its metabolites protect against free radicals and oxidative stress include direct scavenging of radicals and radical products, induction of the expression of antioxidant enzymes, reduction of the activation of pro-oxidant enzymes, and maintenance of mitochondrial homeostasis. In both in vitro and in vivo studies, melatonin has been shown to reduce oxidative damage to lipids, proteins and DNA under a very wide set of conditions where toxic derivatives of oxygen are known to be produced. Although the vast majority of studies proved the antioxidant capacity of melatonin and its derivatives, a few studies using cultured cells found that melatonin promoted the generation of ROS at pharmacological concentrations (μm to mm range) in several tumor and nontumor cells; thus, melatonin functioned as a conditional pro-oxidant. Mechanistically, melatonin may stimulate ROS production through its interaction with calmodulin. Also, melatonin may interact with mitochondrial complex III or mitochondrial transition pore to promote ROS production. Whether melatonin functions as a pro-oxidant under in vivo conditions is not well documented; thus, whether the reported in vitro pro-oxidant actions come into play in live organisms remains to be established.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/jpi.12162

Melatonin: a well‐documented antioxidant with conditional pro‐oxidant actions

Surface-enhanced Raman spectroscopy (SERS) was originally discovered in the 1970s [1, 2] where it was found that submonolayers of small nonresonant organic molecules, such as pyridine, when adsorbed onto the surface of silver nanoparticles (and a few other metals such as copper and gold) would exhibit greatly enhanced Raman intensities (enhancements of 10). These results have always held the promise for using this technique to observe very low concentrations of molecules on nanoparticles and nanostructured surfaces, but only recently has this promise started to be fulfilled in a predictable way. Thanks to exciting advances in techniques for making nanoparticles (such as nanosphere and e-beam lithography), to characterizing the surfaces using electron and scanning probe microscopies, to functionalizing the surfaces of the particles using self-assembled monolayers with attached chemical receptors, and to the laser and optics technology associated with measuring the Raman spectra, a number of important applications have been reported recently [3]. Included in these results have been the determination of SERS excitation spectra for benzenethiol on lithographically fabricated silver surfaces (periodic particle arrays fabricated using nanosphere lihtography) and the first observation of glucose using SERS [4, 5]. Another area of great interest in the SERS community concerns the observation of single-molecule SERS (SMSERS) [6,7,8]. This technique, which was originally developed in 1997 [6, 7], has proven to be of fundamental interest due to the nominal enhancement factor of > 10 required for the observation of any signal, but it has so far proven to be elusive in providing widespread applicability, due to the limited numbers of molecules and substrates for which successful observations have been made. In particular, almost all of the observations to date have been with molecules that are resonant Raman scatterers (such as rhodamine 6G), which typically have larger Raman intensities for non-SERS applications than nonresonant molecules like pyridine by factors of 10 or more. In addition, the range of substrates that yield SMSERS has been limited mostly to colloidal aggregate structures, which presumably are efficient at producing particle junction structures (i.e., dimers and small clus-

Electromagnetic mechanism of SERS

Effect of protic solvents on twisted intramolecular charge transfer state formation in coumarin-152 and coumarin-481 dyes

A systematic study on the structure and stability of nitrate anion hydrated clusters, NO3-·nH2O (n = 1−8) are carried out by applying first principle electronic structure methods. Several possible initial structures are considered for each size cluster to locate equilibrium geometry by applying a correlated hybrid density functional with 6-311++G(d,p) basis function. Three different types of arrangements, namely, symmetrical double hydrogen bonding, single hydrogen bonding and inter-water hydrogen bonding are obtained in these hydrated clusters. A structure having inter-water hydrogen bonding is more stable compared to other arrangements. Surface structures are predicted to be more stable over interior structures. Up to five solvent H2O molecules can stay around solute NO3- anion in structures having an inter-water hydrogen-bonded cyclic network. A linear correlation is obtained for weighted average solvent stabilization energy with the size (n) of the hydrated cluster. Distinctly different shifts of IR b...

Microhydration of NO3(-): a theoretical study on structure, stability and IR spectra.

The surface-enhanced Raman scattering (SERS) studies of 5-amino tetrazole (5AT), a tetrazole derivative, in aqueous silver sol at pH ∼ 9 and on deposited colloidal silver films were carried out and compared with the normal Raman spectrum of the molecule. The experimentally observed Raman bands along with their corresponding infrared bands were assigned based on the results of density functional theory (DFT) calculations. The significant changes evidenced between the SERS and the normal Raman spectra combined with the theoretical data obtained for Ag−5AT system demonstrated that the molecule is adsorbed on colloidal Ag particles through the lone pair of electrons of the nitrogen atom. The contribution of the chemical mechanism for the SERS enhancement was proved by the behavior of the electronic absorption spectrum of the Ag colloid upon addition of 5AT. This is further supported by the theoretical calculations that show that the favorable interaction of the frontier orbitals localized on Ag+ and the negat...

Studies on Adsorption of 5-Amino Tetrazole on Silver Nanoparticles by SERS and DFT Calculations

Emissions from both exciplexes and excited charge-transfer (CT) complexes have been observed for the fullerene−aromatic amine systems in nonaromatic solvents and solvent mixtures using steady-state fluorescence measurements. Support for the exciplex and CT emissions has also been obtained from the time-resolved fluorescence measurements. Both emissions are very sensitive to the polarity of the solvents. From the solvatochromic shifts of the emission maxima, dipole moments (μ) of the exciplexes and the excited CT complexes have been estimated. For C60−N,N-dimethylaniline (DMAN) and C60−N,N-diethylaniline (DEAN) systems, the μ values for the exciplexes and the excited CT complexes are in the ranges 10−12 and 25−27 D, respectively. Both species are thus very polar in nature. In aromatic solvents the fullerene−aromatic amine systems behave differently, without forming any exciplexes, though the fullerene emissions are quenched by the amines with almost diffusion-controlled rates. CT emissions are also not obs...

T. Mukherjee

Papers

Effect of protic solvents on twisted intramolecular charge transfer state formation in coumarin-152 and coumarin-481 dyes

Microhydration of NO3(-): a theoretical study on structure, stability and IR spectra.

Studies on Adsorption of 5-Amino Tetrazole on Silver Nanoparticles by SERS and DFT Calculations

Interaction of Ground and Excited (S1) States of C60 and C70 with Aromatic Amines: Exciplex and Charge-Transfer Emissions

Effect of the amino and hydroxy substituents on the photophysical properties of 1,4-disubstituted-9,10-anthraquinone dyes