Nantanit Wanichacheva

Synthesis of a novel fluorescent sensor bearing dansyl fluorophores for the highly selective detection of mercury (II) ions.

A new macromolecule possessing two dansyl moieties and based on 2-[4-(2-aminoethylthio)butylthio]ethanamine was prepared as a fluorescent sensor and its mercury sensing properties toward various transition metal, alkali, and alkali earth ions were investigated. The designed compound exhibited pronounced Hg2+-selective ON-OFF type fluorescence switching upon binding. The new compound provided highly selective sensing to Hg2+ in acetonitrile-water solvent mixtures with a detection limit of 2.49 x 10-7 M or 50 ppb. The molecular modeling results indicated that ions-recognition of the sensor originated from a self assembly process of the reagent and Hg2+ to form a helical wrapping structure with the favorable electrostatic interactions of Hg2+coordinated with sulfur, oxygen, nitrogen atoms and aromatic moieties.

Highly Hg2+-sensitive and selective fluorescent sensors in aqueous solution and sensors-encapsulated polymeric membrane

Two Hg2+ chemosensors, rhodamine B hydrazide (RBH) and rhodamine 6G hydrazide (R6GH), were synthesized by a single step. In the presence of Hg2+, both of the sensors RBH and R6GH exhibited highly sensitive OFF–ON fluorescence enhancement. Importantly, the sensors showed a selective binding to Hg2+ over other common metal ions such as K+, Na+, Fe3+, Ca2+, Cu2+, Ag+ and Pb2+ in aqueous solutions. The OFF–ON fluorescence enhancement upon Hg2+ binding could be ascribed to conformational change of the spirolactam moiety of the rhodamine fluorophore through a spirolactam ring opening process. Furthermore, encapsulation of the sensors by polymeric membranes (PMMA) provided high selectivity and high sensitivity, especially for the sensors-encapsulated polymeric membrane RBH that showed an extremely low detection limit (0.2 ppb), which was 245 times lower than the sensor RBH in aqueous solution. In addition to fluorescence enhancement, the presence of Hg2+ also induced a noticeable color change from colorless to pink for the sensors dissolved in aqueous solution (10% v/v MeOH/water). The detection limits of sensor RBH and R6GH in both formats were in the range of 10−9–10−7 M of Hg2+ and were sufficient for on-site Hg2+ detection in the environmental and biological systems such as ground water, drinking water and edible fish. In particular, the extremely high sensitivity of the novel sensors-encapsulated polymeric membrane RBH could pave the way for development of a real time Hg2+ detection portable device.

Assessment of heavy metals in sediments of the Don Hoi Lot area in the Mae Klong estuary, Thailand.

The status and seasonal variation of heavy metals in surface sediment were investigated at Don Hoi Lot, located in the Mae Klong estuary, Thailand. Results revealed that all the measured heavy metals, except Zn, in the sediments had lower concentrations than in other nearby estuaries. Only Zn may be of concern for potential negative effects on estuarine biota in the study area. With the exception of Fe, all the studied heavy metals showed seasonal variation, but the patterns were diverse. Organic matter and the clay fraction in sediments were good sinks for heavy metals, excluding Zn, while Fe and Mn were good catchers. Principal component analysis suggested that Zn might have different origins and/or mechanisms of transport, accumulation and circulation, compared with the other heavy metals studied. A better understanding of sources and the behavior of Zn would enhance the efficiency of the estuary management plan in this study area.

Colorimetric and fluorescent sensing of a new FRET system via [5]helicene and rhodamine 6G for Hg2+ detection

A “visually colorimetric” and fluorometric sensor based on [5]helicene connected to rhodamine 6G via a hydrazide moiety, RG5H, was designed and prepared for the highly sensitive and selective detection of Hg2+. The sensor system operated through the FRET process from the [5]helicene energy donor to the ring-opened rhodamine 6G–Hg2+ complex acceptor. The sensor illustrated a very large Stokes shift up to 176 nm. In aqueous acetonitrile solutions, RG5H exhibited high selectivity and sensitivity toward Hg2+ in the presence of various competitive metal ions, such as Cu2+, Ag+, Zn2+, Pb2+, Ca2+, Cd2+, Co2+, Fe2+, Mg2+, Mn2+, Ba2+, Ni2+, Na+, Li+ and K+. The detection limit of RG5H for determination of Hg2+ was found to be 2.3 ppb. The binding of RG5H to Hg2+ was evident in both fluorescence enhancement as well as a colorimetric change in the sensor from greenish-yellow to orange, which could be easily observed by the naked eye.

Dual-Analyte Fluorescent Sensor Based on [5]Helicene Derivative with Super Large Stokes Shift for the Selective Determinations of Cu2+ or Zn2+ in Buffer Solutions and Its Application in a Living Cell

A new fluorescent sensor, M201-DPA, based on [5]helicene derivative was utilized as dual-analyte sensor for determination of Cu2+ or Zn2+ in different media and different emission wavelengths. The sensor could provide selective and bifunctional determination of Cu2+ in HEPES buffer containing Triton-X100 and Zn2+ in Tris buffer/methanol without interference from each other and other ions. In HEPES buffer, M201-DPA demonstrated the selective ON-OFF fluorescence quenching at 524 nm toward Cu2+. On the other hand, in Tris buffer/methanol, M201-DPA showed the selective OFF-ON fluorescence enhancement upon the addition of Zn2+, which was specified by the hypsochromic shift at 448 nm. Additionally, M201-DPA showed extremely large Stokes shifts up to ∼150 nm. By controlling the concentration of Zn2+ and Cu2+ in a living cell, the imaging of a HepG2 cellular system was performed, in which the fluorescence of M201-DPA in the blue channel was decreased upon addition of Cu2+ and was enhanced in UV channel upon addition of Zn2+. The detection limits of M201-DPA for Cu2+ and Zn2+ in buffer solutions were 5.6 and 3.8 ppb, respectively. Importantly, the Cu2+ and Zn2+ detection limits of the developed sensors were significantly lower than permitted Cu2+ and Zn2+ concentrations in drinking water as established by the U.S. EPA and WHO.

Novel Cu2+-specific “Turn-ON” fluorescent probe based on [5]helicene with very large Stokes shift and its potential application in living cells

A novel fluorescent sensor based on a [5]helicene dye bearing hydrazine (1) was synthesized through a simple reaction. The sensor was fully characterized by NMR, single crystal X-ray analysis, and HRMS spectrometry. Fluorescence technique was also employed to study the ability of 1 for the detection of Cu2+ among different ions. It was found that 1 exhibited a highly sensitive fluorescence response toward Cu2+ with a “Turn-ON” fluorescence enhancement and a very large Stokes shift of ∼183 nm. The sensor selectively bound to Cu2+ in the presence of various metal ions, such as Cd2+, Ag+, Pb2+, Zn2+, Ni2+, Hg2+, K+, Li+, Ba2+, Al3+, Fe2+, Co2+, Mn2+, Ca2+, Na+, and Mg2+ in aqueous acetonitrile solution. The Cu2+ detection limit was 2.6 ppb (3σ/slope), which was lower than the permissible concentration in drinking water determined by the US EPA and WHO. In addition, the sensor can enhance fluorescence from the intracellular area in the HepG2 cellular system. Hence, it has the potential for the detection of Cu2+ in biological samples.

Synthesis of Novel Fluorescent Sensors Based on Naphthalimide Fluorophores for the Highly Selective Hg2

With an aim to develop the new sensors for optical detection of Hg2+ ions, two novel fluorometric sensors were designed and successfully prepared using 2-(3-(2-aminoethylsulfanyl)propylsulfanyl)ethanamine and one or two N-methylnaphthalimide moieties (1 and 2). Sensor 1 was obtained via N-alkylation, N-imidation and a one-pot nucleophilic aromatic substitution, and N-formylation of the amine, while sensor 2 was prepared via N-alkylation, N-imidation, and nucleophilic aromatic substitution. The characterization, including 1H NMR, 13C NMR, and mass spectrometry, was then performed for 1 and 2. The Hg2+-binding behaviors of the sensors were investigated in terms of sensitivity and selectivity by fluorescence spectroscopy. Sensor 1 especially provided the reversible and highly Hg2+-selective ON-OFF fluorescence behavior by discriminating various interfering ions such as Pb2+, Co2+, Cd2+, Mn2+, Fe2+, K+, Na+, and in particular Cu2+ and Ag+ with a detection limit of 22 ppb toward Hg2+ ions.