Ahreum Ahn

Conformationally resolved structures of jet-cooled acetaminophen by UV–UV hole-burning spectroscopy

The conformational structures of jet-cooled acetaminophen were investigated in the gas phase by resonant 2-photon ionization and UV-UV hole-burning spectroscopy. In contrast to the results from a previous study, two nearly isoenergetic conformers were distinctly found in a supersonic molecular beam expansion and positively identified as the cis and trans isomers of acetaminophen by UV-UV hole-burning spectroscopy. The 0-0 bands of the cis and trans isomers were found at 33518.7 and 33485.6 cm(-1), respectively. The vibronic bands of the two isomers are close-lying and/or partially overlapping due to the small energy difference (33 cm(-1)) between the two 0-0 bands. As a consequence, the recorded resonant 2-photon ionization spectrum is highly congested in the low excitation energy region, which develops continuously into a featureless, broadened spectrum in the high energy region.

Fluorescence imaging for Fe3+ in Arabidopsis by using simple naphthalene-based ligands

A main source of Fe3+ exposure for mammals is through plant consumption. Thus, sensitive and selective Fe3+ detection in plant tissue is a significant and an urgent need. Although fluorescence probes have been reported for Fe3+ in water, the detection of endogenous biological Fe3+ in plant tissue remains to be refined due to the high background signal and the thickness of the plant tissue that can hamper the effective application of traditional one-photon excitation. To address these issues, we have synthesized naphthalene-based probes, 1 and 1A. Upon an addition of Fe3+ in water–methanol (1 : 1, v/v, pH 7), the fluorescence probes of 1 and 1A were found to dramatically decrease, but no other metal ions had this effect. More interestingly, 1A, which had no diethyl 2,2′-(phenylazanediyl)diacetate moiety, also exhibited high selectivity for Fe3+. These results clearly indicate that the Fe3+ was bound to the nitrogen and oxygen atoms located near the naphthalene moiety. Furthermore, chemical probes of 1 and 1A were embedded into nanofibrous membrane films NF-1 and NF-1A, respectively, prepared by the electrospinning method for use as a portable chemical probe. Fluorescence changes were examined by immersing the films into solutions of various metal ions. The strong fluorescence intensity of both NF-1 and NF-1A dramatically decreased in accordance with concentration of Fe3+ onto the film, which was a “turn-off” system. In contrast, no significant changes of fluorescence intensity were observed compared that of other metal ions, such as Na+, K+, Zn2+, Pb2+, Mn2+, Cu2+, Co2+, Ca2+, Fe2+, and Cd2+. The results indicate that both NF-1 and NF-1A could be used to selectively detect Fe3+. We also investigated the practicality of both 1 and 1A as imaging probes for Fe3+ to operate within living systems like plants. Chemical probes of both 1 and 1A were tested for fluorescence imaging of Fe3+ in Arabidopsis. As expected, the fluorescence probes displayed high fluorescence imaging for Fe3+ in Arabidopsis.

NMR detection of chirality and enantiopurity of amines by using benzene tricarboxamide-based hydrogelators as chiral solvating agents

Enantiomeric excess of chiral compounds is a key parameter that can influence their activity or therapeutic action. Current approaches to the rapid measurement of enantiomeric excess using 1H NMR is based on the formation of diastereomeric complexes between chiral analytes and a chiral host, leading to two species with no symmetry relationship. Here, we demonstrate that a gelator host system can provide a means to elicit distinct chemical shifts in the 1H nuclear magnetic resonance (NMR) of a mixture of diamines or monoamines depending on the corresponding enantiomeric excess of the guest mixture of chiral amines. These gelator hosts provide a unique example of NMR based assessment of the chirality and enantiopurity of guest amines.