다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Because of its fundamental importance in many branches of science, hydrogen bonding is a subject of intense contemporary research interest. The physical and chemical properties of hydrogen bonds in the ground state have been widely studied both experimentally and theoretically by chemists, physicists, and biologists. However, hydrogen bonding in the electronic excited state, which plays an important role in many photophysical processes and photochemical reactions, has scarcely been investigated.Upon electronic excitation of hydrogen-bonded systems by light, the hydrogen donor and acceptor molecules must reorganize in the electronic excited state because of the significant charge distribution difference between the different electronic states. The electronic excited-state hydrogen-bonding dynamics, which are predominantly determined by the vibrational motions of the hydrogen donor and acceptor groups, generally occur on ultrafast time scales of hundreds of femtoseconds. As a result, state-of-the-art femtos...

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Hydrogen Bonding in the Electronic Excited State

The excited state intramolecular proton transfer (ESIPT) mechanisms of 2-(2-hydroxyphenyl)benzoxazole (HBO), bis-2,5-(2-benzoxazolyl)-hydroquinone (BBHQ) and 2,5-bis(5′-tert-butyl-benzoxazol-2′-yl)hydroquinone (DHBO) have been investigated using time-dependent density functional theory (TDDFT). The calculated vertical excitation energies based on the TDDFT method reproduced the experimental absorption and emission spectra well. Three kinds of stable structures were found on the S1 state potential energy surface (PES). A new ESIPT mechanism that differs from the one proposed previously (Mordzinski et al., Chem. Phys. Lett., 1983, 101, 291. and Lim et al., J. Am. Chem. Soc., 2006, 128, 14542.) is proposed. The new mechanism includes the possibility of simultaneous double proton transfer, or successive single transfers, in addition to the accepted single proton transfer mechanism. Hydrogen bond strengthening in the excited state was based on primary bond lengths, angles, IR vibrational spectra and hydrogen bond energy. Intramolecular charge transfer based on the frontier molecular orbitals (MOs) also supports the proposed mechanism of the ESIPT reaction. To further elucidate the proposed mechanism, reduced dimensionality PESs of the S0 and S1 states were constructed by keeping the O–H distance fixed at a series of values. The potential barrier heights among the local minima on the S1 surface imply competitive single and double proton transfer branches in the mechanism. Based on the new ESIPT mechanism, the observed fluorescence quenching can be satisfactorily explained.

Competitive excited-state single or double proton transfer mechanisms for bis-2,5-(2-benzoxazolyl)-hydroquinone and its derivatives

The excited state intramolecular proton transfer (ESIPT) mechanisms of 1,8-dihydroxydibenzo[a,h]phenazine (DHBP) in toluene solvent have been investigated based on time-dependent density functional theory (TD-DFT). The results suggest that both a single and double proton transfer mechanisms are relevant, in constrast to the prediction of a single one proposed previously (Piechowska et al. J. Phys. Chem. A 2014, 118, 144–151). The calculated results show that the intramolecular hydrogen bonds were formed in the S0 state, and upon excitation, the intramolecular hydrogen bonds between −OH group and pyridine-type nitrogen atom would be strengthened in the S1 state, which can facilitate the proton transfer process effectively. The calculated vertical excitation energies in the S0 and S1 states reproduce the experimental UV–vis absorption and fluorescence spectra well. The constructed potential energy surfaces of the S0 and S1 states have been used to explain the proton transfer process. Four minima have been f...

New excited state proton transfer mechanisms for 1,8-dihydroxydibenzo[a,h]phenazine

Two excited state proton transfer mechanisms of 3-hydroxyisoquinoline (3HIQ) in cyclohexane and acetic acid (ACID) were investigated based on the time-dependent density functional theory (TDDFT), suggesting a different double-proton transfer mechanism from the one proposed previously (J Phys Chem B, 1998, 102, 1053) Instead of the formation of keto–enol complexes for 3HIQ self-association in cyclohexane, our theoretical results predicted that 3HIQ self-association exists in two forms: the normal form (enol/enol) and the tautomer form (keto/keto) in cyclohexane A high barrier (37023 kcal mol−1) between the 3HIQ enol monomer and 3HIQ keto monomer form indicated that the 3HIQ keto monomer in the ground state should not exist In addition, the constructed potential energy surfaces of the ground state and excited state have been used to explain the proton transfer process Upon optical excitation, the enol/enol form is excited to the first excited state, then transfers one proton, in turn, transition to the ground state to transfer another proton A relatively low barrier (898 kcal mol−1) demonstrates two stable structures in the ground state In view of the acetic acid solvent effect, two protons of 3HIQ/ACID transfer along the dihydrogen bonds in the first excited state, which is a different transfer mechanism to 3HIQ self-association In addition, the proton transfer process provides a possible explanation for the fluorescence quenching observed

A questionable excited-state double-proton transfer mechanism for 3-hydroxyisoquinoline

Based on the time-dependent density functional theory (TDDFT), the excited state intramolecular proton transfer (ESIPT) mechanism of a new compound 1 chromophore synthesized and designed by Liu et al. [Journal of Photochemistry and Photobiology B: Biology., 138 (2014), 75-79] has been investigated theoretically. The calculations of primary bond lengths, angles and the IR vibrational spectra verified the intramolecular hydrogen bond was strengthened. The fact that reproducing the experimental absorbance and fluorescence emission spectra well theoretically demonstrates that the TDDFT theory we adopted is reasonable and effective. In addition, intramolecular charge transfer based on the frontier molecular orbitals demonstrated the indication of the ESIPT reaction. The constructed potential energy curves of ground state and the first excited state based on keeping the O-H distance fixed at a serious of values have been used to illustrate the ESIPT process. A little barrier of 2.45 kcal/mol in the first excited state potential energy curve provided the transfer mechanism. Further, the phenomenon of fluorescence quenching has been explained reasonably based on the ESIPT mechanism. PACS: 31.25.Jf; 82.39.Jn

An investigation of excited-state intramolecular proton transfer mechanism of new chromophore

Solvent-controlled plasmon-assisted surface catalysis reaction of 4-aminothiophenol dimerizing to p,p'-dimercaptoazobenzene on Ag nanoparticles.

A new strategy for effective distance regulation of the surface plasmon assisted coupling reaction of p-nitrothiophenol to p,p′-dimercaptoazobenzene

4-Aminothiophenol (PATP) and 4-aminophenyl disulfide (APDS) in contact with silver will form H2N-C6H4-S-Ag (PATP-Ag), and under the conditions of surface-enhanced Raman spectroscopy (SERS), a coupling reaction will generate 4,4-dimercaptoazobenzene (DMAB). DMAB is strongly Raman-active, showing strong peaks at ν ≈ 1140, 1390, and 1432 cm–1, and is widely used in surface-plasmon-assisted catalysis. Using APDS, PATP, p-nitrothiophenol (PNTP), and p-nitrodiphenyl disulfide (NPDS) as probe molecules, Raman spectroscopy and imaging techniques have been used to study the effect of intermolecular distance on surface-plasmon-assisted catalysis. Theoretically, PATP-Ag formed from APDS will be bound at proximal Ag atoms on the Ag surface due to S–S bond cleavage. The results show that APDS is more prone to surface-plasmon-assisted catalytic coupling due to the smaller distance between surface PATP-Ag moieties than those derived from PATP. Therefore, APDS has a higher reaction efficiency, better Raman activity, and ...

Jing Wang

Papers

A questionable excited-state double-proton transfer mechanism for 3-hydroxyisoquinoline

An investigation of excited-state intramolecular proton transfer mechanism of new chromophore

Solvent-controlled plasmon-assisted surface catalysis reaction of 4-aminothiophenol dimerizing to p,p'-dimercaptoazobenzene on Ag nanoparticles.

A new strategy for effective distance regulation of the surface plasmon assisted coupling reaction of p-nitrothiophenol to p,p′-dimercaptoazobenzene

Effect of Intermolecular Distance on Surface-Plasmon-Assisted Catalysis