[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The review covers the knowledge on photoremovable protecting
groups and includes all relevant chromophores studied in the
time period of 2000–2012; the most relevant earlier works are
also discussed.

/pdf/photoremovable-protecting-groups-in-chemistry-and-biology-2n33qs6p7b.pdf

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

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...

/pdf/hydrogen-bonding-in-the-electronic-excited-state-1wj02r16hb.pdf

Hydrogen Bonding in the Electronic Excited State

The complexity of the linkages between ozone depletion, UV-B radiation and climate change has become more apparent.

/pdf/environmental-effects-of-ozone-depletion-and-its-1tz7l47o2c.pdf

Environmental effects of ozone depletion and its interactions with climate change: progress report, 2011

The bimetallic platinum complexes are known as unique building blocks and arewidely utilized in the coordination-driven self-assembly of functionalized supramolecular metallacycles Hence, photophysical study of the bimetallic platinum complexes will be very helpful for the understanding on the optical properties and further applications of coordination-driven self-assembled supramolecular metallacycles Herein, we report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the significant intermolecular hydrogen bonding effects on the intramolecular charge transfer (ICT) fluorescence of a bimetallic platinum compound 4,4'-bis(trans-Pt(PEt(3))(2)OTf)benzophenone 3 in solution We demonstrated that the fluorescent state of compound 3 can be assigned as a metal-to-ligand charge transfer (MLCT) state Moreover, it was observed that the formation of intermolecular hydrogen bonds can effectively lengthen the fluorescence lifetime of 3 in alcoholic solvents compared with that in hexane solvent At the same time, the electronically excited states of 3 in solution are definitely changed by intermolecular hydrogen bonding interactions As a consequence, we propose a new fluorescence modulation mechanism by hydrogen bonding to explain different fluorescence emissions of 3 in hydrogen-bonding solvents and nonhydrogen-bonding solvents

The Effect of Intermolecular Hydrogen Bonding on the Fluorescence of a Bimetallic Platinum Complex

Photo-induced proton coupled electron transfer (PCET) is essential in the biological, photosynthesis, catalysis and solar energy conversion processes. Recently, p-nitrophenylphenol (HO-Bp-NO2) has been used as a model compound to study the photo-induced PCET mechanism by using ultrafast spectroscopy. In transient absorption spectra both singlet and triplet states were observed to exhibit PCET behavior upon laser excitation of HO-Bp-NO2. When we focused on the PCET in the triplet state, a new sharp band attracted us. This band was recorded upon excitation of HO-Bp-NO2 in aprotic polar solvents, and has not been observed for p-nitrobiphenyl which is without hydroxyl substitution. In order to find out what the new band represents, acidic solutions were used as an additional proton donor considering the acidity of HO-Bp-NO2. With the help of results in strong (~10−1 mol/L) and weak (~10−4 mol/L) acidic solutions, the new band is identified as open shell singlet O-Bp-NO2H, which is generated through protonation of nitro O in 3HO-Bp-NO2 followed by deprotonation of hydroxyl. Kinetics analysis indicates that the formation of radical O-Bp-NO2 competes with O-Bp-NO2H in the way of concerted electron-proton transfer and/or proton followed electron transfers and is responsible for the low yield of O-Bp-NO2H. The results in the present work will make it clear how the 3HO-Bp-NO2 deactivates in aprotic polar solvents and provide a solid benchmark for the deeply studying the PCET mechanism in triplets of analogous aromatic nitro compounds.

Direct observation of transient species generated from protonation and deprotonation of the lowest triplet of p-nitrophenylphenol

Nanosecond transient absorption and theoretical calculations have been used to investigate the intermolecular hydrogen abstractions from alcohols and 1-naphthol by the lowest excited triplet (T1) o...

Intermolecular Hydrogen Abstraction from Hydroxy Group and Alkyl by T1(ππ*) of 1-Chloro-4-nitronaphthalene.

Time-resolved resonance Raman (TR3) studies of the photochemistry of phenyl azide, 3-hyroxyphenyl azide, 3-methoxyphenyl azide and 3-nitrophenyl azide in acetonitrile:water solutions is reported. After photolysis of these four aryl azides in room temperature solutions, only one species was observed in the TR3 spectra for each azide, respectively at the probe wavelengths employed in the TR3 experiments. The species observed after photolysis of 3-nitrophenyl azide was assigned to 3,3‘-dinitroazobenzene, an azo compound formed from the dimerization reaction of triplet 3-nitrophenylnitrene. In contrast, the species observed after photolysis of phenyl azide, 3-hydroxyphenyl azide and 3-methoxyphenyl azide were tentatively assigned to intermediates formed from the dimerization of didehydroazepines that are produced from the ring expansion reaction of the respective singlet arylnitrene. To our knowledge, this is the first time-resolved vibrational spectroscopic observation of the dimerization reaction of didehyd...

Time-resolved resonance Raman observation of the dimerization of didehydroazepines in solution.

In this study, the absorption spectra of native or thermal protein were measured in 0.2-1.4THz using terahertz time-domain spectroscopy (THz-TDS) system at room temperature, their absorption spectra and the refractive spectra were obtained. Experimental results indicate that protein both has strong absorption but their characteristics were not distinct in the THz region, and the absorption decreased during thermal denatured state. In order to prove protein had been denatured, we used Differential scanning calorimeter (DSC) measured their denatured temperature, from their DSC heating traces, collagen T d =101℃, Bovine serum albumin T d =97℃. While we also combined the Fourier transform infrared spectrometer (FTIR) to investigate their secondary and tertiary structure before and after denatuation, but the results did not have the distinct changes. We turned the absorption spectra and the refractive spectra to the dielectric spectra, and used the one-stage Debye model simulated the terahertz dielectric spectra of protein before and after denaturation. This research proved that the terahertz spectrum technology is feasible in testing protein that were affected by temperature or other factors，which can provide theoretical foundation in the further study about the THz spectrum of protein and peptide temperature stability.

Thermal denaturation of protein studied by terahertz time-domain spectroscopy

Ultrafast time-resolved spectroscopy and time-resolved resonance Raman spectroscopy experimental results in the picoseocond timescales are reported for selected p-hydroxyphenacyl (pHP) ester phototrigger compounds. The results better elucidate the photodeprotection and rearrangement reactions of these important phototriggers and an overall mechanism is proposed for these reactions based on the time-resolved spectroscopy data presented here. This work indicates that site-specific, concerted solvation of the hydroxy proton and phosphate-leaving anion group through their respective intermolecular H-bonding with solvent water molecules promotes the photodeprotection reaction.

/pdf/time-resolved-spectroscopy-studies-of-the-photodeprotection-3d32hotfgb.pdf

Yong Du

Papers

Direct observation of transient species generated from protonation and deprotonation of the lowest triplet of p-nitrophenylphenol

Intermolecular Hydrogen Abstraction from Hydroxy Group and Alkyl by T1(ππ*) of 1-Chloro-4-nitronaphthalene.

Time-resolved resonance Raman observation of the dimerization of didehydroazepines in solution.

Thermal denaturation of protein studied by terahertz time-domain spectroscopy

Time-resolved spectroscopy studies of the photodeprotection reactions of p-hydroxyphenacyl ester phototrigger compounds