Chemo-Enzymatic Synthesis of 1’-Photoreactive Sucrose Derivatives via Ether Linkage

As the 1’-hydroxyl group of sucrose is well known to be less reactive than other primary alcohols, there are no reports on the substitution of a phenoxy group at this position. Chemo-enzymatic synthesis of photoreactive 1’-phenoxy-substituted sucrose was examined to elucidate the functional analysis of sweet receptors

STRUCTURE AND EXCITED-STATE DYNAMICS OF PERYLENE : ULTRAHIGH-RESOLUTION SPECTROSCOPY AND AB INITIO CALCULATION

Author Institution: Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto; 606-8502, JapanPerylene is one of the prototypical compact polycyclic aromatic hydrocarbons (PAHs). The fluorescence quantum yield in the $S_1$ state is considerably high. It is strange because radiationless transitions such as intersystem crossing (ISC) to the triplet state and internal conversion (IC) to the $S_0$ state are expected to be fast due to high density of coupling levels. We observed the ultrahigh-resolution spectrum of the S_1 \;^1B_{2u} $\leftarrow$ S_0 \;^1A_g transition of jet-cooled perylene, and determined the rotational constants in these two states. , {\em J. Mol. Spectrosc.}, {\bf 260}, 72 (2010)} The inertial defect is positive and small, so that the molecule is considered to be planar with $D_{2h}$ symmetry. The obtained rotational constants of the $S_1$ state is very similar to those of the $S_0$ state. It indicates that the structural change upon electronic transition is very small. We performed $ab$ $initio$ calculation, and the calculated geometrical molecular structure and vibrational energies were in good coincidence with the experimental results. The observed high fluorescence quantum yield shows that radiationless transitions are all slow in the $S_1$ state of perylene. The slow IC can be attributed to the small scale of its structural change. We also observed the ultrahigh-resolution spectrum in the magnetic field of 0.5 Tesla. Zeeman broadening was very small, indicating that the singlet-triplet interaction is very weak, and that ISC is minor in the $S_1$ state. In specific vibronic levels, the fluorescence lifetimes are remarkably short. We conclude that the main process is IC, and the accepting mode is in-plane ($a_g$) deformation vibration in the $S_1$ state

Ultrahigh-resolution laser spectroscopy of the S1 1B2u←S0 1Ag transition of perylene

A rotationally resolved ultrahigh-resolution fluorescence excitation spectrum of the S1 ← S0 transition of perylene has been observed using a collimated supersonic jet technique in conjunction with a single-mode UV laser. We assigned 1568 rotational lines of the 000 band, and accurately determined the rotational constants. The obtained value of inertial defect was positive, accordingly, the perylene molecule is considered to be planar with D2h symmetry. We determined the geometrical structure in the S0 state by ab initio theoretical calculation at the RHF/6-311+G(d, p) level, which yielded rotational constant values approximately identical to those obtained experimentally. Zeeman broadening of each rotational line with the external magnetic field was negligibly small, and the mixing with the triplet state was shown to be very small. This evidence indicates that intersystem crossing (ISC) in the S1 1B2u state is very slow. The rate of internal conversion (IC) is also inferred to be small because the fluorescence quantum yield is high. The rotational constants of the S1 1B2u state were very similar to those of the S0 1Ag state. The slow internal conversion (IC) at the S1 zero-vibrational level is attributed to a small structural change upon electronic transition

Organic carbon and microbial biomass in a raised beach deposit under terrestrial vegetation in the High Arctic, Ny-Ålesund, Svalbard

Raised beach deposits are widespread on the north-western coast of Spitsbergen, Svalbard. To elucidate the importance of these deposits in an ecosystem carbon cycle, we measured the concentrations of organic carbon and adenosine 5-triphosphate (ATP; an index of living microbial biomass) in a raised beach deposit found under terrestrial vegetation in Ny-Ålesund. A shell in the deposit found at a depth of ca. 20 cm below the ground surface had a (not calibrated) 14C age of 11080 _ 140 yr BP, whereas soil organic carbon in the same deposit showed an older 14C age (22380 _ 90 yr BP). Organic carbon concentration in the layer of 20–40 cm belowground was about 1–2%, which was comparable to those in shallower mineral soil layers. Results of ATP analyses suggested that low but non-negligible amounts of microorganisms existed in the deposit. The proportion of biomass carbon to soil organic carbon tended to decrease with increasing depth, suggesting that organic carbon in the deep layer was less available to microorganisms than that in the shallow layers

Mode-selective internal conversion of perylene

We observed fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation of jet-cooled perylene-h 12 and perylene-d 12, and carefully examined the vibrational structures of the S0[1] A g and S1[1] B 2u states. We performed vibronic assignments on the basis of the results of ab initio calculation, and found that the vibrational energies in the S1 state are very similar to those in the S0 state, indicating that the potential energy curves are not changed much upon electronic excitation. We conclude that the small structural change is the main cause of its slow radiationless transition and high fluorescence quantum yield at the zero-vibrational level in the S1 state. It has been already reported that the lifetime of perylene is remarkably short at specific vibrational levels in the S1 state. Here, we show that the mode-selective nonradiative process is internal conversion (IC) to the S0 state, and the ν16(a g ) in-plane ring deforming vibration is the promoting (doorway) mode in the S1 state which enhances vibronic coupling with the high-vibrational level (b 2u ) of the S0 state