Light promotes jasmonate biosynthesis to regulate photomorphogenesis in Arabidopsis.

Light acts as the pivotal external environment cue to modulate plant growth and development. Seeds germinate in the soil without light to undergo skotomorphogenesis with rapidly elongating hypocotyls that facilitate emergence from the soil, while seedlings upon light exposure undergo photomorphogenesis with significantly inhibited hypocotyl elongation that benefits plants to stand up firmly and cope with the changing environment. In this study, we demonstrate that light promotes jasmonate (JA) biosynthesis to inhibit hypocotyl elongation and orchestrate seedling photomorphogenesis in Arabidopsis. We showed that JAinhibition on hypocotyl elongation is dependent on JA receptor COI1 and signaling components such as repressor proteins JAZs and transcription activators MYC2/MYC3/MYC4. Furthermore, we found that MYC2/MYC3/MYC4 activate the expression of photomorphogenesis regulator HY5 to repress cell elongation-related genes (such as SAUR62 and EXP2) essential for seedling photomorphogenesis. Our findings provide a novel insight into molecular mechanisms underlying how plants integrate light signal with hormone pathway to establish seedling photomorphogenesis.

Nucleoside-Based Diarylethene Photoswitches: Synthesis and Photochromic Properties.

Diarylethene photoswitches based on the natural nucleoside deoxyadenosine were designed and synthesized. In aqueous solution, some of them exhibited good photochromic properties, including clear changes in color upon irradiation at 365 nm, red-shifts of the absorption wavelength, with good fatigue resistance, thermal stability, conversion efficiency, and base-pairing properties.

Excited-State Photolytic Mechanism of Cyclopentene Containing a Group 14 Element: An MP2-CAS//CASSCF Study.

The potential energy surfaces corresponding to the photolytic reactions of 1,2-dimethyl-cyclopentene, 3,4-dimethyl-silacyclopent-3-ene, and 3,4-dimethyl-germacyclopent-3-ene were investigated by employing the CAS(6,6)/6-311G(d) and MP2-CAS-(6,6)/6-311++G(3df,3pd)//CAS(6,6)/6-311G(d) methods. Also, six kinds of substituted germacyclopent-3-ene were used as model reactants by way of the CASSCF and MP2-CAS methods to study their photolytic mechanisms. The theoretical findings indicate that the photolysis of the above reactants all adopt the same reaction path as follows: reactant → Franck-Condon region → conical intersection → germylene and 1,3-butadiene. However, the theoretical results demonstrate that no photolysis ((1)(π →π*)) can be observed in the 1,2-dimethyl-cyclopentene system. Above all, the theoretical investigations strongly suggest that both steric effects, originating from the bulky substituents, and the atomic radius of the group 14 element (C, Si, and Ge) play a crucial role in determining the cis/trans selectivity of the conformation of 1,3-butadiene during their photolytic reactions.

Keto-enol tautomerization and intermolecular proton transfer in photoionized cyclopentanone dimer in the gas phase.

Time-of-flight mass spectra of cyclopentanone and its clusters cooled in a supersonic jet expansion have been measured following 4-, 3-, and 2-photon ionizations by the 2nd, 3rd, and 4th harmonic wavelengths, respectively, of a Q-switched Nd:YAG laser. The mass spectra reveal signatures of energetically favored keto to enol tautomerization of the molecular ion leading to intermolecular proton transfer, and this observation is found sharply dependent on the ionization wavelengths used. Electronic structure calculation predicts that in spite of the energetic preference, keto-enol conversion barrier of isolated molecular ion is high. However, the barrier is significantly reduced in a CH⋯O hydrogen-bonded dimer of the molecule. The transition states associated with tautomeric conversion of both cyclopentanone monomer and dimer cations have been identified by means of intrinsic reaction co-ordinate calculation. In a supersonic jet expansion, although a weakly bound dimer is readily generated, the corresponding cation and also the protonated counterpart are observed only for ionization by 532 nm. For other two ionization wavelengths, these species do not register in the mass spectra, where the competing reaction channels via α-cleavage of the ring become dominant. In contrast to the report of a recent study, we notice that the intact molecular ion largely survives fragmentations when ionized from the 2-photon resonant 3p Rydberg state as intermediate using nanosecond laser pulses, and the corresponding resonant 3-photon ionization spectrum has been recorded probing the intact molecular ion.

Determining ultraviolet degradation of high-visibility warning clothing with photochromic indicators.

The main purpose of this study was to select an appropriate photochromic dye and to develop a series of photochromic indicators showing ultraviolet (UV) degradation of selected background materials made from different polymers. The photochemistry of a series of photochromic compounds of oxazine and diarylethenes in thin polystyrene films were studied with spectroscopic methods. This paper also discusses the design and results of tests of UV photochromic indicators for high-visibility clothing.

Photoisomerization mechanism of 4-methylpyridine explored by electronic structure calculations and nonadiabatic dynamics simulations.

In the present paper, different electronic structure methods have been used to determine stationary and intersection structures on the ground (S(0)) and (1)ππ∗ (S(2)) states of 4-methylpyridine, which is followed by adiabatic and nonadiabatic dynamics simulations to explore the mechanistic photoisomerization of 4-methylpyridine. Photoisomerization starts from the S(2)((1)ππ∗) state and overcomes a small barrier, leading to formation of the prefulvene isomer in the S(0) state via a S(2)∕S(0) conical intersection. The ultrafast S(2) → S(0) nonradiative decay and low quantum yield for the photoisomerization reaction were well reproduced by the combined electronic structure calculation and dynamics simulation. The prefulvene isomer was assigned as a long-lived intermediate and suggested to isomerize to 4-methylpyridine directly in the previous study, which is not supported by the present calculation. The nonadiabatic dynamics simulation and electronic structure calculation reveal that the prefulvene isomer is a short-lived intermediate and isomerizes to benzvalene form very easily. The benzvalene form was predicted as the stable isomer in the present study and is probably the long-lived intermediate observed experimentally. A consecutive light and thermal isomerization cycle via Dewar isomer was determined and this cycle mechanism is different from that reported in the previous study. It should be pointed out that formation of Dewar isomer from the S(2)((1)ππ∗) state is not in competition with the isomerization to the prefulvene form. The Dewar structure observed experimentally may originate from other excited states.

Support-controlled chemoselective olefin-imine addition photocatalyzed by cadmium sulfide on a zinc sulfide carrier.

The semiconductor catalyzed photoaddition of cyclopentene or cyclohexene to various novel electron-poor imines of type p-XC(6)H(4)(CN)C[double bond, length as m-dash]N(COPh) (X = H, F, Cl, Br, Me, MeO) was investigated as a function of the nature of the cadmium sulfide photocatalyst. Irradiation (lambda>/= 350 nm) of silica supported cadmium sulfide surprisingly did not afford the expected olefin-imine adducts but an imine hydrocyanation product via an unprecedented dark reaction. However, when silica was replaced by zinc sulfide as the support for cadmium sulfide, the expected homoallylic N-benzoyl-alpha-amino cyanides were isolated in yields of 65-84%. Thus, chemoselectivity is introduced through replacing an insulating by a semiconducting support, a hitherto unknown effect in semiconductor photocatalysis. From the sign of the time resolved photovoltage it is found that the mixed metal sulfide interface CdS/ZnS increases the lifetime of photogenerated electron-hole pairs by about one order of magnitude as compared to the SiO(2)/CdS system. The reaction rate increases with increasing imine sigma-Hammett constants and decreasing stability of intermediate benzyl radicals.

Fate of flavins in sensitized photodegradation of isohumulones and reduced derivatives: studies on formation of radicals via EPR combined with detailed product analyses.

Photodegradation of isohumulones accounts for formation of the lightstruck flavor in beer. The reactions involved are mediated by riboflavin, a natural photosensitizer present in beer in ppb quantities. The results of an investigation of this sensitized degradation process are presented herein. Product analyses and electron paramagnetic resonance spectroscopy, in steady-state as well as in time-resolved mode, offer extensive insight into the photophysical and photochemical details of the degradation mechanism. In contrast to energy transfer and Norrish type I alpha-cleavage reactions that take place on direct irradiation of isohumulones, the sensitization pathway proceeds via one-electron redox chemistry involving the excited triplet state of riboflavin and derivatives. The flavin semiquinone radical thus formed could be readily detected, either by steady state or by time-resolved electron paramagnetic resonance spectroscopy. Superimposed signals in the spectra revealed the presence of radical fragments derived from isohumulones or tetrahydroisohumulones, which, on recombination with riboflavin semiquinone radicals, produced stable reaction products that were identified by HPLC-MS. However, no superimposed signals were observed on sensitized irradiation of dihydroisohumulones.

Studies on structure and function of rhodopsin by use of cyclopentatrienylidene 11-cis-locked-rhodopsin.

The photochemical reaction of cyclopentatrienylidene 11-cis-locked-rhodopsin derived from cyclopentatrienylidene 11-cis-locked-retinal and cattle opsin was spectrophotometrically studied. The difference absorption spectrum between the cyclopentatrienylidene 11-cis-locked-rhodopsin and its retinal oxime had its maximum at 495 nm (P-495). Irradiation of P-495 at -196 degrees C with either blue light or orange light caused no spectral change, supporting the cis-trans isomerization hypothesis for formation of bathorhodopsin. Upon irradiation of P-495 at 0 degree C with orange light, however, its absorption spectrum shifted to a shorter wavelength owing to formation of a hypsochromic product. The difference absorption spectrum between this product (P-466) and its retinal oxime showed its maximum at 466 nm. Analysis of retinal isomers by high-performance liquid chromatography showed that this spectral shift was not accompanied by photoisomerization of the chromophore. P-466 could almost completely be photoconverted to the original pigment (P-495) by irradiation at 0 degree C with blue light with little formation of the other isomeric form of its chromophore. The alpha-band of the circular dichroism spectrum of P-495 was very small in comparison with that of rhodopsin, while that of P-466 was comparable to it. These facts suggest that P-495 has a planar conformation in the side chain of the chromophore and that P-466 has a twisted one, probably at the C8-C9 single bond. Cyclic-GMP phosphodiesterase in frog rod outer segment was activated by neither P-495 nor P-466. This result suggests that the isomerization of the retinylidene chromophore of rhodopsin is indispensable in the phototransduction process.

Mass spectrometric investigation of minor products in the radiolysis of liquid cyclopentane.

The following substances have been identified as minor products in the gamma radiolysis of liquid cyclopentane at 3 X 10(22) eV total dose: 1,4-pentadiene; 2-pentene; cyclopentadiene; 1,3-pentadiene; ethyl cyclopentane; vinyl cyclopentane; n-heptane; n-octane; propyl cyclopentane; propenyl cyclopentane or propyl cyclopentene; n-decane; pentenyl cyclopentane or n-pentyl cyclopentene; n-pentyl cyclopentane; and cyclopentyl cyclopentene. The determination of these products was by parent mass number, gas chromatographic retention times, and/or boiling points of the compounds. Ultraviolet spectroscopic studies of the radiolysis of solutions of cyclopentadiene in cyclopentane are also described.