Unified analysis of optical absorption spectra of carotenoids based on a stochastic model.

The chemical structures of the carotenoid molecules are very simple and one might think that their electronic features are easily predicted. However, there is still has so much unknown information excepting the correlation between the electronic energy state and the length of effective conjugation chain of carotenoids. To investigate the electronic feature of the carotenoids, the most essential method is measuring the optical absorption spectra, but simulations based on the resonance Raman spectra are also an effective approach. For this reason, we studied the optical absorption spectra as well as resonance Raman spectra of 15 different carotenoid molecules each possessing a cyclic end-group, recorded in tetrahydrofuran (THF) solutions at room temperature. The whole band shapes of the absorption spectra of all these carotenoid molecules were successfully simulated using a stochastic model and Brownian oscillators. The parameters obtained from the simulation make it possible to discuss the intermolecular interaction between carotenoids and solvent THF molecules quantitatively.

Ultrafast time-resolved vibrational spectroscopies of carotenoids in photosynthesis.

This review discusses the application of time-resolved vibrational spectroscopies to the studies of carotenoids in photosynthesis. The focus is on the ultrafast time regime and the study of photophysics and photochemistry of carotenoids by femtosecond time-resolved stimulated Raman and four-wave mixing spectroscopies. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.

The dependence of the ultrafast relaxation kinetics of the S(2) and S(1) states in beta-carotene homologs and lycopene on conjugation length studied by femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies.

The ultrafast relaxation kinetics of all-trans-beta-carotene homologs with varying numbers of conjugated double bonds n(n=7-15) and lycopene (n=11) has been investigated using femtosecond time-resolved absorption and Kerr-gate fluorescence spectroscopies, both carried out under identical excitation conditions. The nonradiative relaxation rates of the optically allowed S(2)(1(1)B(u) (+)) state were precisely determined by the time-resolved fluorescence. The kinetics of the optically forbidden S(1)(2(1)A(g) (-)) state were observed by the time-resolved absorption measurements. The dependence of the S(1) relaxation rates upon the conjugation length is adequately described by application of the energy gap law. In contrast to this, the nonradiative relaxation rates of S(2) have a minimum at n=9 and show a reverse energy gap law dependence for values of n above 11. This anomalous behavior of the S(2) relaxation rates can be explained by the presence of an intermediate state (here called the S(x) state) located between the S(2) and S(1) states at large values of n (such as n=11). The presence of such an intermediate state would then result in the following sequential relaxation pathway S(2)-->S(x)-->S(1)-->S(0). A model based on conical intersections between the potential energy curves of these excited singlet states can readily explain the measured relationships between the decay rates and the energy gaps.

Ultrafast hydrogen-bonding dynamics in the electronic excited state of photoactive yellow protein revealed by femtosecond stimulated Raman spectroscopy.

The ultrafast structural dynamics in the electronic excited state of photoactive yellow protein (PYP) is studied by femtosecond stimulated Raman spectroscopy. Stimulated Raman spectra in the electronic excited state, S(1), can be obtained by using a Raman pump pulse in resonance with the S(1)-S(0) transition. This is confirmed by comparing the experimental results with numerical calculations based on the density matrix treatment. We also investigate the hydrogen-bonding network surrounding the wild-type (WT)-PYP chromophore in the ground and excited states by comparing its stimulated Raman spectra with those of the E46Q-PYP mutant. We focus on the relative intensity of the Raman band at 1555 cm(-1), which includes both vinyl bond C═C stretching and ring vibrations and is sensitive to the hydrogen-bonding network around the phenolic oxygen of the chromophore. The relative intensity for the WT-PYP decreases after actinic excitation within the 150 fs time resolution and reaches a similar intensity to that for E46Q-PYP. These observations indicate that the WT-PYP hydrogen-bonding network is immediately rearranged in the electronic excited state to form a structure similar to that of E46Q-PYP.

Femtosecond stimulated Raman spectroscopy of the dark S1 excited state of carotenoid in photosynthetic light harvesting complex.

Vibrational dynamics of the excited state in the light-harvesting complex (LH1) have been investigated by femtosecond stimulated Raman spectroscopy (FSRS). The native and reconstituted LH1 complexes have same dynamics. The ν(1) (C=C stretching) vibrational mode of spirilloxanthin in LH1 shows ultrafast high-frequency shift in the S(1) excited state with a time constant of 0.3 ps. It is assigned to the vibrational relaxation of the S(1) state following the internal conversion from the photoexcited S(2) state.

Dark excited States of carotenoid regulated by bacteriochlorophyll in photosynthetic light harvesting.

In photosynthesis, carotenoids play important roles in light harvesting (LH) and photoprotective functions, which have been described mainly in terms of two singlet excited states of carotenoids: S(1) and S(2). In addition to the "dark" S(1) state, another dark state, S*, was recently identified and its involvement in photosynthetic functions was determined. However, there is no consistent picture concerning its nature or the mechanism of its formation. One particularly anomalous behavior obtained from femtosecond transient absorption (TA) spectroscopy is that the S*/S(1) population ratio depends on the excitation intensity. Here, we focus on the effect of nearby bacteriochlorophyll (BChl) on the relaxation dynamics of carotenoid in the LH complex. We performed femtosecond TA spectroscopy combined with pre-excitation of BChl in the reconstituted LH1 complex from Rhodospirillum rubrum S1. We observed that the energy flow from S(1), including its vibrationally excited hot states, to S* occurs only when nearby BChl is excited into Q(y), resulting in an increase in S*/S(1). We also examined the excitation-intensity dependence of S*/S(1) by conventional TA spectroscopy. A comparison between the pre-excitation effect and excitation-intensity dependence shows a strong correlation of S*/S(1) with the number of BChls excited into Q(y). In addition, we observed an increase in triplet formation as the S* population increased, indicating that S* is an electronic excited state that is the precursor to triplet formation. Our findings provide an explanation for observed spectroscopic features, including the excitation-intensity dependences debated so far, and offer new insights into energy deactivation mechanisms inherent in the LH antenna.

Effects of the novel orally active antiestrogen TZE-5323 on experimental endometriosis.

Danazol and gonadotropin-releasing hormone agonists which are used as therapeutic drugs for endometriosis, develop adverse reactions in association with their long-term use. The efficacy of anti-estrogens for endometriosis, an estrogen-dependent disorder, has not been demonstrated. A novel, orally active anti-estrogen, TZE-5323 ((2-cyclohexy-6-hydroxybenzo[b]thien-3-yl)[4-[2-(1- piperidinyl)ethoxy]phenyl] methanone hydrochloride, CAS 150797-71-0; free salt formula) was developed. TZE-5323 showed strong affinity for human estrogen receptor alpha (hER alpha) and beta (hER beta), and dose-dependently inhibited estradiol-stimulated transcriptional activation via hER alpha and hER beta. Furthermore, TZE-5323 dose-dependently reduced estrogen-increased uterine weight in ovariectomized rats. Tamoxifen showed agonistic activity on hER alpha, while TZE-5323 did not show such activity. In the experimental endometriosis model in rats in which endometrial tissue is autotransplanted into the renal subcapsular space, TZE-5323 dose-dependently reduced the volume of the endometrial implant as did danazol and leuprorelin acetate. Furthermore, the long-term administration of TZE-5323 neither showed a decrease in bone mineral density nor did it affect serum estradiol concentrations in intact rats. Therefore, TZE-5323 suggested its potential as a novel therapeutic drug for endometriosis which is effective also in long-term use.

The very early events following photoexcitation of carotenoids.

The recent availability of laser pulses with 10-20 fs duration, tunable throughout the visible and near infrared wavelengths, has facilitated the investigation, with unprecedented temporal resolution, into the very early events of energy relaxation in carotenoids [Science 298 (2002) 2395; Synth. Metals 139 (2003) 893]. This has enabled us to clearly demonstrate the existence of an additional intermediate state, Sx, lying between the S2 (1(1)Bu+) and S1 (2(1)Ag-) states. In addition, by applying time-resolved stimulated Raman spectroscopy with femtosecond time resolution, it has also been shown that vibrational relaxation in electronic excited states plays an important role in these interconversions. In this mini-review, we describe briefly the current understanding of Sx and the other intermediate excited states that can be formed by relaxation from S2, mainly focusing attention on the above two topics. Emphasis is also placed on some of the major remaining unsolved issues in carotenoid photochemistry.