New insights into the photochemistry of carotenoid spheroidenone in light-harvesting complex 2 from the purple bacterium Rhodobacter sphaeroides

Light-harvesting complex 2 (LH2) from the semi-aerobically grown purple phototrophic bacterium Rhodobacter sphaeroides was studied using optical (static and time-resolved) and resonance Raman spectroscopies. This antenna complex comprises bacteriochlorophyll (BChl) a and the carotenoid spheroidenone, a ketolated derivative of spheroidene. The results indicate that the spheroidenone-LH2 complex contains two spectral forms of the carotenoid: (1) a minor, ‘‘blue’’ form with an S2 (11 Bu ?) spectral origin band at 522 nm, shifted from the position in organic media simply by the high polarizability of the binding site, and (2) the major, ‘‘red’’ form with the origin band at 562 nm that is associated with a pool of pigments that more strongly interact with protein residues, most likely via hydrogen bonding. Application of targeted modeling of excited-state decay pathways after carotenoid excitation suggests that the high (92%) carotenoid-to-BChl energy transfer efficiency in this LH2 system, relative to LH2 complexes binding carotenoids with comparable double-bond conjugation lengths, derives mainly from resonance energy transfer from spheroidenone S2 (11 Bu ?) state to BChl a via the Qx state of the latter, accounting for 60% of the total transfer. The elevated S2 (11 Bu ?) ? Qx transfer efficiency is apparently associated with substantially decreased energy gap (increased spectral overlap) between the virtual S2 (11 Bu ?) ? S0 (11 Ag -) carotenoid emission and Qx absorption of BChl a. This reduced energetic gap is the ultimate consequence of strong carotenoid–protein interactions, including the inferred hydrogen bondin

The Sulfur Microbial Diet and Risk of Colorectal Cancer by Molecular Subtypes and Intratumoral Microbial Species in Adult Men

INTRODUCTION: We recently described the sulfur microbial diet, a pattern of intake associated with increased gut sulfur-metabolizing bacteria and incidence of distal colorectal cancer (CRC). We assessed whether this risk differed by CRC molecular subtypes or presence of intratumoral microbes involved in CRC pathogenesis (Fusobacterium nucleatum and Bifidobacterium spp.). METHODS: We performed Cox proportional hazards modeling to examine the association between the sulfur microbial diet and incidence of overall and distal CRC by molecular and microbial subtype in the Health Professionals Follow-Up Study (1986-2012). RESULTS: We documented 1,264 incident CRC cases among 48,246 men, approximately 40% of whom had available tissue data. After accounting for multiple hypothesis testing, the relationship between the sulfur microbial diet and CRC incidence did not differ by subtype. However, there was a suggestion of an association by prostaglandin synthase 2 (PTGS2) status with a multivariable adjusted hazard ratio for highest vs lowest tertile of sulfur microbial diet scores of 1.31 (95% confidence interval: 0.99-1.74, Ptrend = 0.07, Pheterogeneity = 0.04) for PTGS2-high CRC. The association of the sulfur microbial diet with distal CRC seemed to differ by the presence of intratumoral Bifidobacterium spp. with an adjusted hazard ratio for highest vs lowest tertile of sulfur microbial diet scores of 1.65 (95% confidence interval: 1.14-2.39, Ptrend = 0.01, Pheterogeneity = 0.03) for Bifidobacterium-negative distal CRC. We observed no apparent heterogeneity by other tested molecular markers. DISCUSSION: Greater long-term adherence to the sulfur microbial diet could be associated with PTGS2-high and Bifidobacterium-negative distal CRC in men. Additional studies are needed to further characterize the role of gut microbial sulfur metabolism and CRC

Generation of coherently coupled vibronic oscillations in carotenoids

Coherent vibronic oscillations in the ground state of carotenoids have been investigated by means of three-pulse four-wave mixing spectroscopy. Here, we especially focused our attention on the influence of the temporal separation between the first and the second pulses, i.e., the coherent period tau, on the third- order nonlinear signals. The vibronic oscillations of the fundamental modes are clearly observed when tau is set to zero. They appear via an impulsive resonant Raman process and reflect the spectral feature of a conventional Raman spectrum very well. Interestingly, in addition to the coherent vibronic oscillations of the fundamental modes, we found that high-intensity coherent vibronic oscillations of the overtones and the coupled modes appear when a nonzero value of tau is employed. These coupled modes become dominant at a rather large coherent period of tau similar to 60 fs. A simple extension of our previous calculations that assume electronic harmonic potentials and vibronic Brownian oscillators cannot explain the present experimental results. Instead, we propose a model that takes into consideration the mixing between singlet states and the higher-order interaction of molecular vibrations with electronic states, which is in quantitative agreement with the experimental results. Our finding opens the way to controlling even Raman inactive vibronic oscillations using light

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 gap

Femtosecond transient absorption spectroscopic study of a carbonyl-containing carotenoid analogue, 2-(all-trans-retinylidene)-indan-1,3-dione

The photophysical properties of a carbonyl-containing carotenoid analogue in an s-cis configuration, relative to the conjugated pi system, 2-(all-trans-retinylidene)-indan-1,3-dione (C20Ind), were investigated by femtosecond time-resolved spectroscopy in various solvents. The lifetime of the optically forbidden S-1 state of C20Ind becomes long as solvent polarity increases. This trend is completely opposite to the situation of S1-ICT dynamics of carbonyl containing carotenoids, such as peridinin and fucoxanthin. Excitation energy dependence of the transient absorption measurements shows that the transient absorption spectra in nonpolar solvents were originated from two distinct transient species, while those in polar and protic solvents are due to a single transient species. By referring to the results of MNDO-PSDCI (modified neglect of differential overlap with partial single- and double configuration interaction) calculations, we conclude: (1) in polar and protic solvents, the S-1 state is generated following excitation up to the S-2 state; (2) in nonpolar solvents, however, both the S-1 and the (1)n pi* states are generated; and (3) C20Ind does not generate the S1-ICT state, despite the fact that it has two conjugated carbonyl groups