784 research outputs found
Effect of off-diagonal exciton-phonon coupling on intramolecular singlet fission
Intramolecular singlet fission (iSF) materials provide remarkable advantages
in terms of tunable electronic structures, and quantum chemistry studies have
indicated strong electronic coupling modulation by high frequency phonon modes.
In this work, we formulate a microscopic model of iSF with simultaneous
diagonal and off-diagonal coupling to high-frequency modes. A non-perturbative
treatment, the Dirac-Frenkel time-dependent variational approach is adopted
using the multiple Davydov trial states. It is shown that both diagonal and
off-diagonal coupling can aid efficient singlet fission if excitonic coupling
is weak, and fission is only facilitated by diagonal coupling if excitonic
coupling is strong. In the presence of off-diagonal coupling, it is found that
high frequency modes create additional fission channels for rapid iSF. Results
presented here may help provide guiding principles for design of efficient
singlet fission materials by directly tuning singlet-triplet interstate
coupling
Influences of quantum mechanically mixed electronic and vibrational pigment states in 2D electronic spectra of photosynthetic systems: Strong electronic coupling cases
In 2D electronic spectroscopy studies, long-lived quantum beats have recently
been observed in photosynthetic systems, and it has been suggested that the
beats are produced by quantum mechanically mixed electronic and vibrational
states. Concerning the electronic-vibrational quantum mixtures, the impact of
protein-induced fluctuations was examined by calculating the 2D electronic
spectra of a weakly coupled dimer with vibrational modes in the resonant
condition [J. Chem. Phys. 142, 212403 (2015)]. This analysis demonstrated that
quantum mixtures of the vibronic resonance are rather robust under the
influence of the fluctuations at cryogenic temperatures, whereas the mixtures
are eradicated by the fluctuations at physiological temperatures. However, this
conclusion cannot be generalized because the magnitude of the coupling inducing
the quantum mixtures is proportional to the inter-pigment coupling. In this
study, we explore the impact of the fluctuations on electronic-vibrational
quantum mixtures in a strongly coupled dimer. with an off-resonant vibrational
mode. Toward this end, we calculate electronic energy transfer (EET) dynamics
and 2D electronic spectra of a dimer that corresponds to the most strongly
coupled bacteriochlorophyll molecules in the Fenna-Matthews-Olson complex in a
numerically accurate manner. The quantum mixtures are found to be robust under
the exposure of protein-induced fluctuations at cryogenic temperatures,
irrespective of the resonance. At 300 K, however, the quantum mixing is
disturbed more strongly by the fluctuations, and therefore, the beats in the 2D
spectra become obscure even in a strongly coupled dimer with a resonant
vibrational mode. Further, the overall behaviors of the EET dynamics are
demonstrated to be dominated by the environment and coupling between the 0-0
vibronic transitions as long as the Huang-Rhys factor of the vibrational mode
is small.Comment: 20 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1505.0528
Recommended from our members
Immunoregulatory functions for murine intraepithelial lymphocytes: gamma/delta T cell receptor-positive (TCR+) T cells abrogate oral tolerance, while alpha/beta TCR+ T cells provide B cell help.
Past work has shown that a subset of effector T cells with unique characteristics could abrogate hapten- or antigen-induced tolerance, and the reconstitution of this immune response has been termed contrasuppression. We have studied contrasuppression in a model of oral tolerance (OT) in which adoptively transferred antigen-specific T contrasuppressor (Tcs) cells reverse OT and result in antibody responses to the eliciting antigen. In the present study, we show that murine intraepithelial lymphocytes (IELs) from mice orally immunized with sheep red blood cells (SRBC) contain T cells that exhibit Tcs cell activity. This effect was mediated by CD3+ gamma/delta T cell receptor-positive (TCR+), but not alpha/beta TCR+ T cells, and gamma/delta TCR+ Tcs cells were associated with both the CD4-,CD8+ and CD4-,CD8- (double-negative) IEL fractions. The CD4-,CD8+ gamma/delta TCR+ IELs were further separated into Vicia villosa-adherent and -nonadherent fractions. Adoptive transfer of V. villosa-adherent gamma/delta TCR+ T cells to mice with OT to SRBC resulted in splenic IgA, IgM, and IgG subclass anti-SRBC responses, while V. villosa-nonadherent gamma/delta TCR+ T cells were without activity. The gamma/delta TCR+ IELs did not support in vitro antibody responses in B cell cultures, while alpha/beta TCR+ IELs were effective T helper cells. Further, cytokine production by the gamma/delta TCR+ IELs was examined, and the gamma/delta TCR+ V. villosa-adherent fraction, which possessed contrasuppressor function, contained low levels of IL-5 mRNA and small numbers of IL-5-producing cells when compared with alpha/beta TCR+ IELs and V. villosa-nonadherent gamma/delta TCR+ IELs. Our results now show that mouse IELs contain two distinct types of T cells that function in the immune response, e.g., alpha/beta TCR+ T cells that produce IL-5 and function as helper cells, and gamma/delta TCR+ T cells that restore antibody responses in mice that had been orally tolerized with antigen
Oral-Nasopharyngeal Dendritic Cells Mediate T Cell-Independent IgA Class Switching on B-1 B Cells
Native cholera toxin (nCT) as a nasal adjuvant was shown to elicit increased levels of T-independent S-IgA antibody (Ab) responses through IL-5- IL-5 receptor interactions between CD4+ T cells and IgA+ B-1 B cells in murine submandibular glands (SMGs) and nasal passages (NPs). Here, we further investigate whether oral-nasopharyngeal dendritic cells (DCs) play a central role in the induction of B-1 B cell IgA class switch recombination (CSR) for the enhancement of T cell-independent (TI) mucosal S-IgA Ab responses. High expression levels of activation-induced cytidine deaminase, IΞ±-CΞΌ circulation transcripts and IΞΌ-CΞ± transcripts were seen on B-1 B cells purified from SMGs and NPs of both TCRΞ²β/β mice and wild-type mice given nasal trinitrophenyl (TNP)-LPS plus nCT, than in the same tissues of mice given nCT or TNP-LPS alone. Further, DCs from SMGs, NPs and NALT of mice given nasal TNP-LPS plus nCT expressed significantly higher levels of a proliferation-inducing ligand (APRIL) than those in mice given TNP-LPS or nCT alone, whereas the B-1 B cells in SMGs and NPs showed elevated levels of transmembrane activator and calcium modulator cyclophilin ligand interactor (TACI) expression. Interestingly, high frequencies of IgA+ B-1 B cells were induced when peritoneal IgAβ IgM+ B cells were stimulated with mucosal DCs from mice given nasal TNP-LPS plus nCT. Taken together, these findings show that nasal nCT plays a key role in the enhancement of mucosal DC-mediated TI IgA CSR by B-1 B cells through their interactions with APRIL and TACI
Finite-temperature time-dependent variation with multiple Davydov states
The Dirac-Frenkel time-dependent variational approach with Davydov Ans\"atze
is a sophisticated, yet efficient technique to obtain an acuurate solution to
many-body Schr\"odinger equations for energy and charge transfer dy- namics in
molecular aggregates and light-harvesting complexes. We extend this variational
approach to finite temperatures dynamics of the spin-boson model by adopting a
Monte Carlo importance sampling method. In or- der to demonstrate the
applicability of this approach, we compare real-time quantum dynamics of the
spin-boson model calculated with that from numerically exact iterative
quasiadiabatic propagator path integral (QUAPI) technique. The comparison shows
that our variational approach with the single Davydov Ans\"atze is in excellent
agreement with the QUAPI method at high temperatures, while the two differ at
low temperatures. Accuracy in dynamics calculations employing a multitude of
Davydov trial states is found to improve substantially over the single Davydov
Ansatz, especially at low temperatures. At a moderate computational cost, our
variational approach with the multiple Davydov Ansatz is shown to provide
accurate spin-boson dynamics over a wide range of temperatures and bath
spectral densities.Comment: 8 pages, 3 figure
A nasal double DNA adjuvant system induces atheroprotective IgM antibodies via dendritic cell-B-1a B cell interactions
We previously demonstrated that the dendritic cell (DC)-targeting nasal double DNA adjuvant system, which consists of a DNA plasmid expressing Flt3 ligand (pFL) and CpG oligodeoxynucleotide 1826 (CpG ODN), elicits specific immune responses to various antigens in the mucosal and systemic compartments. Here, we investigated, using phosphorylcholine (PC)-conjugated keyhole limpet hemocyanin (PC-KLH) as an antigen, whether the nasal double DNA adjuvant system induces protective immunity to atherosclerosis in apolipoprotein E-deficient (ApoE KO) mice. Further, we assessed the molecular and cellular mechanisms in the induction of anti-PC-specific immune responses. Nasal immunization with PC-KLH plus pFL and CpG ODN enhanced induction of PC-specific IgM in plasma, peritoneal fluids, and nasal washes when compared with mice administered PC-KLH alone. Of importance, these antibodies exhibited highly specific binding to the PC molecule, and dose-dependent binding to anti-T15 idiotype (AB1-2). Twelve weeks after the last immunization, the nasal double DNA adjuvant system with PC-KLH resulted in a reduction of atherogenesis in the aortic arch of ApoE KO mice. Therefore, we next assessed immunocytological mechanism to induce these antibodies. The nasal double DNA adjuvant system with PC-KLH resulted not only in significantly increased frequencies of CD11c+ DCs in the spleen, peritoneal cavity (PEC), and nasopharyngeal-associated lymphoid tissues (NALT), but also significantly increased expression of a proliferation-inducing ligand and B-cell-activating factor by CD11c+ DCs. In addition, the double DNA adjuvant system induced significantly increased numbers of B-1 B cells in the spleen, PEC, and NALT, and increased expression of transmembrane activator and calcium modulator and cyclophilin ligand interactor on CD5+ B220+ (B-1a) B cells. These findings demonstrated that the nasal double DNA adjuvant system with PC-KLH resulted in the induction of T15-like antibodies in the mucosal and systemic lymphoid tissues through interaction between DCs and B-1a B cells, and inhibited the progression of atherogenesis
- β¦