Photosynthetic light-harvesting complexes have a remarkable capacity to perform robust photo-physics at ambient temperatures and in fluctuating environments. Protein conformational dynamics and... Show morePhotosynthetic light-harvesting complexes have a remarkable capacity to perform robust photo-physics at ambient temperatures and in fluctuating environments. Protein conformational dynamics and membrane mobility are processes that contribute to the light-harvesting efficiencies and control photoprotective responses. This short review describes the application of magic angle spinning nuclear magnetic resonance (NMR) spectroscopy for characterizing the structural dynamics of pigment, protein, and thylakoid membrane components related to light harvesting and photoprotection. I will discuss the use of dynamics-based spectral editing solid-state NMR for distinguishing rigid and mobile components and assessing protein, pigment, and lipid dynamics on sub-nanosecond to millisecond timescales. Dynamic spectral editing NMR has been applied to investigate light-harvesting complex II protein conformational dynamics inside lipid bilayers and in native membranes. Furthermore, we used the NMR approach to assess thylakoid membrane dynamics. Finally, it is shown that dynamics-based spectral editing NMR for reducing spectral complexity by filtering motion-dependent signals enabled us to follow processes in live photosynthetic cells. Show less
Materials that feature bistable elements, hysterons, exhibit memory effects. Often, these hysterons are difficult to observe or control directly. Here, we introduce a mechanical metamaterial in... Show moreMaterials that feature bistable elements, hysterons, exhibit memory effects. Often, these hysterons are difficult to observe or control directly. Here, we introduce a mechanical metamaterial in which slender elements, interacting with pushers, act as mechanical hysterons. We show how we can tune the hysteron properties and pathways under cyclic compression by the geometric design of these elements and how we can tune the pathways of a given sample by tilting one of the boundaries. Furthermore, we investigate the effect of the coupling of a global shear mode to the hysterons as an example of the interactions between hysteron and non-hysteron degrees of freedom. We hope our work will inspire further studies on designer matter with targeted pathways. Show less
We review some of the progress of single-molecule optical experiments in the past 20 years and propose some perspectives for the coming years. We particularly focus on methodological advances in... Show moreWe review some of the progress of single-molecule optical experiments in the past 20 years and propose some perspectives for the coming years. We particularly focus on methodological advances in fluorescence, super-resolution, photothermal contrast, and interferometric scattering and briefly discuss a few of the applications. These advances have enabled the exploration of new emitters and quantum optics; the chemistry and biology of complex heterogeneous systems, nanoparticles, and plasmonics; and the detection and study of non-fluorescing and non-absorbing nano-objects. We conclude by proposing some ideas for future experiments. The field will move toward more and better signals of a broader variety of objects and toward a sharper view of the surprising complexity of the nanoscale world of single (bio-)molecules, nanoparticles, and their nano-environments. Published under an exclusive license by AIP Publishing. Show less
The spectral stability of three guest molecules embedded in a quickly frozen n-tetradecane matrix has been investigated on a single-molecular level at liquid-helium temperature. In total, about... Show moreThe spectral stability of three guest molecules embedded in a quickly frozen n-tetradecane matrix has been investigated on a single-molecular level at liquid-helium temperature. In total, about 2500 spectral trajectories of 476 terrylene molecules, 328 dibenzanthanthrene molecules, and 252 pentacene molecules were recorded. Both line broadening and spectral jumps are analyzed and the latter are found to be mainly light induced. The spectral changes in essence reflect the dynamics of the host matrix and the differences between the guest molecules may be reduced to differences in their pumping cycles. (C) 2001 American Institute of Physics. Show less
Dauw, X.L.R.; Berg, G.J.B. van den; Heuvel, D.J. van den; Poluektov, O.G.; Groenen, E.J.J. 2000
Electron-nuclear double resonance spectra at 95 GHz and electron-spin-echo envelope-modulation spectra at 9.5 GHz are reported for a frozen solution of fully C-13 enriched C-60 molecules in their... Show moreElectron-nuclear double resonance spectra at 95 GHz and electron-spin-echo envelope-modulation spectra at 9.5 GHz are reported for a frozen solution of fully C-13 enriched C-60 molecules in their photoexcited triplet state. Analysis of these data reveals that the triplet wave function is largely localized on a part of the molecule. Upon excitation, the C-60 molecule adopts a structure of D-5d symmetry with four symmetry inequivalent carbon atoms. The equator atoms each carry 3.8% of the spin density and the atoms next to the equator 1.1%, together accounting for 98% of the total spin density. These pi-spin densities make the hyperfine interaction mainly anisotropic. A slight s-spin density on the equator atoms adds a sizable isotropic hyperfine coupling. The triplet wave function is calculated quantum-chemically and compared with the observed spin-density distribution. (C) 2000 American Institute of Physics. [S0021-9606(00)00716-9]. Show less
Kok, P.; Groenen, E.J.J.; Amersfoort, P.W. van; Meer, A.F.G. van der 1997
Vibrational transitions of pyrazine in the lowest triplet state have been observed as transient changes in the intensity of the phosphorescence induced by the free-electron laser FELIX. All seven... Show moreVibrational transitions of pyrazine in the lowest triplet state have been observed as transient changes in the intensity of the phosphorescence induced by the free-electron laser FELIX. All seven fundamental infrared-active modes in the range of 250 to 1600 cm(-1) have been detected and all vibrational frequencies are found to be considerably lower than the corresponding ones in the ground state. (C) 1997 American Institute of Physics. Show less
Brouwer, A.C.J.; Köhler, J.; Groenen, E.J.J.; Schmidt, J. 1996
Weak satellites in S-1<--S-0 excitation spectra of natural-abundance pentacene in p-terphenyl due to position-specific C-13 isotope shifts were observed. An assignment of these satellites to the... Show moreWeak satellites in S-1<--S-0 excitation spectra of natural-abundance pentacene in p-terphenyl due to position-specific C-13 isotope shifts were observed. An assignment of these satellites to the various carbon positions is derived. The extremely narrow inhomogeneous linewidth allowed selective excitation of pentacene molecules with C-13 in specific positions. Spectra of the magnetic-resonance transition between triplet sublevels of such ensembles, and of individual pentacene molecules showed position-specific C-13 hyperfine broadening. (C) 1996 American Institute of Physics. Show less
The electron paramagnetic resonance (EPR) signal associated with the photo-accumulated radical anion of the primary electron acceptor (I-.-, a bacteriopheophytin radical) in reaction centers (RCs)... Show moreThe electron paramagnetic resonance (EPR) signal associated with the photo-accumulated radical anion of the primary electron acceptor (I-.-, a bacteriopheophytin radical) in reaction centers (RCs) of the photosynthetic purple bacterium rhodopseudomonas viridis shows a characteristic splitting of about 14.0 mT. This splitting has been attributed to an exchange interaction between I-.- and the reduced complex of the second electron acceptor, a quinone molecule, and a divalent, high-spin (S=2) Fe-ion, [Q(A)(.-)Fe(++)]. The magnetic structure of the three-spin complex, Fe++ (S=2), Q(A)(.-) (S=1/2), and I-.- (S=1/2), is assessed by Q-band (34.8 GHz) and X-band (9.2 GHz) EPR spectroscopy. The EPR spectrum of [I-.- Q(A)(.-)Fe(++)] is simulated accurately for the first time, using the magnetic parameters for the quinone-iron complex [W. F. Butler, R. Calvo, D. R. Fredkin, M. Y. Okamura, and G. Feher [Biophys. J. 45, 947 (1984)]. A largely isotropic interaction between I-.- and Q(A)(.)- is required (J(IQ)=-7.5 mT), together with an anisotropic interaction between I-.- and the F++-ion, whose y-component, C-IFe,C-y, is -3.5 mT. The simulations were insensitive to the magnitude of the x,z-components, C-IFe,C-x/z. The experimental magnetic interactions correspond very well with values calculated from the distances in the RC crystal structure. Thus, the interaction between I-.- and Q(A)(.-) is largely isotropic (exchange), whereas the interaction between I-.- and Fe++ has a purely dipolar character. This result is used to determine the principal directions of the magnetic interaction tensors of the Fe++-ion. (C) 1996 American Institute of Physics. Show less
Donckers, M.C.J.M.; Schwencke, A.M.; Groenen, E.J.J.; Schmidt, J. 1992
The hyperfine and quadrupole tensors of the two nitrogen atoms and the hyperfine tensors of the four hydrogen atoms of pyrazine in the lowest triplet state T0 are obtained from optically-detected... Show moreThe hyperfine and quadrupole tensors of the two nitrogen atoms and the hyperfine tensors of the four hydrogen atoms of pyrazine in the lowest triplet state T0 are obtained from optically-detected electron-nuclear double resonance (ENDOR) experiments on pyrazine-h4 in a single crystal of benzene-d6 at 1.2 K. Analysis of these tensors shows that pyrazine is in good approximation a planar molecule of D2h, symmetry in the lowest triplet state. The in-plane structure changes significantly upon excitation into T0. An increase of the C-N-C angles is observed and a reduction of the C-N bond lengths. From the hyperfine tensors the distribution of the electron-spin density is derived. The nitrogen nonbonding orbitals together carry 36% of the total spin density and it is shown that the lowest triplet state of pyrazine is appropriately described in terms of a 3n-pi* excitation. The results of the optically-detected ENDOR experiments give no indication of vibronic coupling of the lowest 3n-pi* state with nearby 3-pi-pi* states. Show less
The lowest triplet state T0 of the all-trans isomers of dodecapentaenal, decatetraenal, octatrienal, and hexadienal dissolved in polyethylene films has been investigated by electron-spin-echo... Show moreThe lowest triplet state T0 of the all-trans isomers of dodecapentaenal, decatetraenal, octatrienal, and hexadienal dissolved in polyethylene films has been investigated by electron-spin-echo spectroscopy in combination with pulsed laser excitation. Microwave transitions between the spin sublevels have been observed both in magnetic field and in zero field. For these polyenals T0 is found to be of pi-pi* character. The direction of the principal axes of the fine-structure tensors and the frequencies of the zero-field transitions have been determined. The largest zero-field splitting varies from 2496 MHz for dodecapentaenal to 5260 MHz for hexadienal. The zero-field splitting turns out to be inversely proportional to the number of double bonds in the conjugated chain, which is found to be compatible with a description of the triplet excitation as the promotion of an electron from the highest occupied to the lowest unoccupied molecular orbital. The upper spin sublevel is preferentially populated in the intersystem crossing process and decays fastest with a lifetime of 14-mu-s for dodecapentaenal, of 28-mu-s for decatetraenal, and of 77-mu-s for octatrienal. This variation is adequately described by an energy-gap law, which indicates that the Franck-Condon factors play a dominant role in the decay process. Show less
