Effects of Percussive Massage Treatments on Symptoms Associated with Eccentric Exercise-Induced Muscle Damage.

Percussive massage (PM) is an emerging recovery treatment despite the lack of research on its effects post-eccentric exercise (post-EE). This study investigated the effects of PM treatments (immediately, 24, 48, and 72 h post-EE) on the maximal isometric torque (MIT), range of motion (ROM), and an 11-point numerical rating scale (NRS) of soreness of the nondominant arm's biceps brachii from 24-72 h post-EE. Seventeen untrained, college-aged subjects performed 60 eccentric elbow flexion actions with their nondominant arms. Nine received 1 minute of PM, versus eight who rested quietly (control [CON]). In order, NRS, ROM, and MIT (relative to body mass) were collected pre-eccentric exercise (pre-EE) and after treatment (AT) at 24, 48, and 72 h post-EE. NRS was also collected before treatment (BT). Electromyographic (EMG) and mechanomyographic (MMG) amplitudes were collected during the MIT and normalized to pre-EE. There were no interactions for MIT, EMG, or MMG, but there were interactions for ROM and NRS. For ROM, the PM group had higher values than the CON 24-72 h by ~6-8°, a faster return to pre-EE (PM: 48 h, CON: 72 h), and exceeded their pre-EE at 72 h by ~4°. The groups' NRS values did not differ BT 24-72 h; however, the PM group lowered their NRS from BT to AT within every visit by ~1 point per visit, which resulted in them having lower values than the CON from 24-72 h by ~2-3 points. Additionally, the PM group returned their NRS to pre-EE faster than the CON (PM: BT 72 h, CON: never). In conclusion, PM treatments may improve ROM without affecting isometric strength or muscle activation 24-72 h post-EE. Although the PM treatments did not enhance the recovery from delayed onset muscle soreness until 72 h, they consistently provided immediate, temporary relief when used 24-72 h post-EE.

A composite electrodynamic mechanism to reconcile spatiotemporally resolved exciton transport in quantum dot superlattices.

Quantum dot (QD) solids are promising optoelectronic materials; further advancing their device functionality requires understanding their energy transport mechanisms. The commonly invoked near-field Förster resonance energy transfer (FRET) theory often underestimates the exciton hopping rate in QD solids, yet no consensus exists on the underlying cause. In response, we use time-resolved ultrafast stimulated emission depletion (STED) microscopy, an ultrafast transformation of STED to spatiotemporally resolve exciton diffusion in tellurium-doped cadmium selenide-core/cadmium sulfide-shell QD superlattices. We measure the concomitant time-resolved exciton energy decay due to excitons sampling a heterogeneous energetic landscape within the superlattice. The heterogeneity is quantified by single-particle emission spectroscopy. This powerful multimodal set of observables provides sufficient constraints on a kinetic Monte Carlo simulation of exciton transport to elucidate a composite transport mechanism that includes both near-field FRET and previously neglected far-field emission/reabsorption contributions. Uncovering this mechanism offers a much-needed unified framework in which to characterize transport in QD solids and additional principles for device design.

Protein-Based Model for Energy Transfer between Photosynthetic Light-Harvesting Complexes Is Constructed Using a Direct Protein-Protein Conjugation Strategy.

Photosynthetic organisms utilize dynamic and complex networks of pigments bound within light-harvesting complexes to transfer solar energy from antenna complexes to reaction centers. Understanding the principles underlying the efficiency of these energy transfer processes, and how they may be incorporated into artificial light-harvesting systems, is facilitated by the construction of easily tunable model systems. We describe a protein-based model to mimic directional energy transfer between light-harvesting complexes using a circular permutant of the tobacco mosaic virus coat protein (cpTMV), which self-assembles into a 34-monomer hollow disk. Two populations of cpTMV assemblies, one labeled with donor chromophores and another labeled with acceptor chromophores, were coupled using a direct protein-protein bioconjugation method. Using potassium ferricyanide as an oxidant, assemblies containing o-aminotyrosine were activated toward the addition of assemblies containing p-aminophenylalanine. Both of these noncanonical amino acids were introduced into the cpTMV monomers through amber codon suppression. This coupling strategy has the advantages of directly, irreversibly, and site-selectively coupling donor with acceptor protein assemblies and avoids cross-reactivity with native amino acids and undesired donor-donor or acceptor-acceptor combinations. The coupled donor-acceptor model was shown to transfer energy from an antenna disk containing donor chromophores to a downstream disk containing acceptor chromophores. This model ultimately provides a controllable and modifiable platform for understanding photosynthetic interassembly energy transfer and may lead to the design of more efficient functional light-harvesting materials.

Static Disorder has Dynamic Impact on Energy Transport in Biomimetic Light-Harvesting Complexes.

Despite extensive studies, many questions remain about what structural and energetic factors give rise to the remarkable energy transport efficiency of photosynthetic light-harvesting protein complexes, owing largely to the inability to synthetically control such factors in these natural systems. Herein, we demonstrate energy transfer within a biomimetic light-harvesting complex consisting of identical chromophores attached in a circular array to a protein scaffold derived from the tobacco mosaic virus coat protein. We confirm the capability of energy transport by observing ultrafast depolarization in transient absorption anisotropy measurements and a redshift in time-resolved emission spectra in these complexes. Modeling the system with kinetic Monte Carlo simulations recapitulates the observed anisotropy decays, suggesting an inter-site hopping rate as high as 1.6 ps-1. With these simulations, we identify static disorder in orientation, site energy, and degree of coupling as key remaining factors to control to achieve long-range energy transfer in these systems. We thereby establish this system as a highly promising, bottom-up model for studying long-range energy transfer in light-harvesting protein complexes.

Direct Correlation of Single-Particle Motion to Amorphous Microstructural Components of Semicrystalline Poly(ethylene oxide) Electrolytic Films.

Semicrystalline polymers constitute some of the most widely used materials in the world, and their functional properties are intimately connected to their structure on a range of length scales. Many of these properties depend on the micro- and nanoscale heterogeneous distribution of crystalline and amorphous phases, but this renders the interpretation of ensemble averaged measurements challenging. We use superlocalized widefield single-particle tracking in conjunction with AFM phase imaging to correlate the crystalline morphology of lithium-triflate-doped poly(ethylene oxide) thin films to the motion of individual fluorescent probes at the nanoscale. The results demonstrate that probe motion is intrinsically isotropic in amorphous regions and that, without altering this intrinsic diffusivity, closely spaced, often parallel, crystallite fibers anisotropically constrain probe motion along intercalating amorphous channels. This constraint is emphasized by the agreement between crystallite and anisotropic probe trajectory orientations. This constraint is also emphasized by the extent of the trajectory confinement correlated to the width of the measured gaps between adjacent crystallites. This study illustrates with direct nanoscale correlations how controlled and periodic arrangement of crystalline domains is a promising design principle for mass transport in semicrystalline polymer materials without compromising their mechanical stability.

Spectrally Resolved Photodynamics of Individual Emitters in Large-Area Monolayers of Hexagonal Boron Nitride.

Hexagonal boron nitride (h-BN) is a 2D, wide band gap semiconductor that has recently been shown to display bright room-temperature emission in the visible region, sparking immense interest in the material for use in quantum applications. In this work, we study highly crystalline, single atomic layers of chemical vapor deposition grown h-BN and find predominantly one type of emissive state. Using a multidimensional super-resolution fluorescence microscopy technique we simultaneously measure spatial position, intensity, and spectral properties of the emitters, as they are exposed to continuous wave illumination over minutes. As well as low emitter heterogeneity, we observe inhomogeneous broadening of emitter line-widths and power law dependency in fluorescence intermittency; this is strikingly similar to previous work on quantum dots. These results show that high control over h-BN growth and treatment can produce a narrow distribution of emitter type and that surface interactions heavily influence the photodynamics. Furthermore, we highlight the utility of spectrally resolved wide-field microscopy in the study of optically active excitations in atomically thin two-dimensional materials.

Exploiting Chromophore-Protein Interactions through Linker Engineering To Tune Photoinduced Dynamics in a Biomimetic Light-Harvesting Platform.

Creating artificial systems that mimic and surpass those found in nature is one of the great challenges of modern science. In the context of photosynthetic light harvesting, the difficulty lies in attaining utmost control over the energetics, positions and relative orientations of chromophores in densely packed arrays to transfer electronic excitation energy to desired locations with high efficiency. Toward achieving this goal, we use a highly versatile biomimetic protein scaffold from the tobacco mosaic virus coat protein on which chromophores can be attached at precise locations via linkers of differing lengths and rigidities. We show that minor linker modifications, including switching chiral configurations and alkyl chain shortening, lead to significant lengthening of the ultrafast excited state dynamics of the system as the linkers are shortened and rigidified. Molecular dynamics simulations provide molecular-level detail over how the chromophore attachment orientations, positions, and distances from the protein surface lead to the observed trends in system dynamics. In particular, we find that short and rigid linkers are able to sandwich water molecules between chromophore and protein, leading to chromophore-water-protein supracomplexes with intricately coupled dynamics that are highly dependent on their local protein environment. In addition, cyclohexyl-based linkers are identified as ideal candidates to retain rotational correlations over several nanoseconds and thus lock relative chromophore orientations throughout the lifetime of an exciton. Combining linker engineering with judicious placement of chromophores on the hydrated protein scaffold to exploit different chromophore-bath couplings provides a clear and effective path to producing highly controllable artificial light-harvesting systems that can increasingly mimic their natural counterparts, thus aiding to elucidate natural photosynthetic mechanisms.

Resolving and Controlling Photoinduced Ultrafast Solvation in the Solid State.

Solid-state solvation (SSS) is a solid-state analogue of solvent-solute interactions in the liquid state. Although it could enable exceptionally fine control over the energetic properties of solid-state devices, its molecular mechanisms have remained largely unexplored. We use ultrafast transient absorption and optical Kerr effect spectroscopies to independently track and correlate both the excited-state dynamics of an organic emitter and the polarization anisotropy relaxation of a small polar dopant embedded in an amorphous polystyrene matrix. The results demonstrate that the dopants are able to rotationally reorient on ultrafast time scales following light-induced changes in the electronic configuration of the emitter, minimizing the system energy. The solid-state dopant-emitter dynamics are intrinsically analogous to liquid-state solvent-solute interactions. In addition, tuning the dopant/polymer pore ratio offers control over solvation dynamics by exploiting molecular-scale confinement of the dopants by the polymer matrix. Our findings will enable refined strategies for tuning optoelectronic material properties using SSS and offer new strategies to investigate mobility and disorder in heterogeneous solid and glassy materials.

Dissociation Pathways of the CH2CH2ONO Radical: NO2 + Ethene, NO + Oxirane, and a Non-Intrinsic Reaction Coordinate HNO + Vinoxy Pathway.

We first characterize the dissociation pathways of BrCH2CH2ONO, a substituted alkyl nitrite, upon photoexcitation at 193 nm under collision-free conditions, in a crossed laser-molecular beam scattering apparatus using vacuum ultraviolet photoionization detection. Three primary photodissociation pathways occur: photoelimination of HNO, leading to the products HNO + BrCH2CHO; C-Br bond photofission, leading to Br + CH2CH2ONO; and O-NO bond photofission, leading to NO + BrCH2CH2O. The data show that alkyl nitrites can eliminate HNO via a unimolecular mechanism in addition to the commonly accepted bulk disproportionation mechanism. Some of the products from the primary photodissociation pathways are highly vibrationally excited, so we then probe the product branching from the unimolecular dissociation of these unstable intermediates. Notably, the vibrationally excited CH2CH2ONO radicals undergo two channels predicted by statistical transition-state theory, and an additional non-intrinsic reaction coordinate channel, HNO elimination. CH2CH2ONO is formed with high rotational energy; by employing rotational models based on conservation of angular momentum, we predict, and verify experimentally, the kinetic energies of stable CH2CH2ONO radicals and the angular distribution of dissociation products. The major dissociation pathway of CH2CH2ONO is NO2 + ethene, and some of the NO2 is formed with sufficient internal energy to undergo further photodissociation. Nascent BrCH2CHO and CH2Br are also photodissociated upon absorption of a second 193 nm photon; we derive the kinetic energy release of these dissociations based on our data, noting similarities to the analogous photodissociation of ClCH2CHO and CH2Cl.

Competing C-Br and O-NO Photofission upon Excitation of BrCH2CH2ONO at 193 nm.

This study characterizes two of the primary photodissociation channels of 2-bromoethyl nitrite, BrCH2CH2ONO, at 193 nm and the subsequent unimolecular dissociation channels of the nascent vibrationally excited BrCH2CH2O radicals produced from the O-NO bond photofission. We use a crossed laser-molecular beam scattering apparatus with electron bombardment detection. Upon photodissociation of BrCH2CH2ONO at 193 nm, the measured branching ratio between primary O-NO photofission and C-Br photofission is 3.9:1 (O-NO/C-Br). The measured O-NO photofission recoil kinetic energy distribution (P(ET)) peaks near 30 kcal/mol and extends from 20 to 50 kcal/mol. We use the O-NO photofission P(ET) to characterize the internal energy distribution in the nascent ground-electronic-state BrCH2CH2O radicals. At 193 nm, all of the BrCH2CH2O radicals are formed with enough internal energy to unimolecularly dissociate to CH2Br + H2CO or to BrCH2CHO + H. We also investigated the possibility of the BrCH2CH2O → CH2CHO + HBr reaction arising from the vibrationally excited BrCH2CH2O radicals produced from O-NO primary photodissociation. Signal strengths at HBr(+), however, demonstrate that the vinoxy product does not have HBr as a cofragment, so the BrCH2CH2O → HBr + vinoxy channel is negligible compared to the CH2Br + H2CO channel. We also report our computational prediction of the unimolecular dissociation channels of the vibrational excited CH2CH2ONO radical resulting from C-Br bond photofission. Our theoretical calculations on the ground-state CH2CH2ONO potential energy surface at the G4//B3LYP/6-311++G(3df,2p) level of theory give the energetics of the zero-point corrected minima and transition states. The lowest accessible barrier height for the unimolecular dissociation of CH2CH2ONO is a 12.7 kcal/mol barrier from the cis-ONO conformer, yielding NO2 + ethene. Our measured internal energy distribution of the nascent CH2CH2ONO radicals together with this computational result suggests that the CH2CH2ONO radicals will dissociate to NO2 + ethene, with a small possible branching to NO + oxirane.