Energy transfer dynamics and the mechanism of biohybrid photosynthetic antenna complexes chemically linked with artificial chromophores.

A light-harvesting strategy is crucial for the utilisation of solar energy. In this study, we addressed the expanding light-harvesting (LH) wavelength of photosynthetic LH complex 2 (LH2, from Rhodoblastus acidophilus strain 10050) through covalent conjugation with extrinsic chromophores. To further understand the conjugation architecture and mechanism of excitation energy transfer (EET), we examined the effects of the linker length and spectral overlap integral between the emission and absorption spectra of the energy donor and acceptor pigments. In the former case, contrary to the intuition based on the Förster resonance energy transfer (FRET) theory, the observed energy transfer rate was similar regardless of the linker length, and the energy transfer efficiency increased with longer linkers. In the latter case, despite the energy transfer rate increases at higher spectral overlaps, it was quantitatively inconsistent with the FRET theory. The mechanism of EET beyond the FRET theory was discussed in terms of the higher-lying exciton state of B850, which mediates efficient EET despite the small spectral overlap. This systematic investigation provides insights for the development of efficient artificial photosynthetic systems.

Extension of Light-Harvesting Ability of Photosynthetic Light-Harvesting Complex 2 (LH2) through Ultrafast Energy Transfer from Covalently Attached Artificial Chromophores.

Introducing appropriate artificial components into natural biological systems could enrich the original functionality. To expand the available wavelength range of photosynthetic bacterial light-harvesting complex 2 (LH2 from Rhodopseudomonas acidophila 10050), artificial fluorescent dye (Alexa Fluor 647: A647) was covalently attached to N- and C-terminal Lys residues in LH2 α-polypeptides with a molar ratio of A647/LH2 ≃ 9/1. Fluorescence and transient absorption spectroscopies revealed that intracomplex energy transfer from A647 to intrinsic chromophores of LH2 (B850) occurs in a multiexponential manner, with time constants varying from 440 fs to 23 ps through direct and B800-mediated indirect pathways. Kinetic analyses suggested that B800 chromophores mediate faster energy transfer, and the mechanism was interpretable in terms of Förster theory. This study demonstrates that a simple attachment of external chromophores with a flexible linkage can enhance the light harvesting activity of LH2 without affecting inherent functions of energy transfer, and can achieve energy transfer in the subpicosecond range. Addition of external chromophores, thus, represents a useful methodology for construction of advanced hybrid light-harvesting systems that afford solar energy in the broad spectrum.

A wheelchair operation assistance control for a wearable robot using the user's residual function.

Cervical Cord Injury (CCI) is a dysfunction of the upper limb. In an individual with C5-level CCI, which is the most frequent of all eight levels, force can be applied in the direction of flexion by the biceps brachii, but extension force cannot be applied because of the triceps brachii paralysis. Persons with C5-level CCI therefore cannot operate a wheelchair up an incline and over carpet. In this study, we estimated the wheelchair velocity during elbow flexion depending on the angular velocity of the elbow. A wearable assistive robot can assist with the elbow extension movement using this estimated velocity while the wheelchair is being operated.

Control of wearable motion assist robot for upper limb based on the equilibrium position estimation.

In this paper, we propose a robotic system for assisting patients who have upper limb dysfunction in performing reaching movements through flexion. Since upper limb motion is more strongly needed than lower limb mobility for near work, a patient's level of recovery of upper limb function influences daily life. Recently, with the widespread application of robotic technology in rehabilitation medicine, active movement has often been noted to be more important than passive movement for rapid recovery. A novel control method for assisting upper limb movement by using a control system with two degrees of freedom is proposed. In the process of estimating the trajectory, the minimum jerk criterion is used to compute the velocity trajectory and to determine the reach position. The aim is to eventually develop a movement assistance system for the upper limb which will enable wearers to perform flexion and extension covering ranges of motion which are otherwise impossible to achieve autonomously. The effectiveness of the developed system is demonstrated experimentally.