Rapid Exciton Migration and Amplified Funneling Effects of Multi-Porphyrin Arrays in a Re(I)/Porphyrinic MOF Hybrid for Photocatalytic CO2 Reduction.

A porphyrinic metal-organic framework (PMOF) known as PCN-222(Zn) was chemically doped with a molecular Re(I) catalyst-bearing carboxylate anchoring group to form a new type of metal-organic framework (MOF)-Re(I) hybrid photocatalyst. The porphyrinic MOF-sensitized hybrid (PMOF/Re) was prepared with an archetypical CO2 reduction catalyst, (L)ReI(CO)3Cl (Re(I); L = 4,4'-dicarboxylic-2,2'-bipyridine), in the presence of 3 vol % water produced CO with no leveling-off tendency for 59 h to give a turnover number of ≥1893 [1070 ± 80 µmol h-1 (g MOF)-1]. The high catalytic activity arises mainly from efficient exciton migration and funneling from photoexcited porphyrin linkers to the peripheral Re(I) catalytic sites, which is in accordance with the observed fast exciton (energy) migration (≈1 ps) in highly ordered porphyrin photoreceptors and the effective funneling into Re(I) catalytic centers in the Re(I)-doped PMOF sample. Enhanced catalytic performance is convincingly supported by serial photophysical measurements including decisive Stern-Volmer interpretation.

Fungal melanin as a biocompatible broad-spectrum sunscreen with high antioxidant activity.

Melanin is considered a bio-inspired dermo-cosmetic component due to its high UV absorption and antioxidant activity. Among various melanin sources, fungal melanin is a promising candidate for sunscreen because of its sustainability and scalability; however, quantitative assessment of its function has not yet been sufficiently explored. In this study, melanin samples derived from Amorphotheca resinae were prepared, followed by the evaluation of their sunscreen performance, antioxidant activity, and cytotoxicity. Melanin-blended cream was prepared by blending a melanin suspension and a pure cream. The cream showed an in vitro sun protection factor value of 2.5 when the pigment content was 5%. The cream showed a critical wavelength of approximately 388 nm and a UVA/UVB ratio of more than 0.81, satisfying the broad-spectrum sunscreen requirement. Oxygen radical absorbance capacity assays indicated that fungal melanin had antioxidant activity similar to ascorbic acid but higher than reduced glutathione. Fungal melanin had no statistically significant cytotoxicity to human keratinocyte cell lines until 72 h of exposure, even at a concentration of 4 mg mL-1. Consequently, melanin pigment can be used as a biocompatible broad-spectrum sunscreen with high antioxidant activity and as a practical alternative in dermo-cosmetic formulations.

Vision-Based Suture Tensile Force Estimation in Robotic Surgery.

Compared to laparoscopy, robotics-assisted minimally invasive surgery has the problem of an absence of force feedback, which is important to prevent a breakage of the suture. To overcome this problem, surgeons infer the suture force from their proprioception and 2D image by comparing them to the training experience. Based on this idea, a deep-learning-based method using a single image and robot position to estimate the tensile force of the sutures without a force sensor is proposed. A neural network structure with a modified Inception Resnet-V2 and Long Short Term Memory (LSTM) networks is used to estimate the suture pulling force. The feasibility of proposed network is verified using the generated DB, recording the interaction under the condition of two different artificial skins and two different situations (in vivo and in vitro) at 13 viewing angles of the images by changing the tool positions collected from the master-slave robotic system. From the evaluation conducted to show the feasibility of the interaction force estimation, the proposed learning models successfully estimated the tensile force at 10 unseen viewing angles during training.

Organic-inorganic hybrid photocatalyst for carbon dioxide reduction.

Efficient hybrid photocatalysts for carbon dioxide reduction were developed from dye-sensitized TiO2 nanoparticles and their catalytic performance was optimized by ternary organic/inorganic components. Thus, the hybrid system consists of (E)-2-cyano-3-(5'-(5''-(p-(diphenylamino)phenyl)thiophen-2''-yl)thiophen-2'-yl)-acrylic acid as a sensitizer and fac-[Re(4,4'-bis(diethoxyphosphorylmethyl)-2,2'-bipyridine)(CO)3Cl] as a reduction catalyst (ReP), both of which have been fixed onto TiO2 semiconductors (s-TiO2, h-TiO2, d-TiO2). Mott-Schottky analysis on flat-band potential (Efb) of TiO2 mesoporous films has verified that Efb can be finely modulated by volume variation of water (0 to 20 vol%). The increase of added water resulted in substantial positive shifts of Efb from -1.93 V at 0 vol% H2O, to -1.74 V (3 vol% H2O), to -1.56 V (10 vol% H2O), and to -1.47 V (20 vol% H2O). As a result, with addition of 3-10 vol% water in the photocatalytic reaction, conversion efficiency of CO2 to CO increased significantly reaching a TON value of ∼350 for 30 h. Catalytic activity enhancement is mainly attributed to (1) the optimum alignment of Efb by 3-10 vol% water with respect to the of the dye and Ered of ReP for smooth electron transfer from photo-excited dye to RePvia the TiO2 semiconductor and (2) the water-induced acceleration of chemical processes on the fixed ReP. In addition, the energy level was further tuned by variation of the dye and ReP amounts. We also found that the intrinsic properties of TiO2 sources (morphology, size, agglomeration) exert a great influence on the overall photocatalytic activity of this hybrid system. Implications of the present observations and reaction mechanisms are discussed in detail.

Widely Controllable Syngas Production by a Dye-Sensitized TiO2 Hybrid System with ReI and CoIII Catalysts under Visible-Light Irradiation.

Visible-light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H2 evolving CoIII catalyst and a CO-producing ReI catalyst on TiO2 have been found to produce both H2 and CO (syngas) in CO2 -saturated N,N-dimethyl formamide (DMF)/water solution containing a 0.1 m sacrificial electron donor. The H2 /CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the ReI and CoIII catalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO2 to each of the CO2 -reduction and hydrogen-evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.

Highly Robust Hybrid Photocatalyst for Carbon Dioxide Reduction: Tuning and Optimization of Catalytic Activities of Dye/TiO2/Re(I) Organic-Inorganic Ternary Systems.

Herein we report a detailed investigation of a highly robust hybrid system (sensitizer/TiO2/catalyst) for the visible-light reduction of CO2 to CO; the system comprises 5'-(4-[bis(4-methoxymethylphenyl)amino]phenyl-2,2'-dithiophen-5-yl)cyanoacrylic acid as the sensitizer and (4,4'-bis(methylphosphonic acid)-2,2'-bipyridine)Re(I)(CO)3Cl as the catalyst, both of which have been anchored on three different types of TiO2 particles (s-TiO2, h-TiO2, d-TiO2). It was found that remarkable enhancements in the CO2 conversion activity of the hybrid photocatalytic system can be achieved by addition of water or such other additives as Li(+), Na(+), and TEOA. The photocatalytic CO2 reduction efficiency was enhanced by approximately 300% upon addition of 3% (v/v) H2O, giving a turnover number of ≥570 for 30 h. A series of Mott-Schottky (MS) analyses on nanoparticle TiO2 films demonstrated that the flat-band potential (V(fb)) of TiO2 in dry DMF is substantially negative but positively shifts to considerable degrees in the presence of water or Li(+), indicating that the enhancement effects of the additives on the catalytic activity should mainly arise from optimal alignment of the TiO2 V(fb) with respect to the excited-state oxidation potential of the sensitizer and the reduction potential of the catalyst in our ternary system. The present results confirm that the TiO2 semiconductor in our heterogeneous hybrid system is an essential component that can effectively work as an electron reservoir and as an electron transporting mediator to play essential roles in the persistent photocatalysis activity of the hybrid system in the selective reduction of CO2 to CO.