Acrylic-Resin-Based Tubular Micromotors Bearing Magnetic Nanoparticles and Enzymes Driven by Visible Light Irradiation: Implications for Accelerating Reactions and Cargo Transport

We present the synthesis of acrylic-resin-based tubular micromotors incorporating layers of magnetite nanoparticles (MNPs) and catalase (Cat) on the inner pore surface (Cat tube micromotors) and investigate their distinctive self-propulsion capabilities modulated by visible light irradiation. In an aqueous H2O2 solution, the Cat tubes demonstrate autonomous movement by expelling O2 bubbles from their opening ends. The propulsion velocity reaches its maximum at the optimal pH and temperature for the Cat enzyme activity. Remarkably, the swimming velocity undergoes rapid acceleration upon exposure to visible light and promptly decelerates upon the cessation of illumination. This phenomenon is ascribed to the photothermal effect induced by the MNPs, elevating the temperature of the adjacent Cat layer and thereby enhancing enzyme activity. The micromotors exhibit recurrent acceleration and deceleration in response to on/off light irradiation, showcasing a high degree of sensitivity and responsiveness

Molecular Capture in Protein Nanotubes

We describe molecular capturing properties of protein nanotubes with a controllable ligand binding affinity and size selectivity. These practical biocylinders were prepared using an alternating layer-by-layer (LbL) assembly of protein and oppositely charged poly(amino acid) into the nanoporous polycarbonate (PC) membrane (pore diameter, 400 nm), with subsequent dissolution of the template. The tube wall typically comprises six layers of poly-l-arginine (PLA) and human serum albumin (HSA) [(PLA/HSA)3]. Use of high molecular weight PLA (Mw = ca. 70 000) yielded robust nanotubes, which are available as lyophilized powder. The (PLA/HSA)3 nanotubes swelled considerably in water, although the outer diameter was almost unaltered. Uranyl ion, 3,3′-diethylthiacarbocyanine iodide, and zinc(II) protoporphyrin IX (ZnPP) were bound to the HSA component in the cylinder wall. Similar nanotubes comprising recombinant HSA mutant [rHSA(His)], which has a strong binding affinity for ZnPP, captured this ligand more tightly. Furthermore, addition of excess myristic acid released ZnPP from the tubes through a ligand replacement reaction. The hybrid nanotubes bearing a single avidin layer as an internal surface captured FITC-biotin efficiently. Biotin-labeled nanoparticles are also incorporated into the tubes when their particle size is sufficiently small to enter the pores. Subsequent TEM observation revealed a line of loaded nanoparticles (100 nm) in the one-dimensional space interior

Acrylic-Resin-Based Tubular Micromotors Bearing Magnetic Nanoparticles and Enzymes Driven by Visible Light Irradiation: Implications for Accelerating Reactions and Cargo Transport

We present the synthesis of acrylic-resin-based tubular micromotors incorporating layers of magnetite nanoparticles (MNPs) and catalase (Cat) on the inner pore surface (Cat tube micromotors) and investigate their distinctive self-propulsion capabilities modulated by visible light irradiation. In an aqueous H2O2 solution, the Cat tubes demonstrate autonomous movement by expelling O2 bubbles from their opening ends. The propulsion velocity reaches its maximum at the optimal pH and temperature for the Cat enzyme activity. Remarkably, the swimming velocity undergoes rapid acceleration upon exposure to visible light and promptly decelerates upon the cessation of illumination. This phenomenon is ascribed to the photothermal effect induced by the MNPs, elevating the temperature of the adjacent Cat layer and thereby enhancing enzyme activity. The micromotors exhibit recurrent acceleration and deceleration in response to on/off light irradiation, showcasing a high degree of sensitivity and responsiveness

Acrylic-Resin-Based Tubular Micromotors Bearing Magnetic Nanoparticles and Enzymes Driven by Visible Light Irradiation: Implications for Accelerating Reactions and Cargo Transport

We present the synthesis of acrylic-resin-based tubular micromotors incorporating layers of magnetite nanoparticles (MNPs) and catalase (Cat) on the inner pore surface (Cat tube micromotors) and investigate their distinctive self-propulsion capabilities modulated by visible light irradiation. In an aqueous H2O2 solution, the Cat tubes demonstrate autonomous movement by expelling O2 bubbles from their opening ends. The propulsion velocity reaches its maximum at the optimal pH and temperature for the Cat enzyme activity. Remarkably, the swimming velocity undergoes rapid acceleration upon exposure to visible light and promptly decelerates upon the cessation of illumination. This phenomenon is ascribed to the photothermal effect induced by the MNPs, elevating the temperature of the adjacent Cat layer and thereby enhancing enzyme activity. The micromotors exhibit recurrent acceleration and deceleration in response to on/off light irradiation, showcasing a high degree of sensitivity and responsiveness

Effect of Heme Structure on O₂-Binding Properties of Human Serum Albumin−Heme Hybrids: Intramolecular Histidine Coordination Provides a Stable O₂−Adduct Complex

5,10,15,20-Tetrakis[(α,α,α,α-o-pivaloylamino)phenyl]porphinatoiron(II) and 5,10,15,20-tetrakis{[α,α,α,α-o-(1-methylcyclohexanoylamino)]phenyl}porphinatoiron(II) complexes bearing a covalently bound 8-(2-methyl-1-imidazolyl)octanoyloxymethyl or 4-(methyl-l-histidinamido)butanoyloxymethyl side-chain [FeRP(B) series:  R = piv or cyc, B = Im or His] have been synthesized. The histidine-bound derivatives [FepivP(His), FecycP(His)] formed five N-coordinated high-spin iron(II) complexes in organic solvents under an N2 atmosphere and showed large O2-binding affinities in comparison to those of the 2-methylimidazole-bound analogues [FepivP(Im), FecycP(Im)] due to the low O2-dissociation rate constants. On the contrary, the difference in the fence groups around the O2-coordination site (pivaloyl or 1-methylhexanoyl) did not significantly influence to the O2-binding parameters. These four porphinatoiron(II)s were efficiently incorporated into recombinant human serum albumin (rHSA), thus providing the synthetic hemoprotein, the albumin−heme hybrid [rHSA−FeRP(B)]. An rHSA host absorbs a maximum of eight FeRP(B) molecules in each case. The obtained rHSA−FeRP(B) can reversibly bind and release O2 under physiological conditions (in aqueous media, pH 7.3, 37 °C) like hemoglobin and myoglobin. As in organic solutions, the difference in the fence groups did not affect their O2-binding parameters, but the axial histidine coordination significantly increased the O2-binding affinity, which is again ascribed to the low O2-dissociation rates. The most remarkable effect of the heme structure appeared in the half-life (τ1/2) of the O2−adduct complex. The dioxygenated rHSA−FecycP(His) showed an unusually long lifetime (τ1/2:  25 h at 37 °C) which is ca. 13-fold longer than that of rHSA−FepivP(Im)

Solid Nanotubes Comprising α-Fe₂O₃ Nanoparticles Prepared from Ferritin Protein

Solid nanotubes comprising α-Fe2O3 nanoparticles were prepared from iron-storage protein ferritin. Their structure, magnetic properties, and photocatalytic activities were characterized. The initial ferritin nanotube precursors were fabricated using alternating layer-by-layer depositions of poly-l-arginine (PLA) and ferritin into a track-etched polycarbonate membrane (pore diameter, 400 nm) with subsequent dissolution of the template. The obtained uniform cylinders of (PLA/ferritin)3 (outer diameter, 410 ± 14 nm) were calcinated at 500 °C under air, yielding reddish-brown iron oxide nanotubes. The one-dimensional hollow structure remained perfect, but its diameter, wall thickness, and maximum length were markedly diminished. Disappearance of the protein shell and the PLA layers were confirmed using IR and EDX spectroscopy. Subsequent SEM, TEM, and XPS measurements showed that the tubular walls comprise fine α-Fe2O3 nanoparticles with a 5 nm diameter. These α-Fe2O3 nanotubes demonstrated superparamagnetic properties with a blocking temperature of 37 K and efficient photocatalytic activity for degradation of 4-chlorophenol

Transparent Protein Microtubule Motors with Controllable Velocity and Biodegradability

Slender protein microtube motors with a catalase interior surface are self-propelled in aqueous H2O2 by jetting O2 microbubbles from the open-end terminus. Immobilization of a catalase biocatalyst on the internal wall is achieved using avidin–biotin complexation. It is particularly interesting that the migration of O2 bubbles in the 1D channel and their subsequent expulsions were clearly visible because the tube walls are transparent. The microtube motor velocity reached a maximum at the optimum pH and temperature of the catalase. Furthermore, the microtubes were digested completely by proteases, showing sufficient biodegradability

Transparent Protein Microtubule Motors with Controllable Velocity and Biodegradability

Slender protein microtube motors with a catalase interior surface are self-propelled in aqueous H2O2 by jetting O2 microbubbles from the open-end terminus. Immobilization of a catalase biocatalyst on the internal wall is achieved using avidin–biotin complexation. It is particularly interesting that the migration of O2 bubbles in the 1D channel and their subsequent expulsions were clearly visible because the tube walls are transparent. The microtube motor velocity reached a maximum at the optimum pH and temperature of the catalase. Furthermore, the microtubes were digested completely by proteases, showing sufficient biodegradability

Human Serum Albumin Hybrid Incorporating Tailed Porphyrinatoiron(II) in the α,α,α,β-Conformer as an O₂-Binding Site

We have found that recombinant human serum albumin (HSA) incorporating tailed porphyrinatoiron(II) in the α,α,α,β-conformer can reversibly bind and release O2 under physiological conditions (pH 7.3, 37 °C) like hemoglobin and myoglobin. β-2-Methylimidazolyl-tailed porphyrinatoirons (6a, 6b) are synthesized via four steps from the atropisomers of tetrakis(o-aminophenyl)porphyrin. The stereochemistry of the α,α,α,β-conformer has been determined by NMR spectroscopy. 6a and 6b form stable O2-adduct complexes in toluene solution at room temperature. The association rate constants of O2 are 3.1- and 1.9-fold lower than those of the corresponding α,α,α,α-conformers (1a, 1b), indicating that the three substituents (cyclohexanamide or pivalamide groups) are close to each other on the porphyrin platform and construct a narrow encumbrance around the O2-coordination site. Although 6a and 6b are incorporated into the hydrophobic domains of HSA to produce the albumin−heme hybrid, only HSA-6a can bind O2 in aqueous medium. The cyclohexanamide fences are necessary for the tailed porphyrinatoiron to form a stable O2-adduct complex under physiological conditions. The O2-binding affinity (P1/2) of HSA-6a is 45 Torr (37 °C), and the O2 transporting efficiency between lungs and muscle tissues in the human body is estimated to be identical to that of human red blood cells. The HSA-6a solution will become one of the most promising materials for red blood cell substitutes, which can be manufactured on an industrial scale

O₂ Binding to Human Serum Albumin Incorporating Iron Porphyrin with a Covalently Linked Methyl-l-Histidine Isomer

We describe the significant difference in the O2 binding affinities of human serum albumin (HSA) incorporating 5,10,15,20-tetrakis{α,α,α,α-o-(1′-methylcyclohexanamido)phenyl}porphinatoiron(II) with a covalently linked 1-methyl-l-histidine or 3-methyl-l-histidine [HSA-FeP(1-MHis), HSA-FeP(3-MHis)]. The HSA-FeP(3-MHis) showed an extraordinarily high O2 binding affinity (P1/2 = 0.2 Torr, 25 °C, pH 7.4), which is close to those of relaxed-state hemoglobin and myoglobin. However, replacement of the 3-methyl-l-histidine moiety in FeP(3-MHis) by 1-methyl-l-histidine caused a 35-fold reduction in O2 affinity; the P1/2 value of HSA-FeP(1-MHis) (22 Torr, 37 °C, pH 7.4) is almost identical to that of human red blood cells. Results of kinetic studies indicate that the low O2 binding affinity of FeP(1-MHis) is predominantly manifested in the high O2 dissociation rate constant. In a toluene solution, an identical relationship in the O2 binding property was similarly observed for FeP(1-MHis) and FeP(3-MHis). The axial Fe-N(1-MHis) coordination might be restrained by steric interaction between the 4-methylene group of the histidine and the porphyrin plane