Site‐directed mutagenesis was performed to change the substrate specificity of Escherichia coli aspartate aminotransferase (AAT). A double mutant, R292E/L18H, with a 12.9‐fold increase in the ...specific activity toward l‐lysine and 2‐oxo‐4‐phenylbutanoic acid (OPBA) was identified. E. coli cells expressing this mutant enzyme could convert OPBA to l‐homophenylalanine (l‐HPA) with 97% yield and more than 99.9% ee using l‐lysine as amino donor. The transamination product of l‐lysine, 2‐keto‐6‐aminocaproate, was cyclized nonenzymatically to form Δ1‐piperideine 2‐carboxylic acid in the reaction mixture. The low solubility of l‐HPA and spontaneous cyclization of 2‐keto‐6‐aminocaproate drove the reaction completely toward l‐HPA production. This is the first aminotransferase process using l‐lysine as inexpensive amino donor for the l‐HPA production to be reported.
Ce
4+-initiated and plasma-induced grafting polymerization was used to prepare bipolar membranes. The former method used the membrane of copoly(2-hydroxylethylene-methacrylate (2-HEMA)/
...n-butylacrylate (BA)/glycidyl-methacrylate (GMA)) on the surfaces of which were grafted acrylic acid (AA: COO
−) and 4-vinyl pyridine (4VP: NH
+Cl
−), to prepare the bipolar membrane. The latter method utilized the porous PVDF membrane as a substrate, onto one side of which AA (or sodium vinyl sulfonate, SVS) monomer was grafted, and onto the other of which, 4-vinyl pyridine (or
N′,
N-dimethyl amino ethyl acrylate, DMAEA) monomer was grafted. The contact angle of bipolar membranes dramatically decreased when the ionic polymer covered the surface of the membranes by plasma-grafting polymerization. Meanwhile, the swelling level of bipolar membranes was in the range of 25–50%. Furthermore, the cross-section SEM photographs of bipolar membranes further illustrated a sandwich structure that consisted of anionic polymer, cationic polymer and PVDF substrate. The limiting current increased with the diffusion coefficient and the concentration of electrolysis; however, the critical voltage was independent of the concentration and the kind of electrolysis. The 963 of AA–PVDF–DMAEA bipolar membrane exhibited the best ratio of dissociation rate constants (
k
d/
k
d
0) of all membranes. Results concerning the efficiency of the current showed plasma-induced preparation of a bipolar membrane is better than Ce
4+-initiated preparation.
An activated alumina-supported iron oxide-composite (denoted as FeAA-25) was utilized successfully as a catalyst for the heterogeneous photoassisted Fenton degradation of the azo dye C.I. Reactive ...Black 5 (RB5) at a pH of 7.0 in our previous study. In this work, the adsorption and desorption behaviours of RB5 on FeAA-25 were studied. Adsorption thermodynamics of RB5 on FeAA-25 were studied at 288, 303 and 318
K and the thermodynamic parameters, such as equilibrium constant
(
K
0
)
, standard free energy changes
(
Δ
G
0
)
, standard enthalpy change
(
Δ
H
0
)
and standard entropy change
(
Δ
S
0
)
have been obtained. A pseudo-second-order rate model was employed to describe the kinetic adsorption processes. Additionally, desorption studies revealed that RB5 can be easily removed from FeAA-25 by altering the pH of the solution using NaOH. The mechanism of the RB5 adsorption onto FeAA-25 at neutral pH 7.0 will be established through this study.
Solid-state NaBH sub(4)/Ru-based catalyst composites have been fabricated for hydrogen generation through a high-energy ball-milling process, providing uniform dispersion of resin-supported Ru ...super(3+) catalysts among pulverized NaBH sub(4) (SBH) particles, so as to increase the contacts of SBH with active catalytic sites. Consequently, the gravimetric hydrogen storage capacity as high as 7.3 wt% could be achieved by utilizing water as a limiting reagent to overcome the issue of deactivated catalysts whose active sites are often blocked by precipitates caused by limited NaBO sub(2) solubility occurring in conventional aqueous SBH systems for hydrogen productions. Products of hydrolyzed SBH that greatly influence the gravimetric H sub(2) storage capacity are found to be most likely NaBO sub(2) super(.2H) sub(2) and NaBO sub(2) super(.4H) sub(2) from SBH/H sub(2)O reacting systems with initial weight ratios, SBH/H sub(2)O = 1/2 and 1/10, respectively, according to the TGA and XRD analyses.
Solid-state NaBH
4/Ru-based catalyst composites have been fabricated for hydrogen generation through a high-energy ball-milling process, providing uniform dispersion of resin-supported Ru
3+ ...catalysts among pulverized NaBH
4 (SBH) particles, so as to increase the contacts of SBH with active catalytic sites. Consequently, the gravimetric hydrogen storage capacity as high as 7.3
wt% could be achieved by utilizing water as a limiting reagent to overcome the issue of deactivated catalysts whose active sites are often blocked by precipitates caused by limited NaBO
2 solubility occurring in conventional aqueous SBH systems for hydrogen productions. Products of hydrolyzed SBH that greatly influence the gravimetric H
2 storage capacity are found to be most likely NaBO
2·2H
2O and NaBO
2·4H
2O from SBH/H
2O reacting systems with initial weight ratios, SBH/H
2O
=
1/2 and 1/10, respectively, according to the TGA and XRD analyses.
Hydrolysis of sodium borohydride (NaBH sub(4)) is a promising method for on-board hydrogen supply to polymer electrolyte membrane fuel cells (PEMFC). This article presents an attempt to design a ...novel solid-state NaBH sub(4) composite, which is made up of NaBH sub(4) powder, Co super(2+)/IR-120 catalyst and silicone rubber, for hydrogen generator. The silicone rubber can act as a stabilizer in the solid-state NaBH sub(4) composite because of its surface hydrophobicity leading to reduced diffusion rate of water into the composite. The solid-state NaBH sub(4) composite can produce hydrogen stably near 25 mL min super(-1) for at least 2 h without employment of any mechanical control system. Using the hydrogen generated from the solid-state NaBH sub(4) composite, a 2 W PEMFC stack is successfully operated to power a cellular phone.
▶ Ultrapure hydrogen at a stable rate of 25
mL/min was produced from a novel solid-state NaBH
4 composite. ▶ No mechanical control system was in need to maintain the stable production of hydrogen ...from this solid NaBH
4 chemical-hydride system. ▶ A cellular phone was successfully powered at 2
W for 2
h by a PEMFC stack fed with the produced hydrogen. ▶ The generated hydrogen could be successfully converted to electric energy by the PEMFC stack to recharge a 3.7
V/1100
mAh Li-ion battery in 2
h.
Hydrolysis of sodium borohydride (NaBH
4) is a promising method for on-board hydrogen supply to polymer electrolyte membrane fuel cells (PEMFC). This article presents an attempt to design a novel solid-state NaBH
4 composite, which is made up of NaBH
4 powder, Co
2+/IR-120 catalyst and silicone rubber, for hydrogen generator. The silicone rubber can act as a stabilizer in the solid-state NaBH
4 composite because of its surface hydrophobicity leading to reduced diffusion rate of water into the composite. The solid-state NaBH
4 composite can produce hydrogen stably near 25
mL
min
−1 for at least 2
h without employment of any mechanical control system. Using the hydrogen generated from the solid-state NaBH
4 composite, a 2
W PEMFC stack is successfully operated to power a cellular phone.
