The kinetics of protein adsorption/desorption onto peptide microarrays was studied using real-time surface plasmon resonance (SPR) imaging. S protein binding interactions were examined using an array composed of five different peptides: N terminal and C terminal immobilized wild-type S peptide (S1 and S2), an alternate binding sequence derived by phage display (LB2), an NVOC-protected S peptide, and a FLAG peptide control sequence (F). Kinetic measurements of the S protein-S1 peptide interaction were analyzed to determine a desorption rate constant (k(d)) of 1.1 (+/-0.08) x 10(-2) s(-1), an adsorption rate constant (k(a)) of 1.9 (+/-0.05) x 10(5) M(-1) s(-1), and an equilibrium adsorption constant (K(Ads)) of 1.7 (+/-0.08) x 10(7) M(-1). SPR imaging equilibrium measurements of S protein to S1 peptide were performed to independently confirm the kinetically determined value of K(Ads). Rate constants for the S2 and LB2 peptides on the array were measured as follows: 1.6 (+/-0.04) x 10(5) M(-1) s(-1) (k(a)) and 1.1 (+/-0.07) x 10(-2) s(-1) (k(d)) for S2, 1.2 (+/-0.05) x 10(5) M(-1) s(-1) (k(a)) and 1.1 (+/-0.03) x 10(-2) s(-1) (k(d)) for LB2. In addition to S protein adsorption/desorption, real-time SPR imaging of peptide arrays was applied to study the surface enzymatic activities of the protease factor Xa. Enzymatic cleavage of the substrate peptide (P1) was shown to follow first-order kinetics and proceed at a rate 10 times faster than that of the mutant peptide (P2), with cleavage velocities of 5.6 (+/-0.3) x 10(-4) s(-1) for P1 and 5.7 (+/-0.3) x 10(-5) s(-1) for P2.

Electrochemical reduction of CO2 with high current density was studied in a CO2-methanol medium. The mole fraction of CO2 in this medium varied from 0.7% to 94% with changing the pressure of the system from 1 to 60 atm. Carbon dioxide was reduced to CO, CH4, C2H4, and methyl formate at a Cu electrode. A methyl group and a formyl group of methyl formate are derived from methanol and CO2, respectively. Methyl formate production in this system corresponds to formic acid formation in aqueous systems. A Tafel plot obtained at 40 atm (the mole fraction of CO2 is 33%) indicated that the reduction of CO2 to CO was no longer limited by mass transfer of CO2. Total current density and current efficiency of CO2 reduction at -2.3 V were 436 mA cm-2 and 87%, respectively, at 40 atm. The studied pressure range, 0-60 atm, was classified into three regions with boundaries at 20 and 40 atm; 20 atm was the point above which the mass transfer of CO2 is sufficiently high for the reaction under the current density of 200 mA cm-2, and 40 atm was the point at which the significant change occurs in the property of CO2-methanol medium. Reduction of CO2 to CO and methyl formate proceeded even at 60 atm, at which the mole fraction of CO2 is 94%.

No abstract

No abstract

Self-limiting reactions of ammonium salt in CHF3/O2 downstream plasma were demonstrated for thermal-cyclic atomic layer etching (ALE) of Si3N4. In situ x-ray photoelectron spectroscopy analysis shows that an (NH4)2SiF6 by-product of the same thickness forms on Si3N4 in a wide gas composition range. The (NH4)2SiF6 layer prevents etching of Si3N4 during continuous plasma exposure in that wide range. The (NH4)2SiF6 layer was sublimated by heating, which was consistent with the result of the thermodynamic calculation. The reactions of the (NH4)2SiF6 layer in CHF3/O2 downstream plasma are used for thermal-cyclic ALE of Si3N4 with a newly developed 300-mm tool equipped with an in situ ellipsometer. It was confirmed that the amount etched per cycle saturates with respect to both plasma exposure time and infrared irradiation time.