pH‐induced reorientation of microperoxidase‐11 in mesoporous molecular sieves

Abstract

The resonance Raman spectra of microperoxidase-11 loaded into the siliceous materials MCM-41 and SBA-15 demonstrate a pH dependence indicative of a protonation event on the substrate. An unusual change in relative Raman intensities without a shift in wavenumbers is observed upon lowering the system pH. Protonation of the silica surface is suggested to induce a reorientation of the MP-11 fragments within the silica framework.

Bioelectrocatalytic Reduction of Hydrogen Peroxide by Microperoxidase‐11 Immobilized on Mesoporous Antimony‐Doped Tin Oxide

“…The positions of n 4 at 1373 cm À1 , n 3 at 1506 cm À1 , n 2 at 1586 cm À1 and n 10 at 1640 cm À1 are characteristic of an oxidized six-coordinated lowspin heme iron while the n 3 band at 1480 cm À1 indicates the presence of six-coordinated high-spin species. [32][33][34] In contrast, the RR spectra of MP-11 in a mixed solution with PDADMAC as well as immobilized on PDADMAC-modified mpATO demonstrate that in presence of the polyelectrolyte only the 6cLS species is formed confirming the results obtained by UV/Visspectroscopy. The resemblance of the UV/Vis-and Raman spectra of immobilized MP-11 and MP-11 in solution in presence of PDADMAC indicates that no heme dissociation or severe protein denaturation occurs upon adsorption.…”

“…The RR spectrum of MP‐11 in solution in absence of PDADMAC shows the presence of two species. The positions of ν 4 at 1373 cm −1 , ν 3 at 1506 cm −1 , ν 2 at 1586 cm −1 and ν 10 at 1640 cm −1 are characteristic of an oxidized six‐coordinated low‐spin heme iron while the ν 3 band at 1480 cm −1 indicates the presence of six‐coordinated high‐spin species . In contrast, the RR spectra of MP‐11 in a mixed solution with PDADMAC as well as immobilized on PDADMAC‐modified mpATO demonstrate that in presence of the polyelectrolyte only the 6cLS species is formed confirming the results obtained by UV/Vis‐spectroscopy.…”

Adsorption of Microperoxidase-11 in Vertical Silica Mesochannels and Electrochemical Investigation of Its Electron Transfer Properties

“…At pH 4.00, MP-11 is positively charged and water serves as the sixth ligand of Fe(III) atom. In this case, the monomer is its main form in the solution [13,18], which displays a characteristic spectrum of a ferric heme group with a strong Soret band at 396 nm, a poorly resolved Q band in the 500 $ 600 nm range and a shoulder due to ligand-to-metal transfer at about 620 nm (see the black curve). Upon increasing the solution pH to 4.85 and 5.39, the spectrum exhibits a split Soret band with a shoulder at the longer wavelength side and an increase in intensity of the Q band (see the red and blue curves).…”

“…In addition, at a higher pH (6.08) an apparent Q band at ca. 530 nm and a shoulder on the right side due to low-spin heme complex were displayed (see the red, blue and green curves), which is a signature of the formation of polymeric MP-11 [13,14,16,18,33,34].…”

“…Clearly, the problem of aggregation has to be overcome if MP-11 is to be useful as a model of hemoproteins. The prevention of MP-11 aggregate formation has been accomplished by the use of strongly coordinating axial ligands, the addition of appropriate detergents/organic solvents, the derivation of the undecapeptide chain or the immobilization of MP-11 in a suitable host structure [3,7,9,14,[17][18][19][20][21][22]. Herein we demonstrate that silica mesochannels (SMCs) vertically attached to the electrode surface are well suited to act as the nanometer-sized hosts for encapsulation of MP-11 monomers (see Scheme 1b).…”