Interfacial electron transfer kinetics of myoglobins chemically modified with succinic anhydride at an indium oxide electrode

The overview of analytical methods for studying of fossil natural resins

The review presents methods that are used frequently for multi-analytical study of fossil resins. The preliminary characterization relies on physical methods such as microhardness, density and fluorescence in UV light measurements. The spectroscopic methods: infrared spectroscopy, Raman spectroscopy, fluorescence spectroscopy are also presented in the paper. Besides that, the review also contains examples of the application of chromatographic methods: gas chromatography, thin layer chromatography, high-performance liquid chromatography, two-dimensional gas chromatography coupled to time-of-flight mass spectrometry as well as sample preparation methods for chromatographic studies such as pyrolysis. Additionally, thermal methods such as thermogravimetric analysis and differential scanning calorimetry also are covered by the review. Beside the examples of application, a detailed description with development history and perspective for further improvement are presented for each method. Moreover, fit-for-purpose assessment of each method is illustrated based on many examples from literature. The paper also contains examples of the application of multivariate statistical analysis and chemometric methods for comparing multiple properties of different fossil resin specimens for differentiation and classification purposes.

Long-range electron transfer with myoglobin immobilized at Au/mixed-SAM junctions: mechanistic impact of the strong protein confinement

Horse muscle myoglobin (Mb) was tightly immobilized at Au-deposited ~15-Å-thick mixed-type (1:1) alkanethiol SAMs, HS-(CH₂)₁₁-COOH/HS-(CH₂)₁₁-OH, and placed in contact with buffered H₂O or D₂O solutions. Fast-scan cyclic voltammetry (CV) and a Marcus-equation-based analysis were applied to determine unimolecular standard rate constants and reorganization free energies for electron transfer (ET), under variable-temperature (15-55 °C) and -pressure (0.01-150 MPa) conditions. The CV signal was surprisingly stable and reproducible even after multiple temperature and pressure cycles. The data analysis revealed the following values: standard rate constant, 33 s⁻¹ (25 °C, 0.01 MPa, H₂O); reorganization free energy, 0.5 ± 0.1 eV (throughout); activation enthalpy, 12 ± 3 kJ mol⁻¹; activation volume, -3.1 ± 0.2 cm³ mol⁻¹; and pH-dependent solvent kinetic isotope effect (k(H)⁰/k(D)⁰), 0.7-1.4. Furthermore, the values for the rate constant and reorganization free energy are very similar to those previously found for cytochrome c electrostatically immobilized at the monocomponent Au/HS-(CH₂)₁₁-COOH junction. In vivo, Mb apparently forms a natural electrostatic complex with cytochrome b₅ (cyt-b₅) through the "dynamic" (loose) docking pattern, allowing for a slow ET that is intrinsically coupled to the water's removal from the "defective" heme iron (altogether shaping the biological repair mechanism for Mb's "met" form). In contrary, our experiments rather mimic the case of a "simple" (tight) docking of the redesigned (mutant) Mb with cyt-b₅ (Nocek et al. J. Am. Chem. Soc. 2010, 132, 6165-6175). According to our analysis, in this configuration, Mb's distal pocket (linked to the "ligand channel") seems to be arrested within the restricted configuration, allowing the rate-determining reversible ET process to be coupled only to the inner-sphere reorganization (minimal elongation/shortening of an Fe-OH₂ bond) rather than the pronounced detachment (rebinding) of water and, hence, to be much faster.