Adsorption properties of protein Papain at the solid|liquid (0.1 M KCl) interfaces of different hydrophobicity [highly oriented pyrolytic graphite (HOPG), bare gold, CH3, OH, and COOH-terminated self-assembled monolayers on gold] were studied by a combined quartz crystal microbalance and atomic force microscopy techniques. It was found that Papain forms an incomplete monolayer at hydrophobic interfaces (HOPG and CH3-terminated substrate), whereas on more hydrophilic ones, a complete monolayer formation was always observed with either the onset of the formation of a second layer (bare gold substrate) or adsorption in a multilayer fashion, possibly a bilayer formation (OH-terminated substrate). The surface concentration and compact monolayer film thickness was much lower on the COOH-terminated substrate compared to other surfaces studied. This result was explained by partial dissociation of the interfacial COOH groups leading to additional electrostatic interactions between the positively charged protein domains and negatively charged carboxylate anions, as well as to local pH changes promoting protein denaturation.
Air nanobubbles and nanopancakes were investigated in situ by both tapping mode atomic force microscopy (TM AFM) and atomic force nanolithography techniques employing bovine serum albumin (BSA) film supported by highly oriented pyrolytic graphite (HOPG). The BSA denaturation induced by the water-to-ethanol exchange served for conservation of nanobubble and nanopancake sites appearing as imprints in BSA film left by gaseous cavities formerly present on the interface in the aqueous environment. Once the BSA film was gently removed by the nanoshaving technique applied in ethanol, a clean basal plane HOPG area with well-defined dimensions was regenerated. The subsequent reverse ethanol-to-water exchange led to the re-formation of nanopancakes specifically at the nanoshaved area. Our approach paves the way for the study of gaseous nanostructures with defined dimensions, formed at solid-liquid interface under controlled conditions.
- MeSH
- ethanol MeSH
- grafit chemie MeSH
- mikroskopie atomárních sil MeSH
- nanostruktury chemie ultrastruktura MeSH
- nanotechnologie MeSH
- plyny MeSH
- povrchové vlastnosti MeSH
- sérový albumin hovězí chemie MeSH
- skot MeSH
- voda MeSH
- vzduch MeSH
- zvířata MeSH
- Check Tag
- skot MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Nanobubbles formed on monocrystalline gold/water interface by means of the ethanol-to-water solvent exchange were exposed to the solutions of either bovine serum albumin or papain proteins. Both proteins do not change the position of nanobubbles in water, as observed by in situ tapping mode atomic force microscopy imaging before and after the introduction of the protein. The aqueous environment was subsequently replaced by ethanol. While all nanobubbles were found to dissolve in ethanol in the presence of bovine serum albumin, most of them survived when papain was employed. The protective ability of papain was ascribed to its resistance towards the protein denaturation in aqueous solutions of ethanol. The authors employed in situ atomic force nanolithography to investigate the nanomorphology of the papain/nanobubble assemblies in ethanol.
- MeSH
- ethanol chemie MeSH
- nanostruktury chemie MeSH
- papain metabolismus MeSH
- povrchové vlastnosti MeSH
- sérový albumin hovězí metabolismus MeSH
- skot MeSH
- voda chemie MeSH
- zlato metabolismus MeSH
- zvířata MeSH
- Check Tag
- skot MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Cytotoxic properties of radiosensitizers are due to the fact that, in the metabolic pathway, these compounds undergo one-electron reduction to generate radical anions. In this study we focused our interest on the electrochemical transfer of the first electron on radiosensitizer Etanidazole (ETN) and, consequently, on the ETN radical-anion formation in the buffered aqueous media. ETN was electrochemically treated in the broad pH range at various scan rates. Three reduction peaks and one oxidation peak were found. At strong alkaline pH the four-electron reduction peak was separated into one-electron and three-electron reductions. Under these conditions the standard rate constant k(0) for the redox couple ETN-NO(2)+e(-) <--> ETN-NO(2)(*-) was calculated. Moreover, the value of a so called E(7)(1) potential that accounts for the energy necessary to transfer the first electron to an electroactive group at pH=7 in aqueous medium to form a radical anion was also determined. The obtained value of E(7)(1) indicates that lower energy compared to the other possible chemical radiosensitizers is necessary for the system to transfer the first electron to ETN. On the other hand, the necessity of the strong alkaline pH may decrease the ability of ETN to act as hypoxic radiosensitizer in the human body.
- MeSH
- anionty chemie MeSH
- elektrická vodivost MeSH
- elektrochemie MeSH
- etanidazol chemie MeSH
- hypoxie buňky MeSH
- kinetika MeSH
- koncentrace vodíkových iontů MeSH
- radiosenzibilizující látky chemie MeSH
- transport elektronů MeSH
- voda chemie MeSH
- volné radikály chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The oxidation mechanism of hematoxylin was studied in phosphate buffers and 0.1 M KCl by cyclic voltammetry and UV-Vis spectroscopy under deaerated conditions. The redox potential of hematoxylin in buffered solution strongly depends on pH. A two electron oxidation is preceded by deprotonation. The homogeneous rate of deprotonation process of hematoxylin in 0.1 M phosphate buffer is kd = (2.5 ± 0.1) × 104 s–1. The cyclic voltammetry under unbuffered conditions shows the distribution of various dissociation forms of hematoxylin. The dissociation constants pK1 = 4.7 ± 0.2 and pK2 = 9.6 ± 0.1 were determined using UV-Vis spectroscopy. The final oxidation product was identified by gas chromatography with mass spectrometry detection as hemathein. The distribution of oxidation products differs under buffered and unbuffered conditions. The dye degradation in natural unbuffered environment yields hemathein and hydroxyhematoxylin, which is absent in buffered solution.
Electrochemical transfer of the first electron to cytotoxic radiosensitizer etanidazole (ETN) and ETN radical anion formation in the alkaline buffered aqueous solution were studied by means of electrochemical impedance spectroscopy (EIS). The heterogeneous electron transfer rate constant for the first reduction of ETN (radical anion production), k0, was calculated. The value of k0 from EIS measurements and the previously obtained value of so-called E71 potential indicate that ETN, compared with other possible chemical radiosensitizers, requires lower energy to accept the first electron during the metabolic pathway. However, the necessity of the alkaline pH may decrease the ability of ETN to act as hypoxic radiosensitizer in the human body.
The reduction of nitroaromatic compound bifenox (methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate) was studied in aprotic solvents in the absence or presence of cyclodextrin (CD) molecules of different cavity sizes. ßCD and ?CD form complexes with bifenox in DMSO with the complex formation constants (5 ± 2) × 102 M–1 [ßCD–bifenox] and (3 ± 1) × 102 M–1 [?CD–bifenox], respectively. Bifenox yields a relatively stable anion radical in dimethyl sulfoxide, which is further reduced at more negative potentials by an overall addition of three electrons and four protons to the corresponding phenylhydroxylamine. In the presence of ßCD the first reduction wave of bifenox becomes irreversible, it is shifted towards more positive potentials and the uptake of more than one electron is observed (up to four electrons during the exhaustive electrolysis). The first reduction wave of bifenox is not affected by the addition of glucose confirming that a simple availability of protons from the OH groups is not the main factor in further transformation of anion radical in the presence of ßCD. The complex formation with ßCD facilitates the protonation and additionally protects the molecule from disintegration into 2,4-dichlorophenol. A yield of 2,4-dichlorophenol decreases in the order ßCD, ?CD and ?CD, respectively.
This contribution pays a tribute to a humble and talented physical chemist, Professor Heyrovsky, who was for his achievements awarded, as the only Czechoslovak scientist, the Nobel Prize in chemistry on 10th December, 1959.
- MeSH
- ateroskleróza komplikace patofyziologie prevence a kontrola MeSH
- chronická nemoc MeSH
- dospělí MeSH
- hyperlipidemie epidemiologie komplikace terapie MeSH
- ischemická choroba srdeční patofyziologie prevence a kontrola terapie MeSH
- lidé MeSH
- Check Tag
- dospělí MeSH
- lidé MeSH
- Publikační typ
- směrnice pro lékařskou praxi MeSH
