Probes and Polymers for Optical Sensing of Oxygen

Oxygen detection techniques are used in various fields, such as chemical or clinical analysis and environmental monitoring. Recently, a variety of devices and sensors based on photo-luminescent or photoexcited state quenching of organic dyes have been developed to measure oxygen partial pressure on the solid surface. Many optical oxygen sensors are composed of organic dyes, such as polycyclic aromatic hydrocarbons (pyrene, pyrene derivative etc.), transition metal complexes (Ru²⁺, Os²⁺, Ir³⁺ etc.), metalloporphyrins (Pt²⁺, Pd²⁺, Zn²⁺ etc.) and fullerene (C₆₀ and C₇₀) immobilized in oxygen permeable polymer films. In this review, the properties of various oxygen permeable polymers for matrix of optical oxygen sensor and various dye probes for oxygen sensing are described.Received November 19, 2002; accepted May 14, 2003 published online August 22, 2003     

Noninvasive depth profiling of walls by portable nuclear magnetic resonance

A compact and mobile single-sided ¹H NMR sensor, the NMR-MOUSE®, has been employed in the nondestructive characterization of the layer structure of historic walls and wall paintings. Following laboratory tests on a model hidden fresco, paint and mortar layers were studied at Villa Palagione and the Seminario Vescovile di Sant’ Andrea in Volterra, Italy. Different paint and mortar layers were identified, and further characterized by portable X-ray fluorescence spectroscopy where accessible. In the detached and restored fresco “La Madonna della Carcere” from the Fortezza Medicea in Volterra, paint and mortar layers were discriminated and differences in the moisture content of the adhesive that fixes the detached wall painting to its support were found in both restored and original sections. These investigations encourage the use of the portable and single-sided NMR technology for nondestructive studies of the layer structure and conservation state of historic walls.

Electrochemical determination of the total antioxidant capacity of human plasma

Electrochemical reduction of oxygen at a glassy carbon electrode in a 0.05 mol L^–1 solution of (C₂H₅)₄NI in dimethylformamide leads to generation of the superoxide anion-radical. This product of reversible one-electron oxygen reduction reacts with antioxidants, a process which is based on protonation of the anion-radical by the antioxidant. Rate constants of this interaction have been calculated. Human plasma antioxidants also react with electrochemically generated superoxide anion-radical. A voltammetric method is proposed for estimation of the total antioxidant capacity (TAC) of plasma on the basis of on this reaction. The TAC of plasma was also determined using constant-current coulometry with electrogenerated bromine as the active species. A correlation was observed between TAC data obtained by voltammetry ( , in -tocopherol units) and coulometry (Br₂ as titrant). TAC of plasma from patients with purulent infections was determined. Statistically significant differences were found between TAC of patients and control group. Treatment of purulent infections increases the TAC of plasma. So, use of electrochemical methods (voltammetry and coulometry) for determination of TAC can be used for estimation of the effectiveness of treatment.     

Investigation of the Expansion of an Oxygen Microwave Remote Plasma for the Growth of Functional Oxide Thin Films

The expansion of an oxygen low-pressure microwave plasma was investigated in order to determine the optimal plasma parameters for the growth of functional oxide semiconductors. Langmuir probe measurements show that the electron density (n _e ) increases with the injected power up to a saturation value of 3.0 × 10⁹ cm^?3 determined at 10 mTorr while electron temperature (T _e ) remains constant at a value of 1.5 eV. When pressure is varied, n _e shows a maximum value at a range from 12 to 20 mTorr while T _e decreases monotonously with increasing pressure. In addition, both n _e and T _e decrease with the axial distance from the plasma source. These effects were discussed through the loss mechanisms in the remote plasma. For a pressure of 13 mTorr and at a substrate temperature of 500 °C, plasma enhanced oxidation of pure metallic Ti thin films lead to the formation of a pure TiO₂ anatase phase compared to a mixed phase of TiO₂ and TiO in the absence of plasma activation. For Mn thin films, the exposure to oxygen remote plasma led to the formation of MnO₂ as opposed to obtaining Mn₃O₄ when oxidation is performed in the oxygen gas ambient. Remote plasma processing was thus found to provide selective pathways to control oxidation states, stoichiometry and phase composition of technologically attractive oxide thin films.     

Effect of MnO2 and α-Fe2O3 on organic binders degradation investigated by Raman spectroscopy

Vibrational spectroscopy and GC–MS were used to investigate the effect of MnO₂ and α-Fe₂O₃ on the degradation of methyl linoleate and vegetal and animal fatty. The metal oxides are among the most employed pigments in rock art paintings, whereas the organic compounds were used to mimic organic binders potentially used in such paintings.Both oxides were very effective in the catalytic oxidation of the organic substrates and light had no significant effect, qualitatively or quantitatively, on the final products. In the case of methyl linoleate without metal oxide, the effect of light (visible) was investigated and it was demonstrated that the samples kept in the dark produced relatively less oxidation products, although the main products were the same (hexanal, methyl 9-oxononanoate and methyl octanoate). In the presence of MnO₂ and α-Fe₂O₃ methyl 9-oxononanoate was the main product, followed by hexanal. The spectral patterns of the oxidation products were different for manganese and iron oxide and GC–MS demonstrated that more compounds are formed in the former than with α-Fe₂O₃. Vegetal and animal fatty presented the same behavior that methyl linoleate did.The results here reported indicated that the two pigments considered actively contribute to fat degradation and the presence of inorganic pigments is the main factor to take into account when organic binders degradation in rock art paintings are investigated.     

δ 15N measurement of organic and inorganic substances by EA-IRMS: a speciation-dependent procedure

Little attention has been paid so far to the influence of the chemical nature of the substance when measuring δ ¹⁵N by elemental analysis (EA)–isotope ratio mass spectrometry (IRMS). Although the bulk nitrogen isotope analysis of organic material is not to be questioned, literature from different disciplines using IRMS provides hints that the quantitative conversion of nitrate into nitrogen presents difficulties. We observed abnormal series of δ ¹⁵N values of laboratory standards and nitrates. These unexpected results were shown to be related to the tailing of the nitrogen peak of nitrate-containing compounds. A series of experiments were set up to investigate the cause of this phenomenon, using ammonium nitrate (NH₄NO₃) and potassium nitrate (KNO₃) samples, two organic laboratory standards as well as the international secondary reference materials IAEA-N1, IAEA-N2—two ammonium sulphates [(NH₄)₂SO₄]—and IAEA-NO-3, a potassium nitrate. In experiment 1, we used graphite and vanadium pentoxide (V₂O₅) as additives to observe if they could enhance the decomposition (combustion) of nitrates. In experiment 2, we tested another elemental analyser configuration including an additional section of reduced copper in order to see whether or not the tailing could originate from an incomplete reduction process. Finally, we modified several parameters of the method and observed their influence on the peak shape, δ ¹⁵N value and nitrogen content in weight percent of nitrogen of the target substances. We found the best results using mere thermal decomposition in helium, under exclusion of any oxygen. We show that the analytical procedure used for organic samples should not be used for nitrates because of their different chemical nature. We present the best performance given one set of sample introduction parameters for the analysis of nitrates, as well as for the ammonium sulphate IAEA-N1 and IAEA-N2 reference materials. We discuss these results considering the thermochemistry of the substances and the analytical technique itself. The results emphasise the difference in chemical nature of inorganic and organic samples, which necessarily involves distinct thermochemistry when analysed by EA-IRMS. Therefore, they should not be processed using the same analytical procedure. This clearly impacts on the way international secondary reference materials should be used for the calibration of organic laboratory standards.

Single and multiplexed immunoassays for the chemiluminescent imaging detection of animal glues in historical paint cross-sections

The characterization of the organic components in a complex, multilayered paint structure is fundamental for studying painting techniques and for authentication and restoration purposes. Proteinaceous materials, such as animal glue, are of particular importance since they are widely used as binders, adhesives and for gilding. Even though proteins are usually detected by chromatographic and proteomic techniques, immunological methods represent an alternative powerful approach to protein analysis thanks to the high specificity of antigen–antibody reactions. Our previous studies demonstrated that ovalbumin and casein could be localized in paint cross-sections with high sensitivity and good spatial resolution (i.e. within the single painting layers) by using chemiluminescent (CL) immunochemical microscope imaging. In the present research work, we describe for the first time the immunolocalization of collagen (the main protein of animal glue) in paint cross-sections by CL imaging microscopy. Two different analytical protocols have been developed, allowing either the detection of collagen or the simultaneous detection of collagen and ovalbumin in the same paint sample. The assays were used to detect collagen and ovalbumin in cross-sections from model samples and historical paintings (a wall painting dated to 1773–1774 and a painted wood panel of the Renaissance period) in order to achieve information on paint techniques and past restoration interventions.

Interaction of active particles of oxygen plasma with polypropylene

Changes in the chemical composition of surface were studied and the rates of formation of gaseous degradation products during polypropylene treatment in oxygen plasma and its flowing afterglow were determined by means of attenuated total internal reflectance IR spectroscopy and mass spectrometry. It was found that surface oxidation at minimal degradation rates is reached upon the joint action of O₂(a ¹Δ _g ) molecules and ground-state oxygen molecules, whereas O(³ P) atoms participate in both oxidation processes and the processes of degradation of oxygen-containing groups leading to the formation of gaseous products. It was shown that only the action of plasma leads to the formation of vinyl and vinylidene double bonds, which disappear in reactions with O₂(a ¹Δ _g ) molecules and O(³ P) atoms.     

Turn-on fluorometric immunosensor for diethylstilbestrol based on the use of air-stable polydopamine-functionalized black phosphorus and upconversion nanoparticles

The preparation of air-stable black phosphorus (BP) is challenging because atomic layers of BP degrade rapidly on exposure to oxygen. A strategy is presented for the synthesis of BP functionalized with polydopamine (PDA/BP). Dopamine was self-polymerized to yield polydopamine (PDA) which then was used to coat the surface of BP. PDA can be easily reduced and this prevents BP degradation. PDA/BP also is a viable matrix for the adsorption of proteins due to the presence of functional groups. Without any chemical activation, diethylstilbestrol (DES)-specific monoclonal antibody was adsorbed on the PDA/BP surface. PDA/BP quenches the fluorescence antigen-modified NaYF₄:Yb,Ho,Nd upconversion nanoparticles (UCNPs; photoexcited at 808 nm) via specific immuno recognition. Exposure to DES causes the dissociation of UCNP from the PDA/BP surface and fluorescence at 475, 525, 545 and 660 nm to recover. This is due to the DES competition with antigen for binding to the antibody. Based on this competitive immuno mechanism, a turn-on fluorometric immunoassay was constructed. It has a response that covers the 0.1 to 1000 ng mL^?1 DES concentration range with a detection limit of 83 pg mL^?1. This method was successfully applied to the determination of DES in spiked food and human urine samples.

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Graphical abstract Air-stable polydopamine-functionalized black phosphorus was obtained by modification of black phosphorus with polydopamine and then was coupled with specific monoclonal antibody. Combined with antigen-modified upconversion nanoparticles, a turn-on fluorometric immunoassay was constructed to detect diethylstilbestrol.

     

Liquid-phase MnO<Subscript>2</Subscript>-modification of clinoptilolite

Formation mechanism of the MnO₂ phase in the reaction of heterogeneous synthesis between Mn²⁺ and MnO ₄ ^- ions on a solid aluminosilicate surface in aqueous solutions was studied. It was shown that, for lowsilica forms, the Mn²⁺ ion is oxidized by the MnO ₄ ^- ion uniformly across the grain depth to give the MnO₂ phase and manganese manganites. For high-silica materials, the MnO₂ phase is formed on the outer surface of grains, with the decomposition of the MnO ₄ ^- ion and formation of the MnO₂ phase and molecular oxygen. It was found that, for the clinoptilolite rock used as a solid support, the yield of the MnO₂ phase and its distribution over the particle volume depend on the penetration capacity of the MnO ₄ ^- ion into the porous structure of this rock, determined by its composition. It is shown that the amount of the MnO₂ phase grows with increasing concentration of the MnO ₄ ^- ion and treatment duration, with the phase thickness being 15–20 and 350–1050 μm for, respectively, high- and low-silica samples.     

Theory of chemical bonds in metalloenzymes VI: Manganese–oxo bonds in the photosynthesis II system

Electronic and spin structures of high-valent manganese–oxo bonds in the photosynthesis II system (oxygen evolving center, OEC) are investigated by the use of spin polarized hybrid DFT (HDFT) method. Theoretical calculations of a high-valent manganese–oxo porphyrin complex are also performed to elucidate common characteristic of the active MnO bonds in both native OEC and artificial systems. The oxygen site of the high-valent MnO is found to be electrophilic in nature, in accord with our previous work, where the SE₂, ¹O- and ³O-models have been presented for theoretical understanding of complex behaviors of oxygenation reactions by metal–oxo species. The ¹O- and ³O-models are applicable to model complexes examined here, since the manganese–oxo bonds exhibit strong biradical character. Possibility of the SE₂-like transition structure model for OEC is also discussed on both the theoretical and experimental grounds. Implications of present computational results are discussed in relation to hydroxylation reaction by MMO and P450.     

The role of radicals and clusters in thermal plasma flash evaporation processing

The prominent features of plasma flash evaporation may be caused by cluster deposition under high net flux of radicals. In order to clarify such features quantitatively, the atomic oxygen flux (Γ _o ) and cluster size (d) in 200 Torr RF thermal Ar-O₂ plasma were measured on the substrate. It was found that Γ _o higher than 10¹⁹ atoms/cm²·s can be easily acheived in this processing and this value corresponds to frozen atomic oxygen fraction 7 %. The cluster size of YBCO was estimated to be about 0.3 to 10 nm. 0.8 nm cluster deposition under Γ _o higher than 6 × 10¹⁸ atoms/cm²·s made it possible to deposit fine epitaxial YBCO films with Tc = 90K on SrTiO₃ (100) with extremely high deposition rate around 2.2 μm/min.     

High-performance liquid chromatographic determination of diltiazem in human plasma after solid-phase and liquid–liquid extraction

A selective, sensitive, and accurate high-performance liquid chromatographic method for determination of diltiazem in plasma samples has been developed and validated. The effects of mobile phase composition, buffer concentration, mobile phase pH, and concentration of organic modifiers on retention of diltiazem and internal standard were investigated. Solid-phase and liquid–liquid extraction were examined and proposed for isolation of the drug and elimination of endogenous plasma interferences. A 5 m Lichrocart Lichrospher 60 RP-select B chromatographic column was used; the mobile phase was acetonitrile–0.025 mol L^–1 KH₂PO₄ (pH 5.5), 35:65 ( v / v) at a flow-rate of 1.5 mL min^–1. The detection wavelength was 215 nm. The calibration plots were linear in the concentration range 20.0–500.0 ng mL^–1. The method has been implemented to monitor diltiazem levels in patient samples.     

Analysis of egg-based model wall paintings by use of an innovative combined dot-ELISA and UPLC-based approach

The chemical analysis of egg-based wall paintings—the mezzo fresco technique—is an interesting topic in the characterisation of organic binders. A revised procedure for a dot-enzyme-linked immunosorbent assay (dot-ELISA) able to detect protein components of egg-based wall paintings is reported. In the new dot-ELISA procedure we succeeded in maximizing the staining colour by adjusting the temperature during the staining reaction. Quantification of the colour intensity by visible reflectance spectroscopy resulted in a straight line plot of protein concentration against reflectance in the wavelength range 380–780 nm. The modified dot-ELISA procedure is proposed as a semi-quantitative analytical method for characterisation of protein binders in egg-based paintings. To evaluate its performance, the method was first applied to standard samples (ovalbumin, whole egg, egg white), then to model specimens, and finally to real samples (Giotto’s wall paintings). Moreover, amino acid analysis performed by innovative ultra-performance liquid chromatography was applied both to standards and to model samples and the results were compared with those from the dot-ELISA tests. In particular, after protein hydrolysis (24 h, 114 °C, 6 mol L^?1 HCl) of the samples, amino acid derivatization by use of 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate enabled reproducible analysis of amino acids. This UPLC amino acid analysis was rapid and reproducible and was applied for the first time to egg-based paintings. Because the painting technique involved the use of egg-based tempera on fresh lime-based mortar, the study enabled investigation of the effect of the alkaline environment on egg-protein detection by both methods.

Effects of hydroxyl radicals and oxygen species on the 4-chlorophenol degradation by photoelectrocatalytic reactions with TiO2-film electrodes

The supported nano-TiO₂ electrode was prepared by sol–gel and hydrothermal method, and the photoelectrocatalytic degradation of 4-chlorophenol (4-CP) under UV irradiation has been investigated to reveal the roles of hydroxyl radicals and dissolved oxygen species for TiO₂-assisted photocatalytic reactions. The degradation kinetics, the formation and decay of intermediates, the isotopic tracer experiments with H₂O¹⁸, the removal yield of total organic carbon and the formation of active radical species in the presence of oxygen or not were examined by HPLC, GC–MS, TOC and spin-trap ESR spectrometry. It was found that most of OH radicals in the primary hydroxylated intermediates derived from the oxidation of adsorbed H₂O or HO⁻ by photo-holes in the electrochemically assisted TiO₂ photocatalytic system. It also indicates that the enhancement in the separation efficiency of photogenerated charges by applying a positive bias (+0.5 V vs SCE) has little role in the following decomposition and mineralization of these hydroxylated intermediates in the absence of oxygen. According to above experimental results, the pathway of 4-CP photocatalytic degradation was deduced initially. Due to the combined effect of OH radicals and dissolved oxygen species, the hydroxylated 4-chlorphenol, via cis, cis-3-chloromuconic acid, was decomposed into low molecular weight acid and CO₂.     

Atomic layer deposition of tantalum oxide with controlled oxygen deficiency for making resistive memory structures

TaO _x films with controlled ratio of Ta⁴⁺ and Ta⁵⁺ atoms were prepared at different hydrogen concentrations in plasma. As shown by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, the chemical state of Ta⁴⁺ corresponds to oxygen vacancies in the TaO _x film. Electrophysical studies of the metal–dielectric–metal structures revealed an increase in the leakage current by four orders of magnitude as the hydrogen concentration in the plasma was increased from 7 to 70%, which is due to an increase in the concentration of oxygen vacancies in TaO _x . A test structure of a resistive memory cell was made on the basis of the nonstoichiometric TaO _x obtained. It withstood more than 10⁶ rewriting cycles. The suggested atomic layer deposition process shows promise for solving one of the main problems of resistive memory: extension of its working life.     

The Chemistry of Methane Remediation by a Non‐thermal Atmospheric Pressure Plasma

The destruction of methane by a nonthermal plasma in atmospheric pressure gas streams of nitrogen with variable amounts of added oxygen has been investigated. The identities and concentrations of the endproducts are determined by online FTIR spectroscopy and the plasma chemistry is interpreted using kinetic modelling. For a deposited energy of 118 kJ m^–3, the destruction is 12% in nitrogen decreasing monotonically to 5% in air. The major endproducts are HCN and NH₃ in nitrogen and CO, CO₂, N₂O, NO and NO₂ for gas streams containing oxygen. The chemistry in pure nitrogen is predominantly due to reactions of electronicallyexcited nitrogen atoms, N(²D). The addition of oxygen converts the excited state nitrogen into nitrogen oxides reducing the methane destruction which then arises by O and OH reactions yielding CO and, to a lesser extent, CO₂. The modelling correctly predicts the magnitude of the methane destruction as a function of added oxygen and the concentrations of the endproducts for processing in both nitrogen and air.     

A Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Method for the Identification of Anthraquinones: the Case of Historical Lakes

This study deals with the identification of anthraquinoid molecular markers in standard dyes, reference lakes, and paint model systems using a micro-invasive and nondestructive technique such as matrix-assisted laser desorption/ionization time-of-flight-mass spectrometry (MALDI-ToF-MS). Red anthraquinoid lakes, such as madder lake, carmine lake, and Indian lac, have been the most widely used for painting purposes since ancient times. From an analytical point of view, identifying lakes in paint samples is challenging and developing methods that maximize the information achievable minimizing the amount of sample needed is of paramount importance. The employed method was tested on less than 0.5 mg of reference samples and required a minimal sample preparation, entailing a hydrofluoric acid extraction. The method is fast and versatile because of the possibility to re-analyze the same sample (once it has been spotted on the steel plate), testing both positive and negative modes in a few minutes. The MALDI mass spectra collected in the two analysis modes were studied and compared with LDI and simulated mass spectra in order to highlight the peculiar behavior of the anthraquinones in the MALDI process. Both ionization modes were assessed for each species. The effect of the different paint binders on dye identification was also evaluated through the analyses of paint model systems. In the end, the method was successful in detecting madder lake in archeological samples from Greek wall paintings and on an Italian funerary clay vessel, demonstrating its capabilities to identify dyes in small amount of highly degraded samples.

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Graphical Abstract ?

     

The diffusion of oxygen and ion transport in lanthanum cobaltite LaCoO<Subscript>3-δ</Subscript>

The chemical diffusion coefficient of oxygen vacancies and oxygen ion conductivity in lanthanum cobaltite LaCoO₃ were determined by the polarization method as functions of oxygen partial pressure \(p_{O_2 } \) (atm) and temperature T(K) over the ranges ?4 ≤ log \(p_{O_2 } \) ≤ 0 and 1173 K ≤ T ≤ 1323 K. The mobilities (cm²/(V s)) of oxygen vacancies calculated over the temperature range studied satisfy the inequalities 1.8 × 10^?5 ≤ \(v_{v_0 } \) ≤ 3.4 × 10^?5. The transfer numbers of oxygen vacancies were calculated. These numbers change depending on oxygen partial pressure over the range 5 × 10^?7 ≤ t ₀ ≤ 1 × 10^?5. The activation energy of self-diffusion of oxygen vacancies was found to be E _a= 104 ± 10 kJ/mol (1.1 ± 0.1 eV).     

Change of intensity of a1Δg → X3Σ g − transition in oxygen molecule upon interaction with H2, N2, and CS2

The semiempirical MINDO/3 CI method has been used to calculate collision complexes of the oxygen molecule with certain diamagnetic molecules, simulating the effect of solvents in increasing the intensity of the a¹_g X³ _g ^– transition in the oxygen molecule.Cherkassy Engineering Technology Institute, 460 Shevchenko Street, Cherkassy 257006, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 143–146, May–June, 1996. Original article submitted July 12, 1995.