Oxygen-free Conditions Research Articles

Influence of Atmosphere on Carbonaceous Film Formation in Rubbing, Metallic Contacts

Many previous researchers have reported the formation of carbonaceous tribofilms from organic lubricants on rubbing metallic surfaces. This paper shows that a very important factor in the formation of such tribofilms is the presence or absence of molecular oxygen. When steel surfaces are rubbed in saturated hydrocarbon lubricants in the absence of oxygen, for example in nitrogen or hydrogen gas, carbonaceous films form very readily, resulting in low friction and wear. However, when a significant amount of oxygen is present, as is the case in air, carbonaceous tribofilms are not generally formed, so friction and wear are very high, with values comparable to those seen when no lubricant is present. In situ Raman analysis combined with gas-switching experiments show that the carbonaceous films formed during rubbing when no oxygen is present are rapidly removed during rubbing in air, while tests in which lubricant is removed during a test in N2 indicate that the films are quite weak. This suggests that these carbonaceous films are being continually removed and replenished during rubbing in oxygen-free conditions. It is proposed that these carbonaceous films are formed from hydrocarbyl free radicals that are generated mechanochemically from hydrocarbon molecules during rubbing. In the absence of oxygen, these free radicals then react together to form a carbonaceous film. However, when oxygen is present, the hydrocarbyl free radicals react extremely rapidly with oxygen molecules to produce hydroperoxyl free radicals and so are no longer available to generate a carbonaceous tribofilm.Graphical abstract

A Fluidizable Catalyst for N-Butane Oxidative Dehydrogenation under Oxygen-Free Reaction Conditions

This study evaluates the effectiveness of fluidizable VOx/MgO-γAl2O3 catalysts for C4-olefin production via n-butane oxidative dehydrogenation (BODH). Catalysts were prepared via vacuum incipient wetness impregnation and then characterized by employing several techniques such as BET (Brunauer–Emmett–Teller) method, XRD (X-ray diffraction), LRS (laser Raman spectroscopy), XPS (X-ray photoelectron spectroscopy), TPR/TPO (temperature-programmed reduction/temperature-programmed oxidation), NH3-TPD (temperature-programmed desorption), NH3 -desorption kinetics and pyridine-FTIR. The BET analysis showed the prepared catalysts’ mesoporous structure and high surface areas. The XRD, LRS and XPS established the desirable presence of amorphous VOx phases. The TPR/TPO analyses corroborated catalyst stability over repeated reduction and oxidation cycles. The NH3-TPD and NH3 desorption kinetics showed that the catalysts had dominant moderate acidities and weak metal-support interactions. In addition, Pyridine-FTIR showed the critical influence of Lewis acidity. The VOx/MgO-γAl2O3 catalysts were evaluated for BODH using a fluidized CREC Riser Simulator, operated under gas-phase oxygen-free conditions, at 5 to 20 s reaction times, and at 450 °C to 600 °C temperatures. The developed VOx/MgO-γAl2O3 catalysts demonstrated performance stability throughout multiple injections of butane feed. Catalyst regeneration was also conducted after six consecutive BODH runs, and the coke formed was measured using TOC (Total Organic Carbon). Regarding the various BODH catalyst prepared, the 5 wt% V-doped MgO-γAl2O3 yielded in a fluidized CREC Riser Simulator the highest selectivity for C4-olefins, ranging from 82% to 86%, alongside a butane conversion rate of 24% to 27%, at 500 °C and at a 10 s reaction time.

Ni-modified MIL-100(Fe) catalysts for CO-SCR of NO and reaction mechanism

To promote the activation of the catalysts in the presence of oxygen and at lower temperatures for the selective catalytic reduction of NO with CO (CO-SCR), iron-based metal-organic frameworks (MOFs) catalysts, called MIL-100 (Fe), were prepared by hydrothermal synthesis and further modified with Ni by wet impregnation method. The CO-SCR of NO was evaluated in a fixed-bed reactor. Results proved that the NO conversion over MIL-100(Fe) and 5.8 %Ni-modified catalysts under oxygen-free conditions was 96.6 % and 100 % at 325 °C, respectively. When 2 vol% oxygen was present, the NO conversions over MIL-100(Fe) and 5.8 %Ni modified catalysts at 250 °C were 37.2 % and 96.6 %, respectively, demonstrating that the Ni-modified MIL-100(Fe) catalyst obviously improved the CO-SCR reactivity under O2 atmosphere. UV–vis DRS, HRTEM, FTIR, TGA, etc., and in situ DRIFTS techniques were used to characterize the physical and chemical properties of the catalysts and study the reaction mechanism. The outcomes demonstrated that the incorporated Ni engaged in interactions with Fe the CO-SCR reaction, resulting in the formation of additional surface or surface synergistic oxygen vacancies (SOV and SSOV), thus improving the redox performance of catalysts. Additionally, the Ni-modified catalyst had better redox performance, which was beneficial to converting the adsorbed NOx substances into active substances. The adsorption behavior of NO, CO, and the reaction intermediates were investigated by in situ DRIFTS and a preliminary reaction path was proposed.

Experimental study of water-extractable sulphate in Opalinus Clay and implications for deriving porewater concentrations

In northern Switzerland, the Opalinus Clay, a Jurassic claystone formation, is foreseen as host rock for a deep geological repository for radioactive waste. Characterizing its porewater is of particular importance for assessing the mobility of radionuclides and the stability of the engineered barriers. Although the porewater composition of the Opalinus Clay is fairly well known, there is still controversy on the sources of sulphate obtained by different porewater characterization methods. A striking observation is that sulphate concentrations from aqueous extraction and recalculated to in-situ conditions are consistently much higher than sulphate concentrations measured in borehole waters, squeezed waters and advectively displaced waters (“excess sulphate”). Accordingly, the main objective of this study is to better investigate the processes affecting dissolved sulphate concentrations during aqueous extraction and, thus, to reduce uncertainties in predicting the concentrations of this compound in the Opalinus Clay porewater. To this end, a series of extraction experiments were conducted using variable solid/liquid ratios, extraction times and extract solutions. In order to suppress sulphide-mineral oxidation, all the experiments were performed in a glovebox under oxygen-free conditions (atmosphere and solutions). Measurements of the sulphur and oxygen isotope composition of the dissolved sulphate in aqueous extracts are aimed to further constrain the source of the “excess sulphate”. Finally, the plausibility of the SO4 data from extraction experiments in terms of their representativeness for in-situ conditions was evaluated by simple geochemical modelling. The modelling shows that SO4 concentrations from aqueous extracts recalculated to in-situ conditions imply dissolved and exchangeable cation concentrations which are not consistent with measured data, thus, attesting non-conservative behaviour for sulphate during aqueous extraction. However, the various extraction experiments showed that pyrite oxidation was successfully suppressed during the experiments and neither contributions from e.g. organic material, congruent calcite dissolution and/or sulphate mineral dissolution provide enough SO4 to explain the “excess sulphate”. Ultimately, the various extraction experiments failed to definitely identify the source of the “excess sulphate” in aqueous extracts. However, the good agreement found between the δ18O and δ34S values of dissolved SO4 in aqueous extracts and those of borehole waters suggest that the “excess sulphate” might be weakly bound to mineral surfaces.

Effects of excitation power density on the Stern-Volmer constant measurement.

The Stern-Volmer constant (KSV) is an important parameter to describe the capability of energy transfer to oxygen for porphyrin and its derivatives. By fitting Stern-Volmer equation, IP0/IP = 1 + KSV[O2], the KSV is generally determined through phosphorescence intensities (IP) under aerobic and oxygen-free conditions. In this work, the effect of excitation power density on the KSV measurement is theoretically analyzed and experimentally studied, using palladium octaethylporphyrin (PdOEP) as an example. The IP of PdOEP increased nonlinearly with excitation power density, and the power dependent slope of IP0/IP could be obtained. By way of the functional relationship between the slope of IP0/IP and power density, the real KSV of PdOEP was fitted to be 58 ± 2 kPa-1. The oxygen-dependent phosphorescence lifetimes (τP) and IP under a weak excitation power are also measured to calculate the real KSV, which verifies our analysis.

Measurements of the mechanical properties of larch at elevated and high temperature under nitrogen conditions

The mechanical characteristics of wood members in a fire are reduced as a result of strength loss of the outermost charring layer and strength reduction of the secondary outer layer in high temperature zones. The charring layer has strong oxygen isolation effects. The main mechanical characteristics of larch wood, including modulus of elasticity (MOE), parallel-to-grain compressive (fc), tensile (ft), bending strengths (fb), and ductility coefficient, were determined under oxygen-free conditions at higher temperatures. Fourier transform-infrared (FT-IR) and scanning electron microscopies (SEM) were used to analyze chemical composition and microscopic changes of wood. The results suggested that hemicellulose softening resulted in decreases in mechanical properties of wood between 20 and 70 °C. From 70 to 190 °C, FT-IR spectroscopy provided evidence that increases in MOE and fc, with relatively minor changes in fb and ft, were associated with cellulose crystallinity and lignin cross-linking/condensation. The use of SEM further indicated degradation of wood composition.

Wear Behavior of Metal Bonded Grinding Tools When Grinding Ti-6Al-4V in an Oxygen-Free Atmosphere

In the current study, the wear behavior of bronze-bonded grinding tools when grinding the titanium alloy Ti-6Al-4V was explored. In this process, oxidation plays a key role since both the bronze bond and the titanium workpiece chemically react with oxygen. The oxidation effect is intensified further due to increased temperatures during grinding and can cause tribo-oxidation. This wear effect can be reduced or even eliminated by grinding in an extreme high-vacuum (XHV) adequate atmosphere. This atmosphere is nearly oxygen-free and is generated using a silane-doped argon gas that chemically reacts with oxygen. This reaction is able to decrease the oxygen partial pressure (pO2 ≤ 10−12 mbar) down to an XHV-adequate atmosphere. The aim of this paper is to investigate the influence of oxygen in the atmosphere on the application and wear behavior during grinding and to demonstrate the potential of this novel approach. The results presented show that during grinding with cBN, the process forces are significantly influenced by the atmosphere. Depending on the process parameters, a reduction of up to 93% is thus possible. This force reduction correlates with radial tool wear. When grinding under oxygen-free conditions, it can be reduced by up to 64%.

MnO2/La2O3/rGO composite catalyst prepared by electrodeposition as corona discharge anode for electrocatalytic cracking of toluene

To achieve the purification of coke oven gas and pyrolysis gas under oxygen-free conditions, the MnO2/La2O3/rGO composite catalyst was innovatively loaded directly onto the surface of porous titanium mesh anode by electrodeposition in this study, together with corona discharge for toluene cracking. During the catalyst preparation, the effects of potential and pH on the catalyst were verified in combination with cyclic voltammetry (CV) curves. The results showed that the toluene cracking rate reached 90% at 7 kV when the electrolyte concentrations of Mn2+, La3+ and rGO were 0.1 mol/L, 0.05 mol/L and 0.005 g/L, respectively. In addition, in this study, the distribution and changes of potential and electron temperature inside the reactor were simulated by COMSOL, and the concentration and change pattern of positive and negative ions at 7 kV were calculated. The results showed that both the plasma and the catalyst play a very significant role in this process.

Evolution of physico-chemical parameters, microorganism diversity and volatile organic compound of apple pomace exposed to ambient conditions

In apple processing, waste material known as apple pomace amounts to 45% of production volumes. When this residue is stored in open-air for its stabilization and potential uses, Volatile Organic Compounds (VOCs) are produced, resulting in environmental and odor pollution, and must be managed to avoid their impact. This work aims to study the emission of VOCs utilizing TD-GC/MS and its relationship with changes in physico-chemical (moisture, pH, proteins, among others) and biological (bacteria and fungi using Illumina MiSeq) parameters under three environmental conditions: open-air (outdoors), under-roof (indoors) and oxygen-free. The 8-month study results showed a gradual increase in odorous VOCs and microbial diversity, a product of chemical and biological transformation processes in the samples. A 30% increase in odorant compounds responsible for the unpleasant smell was observed, especially esters, aldehydes and hydrocarbons in samples stored in oxygen-free and Open-air conditions. Increases in VOCs over time were associated with changes in physico-chemical and biological parameters, as well as fluctuations in environmental variables (temperature, relative humidity, and precipitation). The results of this research allow establishing a relationship between storage conditions and the production of VOCs. In addition, recommendations for waste storage time are provided for the most common uses of apple pomace based on the physico-chemical parameters observed, in order to avoid the generation of odorous compounds. Of all storage methods analyzed, under-roof is the most adequate in practice. This study's findings are pertinent for managing agribusiness waste and its potential environmental pollution.

Extracellular electron transfer drives ATP synthesis for nitrogen fixation by Pseudomonas stutzeri

Biological nitrogen fixation is a key step in the reduction of N2 to available nitrogen in the global nitrogen cycle. Pseudomonas stutzeri A1501 is an electroactive diazotroph and previous studies have shown that its nitrogen fixation performance is better in a micro-oxygen environment than in an oxygen-free environment. In this study, a bioelectrochemical system (nitrogen fixation in an anode chamber) was set up to explore whether extracellular electrodes can replace oxygen in acting as electron acceptors to drive ATP synthesis for nitrogen fixation by P. stutzeri under oxygen-free conditions. Nitrogenase activity, extracellular NH4+ production, increase of total nitrogen, 15N/14N atom ratio and the genes related to nitrogen fixation by P. stutzeri in the anodic bioelectrochemical group under oxygen-free conditions were at least 1.64 times higher than the corresponding values without electron output to the anode. The planktonic cells in the anode chamber were responsible for most of the electron output via an electron shuttle–electron transfer pathway. The transmembrane proton motive force produced by the transfer of electrons from the intracellular environment to the anode drives ATP synthesis to meet the high energy demand of the nitrogen fixation reaction in the absence of O2. These findings provide a basis for optimization of the nitrogen fixing performance of P. stutzeri in an oxygen-free environment.

Influence of an Oxygen-Free Atmosphere on Process Forces and Workpiece Quality during the Surface Grinding of Ti-6Al-4V

Most manufacturing processes, such as grinding, are usually conducted in a standard air atmosphere. The oxygen within this atmosphere leads to oxidation effects on tools and workpieces when machining metal components. This is primarily a factor in the processing of titanium due to its high affinity for oxygen. The oxidation of the surface increases tool wear and reduces surface quality. Hence, this paper investigates the influence of the atmosphere on process forces and workpiece quality when grinding titanium (Ti6Al4V) with metal-bonded diamond grinding tools. To generate oxygen-free conditions in production processes, a novel approach allows an atmosphere with a very low oxygen partial pressure. Using a silane gas, which reacts with oxygen, the oxygen partial pressure, pO2, can be reduced below 10−12 mbar, equal to the oxygen partial pressure in an extremely high vacuum (XHV). The results show a significant influence of the atmosphere on the process forces. When grinding in XHV-adequate conditions, the grinding forces are reduced by 16% in the tangential direction and 50% in the normal direction on average, while the quality of the ground titanium surfaces is consistent (both atmospheres: Rz = 13–21 µm). Phase analysis via XRD revealed a distinct amount of titanium nitride (TiN) on the ground surfaces independently of the atmospheric conditions.

Dual functional materials based on Ni and different alkaline metals on alumina for the cyclic stepwise CO2 capture and methanation

Bimetallic catalysts consisting of nickel and one alkali or alkaline-earth metal (Na, K or Ba) on alumina support have been tested in the cyclic CO2 capture and subsequent methanation. The best performance was attained with a different material for cyclic tests (K-Ni/Al) than for Sabatier reaction (Ba-Ni/Al). In cyclic tests, the methane productivity shows different dependence with the temperature for each alkali and alkaline-earth metal. For temperature of 300 °C or above, the dual functional materials show stable cyclic performance when the capture is performed both from 5% CO2 in Ar and from simulated flue gas containing also O2 and H2O. Using the later feed, the CH4 productivity diminish reversibly compared to oxygen free conditions and nickel metal oxidises significantly. K-Ni/Al exhibited the best cyclic performance in terms of CH4 productivity and stability, which is associated to the highest reducibility of oxidised nickel species and the lowest formation of unreducible carbonates.

Production of Biochar from Coconut Husks for Adsorption of Heavy Metals in Water

This study focused on the production, characterization, and application of biochar from coconuthusks as an effective and cheap adsorbent for the removal of heavy metals (i.e. Pb, Fe, Mn,and Cr) in water. The biochar was produced by pyrolysis of coconut husk at 600 °C in oxygen-free conditions and then characterized by various surface analysis technologies to explore itsphysical and chemical properties. In the metal adsorption test, the produced biochar gave highmetal removal performance with maximum adsorption capacities of 95.24 mgPb2+/g, 40.16mgFe2+/g, 35.46 mgCr6+/g, and 23.09 mgMn2+/g under pH 5, 4.5, 2, and 5.5, respectively. Studiesin kinetics, isotherms, thermodynamics, and mechanism were then conducted to understandthe adsorption process of metal ions in water using coconut husk biochar.

Direct observation of the thermo-oxidative degradation of PA66 by spin-trapping ESR analysis

We succeeded in detecting the radical intermediates produced during the thermo-oxidative degradation of polyamide 66 (PA66) in air between 80°C to 240°C, the temperature range for practical applications, using spin-trapping electron spin resonance (ST-ESR) even in the presence of oxygen, which interferes with ESR measurements. As a result, ST-ESR analysis has newly revealed the presence of two more radical intermediates, −•CH−NH− and •(C=O)NH−, under air in addition to the two radical intermediates, •CH2− and −CH2−•CH−CH2−, already found in the previous report, which was examined under oxygen-free conditions. The formation of those four radicals can be explained by hydrogen abstraction and β-scission in the autoxidation mechanism. The onset temperature of the rapid oxidation reaction observed in chemiluminescence (CL) measurement coincides with the one for generating the −•CH−NH− radical, indicating that the initial radical of thermo-oxidative degradation of PA66 is −•CH−NH− radical generated by selective oxygen attack on the NH-adjacent methylene group. This finding strongly supports previous reports that concluded hydrogen abstraction from the NH-adjacent methylene group is the main reaction under air.

Ignition kinetics of nitrocyclohexane behind reflected shock waves in inert and air environments

Nitrocyclohexane is an important propellant within the class of nitroalkane based energetic fuels characterized by the nitro functional group. Although several studies were reported on the ignition of small nitroalkanes, very few kinetic studies are performed on their ignition characteristics under oxygen-free conditions. Herein, the ignition kinetics of nitrocyclohexane in inert and air environments are studied using a high-pressure shock tube facility. The experiments are performed at pressure of 2, 5, 10, and 20 bar with equivalence ratios of 0.5, 1.0 and 2.0 under the temperature range from 950 K to 1420 K. The effect from fuel concentrations at 0.61%, 1.14% and 2.05% with nitrogen as the inert gas are also studied. Comparisons of the ignition kinetics with other fuels including nitromethane, 1-nitropropane, methylcyclohexane, and cyclohexylamine are performed. The present manuscript provides the first experimental data for nitroalkanes in inert conditions, and should be valuable to understand the combustion chemistry of nitroalkanes.

Investigation into Propolis Components Responsible for Inducing Skin Allergy: Air Oxidation of Caffeic Acid and Its Esters Contribute to Hapten Formation.

Propolis is a resin-like material produced by bees from the buds of poplar and cone-bearing trees and is used in beehive construction. Propolis is a common additive in various biocosmetics and health-related products, despite the fact that it is a well-known cause of contact allergy. Caffeic acid and its esters have been the primary suspects behind the sensitization potency of propolis-induced contact allergy. However, the chemical structures of the protein adducts formed between these haptens and skin proteins during the process of skin sensitization remain unknown. In this study, the reactivity of three main contact allergens found in propolis, namely, caffeic acid (CA), caffeic acid 1,1-dimethylallyl ester (CAAE), and caffeic acid phenethyl ester (CAPE), was investigated. These compounds were initially subjected to the kinetic direct peptide reactivity assay to categorize the sensitization potency of CA, CAAE, and CAPE, but the data obtained was deemed too unreliable to confidently classify their skin sensitization potential based on this assay alone. To further investigate the chemistry involved in generating possible skin allergy-inducing protein adducts, model peptide reactions with CA, CAAE, and CAPE were conducted and analyzed via liquid chromatography-high-resolution mass spectrometry. Reactions between CA, CAAE, and CAPE and a cysteine-containing peptide in the presence of oxygen, both in closed and open systems, were monitored at specific time points. These studies revealed the formation of two different adducts, one corresponding to thiol addition to the α,β-unsaturated carbonyl region of the caffeic structure and the second corresponding to thiol addition to the catechol, after air oxidation to o-quinone. Observation of these peptide adducts classifies these compounds as prehaptens. Interestingly, no adduct formation was observed when the same reactions were performed under oxygen-free conditions, highlighting the importance of air oxidation processes in CA, CAAE, and CAPE adduct formation. Additionally, through NMR analysis, we found that thiol addition occurs at the C-2 position in the aromatic ring of the CA derivatives. Our results emphasize the importance of air oxidation in the sensitization potency of propolis and shed light on the chemical structures of the resultant haptens which could trigger allergic reactions in vivo.

Sampling of Gas-Phase Intermediate Pyrolytic Species at Various Temperatures and Residence Times during Pyrolysis of Methane, Ethane, and Butane in a High-Temperature Flow Reactor

Air pollution in many major cities is endangering public health and is causing deterioration of the environment. Particulate emissions (PM) contribute to air pollution as they carry toxic polyaromatic hydrocarbons (PAHs) on their surface. Abatement of PM requires continuous strict emission regulation and, in parallel, the development of fuels with reduced formation of PM. Key processes in the formation of PM are the decomposition of hydrocarbon fuels and the synthesis of potential precursors that lead to the formation of benzene rings and thereafter growth to PAHs and eventually PM. Methane, ethane and butane are important components of natural gas and liquefied petroleum gas, and are also widely used in transportation, industrial processes and power generation. This paper reports on a quantitative investigation of the intermediate gaseous species present during pyrolysis of methane, ethane and butane in a laminar flow reactor. The investigation aimed to further the understanding of the decomposition process of these fuels and the subsequent formation of aromatic rings. The pyrolysis of methane, ethane and butane were carried out in a tube reactor under laminar flow conditions and within a temperature range of 869–1213 °C. The fuels were premixed in nitrogen carrier gas at a fixed carbon atom concentration of 10,000 ppm, and were pyrolysed under oxygen-free conditions. Intermediate gaseous species were collected from within the tube reactor at different residence times using a specially designed high-temperature ceramic sampling probe with arrangements to quench and freeze the reactions at entry to the probe. Identification and quantification of intermediate species were carried out using a gas chromatography-flame ionization detector (GC-FID). During methane pyrolysis, it was observed that as the concentration of acetylene increased, the concentration of benzene also increased, suggesting that the benzene ring is formed via the cyclo trimerisation of acetylene. With all three fuels, all intermediate species disappeared at higher temperatures and residence times, suggesting that those species converted into species higher than benzene, for example naphthalene. It was observed that increasing carbon chain length lowered the temperature at which fuel breakdown occurred and also affected the relative abundance of intermediate species.

Ru/Pt@BSA nanoparticles for efficient photo-catalytic oxidation of NAD(P)H and targeted cancer treatment under hypoxic conditions

Photo-catalytic oxidation of intracellular nicotinamide adenine dinucleotide (2′-phosphate) (NAD(P)H) has attracted much attention for cancer therapy. However, the general oxygen-dependent mechanism heavily depresses the efficacy in hypoxic tumors. To solve this problem, herein platinum nanoparticles (Pt NPs) with catalase-like (CAT-like) and catalytic H2 evolution activities were introduced as a powerful assistant to enhance the photo-catalytic NAD(P)H oxidation of Ru1 ([Ru(phen)2(PIP-OCH3)]2+, phen = 1,10-phenanthroline, PIP-OCH3 = 2-(4‑methoxy phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) under hypoxic and even oxygen-free conditions. Firstly, Pt NPs can transform the original and in situ formed H2O2 once again into O2 by the CAT-like activity, thus relieving tumor hypoxia and realizing cyclic utilization (at least in part) of the precious oxygen in hypoxia. Secondly, Pt NPs can also be served as H2 evolution catalysts while using Ru1 as the photosensitizer and NAD(P)H as the electron and proton donor. In this process, NAD(P)H is oxidized without the participation of oxygen, which can provide an effective way even under oxygen-free conditions. Via co-encapsulation of Ru1 and Pt NPs in bovine serum albumin (BSA) with tumor targeting ability, the resultant Ru/Pt@BSA could photo-catalyze intracellular NAD(P)H oxidation under hypoxic conditions (3% O2), and exhibited an efficient and selective anticancer activity both in vitro and in vivo. Our results may provide new sights for efficient and targeted cancer treatment under hypoxic conditions.

Effect of oil pressing and packaging under oxygen-free conditions on yield, oxidative stability, antioxidant activity, and physicochemical characteristics of perilla oil

Perilla seeds for obtaining oils were pressed at vacuum levels of 101.33 (control) and 2.67 kPa using a specially designed vacuum container and packaging device. This work investigates the effect of the presence of oxygen on viscosity, oxidative stability, fatty acid composition, and volatile compounds during a 6-month storage. The acid and peroxide values for the control oil increased by 12.80 and 30.76 fold, respectively, but did not change over time for the perilla oil stored in vacuum. Eight volatile compounds related to oxidation were detected as the control oil became rancid. Some of these compounds were present in small amounts or not at all in the vacuum oil. In conclusion, our results show that oxygen-free pressed oil and packaging are excellent in preserving the physicochemical properties, and oxidative stability in perilla oils.

Supramolecular Photosensitizer Enables Oxygen-Independent Generation of Hydroxyl Radicals for Photodynamic Therapy.

The highly oxygen-dependent nature of photodynamic therapy (PDT) limits its therapeutic efficacy against hypoxic solid tumors in clinics, which is an urgent problem to be solved. Herein, we develop an oxygen-independent supramolecular photodynamic agent that produces hydroxyl radical (•OH) by oxidizing water in the presence of intracellularly abundant pyruvic acid under oxygen-free conditions. A fluorene-substituted BODIPY was designed as the electron donor and coassembled with perylene diimide as the electron acceptor to form the quadruple hydrogen-bonded supramolecular photodynamic agent. Detailed mechanism studies reveal that intermolecular electron transfer and charge separation upon light irradiation result in an efficient generation of radical ion pairs. Under oxygen-free conditions, the cationic radicals directly oxidize water to generate highly cytotoxic •OH, and the anionic radicals transfer electrons to pyruvic acid, realizing the catalytic cycle. Thus, this photodynamic agent exhibited superb photocytotoxicity even under severe hypoxic environments and excellent in vivo antitumor efficacy on HeLa-bearing mouse models. This work provides a strategy for constructing oxygen-independent photodynamic agents, which opens up an avenue for effective PDT against hypoxic tumors.