Presence Of Molecular Oxygen Research Articles

Sub‐Thermionic Negative Capacitance Field Effect Transistors with Solution Combustion‐Derived Hf0.5Zr0.5O2

AbstractThe fabrication of Hf0.5Zr0.5O2‐ferroelectric negative capacitor using solution combustion is presented for the first time. The starting materials used for the solution combustion to form equimolar Hf0.5Zr0.5O2 are to act as both combustible elements and cation sources. Jain's method, which is used for estimating the stoichiometric quantities of precursors in propellant chemistry, has also been modified and applied. The conventional assumption for this method that molecular oxygen does not take part in the reaction is refuted and stoichiometric combustion in the presence of molecular oxygen is proposed. This reaction is followed by post‐rapid thermal processing to stabilize the metastable, non‐centrosymmetric orthorhombic phase. The thin film stacks, Hf0.5Zr0.5O2/HfO2, are used to achieve sub‐thermionic swing (forward sweep: 25.42 ± 8.05 mV dec−1, reverse sweep: 42.56 ± 4.87 mV dec−1) in MoS2 negative capacitance field effect transistors with a hysteresis of ≈40 mV at 1 nA, resulting in ultra‐low‐power operation.

Porphyrin-Containing MOFs and COFs as Heterogeneous Photosensitizers for Singlet Oxygen-Based Antimicrobial Nanodevices.

Visible-light irradiation of porphyrin and metalloporphyrin dyes in the presence of molecular oxygen can result in the photocatalytic generation of singlet oxygen (1O2). This type II reactive oxygen species (ROS) finds many applications where the dye, also called the photosensitizer, is dissolved (i.e., homogeneous phase) along with the substrate to be oxidized. In contrast, metal-organic frameworks (MOFs) are insoluble (or will disassemble) when placed in a solvent. When stable as a suspension, MOFs adsorb a large amount of O2 and photocatalytically generate 1O2 in a heterogeneous process efficiently. Considering the immense surface area and great capacity for gas adsorption of MOFs, they seem ideal candidates for this application. Very recently, covalent-organic frameworks (COFs), variants where reticulation relies on covalent rather than coordination bonds, have emerged as efficient photosensitizers. This comprehensive mini review describes recent developments in the use of porphyrin-based or porphyrin-containing MOFs and COFs, including nanosized versions, as heterogeneous photosensitizers of singlet oxygen toward antimicrobial applications.

Photochemical Reactivities and Photodynamic Effects of an Organorhodium Phthalocyanine

The light-triggered uncaging of bioactive molecules is attractive for a new type of photodynamic therapy (PDT) as it enables the tumor-selective cell attack in various mechanism of action. In particular, photochemical release of formaldehyde is promising as they exhibit cytotoxicity by the alkylation and crosslinking of biological tissues.[1] Meanwhile, methyl-cobalt porphyrinic compounds are known to give formaldehyde by the homolytic cleavage of a metal-carbon bond under visible light irradiation in the presence of molecular oxygen.[2] However, there has been no report on the photochemical formation of formaldehyde under irradiation of red light which shows high permeability toward biological tissues. In this study, the organometallic phthalocyanine complexes possessing a group 9 metal center were synthesized, and their photophysical properties, photochemical reactivities and photodynamic effects were investigated under red light irradiation.Through the screening of reaction conditions, the methyl-rhodium phthalocyanine complex (1) was found to give formaldehyde by irradiation of pulsed laser of red light in the presence of oxygen. The laser-power dependency on the conversion rate indicated that the metal-carbon bond of 1 is activated through the stepwise, two-photon excitation. In order to realize the photochemical formation of formaldehyde in biological environment, 1 was encapsulated into a liposome of 1,2-Dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC). By irradiation of red light, the liposomal 1 released formaldehyde in water under air. Finally, the phototoxicity and cytotoxicity of liposomal 1 toward HeLa cells were investigated. The HeLa cells treated by liposomal 1 were successfully killed by light irradiation, indicating that 1 exhibits the photodynamic effect.

Luminescent lanthanide complexes for reactive oxygen species biosensing and possible application in Alzheimer's diseases.

Histopathological hallmarks of Alzheimer's disease (AD) are intracellular neurofibrillary tangles and extracellular formation of senile plaques composed of the aggregated amyloid-beta peptide along with metal ions (copper, iron or zinc). In addition, oxidative stress is considered as an important factor in the etiology of AD and a multitude of metalloproteins and transporters is affected, leading to metal ion misregulation. Redox-active metal ions (e.g., copper) can catalyze the production of reactive oxygen species (ROS) in the presence of molecular oxygen and a reductant such as ascorbate. The ROS thus produced, in particular the hydroxyl radical which is the most reactive one, may contribute to oxidative stress conditions. Thus, detecting ROS invivo or in biological models of AD is of interest for better understanding AD etiology. The use of biocompatible and highly specific and sensitive probes is needed for such a purpose, since ROS are transient species whose steady-state concentrations are very low. Luminescent lanthanide complexes are sensitive probes that can meet these criteria. The present review focuses on the recent advances in the use of luminescent lanthanide complexes for ROS biosensing. It shows why the use of luminescent lanthanide complexes is of particular interest for selectively detecting ROS ( , HO• , 1 O2 , H2 O2 , etc.) in biological samples in the µM-nM range. It particularly focuses on the most recent strategies and discusses what could be expected with the use of luminescent lanthanide complexes for better understanding some of the molecular mechanisms underlying the development of Alzheimer's disease.

Efficient transformation of cyclohexanone to ε-caprolactone in the oxygen-aldehyde system over single-site titanium BEA zeolite

Ti x SiBEA zeolites prepared by a two-step post-synthesis method are applied in the liquid-phase Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone in the oxygen-aldehyde system. Such method of ε-caprolactone synthesis offers the application of milder reaction conditions with the catalytic system which transforms cyclic ketones into lactones in the presence of molecular oxygen and aldehyde. They are the source of in situ peracid formation. The Ti incorporation into SiBEA involves the formation of Ti(IV) (OSi) 4 as main species and small numbers of Ti(III) (OSi) 3 –O(H)–Si sites having Brønsted and Lewis acid properties. The acidity is a key factor for efficient transformation of cyclohexanone to ε-caprolactone in the BV oxidation depending on the titanium oxidation state and environment. Among all of the studied catalysts, the highest catalytic activity is observed for Ti 2.0 SiBEA zeolite. The active catalyst of the studied BV oxidation reaction is bi-functional, possessing both the acidic and redox properties, catalyzing different reaction stages. • The incorporation of Ti into the SiBEA framework evidenced by FTIR and NMR. • DR UV–vis and XPS showed the presence of framework tetrahedral Ti(IV). • Ti(IV) (OSi) 4 sites appeared as main redox centres. • Ti(III) (OSi) 3 –O(H)–Si sites possessed both Brønsted and Lewis acid properties. • The Ti x SiBEA catalysts applied in BV oxidation reaction have bifunctional character.

The localization of the photosensitizer determines the dynamics of the secondary production of hydrogen peroxide in cell cytoplasm and mitochondria

Photodynamic therapy (PDT) is based on the production of the cytotoxic reactive oxygen species (ROS) by light irradiation of a photosensitizer dye in the presence of molecular oxygen. Along with photochemical ROS production, it becomes evident that PDT induces massive secondary production of ROS which is registered long after the irradiation is completed. We created cell lines of human epidermoid carcinoma with the cytoplasmic and mitochondrial localization of protein sensor HyPer sensitive to hydrogen peroxide to compare its concentration in two cellular compartments. The lag-period between irradiation and accumulation of hydrogen peroxide in cells was registered; its duration was dose-dependent and increased up to 80 min when lowering the exposition dose from 50 to 15 J/cm2. We have shown that localization of the photosensitizer determines the spatiotemporal pattern of the cell response to PDT: secondary hydrogen peroxide accumulation in cell cytoplasm induced by photodynamic treatment with lysosome-localized phtalocyianine Photosens occurs several minutes prior to that in mitochondria; on the contrary, membranotropic arylcyanoporphyrazine dye leads to massive mitochondrial hydrogen peroxide production followed by its cytoplasmic accumulation. We hypothesize that photosensitizers with various physicochemical properties and intracellular localization can trigger different patterns not only of primary but also secondary ROS production leading to different cell fate outcomes.

A novel selective oxidative cleavage of C[sbnd]C bond mediated by black nickel oxide in the presence of molecular oxygen

A selective aerobic oxidative cleavage of CC bond is developed with black nickel oxide (NiOx) as the catalyst. For the oxidation of 1-phenyl-1, 2-ethanediol, a 97.5% conversion in 96.7% selectivity of benzaldehyde is obtained under 0.3 MPa of O2 at 140 °C for 3 h. The relationship between the catalytic performance of NiOx and structure is discussed. It is concluded that the existence of Ni3+ should be crucial to the activity of catalyst. Moreover, the recycling experiments showed that the catalyst can retain a high activity even after being reused for five times.

Bicyclic Phenyl-Ethynyl Architectures: Synthesis of a 1,4-Bis(phenylbuta-1,3-diyn-1-yl) Benzene Banister.

The novel diacetylene bridged terphenylic macrocycle 1 is presented and discussed in the context of rotationally restricted “Geländer” oligomers. The 1,4‐bis(phenylbuta‐1,3‐diyn‐1‐yl) benzene bridge of diacetylene 1 is significantly longer than its terphenyl backbone, forcing the bridge to bend around the central pylon. The synthesis of molecule 1 is based to a large extent on acetylene scaffolding strategies, profiting from orthogonal alkyne protection groups to close both macrocyclic subunits by oxidative acetylene coupling sequentially. The spatial arrangement and the dynamic enantiomerization process of the bicyclic target structure 1 are analyzed. In‐depth NMR investigations not only reveal an unexpected spatial arrangement with both oligomer strands bent alongside the backbone, but also display the limited stability of the model compound in the presence of molecular oxygen.

Selective electrooxidation of acetaldehyde in aqueous ethanol alkaline solutions on silver-containing electrodes

Selective electrochemical oxidation of acetaldehyde in aqueous alkaline ethanol solutions on the silver-containing electrodes has been presented. Several types of silver-containing electrode were used: the smooth silver disk electrode, rough silver electrode and the glassy carbon electrode modified with the silver-polypyrrole composite ink. Silver-polypyrrole (Ag-PPy) composite was synthesized via single-step chemical oxidation with the use of diluted aqueous solutions of silver nitrate and pyrrole in molar ratio 1:50. It has been shown that acetaldehyde is oxidized selectively on silver in the presence of ethanol in alkaline solutions. The influence of various factors (pH, the presence of molecular oxygen, ethanol and acetate anions, surface area extension and polypyrrole presence) on the aldehyde electrooxidation process has been studied. It was shown that for the silver-polypyrrole composites the aldehyde electrooxidation peak potential is shifted to negative direction in comparison with the silver electrode. However, the sensitivity of the silver-polypyrrole composite modified electrode is lower than for smooth or rough silver electrode. The addition of nitrate anions in alkaline solution permits to increase the peak currents for Ag-PPy modified electrode.

A tetra-cationic tetrapyridinoporphyrazinato Iron(II) grafted onto sulfonated SBA-15 as a novel heterogeneous catalyst for the aerobic oxidation of C(sp3)-H bonds in alkanes

An iron (II) tetramethylated tetrapyridinoporphyrazine (FeII(2,3-tmtppa)) grafted onto sulfonated SBA-15 (SBA-15@n-Pr-SO3@Fetmtppa)) has been synthesized. The catalyst was characterized using X-ray diffraction, nitrogen adsorption–desorption measurements, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, thermogravimetric analysis and scanning electron microscopy. XRD, XPS and ICP analyses confirmed the incorporation of iron (II) ion onto the surface of functionalized support. TGA and BET diagrams, FESEM and TEM images showed the grafting of (FeII(2,3-tmtppa)) on SBA-15 with mesoporous structure and ordered channels after immobilization process. This catalyst is able to perform C-H oxidation reaction of alkanes including toluene and ethylbenzene derivatives in the presence of molecular oxygen under the mild reaction in water. The hot filtration and reusability tests of the catalyst were studied which showed that the C-H activation reaction proceeds via heterogeneous pathway and catalyst is recoverable for at least 5 times.

Investigations on the formation of α-dicarbonyl compounds and 5-hydroxymethylfurfural in apple juice, orange juice and peach puree under industrial processing conditions

The formation of α-dicarbonyl compounds and 5-hydroxymethylfurfural during industrial processing of apple juice, orange juice, and peach puree samples was investigated in this study. Changes in the concentrations of sugars, free amino acids, α-dicarbonyl compounds, and 5-hydroxymethylfurfural in the samples from the critical process stages such as pasteurization, enzyme treatment, concentration, were monitored. The concentrations of sugars and free amino acids showed no statistically significant change during processing. 3-deoxyglucosone was identified as the dominant dicarbonyl compound formed during orange juice and peach puree processes, while glucosone was the main one formed in apple juice samples at all sampling points. In general, total dicarbonyl compounds significantly increased (p < 0.05) in apple juice, orange juice, and peach puree samples during processing, varied between 2.04 and 28.09 mg/L, 9.16 and 31.2 mg/L, and 8.9 and 48.31 mg/kg, respectively. The concentration of 5-hydroxymethylfurfural was found to be low in apple and orange samples and not detected in peach puree samples. The presence of molecular oxygen, the temperature and the duration of the process were determined as the remarkable processing parameters that affect the formation of α-dicarbonyl compounds.

New insights into the Ar-matrix-isolation FTIR spectroscopy and photochemistry of dichloroacetyl chloride, ClC(O)CHCl2: Influence of O2 and comparison with gas-phase photochemistry

Photolysis products of dichloroacetyl chloride (DCAC) isolated in Ar matrix and in gas phase, in the absence and presence of molecular oxygen, were studied by means of FTIR spectroscopy. The samples were exposed to light of different energy ranges (200–800, 280–320, 350–450 and 400–800 nm). DCAC is photostable when irradiated with light of wavelengths above 400 nm, and gives dichloroketene after photolysis with light between 280–320 and 350–450 nm. Exposure of DCAC to broad-band radiation (200–800 nm) produces dichloroketene as an intermediate photoproduct, and different 1:1 CHCl3:CO molecular complexes after further irradiation. HCl, CO and CHCl3 were detected in gas-phase DCAC photolysis. ClC(O)CCl2CCl2H molecule was also proposed, in a mechanism that involve the insertion of:CCl2 biradical into the C−C bond of DCAC. The photochemical reaction of DCAC with O2 in Ar matrix gives Cl2CO and CO2. The same photoproducts, together with HCl, were observed in the gas-phase photochemical reaction. Additionally, the FTIR spectra of DCAC isolated in solid Ar were fully interpreted in terms of an equilibrium between syn (the H−C bond syn with respect to the C=O bond) and gauche conformers. Some absorptions, which grow as the DCAC:Ar ratio increases, were attributed to dimeric forms. The most stable dimer was predicted by DFT calculations as composed by two DCAC molecules with syn conformations, interacting through two H-bonds in a structure with Ci symmetry.

Water and Life: The Medium is the Message

Water, the most abundant compound on the surface of the Earth and probably in the universe, is the medium of biology, but is much more than that. Water is the most frequent actor in the chemistry of metabolism. Our quantitation here reveals that water accounts for 99.4% of metabolites in Escherichia coli by molar concentration. Between a third and a half of known biochemical reactions involve consumption or production of water. We calculated the chemical flux of water and observed that in the life of a cell, a given water molecule frequently and repeatedly serves as a reaction substrate, intermediate, cofactor, and product. Our results show that as an E. coli cell replicates in the presence of molecular oxygen, an average in vivo water molecule is chemically transformed or is mechanistically involved in catalysis ~ 3.7 times. We conclude that, for biological water, there is no distinction between medium and chemical participant. Chemical transformations of water provide a basis for understanding not only extant biochemistry, but the origins of life. Because the chemistry of water dominates metabolism and also drives biological synthesis and degradation, it seems likely that metabolism co-evolved with biopolymers, which helps to reconcile polymer-first versus metabolism-first theories for the origins of life.

The Influence of Supercritical Carbon Dioxide on Graham Flour Enzyme Polyphenol Oxidase Activity.

Graham flour is a form of whole wheat flour made by grinding the endosperm and is thus also the most nutritious. Generally, the enzyme polyphenol oxidase (PPO) catalyzes two different reactions in the presence of molecular oxygen: the hydroxylation of monophenols to ortho-diphenol and the oxidation of o-diphenol to o-quinone. The purpose of the work was to inactivate PPO activity to extend the shelf life of graham flour and at the same time preserve all the of its high-quality properties. The influence of supercritical CO2 (scCO2) treatment on PPO activity in graham flour was investigated. First, graham flour was exposed to scCO2 conditions, then the proteins were extracted, and in the last step the concentration of total proteins and the specific activity of the PPO enzyme were determined by spectrophotometric assay. PPO activity decreased with an increase in treatment pressure. Furthermore, the flour quality characteristics that meet all needs for wheat end-use products after scCO2 treatment have been preserved. No major changes in the structure of the granulate or shape of the flour particles were observed. A slightly reduced value of the moisture content in scCO2-treated graham flour also implies an extension of the shelf life.

Synthesis of (-)-Flavoskyrins by Catalyst-Free Oxidation of (R)-Configured Dihydroanthracenones in Aqueous Media and Its (Bio)synthetic Implications.

A catalyst-free method for the synthesis of dimeric (-)-flavoskyrins has been developed. It involves the autoxidation of chemoenzymatically synthesized (R)-configured dihydroanthracenones in the presence of molecular oxygen in buffer of pH 6.0 followed by spontaneous [4 + 2] cycloaddition in stereocontrolled exo-anti fashion to form (-)-flavoskyrins. The method is applied to obtain several homo- as well as heterodimerized flavoskyrins (nine examples) in 27-72% yield and implies the involvement of a similar pathway in the (bio)synthesis of modified bisanthraquinones and their analogues.

Synthesis, Crystal Structure, and Luminescence of Metal Iodide Cluster Compounds (nBu4N)2[M6I8(NCO)6] with M = Mo, W

Molybdenum and tungsten iodide clusters with the [M6I8] cluster core show versatile photophysical properties that strongly depend on the nature of six apical ligands (L) in [M6I8L6]2–. In course of our syntheses we report a new efficient preparation of Cs2[Mo6I14] as precursor. Target compounds (nBu4N)2[M6I8(NCO)6] with M = Mo, W with cyanate ligands were synthesized and structurally characterized to study their photophysical properties. (nBu4N)2[M6I8(NCO)6] compounds appear as deep red (Mo) and light yellow (W) crystal powders showing strong phosphorescence. Compared to other cluster compounds of this type there is no significant concentration quenching obtained by the presence of molecular oxygen.

Autoxidation and photooxidation of tetrahydrobiopterin: a theoretical study

Pterins are naturally occurring pigments and enzyme cofactors widespread in living organisms. Tetrahydrobiopterin (H4Bip) is a coenzyme of aromatic amino acid hydroxylases, NO-synthases, and alkylglycerol monooxygenases. This coenzyme is prone to oxidation in the presence of molecular oxygen, a so-called autoxidation. The reactions participating in H4Bip autoxidation are well known. However, our study is an attempt to evaluate theoretically the feasibility of reactions participating in autoxidation. To do so, we have calculated the Gibbs free energy of elementary reactions between H4Bip, its derivatives, molecular oxygen, and reactive oxygen species (ROS). In the last few years, we have established the photosensitized oxidation of H4Bip experimentally. Thus, we have also evaluated the feasibility of H4Bip photooxidation reactions, which may occur according to both type-I and type-II photosensitized oxidation. We calculated Fukui indices for H4Bip and found particular atoms in the molecule that interact with nucleophiles (for example, singlet oxygen 1O2) and radicals (in particular, molecular oxygen 3O2). Therefore, we evaluated the probability of H4Bip autoxidation reactions, photooxidation reactions, and the reactivity of particular atoms in H4Bip molecule using the theoretical methods of quantum chemistry.

Recent Emergence of Rhenium(I) Tricarbonyl Complexes as Photosensitisers for Cancer Therapy.

Photodynamic therapy (PDT) is emerging as a significant complementary or alternative approach for cancer treatment. PDT drugs act as photosensitisers, which upon using appropriate wavelength light and in the presence of molecular oxygen, can lead to cell death. Herein, we reviewed the general characteristics of the different generation of photosensitisers. We also outlined the emergence of rhenium (Re) and more specifically, Re(I) tricarbonyl complexes as a new generation of metal-based photosensitisers for photodynamic therapy that are of great interest in multidisciplinary research. The photophysical properties and structures of Re(I) complexes discussed in this review are summarised to determine basic features and similarities among the structures that are important for their phototoxic activity and future investigations. We further examined the in vitro and in vivo efficacies of the Re(I) complexes that have been synthesised for anticancer purposes. We also discussed Re(I) complexes in conjunction with the advancement of two-photon PDT, drug combination study, nanomedicine, and photothermal therapy to overcome the limitation of such complexes, which generally absorb short wavelengths.

Role of Photoactive Phytocompounds in Photodynamic Therapy of Cancer.

Cancer is one of the greatest life-threatening diseases conventionally treated using chemo- and radio-therapy. Photodynamic therapy (PDT) is a promising approach to eradicate different types of cancers. PDT requires the administration of photosensitisers (PSs) and photoactivation using a specific wavelength of light in the presence of molecular oxygen. This photoactivation exerts an anticancer effect via apoptosis, necrosis, and autophagy of cancer cells. Recently, various natural compounds that exhibit photosensitising potentials have been identified. Photoactive substances derived from medicinal plants have been found to be safe in comparison with synthetic compounds. Many articles have focused on PDT mechanisms and types of PSs, but limited attention has been paid to the phototoxic activities of phytocompounds. The reduced toxicity and side effects of natural compounds inspire the researchers to identify and use plant extracts or phytocompounds as a potent natural PS candidate for PDT. This review focusses on the importance of common photoactive groups (furanocoumarins, polyacetylenes, thiophenes, curcumins, alkaloids, and anthraquinones), their phototoxic effects, anticancer activity and use as a potent PS for an effective PDT outcome in the treatment of various cancers.

The formation of marine red beds and iron cycling on the Mesoproterozoic North China Platform

Abstract Marine red beds (MRBs) are common in sedimentary records, but their genesis and environmental implications remain controversial. Genetic models proposed for MRBs variably invoke diagenetic or primary enrichments of iron, with vastly different implications for the redox state of the contemporaneous water column. The Xiamaling Formation (ca. 1.4 Ga) in the North China Platform hosts MRBs that offer insights into the iron cycling and redox conditions during the Mesoproterozoic Era. In the Xiamaling MRBs, well-preserved, nanometer-sized flaky hematite particles are randomly dispersed in the clay (illite) matrix, within the pressure shadow of rigid detrital grains. The presence of hematite flake aggregates with multiple face-to-edge (“cardhouse”) contacts indicates that the hematite particles were deposited as loosely bound, primary iron oxyhydroxide flocs. No greenalite or other ferrous iron precursor minerals have been identified in the MRBs. Early diagenetic ankerite concretions hosted in the MRBs show non-zero I/(Ca+Mg) values and positive Ce anomalies (&amp;gt;1.3), suggesting active redox cycling of iodine and manganese and therefore the presence of molecular oxygen in the porewater and likely in the water column during their formation. These observations support the hypothesis that iron oxyhydroxide precipitation occurred in moderately oxygenated marine waters above storm wave base (likely &amp;lt;100 m). Continentally sourced iron reactivated through microbial dissimilatory iron reduction, and distal hydrothermal fluids may have supplied Fe(II) for the iron oxyhydroxide precipitation. The accumulation of the Xiamaling MRBs may imply a slight increase of seawater oxygenation and the existence of long-lasting adjacent ferruginous water mass.