: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Functional π-Gelators and Their Applications

Trifluoromethyltrimethylsilane: nucleophilic trifluoromethylation and beyond.

Reactive species play an important role in physiological functions. Overproduction of reactive species, notably reactive oxygen (ROS) and nitrogen (RNS) species along with the failure of balance by the body's antioxidant enzyme systems results in destruction of cellular structures, lipids, proteins, and genetic materials such as DNA and RNA. Moreover, the effects of reactive species on mitochondria and their metabolic processes eventually cause a rise in ROS/RNS levels, leading to oxidation of mitochondrial proteins, lipids, and DNA. Oxidative stress has been considered to be linked to the etiology of many diseases, including neurodegenerative diseases (NDDs) such as Alzheimer diseases, Amyotrophic lateral sclerosis, Friedreich's ataxia, Huntington's disease, Multiple sclerosis, and Parkinson's diseases. In addition, oxidative stress causing protein misfold may turn to other NDDs include Creutzfeldt-Jakob disease, Bovine Spongiform Encephalopathy, Kuru, Gerstmann-Straussler-Scheinker syndrome, and Fatal Familial Insomnia. An overview of the oxidative stress and mitochondrial dysfunction-linked NDDs has been summarized in this review.

Oxidative stress and mitochondrial dysfunction-linked neurodegenerative disorders

Nanomaterials represent one of the most promising frontiers in the research for improved antioxidants. Some nanomaterials, including organic (i.e. melanin, lignin) metal oxides (i.e. cerium oxide) or metal (i.e. gold, platinum) based nanoparticles, exhibit intrinsic redox activity that is often associated with radical trapping and/or with superoxide dismutase-like and catalase-like activities. Redox inactive nanomaterials can be transformed into antioxidants by grafting low molecular weight antioxidants on them. Herein, we propose a classification of nanoantioxidants based on their mechanism of action, and we review the chemical methods used to measure antioxidant activity by providing a rationale of the chemistry behind them.

Antioxidant activity of nanomaterials

The conjugate addition of nitroalkanes to activated alkenes is a useful reaction that involves the formation of a new C C bond and the installation of an aliphatic nitro group: a precursor of an amine, a ketone, or a carboxylate. Several catalytic asymmetric variants of this transformation have been reported for alkenes that act as soft electrophiles. However, reported methods are not suitable for a,bunsaturated esters or acids, such as cinnamates, which are poor substrates in catalytic enantioselective Michael reactions. This experimental finding is justified by the electrophilic nature of cinnamates, which is not well-matched with soft nitroalkane nucleophiles. Additionally, since the carbonyl group of cinnamates does not establish well-defined interactions with commonly used catalysts (e.g. amines or chiral Lewis acid complexes), an efficient transfer of chirality from the catalyst to the substrate is problematic. To overcome these problems, various a,b-unsaturated carbonyl compounds have been used in catalytic enantioselective Michael reactions to give products in which the desired carboxylates could be unveiled in a subsequent step. Notable examples of such compounds include chalcones, enals, a’-hydroxyenones, alkylidene malonates, and alkenoyl pyrazoles and pyrroles. We have developed styrylisoxazoles 1 as cinnamate equivalents that show high reactivity towards stabilized (soft) nucleophiles. Compounds 1 are stable solids that can be obtained in large quantities (10–100 mmol) as single E isomers through the reaction of commercially available 3,5dimethyl-4-nitroisoxazole with an aromatic or heteroaromatic aldehyde. We previously described efficient Michael addition reactions of compounds 1 with soft nucleophiles, such as enolates, nitroalkanes, and indoles. The 4-nitroisoxazol-5-yl core present in adducts 2 (Scheme 1) could be opened to display a carboxylic acid by a reaction described by SartiFantoni and co-workers: an operationally simple procedure involving the treatment of 4-nitroisoxazoles with excess aqueous NaOH. Therefore, compounds 1 constitute a valuable synthetic alternative to cinnamic esters in procedures that require tuning of the acceptor electrophilicity. We now report the use of compounds 1 in catalytic asymmetric settings in combination with phase-transfer catalysis (PTC) and the use of the resulting adducts 2 for the preparation of g-nitroesters 3 and g-amino acids 4. The high enantioselectivity observed when the reactions were carried out at room temperature with a low catalyst loading (2–5 mol%), the compatibility of nitromethane as well as secondary and tertiary nitroalkanes with the reaction conditions, and the unusual diastereocontrol when secondary nitroalkanes were used, are advantages of this process over many other procedures in which a,b-unsaturated carboxylic acid analogues are used. As the substrate and catalyst could be prepared in one step from inexpensive starting materials, the procedure is also practical to execute. We initially treated the styrylisoxazole 1a with nitromethane (5 equiv) in the presence of various inorganic bases in suitable organic solvents. This study identified solid K2CO3 and toluene as the most suitable combination of a base and a solvent. Having identified suitable reaction conditions, we tested a range of quaternary ammonium salts derived from cinchona alkaloids as catalysts (Table 1). Use of the Scheme 1. Catalytic asymmetric conjugate addition of nitroalkanes to 4-nitro-5-styrylisoxazoles 1 and synthetic applications of Michael adducts 2.

Catalytic asymmetric conjugate addition of nitroalkanes to 4-nitro-5-styrylisoxazoles.

Explaining the antioxidant activity of some common non-phenolic components of essential oils

Magnolol and honokiol, the bioactive phytochemicals contained in Magnolia officinalis, are uncommon antioxidants bearing isomeric bisphenol cores substituted with allyl functions. We have elucidated the chemistry behind their antioxidant activity by experimental and computational methods. In the inhibited autoxidation of cumene and styrene at 303 K, magnolol trapped four peroxyl radicals, with a kinh of 6.1 × 10(4) M(-1) s(-1) in chlorobenzene and 6.0 × 10(3) M(-1) s(-1) in acetonitrile, and honokiol trapped two peroxyl radicals in chlorobenzene (kinh = 3.8 × 10(4) M(-1) s(-1)) and four peroxyl radicals in acetonitrile (kinh = 9.5 × 10(3) M(-1) s(-1)). Their different behavior arises from a combination of intramolecular hydrogen bonding among the reactive OH groups (in magnolol) and of the OH groups with the aromatic and allyl π-systems, as confirmed by FT-IR spectroscopy and DFT calculations. Comparison with structurally related 3,3',5,5'-tetramethylbiphenyl-4,4'-diol, 2-allylphenol, and 2-allylanisole allowed us to exclude that the antioxidant behavior of magnolol and honokiol is due to the allyl groups. The reaction of the allyl group with a peroxyl radical (C-H hydrogen abstraction) proceeds with rate constant of 1.1 M(-1) s(-1) at 303 K. Magnolol and honokiol radicals do not react with molecular oxygen and produce no superoxide radical under the typical settings of inhibited autoxidations.

Andrea Baschieri

Papers

Antioxidant activity of nanomaterials

Catalytic asymmetric conjugate addition of nitroalkanes to 4-nitro-5-styrylisoxazoles.

Explaining the antioxidant activity of some common non-phenolic components of essential oils

Antioxidant activity of nanomaterials

Antioxidant Activity of Magnolol and Honokiol: Kinetic and Mechanistic Investigations of Their Reaction with Peroxyl Radicals