Enolic Group Research Articles

Co(II), Mn(II), and Fe(III) complexes of water‐soluble hydrazone bearing 2‐nicotinoylhydrazineylidene moiety: Preparation, characterization, cyclic voltammetry, computational and biological studies

A water‐soluble hydrazone ligand bearing 2‐nicotinoylhydrazineylidene moiety, sodium 4‐hydroxy‐3‐([2‐nicotinoylhydrazineylidene]methyl) benzenesulfonate (NaH2NH), and its complexes with Co(II), Fe(III), and Mn(II) have been synthesized and characterized. The structure of the ligand and its complexes were analyzed using various spectroscopic techniques such as FT‐IR, 1H‐ and 13C‐NMR, EI‐mass, powder X‐ray diffraction, UV–visible spectra, and magnetic measurements. The infrared spectra indicated that the ligand behaves as a negatively charged bidentate ligand (ON) through the deprotonation of the enolic (OH) group and the azomethine (C=N) group in the [Co (NaHNH)2(H2O)4Cl2].3H2O complex. In the [Fe (NaNH)2(H2O)Cl].2H2O complex, the ligand behaves as bi‐negative tetradentate (O2N2) through the protonation of the enolic oxygen and the nitrogen atom of the azomethine group in two nicotinic hydrazone molecules. Another coordination type was observed for [Mn (NaNH)(H2O)3] complex in which NaH2NH acts as bi‐negative tridentate ONO through the nitrogen atom of the azomethine group, the protonated of enolic and phenolic groups. The fluorescence spectrum of the NaH2NH was found to be quenched upon addition of these Co(II) and Mn(II) ions. The antimicrobial results indicated that the Mn(II) complex exhibited the highest antibacterial potency against all targeted organisms. The results of antioxidants demonstrated that the complexes exhibited higher activity compared to the free ligand, indicating an enhancement of antioxidant activity through complexation. The tested substances established strong nuclease‐like activity at a high concentration of 7.5 mM, leading to the complete degradation of DNA as observed in agarose gel electrophoresis. This suggests that these compounds have the potential to serve as antitumor agents in vivo by inhibiting DNA replication in cancer cells and preventing tumor growth. The interaction of the isolated compounds with 1c14 and 6vj3 targets was discussed using molecular docking.

Synthesis, Characterization and Antimicrobial Study of Some Transition Metal Complexes with Aldimine

Abstract: Aldimine ligand 2-Hydroxy-4,5- diiodo-benzylidene-4-hydroxy-aniline (L) and its complexes with Cu (II), Ni (II), Co (II) and Zn (II) were prepared and characterized by analytical, spectroscopic (IR, UV-Vis) techniques, thermal study, electrical conductivity and magnetic measurements. The results indicate that the ligand coordinate through azomithine nitrogen and oxygen of enolic group. The complexes were further screened for antimicrobial activity.

Acidity constants and protonation sites of cyclic dinucleotides determined by capillary electrophoresis, quantum chemical calculations, and NMR spectroscopy.

Cyclic dinucleotides (CDNs) are important second messengers in bacteria and eukaryotes. Detailed characterization of their physicochemical properties is a prerequisite for understanding their biological functions. Herein, we examine acid-base and electromigration properties of selected CDNs employing capillary electrophoresis (CE), density functional theory (DFT), and nuclear magnetic resonance (NMR) spectroscopy to provide benchmark pKa values, as well as to unambiguously determine the protonation sites. Acidity constants (pKa) of the NH+ moieties of adenine and guanine bases and actual and limiting ionic mobilities of CDNs were determined by nonlinear regression analysis of the pH dependence of their effective electrophoretic mobilities measured by CE in aqueous background electrolytes in a wide pH range (0.98-11.48), at constant temperature (25°C), and constant ionic strength (25mM). The thermodynamic pKa values were found to be in the range 3.31-4.56 for adenine and 2.28-3.61 for guanine bases, whereas the pKa of enol group of guanine base was in the range 10.21-10.40. Except for systematic shifts of ∼2pKa, the pKa values calculated by the DFT-D3//COSMO-RS composite protocol that included large-scale conformational sampling and "cross-morphing" were in a relatively good agreement with the pKas determined by CE and predict N1 atom of adenine and N7 atom of guanine as the protonation sites. The protonation of the N1 atom of adenine and N7 atom of guanine in acidic background electrolytes (BGEs) and the dissociation of the enol group of guanine in alkaline BGEs was confirmed also by NMR spectroscopy.

Photocatalytic Enantioselective Hydrosulfonylation of α,β-Unsaturated Carbonyls with Sulfonyl Chlorides.

This research explores the enantioselective hydrosulfonylation of various α,β-unsaturated carbonyl compounds via the use of visible light and redox-active chiral Ni-catalysis, facilitating the synthesis of enantioenriched α-chiral sulfones with remarkable enantioselectivity (exceeding 99 % ee). A significant challenge entails enhancing the reactivity between chiral metal-coordinated carbonyl compounds and moderate electrophilic sulfonyl radicals, aiming to minimize the background reactions. The success of our approach stems from two distinctive attributes: 1) the Cl-atom abstraction employed for sulfonyl radical generation from sulfonyl chlorides, and 2) the single-electron reduction to produce a key enolate radical Ni-complex. The latter process appears to enhance the feasibility of the sulfonyl radical's addition to the electron-rich enolate radical. An in-depth investigation into the reaction mechanism, supported by both experimental observations and theoretical analysis, offers insight into the intricate reaction process. Moreover, the versatility of our methodology is highlighted through its successful application in the late-stage functionalization of complex bioactive molecules, demonstrating its practicality as a strategy for producing α-chiral sulfones.

Insighting the inhibitory potential of new diorganotin(IV) complexes derived from tridentate ligands: Synthesis, structural elucidation and biological evaluation

In the present study, a series of diorganotin(IV) complexes (1-20) with the general formula R2SnL1-4 were synthesized by the reaction of R2SnCl2 (R = Me, Et, Bu, and Ph) with the hydrazone ligands (H2L1-4). Spectral and physico-analytical techniques such as multinuclear (1H, 13C, 119Sn) NMR, HRMS, FTIR, XRD and SEM studies collectively with elemental analyses were utilized to structurally elucidate the synthesized compounds. Based on the structural investigations, it can be concluded that hydrazone ligands coordinated to the central tin metal in a tridentate manner (ONO) through nitrogen atom of the azomethine group, oxygen atoms of the enolic and phenolic groups. The synthesized compounds have been screened for their in vitro antimicrobial potential against four bacterial (two Gram positive; two Gram negative) and two fungal strains. Antimicrobial activity results concluded that metal complexes exhibited better activity than free ligands towards the tested strains. Among the tested compounds, complexes 8, 12 and 20 were found to be the most active. Furthermore, the in vitro anticancer evaluation of synthesized compounds (1-20) was done against a panel of three cell lines viz; A549, MCF7 and HCT-116 using MTT assay. Complexes 5, 6 and 8 were found to be most active against the three cancer cell lines with lowest IC50 values.

Whether Carotenoids and Quercetin Affect the Proliferation andExpression of PPARγ Protein in Leukemia K562 Cells

Carotenoids are some of the most abundant pigments in nature, ranging from yellow to red. Carotenoids can divide intotwo categories: carotenoids composed of hydrocarbon elements and lutein-containing oxygen elements. They are lipidsoluble pigments, and some contain carbonyl or enol groups, which are water-soluble. Carotenoids absorb visible lightfrom 400 nm to 600 nm, while special ones such as octa-hydro lycopene and hexahydrolycopene only absorb ultravioletlight. Quercetin is a flavonoid compound widely found in fruits and vegetables. Its chemical structure phenolic hydroxylgroup is the basis of antioxidant action, which can be used for hydrogen to quench oxygen free radicals. It is oxidizedto form a highly stable catechol structure. It has a variety of biological activities and pharmacological effects, such asexpanding coronary blood vessels and inhibiting tumor cell proliferation. This paper shows that the K562 cell growthrate in carotenoids and quercetin treatment groups was slower than the control group.

Effect of anion structure on the network of hydrogen bonds formed between counter ions in salts composed of triethylamine and derivatives of 2,1-benzothiazine 2,2-dioxide and 1,2-benzoxathiine 2,2-dioxide

The investigated symmetrical bis-adducts, i.e., bis(1-ethyl-4‑hydroxy-2,2-dioxido-1H-2,1-benzothiazin-3-yl)(furan-2-yl/phenyl)methane and bis(4‑hydroxy-2,2-dioxido-2H-1,2-benzoxathiin-3-yl)(furan-2-yl/4-methoxyphenyl)methane, essential objects for pharmacological studies, were found to exist in the liquid and solid phases in a double tautomeric enol form which allows the existence of acid-base interactions related to the proton transfer to the triethylamine and the formation of an intramolecular O―H···O− hydrogen bond between the intact OH group and the enolate O− atom. In the crystal lattice of triethylammonium salts containing 1,2-benzoxathiine 2,2-dioxide moieties in the anion molecules, counter ions are connected by N―H···O hydrogen bonds, in which the enolate O− atom plays the role of a proton acceptor. Whereas in crystals with 2,1-benzothiazine 2,2-dioxide fragments in the anion molecules cation and anion molecules are linked by N—H···O hydrogen bonds, in which the role of a proton acceptor is played by an O atom of a sulphonyl group that belongs to a bicyclic fragment which contains an enolate group. We have shown that the dipole-dipole interactions in the investigated ammonium salts may explain the orientation of the cationic N−H group once to the O− atom of the enolate group, another time to the O atom of the sulfonyl group. The effect of the structure of the anion molecule on the hydrogen bonding network in the crystals studied was analyzed by the X-ray diffraction method, the 1H and 13C NMR technique including COSY, NOESY, HSQC and HMBC two-dimensional patterns, and the Fourier transform infrared (FTIR) spectroscopy. Theoretical analysis of the interactions in the crystals was performed using Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM).

Study of the Antioxidant Activity of Synthetic 3-hydroxyflavone Derivatives by DPPH and Hydrogen Peroxide Methods

Flavonoids have good efficacy as antioxidants due to their ability to scavenge free radicals within cells. In our previous study, synthetic flavonoid derivatives (A2-A13) were prepared in vitro through condensation, oxidative cyclization, alkylation and esterification reactions. The antioxidant activity of the alkyl and esterified derivatives of the flavonoid compound (A2) 3-hydroxy-2-(4-[dimethylamino]phenyl) benzo-4-pyrone was studied by two methods: 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition method and inhibition of hydrogen peroxide (H2O2) and compared to the activity of standard antioxidant compounds, ascorbic acid and quercetin. The flavonoids (prepared samples) A2, A5, and A7 showed high activity approaching that of ascorbic acid and quercetin as well-known antioxidants. As for the compounds (A3, A6, A8, A9, A10, A11, A12, A13), which contain an -OH enol group, a benzyl group, and a chlorine group and the acetate group, its effectiveness has decreased significantly.

Optimisation of GraPhage13 macro-dispersibility via understanding the pH-dependent ionisation during self-assembly: towards the manufacture of graphene-based nanodevices.

GraPhage13 aerogels (GPAs) are micro-porous structures generated through the self-assembly of graphene oxide (GO) and M13 bacteriophage. As GPA fabrication involves the aggregation of GO and M13 in aqueous solution, we aim to understand its dispersibility across a wide pH range. Herein, a novel technique has been developed to relate the ionisation of functional groups to the surface charge, offering insights into the conditions required for GPA fabrication and the mechanism behind its self-assembly. The aggregation of GO and M13 was observed between pH 2-6 and exhibited dependence on the surface charge of the resulting aggregate with the M13 bacteriophage identified as the primary factor contributing to this, whilst originating from the ionisation of its functional groups. In contrast, GO exhibited a lesser impact on the surface charge due to the deprotonation of its carboxylic, enolic and phenolic functional groups at pH 6 and above, which falls outside the required pH range for aggregation. These results enhance our understanding of the GPA self-assembly mechanism, the conditions required for their fabrication and the optimal processability, laying the foundation towards its broad range of applications and the subsequent manufacture of graphene-based nanodevices.

Thermosensitive visible-light-excited visible-/NIR-luminescent complexes with lanthanide sensitized by the π-electronic system through intramolecular H-bonding.

Visible-luminescent lanthanide (LnL) complexes with a highly planar tetradentate ligand were successfully developed for a visible-light solid-state excitation system. L was designed by using two 2-hydroxy-3-(2-pyridinyl)-benzaldehyde molecules bridged by ethylenediamine, which was then coordinated to a series of Ln ions (Ln = Nd, Sm, Eu, Gd, Tb, Dy, and Yb). From the measurement of single-crystal X-ray analysis of EuL, two phenolic O atoms and two imine N atoms in L were coordinated to the Eu ion, and each π-electronic system took coplanar with the edged-pyridine moiety through an intramolecular hydrogen bond. The enol group on the phenolic skeleton changed to the keto form, and the pyridine was protonated. Thus, intramolecular proton transfer occurred in L after the complexation. Other complexes take isostructure. The space group is P-1, and the c-axis shrinks with decreasing temperature without a phase transition in EuL. The yellow color caused by the planar structure of L can sensitize ff emission by visible light, and the luminescence color of each complex depends on central Ln ions. Furthermore, a phosphorescence band also appeared at rt with ff emission in LnL. Drastic temperature dependence of luminescence was clarified quantitatively.

The Single-Component Flavin Reductase/Flavin-Dependent Halogenase AetF is a Versatile Catalyst for Selective Bromination and Iodination of Arenes and Olefins.

Flavin-dependent halogenases (FDHs) natively catalyze selective halogenation of electron rich aromatic and enolate groups. Nearly all FDHs reported to date require a separate flavin reductase to supply them with FADH2 , which complicates biocatalysis applications. In this study, we establish that the single component flavin reductase/flavin dependent halogenase AetF catalyzes halogenation of a diverse set of substrates using a commercially available glucose dehydrogenase to drive its halogenase activity. High site selectivity, activity on relatively unactivated substrates, and high enantioselectivity for atroposelective bromination and bromolactonization was demonstrated. Site-selective iodination and enantioselective cycloiodoetherification was also possible using AetF. The substrate and reaction scope of AetF suggest that it has the potential to greatly improve the utility of biocatalytic halogenation.

The Single‐Component Flavin Reductase/Flavin‐Dependent Halogenase AetF is a Versatile Catalyst for Selective Bromination and Iodination of Arenes and Olefins**

AbstractFlavin‐dependent halogenases (FDHs) natively catalyze selective halogenation of electron rich aromatic and enolate groups. Nearly all FDHs reported to date require a separate flavin reductase to supply them with FADH2, which complicates biocatalysis applications. In this study, we establish that the single component flavin reductase/flavin dependent halogenase AetF catalyzes halogenation of a diverse set of substrates using a commercially available glucose dehydrogenase to drive its halogenase activity. High site selectivity, activity on relatively unactivated substrates, and high enantioselectivity for atroposelective bromination and bromolactonization was demonstrated. Site‐selective iodination and enantioselective cycloiodoetherification was also possible using AetF. The substrate and reaction scope of AetF suggest that it has the potential to greatly improve the utility of biocatalytic halogenation.

Organic Small Molecules with Electrochemical-Active Phenolic Enolate Groups for Ready-to-Charge Organic Sodium-Ion Batteries.

Organic materials have attracted much attention in sodium ion batteries (SIBs) because of their advantages such as being environmentally benign and having high designability. Capacities and cycle life of organic materials are the most important parameters in most research which has been paid much effort to obtain an impressive electrochemical performance on the material level, and the sodium-detachable ability of these materials to directly match with the sodium-free anode is neglected. In this work, one organic sodium salt (C6 H2 Na2 O6 ) exhibits the unique ability (charging first in half cell) unlike other reported organic cathode materials (normally discharging first) for SIBs. The redox mechanism and structure change are investigated by in situ and ex situ tests to give a better understanding for C6 H2 Na2 O6 . Satisfying electrochemical performance (74% capacity retention after 600 cycles at 0.05Ag-1 and 63% capacity retention at 5 A g-1 when compared with capacity at 0.05 A g-1 ) is achieved by the C6 H2 Na2 O6 electrode. In addition, matched with hard carbon, full cells are assembled successfully like other transition metal containing cathode materials because C6 H2 Na2 O6 electrode can deliver its sodium ions to a sodium-free anode directly without any presodiation.

Kinetics and mechanistic aspects of superoxide radical-mediated transformation of ascorbate

Ascorbate (Asc) has long been known to be an antioxidant against reactive oxygen species (ROS) for cytotoxicity and human diseases. However, its reported reactivity with superoxide radical (O2•−), an important ROS involved in aerobic metabolism system, exhibits great discrepancy; its mechanistic mode of actions on the molecular level is also largely debatable. Here, we investigated the reaction of Asc and O2•− by a combination of experimental and theoretical approaches. The rate constant measured by a competitive technique method was determined to be 3.3 × 104 M−1 s−1 under physiological condition. Mechanistically, our theoretical result indicated that O2•− abstracts a hydrogen atom on the enolic hydroxyl group forming ascorbyl radical (Asc•), which is unreactive with O2•− or Asc• itself. However, with different protonation state of Asc• (i.e., AscH•) in acidic environment, its reactivity was demonstrated to be significantly altered. AscH• can react with O2•−via hydrogen atom abstraction and single electron transfer and/or undergo self−disproportionation. These complementary results provided fundamental principles for the ecotoxicological function and environmental potentials of Asc against ROS.

Are Redox-Active Organic Small Molecules Applicable for High-Voltage (>4V) Lithium-Ion Battery Cathodes?

While organic batteries have attracted great attention due to their high theoretical capacities, high‐voltage organic active materials (> 4 V vs Li/Li+) remain unexplored. Here, density functional theory calculations are combined with cyclic voltammetry measurements to investigate the electrochemistry of croconic acid (CA) for use as a lithium‐ion battery cathode material in both dimethyl sulfoxide and γ‐butyrolactone (GBL) electrolytes. DFT calculations demonstrate that CA dilitium salt (CA–Li2) has two enolate groups that undergo redox reactions above 4.0 V and a material‐level theoretical energy density of 1949 Wh kg–1 for storing four lithium ions in GBL—exceeding the value of both conventional inorganic and known organic cathode materials. Cyclic‐voltammetry measurements reveal a highly reversible redox reaction by the enolate group at ≈4 V in both electrolytes. Battery‐performance tests of CA as lithium‐ion battery cathode in GBL show two discharge voltage plateaus at 3.9 and 3.1 V, and a discharge capacity of 102.2 mAh g–1 with no capacity loss after five cycles. With the higher discharge voltages compared to the known, state‐of‐the‐art organic small molecules, CA promises to be a prime cathode‐material candidate for future high‐energy‐density lithium‐ion organic batteries.

Organotin (IV) complexes derived from tridentate Schiff base ligands: Synthesis, spectroscopic analysis, antimicrobial and antioxidant activity

Organotin complexes of Schiff bases (derived from the condensation of hydrazides with salicylaldehyde derivatives) were prepared and their characterization was done using several spectroscopic techniques like FTIR, NMR (1H, 13C, and 119Sn) and mass spectrometry. The spectroscopic data of the ligands and their corresponding complexes revealed that the Schiff bases chelated to the tin metal in a tridentate manner through –ONO atoms (oxygen atom of the hydroxyl group of the salicylaldehydic derivatives, the nitrogen atom of azomethine group, and the oxygen atom of enolic group present in the carboxylic acid hydrazides). Around tin atom pentacoordinated geometry was exhibited. The synthesized ligands and their complexes have been assessed for their biological potency (antibacterial, antifungal and antioxidant using Ciprofloxacin, Fluconazole and Ascorbic acid as reference compounds) and few of the compounds showed optimistic activity. The ligands having electron withdrawing group attached showed greater antimicrobial activity as compared to the other ligands. The complexes showed the better activity than the ligands. The general trend followed by the complexes was diphenyl ​> ​dibutyl ​> ​dimethyl substituted complexes. Compound 11 was the most active against microbes. The antioxidant activity increased with electron donating group. The phenyl substituted complexes showed better activity as compared to the dibutyl and dimethyl substituted complexes. Compound 20 was the best antioxidant.

DFT Study of Chitosan Ascorbate Nanoparticles Structure

In recent years, use of chitosan (CS) nanoparticles as nanocarriers has received much attention due to their biodegradability, biocompatibility, and non-toxicity. CS nanoparticles containing drugs, flavors, enzymes, and antimicrobial agents can maintain their activity. Such nanoparticles can stimulate the stabilization of ascorbic acid (AA) and improve controlled release. This study investigates the interaction of CS monomer with AA and sodium tripolyphosphate (TPP) using density functional theory (DFT) during the formation of chitosan ascorbate (CA) nanostructure (CAN). Based on existing results, the formation of the CS monomer from the complexes occurs due to the donor-acceptor interaction, which is energetically favorable in all considered interactions according to the calculations. At close range, proton transfer has been identified with interaction energies, namely CS-AА (-6.82 kcal/mol), CS-TPP (–4.56 kcal/mol) in the aqueous phase, which indicates that in the process of CAN formation, in most cases, the formation of a donor-acceptor bond occurs between the amino groups of CS with the enol group of AA and the relative coordination of CS with TPP. The introduction of the aqueous phase led to a drop in the interaction energy. Based on our results for the linking types (interaction energies), we propose a simple mechanism for their impact on the CAN formation process.

Visible-Light-Induced Photoannulation of α-Naphthyl Cyclopropane Carboxylic Esters to Functionalized Dihydrophenalenes.

A general synthetic entry to functionalized dihydrophenalenes has been found using naphthyl-cyclopropane esters as starting materials. The desired annulation was possible with visible light, Ir(Fppy)3 as photocatalyst, BnNMe2 or DABCO as electron donor, HAT-catalyst, and proton source. A broad scope of substituted naphthyl and azanaphthyl derivatives provided the photoannulation products in high yield. Deuteration studies support a photoredox mechanism involving the photoreductive cyclopropane opening to an enolate radical followed by an aryl radical trapping.

A Dipolar Cyclization/Fragmentation Strategy for the Catalytic Asymmetric Synthesis of Chiral Eight-Membered Lactams

A Dipolar Cyclization/Fragmentation Strategy for the Catalytic Asymmetric Synthesis of Chiral Eight-Membered Lactams

General, Metal-free Synthesis of Carbon Nanofiber Assemblies from Plant Oils.

We designed a metal‐free synthesis of carbon nanofiber based on ketene chemistry using phosphorus pentoxide (P2O5) and vegetable oil. Based on the characterization of intermediates, P2O5‐oil reaction yielded most possibly alkylketenes, which polymerized into poly(ketene) with abundant enol groups. The enol groups further reacted with P2O5, forcing the poly(ketene) to assemble into a nano‐sized preassembly structure. Moderate heating transforms these structures into carbonaceaus nanofibers. This approach is applicable to other chemicals with similar structure to vegetable oil. The carbon nanofibers with P‐O‐C functionalization show relatively high graphitization degree and promising textural properties. The C‐O‐P environment accounts for 66 at % of the total P and creates a superior thermal stability. As a model application, a CDI system built of a carbon‐nanofiber‐based electrode countered by an activated carbon‐based electrode exhibited exceptional performance.