Biferrocenyl Schiff bases as efficient corrosion inhibitors for an aluminium alloy in HCl solution: a combined experimental and theoretical study

The corrosion inhibitive capabilities of some ferrocene-based Schiff bases on aluminium alloy AA2219-T6 in acidic medium were investigated using Tafel polarization, electrochemical impedance spectroscopy (EIS), weight loss measurement, FT-IR spectroscopy and scanning electron microscopic (SEM) techniques. The influence of molecular configuration on the corrosion inhibition behavior has been explored by quantum chemical calculation. Ferrocenyl Schiff bases 4,4′-((((ethane-1,2-diylbis(oxy))bis(4,1-phenylene))bis(methaneylylidene))bis(azaneylylidene))bisferrocene (Fcua), 4,4′-((((ethane-1,2-diylbis(oxy))bis(2-methoxy-1,4-phenylene))bis(methaneylylidene))bis(azaneylylidene))bisferrocene (Fcub) and 4,4′-((((ethane-1,2-diylbis(oxy))bis(2-ethoxy-1,4-phenylene))bis(methaneylylidene))bis(azaneylylidene))bisferrocene (Fcuc) have been synthesized and characterized by FT-IR, ¹H and ¹³C NMR spectroscopic studies. These compounds showed a substantial corrosion inhibition against aluminium alloy in 0.1 M of HCl at 298 K. Fcub and Fcuc showed better anticorrosion efficiency as compared with Fcua due to the electron donating methoxy and ethoxy group substitutions, respectively. Polarization curves also indicated that the studied biferrocenyl Schiff bases were mixed type anticorrosive materials. The inhibition of the aluminium alloy surface by biferrocenyl Schiff bases was evidenced through scanning electron microscopy (SEM) studies. Semi-empirical quantum mechanical studies revealed a correlation between corrosion inhibition efficiency and structural functionalities.

The anticorrosion activity of biferrocenyl Schiff bases on AA2219-T6 in acidic medium were studied using Tafel polarization, electrochemical impedance spectroscopy, weight loss analysis, FT-IR spectroscopy and scanning electron microscopic technique.     

Multifunctional lubricant additive based on difluoroboron derivatives of a diphenylamine antioxidant

A metal-free and phosphorus-free novel multifunctional additive (E)-4-((3-(tert-butyl)-2-((difluoroboranyl)oxy)-5-((octylthio)methyl)benzylidene)amino)-N-phenylaniline (difluoroboron derivative 4a) was synthesized and characterized. The results show that its antioxidation and tribological properties are better than those of base oil, diphenylamine and zinc dialkyldithiophosphate (ZDDP), and it can also increase the extreme pressure performance of the base oil. In addition, it can be found that the diphenylamine functional group, boron and fluorine are the main contributors to the excellent antioxidation and antiwear properties of difluoroboron derivative 4a, respectively. Finally, the results of X-ray photoelectron spectroscopy on the worn surfaces reveal that B₂O₃, Fe₂O₃, a N-containing organic compound and iron fluoride comprise the boundary films, which effectively improve the difluoroboron derivative 4a''s antiwear properties.

Difluoroboron derivatives of an antioxidant with excellent antioxidation and antiwear properties provide a new strategy for metal-free and phosphorus-free multifunctional additives.     

Adsorption characteristics and inhibition effect of two Schiff base compounds on corrosion of mild steel in 0.5 M HCl solution: experimental,DFT studies,and Monte Carlo simulation

In this work, we report the synthesis of two Schiff bases of substituted gallic acid derivatives via amidation reaction and their characterization using ¹H-NMR spectroscopy to study their inhibition performance on the aggressive attack of HCl on mild steel (MS). The inhibitive performance was examined using chemical (weight loss) and electrochemical (Tafel and EIS) test methods. The results indicate that these derivatives significantly suppress the dissolution rate of mild steel via adsorption phenomena, which correlates to the Langmuir adsorption model. Tafel data display the mixed-type properties of these compounds and EIS results show that increasing Schiff base concentration not only leads to delaying the charge transfer (R_ct) of iron from 26.4 ohm cm⁻² to 227.7 ohm cm⁻² but also decreases the capacitance of the adsorbed double layer (C_dl) from 8.58 (F cm⁻²) × 10⁻⁵ to 2.55 (F cm⁻²) × 10⁻⁵. The inhibition efficiency percentage reaches the peak (90%) at optimum concentration of 250 ppm. The Monte Carlo simulations confirm the adsorption ability of the as-prepared compounds on the Fe (1 1 0) crystal. The SEM/EDX results revealed the presence of a protective film on the mild steel sample.

Structures of the synthesized Schiff bases inhibitor.     

Understanding the adsorption performance of two glycine derivatives as novel and environmentally safe anti-corrosion agents for copper in chloride solutions: experimental,DFT, and MC studies

The inhibition impacts of two non-toxic glycine derivatives, namely, bicine (N,N-bis(2-hydroxyethyl)glycine) and tricine (N-(tri(hydroxymethyl)methyl) glycine) on copper corrosion were investigated in 3.5% NaCl solutions. Surprisingly, there is no report on using bicine and/or tricine as corrosion inhibitors for Cu and its alloys in a seawater-like environment. The effects of bicine and tricine on the corrosion behavior of Cu in 3.5% NaCl were examined using the open circuit potential, Tafel polarization, and AC spectroscopy (EIS) techniques. The corrosion rate decreased as a function of the inhibitor dose. The Tafel and EIS parameters showed that the inhibitors decreased both the anodic and cathodic corrosion currents and inhibited the charge transfer process by adsorption on the Cu surface. The inhibition property was attributed to the adsorption of inhibitor molecules with the Langmuir model. Tricine showed a superior inhibition performance of more than 98% at a concentration of ∼5 mmol L⁻¹. The free energy of adsorption data revealed physical adsorption. The outcomes of Monte Carlo simulations and theoretical studies well supported the experimental data.

The inhibition impacts of two non-toxic glycine derivatives, namely, bicine (N,N-bis(2-hydroxyethyl)glycine) and tricine (N-(tri(hydroxymethyl)methyl) glycine) on copper corrosion were investigated in 3.5% NaCl solutions.     

Adsorption and anti-corrosion characteristics of vanillin Schiff bases on mild steel in 1 M HCl: experimental and theoretical study

Herein, two Schiff base derivatives of vanillin and divanillin with 2-picolylamine, namely, 2-methoxy-4-((pyridin-2-ylmethylimino)methyl)phenol (compound A) and 3,3′-dimethoxy-5,5′-bis-((pyridin-2-ylmethylimino)methyl)-[1,1′-biphenyl]-2,2′-diol (compound B), respectively, were synthesized. Additionally, their adsorption characteristics and corrosion inhibition behavior were compared for mild steel in 1 M HCl using electrochemical impedance spectroscopy, potentiodynamic polarization and weight loss methods. Compound B was found to impart a better anti-corrosive effect (around 95% inhibition efficiency at 313 K) than compound A. The inhibitors act as effective mixed-type inhibitors and exhibit Langmuir-type adsorption behaviour. The kinetic–thermodynamic parameters together with the data obtained from density functional theory (DFT) and molecular dynamics (MD) simulations illustrate the mechanism of corrosion and mode of adsorption of both inhibitors on the metal surface. The better corrosion mitigation propensity of the dimeric form of the inhibitor (compound B) over the monomeric form (compound A) was tested experimentally and explained according to the theoretical data.

Two Schiff base derivatives of vanillin and divanillin with 2-picolylamine are synthesized and their anti-corrosive propensity for mild steel in aqueous HCl are compared.     

Photoresponsive behavior of hydrophilic/hydrophobic-based novel azobenzene mesogens: synthesis,characterization and their application in optical storage devices

Three series of alkoxy chain-bearing azobenzene-derived quaternary ammonium iodides with an alkoxy chain at one end, namely N,N-diethanol-6-(4-((4′-alkyloxyphenyl)diazenyl)phenoxy)hexan-1-ammonium iodides, N-ethyl-N-ethanol-6-(4-((4′-alkyloxyphenyl)diazenyl)phenoxy)hexan-1-ammonium iodides and N,N-diethyl-6-(4-((4′-alkyloxyphenyl)diazenyl)phenoxy)hexan-1-ammonium iodides were synthesized and characterized. Their mesomorphic and photoswitching properties were examined via polarising optical microscopy (POM), differential scanning calorimetry (DSC) and UV-vis spectrophotometry. The liquid crystalline tilted schlieren texture of smectic C, non-tilted natural focal conic texture of smectic A and smectic B phases were observed in the N,N-diethanol- and N-ethyl-N-ethanol-bearing ammonium group substituted at the terminal via the alkoxy chain of the azo moiety. In these azo moieties, the equilibrium time for trans–cis isomerization was about 1 min and cis–trans isomerization occurred at around 590 min, which had the highest alkoxy chain and no hydroxyl group on their head group. The absence of a hydroxyl group on the terminal head group resulted in slow thermal back relaxation, whereas the hydroxyl group-bearing head group showed fast thermal back relaxation. These results suggest that the influence of the substituent on the cationic ammonium head group and alkoxy chain length on the photoisomerization of the azo compounds is vital for optical storage devices. Furthermore, the device fabricated using these materials demonstrated that they are excellent candidates for optical image storage applications.

Effect of Photoresponsive behaviour of hydrophilic/hydrophobic based novel azobenzene''s. Powerful structure property relationship. Light plays the dominant role in photoisomerization properties.     

Synthesis of Schiff and Mannich bases of new s-triazole derivatives and their potential applications for removal of heavy metals from aqueous solution and as antimicrobial agents

An efficient, simple, and one-pot double Mannich reaction was performed for the synthesis of cyclized 2-methyl-6-substituted-6,7-dihydro-5H-s-triazolo[5,1-b]-1,3,5-thiadiazines via a reaction of 5-methyl-1H-s-triazole-3-thiol (1) with formaldehyde and primary aliphatic amines in ethanol at room temperature, while with primary aromatic amines, uncyclized 3-methyl-1-((substituted-amino)methyl)-1H-s-triazole-5-thiols were produced. Under Mannich reaction conditions, 4-amino-3-methyl-s-triazole-5-thiol (8) reacted with formaldehyde only in boiling ethanol or at room temperature to afford 3-methyl-5,6-dihydro-s-triazolo[3,4-b]-1,3,4-thiadiazole without incorporation of secondary amine. Furthermore, after reaction of compound 8 with aromatic aldehydes under different reaction conditions, uncyclized Schiff''s bases were produced. Therefore, reaction of these Schiff''s bases with primary or secondary amines with formaldehyde in ethanol at room temperature afforded the corresponding Mannich bases 13–14. The structures of all new compounds were confirmed using spectral analysis. Furthermore, most of the synthesized derivatives showed high efficiency for removal of Pb²⁺, Cd²⁺, Ca²⁺, and Mg²⁺ from aqueous solutions, as well as antimicrobial activity.

An efficient synthesis of Schiff and Mannich bases of new s-triazole derivatives under mild conditions has been developed for the removal of Pb²⁺, Cd²⁺, Ca²⁺, and Mg²⁺ from aqueous solutions and as antimicrobial agents.     

D–π–A azine based AIEgen with solvent dependent response towards a nerve agent

We developed a D–π–A based unsymmetrical azine molecule 4-((E)-((E)-(4-(dipropylamino)benzylidene)hydrazono)methyl)benzonitrile [DPBN] and studied its optical and aggregation induced emission properties. The DPBN molecule shows good aggregation induced emission (AIE) behaviour with 1157-fold fluorescence enhancement in the aggregated state. In addition to that, both colorimetric as well as fluorometric sensing studies revealed that DPBN selectively detects diethylchlorophosphate (DCP), a potent nerve agent. Interestingly, DPBN shows solvent dependent optical output in the presence of DCPvia two different mechanisms. In the monomer state, it shows red shifted fluorescence enhancement along with color change from colorless to orange color via the formation of a new intramolecular charge transfer state in pure tetrahydrofuran (THF). In the aggregated state, DPBN shows blue shifted emission with fluorescence enhancement in THF–water mixture by protonation at the amine nitrogen centre. Thus, DPBN can be used as a diagnostic measure to selectively detect nerve agents like DCP. This study also paves the way for further development of molecular probes for nerve agents that would represent immense implications in various fields of chemistry and biology.

Selective detection of diethylchlorophosphate using a D–π–A based AIEgen in aqueous as well as non-aqueous environment via different sensing mechanisms.     

Synthesis and characterization of novel dicarbohydrazide derivatives with electrochemical and theoretical approaches as potential corrosion inhibitors for N80 steel in a 3.5% NaCl solution

Two novel ethanoanthracene-11,12-dicarbohydrazide derivatives N′¹¹,N′¹²-bis((Z)-4-hydroxybenzylidene)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarbohydrazide (H₂HEH) and N′¹¹,N′¹²-bis((Z)-4-methoxybenzylidene)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarbohydrazide (H₂MEH) were synthesized and characterized by FT-IR spectroscopy, electronic spectra, and NMR spectroscopy. These two derivatives as novel anticorrosion inhibitors for N80 steel in a 3.5% NaCl solution were studied using electrochemical techniques including potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM). Corrosion parameters and adsorption isotherms were determined from current–potential diagrams (i.e., Tafel slopes). The impact of temperature and inhibitor concentration on the corrosion performance was studied using the PP method. The PP results suggested mixed-type inhibitors. The inhibition prohibition increased and decreased when the dose was increased and the temperature was increased, respectively. The adsorption of the hydrazides on the N80 exterior followed the Langmuir isotherm. The maximum inhibition proficiency for H₂MEH and H₂HEH were 93.3% and 92.2%, respectively, at 1 × 10⁻⁴ M. Moreover, the investigated surface was studied with the synthesized compounds through X-ray photoelectron spectroscopy (XPS) to confirm the construction of an adsorbed shielding barrier. An evident association was established between the corrosion inhibition proficiency and theoretical variables acquired using the density functional theory (DFT) method and Monte Carlo (MC) simulations. The experimental data were in good agreement with the theoretical results.

Two novel dicarbohydrazide derivatives (H₂HEH) and (H₂MEH) were synthesized and tested as corrosion inhibitors for N80 steel in 3.5% NaCl solution via electrochemical and theoretical approaches.     

Novel sulphonic acid liquid crystal derivatives: experimental,computational and optoelectrical characterizations

A novel liquid crystal homologous series based on the benzene sulphonic acid moiety, namely (E)-4-((4-((4-(alkoxy)benzoyl)oxy)benzylidene)amino)benzenesulfonic acid (Sn), was synthesized and examined via different experimental and theoretical measurements. The four synthesized members have terminally connected alkoxy chain groups, which vary between 6 and 12 carbons. FT-IR and NMR spectroscopy, as well as elemental analyses, were used to confirm their molecular structures. Mesomorphic and optical investigations of the prepared homologues were also conducted using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The DSC and POM characterization revealed that all of the synthesized sulphonic acid members are monomorphic, exhibiting a pure smectic A (SmA) mesophase with enantiotropic properties. Moreover, all compounds in the group have high thermal transition temperatures. The terminal electron-withdrawing group –SO₃H plays a considerable role in the stabilization of the molecule, which in return resulted in high thermal SmA stability. Furthermore, the experimental data relating to the mesophase behavior were substantiated via computational studies using the DFT approach. In addition, the terminal –SO₃H moiety has an essential impact on the thermal and physical parameters of possible geometries. All members of the synthesized Sn series exhibit ohmic behavior with electrical resistance in the GΩ range, as revealed by electrical measurements. The S10 electrode had the highest electrical conductivity: 35.16 pS. It also showed two direct optical band gaps of 3.58 and 3.23 eV with Urbach energies of 1261.1 and 502.4 meV. Upon decreasing the number of carbon atoms to n = 6, the main bandgap for S6 reduced to 3.3 eV. The highest conductivity, good absorption, and two large bandgaps recorded for the chain derivative S10 make it suitable for investigations relating to energy-based applications.

A novel liquid crystal homologous series based on the benzene sulphonic acid moiety, namely (E)-4-((4-((4-(alkoxy)benzoyl)oxy)benzylidene)amino)benzenesulfonic acid (Sn), was synthesized and examined via different experimental and theoretical measurements.     

Appraisal of novel azomethine–thioxoimidazolidinone conjugates as ecto-5′-nucleotidase inhibitors: synthesis and molecular docking studies

Purinergic signaling is regulated by a group of extracellular enzymes called ectonucleotidases. One of its members i.e., ecto-5′-nucleotidase (h-e5′NT) is involved in the final step of the enzymatic hydrolysis cascade that is the conversion of adenosine monophosphate (AMP) to adenosine and therefore, involves the regulation of adenosine level in extracellular space. The overexpression of h-e5′NT has been observed in various pathological conditions such as hypoxia, inflammation and cancers, and led to various complications. Hence, the identification of a potent as well as selective inhibitor of h-e5′NT is of greater importance in therapeutic treatment of various diseases. Azomethine-thioxoimidazolidinone derivatives were studied for their inhibition potential against e5′NT enzyme along with cytotoxic potential against cancer cell lines possessing overexpression of e5′NT enzyme. The derivative (E)-3-((4-((3-methoxybenzyl)oxy)benzylidene)amino)-2-thioxoimidazolidin-4-one (4g) displayed selective and significant inhibition towards h-e5′NT with an IC₅₀ value of 0.23 ± 0.08 μM. While two other derivatives i.e., (E)-3-(((5-bromothiophen-2-yl)methylene)amino)-2-thioxoimidazolidin-4-one (4b) and 2-thioxo-3-((3,4,5-trimethoxybenzylidene)amino)imidazolidin-4-one (4e), exhibited non-selective potent inhibitory behavior against both human and rat enzymes. Moreover, these derivatives (4b, 4e and 4g) were further investigated for their effect on the expression of h-e5′NT using quantitative real time polymerase chain reaction. Additionally, molecular docking and DFT studies were also performed to determine the putative binding mode of potent inhibitors within the enzyme active site. HOMO, LUMO, ΔE, and molecular electrostatic potential maps were computed by DFT and the charge transfer regions within the molecules were identified to find out the regions for electrophilic and nucleophilic attack.

Azomethine–thioxoimidazolidinone conjugates as ecto-5′-nucleotidase inhibitors.     

One pot synthesis of two cobalt(iii) Schiff base complexes with chelating pyridyltetrazolate and exploration of their bio-relevant catalytic activities

Two new cobalt(iii) tetrazolato complexes [Co(L¹)(PTZ)(N₃)] (1) and [Co(L²)(PTZ)(N₃)] (2) {where H₂L¹ = 2((3-(methylamino)propylimino)methyl)-6-methoxyphenol, H₂L² = 2((3-(dimethylamino)propylimino)methyl)-6-ethoxyphenol and HPTZ = 5-(2-pyridyl)tetrazole}, have been synthesized via in situ 1,3-dipolar cycloaddition reaction of 2-cyanopyridine and sodium azide in the presence of cobalt(ii) nitrate hexahydrate and respective Schiff bases in the open atmosphere. The structures of both complexes have been confirmed by single crystal X-ray diffraction studies. Features of noncovalent interactions in the solid state of both complexes have been studied by means of DFT and MEP calculations and characterized using Bader''s theory of “atoms in molecules” (AIM). These complexes act as biomimetic catalysts promoting the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to the corresponding o-benzoquinone at room temperature. The reaction follows Michaelis–Menten enzymatic reaction kinetics with turnover numbers of ∼0.030 s⁻¹ in an acetonitrile–methanol (2 : 1) mixture. Both complexes are also reactive towards aerobic oxidation of o-aminophenol in acetonitrile–methanol (2 : 1) with turnover numbers ∼0.095 s⁻¹.

Two cobalt(iii) tetrazolato complexes have been synthesized and characterized. Noncovalent interactions have been analysed by DFT and MEP calculations and characterized using Bader''s theory of AIM. Both complexes catalyze the aerial oxidation of 3,5-DTBC and OAPH.     

Bis-Schiff bases of 2,2′-dibromobenzidine as efficient corrosion inhibitors for mild steel in acidic medium

In this work, three new bis-Schiff bases, namely 1,1′-(2,2′-dibromo-[1,1′-biphenyl]-4,4′-diyl)bis(N-phenylmethanimine) (BNSB01), 1,1′-(2,2′-dibromo-[1,1′-biphenyl]-4,4′-diyl)bis(N-(4-bromophenyl)methanimine) (BNSB02) and 4,4′-(((2,2′-dibromo-[1,1′-biphenyl]-4,4′-diyl)bis(methanylylidene))bis(azanylylidene))diphenol (BNSB03), were synthesized. These Schiff bases were evaluated for their corrosion inhibition ability on mild steel specimens in 0.5 M HCl by using electrochemical and weight loss techniques. The inhibition performance was found to increase with an increase in the inhibitor concentration and decrease with an increase in temperature. The results revealed that the synthesized compounds followed the Langmuir isotherm model and were efficient mixed-type inhibitors. The electrochemical impedance studies also indicated that with a rise in the concentration of inhibitors, the charge transfer resistance increased. The surface morphology of the inhibited and uninhibited specimens was examined using scanning electron microscopy (SEM). The efficiency of the compounds was in the order BNSB02 > BNSB03 > BNSB01. All the results obtained were in good correlation with each other.

The inhibitory effect of three new bis-Schiff bases on mild steel corrosion in 0.5 M HCl was studied by the weight loss method and the electrochemical method.     

Analysis of energies of halogen and hydrogen bonding interactions in the solid state structures of vanadyl Schiff base complexes

Two mononuclear and two dinuclear vanadium(v) complexes, [VO₂L¹] (1), [VO₂L²] (2), (μ-O)₂[V(O)(L³)]₂ (3) and (μ-O)₂[V(O)(L⁴)]₂·2H₂O (4), where HL¹ = 4-bromo-6-[(2-phenylaminoethylimino)methyl]phenol, HL² = 2-((2-(diethylamino)ethylimino)methyl)-4-chlorophenol, HL³ = 2-((2-(ethylamino)ethylimino)methyl)-4-chlorophenol and HL⁴ = 2-(1-(2-(ethylamino)ethylimino)ethyl)phenol have been synthesized and characterized. Structures of all complexes have been confirmed by single crystal X-ray diffraction studies. Complexes 1, 2, and 3 exhibit significant halogen bonding interactions in their solid state structures. The energies associated to the supramolecular interactions have been explored using Density Functional Theory (DFT) calculations, and further confirmed with non-covalent interaction (NCI) plots.

Four vanadyl Schiff base complexes have been prepared and characterized. Energies of supramolecular interactions in complexes 1, 2 and 3 were estimated using DFT calculations, and further corroborated with NCI plot index computational tool.     

Synthesis and physicochemical,DFT, thermal and DNA-binding analysis of a new pentadentate N3S2 Schiff base ligand and its [CuN3S2]2+ complexes

A new N₃S₂ pentadentate Schiff base ligand derived from 5-bromothiophene-2-carbaldehyde, (E)-N1-((5-bromothiophen-2-yl)methylene)-N2-(2-((E)-((5-bromothiophen-2-yl)-methylene amino) ethyl ethane-1,2-diamine, is prepared. The ligand and its complexes are subjected to extensive physical and theoretical analyses and the results are consistent with their predicted compositions. Dicationic Cu(ii) complexes ([CuN₃S₂]X₂) with a coordination number of 5 are proposed on the basis of the spectral data with N₃S₂ serving as a pentadentate ligand. The prepared complexes display a square pyramidal geometry around the Cu(ii) center. TG shows different thermal behavior for the N₃S₂ ligand and its complexes. Solvatochromism of the complexes is promoted by the polarity of the solvent used. A one-electron transfer Cu(ii)/Cu(i) reversible redox reaction is promoted by CV. SEM and EDS of the free ligand and its complexes support the morphology and composition changes observed upon the complexation of Cu(ii). As an outstanding goal to develop anticancer new metal chemotherapy, preliminary studies of the binding of the desired complexes with DNA were carried out, as it is through judging the strength of interactions that a future drug can be designed and synthesized. The viscosity and absorption results obtained for complex 1 indicated its enhanced CT-DNA binding properties as compared to those of complex 2 with K_b values of 3.2 × 10⁵ and 2.5 × 10⁵ M⁻¹, respectively.

A new N₃S₂ pentadentate Schiff base ligand derived from 5-bromothiophene-2-carbaldehyde, (E)-N1-((5-bromothiophen-2-yl)methylene)-N2-(2-((E)-((5-bromothiophen-2-yl)-methylene amino) ethyl ethane-1,2-diamine, is prepared.     

Synthesis,X-ray crystal structure elucidation and Hirshfeld surface analysis of N-((4-(1H-benzo[d]imidazole-2-yl)phenyl)carbamothioyl)benzamide: investigations for elastase inhibition,antioxidant and DNA binding potentials for biological applications

The interest in the present study pertains to the development of a new compound based upon a benzimidazole thiourea moiety that has unique properties related to elastase inhibition, free radical scavenging activity and its DNA binding ability. The title compound, N-(4-(1H-benzo[d]imidazol-2-yl)phenyl)-3-benzoyl thiourea (C₂₁H₁₈N₄O₂SH₂O:TUBC), was synthesized by reacting an acid chloride of benzoic acid with potassium thiocyanate (KSCN) along with the subsequent addition of 4-(1H-benzo[d]imidazol-2-yl)benzenamine via a one-pot three-step procedure. The structure of the resulting benzimidazole based thiourea was confirmed by spectroscopic techniques including FTIR, ¹H-NMR, ¹³C-NMR and single crystal X-ray diffraction and further examined by Hirshfeld surface analysis. TUBC was also investigated by using both in silico methodology including molecular docking for elastase inhibition along with quantum chemical studies and in vitro experimental methodology utilizing elastase inhibition and free radical scavenging assay along with DNA binding experiments. Docking results confirmed that TUBC binding was within the active region of elastase. In comparison to the reference drug oleanolic acid, the low IC₅₀ value of TUBC also indicated its high tendency towards elastase inhibition. TUBC scavenged 80% of DPPH˙ radicals which pointed towards its promising antioxidant activity. TUBC–DNA binding by DFT, docking, UV-visible spectroscopy and viscosity measurements revealed TUBC to be a potential drug candidate that binds spontaneously and reversibly with DNA via a mixed binding mode. All theoretical and experimental findings pointed to TUBC as a potential candidate for a variety of biological applications.

A new compound based upon a benzimidazole thiourea moiety that has unique properties related to elastase inhibition, antioxidant and DNA binding ability has been studied.     

Persulfate-activated charcoal mixture: an efficient oxidant for the synthesis of sulfonated benzo[d][1,3]oxazines from N-(2-vinylphenyl)amides and thiols in aqueous solution

A series of 2,4-aryl-4-((arylsulfonyl)methyl)-4H-benzo[d][1,3]oxazines in good to excellent yields have directly been obtained from N-(2-vinylphenyl)amides and thiols by employing a mixture of K₂S₂O₈-activated charcoal in aqueous acetonitrile solution at 50 °C. A plausible mechanism for the reaction is reported. It reveals that the reaction follows a radical pathway and the persulfate has been the oxygen source for formation of the sulfone group in the products. It is worth mentioning that this protocol utilizes an easily accessible K₂S₂O₈-activated charcoal mixture and thiols, respectively, as an oxidant and sulfonylating precursors for the first time.

A simple method for the synthesis of 2,4-aryl-4-((arylsulfonyl)methyl)-4H-benzo[d][1,3]oxazines using an easily accessible K₂S₂O₈-activated charcoal mixture and thiols, respectively, as an oxidant and sulfonylating precursors has been described.     

Quantum chemical elucidation of the turn-on luminescence mechanism in two new Schiff bases as selective chemosensors of Zn2+: synthesis,theory and bioimaging applications

We report the synthesis and characterization of two new selective zinc sensors (S,E)-11-amino-8-((2,4-di-tert-butyl-1-hydroxybenzylidene) amino)-11-oxopentanoic acid (A) and (S,E)-11-amino-8-((8-hydroxybenzylidene)amino)-11-oxopentanoic acid (B) based on a Schiff base and an amino acid. The fluorescent probes, after binding to Zn²⁺ ions, presented an enhancement in fluorescent emission intensity up to 30 times (ϕ = A 50.10 and B 18.14%). The estimated LOD for compounds A and B was 1.17 and 1.20 μM respectively (mixture of acetonitrile : water 1 : 1). Theoretical research has enabled us to rationalize the behaviours of the two selective sensors to Zn²⁺ synthesized in this work. Our results showed that in the free sensors, PET and ESIPT are responsible for the quenching of the luminescence and that the turn-on of luminescence upon coordination to Zn²⁺ is mainly induced by the elimination of the PET, which is deeply analysed through EDA, NOCV, molecular structures, excited states and electronic transitions via TD-DFT computations. Confocal fluorescence microscopy experiments demonstrate that compound A could be used as a fluorescent probe for Zn²⁺ in living cells.

Two new selective zinc sensors (S,E)-11-amino-8-((2,4-di-tert-butyl-1-hydroxybenzylidene)amino)-11-oxopentanoic acid (A) and (S,E)-11-amino-8-((8-hydroxybenzylidene)amino)-11-oxopentanoic acid (B) based on a Schiff base and an amino acid are reported.     

A low molecular weight OLED material: 2-(4-((2-hydroxyethyl)(methyl)amino)benzylidene)malononitrile. Synthesis,crystal structure,thin film morphology,spectroscopic characterization and DFT calculations

2-(4-((2-Hydroxyethyl)(methyl)amino)benzylidene)malononitrile (HEMABM) was synthesized from 4-[hydroxymethyl(methyl)amino]benzaldehyde and propanedinitrile to obtain a low molecular weight fluorescent material with an efficient solid-state emission and electroluminescence properties comparable to the well-known poly(2-methoxy-5(2′-ethyl)hexoxyphenylenevinylene) (MEH-PPV). The HEMABM was used to prepare an organic light-emitting diode by a solution process. Despite the title compound being a small molecule, it showed optical properties and notable capacity to form a film with smooth morphology (10.81 nm) closer to that of polymer MEH-PPV (10.63 nm). The preparation of the device was by spin coating, the electrical properties such as threshold voltage were about 1.0 V for both HEMABM and MEH-PPV, and the luminance 1300 cd m⁻² for HEMABM and 2600 cd m⁻² for MEH-PPV. This low molecular weight compound was characterized by SCXRD, IR, NMR, and EI. Besides a quantitative analysis of the intermolecular interactions by PIXEL, density functional theory (DFT) calculations are reported.

A low molecular weight fluorescent malononitrile derivative showed an efficient solid-state emission and electroluminescence properties.     

Nano-aggregates of furan-2-carbohydrazide derivatives displaying enhanced emission with a bathochromic shift

The non-fluorescent Schiff base compound C1 (N''-((4′-ethyl-3-hydroxy-[1,1′-biphenyl]-4-yl)methylene)furan-2-carbohydrazide) in organic solvent (e.g., THF) was found to produce yellow-green fluorescence emission upon addition of H₂O, and granular-shaped aggregates in a THF/H₂O mixed solution formed and exhibited obvious aggregation-induced emission (AIE). Especially its keto fluorescence band intensified dramatically, while the enol emission band remained almost unchanged. Hence, a change in fluorescence from no emission of light to emission of bright yellow-green light under a UV lamp was observed with the naked eye. In contrast, the reference compound C2 (N''-((4′-ethyl-3-methoxy-[1,1′-biphenyl]-4-yl)methylene)furan-2-carbohydrazide) showed no intensified fluorescence emission under the same experimental conditions. These results indicated the significant role played by intramolecular H-bonding in the formation of the C1 aggregates and the AIE process.

C1 exhibited obvious AIE phenomena. A change from a lack of fluorescence emission to the emission of yellow-green light under a UV lamp was observed upon the inclusion of water in the solvent.