Concentration and solvent dependent SERS, DFT, MD simulations and molecular docking studies of a thioxothiazolidine derivative with antimicrobial properties

Quantum chemical treatment, electronic energy in various solvents, spectroscopic, molecular docking and dynamic simulation studies of 2-amino-N-(2-chloro-6-methylphenyl)thiazole-5-carboxamide: A core of anticancer drug

The titled molecule 2-Amino-N-(2-chloro-6-methylphenyl)thiazole-5-carboxamide (ANMC) is a core of anticancer drug dasatinib (leukemia). Its derivatives exhibited bioactivity against breast cancer. Experimentally, the titled compound was described using NMR (1H NMR and 13C NMR), FTIR and UV-visible spectroscopy. The results were compared with the theoretical predictions, showing good agreement such as theoretical NH vibrations showed symmetric stretching and asymmetric stretching at 3429 and 3440 cm-1 respectively, λmax values appear at 305 nm for experimental and 307.75 nm for theoretical observations in acetone medium. Hirshfeld surface analysis well described the secondary internal and external interactions obtained like dnorm and di ranges -1.8551 to 1.4590 and 0.0918 to 2.6756 respectively. Comparing UV-visible spectra obtained in various solvents with the calculated TD-DFT results revealed minimal solvent effects. Molecular electrostatic potential (MEP) map and Fukui functions were employed, which indicated reactive sites of the molecule and the obtained order of nucleophilic reactivity was C16 > C2 > C8 > Cl1 > C22 > C21. The bioactivity profile probability of ANMC was theoretically explored by calculation of electrophilicity index and drug-likeness. Molecular docking of the ANMC molecule was performed with ten receptors to obtain the best ligand-protein interaction and the minimum binding energy obtained was -8.0 kcal/mol. Biomolecular stability of ANMC was investigated by Molecular Dynamic Simulation (MDS). And also the analysis of free energies showed strong interactions between the ligand and the protein.

Utilizing a synergistic strategy that combines electromagnetic and chemical enhancement to analyze the SERS effect of the Fe3O4@GO@Ag on PAHs detection

A comprehensive understanding of the enhancement mechanism of the substrate material is crucial to ensure the repeatability and functionality of SERS detection technology. Therefore, this study introduces a theoretical analysis method that integrates electromagnetic and chemical enhancement to achieve a comprehensive understanding of the SERS effect on the magnetic composite substrate. The visual model is employed in this study to comprehensively analyze and illustrate the electric field enhancement and optical effects of composite substrate materials. The study also elucidated the adsorption and charge transfer between the substrate material and target molecules. Based on this theory, Fe3O4@GO@Ag material was prepared and used to detect hydrophobic organic molecules such as polycyclic aromatic hydrocarbons (PAHs), with a concentration as low as 0.5 nM. This study comprehensively analyzed the SERS enhancement effect of the composite substrate for the first time, and prepared a magnetic composite substrate material for the detection of hydrophobic organic molecules, opening up a new avenue for theoretical guidance and experimental exploration in SERS detection and analysis.

Toward Modeling the Complexity of the Chemical Mechanism in SERS

Surface-enhanced Raman scattering (SERS) provides detailed information about the binding of molecules at interfaces and their interactions with the local environment due to the large enhancement of Raman scattering. This enhancement arises from a combination of the electromagnetic mechanism (EM) and chemical mechanism (CM). While it is commonly accepted that EM gives rise to most of the enhancement, large spectral changes originate from CM. To elucidate the rich information contained in SERS spectra about molecules at interfaces, a comprehensive understanding of the enhancement mechanisms is necessary. In this Perspective, we discuss the current understanding of the enhancement mechanisms and highlight their interplay in complex local environments. We will also discuss emerging areas where the development of computational and theoretical models is needed with specific attention given to how the CM contributes to the spectral changes. Future efforts in modeling should focus on overcoming the challenges presented in this review in order to capture the complexity of CM in SERS.

SERS analysis, DFT, and solution effects regarding the structural and optical characteristics of folic acid biomolecule adsorbed on a Cu3 metal cluster

The optical characteristics of folic acid (ABP) and metal clusters of copper (Cu3) at various locations were investigated by means of density functional theory (DFT) computations. Mulliken charge analysis and molecular electrostatic potential (MEP) surface show how charge moves from Cu3 to ABP through the various groups. The peak in the UV-Vis spectra of ABP-Cu3 is caused by bonding and anti-bonding orbitals. In both vacuum and aqueous conditions, the polarizability values of ABP-Cu3 cluster are significantly higher than those of pure ABP, indicating a possible enhancement of the nonlinear optical (NLO) effect. Our research investigates the possibility of using ABP adsorbed metal clusters for NLO materials. Surface enhanced Raman scattering (SERS) in the ABP adsorbed metal clusters enhances the vibrational modes of ABP. Adsorption energies are found to be in the range -17.08 to -58.52 kcal/mol in vacuum and -53.34 to -93.44 kcal/mol in aqueous medium for the different configurations for ABP-Cu3. It indicates that metal clusters adsorbed by ABP are stable in the aqueous media. Experimental IR and UV-Vis of ABP is in agreement with theoretically predicted ones.

Unveiling the Crucial Role of Chemical Enhancement in the SERS Analysis of Amphetamine-Metal Interactions on Gold and Silver Surfaces: Importance of Selective Amplification of the Narrow Interval of Vibrational Modes

The use of addictive substances, including drugs, poses significant health risks and contributes to various social problems, such as increased crime rates associated with substance-induced aggressive behavior. To address these challenges, possession of addictive substances is legally prohibited. However, detecting and analyzing these substances remain a complex task for law enforcement, primarily due to the presence of adulterants or limited sample quantities. In response to the evolving illicit market, continuous development and adaptation of analytical techniques are essential. One approach is the utilization of surface-enhanced Raman scattering (SERS) spectroscopy, which involves adsorbing the analyte onto nanostructured plasmonic surfaces. This study explores the potential of SERS in detecting amphetamine-based addictive stimulants with a specific focus on the properties of enhancing surfaces chosen. Comparative investigations were performed using silver and gold surfaces, with gold colloidal systems demonstrating a favorable performance. Moreover, to provide a comprehensive interpretation of the measured spectra, extensive density functional theory (DFT) calculations were conducted, allowing for a deeper understanding of the observed spectral features and molecular interactions with the metal surfaces. This review presents insights into the role of chemical enhancement in SERS analysis of amphetamine-metal interactions, shedding light on the selective amplification of vibrational modes. These findings, supported by DFT calculations, have implications in the fields of spectroscopy, physical chemistry, and drug analysis, providing valuable contributions to forensic applications and a deeper understanding of chemical enhancement phenomena. We present the impact of the secondary resonances of Stokes-scattered photons. This illustrates the significance of recognizing the constraints of the frequently employed "E4" approximation, even in measurements involving multiple molecules rather than single molecules.

TD-DFT, DFT, docking, MD simulations, and concentration-dependent SERS investigations of a bioactive trifluoromethyl derivative having human acetylcholinesterase and butyrylcholinesterase in silver colloids

CONTEXT

Various concentrations of (E)-4-methoxy-N'-(2-(trifluoromethyl)benzylidene) benzohydrazide (EMT) adsorbed on colloidal silver nanoparticles were studied using SERS and results were compared to the normal Raman spectrum. DFT calculations were used to validate experimental findings. Theoretically, the structures of the EMT and EMT-Ag6 systems were optimized. The UV-Vis spectral analysis's red shift and lower intensity behavior show that EMT has chemisorbed onto Ag nanoparticles. Charge transfer (CT) from Ag to EMT is highlighted by FMO analysis. The CT interaction in EMT and EMT-Ag6 was further verified by MEP and Mulliken charge analyses. The EMT was adsorbed on Ag nanoparticles with tilted orientation and orientation changes with colloidal concentration, according to SERS spectrum analysis. Docking EMT with 4PQE and 5DYW binding affinities are found to be -9.7 and -8.1 kcal/mol. MD simulations give the competence of 5DYW-EMT and 4PQE-EMT in their intended binding interactions and their ability to establish enduring associations with the protein of interest.

METHODS

DFT was used to optimize the molecular structures of EMT and EMT-Ag6 using B3LYP/6-311++G* (LANL2DZ basis set for Ag). A molecular dynamics simulation study was conducted on the 4PQE-EMT and 5DYW-EMT systems using the Desmond software for 100 ns.

Multi-method evaluation of a 2-(1,3,4-thiadiazole-2-yl)pyrrolidine corrosion inhibitor for mild steel in HCl: combining gravimetric, electrochemical, and DFT approaches

The corrosion inhibition properties of 2-(1,3,4-thiadiazole-2-yl)pyrrolidine (2-TP) on mild steel in a 1 M HCl solution were investigated using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements. In addition, DFT calculations were performed on 2-TP. The polarization curves revealed that 2-TP is a mixed-type inhibitor. The results indicate that 2-TP is an effective inhibitor for mild steel corrosion in a 1.0 M HCl solution, with an inhibition efficiency of 94.6% at 0.5 mM 2-TP. The study also examined the impact of temperature, revealing that the inhibition efficiency increases with an increasing concentration of 2-TP and decreases with a rise in temperature. The adsorption of the inhibitor on the mild steel surface followed the Langmuir adsorption isotherm, and the free energy value indicated that the adsorption of 2-TP is a spontaneous process that involves both physical and chemical adsorption mechanisms. The DFT calculations showed that the adsorption of 2-TP on the mild steel surface is mainly through the interaction of the lone pair of electrons on the nitrogen atom of the thiadiazole ring with the metal surface. The results obtained from the weight loss, potentiodynamic polarization, EIS and OCP measurements were in good agreement with each other and confirmed the effectiveness of 2-TP as a corrosion inhibitor for mild steel in 1.0 M HCl solution. Overall, the study demonstrates the potential use of 2-TP as a corrosion inhibitor in acid environments.

Interaction between a photoisomerizable azobenzene compound and alpha-lactalbumin: Spectroscopic and computational simulation studies

The combination of light and photoresponsive compounds provides a peculiar way of regulating biological systems. Azobenzene is a classical organic compound with photoisomerization properties. Exploring the interactions between azobenzene and proteins can deepen the biochemical applications of the azobenzene compounds. In this paper, the interaction of 4-[(2,6-dimethylphenyl)diazenyl]-3,5-dimethylphenol with alpha-lactalbumin was investigated by UV-Vis absorption spectra, multiple fluorescence spectra, computer simulations, and circular dichroism spectra. Most critically, the interaction differences between proteins and the trans- and cis-isomer of ligands have been analyzed and compared. Results showed that both isomers of ligands were bound to alpha-lactalbumin to form ground state complexes and statically quenched the steady-state fluorescence of alpha-lactalbumin. The van der Waals forces and hydrogen bonding dominated the binding; the difference is that the binding of the cis-isomer to alpha-lactalbumin is more rapidly stabilized, and the binding strength is greater than the trans-isomer. These binding differences were modeled and analyzed by molecular docking and kinetic simulations, and we found that both isomers bind through the hydrophobic aromatic cluster 2 of alpha-lactalbumin. However, the bent structure of the cis-isomer is more closely aligned with the construction of the aromatic cluster and may have contributed to the above differences.

Evaluation of 2,3-Dihydro-1,5-benzothiazepine Derivatives as Potential Tyrosinase Inhibitors: In Vitro and In Silico Studies

Benzothiazepines are pharmacologically active compounds, frequently utilized as a precursor for acquiring versatile molecules with several bioactivities including anti-inflammatory, anti-human immunodeficiency virus (anti-HIV), analgesic, antitumor, antimicrobial, and antitubercular. In this study, the 2,4-diphenyl-2,3-dihydro-1,5-benzothiazepine scaffold was selected for their in vitro, docking, and druglikeness studies to evaluate their inhibitory potential against mushroom tyrosinase. All synthesized analogues, 1-14, exhibited moderate to good IC₅₀ values ranging from 1.21 to 70.65 μM. The synthesized benzothiazepine derivatives were potent tyrosinase inhibitors, which outperformed the reference kojic acid (IC₅₀ = 16.69 μM). The kinetic analysis revealed that compound 2 (2-(3,4-dimethoxyphenyl)-4-(p-tolyl)-2,3-dihydrobenzo[b][1,4]thiazepine) was a mixed-type tyrosinase inhibitor with a K_i value of 1.01 μM. Molecular modeling studies against tyrosinase protein (PDB ID: 2Y9X) were conducted to recognize the binding modes of these analogues. The utilization of molecular dynamic (MD) simulations enabled the assessment of the protein-ligand complex's dynamic behavior, stability, and binding affinity for the compounds. These simulations ultimately led to the identification of compound 2 as a potential inhibitor of tyrosinase. Additionally, a druglikeness study was conducted, which supported the promising potential of the new analogues as novel antityrosinase agents. The in silico studies were consistent with the in vitro results, showing that these ligands had good binding scores against tyrosinase and interacted with the core residues of the target protein. Gaussian 09 was used for the geometry optimization of all complexes.

Can DFT Calculations Provide Useful Information for SERS Applications?

Density functional theory (DFT) calculations allow us to reproduce the SERS (surface-enhanced Raman scattering) spectra of molecules adsorbed on nanostructured metal surfaces and extract the most information this spectroscopy is potentially able to provide. The latter point mainly concerns the anchoring mechanism and the bond strength between molecule and metal as well as the structural and electronic modifications of the adsorbed molecule. These findings are of fundamental importance for the application of this spectroscopic technique. This review presents and discusses some SERS-DFT studies carried out in Italy as a collaboration between the universities of Modena and Reggio-Emilia and of Florence, giving an overview of the information that we can extract with a combination of experimental SERS spectra and DFT modeling. In addition, a selection of the most recent studies and advancements on the DFT approach to SERS spectroscopy is reported with commentary.

Synthesis and Corrosion Inhibition Performance of Mannich Bases on Mild Steel in Lactic Acid Media

Heterocyclic Mannich bases, N-(3-oxo-3-phenylpro-pyl)thiazol-2-aminium chloride (DTZA) and N-(3-oxo-3-phenylpropyl)-1H-pyrazol-3-aminium chloride (DPZA), were developed for the corrosion inhibition of N80 steel in a 15 wt % lactic acid solution. Weight loss measurements, electrochemical techniques, surface characterization, and theoretical calculations were combined to investigate their anticorrosion performance and mechanism. The results showed that DTZA exhibited a satisfactory inhibitor efficiency of 97.56% with a dosage of 0.15% at 363 K, while DPZA achieved only 58.3% under the same conditions. Adsorptions of both inhibitors on the metal surface followed the Langmuir model with physical and chemical adsorptions. Based on X-ray photoelectronic spectroscopy (XPS) analysis, DFT calculations, and molecular dynamics (MD) simulations, stronger interactions between DTZA and iron than those in the case of DPZA were revealed, leading to the formation of a compact protective film on the metal surface, which is attributed to the presence of a thiazole ring in the DTZA chemical structure.