DFT study of structural and electronic properties of gallic acid and its anions in gas phase and in aqueous solution

pH and Medium Polarity-Induced Self-Assembly of Fmoc-Tryptophan into Multiple Superstructures: An Experimental and Theoretical Investigations

Self-assembly of functionalized molecular building blocks is an effective and resource-saving bottom-up technique to generate multiple superstructures with various functionality and morphologies. The nature of the molecule and the factors controlling the overall self-assembly process are extremely vital in fundamental aspects of self-assembly, which deliver insights into the fabrication of multiple assemblies with specific functionality. The self-assembly of suitably functionalized amino acids leads to the formation of diverse structures with distinct properties, making them ideal bio-organic scaffolds for various applications. The present study reports, the pH and solvent polarity-induced self-assembly of 9-fluorenylmethoxycarbonyl (Fmoc)-Tryptophan into various self-assembled superstructures with morphological individualities, explore the plausible pathway of morphological transformation of Fmoc-Trp into multiple superstructures having a wide range of well-defined morphologies, including spheres, hollow spheres, nanoflowers, nanosheets, nanorods, and cube-like structures, as characterized through conventional microscopic techniques. Detailed UV-vis, fluorescence, powder X-ray diffraction analysis, and Fourier transform infrared analyses reveal significant insights into the intermolecular interactions, which trigger the overall self-assembly process. The computational studies, including full geometry optimization and molecular dynamics simulations, are conducted to investigate the aggregation properties of modified amino acids (Fmoc-Trp). These studies highlight the crucial role of π-π stacking and hydrogen bonding in tuning the overall self-assembly with morphological variation.

Folic-Acid-Conjugated Poly (Lactic-Co-Glycolic Acid) Nanoparticles Loaded with Gallic Acid Induce Glioblastoma Cell Death by Reactive-Oxygen-Species-Induced Stress

Glioblastoma (GBM) conventional treatment is not curative, and it is associated with severe toxicity. Thus, natural compounds with anti-cancer properties and lower systemic toxicity, such as gallic acid (GA), have been explored as alternatives. However, GA's therapeutic effects are limited due to its rapid metabolism, low bioavailability, and low permeability across the blood-brain barrier (BBB). This work aimed to develop poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) modified with folic acid (FA), as its receptor is overexpressed in BBB and GBM cells, for GA delivery to enhance its therapeutic efficacy. The preparation of NPs was optimized by a central composite design (CCD). The obtained NPs showed physicochemical features suitable for drug internalization in BBB and tumor cells (sizes below 200 nm, monodispersity, and negative surface charge) and the ability to maintain a slow and sustained release for 40 days. In vitro studies using a human GBM cell line (U215) revealed the NPs' ability to accumulate in the target cells, further promoting GA antiproliferative activity by inducing the production of intracellular reactive oxygen species (ROS). Furthermore, GA encapsulation in the developed nanosystems conferred higher protection to healthy cells.

Unlocking the Potential of Chemically Modified Carbon Gels in Gallic Acid Adsorption

This study deals with the preparation of adsorbents from a commercial xerogel by chemically modifying its surface with concentrated mineral acids and alkali metal chlorides, their physicochemical characterization, and their use as adsorbents for gallic acid in aqueous solution. Although there are publications on the use of carbon xerogels as adsorbents, we propose and study simple modifications that can change their chemical properties and, therefore, their performance as adsorbents. The adsorbate of choice is gallic acid and, to our knowledge, there is no history of its adsorption with carbon xerogels. The prepared adsorbents have a high specific surface area (347-563 m2 g-1), better pore development for samples treated with alkali metal chlorides than with mineral acids, and are more acidic than the initial xerogel (p.z.c range 2.49-6.87 vs. 7.20). The adsorption equilibrium is reached in <16 h with a kinetic constant between 0.018 and 0.035 h-1 for the pseudo-second-order model. The adsorption capacity, according to the Langmuir model, reaches 62.89 to 83.33 mg g-1. The adsorption properties of the commercial xerogel improved over a wide range of pH values and temperatures. The experimental results indicate that the adsorption process is thermodynamically favored.

Synthesis of gallic acid-grafted epoxidized natural rubber and its role in self-healable flexible temperature sensors

Developing a flexible temperature sensor with appreciable sensitivity is critical for advancing research related to flexible electronics. Although various flexible sensors are available commercially, most such temperature sensors are made from polymeric materials obtained from petrochemical resources. Such sensors will contribute to electronic waste and increase the carbon footprint after usage. While there are reports on various sensors made from sustainable polymers, research related to developing self-healable flexible temperature sensors made from sustainable polymers is significantly less. Herein, we report on developing a flexible temperature sensor made of gallic acid-grafted epoxidized natural rubber and multi-walled carbon nanotubes. Various spectroscopic and thermal techniques vetted the modification of the epoxidized natural rubber. The highest grafting of 20.9% was achieved in the selected window of stoichiometry. A self-healing behavior was achieved by leveraging the FeCl3 based metal-ligand crosslinking of the composite. The healing efficiency was noted to be 31.2% for the composite material. The fabricated sensor demonstrated an electrical resistance of 4.46 × 103 Ω, thereby warranting the composite to demonstrate an Ohmic behavior in the I-V plot. Appropriate data fitting suggested a variable range hopping mechanism as causation towards excellent electrical conduction. The temperature sensitivity and the thermal index of the developed sensor were noted to be -0.17% °C-1 and 781.2 K, respectively, in the temperature range of 30 °C to 50 °C. The proposed method of fabricating sustainable, high-strength, self-healable, and robust temperature sensors and conductors is a unique and value-added approach for next-generation flexible electronics.

Unraveling the effects of low protein-phenol binding affinity on the structural properties of beta-lactoglobulin

Non-covalent interactions of phenolics with proteins cannot always be readily identified, often leading to contradictory results described in the literature. This results in uncertainties as to what extent phenolics can be added to protein solutions (for example for bioactivity studies) without affecting the protein structure. Here, we clarify which tea phenolics (epigallocatechin gallate (EGCG), epicatechin and gallic acid) interact with the whey protein β-lactoglobulin by combining various state-of-the-art-methods. STD-NMR revealed that all rings of EGCG can interact with native β-lactoglobulin, indicating multidentate binding, as confirmed by the small angle X-ray scattering experiments. For epicatechin, unspecific interactions were found only at higher protein:epicatechin molar ratios and only with ¹H NMR shift perturbation and FTIR. For gallic acid, none of the methods found evidence for an interaction with β-lactoglobulin. Thus, gallic acid and epicatechin can be added to native BLG, for example as antioxidants without causing modification within wide concentration ranges.

Surface Functionalization of Bioactive Hybrid Adsorbents for Enhanced Adsorption of Organic Dyes

In this study, a valuable adsorbent was functionalized using commercial ZnO and a mango seed extract (MS-Ext) as a green approach for synthesis. Fourier-transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and energy-dispersive X-ray analysis spectraconfirmed the presence of bioactive phenolic compounds and Cu2+ ions on the surface of ZnO. Functionalized Cu-doped ZnO/MS-Ext exhibits high efficacy in acidic, neutral, and alkaline medium, as indicated by 98.3% and 93.7% removal of methylene blue (MB) and crystal violet (CV) dyes, respectively. Cu-doped ZnO/MS-Ext has a zeta potential significantly lower than pristine zinc oxide (p-ZnO), which results in enhanced adsorption of cationic MB and CV dyes. In binary systems, both MB and CV were significantly removed in acidic and alkaline media, with 92% and 87% being removed for CV in acidic and alkaline media, respectively. In contrast, the removal efficiency of methyl orange dye (MO) was 16.4%, 6.6% and 11.2% for p-ZnO, ZnO/Ext and Cu-doped ZnO/Ext, respectively. In general, the adsorption kinetics of MB on Cu-doped ZnO/MS-Ext follow this order: linear pseudo-second-order (PSO) > nonlinear pseudo-second-order (PSO) > nonlinear Elovich model > linear Elovich model. The Langmuir isotherm represents the adsorption process and indicates that MB, CV, and MO are chemisorbed onto the surface of the adsorbent at localized active centers of the MS-extract functional groups. In a binary system consisting of MB and CV, the maximum adsorption capacity (q_m) was 72.49 mg/g and 46.61 mg/g, respectively. The adsorption mechanism is governed by electrostatic attraction and repulsion, coordination bonds, and π-π interactions between cationic and anionic dyes upon Cu-doped ZnO/Ext surfaces.

Lotus Root Polysaccharide-Phenol Complexes: Interaction, Structure, Antioxidant, and Anti-Inflammatory Activities

This research aimed to explore the interaction between lotus root polysaccharides (LRPs) and phenolic compounds, and to study the effects of phenolic binding on the structural and functional properties of LRPs. The influences of pH, temperature, and NaCl and phenol concentration on the binding ratio of gallic acid (GA)/epigallocatechin (EGC) to LRPs were evaluated. LRP-GA/EGC complexes with different phenolic binding amounts were then prepared and characterized via ultraviolet-visible (UV-Vis) and Fourier-transform infrared (FTIR) spectroscopy, and average molecular weight (MW) measurements. The results suggest that hydrogen bonds contributed to the binding of GA/EGC and LRPs. The phenolic binding led to significant changes in the structure and MW of LRPs. Moreover, antioxidant activity and the macrophage-stimulating effect of LRPs were improved after binding with GA/EGC, depending on the binding amount and type of polyphenol. Interestingly, LRP-GA/EGC complexes with polyphenol binding amounts of 105.4 mg/g and 50.71 mg/g, respectively, showed better stimulation effects on the anti-inflammatory cytokine IL10 secretion of macrophages when compared to LRPs. These results show the great potential of phenolic binding to be applied to improve the structure and functional activity of LRPs.

The Conformations of Isolated Gallic Acid: A Laser-Ablation Rotational Study

The rotational spectrum of laser-ablated gallic acid has been recorded using CP-FTMW spectroscopy. Two rotamers have been detected, and their rotational spectra have been assigned and analyzed to obtain the molecular spectroscopic parameters. The observed rotamers have been unambiguously identified in the light of theoretical computations, based on the comparison of the experimental line intensities and rotational parameters with the rotational constants and electric dipole moments predicted from theoretical calculations. The values of the planar inertial moments confirm that the observed conformers are planar, and their relative stability and population have been determined from relative intensity measurements. The B3LYP-D3/6-311++G(2d,p) level has been shown to be the best method among a series of levels normally used to predict the rotational parameters in rotational spectroscopy. In the observed conformers, the three adjacent OH groups are arranged in a sequential form, and the only difference between them lies in the orientation of the COOH group. Although weak attractive OH···O interactions seem to exist, the analysis of the electron density topology does not show the existence of any critical point corresponding to these interactions.

Experimental spectra, electronic properties (liquid and gaseous phases) and activity against SARS-CoV-2 main protease of Fluphenazine dihydrochloride: DFT and MD simulations

The Gaussian 09 DFT tool is used to investigate the formational electronic behaviour, reactivity analysis and biological properties of fluphenazine dihydrochloride (FDD). The quantum computation is used to determine the spectroscopic and vibrational assignments of FDD. The NBO method explains charge transfer and molecular interactions. Energy gap values are determined using FMO analysis in different solvents and toluene is a better solvent due to higher value of solvation energy. The UV-visible spectra are investigated in various solvents using the TD-DFT method. Electrostatic potential, the wave function related properties such as LOL, NCI and RDG are determined in gaseous phase. Furthermore, the drug likeness is analyzed. At last, a docking study with MD simulation is used to investigate FDD's antiviral activity against SARS-CoV-2 main protease.

Enhancing bioactive compounds accumulation in red beet (Beta Vulgaris L.) plants by managing N nutrition. The identification of the 'critical' zone as a cultivation technique

The increasing interest in natural health-promoting compounds, which are mostly plant secondary metabolites, inspired attempts to stimulate mechanisms strengthening their bioaccumulation in crop plants via abiotic stress while maintaining the yield potential. This study investigates the long-term effects of limiting nitrogen (N) supply on the concentration of total phenolics, free radical activity of natural antioxidants, betacyanin content, biomass production, net photosynthetic rate, total chlorophyll content, and plant water relations in red beetroot plants (Beta vulgaris L.) grown hydroponically. Depending on fertilization, the range of N supply for evaporative demand comprises two contrasted nutrient zones, in which N is limiting (zone-1) or non-limiting (zone-2). Based on the carbon-nutrient-balance hypothesis, at the transition from 1st-zone to 2nd-zone, there is a narrow transition zone in which the plant nutrient status is considered 'critical'. Herein, to determine the 'critical' zone, a modified Michaelis-Menten (M-M) model was used using a piecewise linear regression on two indexes: net photosynthetic rates and free radical-scavenging capacity of phenolic antioxidants. The model showed that the 'critical' transition points of net photosynthetic rate and phenolic free radical content are located in a narrow zone ranging between 196.70 ± 8.75 and 271.54 ± 75.50 ppm NO₃^-, while the cropping season appears to affect slightly the range of 'critical' (transition) zone. Thus, supplying N to red beetroot plants to levels ranging within this 'critical' zone may be an efficient, profitable and sustainable way to increase the accumulation of health-promoting plant bioactive compounds (total phenolic compounds with radical activity and betacyanins) in hydroponically cultivated reed beetroot plants.

Excellent Antimicrobial, Antioxidant, and Catalytic Activities of Medicinal Plant Aqueous Leaf Extract Derived Silver Nanoparticles

Antimicrobial resistance is one of the crucial public health challenges that we need to combat. Thus, in concern over public health and the economy, controlling the emergence of infectious diseases is critical worldwide. One of the ways to overcome the influences of antimicrobial resistance is by developing new, efficient, and improved antimicrobial agents. Medicinal plant-derived silver nanoparticles (AgNPs) are under intensive examination for a variety of therapeutic purposes and targeted applications in nanomedicine and nanotechnology. Plants belonging to the genus Thevetia [Syn. Casabela], which is known for its medicinal uses and has rarely been applied for the synthesis of AgNPs, is an attractive alternative as they have a high content of secondary metabolites. Herein, using aqueous leaf extract of Cascabela thevetia, which was locally found in the Makkah region, Saudi Arabia, green synthesis of AgNPs is reported. Active components of Cascabela thevetia aqueous leaf extract were sufficient to reduce AgNO3 into AgNPs and stabilize them as this was confirmed through UV-Visible absorption, Fourier transforms infrared (FTIR), X-ray diffraction (XRD), filed emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) studies. UV-Visible, HPLC, and FTIR analysis demonstrated the presence of gallic acid in aqueous extract and solution of C-AgNPs. The spherical Cascabela thevetia derived C-AgNPs with an average diameter in the range of 20–30 nm were highly dispersed, as seen from FESEM and TEM images, and demonstrated the high antibacterial and antifungal activities when incubated with Gram-positive bacteria Methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus aureus (S. aureus), Enterococcus faecalis (E. faecalis), Gram-negative bacteria Escherichia coli (E. coli), Salmonella typhimurium (S. typhimurium), Klebsiella pneumoniae (K. pneumoniae), Pseudomonas aeruginosa (P. aeruginosa) and fungi Candida albicans (C. albicans) and Candida parapsilosis (C. parapsilosis). The lowest MIC values of C-AgNPs versus S. aureus, E. faecalis, and E. coli were found. Finally, the antioxidant activity and catalytic property of C-AgNPs were assessed by neutralizing DPPH free radical and reducing methylene blue and rhodamine B dyes, respectively.

Insights on thermodynamic thermal properties and infrared spectroscopic band assignments of gallic acid

Gallic acid (3,4,5-trihydroxybenzoic acid) is a popular nutraceutical found in various natural sources. A confusion regarding its thermodynamic properties, e.g., melting point, can be detected in the reported literature values. Similar issues exist for the assignment of its spectroscopic bands in the region of hydroxyl stretching vibrations. In this study, thermal analysis techniques, infrared spectroscopy and X-ray diffraction were used to study the thermal behavior of gallic acid. It is shown that gallic acid exhibits various thermochemical transitions (solid-solid and solid-liquid transitions). The value of the specific heat of the thermal transition around 90 °C indicates that this effect is not only related to water removal, but to decomposition. The absence of significant/exclusive water removal at 90 °C suggests that water being present in the structure of gallic acid is strongly bounded, while the main pathway for the decomposition around 90 °C seems to be the dehydration through esterification reaction between -COOH and -OH groups of gallic acid. Recrystallization of gallic acid from methanol-heavy water solvent mixture, leads to the incorporation of heavy water in its structure. The comparative evaluation of the recrystallized and raw gallic acid allows for a proper spectroscopic band assignment of various vibrations. The thermal effect around 260 °C is a typical thermochemical transition and not a melting point. The extensive polymorphism of gallic acid and the respective solid-solid transformations are also related to partial decomposition.

Photoelectron Spectroscopic and Computational Study of the Deprotonated Gallic Acid and Propyl Gallate Anions

Antioxidants play important roles in eliminating reactive oxygen species (ROS), which have been associated with various degenerative diseases, such as cancer, aging, and inflammatory diseases. Gallic acid (GA) and propyl gallate (PG) are well-known antioxidants and have been widely studied in vitro and in vivo. The biological antioxidant abilities of GA and PG are related to the electronic structure of their dehydro-radicals. In this work, we report a combined photoelectron spectroscopic and computational study of the deprotonated gallic acid anion, [GA - H]^-, and deprotonated propyl gallate anion, [PG - H]^-. Adiabatic electron affinities of the dehydro-gallic acid radical, [GA - H]· and of the dehydro-propyl gallate radical, [PG - H]·, are measured to be 2.90 ± 0.05 eV and 2.85 ± 0.05 eV, respectively, and compared to computational results.

Effects of gallic acid and Zn, Cu, and Ni on antioxidant enzyme activities of Hyphantria cunea larvae infected with Bacillus thuringiensis

The effects of copper, nickel, and zinc and the potent antioxidant gallic acid on the antioxidant enzyme activities of Hyphantria cunea larvae infected with Bacillus thuringiensis subsp. kurstaki have been identified in this study. With metal exposure, all the enzyme activities have increased. Antagonistic effects were observed in the combination of gallic acid with all three metals on the activities of superoxide dismutase and catalase. In glutathione peroxidase activity, an antagonistic effect was observed in gallic acid plus nickel group, while there was a synergistic effect for gallic acid plus zinc and gallic acid plus copper. Activities of these enzymes in larvae exposed only to the metals increased in the infected groups; while exposure to gallic acid alone elicited a decrease. As a consequence, it was found that enzyme activities were affected by both metals and gallic acid and infection.

Gallic Acid as a Potential Green Corrosion Inhibitor for Aluminum in Acidic Solution

Plant extracts are intensively studied as green corrosion inhibitors of aluminum. Because these extracts are complex systems, the influence of their individual constituents on the corrosion of aluminum should be determined. In this work, gallic acid was tested for the first time as a corrosion inhibitor of aluminum in orthophosphoric acid aqueous solution. So far, its potential inhibiting properties in acidic solutions were only suggested based on promising results obtained for various plant extracts. Evaluation of the potential inhibiting properties of gallic acid was performed using electrochemical methods. The corrosion potential, polarization curves, and impedance spectra of aluminum in 0.5 M orthophosphoric acid, at T = 303 K, were determined. The corrosion potential, corrosion current density, and corrosion rate of aluminum in orthophosphoric acid were equal to −1.151 V vs. Ag|AgCl (3M KCl) reference electrode, 36 μA∙cm−2 and 0.39 mm∙year−1, respectively. These values did not change with the addition of gallic acid. The results obtained show that gallic acid does not inhibit aluminum corrosion. UV-Vis absorption spectra of gallic acid solutions and quantum mechanical calculations show that this organic compound did not adsorb onto the aluminum surface under the studied conditions.

Absorption Spectra and the Electronic Structure of Gallic Acid in Water at Different pH: Experimental Data and Theoretical Cluster Models

Gallic acid (GA) has been characterized in terms of its optical properties in aqueous solutions at varying pH in experiments and in theoretical calculations by analyzing the protonated and deprotonated forms of GA. This work is part of a series of studies of the optical properties of different carboxylic acids in aqueous media. The experimental electronic spectra of GA exhibit two strong well-separated absorption peaks (B- and C-bands), which agree with previous studies. However, in the current study, an additional well-defined low-energy shoulder band (A-band) in the optical spectra of GA was identified. It is likely that the A-band occurs for other carboxylic acids in solution, but because it can overlap with the B-band, it is difficult to discern. The theoretical calculations based on density functional theory were used to simulate the optical absorption spectra of GA in water at different pH to prove the existence of this newly found shoulder band and to describe and characterize the full experimental optical spectra of GA. Different cluster models were tested: (i) all water molecules are coordinated near the carboxy-group and (ii) additional water molecules near the hydroxy-groups of the phenyl ring were included. In this study, we found that both the polarizable continuum model (dielectric property of a medium) and neighboring water molecules (hydrogen-bonding) play significant roles in the optical spectrum. The results showed that only an extended cluster model with water molecules near carboxy- and hydroxy-groups together with the polarizable continuum model allowed us to fully reproduce the experimental data and capture all three absorption bands (A, B, and C). The oscillator strengths of the absorption bands were obtained from the experimental data and compared with theoretical results. Additionally, our work provides a detailed interpretation of the pH effects observed in the experimental absorption spectra.

Impact of intramolecular hydrogen bonding of gallic acid conformers on chemical shift through NMR spectroscopy

Intramolecular hydrogen bonding of gallic acid conformers was probed as a function of their dihedral angles using ¹³C nuclear magnetic resonance (NMR) chemical shift (δ_C). The quantum mechanically calculated ¹³C NMR chemical shift based on the most stable conformer (GA-I) in dimethylsulfoxide (DMSO) solution agrees to available measurement in the same solvent (RMSD = 0.95 ppm), better than to the measurement in solid phase (RMSD = 1.93 ppm). The accuracy of the calculated NMR chemical shift of the nominal but non-equivalent phenyl carbons C₍₃₎/C₍₇₎ and C₍₄₎/C₍₆₎ (ortho and meta to the acid -C₍₁₎OOH group) of GA may not be evaluated using the experimental measurements at room temperature. The splitting in chemical shift of the nominal phenyl carbons is able to be experimentally measured only in low temperature NMR and using quantum mechanical calculations. We further recognised that the C NMR chemical shifts of the nominal phenyl carbons (C₍₃₎/C₍₇₎ and C₍₄₎/C₍₆₎) encode information for intramolecular hydrogen bonding network formed by GA conformers. The ability to obtain accurate splitting of NMR chemical shifts for nominal carbons, therefore, determines the usefulness of the NMR technique as a probe for conformation of GA.