Sappidi, Praveen Kumar

The monitoring of antioxidants is crucial to prevent damage caused by reactive oxygen species (ROS). In this study, we introduce an innovative electrochemical sensor tailored for detecting riboflavin (RF), a powerful antioxidant. The sensor was developed by modifying a gold electrode (AuE) with cobalt oxide (Co3O4) and reduced graphene oxide (rGO). The resulting nanocomposite-modified electrode (AuE/Co3O4-rGO) exhibited a substantial surface area of 0.41 cm2 in the redox probe, leading to an enhanced RF peak characterized by remarkably low charge transfer resistance (1.61 KΩ) and a high exchange current density (18.6 μA/cm2). Under optimized conditions, the sensor achieved a limit of detection (LOD) for RF at 1.30 μM, over a concentration range of 6.5–42.2 μM. These results highlight the sensor's potential applicability in real-world scenarios, including the analysis of milk and pharmaceutical samples. A kinetics study revealed that the electrochemical reaction involving RF is adsorption-controlled, emphasising the critical role of surface interactions. The modified electrode's interaction with RF significantly influences overall reaction kinetics. These findings were further supported by density functional theory (DFT) calculations and molecular simulations. Our nanocomposite-modified electrode provides valuable insights into the atomistic interactions governing sensor performance, advancing the field of electrochemical sensing for antioxidants like riboflavin.

In this paper, we have performed all-atom molecular dynamics simulations to understand the structure, dynamics, and thermodynamic behavior of Na+ ions in water-mixed ionic liquids. We have considered seven different combinations of water-mixed ionic liquids having common cation 1-ethyl-3-methylimidazolium [EMIM+] along with seven different anions such as acetate [ACT]−, formate [FRM]−, trifluoromethyl-sulfonate [TFS]−, benzoate [BEZ]−, nitrate [NO3]−, hexafluorophosphate [PF6]−, and tetrafluoroborate [BF4]−. Two different water mole fractions (x) are considered: 0.55 to 0.71. Various structural and dynamic properties are investigated such as radial distribution functions, ion self-diffusion coefficients, and ionic conductivity. We understand that hydrophilic anions interact more with water, which would lead to enhanced mobility of the Na+ ions in the neat IL [EMIM]+ [TFS]− that presents higher ionic conductivity values; on the other hand, water-mixed IL presents higher conductivity values for the [EMIM]+ [BF4]− and [EMIM]+[NO3]−. The self-diffusion coefficient values of Na+ ions present higher values in [EMIM]+ [BF4] and [EMIM]+ [NO3]− in water-mixed ILs compared to other ionic liquid-water combinations. Overall, the results presented in this manuscript will help in understanding the molecular-level behavior of imidazolium-based electrolytes for battery applications.

The conducting polymer polyaniline (PANI) has shown significant interest for the development of electrified membranes (EMs) with superior antifouling characteristics. However, the blending and doping of PANI with other polymers and nanomaterials highly influence the properties of the membrane surface. PANI exists in two forms: oxidized, known as emeraldine salt (ES), and unoxidized, referred to as emeraldine base (EB). Therefore, understanding the different forms of PANI and the variations between the oxidized and unoxidized forms along the length of the polymer chain is intriguing. In this paper, we present the design of a novel copolymer consisting of EB and ES monomers with varying charge densities and different segmental arrangements. We present various intra- and intermolecular structural properties of the PANI chains using all-atom molecular dynamics (MD) simulations. Herein, we present a detailed conformational free energy analysis to understand the conformational transitions of the PANI chains. Our results show increased radius of gyration (Rg) values with increased charge density. Furthermore, we also present the H-bonding, free energy analysis, reduced density gradient (RDG), and solvent-accessible surface area (SASA) values for the observed conformational transitions of PANI. Therefore, these observations are crucial in understanding the complex behavior of chains for designing target-specific polymeric materials.

In this paper, we present atomistic molecular dynamics simulations to understand the directional solvent extraction (DSE) for separating lanthanide metals from aqueous waste. We consider four different lanthanide metals such as lanthanum (La3+), neodymium (Nd3+), europium (Eu3+), and ytterbium (Yb3+) using decanoic acid (DEC) as a directional solvent. We analyze various molecular mass density profiles, intermolecular structural properties, ion dynamic behaviors, and solvation free energy values of metal ions with the variation in temperature (T). We observe strong intermolecular interactions between the lanthanide ions (Ln3+-Ln3+) and lanthanide-nitrate (Ln3+-NO3) as the temperature increases. The self-diffusion coefficient (D) of all of the metal ions shows a significant rise with an increase in T values. The detailed solvation free energy ΔGsolv (kJ/mol) and transfer free energy ΔGtransfer (kJ/mol) calculations provide favorable values in the organic and aqueous phases with the rise in T values. The partition coefficient (log P) values indicates favorable separation of lanthanide ions using DEC. Overall, the molecular level findings described in this manuscript provide great insights into the design of the DSE method for the separation of lanthanide metals from aqueous waste.

This paper presents all-atom molecular dynamics to understand the separation behavior of 5-hydroxymethylfurfural (5-HMF) from 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM]+[BF4]− using alkylated phenols as extractants. We have utilized four solvents such as 4-methyl phenol (4-MP), 4-ethyl phenol (4-EP), 4-propyl phenol (4-PP), and 4-butyl phenol (4-BP). We perform structural, dynamic, and rigorous thermodynamic analyses of 5-HMF in the mixture of ILs and solvents. The [BMIM]+[BF4]− show a strong interaction with phenols. The self-diffusion coefficient of 5-HMF shows a 3-fold increase with a decrease in the methyl group on the phenol. The solvation-free energy (ΔGsolvation) of 5-HMF shows favorably in phenols. On the other hand, the transfer free energy (ΔGtransfer) of 5-HMF presents favorable from ILs to phenols. The partition coefficient (log P) values show favorability for separation of 5-HMF using phenols. Overall, the molecular level analysis provides the role of the alkyl group effect on the phenols for extracting 5-HMF from the ILs.

In this paper, we have performed an all-atom molecular dynamics simulation to understand the structure and dynamics of Na+ ions in water mixed Ionic liquids (Water in Ionic liquid). Two ionic liquid (IL) systems consist of (1) 1-butyl-3-methylimidazolium [BMIM] tetrafluoroborate [BF4] and (2) 1-butyl-3-methylimidazolium [BMIM] hexafluorophosphate [PF6] were considered in this work. We understand various inter-molecular structures and dynamic and thermodynamic behaviours of Na+ ions in the water-mixed IL systems. The water (H2O) mole fractions (x) varied from 0.33 to 0.71. The neat ILs [BMIM][BF4] and [BMIM][PF6] pairwise radial distribution functions show a decrease with an increase in x. The [BMIM][PF6] exhibits a strong coordination structure with Na+ ions across the entire range of x values. The rdf between the pairs of Na+-[PF6] presents a significant interaction compared to Na+ and [BF4]. The Na + ions manifested greater coordination with H2O In H2O-[BMIM][PF6] compared to H2O-[BMIM][BF4]. The self-diffusion coefficient (D) values of Na + ions increase with the rise in x in both ILs. The D values of Na + ions are 10-fold higher in [BMIM][BF4] than [BMIM][PF6]. The ionic conductivity values are higher for [BMIM][BF4]. Overall, this paper unveils molecular-level insights for understanding the behavior of Na+ ions in the water in ionic liquid systems.

The separation of aromatics and aliphatic from the hydrocarbon mixture stands a significant challenge. In this manuscript we present atomistic molecular dynamic simulations to understand the structure and separation thermodynamic properties of BTX (Benzene, toluene, xylene) from n-heptane using ionic liquids. Here we considered the amino acid derived ionic liquid considering the tetra butyl phosphonium as cation and valine anion at three different temperatures 298 K, 323 K and 348 K. We observe that IL show strong intermolecular structure with BEN (benzene) when compared to TOL (toluene) and XYL (p-xylene). Based on the solvation free energy (ΔGsolv), transfer free energy (ΔGtransfer) and partition coefficient (log P) analysis of BEN show favourable for the transfer from n-heptane to IL phase when compared to TOL and XYL. Overall results presented in this paper provide molecular level understanding of the design of amino acid-based IL for the separation BTX from the hydrocarbon mixture.

We utilize all-atom molecular dynamics simulations to explore the intermolecular structure, dynamics and thermodynamic properties of Zn2+ ions in water-in-ionic liquid. Two ionic liquid systems featuring the same cation 1-ethyl-3-methyl-imidazolium [EMIM]+ and distinct anions tetrafluoroborate [BF4]− and hexafluorophosphate [PF6]− are considered. We consider the water (H2O) mole fractions (x) varying from 0.33 to 0.71. We observe a significant interactions of Zn2+ ions with water in the case of [BF4]− when compared to [PF6]−. On the other hand Zn2+ ions mobility rises more in [EMIM]+[BF4]− as compared to [EMIM]+[PF6]− with x. Higher self-diffusion (D) of Zn2+ ions is seen in the case of [EMIM]+[BF4]−. The ionic conductivity (σ) of [EMIM]+[BF4]− is greater compared to [EMIM]+[PF6]− with the rise in x. Overall, this article furnishes in-depth molecular-level insights into the behaviour of Zn2+ ions in the presence of water mixed ionic liquid electrolytes.

5-Hydroxymethylfurfural (5-HMF) is an important chemical generated from lignocellulosic biomass (LCB) to produce a wide variety of value-added chemicals, biofuels, and biochemicals. Different forms of ionic liquids (ILs) have been utilized for the formation of 5-HMF from LCB. However, 5-HMF is highly soluble in imidazolium-based ionic liquids (IMILs), which makes it difficult to separate after its formation from LCB. In this manuscript, we perform all-atom molecular dynamics simulations to investigate the performance of several aprotic solvents in the extraction of 5-HMF from various IMILs. We consider twelve aprotic solvents with different physicochemical properties, such as acetonitrile (AN), acetone (AT), 1,4-dioxane (DI), N,N-dimethyl acetamide (DMA), N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), gamma-butyrolactone (GBL), gamma-valerolactone (GVL), hexamethylphosphoramide (HMPA), N-methyl pyrrolidone (NMP), propylene carbonate (PC), and sulfolane (SF). We analyze various structures and dynamics and perform a detailed thermodynamic analysis to understand the underlying molecular behavior. The results indicate that solvents AT and DI showed the least favorable interactions with 5-HMF, whereas HMPA showed the most favorable interactions with 5-HMF. Based on the detailed structural insights, HMPA enhances the separation of 5-HMF from the ILs. Furthermore, different anion combinations were tested to benchmark their separation capability. Overall, the results presented in this manuscript guide the selection of solvent and IL combinations for the effective separation of 5-HMF.

The development of antifouling membranes for water filtration applications is challenging. Conducting polymers can show enhanced antifouling characteristics by blending with various polymers, nanomaterials, and Ionic liquids (ILs). In this paper, we perform an all-atom molecular dynamics simulation on a conducting polymer polyaniline (PANI) immersed in IL-water mixtures. Two forms of PANI were considered, namely Emeraldine base (EB) and Emeraldine salt (ES) as well as two different water-mixed ILs are considered namely (a) 1-ethyl-3-methyl imidazolium [EMIM]+ hexafluorophosphate [PF6]- and (b) 1-ethyl-3-methyl imidazolium [EMIM]+ tetra-fluoroborate [BF4]-. We present various intra- and inter-molecular structural properties, solvation thermodynamics, and dynamic properties. We observe that with an increase in IL concentration, the radius of gyration (Rg) value shows a decrease for ES in pure state in both ILs; on the other hand, we see a minimal increase in the Rg values of EB in both ILs. The dihedral angle distribution analysis shows a combination of gauche and trans state for ES, whereas trans state is more pronounced for the case of EB in both water-IL mixtures. The radial distribution function (RDF) analysis between the ortho, meta carbons of the benzene rings, and the amine groups on ES with [BF4]- and [PF6]- show significant structural peaks. On the other hand, EB and ES show lower interaction with the water molecules. The number of hydrogen bonds (h-bonds) between polymer and water is higher for EB than ES in both IL-water mixtures. The hydrogen bond lifetime (τ) values show one-fold higher values for EB than ES. The self-diffusion coefficient (D) values of water show a decrease with an increase in IL concentration. The thermodynamic properties solvation enthalpy (ΔH) and excess molar volume (VmE) for both ES and EB show a more favorable solvation in [EMIM]+[BF4]- when compared to [EMIM]+[PF6]- with an increase in IL concentration. These observations are crucial for selecting ILs and designing sustainable polymers for antifouling membranes.