Spectroscopic insight into the interaction of bovine serum albumin with imidazolium-based ionic liquids in aqueous solution

High-sensitivity liquid chromatography-tandem mass spectrometry quantitative for alkyl imidazolium ionic liquids in human serum: Advancing biomonitoring of human exposure concerns

Alkyl imidazolium ionic liquids (Cn[MIM]), initially heralded as eco-friendly green solvents for diverse industrial applications, have increasingly been recognized fortheir biodegradability challenges and multiple biotoxicity. Despite potential health risks, research into the effects of Cn[MIM] on human health remains scarce, particularly regarding their detection in biological serum samples. This study validated a matrix-matched calibration quantitative method that utilizes solid-phase extraction (SPE) coupled with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The method was used to analyze the presence of 10 ionic liquids (ILs) with varying alkyl carbon chain lengths (C2-C12) across 300 human serum samples. Efficient separation was achieved using optimized SPE conditions and a BEH C18 column with an appropriate mobile phase. Results demonstrated a strong linear relationship (0.05-100 ng/mL; R2 = 0.995-0.999), with detection and quantification limits with detection and quantification limits ranging from 0.001 to 0.107 ng/mL and 0.003-0.355 ng/mL, respectively. Intraday and inter-day precisions were 0.85-6.99 % and 1.50-7.46 %, with recoveries between 82 and 113 %. The validated method detected C6MIM in 19 % of samples and C8MIM in 8.3 % of samples, with concentrations ranging from 0.02 to 111.70 μg/L and 0.09-16.99 μg/L, respectively, suggesting a potential risk of human exposure. This underscores the importance of robust detection methods in monitoring environmental and human health impacts of alkyl imidazolium compounds.

Invitro anti-biofilm activity and the artificial chaperone activity of quinoline-based ionic liquids

The maintenance of protein conformation under stressful conditions is one of the prevailing challenges. This has led to a rapid growth in the ingenious protein therapies, in the past few decades, prioritizing the investigation of the structure and function of proteins in novel environments. Ionic Liquids (ILs) are currently dominating the biomedical industry, by endowing great solubility and stability to bio-molecules, especially proteins. Recently, researchers have devoted their attention towards the artificial chaperone activity of several classes of ILs. Thus, comprehending the long-term as well as momentary stability of protein conformation in IL formulations is an absolute necessity. In this context, we present the activity of quinoline-based ionic liquids (ILs) as artificial cheperones against time-dependent, self induced fibril formation in Bovine Serum Albumin (BSA). Herein, a series of quinoline-based ILs were synthesized and characterized. The structural and morphological changes induced in BSA in the presence and absence of these ILs are corroborated using several spectroscopic measurements and in-silico studies. The anti-microbial and antibiofilm activity of these compounds demonstrating their medicinal properties is substantiated in this study. Furthermore, the present research also gives an account of the toxicity of these compounds under in vivo conditions, using C. elegans as the model organism.

Unveiling the molecular interactions between alkyl imidazolium ionic liquids and human serum albumin: Implications for toxicological significance

Alkyl imidazolium-based ionic liquids (ILs) are promising for diverse industrial applications; however, their growing prevalence has raised concerns regarding human exposure and potential health implications. A critical aspect to be clarified to address the adverse health effects associated with ILs exposure is their binding mode to human serum albumin (HSA). In this study, we delved into the binding interactions between three alkyl imidazolium ILs (1-hexyl-3-methyl-imidazolium (C6[MIM]), 1-ethyl-3-methyl-imidazolium chloride (C8[MIM]) and 1-decyl-3-methyl-imidazolium (C10[MIM]) and human serum albumins (HSAs) using a comprehensive approach encompassing molecular docking and multi-spectroscopy (UV-visible, Fluorescence, Circular Dichroism, FTIR). Furthermore, for the first time, we developed an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) approach time to quantify plasma protein binding rates. Our results revealed that the ILs primarily bind to the hydrophobic cavity of HSA through hydrogen bonding and van der Waals forces, forming stable complexes via static quenching. This affected HSA's secondary structure, reducing α-helical content, particularly around specific residues. Equilibrium dialysis and ultrafiltration coupled with UPLC-MS/MS analysis showed modest plasma protein binding rates (17.84%-31.85%) for the three ILs, with no significant influence from alkyl chain effects or concentration relationship. Lower plasma protein binding rates can affect bioavailability and distribution of ILs, potentially influencing their toxicity. These findings provide critical insights into the potential toxicological implications at the molecular level, thereby contributing to continuous efforts to evaluate the risk profiles and ensure the safe utilization of these compounds.

Insights into the interaction of human serum albumin with ionic liquids - Thermodynamic, spectroscopic and molecular modelling studies

Human serum albumin (HSA) effectively binds different types of low-molecular-weight compounds and thus enables their distribution in living organisms. Recently, it has been reported that the protein-ligand interactions play a crucial role in bioaccumulation processes and provide an important sorption phase, especially for ionogenic compounds. Therefore, the binding interactions of such compounds with proteins are the subject of an ongoing interest in environmental and life sciences. In this paper, the influence of some counter-ions, namely [B(CN)4]- and [C(CN)3]- on the affinity of the [IM1-12]+ towards HSA has been investigated and discussed based on experimental methods (isothermal titration calorimetry and steady-state fluorescence spectroscopy) and molecular dynamics-based computational approaches. Furthermore, the thermal stability of the resulting HSA/ligand complexes was assessed using DSC and CD spectroscopy. As an outcome of the work, it has been ascertained that the protein is able to bind simultaneously the ligands under study but in different regions of HSA. Thus, the presence in the system of [IM1-12]+ does not disturb the binding of [C(CN)3]- and [B(CN)4]-. The presented results provide important information on the presence of globular proteins and some ionogenic compounds in the distribution and bioaccumulation of ILs in the environment and living organisms.

Probing the interaction between niobium pentoxide nanoparticles and serum albumin proteins by Spectroscopic approaches

Nanoparticles (NPs) can directly or indirectly enter into the body because of their small size; then they tend to alter the conformation and function of proteins upon interaction with them. Thus, it is crucial to understand the impact of NPs in a biological medium. Recently, niobium pentoxide nanoparticles (Nb2O5 NPs) are finding increasing applications in the biological system, for example, bone tissue and dental material, matrix for biosensing of proteins, etc. In all such applications, the Nb2O5 NP interacts with proteins and other biomolecules. Hence, the study of such interactions is of considerable importance. Here in this work, we present the impact of Nb2O5 NP on the structure, stability and activity of blood proteins, bovine serum albumin (BSA) and human serum albumin (HSA) by means of various spectroscopic approaches. Steady-state fluorescence studies indicated that intrinsic fluorescence intensities of both serum albumin proteins got quenched upon their interaction with NP. The nature of the quenching was elucidated by time-resolved fluorescence and absorption measurements. Using circular dichroism (CD) and synchronous fluorescence spectroscopy (SFS), the structural perturbations of the protein molecules after interaction with NP were investigated. Moreover, the role of temperature on protein stability upon complexation with NP was also explored. In addition, the effect of NP on protein functionality was probed by esterase-like activity assays.Communicated by Ramaswamy H. Sarma.

Spectroscopic Investigation on the Interaction of Direct Yellow-27 with Protein (BSA)

Direct yellow 27 (DY-27) interaction with bovine serum albumin (BSA) was investigated using multi-spectroscopic techniques to understand the toxicity mechanism. Fluorescence quenching of BSA by DY-27 was observed as a result of the formation of a BSA-DY27 complex with a binding constant of 1.19 × 10⁵M^-1and followed a static quenching mechanism with a quenching constant K_svof 7.25 × 10⁴M^-1. The far UV circular dichroism spectra revealed the conformational changes in the secondary structure of BSA in the presence of DY-27. The calculated average lifetime of BSA is 6.04 ns and is nearly constant (5.99 ns) in the presence of dye and supports the proposed quenching mechanism. The change in free energy (ΔG) was calculated to be -28.96 kJ mol^-1and confirmed the spontaneity of the binding process. Further, docking studies have been conducted to gain more insights into the interactions between DY-27 and serum albumin.

An Overview on the Recent Advances in Alternative Solvents as Stabilizers of Proteins and Enzymes

Currently, the use of alternative solvents is increasing, namely ionic liquids (ILs) and deep eutectic solvents (DESs) in diverse fields of knowledge, such as biochemistry, chemistry, chemical engineering, biotechnology and biomedicine. Particularly, when compared to traditional solvents, these alternative solvents have great importance for biomolecules due to the enhanced solubility, structure stability and the biological activity of biomolecules, such as protein and enzymes. Thus, in this review article, the recent developments and efforts on the technological developments carried out with ILs and DESs for the stabilization and activation of proteins and enzymes are provided. The most studied IL- and DES-based formulations for proteins and enzymes are discussed and the molecular mechanisms and interactions related to the increased stability promoted by these alternative solvents are disclosed, while emphasizing their main advantages.

Insights into protein-ionic liquid interaction: A comprehensive overview on theoretical and experimental approaches

Owing to highly tunable nature, ionic liquids are nesting stance in the scientific community for a wide variety of applications ranging from electrochemistry to product purification, from chemical and biomedical applications to biotechnological interventions and proteomics. Proteins are unstable in its native form and several attempts have been made to stabilize them by addition of various additives. This review focusses on the studies conducted to improve protein stability with ionic liquids along with an emphasis on the mechanism of interaction. This review also specifies and discusses about the brief introduction to ionic liquids, evolution of first-, second-, and third generation of liquids over the years and their selection criterion and applications. Though, there are several elegant reviews available on proteins-ionic liquids interaction, this review systematically highlights the effect of ionic liquids viz., imidazolium, ammonium, phosphonium and choline-based ionic liquids (amino acid-based anions & classical anions) on fibrous proteins viz., collagen and keratin and globular proteins viz., bovine serum albumin and cytochrome c. Thus, this review elaborates the thorough investigations conducted to explore the stabilizing properties of ionic liquids over fibrous and globular proteins.

The anion of choline-based ionic liquids tailored interactions between ionic liquids and bovine serum albumin, MCF-7 cells, and bacteria

Choline-based ionic liquids (ILs) have been widely applied because of their good biocompatibility. Herein, the toxicity of choline-based ILs containing different anions was studied by UV-vis absorption spectra, fluorescence spectra, MTT assays and antibacterial experiments. The results explained that choline chloride ([Ch][Cl]) had no obvious effect on the conformation of bovine serum albumin (BSA), while the conformation could be slightly changed by choline bromide ([Ch][Br]). In the presence of choline iodide ([Ch][I]), choline bitartrate ([Ch][Bit]) and choline dihydrogen citrate ([Ch][Dhc]), the conformation of BSA changed significantly. The quenching mechanisms of [Ch][Bit] and [Ch][Dhc] were static quenching procedure, while there were charge transfer quenching and static quenching for [Ch][I]. ILs combined with BSA in spontaneous manner driven by hydrogen bond and van der Waals force, which was proved by thermodynamic constants and molecular docking. The toxicity of the five ILs to mammalian cells and bacteria came to a similar conclusion. [Ch][Cl] had little toxicity to cells, which was less than [Ch][Br] and [Ch][I]. [Ch][Bit] and [Ch][Dhc] were more toxic. These results provide more information to understand the effect of anions on choline-based ILs, in order to find low toxic choline-based ILs that can be used in biological and pharmaceutical fields.

PARAFAC study of L-cys@CdTe QDs interaction to BSA, cytochrome c and trypsin: An approach through electrostatic and covalent bonds

Utilizing fluorescence spectroscopy, non-covalent and covalent interactions of L-cys@CdTe quantum dots to bovine serum albumin (BSA), cytochrome c and trypsin were investigated. L-cys@CdTe QDs with the emission maximum at 530 nm and an average diameter of 2.6 nm were synthesized in the aqueous medium. Formaldehyde, N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC) with N-hydroxysuccinimide (NHS), and glutaraldehyde was applied as cross-linkers. In the case of both electrostatic and covalent strategies PARAFAC, as a powerful multi-way chemometrics technique, was utilized to analyze fluorescence excitation-emission (EEM) spectra. For non-covalent and covalent bonding, two and three significant components composed the PARAFAC models. Resolved EEM shows that in the presence of formaldehyde, a new component with an emission peak similar to BSA was obtained. Using EDC-NHS cross-linker, the fluorescence peak of the newly formed component was in a distinct wavelength with similar emission intensity, compared to L-cys@CdTe QDs and BSA. Employing glutaraldehyde, a distinguished component was easily detected at emission wavelengths higher than that of L-cys@CdTe QDs and proteins. It was concluded that the choice of cross-linker is a critical step to create different emission spectra when dealing with nano-bio-conjugations. This study shows that glutaraldehyde cross-linker leads to increase sensitivity, selectivity, and accuracy of protein analysis.

Structural-functional integrity of lysozyme in imidazolium based surface active ionic liquids

The present study was designed to explore the hydrophobicity and concentration dependence of imidazolium based surface active ionic liquids (SAILs) effects on the structural-functional integrity of proteins. Specifically, we investigated the impact of SAILs viz. 1-octyl-3-methylimidazolium dodecylbenzenesulfonate ([OMIM][DBS]) and 1-dodecyl-3-methylimidazolium dodecylbenzenesulfonate ([DDMIM][DBS]) on activity, structure and stability of lysozyme. Activity measurements revealed that, in contrast to [DDMIM][DBS] that renders lysozyme either feebly active or inactive, [OMIM][DBS] significantly enhances the lysozyme activity in the concentration range of critical aggregation concentrations (CAC) to C_s (SAIL saturation concentration of protein backbone) i.e., 0.5 mM-1.35 mM. Tensiometric results in agreement with turbidity measurements inferred significant composition and concentration dependence of the lysozyme-SAIL interactions. Spectroscopic investigations revealed that compared to destabilizing behaviour of [DDMIM][DBS], [OMIM][DBS] significantly enhances both conformational as well as thermal stability of lysozyme in the CAC to C_s concentration regime. Altogether, results obtained do indicate that [OMIM][DBS], in the concentration regime of CAC to C_s, serves as an efficient stabiliser with an ability to appreciably enhance the activity, thermal stability and overall conformational stability of lysozyme. We firmly believe that [OMIM][DBS], at least in the CAC to C_s concentration ranges, can be exploited as a promising stabiliser and activity enhancer for numerous industrially important enzymes.

Investigation of binding interactions between BSA and [EPMpyr][Sal] through spectroscopy studies, thermophysical and thermodynamic properties

The intensity of research, probing the interactions between proteins and ionic liquid (IL), has been increasing and parallels the fast-growing applications of ILs in biotechnology. The specific aspects which have attracted the involvement of researchers are stabilization, separation, biochemical and enzymatic reactions of proteins. In this work the synthesis of IL, epoxypropyl and N-methyl substituted 2‑oxopyrrolidinium cation with salicylate anion, [EPMpyr][Sal], and its interaction with aqueous BSA{BSA_(aq)-[EPMpyr][Sal]}. Measurements of thermophysical properties (density (ρ), and speed of sound (u)) showed that both moderately strong and weak interactions occur on treatment of BSA with that chosen IL. H-bond formation, dipole-dipole interactions and ionic interactions occurring in this system were investigated via thermophysical and thermodynamic properties as well as spectroscopic data. Thermodynamic data (excess molar volume (V_m^E), isentropic compressibility (k_s), deviation in isentropic compressibility (∆k_s) and intermolecular free length (L_f)) showed that there were stronger interaction between IL and BSA at higher temperature. The data from all the studies were correlated with Redlich Kister polynomial equation. The blue shift observed in the fluorescent spectra was interpreted to indicate that thetryptophan (Trp) residue of BSA moves to a more hydrophobic environment. It was also observed that the addition of more IL to BSA resulted in denaturation of BSA due to high hydrophobic nature of IL. Circular dichroism studies show that there were significant changes in the fine structure of BSA on interaction with IL. From the FTIR spectra the position of H-bond in the secondary structure of BSA was deduced.

Binding and inhibitory effect of the food colorants Sunset Yellow and Ponceau 4R on amyloid fibrillation of lysozyme

Amyloid fibrillogenesis of proteins is known to be the root cause of a large number of diseases like Parkinson's, Alzheimer's, and Huntington's disease, spongiform encephalopathy, amyloid polyneuropathy, type-II diabetes, etc.

Heme Dissociation from Myoglobin in the Presence of the Zwitterionic Detergent N,N-Dimethyl-N-Dodecylglycine Betaine: Effects of Ionic Liquids

We have investigated myoglobin protein denaturation using the zwitterionic detergent Empigen BB (EBB, N,N-Dimethyl-N-dodecylglycine betaine). A combination of absorbance, fluorescence, and circular dichroism spectroscopic measurements elucidated the protein denaturation and heme dissociation from myoglobin. The results indicated that Empigen BB was not able to fully denature the myoglobin structure, but apparently can induce the dissociation of the heme group from the protein. This provides a way to estimate the heme binding free energy, ΔG_dissociation. As ionic liquids (ILs) have been shown to perturb the myoglobin protein, we have investigated the effects of the ILs 1-butyl-3-methylimidazolium chloride (BMICl), 1-ethyl-3-methylimidazolium acetate (EMIAc), and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄) in aqueous solution on the ΔG_dissociation values. Absorbance experiments show the ILs had minimal effect on ΔG_dissociation values when compared to controls. Fluorescence and circular dichroism data confirm the ILs have no effect on heme dissociation, demonstrating that low concentrations ILs do not impact the heme dissociation from the protein and do not significantly denature myoglobin on their own or in combination with EBB. These results provide important data for future studies of the mechanism of IL-mediated protein stabilization/destabilization and biocompatibility studies.

Construing the interactions between MnO2 nanoparticle and bovine serum albumin: insight into the structure and stability of a protein–nanoparticle complex

Systematic experimental investigation of MnO₂–BSA complexes in terms of the structure and stability of the protein as well as the aggregation of the nanoparticle.

A spectroscopic and molecular dynamics simulation approach towards the stabilizing effect of ammonium-based ionic liquids on bovine serum albumin

Experimental and theoretical evidence in support of the stabilizing effect of ammonium-based ionic liquids on thermal unfolding/refolding of bovine serum albumin is provided in this article.