Cholinium amino acid-based ionic liquids

An insight into pharmaceutical challenges with ionic liquids: where do we stand in transdermal delivery?

Ionic liquids (ILs) represent an exciting and promising solution for advancing drug delivery platforms. Their unique properties, including broad chemical diversity, adaptable structures, and exceptional thermal stability, make them ideal candidates for overcoming challenges in transdermal drug delivery. Despite encountering obstacles such as side reactions, impurity effects, biocompatibility concerns, and stability issues, ILs offer substantial potential in enhancing drug solubility, navigating physiological barriers, and improving particle stability. To propel the use of IL-based drug delivery in pharmaceutical innovation, it is imperative to devise new strategies and solvents that can amplify drug effectiveness, facilitate drug delivery to cells at the molecular level, and ensure compatibility with the human body. This review introduces innovative methods to effectively address the challenges associated with transdermal drug delivery, presenting progressive approaches to significantly improve the efficacy of this drug delivery system.

A New 2-Aminospiropyrazolylammonium Cation with Possible Uses in the Topical Areas of Ionic Liquids

Based on the fact that 2-aminospiropyrazolinium compounds and structurally related azoniaspiro compounds belong, in a broad sense, to the class of ionic liquids, we have reviewed them and studied their practical applications. To search for possible uses of a new 2-aminospiropyrazolinium compounds, it is necessary to undertake a comparison with the related class of azoniaspiro compounds based on available information. The structures of the well-studied class of azoniaspiro compounds and the related but little-studied class of 2-aminospiropyrazolinium have rigid frameworks, limited conformational freedom, and a salt nature. These properties give them the ability to organize the nearby molecular space and enable the structure-forming ability of azoniaspiro compounds in the synthesis of zeolites, as well as the ability to act as phase-transfer catalysts and have selective biological effects. Additionally, these characteristics enable their ability to act as electrolytes and serve as materials for anion exchange membranes in fuel cells and water electrolyzers. Thus, the well-studied properties of azoniaspiro compounds as phase-transfer catalysts, structure-directing agents, electrolytes, and materials for membranes in power sources would encourage the study of the similar properties of 2-aminospiropyrazolinium compounds, which we have studied in relation to in vitro antitubercular, antidiabetic, and antimicrobial activities.

Solvation of Model Biomolecules in Choline-Aminoate Ionic Liquids: A Computational Simulation Using Polarizable Force Fields

One can foresee a very near future where ionic liquids will be used in applications such as biomolecular chemistry or medicine. The molecular details of their interaction with biological matter, however, are difficult to investigate due to the vast number of combinations of both the biological systems and the variety of possible liquids. Here, we provide a computational study aimed at understanding the interaction of a special class of biocompatible ionic liquids (choline-aminoate) with two model biological systems: an oligopeptide and an oligonucleotide. We employed molecular dynamics with a polarizable force field. Our results are in line with previous experimental and computational evidence on analogous systems and show how these biocompatible ionic liquids, in their pure form, act as gentle solvents for protein structures while simultaneously destabilizing DNA structure.

Bioinspired Herbicides-Ionic Liquids or Liquid Cocrystals?

This research provides information about combinations of several amino acids, including l-proline (Pro), l-arginine (Arg), and l-histidine (His), with phenoxyacetic acid herbicides (MCPA and 2,4-D). Five amino acid ionic liquids (AAILs), one amino acid higher-melting salt (AAHMS), and two amino acid liquid cocrystals (AALCs) were obtained in high yields (>90%). The ionization of the six new structures was confirmed by NMR, IR, and molecular modeling. X-ray crystallography was used to definitively confirm the binding location of the mobile hydrogen. Furthermore, we propose a computational method for estimating the energy of specific hydrogen bond(s) in AAIL crystals based on the NBO and QTAIM hydrogen bond parameters obtained by model calculations. An in-depth analysis of the structures allowed to answer the question posed in the title, ionic liquids or liquid cocrystals? AAILs based on arginine and histidine were obtained. In contrast, combining proline with MCPA and 2,4-D led to AALCs. Finally, the compounds were analyzed to measure their herbicidal activity. These studies proved that the novel form of MCPA or 2,4-D improved its ability to control weeds compared to commercial formulations containing the same active ingredients.

Reaction Mechanism of CO2 with Choline-Amino Acid Ionic Liquids: A Computational Study

Carbon capture and sequestration are the major applied techniques for mitigating CO2 emission. The marked affinity of carbon dioxide to react with amino groups is well known, and the amine scrubbing process is the most widespread technology. Among various compounds and solutions containing amine groups, in biodegradability and biocompatibility perspectives, amino acid ionic liquids (AAILs) are a very promising class of materials having good CO2 absorption capacity. The reaction of amines with CO2 follows a multi-step mechanism where the initial pathway is the formation of the C-N bond between the NH2 group and CO2. The added product has a zwitterionic character and can rearrange to give a carbamic derivative. These steps of the mechanism have been investigated in the present study by quantum mechanical methods by considering three ILs where amino acid anions are coupled with choline cations. Glycinate, L-phenylalanilate and L-prolinate anions have been compared with the aim of examining if different local structural properties of the amine group can affect some fundamental steps of the CO2 absorption mechanism. All reaction pathways have been studied by DFT methods considering, first, isolated anions in a vacuum as well as in a liquid continuum environment. Subsequently, the role of specific interactions of the anion with a choline cation has been investigated, analyzing the mechanism of the amine-CO2 reaction, including different coupling anion-cation structures. The overall reaction is exothermic for the three anions in all models adopted; however, the presence of the solvent, described by a continuum medium as well as by models, including specific cation- -anion interactions, modifies the values of the reaction energies of each step. In particular, both reaction steps, the addition of CO2 to form the zwitterionic complex and its subsequent rearrangement, are affected by the presence of the solvent. The reaction enthalpies for the three systems are indeed found comparable in the models, including solvent effects.

Choline-Amino Acid-Derived Bio-ionic Liquids for Solubility Enhancement of Zafirlukast

This study investigated the application of bio-ionic liquids (ILs) prepared from choline as cation and amino acid as anion for solubility enhancement of poorly water-soluble drug, Zafirlukast (ZFL). Herein, the solubility of ZFL in water and mixtures of water and ILs was assessed using UV spectroscopy at two temperature points 25°C and 37°C with increasing concentrations of IL. ZFL solubility was found to improve linearly with increasing concentration of [Ch][Pro] in water, representing 35- to 37-fold improvement in ZFL solubility at maximum concentration of [Ch][Pro] (1% w/v) compared to when only pure water was present. Also, the effect of IL on ZFL solubility was analyzed using NMR, DSC, and TGA. These results clearly suggest that ZFL solubility was increased by forming hydrogen bonds with selected [Ch][Pro] IL. Toxicity study of ILs was tested against gram-positive and gram-negative bacteria. Since IL solvent was found to increase the solubility of ZFL, this may serve as "functional excipient solvent" for solubility enhancement in its commercialized formulations.

Aqueous Biphasic Systems Comprising Natural Organic Acid-Derived Ionic Liquids

Despite the progress achieved by aqueous biphasic systems (ABSs) comprising ionic liquids (ILs) in extracting valuable proteins, the quest for bio-based and protein-friendly ILs continues. To address this need, this work uses natural organic acids as precursors in the synthesis of four ILs, namely tetrabutylammonium formate ([N4444][HCOO]), tetrabutylammonium acetate ([N4444][CH3COO]), tetrabutylphosphonium formate ([P4444][HCOO]), and tetrabutylphosphonium acetate ([P4444][CH3COO]). It is shown that ABSs can be prepared using all four organic acid-derived ILs paired with the salts potassium phosphate dibasic (K2HPO4) and tripotassium citrate (C6H5K3O7). According to the ABSs phase diagrams, [P4444]-based ILs outperform their ammonium congeners in their ability to undergo liquid–liquid demixing in the presence of salts due to their lower hydrogen-bond acidity. However, deviations to the Hofmeister series were detected in the salts’ effect, which may be related to the high charge density of the studied IL anions. As a proof of concept for their extraction potential, these ABSs were evaluated in extracting human transferrin, allowing extraction efficiencies of 100% and recovery yields ranging between 86 and 100%. To further disclose the molecular-level mechanisms behind the extraction of human transferrin, molecular docking studies were performed. Overall, the salting-out exerted by the salt is the main mechanism responsible for the complete extraction of human transferrin toward the IL-rich phase, whereas the recovery yield and protein-friendly nature of these systems depend on specific “IL-transferrin” interactions.

Perspectives in the Computational Modeling of New Generation, Biocompatible Ionic Liquids

In this Perspective, I review the current state of computational simulations on ionic liquids with an emphasis on the recent biocompatible variants. These materials are used here as an example of relatively complex systems that highlights the limits of some of the approaches commonly used to study their structure and dynamics. The source of these limits consists of the coexistence of nontrivial electrostatic, many-body quantum effects, strong hydrogen bonds, and chemical processes affecting the mutual protonation state of the constituent molecular ions. I also provide examples on how it is possible to overcome these problems using suitable simulation paradigms and recently improved techniques that, I expect, will be gradually introduced in the state-of-the-art of computational simulations of ionic liquids.

Biophysical Reviews- 2021, the year that was

The current issue (volume 13 issue 6, 2021) is a Special Issue jointly dedicated to scientific content presented at the 20th triennial IUPAB Congress that was held in conjunction with both the 45th Annual Meeting of the Brazilian Biophysical Society (Sociedade Brasileira de Biofísica - SBBf) and the 50th Annual Meeting of the Brazilian Society for Biochemistry and Molecular Biology (Sociedade Brasileira de Bioquímica e Biologia Molecular - SBBq). In addition to describing the scientific and nonscientific content arising from the meeting this sub-editorial also provides a look back at some of the high points for Biophysical Reviews in the year 2021 before going on to describe a number of matters of interest to readers of the journal in relation to the coming year of 2022.

An experimental approach probing the conformational transitions and energy landscape of antibodies: a glimmer of hope for reviving lost therapeutic candidates using ionic liquid

Understanding protein folding in different environmental conditions is fundamentally important for predicting protein structures and developing innovative antibody formulations. While the thermodynamics and kinetics of folding and unfolding have been extensively studied by computational methods, experimental methods for determining antibody conformational transition pathways are lacking. Motivated to fill this gap, we prepared a series of unique formulations containing a high concentration of a chimeric immunoglobin G4 (IgG4) antibody with different excipients in the presence and absence of the ionic liquid (IL) choline dihydrogen phosphate. We determined the effects of different excipients and IL on protein thermal and structural stability by performing variable temperature circular dichroism and bio-layer interferometry analyses. To further rationalise the observations of conformational changes with temperature, we carried out molecular dynamics simulations on a single antibody binding fragment from IgG4 in the different formulations, at low and high temperatures. We developed a methodology to study the conformational transitions and associated thermodynamics of biomolecules, and we showed IL-induced conformational transitions. We showed that the increased propensity for conformational change was driven by preferential binding of the dihydrogen phosphate anion to the antibody fragment. Finally, we found that a formulation containing IL with sugar, amino acids and surfactant is a promising candidate for stabilising proteins against conformational destabilisation and aggregation. We hope that ultimately, we can help in the quest to understand the molecular basis of the stability of antibodies and protein misfolding phenomena and offer new candidate formulations with the potential to revive lost therapeutic candidates.

CO2 Capture in Biocompatible Amino Acid Ionic Liquids: Exploring the Reaction Mechanisms for Bimolecular Absorption Processes

CO2 capture at the production site represents one of the accessible ways to reduce its emission in the atmosphere. In this context, CO2 chemisorption is particularly advantageous and is often based on exploiting a liquid containing amino groups that can trap CO2 due to their propensity to react with it to yield carbamic derivatives. A well-known class of ionic liquids based on amino acid anions might represent an ideal medium for CO2 capture because, at difference with present implementations, they are known to be fully biocompatible. One of the problems is however the relatively low molar ratio of CO2 absorption. Increasing this ratio turns out to be possible by choosing appropriate anions. We present here a set of accurate computations to elucidate the possible reaction paths that allow the anion to absorb two CO2 molecules, thus effectively doubling the overall intake. An extensive exploration of some reaction mechanisms suggests that some of them might be quite efficient even under mild conditions.

Modelling biocompatible ionic liquids based on organic acids and amino acids: challenges for computational models and future perspectives

In this short review I shall highlight the basic principle and the difficulties that arise in attempting the computational modeling of seemingly simple systems which hide an unexpected complexity. Biocompatible ionic liquids which are based on the coupling of organic or amino acid anions with metabolic cations such as cholinium are the target of this review. These substances have been the subject of intense research activities in the last few years and have attracted the attention of computational chemists. I shall show that the computational description of these substances is far from trivial and requires the use of sophisticated techniques in order to account for a surprisingly rich chemistry that is due to several phenomena such as polarization, charge transfer, proton transfer equilibria and tautomerization reactions.

Unique and generic structural features of cholinium amino acid-based biocompatible ionic liquids

Cholinium amino acid-based (Ch-AA) biocompatible ionic liquids (bio-ILs) are synthesized from renewable components and are efficiently used for biomass processing. However, their microscopic structural features that lead to their application as biomass solvents remain undetermined. Herein, we use atomistic simulations to investigate the structures of six different Ch-AA bio-ILs up to the nanometer length scale and demonstrate that, depending on the anion side chain structure, the respective IL exhibits structural ordering at different length scales. All the six Ch-AA bio-ILs investigated here show a generic feature of having a strong hydrogen bonding network between the hydroxyl group of the cholinium cation and the carboxyl group of the amino acid anions. We illustrate that each of these bio-ILs also displays a unique feature. Distinctive intermediate range structural ordering leads to heterogeneity in methioninate- and phenylalaninate-based ILs caused by the anion side chain segregation. Intermediate range ordering is not observed in glutaminate- and glutamate-based ILs because significant anion side chain and backbone interactions hinder the formation of side chain clusters. Interestingly, for the cysteinate-based IL, the side chains do not interact with the backbones and the intermediate range ordering is not observed because of a shorter anionic side chain.