Evaporation Behavior and Characterization of Eutectic Solvent and Ibuprofen Eutectic Solution

Menthol-Based (Deep) Eutectic Solvents: A Review on Properties and Application in Extraction

In the last 10 years the interest in deep eutectic solvents (DESs) as a new class of green solvents has considerably increased. The emergence of numerous of hydrophobic DESs has stimulated intensive research into their application in extraction technologies, including sample preparation. As the properties of such systems are highly dependent on the properties of their components (hydrogen bond donors and acceptors) and can be finely tuned, DESs can be successfully used for the extraction of both metal ions and organic substances, including biomolecules. Despite the rapidly increasing number of publications on the use of DESs as an extraction medium, including review articles, information on the extraction properties of DESs in terms of their chemical composition has not yet been summarized. This review covers available literature data on the physicochemical properties of menthol-based eutectic solvents and the results of their practical application as an extraction medium. Also, the appropriateness of using the term "DES" for all mixtures with melting points lower than the melting points of their components is discussed.

Deep Eutectic Solvents: An Eco-friendly Design for Drug Engineering

In the spirit of circular economy and sustainable chemistry, the use of environmentally friendly chemical products in pharmacy has become a hot topic. In recent years, organic solvents have been the subject of a great range of restriction policies due to their harmful effects on the environment and toxicity to human health. In parallel, deep eutectic solvents (DESs) have emerged as suitable greener solvents with beneficial environmental impacts and a rich palette of physicochemical advantages related to their low cost and biocompatibility. Additionally, DESs can enable remarkable solubilizing effect for several active pharmaceutical ingredients (APIs), thus forming therapeutic DESs (TheDESs). In this work, special attention is paid to DESs, presenting a precise definition, classification, methods of preparation, and characterization. A description of natural DESs (NaDESs), i. e., eutectic solvents present in natural sources, is also reported. Moreover, the present review article is the first one to detail the different approaches for judiciously selecting the constituents of DESs in order to minimize the number of experiments. The role of DESs in the biomedical and pharmaceutical sectors and their impact on the development of successful therapies are also discussed.

Frozen, Cold, or Cool? Chemical Assessment of the Effectiveness of Storage Conditions for Celluloid 3D Objects

Preserving celluloid artifacts is challenging for museums, as this plastic is highly prone to degradation. Frozen, cold, and cool storage solutions are typically recommended for inhibiting the chemical degradation of celluloid. However, they are rarely implemented for three-dimensional celluloid (3D-CN) objects because low temperatures might cause irreversible effects (e.g., microcracking). This work presents the effects of four different storage temperatures (+23 °C, +13 °C, +9 °C, -15 °C) on the preservation of artificially aged 3D-CN mock-ups, aiming at understanding their effectiveness by measuring molecular weight distribution, camphor, and nitrogen contents after storage. Gel permeation chromatography (GPC) results showed that the least loss of camphor content and fewer polymer chain scissions happened at -15 °C, hinting that this temperature was the best for preservation. However, the heterogeneous nature of celluloid alteration, i.e., the development of degradation gradients in thicker 3D-CN objects (>0.5 mm), made it necessary to apply a novel sampling technique, which selectively considers several depths for analyses from the surface to the core (depth profiling). This depth profiling made monitoring the degradation evolution dependent on the storage conditions in the thicker mock-ups possible. This approach was also used for the first time to quantify the polymer chain scission, camphor loss, and denitration of historical artifacts, indicating a dramatic difference in the degradation stage between surface and core. The effectiveness of frozen storage on the chemical stability of 3D-CN after seven months could support museums to consider reducing the storage temperatures to preserve precious artifacts.

Analytical Quality by Design-Driven RP-HPLC Method Conditions to Concomitantly Determine Cinnarizine and Morin Hydrate in Combined Drug Solution and Dual Drug-Loaded Formulations

BACKGROUND

The replacement of traditional oils with a camphor and menthol-based eutectic mixture is done to prepare oil-less emulsion-like dispersions for co-delivery of cinnarizine (CNZ) and morin hydrate (MH) for managing Meniére's disease (MD). Since two drugs are loaded into the dispersions, the development of a suitable reverse phase-high performance liquid chromatography (RP-HPLC) method for their simultaneous analysis becomes inevitable.

OBJECTIVE

By applying the analytical quality by design (AQbD) approach, the RP-HPLC method conditions were optimized for the concomitant determination of two drugs.

METHODS

The systematic AQbD started with identifying critical method attributes (CMA) through an Ishikawa fishbone diagram, risk estimation matrix, and risk priority number-based failure mode effect analysis followed by screening using fractional factorial design and optimization by face-centered central composite design. The concomitant determination of two drugs by the optimized RP-HPLC method condition was substantiated via specificity checking using combined drug solution, drug entrapment efficiency, and in vitro release of the two drugs from emulsion-like dispersions.

RESULTS

The AQbD optimized RP-HPLC method conditions revealed the retention time for CNZ and MH at 5.017 and 5.323, respectively. The studied validation parameters were found within the ICH-prescribed limits. Exposing the individual drug solutions to acidic and basic hydrolytic conditions yielded extra chromatographic peaks for MH, probably due to the degradation of MH. The DEE % values of 87.40 ± 4.70 and 74.79 ± 2.94, respectively, were noticed for CNZ and MH in emulsion-like dispersions. More than 98% CNZ and MH release was occurred from emulsion-like dispersions within 30 min post-dissolution in artificial perilymph.

CONCLUSIONS

Overall, the AQbD approach could be helpful for systematic optimization of RP-HPLC method conditions to estimate concomitantly other therapeutic moieties.

HIGHLIGHTS

The proposed article shows the successful application of AQbD for the optimization of RP-HPLC method conditions to concomitantly estimate CNZ and MH in combined drug solution and dual-drug-loaded emulsion-like dispersions.

Co-Amorphous Versus Deep Eutectic Solvents Formulations for Transdermal Administration

Transdermal administration can be considered as an interesting route to overcome the side-effects inherent to oral intake. Designing topical formulations with maximum drug efficiency requires the optimization of the permeation and the stability of the drug. The present study focuses on the physical stability of amorphous drugs within the formulation. Ibuprofen is commonly used in topical formulations and then was selected as a model drug. Additionally, its low Tg allows easy, unexpected recrystallization at room temperature with negative consequence on skin penetration. In this study, the physical stability of amorphous ibuprofen was investigated in two types of formulations: (i) in terpenes-based deep eutectic solvents (DES) and (ii) in arginine-based co-amorphous blends. The phase diagram of ibuprofen:L-menthol was mainly analyzed by low-frequency Raman spectroscopy, leading to the evidence of ibuprofen recrystallization in a wide range of ibuprofen concentration. By contrast, it was shown that amorphous ibuprofen is stabilized when dissolved in thymol:menthol DES. Forming co-amorphous arginine-ibuprofen blends by melting is another route for stabilizing amorphous ibuprofen, while recrystallization was detected in the same co-amorphous mixtures obtained by cryo-milling. The mechanism of stabilization is discussed from determining T_g and analyzing H-bonding interactions by Raman investigations in the C=O and O-H stretching regions. It was found that recrystallization of ibuprofen was inhibited by the inability to form dimers inherent to the preferential formation of heteromolecular H-bonding, regardless of the glass transition temperatures of the various mixtures. This result should be important for predicting ibuprofen stability within other types of topical formulations.

The Study of Deep Eutectic Solvent Based on Choline Chloride and L-(+)-Tartaric Acid Diethyl Ester for Transdermal Delivery System

Deep eutectic solvents (DESs) based on choline chloride (C) and L-(+)-tartaric acid diethyl ester (L) were prepared and used in transdermal drug delivery system (TDDS). The internal chemistry structure including the formation and changes of hydrogen bonds of choline chloride and L-(+)-tartaric acid diethyl ester DES was characterized via attenuated total reflection Fourier transform infrared (ATR-FTIR) and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. The stoichiometric ratio of choline chloride to L-(+)-tartaric acid diethyl ester as well as water content affected the viscosity, glass transition temperature (T_g), and drug solubility of the DES. The viscosity and glass transition temperature of the DES (CL14) prepared at the ratio of 1:4 of choline chloride to L-(+)-tartaric acid diethyl ester were 1.19 Pa·s and - 44.01°C, respectively, and decreased to 0.10 Pa·s and - 55.31°C when 10% water (CL1410) was added. Taking diclofenac diethylamine (DDEA), the nonsteroidal anti-inflammatory drug as model, drug solubility was as high as 60 mg/ml and 250 mg/ml in CL14 and CL1410, respectively. The cumulative amount of DDEA was 4.63 ± 2.67 μg/cm² and 15.27 ± 4.63 μg/cm² for CL14 and CL1410, respectively, at 8 h. The mechanism of percutaneous permeability by the DES may be the disturbance of stratum corneum (SC) lipids as well as changes in the protein conformations. CL14 and CL1410 were also verified as low-cytotoxic and nonirritant. Therefore, the DESs studied are promising to be used in drug solubilization enhancement and transdermal drug delivery system.

Deep Eutectic Solvent Formulations and Alginate-Based Hydrogels as a New Partnership for the Transdermal Administration of Anti-Inflammatory Drugs

The transdermal administration of nonsteroidal anti-inflammatory drugs (NSAIDs) is a valuable and safer alternative to their oral intake. However, most of these drugs display low water solubility, which makes their incorporation into hydrophilic biopolymeric drug-delivery systems difficult. To overcome this drawback, aqueous solutions of bio-based deep eutectic solvents (DES) were investigated to enhance the solubility of ibuprofen, a widely used NSAID, leading to an increase in its solubility of up to 7917-fold when compared to its water solubility. These DES solutions were shown to be non-toxic to macrophages with cell viabilities of 97.4% (at ibuprofen concentrations of 0.25 mM), while preserving the anti-inflammatory action of the drug. Their incorporation into alginate-based hydrogels resulted in materials with a regular structure and higher flexibility. These hydrogels present a sustained release of the drug, which is able, when containing the DES aqueous solution comprising ibuprofen, to deliver 93.5% of the drug after 8 h in PBS. Furthermore, these hydrogels were able to improve the drug permeation across human skin by 8.5-fold in comparison with the hydrogel counterpart containing only ibuprofen. This work highlights the possibility to remarkably improve the transdermal administration of NSAIDs by combining new drug formulations based on DES and biopolymeric drug delivery systems.

Solids Turn into Liquids—Liquid Eutectic Systems of Pharmaceutics to Improve Drug Solubility

The low solubility of active pharmaceutical ingredients (APIs) is a problem in pharmaceutical development. Several methodologies can be used to improve API solubility, including the use of eutectic systems in which one of the constituents is the API. This class of compounds is commonly called Therapeutic Deep Eutectic Systems (THEDES). THEDES has been gaining attention due to their properties such as non-toxicity, biodegradability, and being non-expensive and easy to prepare. Since the knowledge of the solid liquid diagram of the mixture and the ideal eutectic point is necessary to ascertain if a mixture is a deep eutectic or just a eutectic mixture that is liquid at ambient temperature, the systems studied in this work are called Therapeutic Liquid Eutectic Systems (THELES). Therefore, the strategy proposed in this work is to improve the solubility of chlorpropamide and tolbutamide by preparing THELES. Both APIs are sulfonylurea compounds used for the treatment of type 2 diabetes mellitus and have low solubility in water. To prepare the THELES, several coformers were tested, namely, tromethamine, L(+)-arginine, L-tryptophan, citric acid, malic acid, ascorbic acid, and p-aminobenzoic acid, in molar ratios of 1:1 and 1:2. To improve viscosity, water was added in different molar ratios to all systems. THELES were characterized by mid-infrared spectroscopy (MIR), and differential scanning calorimetry. Their viscosity, solubility, and permeability were also determined. Their stability at room temperature and 40 °C was accessed by MIR. Cytocompatibility was performed by metabolic activity and cell lysis evaluation, according to ISO10993-5:2009, and compared with the crystalline APIs. THELES with TRIS were successfully synthesized for both APIs. Results showed an increased solubility without a decrease in the permeability of the APIs in the THELES when compared with the pure APIs. The THELES were also considered stable for 8 weeks at ambient temperature. The cells studied showed that the THELES were not toxic for the cell lines used.

Deep Eutectic Solvents as Active Pharmaceutical Ingredient Delivery Systems in the Treatment of Metabolic Related Diseases

Metabolic related diseases such as cancer, diabetes mellitus and atherosclerosis are major challenges for human health and safety worldwide due to their associations with high morbidity and mortality. It is of great significance to develop the effective active pharmaceutical ingredient (API) delivery systems for treatment of metabolic diseases. With their unique merits like easy preparation, high adjustability, low toxicity, low cost, satisfactory stability and biodegradation, deep eutectic solvents (DESs) are unarguably green and sustainable API delivery systems that have been developed to improve drug solubility and treat metabolic related diseases including cancer, diabetes mellitus and atherosclerosis. Many reports about DESs as API delivery systems in the therapy of cancer, diabetes mellitus and atherosclerosis exist but no systematic overview of these results is available, which motivated the current work.

Theoretical insights into the cineole-based deep eutectic solvents

Deep eutectic solvents based on cineole as hydrogen bond acceptors and organic acids (succinic, malic, and lactic) as hydrogen bond donors are studied using a theoretical approach. The nature, strength, and extension of hydrogen bonding are analyzed, thus quantifying this prevailing interaction and its role in the fluid properties. Density functional theory was used to study small molecular clusters, and the topological characterization of the intermolecular forces was carried out using atoms in a molecule theory. Classical molecular dynamics simulations were considered to study nanoscopic bulk liquid properties and their relationship with relevant macroscopic properties such as density or thermal expansion. The reported results provide the characterization of environmentally friendly deep eutectic solvents and show the suitability of cineole for developing these sustainable materials.

A Data-Mining Approach for the Quantitative Assessment of Physicochemical Properties of Molecular Compounds in the Skin Flux

This paper aimed to provide an insight into the mechanism of transdermal penetration of drug molecules with respect to their physicochemical properties, such as solubility (S), the presence of enantiomer (ET) and logarithm of octanol-water partition coefficient (log P), molecular weight (MW), and melting point (MP). Propionic acid derivatives were evaluated for their flux through full-thickness skin excised from hairless mice upon being delivered from silicone-based pressure-sensitive adhesive (PSA) matrices in the presence or absence of various enhancers. The skin fluxes of model compounds were calculated based on the data obtained using the method engaged with the diffusion cell system. The statistical design of experiments (DoE) based on the factorial approach was used to find variables that have a significant impact on the outcomes. For the prediction of skin flux, a quantitative equation was derived using the data-mining approach on the relationship between skin permeation of model compounds (~125 mg/ml) and involved physicochemical variables. The most influential variables for the skin flux of propionic acid derivatives were the melting point (0.97) followed by the presence of enantiomer (0.95), molecular mass (0.93), log P values (0.86), and aqueous solubility (0.80). It was concluded that the skin flux of molecular compounds can be predicted based on the relationship between their physicochemical properties and the interaction with cofactors including additives and enhancers in the vehicles.

Exploring the novel green eutectic solvent for the synthesis of 4-hydroxy-2-methyl-N-2-pyridinyl-2H-1,2,-benzothiazine-3-carboxamide 1,1-dioxide with benzoic acid cocrystal using a co-grinding technique

In the present study, the suitability of a green eutectic solvent, a mixture of menthol and camphor for cocrystal synthesis has been investigated to improve the biopharmaceutical properties of poorly water-soluble drugs.

Sketching neoteric solvents for boosting drugs bioavailability

Emerging neoteric solvents are being the subject of growing attention due to their lower cost and environmental impact, so they are being applied in a broad spectrum of industries. Among them, the pharmaceutical sector is demanding new environmentally friendly and non-toxic solvents able to enhance drugs solubility and stability. The introduction of ionic liquids turned out to be a breakthrough in the field of Green Chemistry opening up new separation and catalysis opportunities. In this sense, the options represented by Deep Eutectic Solvents make up an attractive alternative due to the low cost of their raw material, simple synthesis, and eco-friendly character. In line with these findings, Therapeutic Deep Eutectic Solvents and Natural Deep Eutectic Solvents are new and promising alternatives to improve the bioavailability of drugs in pharmaceutical formulations. This leading article is focused on providing a general picture of the advantages and drawbacks of these new solvents as well as the main research lines and perspectives to achieve efficient drugs delivery systems.

Deep eutectic solvents comprising active pharmaceutical ingredients in the development of drug delivery systems

INTRODUCTION

Deep eutectic solvents comprising or acting as solvents of active pharmaceutical ingredients (API-DES) emerged as promising alternatives to improve therapeutic efficiency, with the additional possibility to integrate them in (bio)polymer-based systems to enhance their delivery.

AREAS COVERED

A critical review of the API-DES field evolution is herein presented, namely on the capacity of DES to integrate APIs in their composition and on the use of DES as solvents for APIs. These strategies avoid a current major concern related to drugs and APIs, i.e. polymorphism, and increase the solubility and bioavailability of the target API which leads to increased bioavailability. Owing to their composition versatility, polymerizable API-DES can also be prepared. Finally, the incorporation of API-DES in (bio)polymer-based systems to improve drug delivery is presented and discussed.

EXPERT OPINION

The relatively easy preparation of API-DES and their capacity to tune the API's release profile when incorporated in (bio)polymer-based systems represent an effective alternative to improve the APIs therapeutic action and to develop controlled drug delivery systems. Given the potential and progress demonstrated so far, the authors foresee further research on novel API-DES and on their delivery routes, envisaging the development of alternative therapies and final approval as therapeutics.

Polymorphism and thermophysical properties of L- and DL-menthol

The thermodynamic properties, phase behavior, and kinetics of polymorphic transformations of racemic (DL-) and enantiopure (L-) menthol were studied using a combination of advanced experimental techniques, including static vapor pressure measurements, adiabatic calorimetry, Tian-Calvet calorimetry, differential scanning calorimetry (DSC), and variable-temperature X-ray powder diffraction. Several concomitant polymorphs (α, β, γ, and δ forms) were observed and studied. A continuous transformation to the stable α form was detected by DSC and monitored in detail using X-ray powder diffraction. A long-term coexistence of the stable crystalline form with the liquid phase was observed. The vapor pressure measurements of both compounds were performed using two static apparatus over a temperature range from 274 K to 363 K. Condensed-phase heat capacities were measured by adiabatic and Tian-Calvet calorimetry in the wide temperature interval from 5 K to 368 K. Experimental data of L- and DL-menthol are compared mutually as well as with available literature results. The thermodynamic functions of crystalline and liquid L-menthol between 0 K and 370 K were calculated from the calorimetric results. The thermodynamic properties in the ideal-gas state were obtained by combining statistical thermodynamics and quantum chemical calculations based on a thorough conformational analysis. Calculated ideal-gas heat capacities and experimental data on vapor pressure and condensed-phase heat capacity were treated simultaneously to obtain a consistent thermodynamic description. Based on the obtained results, the phase diagrams of L-menthol and DL-menthol were suggested.

Mesoporous and hollow hydroxyapatite nanostructured particles as a drug delivery vehicle for the local release of ibuprofen

The high risk of infection caused by implantation of orthopedic bio-metals is still a daunting challenge for surgeons as it can lead to implant failure. One approach to overcome this issue is the local release of antibacterial drug through coating on the surface of a metallic implant. One ideal carrier for this purpose is hydroxyapatite (HA) particles which are bioactive, biodegradable, biocompatible and have the potential to bond to bone. In the current study, highly crystalline mesoporous HA nanostructure particles were successfully synthesized in a low-temperature solvent process with the aid of an inorganic CaCO₃ template and then fully characterized. The specific surface area and the average size of the cavities of the nanostructured mesoporous HA particles were 85 m²/g and 20 nm, respectively. The feasibility of the prepared HA mesoporous nanostructures for drug delivery, using ibuprofen as a model drug, was also investigated. The as-prepared HA mesoporous nanostructures showed a high drug-loading capacity, as well as sustained drug release in a phosphate buffered saline (PBS) at a pH of 7.4. Overall, results show that HA mesoporous nanostructures gave great potential in bone regeneration and local delivery of either drugs or biomolecules.

Transformation of eutectic emulsion to nanosuspension fabricating with solvent evaporation and ultrasonication technique

Eutectic solvent can solubilize high amount of some therapeutic compounds. Volatile eutectic solvent is interesting to be used as solvent in the preparation of nanosuspension with emulsion solvent evaporation technique. The mechanism of transformation from the eutectic emulsion to nanosuspension was investigated in this study. The 30% w/w ibuprofen eutectic solution was used as the internal phase, and the external phase is composed of Tween 80 as emulsifier. Ibuprofen nanosuspension was prepared by eutectic emulsion solvent evaporating method followed with ultrasonication. During evaporation process, the ibuprofen concentration in emulsion droplets was increased leading to a drug supersaturation but did not immediately recrystallize because of low glass transition temperature (T_g) of ibuprofen. The contact angle of the internal phase on ibuprofen was apparently lower than that of the external phase at all times of evaporation, indicating that the ibuprofen crystals were preferentially wetted by the internal phase than the external phase. From calculated dewetting value ibuprofen crystallization occurred in the droplet. Crystallization of the drug was initiated with external mechanical force, and the particle size of the drug was larger due to Ostwald ripening. Cavitation force from ultrasonication minimized the ibuprofen crystals to the nanoscale. Particle size and zeta potential of formulated ibuprofen nanosuspension were 330.87±51.49 nm and −31.1±1.6 mV, respectively, and exhibited a fast dissolution. Therefore, the combination of eutectic emulsion solvent evaporation method with ultrasonication was favorable for fabricating an ibuprofen nanosuspension, and the transformation mechanism was attained successfully.