DL-Menthol

Terpenes increase the partitioning and molecular dynamics of an amphipathic spin label in stratum corneum membranes.[Pubmed:17950546]

Int J Pharm. 2008 Feb 28;350(1-2):103-12.

In this work, the interaction of the skin penetration enhancers DL-Menthol, alpha-terpineol, 1,8-cineole and (+)-limonene with the uppermost skin layer, the stratum corneum and with multilamellar vesicles from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) is investigated by electron paramagnetic resonance (EPR) spectroscopy of the small spin label 2,2,6,6,-tetramethylpiperedine-1-oxyl (TEMPO), which partitions the aqueous and hydrocarbon phases. The EPR spectrum allows for the determination of the actual partition coefficient and the rotational diffusion rates of the spin probe in the two environments. The enthalpy changes, DeltaH degrees , to transfer the spin probe from the aqueous to the hydrocarbon phase, as well as the activation energies associated to its rotational motion, were considerably smaller for stratum corneum, indicating less pronounced thermal reorganization. For DPPC, the terpenes increased both the partition coefficient and the rotational diffusion rate of the spin label in the membrane, except in the liquid-crystalline phase, while these increases in stratum corneum were observed in the entire temperature range measured with the exception of the rotational motion parameter for DL-Menthol and alpha-terpineol at temperatures below their melting point (32-41 degrees C). It is suggested that the terpenes effectively acting as spacers in the membrane fluidize the lipids and cause ruptures in the hydrogen-bonded network of the polar interface.

Investigation of factors affecting the adsorption of functional molecules onto gel silicas. 1. Flow microcalorimetry and infrared spectroscopy.[Pubmed:15925601]

J Colloid Interface Sci. 2005 Jul 15;287(2):379-87.

Flow microcalorimetry and infrared spectroscopy were used to study the surface structure and adsorptive properties of a series of calcined and uncalcined porous silicas. The adsorbates DL-Menthol, (R)-(+)-limonene, (+/-)-citronellal and carvone were selected for their functionality, that included carbonyl, vinylic and hydroxyl groups. The amounts of probe retained by the silicas together with the energy exchange involved in the adsorption/desorption process were determined by flow microcalorimetry. The functional groups involved in these interactions were studied by means of infrared spectroscopy. It was observed that the strongest interactions with the silica surface took place through hydrogen bonding onto the surface silanol. The most retentive probes were found to be those with a carbonyl group in their structure. Adsorption onto calcined silicas was found to be less energetic than onto the equivalent calcined samples. The adsorption densities were compared with theoretical predictions based on molecular models. In all cases apart from citronellal monolayer coverage were not observed due to steric effects.

Comparison of acid anhydrides with carboxylic acids in enantioselective enzymatic esterification of racemic menthol.[Pubmed:9631262]

Chin J Biotechnol. 1997;13(4):263-9.

Optical resolution of racemic menthol has been efficiently achieved by lipase-catalyzed enantioselective esterification in an organic solvent. The performance of the reaction using an acid anhydride as an acyl donor was compared with that using its corresponding free acid. The reactivities of acid anhydrides were found to be higher than their corresponding free acids, but acid anhydrides were also found to be easily hydrolyzed into free acids under the catalysis of the same enzyme. The existence of a too-high concentration of an acid anhydride in a micro-aqueous reaction system will cause dehydration and thus deactivation of the enzyme, and will enhance non-selective esterification of a chiral alcohol, which will reduce the optical purity of the product. All these drawbacks, however, could be effectively overcome in a semi-batch reaction system into which propionic anhydride was continuously fed. This system showed some advantages over a batch reaction system using free propionic acid: the reaction time of DL-Menthol was shortened by half, the stability of the enzyme was much enhanced, and the optical purity of the product (l-menthyl ester) was kept at a similarly high level (> 98% ee).

A closer look into deep eutectic solvents: exploring intermolecular interactions using solvatochromic probes.[Pubmed:29199751]

Phys Chem Chem Phys. 2017 Dec 20;20(1):206-213.

Deep eutectic solvents (DESs) constitute a new class of ionic solvents that has been developing at a fast pace in recent years. Since these solvents are commonly suggested as green alternatives to organic solvents, it is important to understand their physical properties. In particular, polarity plays an important role in solvation phenomena. In this work, the polarity of different families of DESs was studied through solvatochromic responses of UV-vis absorption probes. Kamlet-Taft alpha, beta, pi* and ETN parameters were evaluated using different solvatochromic probes, as 2,6-dichloro-4-(2,4,6-triphenyl-N-pyridino)-phenolate (Reichardt's betaine dye 33), 4-nitroaniline, and N,N-diethyl-4-nitroaniline for several families of DESs based on cholinium chloride, DL-Menthol and a quaternary ammonium salt ([N4444]Cl). In addition, a study to understand the difference in polarity properties between DESs and the corresponding ILs, namely ILs based on cholinium cation and carboxylic acids as anions ([Ch][Lev], [Ch][Gly] and [Ch][Mal]), was carried out. The chemical structure of the hydrogen bond acceptor (HBA) in a DES clearly controls the dipolarity/polarizability afforded by the DES. Moreover, Kamlet-Taft parameters do not vary much within the family, but they differ among families based on different HBA, either for DESs containing salts ([Ch]Cl or [N4444]Cl) or neutral compounds (DL-Menthol). A substitution of the HBD was also found to play an important role in solvatochromic probe behaviour for all the studied systems.

Factors affecting the resolution of dl-menthol by immobilized lipase-catalyzed esterification in organic solvent.[Pubmed:11782192]

J Agric Food Chem. 2002 Jan 16;50(2):262-5.

Among 10 lipases tested, Candida rugosa lipase exhibited the best ability to catalyze the resolution of DL-Menthol in organic solvent. The lipase was immobilized on different carriers, and the experiment was carried out with different acyl donors. The high yield and optical purity of the product were achieved in cyclohexane with valeric acid as acyl donor using C. rugosa lipase immobilized on DEAE-Sephadex A-25. The conversion of DL-Menthol depended on the water content of immobilized lipase and on the pH of the aqueous solution from which lipase was immobilized. The operational stability of the DEAE-Sephadex A-25 immobilized lipase in catalysis of the esterification reaction showed that >85% activity remained after 34 days of repeated use. The resolution of racemic menthol in organic medium catalyzed by immobilized C. rugosa lipase-catalyzed esterification is very convenient, and it represents a significant improvement in the use of enzyme for the preparative production of optically active menthol. This process is readily applicable to large-scale preparation.

Air-assisted dispersive liquid-liquid microextraction based on a new hydrophobic deep eutectic solvent for the preconcentration of benzophenone-type UV filters from aqueous samples.[Pubmed:29282887]

J Sep Sci. 2018 Apr;41(7):1635-1643.

Deep eutectic solvents are considered as new and green solvents that can be widely used in analytical chemistry such as microextraction. In the present work, a new DL-Menthol-based hydrophobic deep eutectic solvent was synthesized and used as extraction solvents in an air-assisted dispersive liquid-liquid microextraction method for preconcentration and extraction of benzophenone-type UV filters from aqueous samples followed by high-performance liquid chromatography with diode array detection. In an experiment, the deep eutectic solvent formed by DL-Menthol and decanoic acid was added to an aqueous solution containing the UV filters, and then the mixture was sucked up and injected five times by using a glass syringe, and a cloudy state was achieved. After extraction, the solution was centrifuged and the upper phase was subjected to high-performance liquid chromatography for analysis. Various parameters such as the type and volume of the deep eutectic solvent, number of pulling, and pushing cycles, solution pH and salt concentration were investigated and optimized. Under the optimum conditions, the developed method exhibited low limits of detection and limits of quantitation, good linearity, and precision. Finally, the proposed method was successfully applied to determine the benzophenone-type filters in environmental water samples with relative recoveries of 88.8-105.9%.

Synergistic retention strategy of RGD active targeting and radiofrequency-enhanced permeability for intensified RF & chemotherapy synergistic tumor treatment.[Pubmed:27209261]

Biomaterials. 2016 Aug;99:34-46.

Despite gaining increasing attention, chelation of multiple active targeting ligands greatly increase the formation probability of protein corona, disabling active targeting. To overcome it, a synergistic retention strategy of RGD-mediated active targeting and radiofrequency (RF) electromagnetic field-enhanced permeability has been proposed here. It is validated that such a special synergistic retention strategy can promote more poly lactic-co-glycolic acid (PLGA)-based capsules encapsulating camptothecin (CPT) and solid DL-Menthol (DLM) to enter and retain in tumor in vitro and in vivo upon exposure to RF irradiation, receiving an above 8 fold enhancement in HeLa retention. Moreover, the PLGA-based capsules can respond RF field to trigger the entrapped DLM to generate solid-liquid-gas (SLG) tri-phase transformation for enhancing RF ablation and CPT release. Therefore, depending on the enhanced RF ablation and released CPT and the validated synergistic retention effect, the inhibitory outcome for tumor growth has gained an over 10-fold improvement, realizing RF ablation & chemotherapy synergistic treatment against HeLa solid tumor, which indicates a significant promise in clinical RF ablation.

Characterization of cytotoxic and genotoxic effects of different compounds in CHO K5 cells with the comet assay (single-cell gel electrophoresis assay).[Pubmed:12787820]

Mutat Res. 2003 Jun 6;537(2):151-68.

Different variants of the comet assay were used to study the genotoxic and cytotoxic properties of the following eight compounds: chloral hydrate, colchicine, hydroquinone, DL-Menthol, mitomycin C, sodium iodoacetate, thimerosal and valinomycin. Colchicine, mitomycin C, sodium iodoacetate and thimerosal induced genotoxic effects. The other compounds were found to be inactive. The compounds were tested in the standard comet assay as well as in the all cell comet assay (recovery of floating cells after treatment), designed in our laboratory for adherently-growing cells. This latter procedure proved to be more adequate for the assessment of the cytotoxicity for some of the compounds tested (hydroquinone, DL-Menthol, thimerosal, valinomycin). Colchicine was positive in the standard comet assay (3h treatment) and in the all cell comet assay (24h treatment). Sodium iodoacetate and thimerosal were positive in the standard and/or the all cell comet assay. Chloral hydrate, hydroquinone, sodium iodoacetate, mitomycin C and thimerosal were also tested in the modified comet assay using lysed cells. Mitomycin C and thimerosal showed effects in this assay, whereas sodium iodoacetate was inactive. This indicates that it does not induce direct DNA damage. Compounds that are known or suspected to form DNA-DNA cross-links or DNA-protein cross-links (chloral hydrate, hydroquinone, mitomycin C and thimerosal) were checked for their ability to reduce ethyl methanesulfonate (EMS)-induced DNA damage. This mode of action could be demonstrated for mitomycin C only.