Crystal engineering of nutraceutical phytosterols: new cocrystal solid solutions

A cocrystal screening of solid solutions of three phytosterols (β-sitosterol, campesterol, stigmasterol) reveals that cocrystal solid solutions are enriched with β-sitosterol with respect to stigmasterol, a natural product with cytotoxicity concerns.

New look for an old molecule - Solid/solid phase transition in cholesterol monolayers

Surface pressure (π) - molecular area (A) isotherms of cholesterol were precisely measured to get insight into the orientation of molecules in Langmuir monolayers, which allowed to obtain detailed information on their phase behaviour. This was possible from the detailed analysis of the interfacial compressibility modulus versus surface pressure (C_s^-1- π) plots (obtained from the experimental surface pressure, π - area, A isotherms) and films thickness measurements (applying Brewster angle microscope, BAM) complemented with polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). At first glance, the isotherm for cholesterol is characterized by the major slope change of surface pressure versus area per molecule. However, a more detailed analysis showed the presence of a discontinuity and slope change both upon the compression and expansion of the monolayer. This discontinuity is more accurately reflected in the C_s^-1- π plot as a pseudo-plateau visible at π values between approximately 5 and 10 mN/m. This plateau was found to be temperature-dependent. Also, film thickness versus area plot (th-A) exhibits a pseudo-plateau in this region of surface pressures, in which the monolayer thickness increased gradually from 1.15 nm to 1.5 nm. Interestingly, although cholesterol has been intensively investigated in Langmuir monolayers, the existence of such a plateau have been overlooked previously. By linking experimental thickness values with theoretical molecular conformations, we have identified the presence of this plateau to the solid-solid (S-S') second-order transition. Using 2D analog of Clausius-Clapeyron equation, the thermodynamic functions (ΔH and ΔS) for this transition have been calculated. Based on monolayer experiments, the orientation of molecules in both solid phases was assumed to differ in the orientation of short alkyl chain attached to C17, which has additionally been confirmed with PM-IRRAS analysis.

Rapid purification of gram quantities of β-sitosterol from a commercial phytosterol mixture

Background

β-Sitosterol, a plant sterol or phytosterol, has commercial uses in the nutraceutical and pharmaceutical industries, but is also employed frequently in biological research. Phytosterols always accumulate as mixtures, and obtaining highly pure β-sitosterol in larger quantities for biological assays has been a challenge.

Findings

An improved method for the rapid purification of β-sitosterol from a commercial phytosterol extract is presented. Fractional crystallization of soybean oil yielded a soluble and an insoluble fraction. β-Sitosterol was purified by silica gel and Na-Y zeolite chromatography.

Conclusion

The rapid and cost effective three-step purification described here afforded β-sitosterol in gram quantities with high purity (>92%) and yield (>22%).

Cholesterol and phytosterols effect on sphingomyelin/phosphatidylcholine model membranes--thermodynamic analysis of the interactions in ternary monolayers

In this work thermodynamic analysis of the interactions between lipids in ternary sphingomyelin/DPPC/sterol Langmuir films were performed to compare the effect of cholesterol, beta-sitosterol and stigmasterol on a model membrane. The condensing effect of the respective sterols and the interactions between molecules in ternary mixtures were analyzed on the basis of the excess area per molecule and the excess free energy of mixing values. The stability of the mixed monolayers was verified with the free energy of mixing values. The conclusions on the ordering effect of sterols were drawn from the analysis of the compression modulus values. It was found that the stoichiometry of the mixed films of the highest thermodynamic stability and of the strongest interactions is the same for all the sterols investigated. The results obtained prove that the mammalian sterol induces the strongest contraction of the area and reveals the strongest stabilizing and ordering effect among the investigated sterol. Stigmasterol was found to condense a model membrane in a weaker extent as compared to beta-sitosterol, however, the differences in ordering properties of both phytosterols are less pronounced. The magnitude of the influence of the investigated sterols on a model membrane was thoroughly discussed from the point of view of the structure of their side chain, which determines the geometry of a sterol molecule.

K+ and Ca2+ modified Na-X zeolites as possible bile acids sequestrant

Modified zeolite X, previously exchanged with K+ and Ca2+ cations were characterized by XRD, FT-IR, chemical analysis and BET techniques. Different masses of these solids were mixed with an ox bile solution at different reaction times. The supernatants obtained by centrifugations were submitted to bile acid and phospholipids quantitative determinations. The amount of bile acids adsorbed was 65, 28 and 77% and for phospholipids was 45, 67 and 98% for KX, NaX and CaX respectively. As expected, as the amount of mass used increases more bile acids and phospholipids are adsorbed due to a larger surface of the solid being available for adsorption. On the other hand, 120 min of reaction time were sufficient for the adsorption of both components. The solids, after incubations with bile solutions were treated with abundant distilled water and dried at room temperature. The FT-IR analysis of these solids did not detect any bile and on the zeolite surface with suggested that the bile acid adsorption on the exchanged zeolites is moderated by weak and non covalent interactions.

Utility of 5Å molecular sieves to measure carbon isotope ratios in lipid biomarkers

A procedure using 5A zeolite sorption to separate cyclic/branched organic compounds from the linear ones was developed and carbon isotopic fractionation effects were investigated in different families of compounds, e.g. within the hydrocarbon and alcohol compounds. The 5A sieve has a pore size such that only linear components can be incorporated into the pores whereas the cyclic/branched compounds are remaining free in the organic solution. The sorbed compounds were released from the molecular sieve with HF and solvent extracted with hexane. The method enables the isolation of linear saturated classes, such as n-alkanes and n-fatty alcohols from branched/cyclic compounds without isotopic fractionation for compound-specific isotope analysis (CSIA) of delta(13)C. However, alkene hydrocarbons, sterols and some aromatics were completely or partly degraded with the molecular sieve.

Phytosterols: applications and recovery methods

Phytosterols, or plant sterols, are compounds that occur naturally and bear close structural resemblance to cholesterol, but have different side-chain configurations. Phytosterols are relevant in pharmaceuticals (production of therapeutic steroids), nutrition (anti-cholesterol additives in functional foods, anti-cancer properties), and cosmetics (creams, lipstick). Phytosterols can be obtained from vegetable oils or from industrial wastes, which gives an added value to the latter. Considerable efforts have been recently dedicated to the development of efficient processes for phytosterol isolation from natural sources. The present work aims to summarize information on the applications of phytosterols and to review recent approaches, mainly from the industry, for the large-scale recovery of phytosterols.

A sol-gel method using acetic anhydride in the presence of cholesterol in organic solution media: preparation of silicas that recognize steroid hormones

Silicas were prepared by a sol-gel method from tetraethoxysilane and acetic anhydride in the presence of cholesterol in organic solution media. Some silicas had higher pore volumes than silicas obtained in the absence of cholesterol. The adsorption abilities by these silicas were compared using various compounds in benzene solution. Although no clear difference among their adsorptions of cholesterol was observed, progesterone and other analogous steroid hormones were well adsorbed by silicas prepared in the presence of cholesterol, especially, prepared with n-heptane as an additional solvent. This silica adsorbed steroid hormones more selectively than other analogous compounds such as bisphenol A and hexestrol. On the other hand, a silica prepared by the usual aqueous sol-gel method with cholesterol had no clear adsorption selectivity to steroid hormones. Furthermore, no selective adsorption of steroid hormones was observed in the case of a common silica gel for column chromatography. This unique property of adsorption observed in silicas prepared using acetic anhydride in the presence of cholesterol is likely to be induced by the imprinting effect of the steroid skeleton part of cholesterol in silica matrix.

Photocontrolled reversible release of guest molecules from coumarin-modified mesoporous silica

Since the discovery of MCM-41 more than ten years ago, many investigations have explored the suitability of hexagonal mesoporous silicas for potential practical applications. These range from catalysis and optically active materials to polymerization science, separation technology and drug delivery, with recent successes in the fabrication of hybrid mesoporous organosilicas expected to open up further application possibilities. Because the pore voids of this class of materials exhibit relatively narrow pore size distributions in the range of 2-4 nm in diameter, mesoporous silicas can selectively include organic compounds and release them continuously at a later stage. The functionalization of MCM-41 pore voids with photoactive derivatives provides influence over the material's absorption behaviour, but full control over the release process remains difficult. Here we show that the uptake, storage and release of organic molecules in MCM-41 can be regulated through the photocontrolled and reversible intermolecular dimerization of coumarin derivatives attached to the pore outlets. Successful functionalization requires uncalcined MCM-41 still filled with the template molecules that directed the formation of its pores, to ensure that coumarin derivatives attach preferentially to the pore outlets, rather than their inside walls. We find that this feature and the one-dimensional, isolated nature of the individual pores allow for efficient and reversible photocontrol over guest access to the material's interior.