Absolute configuration of an axially chiral sulfonate determined from its optical rotatory dispersion, electronic circular dichroism, and vibrational circular dichroism spectra.

The absolute configuration (AC) of an axially chiral sulfonate (aCSO), 3,5-dimethyl-2-(naphthalen-1-yl)-6-(naphthalen-1-yl)benzenesulfonate (labeled as aCSO5), was investigated using optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectroscopies. All three methods led to the same conclusion and the AC of aCSO5 is reliably determined to be (-)-(aR, aR), or conversely (+)-(aS, aS).

Analysis of Long-Chain Unsaturated Fatty Acids by Ionic Liquid Gas Chromatography.

Four ionic liquid (IL) columns, SLB-IL59, SLB-IL60, SLB-IL65, and SLB-IL111, were evaluated for more rapid analysis or improved resolution of long-chain methyl and ethyl esters of omega-3, omega-6, and additional positional isomeric and stereoisomeric blends of fatty acids found in fish oil, flaxseed oil, and potentially more complicated compositions. The three structurally distinct IL columns provided shorter retention times and more symmetric peak shapes for the fatty acid methyl or ethyl esters than a conventional polyethylene glycol column (PEG), resolving cis- and trans-fatty acid isomers that coeluted on the PEG column. The potential for improved resolution of fatty acid esters is important for complex food and supplement applications, where different forms of fatty acid can be incorporated. Vacuum ultraviolet detection contributed to further resolution for intricate mixtures containing cis- and trans-isomers, as exemplified in a fatty acid blend of shorter chain C18:1 esters with longer chain polyunsaturated fatty acid (PUFA) esters.

Separation of therapeutic peptides with cyclofructan and glycopeptide based columns in hydrophilic interaction liquid chromatography.

Three cyclofructan-based, two glycopeptide-based, and one zwitterionic column used in the HILIC mode were assessed within a graphical framework based on different functional characteristics contributing to selectivity. The characteristics of these six HILIC columns are put in the perspective of 33 columns evaluated previously. The isopropyl carbamate modified cyclofructan 6 (CF6) stationary phase, Larihc P, showed reduced component contributions for hydrophilicity and hydrogen bonding relative to the native cyclofructan 6 column (Frulic N). Both Frulic N and Larihc P exhibited cation exchange attributed primarily to deprotonation of residual unsubstituted silica with the greater exchange ascribed to the reduced loading of CF6 observed for Larihc P. The cyclofructan 6 column with a polymeric styrene divinylbenzene support (MCI GEL™ CRS100) showed distinct selectivities consistent with its decreased cation exchange attributable to its nonionic core. The Chirobiotic T, Chirobiotic V, and ZI-DPPS columns displayed hydrophilicity and ion exchange selectivities similar to other zwitterionic stationary phases. All of the more hydrophilic columns showed excellent separation for the four classes of therapeutic peptides investigated: microbial secondary metabolites used as immune suppressants, synthetic gonadotropin hormones, synthetic cyclic disulfide-linked hormone-regulating hormones, and non-ribosomally derived polycyclic antibiotics. Resolution provided by these columns and ZIC-HILIC is compared for each class of peptide. Frulic N is primarily suitable for use in the HILIC mode whereas Chirobiotic T, because of its increased efficiency and selectivity, can be useful in both HILIC and reverse phase modes. In some Chirobiotic T applications, addition of low levels of a strong additive (trifluoroacetic acid, formic acid, etc.) to the mobile phase can be beneficial. In these peptide analyses, a relative weakening of the often-dominant ionic interaction between analyte and residual charge on the stationary phase improved resolution and selectivity.

PREPARATION AND EVALUATION OF HPLC CHIRAL STATIONARY PHASES BASED ON CATIONIC/BASIC DERIVATIVES OF CYCLOFRUCTAN 6.

The cyclofructan 6 (CF6) macrocyclic-oligosaccharide was derivatized with five different substituents able to bear positive charges: propyl imidazole (IM) methyl benzimidazole (BIM), dimethyl aminopropyl (AP), pyridine (PY) and dimethyl aminophenyl (DMAP). The derivatized cyclofructans were reacted with triethoxysilyl-propylisocyanate as a linker to bond them to 5 µm spherical silica gel particles and then used to prepare HPLC columns. The bonded silica particles were analyzed to establish the bonding densities. A set of 34 chiral compounds including acids, neutral compounds and bases was tested with nine different mobile phase compositions including two reverse phase (RP) acetonitrile/pH 4 buffer, three polar organic (PO) acetonitrile/methanol and four normal phase (NP) heptane/ethanol mobile phases. No compounds could be separated in the RP mode. Eight compounds only could be enantioseparated in the PO mode and 21 compounds in the NP mode. The most effective chiral stationary phase was the propyl imidazole derivatized CF6 phase, provided that no more than six imidazole substituents and two linkers are attached per CF6 unit.

Enantiomeric separations of chiral sulfonic and phosphoric acids with barium-doped cyclofructan selectors via an ion interaction mechanism.

New cyclofructan-6 (CF6)-based chiral stationary phases (CSPs) bind barium cations. As a result, the barium-complexed CSPs exhibit enantioselectivity toward 16 chiral phosphoric and sulfonic acids in the polar organic mode (e.g., methanol or ethanol mobile phase containing a barium salt additive). Retention is predominantly governed by a strong ionic interaction between the analyte and the complexed barium cation as well as hydrogen bonding with the cyclofructan macrocycle. The log k versus log [X], where [X] = the concentration of the barium counteranion, plots for LARIHC-CF6-P were linear with negative slopes demonstrating typical anion exchange behavior. The nature of the barium counteranion also was investigated (acetate, methanesulfonate, trifluoroacetate, and perchlorate), and the apparent elution strength was found to be acetate > methanesulfonate > trifluoroacetate > perchlorate. A theory based upon a double layer model was proposed wherein kosmotropic anions are selectively adsorbed to the cyclofructan macrocycle and attenuate the effect of the barium cation. van't Hoff studies for two analytes were conducted on the LARIHC-CF6-P for three of the barium salts (acetate, trifluoroacetate, and perchlorate), and the thermodynamic parameters governing retention and enantioselectivity are discussed. Interestingly, for the entropically driven separations, enantiomeric selectivity can increase at higher temperatures, even with decreasing retention.

Enantioseparation of flinderoles and borreverines by HPLC on Chirobiotic V and V2 stationary phases and by CE using cyclodextrin selectors.

Racemic mixtures of the promising anti-malarial bisindole alkoids, flinderole A-C, desmethyl flinderole C, borreverine and isoborreverine, are baseline-separated for the first time by HPLC using vancomycin-based stationary phases and partially separated by capillary electrophoresis (CE) using cyclodextrin selectors. The HPLC results compare the performance of Chirobiotic V and V2 in the polar organic and reversed phase modes and their complementary selectivity is discussed. The performance of the cyclodextrin selectors in CE, while less effective, are discussed in terms of their selectivity in normal and reversed polarity modes.

Degradation study of carnosic acid, carnosol, rosmarinic acid, and rosemary extract (Rosmarinus officinalis L.) assessed using HPLC.

Rosemary, whose major caffeoyl-derived and diterpenoid ingredients are rosmarinic acid, carnosol, and carnosic acid, is an important source of natural antioxidants and is being recognized increasingly as a useful preservative, protectant, and even as a potential medicinal agent. Understanding the stability of these components and their mode of interaction in mixtures is important if they are to be utilized to greatest effect. A study of the degradation of rosmarinic acid, carnosol, carnosic acid, and a mixture of the three was conducted in ethanolic solutions at different temperatures and light exposure. As expected, degradation increased with temperature. Some unique degradation products were formed with exposure to light. Several degradation products were reported for the first time. The degradation products were identified by HPLC/MS/MS, UV, and NMR. The degradation of rosemary extract in fish oil also was investigated, and much slower rates of degradation were observed for carnosic acid. In the mixture of the three antioxidants, carnosic acid serves to maintain levels of carnosol, though it does so at least in part at the cost of its own degradation.