High-performance liquid chromatographic separation of ascorbic acid,erythorbic acid,dehydroascorbic acid,dehydroerythorbic acid,diketogulonic acid,and diketogluconic acid

High-performance liquid chromatography on a Zorbax NH₂ analytical column, with acetonitrile: 0.05 m KH₂PO₄ (75:25, $\text{w}\text{w}$) used as eluant, has allowed the separation, in less than 14 min, of ascorbic acid, erythorbic acid, dehydroascorbic acid, dehydroerythorbic acid, diketogulonic acid, and diketogluconic acid. Ultraviolet monitoring at 268 nm allows ascorbic acid and erythorbic acid to be detected at the 25-ng level, while refractive index detection monitors the elution of all six compounds. Tyrosine is a good internal standard, being well separated from the other compounds and having an adequate ultraviolet absorption at 268 nm. We have found dithiothreitol to be effective in rapidly reducing dehydroascorbic acid to ascorbic acid, providing the basis for indirectly determining dehydroascorbic acid after its reduction. The potential of this high-performance liquid chromatographic procedure for evaluating the levels of these compounds in orange juice and urine is demonstrated.     

Aluminium-organic acid interactions in acid soils

A study was undertaken to quantify the rates of aluminum release in an acid soil (pH 4.40) which was known to produce differential growth responses to Al in Al-resistant and sensitive wheat cultivars which are characterized by differences in root organic acid exudation. Soil columns were leached with artificial soil solutions containing no Al in the presence or absence of citrate for periods of up to 12 days. The Al release rates could be resolved into two dissolution phases: A fast release phase for Al was attributed to the cation exchangeable pool while a second slower phase was attributable to the dissolution of readily weatherable minerals. Citrate increased the dissolution rates two fold in comparison to experiments performed without citrate. It was concluded that for rhizosphere considerations, the total releasable Al pool was finite in size and constituted approximately 2% of the soil's total Al reserves. This pool was not increased markedly in the presence of citrate. It was concluded that citrate not only complexed Al in solution but also complexed Al directly from the mineral phase. From experimental Al release rates, it was deduced that only the soil solution and exchangeable Al pools were responsible for Al rhizotoxicity and that organic acids exuded from the root probably provide an efficient mechanism for excluding Al from the root. Empirical equations were also constructed to describe Al dissolution from the two release pools for use in soil Al flux models.     

Solid-liquid phase behavior of binary fatty acid mixtures. 1. Oleic acid/stearic acid and oleic acid/behenic acid mixtures

Solid-liquid phase behavior of binary fatty acid mixtures was investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR) for the mixture composed of oleic acid (OA) and stearic acid (SA) and that composed of OA and behenic acid (BA). The DSC results provided a monotectic type T-X phase diagram for these mixtures, from which it was suggested that the two fatty acid species are completely immiscible in a solid phase regardless of the two polymorphs of OA, i.e., alpha-form or gamma-form. The solid phase immiscibility was confirmed by the FT-IR observation that the spectra obtained for the mixtures correspond to the superposition of the two spectra for respective components. Thermodynamic analysis of liquidus line demonstrated that OA and SA form an ideal mixture in a liquid phase, whereas the mixing of OA and BA in a liquid phase is slightly non-ideal.     

Solid-liquid phase behavior of binary fatty acid mixtures 3. Mixtures of oleic acid with capric acid (decanoic acid) and caprylic acid (octanoic acid)

Solid-liquid phase behavior of binary mixtures of oleic acid (OA)/capric acid (C10A) and OA/caprylic acid (C8A) were investigated by means of differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction. The phase diagram of OA/C10A mixture constructed from the DSC results suggested that a molecular compound with the composition of OA:C10A = 3:2 is formed in a solid phase, and OA and the molecular compound are miscible, while C10A and the molecular compound are completely immiscible. The formation of the molecular compound was supported by the IR spectroscopic observation, and a possible model of the structure was proposed on the basis of X-ray diffraction spectrum in small angle region. This compound formation is characteristic of the OA/C10A mixture, and may be attributed to the similarity of the acyl chain length of C10A to the lengths of Delta- and omega-chains of OA (i.e., the chain segments divided by cis-double bond). The mixture of OA and C8A, whose chain length is close to but shorter than the two chain segments of OA, provided a eutectic-type phase diagram showing a partial mixing of the two components in OA-rich region. Thermodynamic analysis of the liquidus line in the phase diagram exhibits a systematic trend for the non-ideality parameter of mixing with the variation of the chain length difference between OA and saturated fatty acid species.     

Identity of daniellic acid with illurinic acid

African copaiba balsam is the product of Daniellia olliveri (Rolfe) Hutch. and Dalz. Daniellic acid is identical with illurinic acid.     

Interconversion between dehydro-L-ascorbic acid and L-ascorbic acid

L-Ascorbic acid (AA) plays an important role in biological systems as an electron donor. Erythorbic acid (EA) is the epimer of AA and has chemical characteristics very similar to those of AA. It is demonstrated in the present study by 1H-NMR that dehydro-L-ascorbic acid (DAA) was reduced by EA under neutral conditions but not acidic, and that dehydroerythorbic acid (DEA) was also reduced by AA under the same conditions. These reactions also occurred at a low concentration close to the concentration of AA in such biological tissue as the liver. Furthermore, the interconversion of DAA and AA at neutral pH and low concentration was also confirmed by radioluminography. These results suggest the interconversion between DAA and AA in vivo.