Abstract
From the early precipitation-based techniques, introduced more than a century ago, to the latest development of enzymatic bio- and nano-sensor applications, the analysis of phytic acid and/or other inositol phosphates has never been a straightforward analytical task. Due to the biomedical importance, such as antinutritional, antioxidant and anticancer effects, several types of methodologies were investigated over the years to develop a reliable determination of these intriguing analytes in many types of biological samples; from various foodstuffs to living cell organisms. The main aim of the present work was to critically overview the development of the most relevant analytical principles, separation and detection methods that have been applied in order to overcome the difficulties with specific chemical properties of inositol phosphates, their interferences, absence of characteristic signal (e.g., absorbance), and strong binding interactions with (multivalent) metals and other biological molecules present in the sample matrix. A systematical and chronological review of the applied methodology and the detection system is given, ranging from the very beginnings of the classical gravimetric and titrimetric analysis, through the potentiometric titrations, chromatographic and electrophoretic separation techniques, to the use of spectroscopic methods and of the recently reported fluorescence and voltammetric bio- and nano-sensors.
Highlights
Myo-orientation is found in the case of phytic acid, which is due to the fact that the maximal number of phosphate groups are present in thermodynamically stabilized equatorial position [1]
In the presence of phytic acid, iron(III) is converted to the more stable phytate complex, resulting in a decreased absorbance of initial sulfosalicylic acid complex, which gave the linear response of the spectrophotometer in the concentration range of 5–50 μg/mL and limit of detection around 0.02% of phytate
From the first simple gravimetric methods, developed more than a century ago, to the novel bio- and nano-sensor application, the determination of phytic acid was never an easy analytical task. This is mostly due to (i) intriguing chemical properties of phytates and interferences of accompanying lower inositol phosphates and other hydrolyzation products, such as inorganic phosphate, (ii) absence of characteristic signals, as well as (iii) strong interactions with most of metal cations and biomolecules that are generally present in the sample matrix
Summary
Phytate (InsP6) represents a deprotonated (salt) form of dodecaprotic phytic acid (Figure 1) which can be found in the literature by other names, including the commonly used inositol hexakisphosphate (generally abbreviated as InsP6, IP6), 1,2,3,4,5,6hexakis(dihydrogenphosphate) myo-inositol, or by the following IUPAC name; (1s,2R,3R,4r, 5S,6S)-cyclohexane-1,2,3,4,5,6-hexayl hexakis(dihydrogen (phosphate)). It is a six-fold dihydrogenphosphate ester of myo-inositol or cis-1,2,3,5-trans-4,6-cyclohexanehexol which is the most abundant of nine possible isomers of inositol (Ins). The molecule can be inverted from equatorial (1a5e) to the axial (5a1e) orientation between pH 9.0 and pH 9.5 [2,3]
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