Angelo Panzanelli

RP-HPLC determination of water-soluble vitamins in honey

The assessment and validation of reliable analytical methods for the determination of vitamins in sugar-based matrices (e.g. honey) are still scarcely explored fields of research. This study proposes and fully validates a simple and fast RP-HPLC method for the simultaneous determination of five water-soluble vitamins (vitamin B(2), riboflavin; vitamin B(3), nicotinic acid; vitamin B(5), pantothenic acid; vitamin B(9), folic acid; and vitamin C, ascorbic acid) in honey. The method provides low detection and quantification limits, very good linearity in a large concentration interval, very good precision, and the absence of any bias. It has been successfully applied to 28 honey samples (mainly from Sardinia, Italy) of 12 different botanical origins. While the overall amount of the analytes in the samples is quite low (always below 40 mg kg(-1)), we have observed a marked dependence of some of their concentrations (i.e. vitamin B(3) and vitamin B(5)) and the botanical origin of the honey. This insight might lead to important characterization features for this food item.

An RP-HPLC determination of 5-hydroxymethylfurfural in honey The case of strawberry tree honey.

The use of the RP-HPLC official method of the International Honey Commission (IHC) for the determination of 5-hydroxymethylfurfural (HMF) in strawberry tree honey (Arbutus unedo, a typical Sardinian honey) has brought to light a specific and heavy chromatographic interference that prevents accurate quantification. The interference has been identified as homogentisic acid (HA), i.e. the marker of the botanical origin of the honey. For this reason, an alternative RP-HPLC method is proposed. The bias-free method allows a complete separation of HMF from HA to the baseline level and is faster and more precise than the RP-HPLC official method: the detection and quantification limits are 1.9 and 4.0mgkg(-1), respectively, whereas the repeatability is ca. 2% in the HMF concentration range of 5-140mgkg(-1).

Interaction of metal ions with humic-like models. Part. I. Synthesis, spectroscopic and structural properties of diaquabis(2,6-dihydroxybenzoato) copper(II) and hexaaquaM(II) bis(2,6-dihydroxybenzoate) dihydrate (M = Mn, Fe, Co, Ni, Cu and Zn)

Abstract Compounds of the type M(2,6-DHB) 2 ·8H 2 O (M = Mn, Fe, Co, Ni, and Zn; 2,6-DHB = 2,6-dihydroxybenzoate ion) and Cu(2,6-DHB) 2 (H 2 O) 2 were prepared and characterized by means of infrared and electronic spectroscopy, electron spin resonance and thermal analysis. For Cu(2,6-DHB) 2 (H 2 O) 2 ( 1 ) and Zn(2,6-DHB) 2 ·8H 2 O ( 2 ) the crystal structure was also determined by single-crystal X-ray diffraction methods. The compound ( 1 ) has a polymeric nature, the coordination around each copper atom being tetragonally-distorted octahedral, with two water oxygens [CuO, 1.966(3) A] and two carboxyl oxygens [CuO, 1.935(2) A] from 2,6-DHB molecules about the square plane and two phenolic groups from adjacent units in the axial positions. The structure of ( 2 ) consists of almost regular octahedral [Zn(H 2 O) 6 ] 2+ cations surrounded by 2,6-DHB anions. The remaining two water molecules are involved in hydrogen bonding with the coordinated water molecules. X-ray data show that all the M(2,6-DHB) 2 ·8H 2 O are isomorphous with ( 2 ). The thermal, spectroscopic and magnetic properties are interpreted on the basis of the crystal structures. In particular, the ESR and absorption data of the copper(II) compounds are compared with those of the salicylate complexes.

A direct RP-HPLC method for the determination of furanic aldehydes and acids in honey.

In this study 5-hydroxymethyl-2-furaldehyde (HMF), 2-furaldehyde, 3-furaldehyde, 2-furoic acid and 3-furoic acid are contemporarily determined in honey using a swift and direct RP-HPLC approach. The validation protocol was performed in terms of detection and quantification limits, precision (by repeatability and reproducibility), linearity and accuracy (by recovery tests); the acceptability of the precision and accuracy results was positively verified using Horwitzs model and AOAC guidelines, respectively. The method was tested on 18 honey samples of different ages, and botanical and geographical origin. HMF and 2-furaldehyde correlated highly with the age of the samples, whereas no correlation was observed with regards to 2-furaldehyde and 2-furoic acid. Hypotheses relating to the formation of minority furanic compounds are also proposed.

Molecular structure, characterization and reactivity of dioxo complexes formed by vanadium(V) with α-hydroxycarboxylate ligands

Abstract The structure of the dioxovanadium(V) complexes of glycolic, lactic and malic acids Rb2[{VO2(glyc)}2] [glyc=glycolato(2−)] (1), Cs2[{VO2(mal)}2] [mal=malato(2−)] (2), and Cs2[{VO2(lact)}2]·2H2O [lact=lactato(2−)] (3) has been studied by single-crystal X-ray diffraction. In order to assign the features of the peculiar arrangement adopted by these kinds of complexes, the metrical details of these compounds have been examined and compared to the data available in literature for analogous complexes. The reactivity of the compounds has also been studied. In particular, the reduction of the metal ion by a biological reductant like cysteine, relevant to the role of these complexes in the constitution of the cofactor of the active site of vanadium nitrogenase, has been followed by EPR spectroscopy in an aqueous solution. In addition, the effect of peroxo complex formation on the structure of the dinuclear V2O2 cage has been analyzed by comparison with previously published results.

Bis(triphenylphosphine)pyridine- and pyrazine-carboxylatecopper(I) complexes

Abstract Several complexes obtained by the reactions of tetrahydroboratebis(triphenylphosphine)copper(I) with pyridine(py)- and pyrazine(pyz)-carboxylic acids have been obtained and characterized by infrared spectra. Crystal structures of the L 2 Cu(3-py(CO 2 )) and the L 2 Cu(2,3-py(CO 2 )(COOH)) (L = triphenylphosphine) complexes have been determined. The L 2 CU(3-py(CO 2 )) complex has a polymeric structure in which each copper(I) atom is tetrahedrally coordinated to two molecules of triphenylphosphine and two nicotinate anions, one of which is bonded through the nitrogen atom and the other through the carboxylate group. The L 2 Cu(2,3-py(CO 2 )(COOH)) complex consists of tetrahedral monomeric units, in which the anion is coordinated through the nitrogen atom and unidentate ortho carboxylate group. The structures of the other complexes are proposed on the basis of their analytical and infrared data.

Molecular structure of a mono-peroxo vanadium(V) complex formed by d,l-lactic acid

Abstract The peroxo complex formed by vanadium(V) in the presence of d , l -lactic acid (H2lact) as heteroligand, K2[{VO(O2)(lact)}2] (1), is described. A single-crystal X-ray diffraction study indicates that the ligand behaves as a bidentate chelator adopting the (O−, COO−) donor set. The complex has a dinuclear core based on the V2O2 cyclic arrangement arising from two vanadium(V) atoms sharing the hydroxyl oxygens of two ligands. The coordination sphere of each vanadium includes two hydroxyl oxygens, an oxygen atom from a carboxylate group, an oxo ligand and two peroxo oxygens. The geometry at the metal ion is severely distorted and, in the ideal limit, it could be described as a trigonal bipyramid, in which one of the equatorial bonds corresponds to the axis joining the vanadium atom and the centre of the peroxo group. A strikingly short interatomic OO distance, 1.35 A, is measured for the peroxo group, suggesting both σ- and π-donor ability in the bonding to the metal ion.

A POTENTIOMETRIC, SPECTROPHOTOMETRIC AND 1H NMR STUDY ON THE INTERACTION OF CIMETIDINE, FAMOTIDINE AND RANITIDINE WITH PLATINUM(II) AND PALLADIUM(II) METAL IONS

Abstract Spectrophotometric, potentiometric and 1H NMR results on the M-L systems [M = PdII or PtII and L = cimetidine, famotidine or ranitidine] are clearly indicative of the strong chelating ability of these antiulcerative drugs towares metal ions. In view of the great biological interest in these two metals, their coordination to such drugs should have significant implications.

L-mimosine: an amino acid with maltol-type binding properties toward copper(II), oxovanadium(IV) and other metal ions

Abstract The complex formation between L -mimosine, α-amino-β-(3-hydroxy-4-oxo-1,4-dihydropyridin-1-yl)-propanoic acid, a rare α-amino acid provided with a 3-hydroxypyridin-4(1H)one moiety, and some metal ions — Cu(II), VO(IV), Ni(II) and Zn(II) — was studied by spectroscopic (EPR and electron absorption) and potentiometric techniques in aqueous solution. It was found that L -mimosine prefers the maltol-like donor set of the 3-hydroxypyridin-4(1H)one fragment for binding copper(II) and oxovanadium(IV). However, the presence of two alternative donor centres in the ligand, (COO−, NH2) and (CO, O−), both suitable for chelating behaviour, makes possible the formation of very stable polynuclear species in which the L -mimosine ligand coordinates at both the (CO, O−) maltol-like and the (COO−, NH2) α-aminocarboxylate sites. Nickel(II) interacts with the ligand, but prefers a mixed bonding mode in the bis chelated species. Zn(II) only forms complexes with the 3-hydroxypyridin-4(1H)one fragment.

COORDINATION OF METAL IONS BY INDOLIC ACIDS. COMPLEXES OF INDOLE-2-CARBOXYLIC, -3-ACETIC, -3-PROPANOIC AND -3-BUTANOIC ACIDS WITH SOME DIVALENT METAL IONS

Abstract Metal complexes of indole-2-carboxylic (ICH), -3-acetic (IAH), -3-propanoic (IPH) and -3-butanoic (IBH) acids, were prepared and characterized by means of thermal analysis, magnetic measurements. ESR. IR and electronic spectroscopy. While Cu(IA)2 · H2O, Cu(IP)2 · H2O, Cu(IP)2 and Cu(IB)2 are tetracarboxylatebridged dimers of the copper(II) acetate monohydrate-type, Cu(IC)2 · 2H2O appears to be monomeric with the copper atom in square planar coordination involving two carboxylate groups and two water molecules. Six-coordination at the metal ions, most likely involving bjdentate carboxylate groups and water molecules, is suggested for the complexes M(IC)2 · 2 H2O (M=Co, Ni, Mn and Zn). All the ligands appear to behave as simple carboxylic acids, being able to coordinate metal ions through the carboxylic groups alone.