Maria Carla Aragoni

Marked Increase in PROP Taste Responsiveness Following Oral Supplementation with Selected Salivary Proteins or Their Related Free Amino Acids

The genetic predisposition to taste 6-n-propylthiouracil (PROP) varies among individuals and is associated with salivary levels of Ps-1 and II-2 peptides, belonging to the basic proline-rich protein family (bPRP). We evaluated the role of these proteins and free amino acids that selectively interact with the PROP molecule, in modulating bitter taste responsiveness. Subjects were classified by their PROP taster status based on ratings of perceived taste intensity for PROP and NaCl solutions. Quantitative and qualitative determinations of Ps-1 and II-2 proteins in unstimulated saliva were performed by HPLC-ESI-MS analysis. Subjects rated PROP bitterness after supplementation with Ps-1 and II-2, and two amino acids (L-Arg and L-Lys) whose interaction with PROP was demonstrated by 1H-NMR spectroscopy. ANOVA showed that salivary levels of II-2 and Ps-1 proteins were higher in unstimulated saliva of PROP super-tasters and medium tasters than in non-tasters. Supplementation of Ps-1 protein in individuals lacking it in saliva enhanced their PROP bitter taste responsiveness, and this effect was specific to the non-taster group.1H-NMR results showed that the interaction between PROP and L-Arg is stronger than that involving L-Lys, and taste experiments confirmed that oral supplementation with these two amino acids increased PROP bitterness intensity, more for L-Arg than for L-Lys. These data suggest that Ps-1 protein facilitates PROP bitter taste perception and identifies a role for free L-Arg and L-Lys in PROP tasting.

Simultaneous decomposition of several spectra into the constituent Gaussian peaks

A computer program is proposed for the decomposition of spectra into their constituent Gaussian peaks. A new feature of this program is the possibility of operating on different spectra from two or more components of variable concentration at the same time, by optimising the wavelengths of the maxima and the halfbandwidths of all the spectra while the height of each peak is optimized in each single spectrum. This distinct treatment is possible due to the fact that the Gaussian functions are linear with respect to the heights and non-linear with respect to the remaining parameters. A linear and non-linear least-squares analysis, respectively, is therefore possible. Besides its intrinsic utility in handling spectral data of different origin this procedure proves more useful than the single spectrum decomposition both in increasing the reliability of the parameters and in improving the convergence properties of the procedure.

Characterization of the ionization and spectral properties of mercapto-carboxylic acids Correlation with substituents and structural features.

The ionization constants in aqueous solutions of meso- and dl-dimercaptosuccinic acid and of monomethyl and dimethyl meso-succinates were carefully determined by potentiometric and spectrophotometric methods as a result of the increasing interest in these molecules as heavy metal chelators. In order to explain the influence of various substituents on ionization and (13)C NMR properties, the study was extended to the related oxygen derivatives of succinic acid and to simpler ethanoic derivatives. With the Swain-Lupton dual substituent treatment it was possible to clarify the influence of substituents on both spectral and equilibrium parameters. The differences in pK due to conformation are also discussed.

Dose-Dependent Effects of L-Arginine on PROP Bitterness Intensity and Latency and Characteristics of the Chemical Interaction between PROP and L-Arginine

Genetic variation in the ability to taste the bitterness of 6-n-propylthiouracil (PROP) is a complex trait that has been used to predict food preferences and eating habits. PROP tasting is primarily controlled by polymorphisms in the TAS2R38 gene. However, a variety of factors are known to modify the phenotype. Principle among them is the salivary protein Ps-1 belonging to the basic proline-rich protein family (bPRP). Recently, we showed that oral supplementation with Ps-1 as well as its related free amino acids (L-Arg and L-Lys) enhances PROP bitterness perception, especially for PROP non-tasters who have low salivary levels of Ps-1. Here, we show that salivary L-Arg levels are higher in PROP super-tasters compared to medium tasters and non-tasters, and that oral supplementation with free L-Arg enhances PROP bitterness intensity as well as reduces bitterness latency in a dose-dependent manner, particularly in individuals with low salivary levels of both free L-Arg and Ps-1 protein. Supplementation with L-Arg also enhanced the bitterness of caffeine. We also used 1H-NMR spectroscopy and quantum-mechanical calculations carried out by Density Functional Theory (DFT) to characterize the chemical interaction between free L-Arg and the PROP molecule. Results showed that the –NH2 terminal group of the L-ArgH+ side chain interacts with the carbonyl or thiocarbonyl groups of PROP by forming two hydrogen bonds with the resulting charged adduct. The formation of this PROP•ArgH+ hydrogen-bonded adduct could enhance bitterness intensity by increasing the solubility of PROP in saliva and its availability to receptor sites. Our data suggest that L-Arg could act as a ‘carrier’ of various bitter molecules in saliva.

Stereospecific generation of homochiral helices in coordination polymers built from enantiopure binaphthyl-based ligands

The novel enantiopure dipyridyl spacer 2,2′-dimethoxy-1,1′-binaphthyl-3,3′-bis(4-pyridyl-amido) (R)-L has been designed as a robust source of axial chirality to obtain helical coordination polymers. The reaction of (R)-L and the differently substituted dithiophosphato complexes [Ni((RO)2PS2)2] [R = Me (1), Et (2)] efficiently yielded coordination polymers (1·L)∞ and (2·L)∞, respectively, consisting of helical chains in which the nickel(II) ions of the [Ni((RO)2PS2)2] units are bridged by the enantiopure L ligands. The obtained polymers differ in terms of the configuration at the metal centres, which is trans and cis for (1·L)∞ and (2·L)∞, respectively. The cis configuration in (2·L)∞ generates a further element of chirality around the metal center, which occurs stereospecifically, as only one enantiomeric form is present, with homochiral helices packed with opposite screw sense in the crystal. The electronic and structural features of L, (1·L)∞, and (2·L)∞ have been investigated by means of DFT theoretical calculations, and the theoretical results have been compared with the experimental ones coming from single-crystal X-ray diffraction. The cis/trans isomerism displayed by the metal centers in (1·L)∞ and (2·L)∞ has been tentatively explained on the basis of the results of theoretical calculations performed on hypothetical pentacoordinated intermediates.

Polyiodides and Polytellurides: Analogies and Differences

Analogies and differences between polytellurides and polyiodides are discussed with the help of quantum chemical DFT calculations.

Gold and palladium oxidation/complexation in water by a thioamide–iodine leaching system

This paper concerns the oxidative dissolution ability of a thioamide/iodine leaching system in water towards gold, palladium and silver metals in powder in view of a potential application in the recovery process of these metals from electrical and electronic waste equipment (E-waste). The leaching mixture composed of equimolar amounts of thioamide 3-methyl-benzothiazole-2-thione and I2 in water can oxidize/complex gold and palladium metals in powder in order to form the complexes [AuI(mbtt)2]I3 and [PdII(mbtt)3I]I3. Considering the mild conditions under which the processes were performed ([I2] = 1.14 × 10−3 M, T = 20 °C, pH = 5.0, leaching time = 24 h), the obtained oxidation yield of Au0 and Pd0 are to be considered satisfactory with values of 65% and 69%, respectively. No oxidation was observed for the silver powder. The oxidising/complexing properties of the leaching mixture mbtt + I2 were interpreted considering the formation of the mbtt–I2 adduct that features, as a consequence of the S-donor to I2 interaction, a charge separation between the bridging and terminal iodine atoms in the fragment S–Ib–It. The feasibility of recovering gold from the complex [AuI(mbtt)2]I3 was verified by performing a cementation with magnesium powder.