Photochemical and antioxidant properties of gamma-oryzanol in beta-cyclodextrin-based nanosponges

Gamma-oryzanol (GO), a mixture of ferulic acid esters, has recently attracted a great interest as natural antioxidant extracted from rice-bran oil, usually employed to stabilize food and pharmaceutical raw materials, moreover as sunscreen in cosmetic formulations. Its usefulness, however, is limited by its fast degradation. A recently proposed approach to increase the stability and effectiveness of antioxidants is based on the inclusion in supramolecular structures (nanoparticles, cyclodextrins, liposomes, etc.). In this work we studied the inclusion of GO in β-cyclodextrin-based nanosponges which in the last few years have been chosen for their ability to encapsulate a great variety of substances to decrease their side-effects and to protect them from degradation. The inclusion complex was prepared in 1:1 w/w ratio and characterized by DSC, XRPD and membrane diffusion runs. The photodegradation of GO upon either UVA or UVB irradiation was found to be slowed down by inclusion in nanosponges. The antioxidant effectiveness of the inclusion complex was also assessed and in vitro experiments on porcine ear skin revealed a certain accumulation of GO also when entrapped in the host structure.     

Binding of monovalent metal cations by the p-sulfonatocalix[4]arene: experimental evidence for cation-pi interactions in water

Gibbs free energies, enthalpies and entropies for the binding of Na+, K+, Rb+, Cs+, Ag+, Tl+ and NH4+ by the p-sulfonatocalix[4]arene in water are determined by microcalorimetry. Whereas no significant heat effect is detected with Na+ or Ag+, suggesting that these cations are not complexed, weak but selective binding is observed with the other cations. The whole set of thermodynamic parameters, which demonstrate that the cations bind inside the cavity of the calixarene, evidence the importance of the cation-pi interactions for these complexes in water.     

Anion exchange liquid chromatography--inductively coupled plasma-mass spectrometry detection of the Co2+, Cu2+, Fe3+ and Ni2+ complexes of mugineic and deoxymugineic acid

Phytosiderophores, such as mugineic and deoxymugineic acid, are produced by graminaceous plant species in response to Fe deficiency conditions normally experienced in calcareous and alkaline non-calcareous soils. As these phytosiderophores have the ability to form thermodynamically stable complexes with other metal cations present in the growing medium, they have also been implicated in the transport and bioavailability of these metals in the environment. However, routine analytical methodology to detect the various metal complexes formed by these phytosiderophores is lacking. Therefore, as these complexes are negatively charged over a wide range of pH values, anion exchange liquid chromatography (AE LC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) was investigated as a means to separate and quantify these complexes. The metal-phytosiderophore complexes were prepared at pH 7 and separated by NaOH or NH4NO3 gradient elution on a Dionex AS11 anion exchange column. Of the metals tested only the Co2+ and Ni2+ complexes of mugineic and deoxymugineic acid were detected when using a 0-20mM NaOH gradient elution profile. However, the phytosiderophore complexes of Cu2+ and Fe3+ were also detected when using NH4NO3 as the mobile phase at pH 7. Base-assisted hydrolysis of the latter two complexes is proposed to explain their apparent 'instability' in the high pH NaOH mobile phase. The absolute detection limits of the developed methodologies for these metal complexes ranged from 0.1 to 2.8pmol. As phytosiderophore complexes with Cd2+ and Zn2+ were not detected, it was concluded that the dissociation kinetics of these metal-phytosiderophore complexes were too rapid for these complexes to be observed in the present chromatographic conditions.     

5‐aminothiazolium salts as potential cyclic azomethine ylides: Base‐induced cycloaddition reactions with aryl,alkyl, and benzoyl isothiocyanates

Reactions of the in situ generated thiazoles 2 with aryl and alkyl isothiocyanates appear to be totally regioselective and give the unexpected 5‐(phenylthio)imidazolium‐4‐thiolates 3 . Such rapid interconversion of mesoionic compounds is explained by a 1,3‐dipolar addition to the C=N bond of the heterocumulene followed by tBuNCS elimination. Similar interactions with benzoyl isothiocyanate exclusively proceed on the C=S unsaturation of the heteroallene moiety and produce the 4‐(phenylthio)thiazolium‐5‐amidines 12 . Structural assignment of isolated imidazoles and thiazoles is based on ¹³C NMR data and chemically confirmed by the NaBH₄ reduction of the alkylated derivatives 5 and 13 . Efforts to isomerize the starting mesoionic thiazole 2a without the use of tBuNCS are unsuccessful. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 10:16–26, 2000     

Thermoplastic processing of protein-based bioplastics: chemical engineering aspects of mixing,extrusion and hot molding

Proteins, as heteropolymers, offer a large range of possible interactions and chemical reactions. The thermoplastic behavior of proteins has been studied in order to produce bioplastics by thermal or thermomechanical processes such as mixing, extrusion or hot molding. The extrusion trials were performed by using a co-rotating twin-screw extruder, recording torque, temperature and die pressure. Batch mixing was done in a two blade counter-rotating mixer, with continuous recording of torque and product temperature. Proteins were alternatively extruded, mixed or hot molded under a large range of processing conditions. Protein aggregation during each process was estimated from the accumulation of SDS-insoluble protein fraction. Protein aggregation evidences a cross-linking reaction the activation energy of which was dependent on the thermoplastic process used. The increase in network density appears to be induced by the severity of the treatment: temperature and shear strongly affect the structural characteristics of the protein-based bioplastics.