Reaction of Amino-Terminated PAMAM Dendrimers with Carbon Dioxide in Aqueous and Methanol Solutions.

Polyamines have been used as active materials to capture carbon dioxide gas based on its well-known reaction with amines to form carbamates. This work investigates the reactions between three amino-terminated poly(amidoamine) (PAMAM) dendrimers (G1, G3 and G5) and CO2(g) in aqueous (D2O) and methanolic (CD3OD) solutions. The reactions were monitored using 1H NMR spectroscopy, and yielded dendrimers with a combination of terminal carbamate and terminal ammonium groups. In aqueous media the reaction was complicated by the generation of soluble carbonate and bicarbonate ions. The reaction was cleaner in CD3OD, where the larger G5 dendrimer solution formed a gel upon exposure to CO2(g). All reactions were reversible, and the trapped CO2 could be released by treatment with N2(g) and mild heating. These results highlight the importance of the polyamine dendrimer size in terms of driving changes to the solution's physical properties (viscosity, gel formation) generated by exposure to CO2(g).

On the Differential Roles of Mg2+, Zn2+, and Cu2+ in the Equilibrium of ß-N-Methyl-Amino-L-Alanine (BMAA) and its Carbamates.

ß-N-methyl-amino-L-alanine (BMAA) in the presence of bicarbonate (HCO3-) undergoes structural modifications generating two carbamate species, α-carbamate and ß-carbamate forms of BMAA. The chemical structure of BMAA and BMAA-carbamate adducts strongly suggest they may interact with divalent metal ions. The ability of BMAA to cross the blood-brain barrier and possibly interact with divalent metal ions may augment the neurotoxicity of these molecules. To understand the effects of divalent metal ions (Mg2+, Zn2+, and Cu2+) on the overall dynamic equilibrium between BMAA and its carbamate adducts, a systematic study using nuclear magnetic resonance (NMR) is presented. The chemical equilibria between BMAA, its carbamate adducts, and each of the divalent ions were studied using two-dimensional chemical exchange spectroscopy (EXSY). The NMR results demonstrate that BMAA preferentially interacts with Zn2+ and Cu2+, causing an overall reduction in the production of carbamate species by altering the dynamic equilibria. The NMR-based spectral changes due to the BMAA interaction with Cu2+ is more drastic than with the Zn2+, under the same stoichiometric ratios of BMAA and the individual divalent ions. However, the presence of Mg2+ does not significantly alter the dynamic equilibria between BMAA and its carbamate adducts. The NMR-based results are further validated using circular dichroism (CD) spectroscopy, observing the n ➔ π interaction in the complex formation of BMAA and the divalent metal ions, with additional verification of the interaction with Cu2+ using UV-Vis spectroscopy. Our results demonstrate that BMAA differentially interacts with divalent metal ions (Mg2+ < Zn2+ < Cu2+), and thus alters the rate of formation of carbamate products. The equilibria between BMAA, the bicarbonate ions, and the divalent metal ions may alter the total population of a specific form of BMAA-ion complex at physiological conditions and, therefore, add a level of complexity of the mechanisms by which BMAA acts as a neurotoxin.

Assessing the Potential Content of Ethyl Carbamate in White, Red, and Rosé Wines as a Key Factor for Pursuing Urea Degradation by Purified Acid Urease.

The ethyl carbamate (EC) content of a wine after a given temperature-time storage was theoretically predicted from the potential concentration of ethyl carbamate (PEC), as determined via an accelerated EC formation test. Such information was used to decide whether an enzymatic treatment was needed to reduce the wine urea level before bottling/aging. To this end, 6 white, red, and rosé wines, manufactured in Italy as such or enriched with urea, were tested for their PEC content either before or after enzymatic treatment using a purified acid urease preparation derived from Lactobacillus fermentum. The treatment was severely affected by the total phenolic content (TP) of the wine, the estimated pseudo-first-order kinetic rate constant for NH3 formation reducing by a factor of approximately 2000 as the TP increased from 0 to 1.64 g L(-1) . Such a sensitivity to TP was by far greater than that pertaining to a killed cell-based enzyme preparation used previously. Urea hydrolysis was successful at reducing EC concentration in wines with low levels of TP and other EC precursors.