Density functional theory (DFT) periodic ab initio molecular dynamics calculations are used to study the adsorption of gaseous and microsolvated glycine on a hydroxylated, hydrophilic silica surface. The silica model is presented and the interaction of water with surface silanols is studied. The heat of interaction of water is higher with the associated silanols (be they terminal or geminal ones) studied here than with isolated silanols presented in past works. Glycine is stabilized in a parallel mode on the hydroxylated surface. Terminal silanols do not allow the stabilization of the zwitterionic form, whereas geminal silanols do. Molecular dynamics (MD) first-principle calculations show that microsolvated zwitterion glycine directly binds through the carboxylate function to a surface silanol rather than through water molecules. The adsorption mode, whether with or without additional water molecules, is parallel to the surface. The ammonium function does not interact directly with the silanol groups but rather through water molecules. Thus, the carboxylate and ammonium functions exhibit two different reactivities towards silanols. The calculated free energies, taking into account the chemical potentials of water and glycine in the gas phase, suggest the existence of a thermodynamic domain in which the glycine is present in the gas phase as well as strongly adsorbed on specific sites of the surface.

The adsorption of neutral glycine onto amorphous silica was investigated both theoretically and experimentally. DFT calculations were performed at the BLYP-631++G** level using a cluster approach. Several possible configurations involving the formation of H-bonds between glycine and one, two or three silanols, (SiOH) were considered. The most favorable bonding of glycine with one silanol (45 kJ/mol) occurs through the COOH moiety, forming a cycle in which the CO group is H-bond acceptor whereas the acidic OH group is H-bond donor. With two or three silanols, additional H-bonds are formed between the amine moiety and the silanols, leading to an increased adsorption energy (70 and 80 kJ/mol for two and three silanols respectively). Calculated ν CO , δ HNH and δ ΗCH are sensitive to the adsorption mode. A bathochromic shift of νCO as compared to νCO of free glycine (calculated in the 1755-1790 cm -1 range) is found for glycine in interaction with silanol(s). The more H-bonds of COOH with silanol groups, the higher the bathochromic shift. For δHNH, no shift is found for glycine adsorbed on one and two silanols (where the amine is either not bound or H bond donor), whereas a bathochromic shift is calculated with three silanols when the amine moiety is H-bond acceptor.Experimental FTIR spectra performed at RT for glycine adsorbed at 160°C on Aerosil amorphous silica exhibit bands at 1371, 1423, 1630 and 1699 cm -1 . The experimental/calculated frequencies have their best correspondance for glycine adsorbed on two silanols. It is important to note that the forms giving the best correspondence to experimental frequencies are the most stable ones. TITLE RUNNING HEAD : Adsorption of Glycine on Silica

The geometry, energetic, and spectroscopic properties of molecular structures of silica-supported vanadium oxide catalysts are studied using periodic density functional calculations. Isolated vanadia units deposed on amorphous silica are modeled at low coverage, 0.44 atoms nm -2 . The models are built following the grafting process through the reaction of a vanadium precursor with surface silanols: OV(OHThe most stable grafted structures involve one vanadyl group together with n(V-O-Si) bonds. The predominance of the vanadate groups is analyzed as a function of hydration by means of atomistic thermodynamics. At dehydrated conditions, the trigrafted pyramidal OV(O-Si) 3 species are predominant, whereas partial hydration stabilizes digrafted OV(OH)(O-Si) 2 and monografted OV(OH) 2 (O-Si) species. The harmonic vibrational spectra for selected models are compared to recent experimental infrared and Raman data, for representative bands, and vibrational modes. Hydration effects are discussed in terms of thermodynamic stability and vibrational spectra. The results obtained in this study show that the pyramidal OV(O-Si) 3 , digrafted OV(OH)(O-Si) 2 , and monografted OV(OH) 2 (O-Si) models can exist at a support surface, a trend in agreement with recent experimental findings.

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The demand for natural antioxidant active packaging is increasing due to its unquestionable advantages compared with the addition of antioxidants directly to the food. Therefore, the search for antioxidants perceived as natural, namely those that naturally occur in herbs and spices, is a field attracting great interest. In line with this, in the last few years, natural antioxidants such as α-tocopherol, caffeic acid, catechin, quercetin, carvacrol and plant extracts (e.g. rosemary extract) have been incorporated into food packaging. On the other hand, consumers and the food industry are also interested in active biodegradable/compostable packaging and edible films to reduce environmental impact, minimise food loss and minimise contaminants from industrial production and reutilisation by-products. The present review focuses on the natural antioxidants already applied in active food packaging, and it reviews the methods used to determine the oxidation protection effect of antioxidant active films and the methods used to quantify natural antioxidants in food matrices or food simulants. Lastly consumers' demands and industry trends are also addressed.

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The adsorption behavior of the amino acid glycine in mesoporous silica has been investigated using a combination of quantum chemical calculations and NMR spectroscopy experiments. Glycine adsorption on two representative sites of an amorphous silica surface, vicinal silanols and a silanol nest, was investigated by DFT-D. The effect of water coadsorption on the energetics of adsorption and NMR shifts was characterized. It was found that the silanol nest is a more favorable site for glycine adsorption due to a local increased H-bond density. Co-adsorption with water is also favored, especially a water molecule between a SiOH and the ammonium moiety. NMR chemical shifts computed on these models fall into the observed 13 C and 15 N experimental range, suggesting that the presence of different energetically comparable adsorption configurations cannot be excluded.