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Chitosan/silica hybrid powders, obtained by the sol-gel method (pH 6, 7, 8) are studied for proposing surface chemical models and rationalizing their behaviour as adsorbents. The chitosan and silica exposed groups in dried powders and their protonation state are inferred. Solid-state 29Si-NMR, XPS, zeta potential experiments and DFT computational calculations reveal the synthesis pH history of each sample. These details, summarized in surface models, are validated by copper adsorption: The pH 8 sample exhibits the highest hydrophilic and negative character, due to the deprotonated free silanol and neutral amine groups. These favor higher copper adsorption efficiency (30.4%) and loading capacity (0.077 mg Cu(II)/m2), through SiO−-Cu(II) electrostatic interactions and [Cu-(NH2)x]2+ complexation. For lower synthesis-pH samples, the neutral silanol and protonated amine populations increase, and the net surface charge becomes positive. This reduces the copper adsorption through electrostatic repulsions. The protonated amine and deprotonated silanol groups are the main responsible of electrokinetic surface response of materials prepared at lower and higher pH, respectively. The complexation is also involved in copper interactions, especially in surfaces populated by neutral amines. In conclusion, this work helps to understand the pH-dependent surface activity of chitosan/hybrid materials, being helpful for their further functionalization and applications.

Chitosan-silica materials offer a specific environment for the adsorption of biofunctional molecules, such as the antimicrobial peptide KR-12. The objective here is to rationalize the changes in the physicochemical properties of these chitosan-silica materials in function of the synthesis pH, using 0.02 w/v % chitosan as catalyst and aggregation agent and, to correlate these characteristics with the loading/delivery and activity/stability of KR-12 antimicrobial peptide. The CS-6 material, prepared at pH 6, exhibits higher surface area (745 m2/g) and total pore volume (0.58 cm3/g) due to the lower incorporation of chitosan swollen chains (9.36 wt %). Higher pHs produced denser materials (CS-7 and CS-8) with higher entangled chitosan incorporated (> 17 wt%). Adsorption of KR-12 peptide was found to take two different mechanisms depending on the chitosan-silica support, Langmuir-type for CS-6 material and Freundlich-type for CS-7 and CS-8 materials. According to the KR-12 release profiles, more hydrophobic interactions were observed in the CS-6 material exposing Lys and Arg residues from the peptide towards the material surface. This was correlated with the higher antimicrobial activity of this material against S. aureus strain (MIC = 128 μg/mL). Additionally, the KR-12 peptide adsorbed in the CS-6 hybrid support is 34 % more protected from the proteolytic action of α-chymotrypsin than the free one. In conclusion, the proposed models of different porous environments in the studied chitosan-silica materials supports the KR-12 peptide loading/delivery mechanisms, leading to biofunctionalized solid antimicrobial materials exhibiting proteolytic stability. This knowledge is useful for designing new antibacterial materials for biomedical applications. Keywords: Chitosan-silica particle mechanism formation, KR-12 peptide adsorption/delivery mechanisms, KR-12 controlled release, KR-12/chitosan-silica antimicrobial solid materials, Proteolysis stability