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Zwitterioniccarboxybetaine and sulfobetaine materials have shownan excellent ability to resist nonspecific protein adsorption. Itis desirable to obtain a better understanding of zwitterionicmaterials based on their molecular structures. This work aims to understandthe roles of charged groups in zwitterionic moieties and todesign new protein-resistant zwitterionic moieties beyond carboxybetaineand sulfobetaine. We conducted molecular simulations to studythe hydration, self-association, and protein interactions of 12 zwitterionicmoieties derived from three anionic groups (carboxylic, sulfonate,and sulfate) and four cationic groups (quaternary ammonium, tertiaryammonium, secondary ammonium, and primary ammonium). The partial chargesof atoms in these moieties were obtained from quantum chemical calculations.Hydration was studied by evaluating the hydration free energy of moietiesand the hydration structure and dynamics of the charged groups. Allzwitterionic moieties have strong hydration, but their structuraland dynamic properties depend on the types of cationic and anionicgroups involved. The self-association and protein interactions ofzwitterionic moieties also show relationships with the chargedgroups. Our simulation results indicate good protein-resistant abilityof several zwitterionic moieties, one of which has also beenshown by recent experiments. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulations, we investigated the associations between two zwitterions (carboxybetaine and sulfobetaine) and four types of cations (Li, Na, K, and Cs) in aqueous solutions. We studied the number and lifetime of various zwitterion–cation associations and observed that both carboxybetaine and sulfobetaine have the same order of association number and lifetime: Li> Na> K> Cs. Simulation results showed that the association variation as a function of cation types for these two zwitterions is significantly different. The effect of anion type on the order was also investigated by varying the type of anions from Cl–to Br–and F–. In order to further investigate zwitterion–cation association, we simulated the systems either with one type of zwitterion and two types of cations or with one type of cation and both carboxybetaine and sulfobetaine presented. This allowed direct competition between the solutes, and the observed association number and lifetime validated the order. Simulation results further demonstrated that, although CB associates stronger with Li橷 Na똖 SB, the latter is associated preferentially by K橷 Cs. [ABSTRACT FROM AUTHOR]

Chargedamino acids are the most common on surfaces of proteinsand understanding the interactions between these charged amino acids,salt bridging, is crucial for understanding protein–proteininteractions. Previous simulations have been limited to implicit solventor fixed binding geometry due to the sampling required for convergedfree energies. Using well-tempered metadynamics, we have calculatedsalt bridge free energy surfaces in water and confirmed the resultswith NMR experiments. The simulations give binding free energies,quantitative ranking of salt bridging strength, and insights intothe hydration of the salt bridges. The arginine–aspartate saltbridge was found to be the weakest and arginine-glutamate the strongest,showing that arginine can discriminate between aspartate and glutamate,whereas the salt bridges with lysine are indistinguishable in theirfree energy. The salt bridging hydration is found to be complementaryto salt bridge orientation with arginine having specific orientations. [ABSTRACT FROM AUTHOR]