No abstract

Zwitterionic polymers exhibit excellent nonfouling performance due to their strong surface hydrations. However, salt molecules may severely reduce the surface hydrations of typical zwitterionic polymers, making the application of these polymers in real biological and marine environments challenging. Recently, a new zwitterionic polymer brush based on the protein stabilizer trimethylamine N-oxide (TMAO) was developed as an outstanding nonfouling material. Using surface-sensitive sum frequency generation (SFG) vibrational spectroscopy, we investigated the surface hydration of TMAO polymer brushes (pTMAO) and the effects of salts and proteins on such surface hydration. It was discovered that exposure to highly concentrated salt solutions such as seawater only moderately reduced surface hydration. This superior resistance to salt effects compared to other zwitterionic polymers is due to the shorter distance between the positively and negatively charged groups, thus a smaller dipole in pTMAO and strong hydration around TMAO zwitterion. This results in strong bonding interactions between the O– in pTMAO and water, and weaker interaction between O– and metal cations due to the strong repulsion from the N+ and hydration water. Computer simulations at quantum and atomistic scales were performed to support SFG analyses. In addition to the salt effect, it was discovered that exposure to proteins in seawater exerted minimal influence on the pTMAO surface hydration, indicating complete exclusion of protein attachment. The excellent nonfouling performance of pTMAO originates from its extremely strong surface hydration that exhibits effective resistance to disruptions induced by salts and proteins.

Saturation transfer difference (STD) methods recently have been proposed to be a promising tool for self-recognition mapping at residue and atomic resolution in amyloidogenic peptides. Despite the significant potential of the STD approach for systems undergoing oligomer/monomer (O/M) equilibria, a systematic analysis of the possible artifacts arising in this novel application of STD experiments is still lacking. Here, we have analyzed the STD method as applied to O/M peptides, and we have identified three major sources of possible biases: offset effects, intramonomer cross-relaxation, and partial spin-diffusion within the oligomers. For the purpose of quantitatively assessing these artifacts, we employed a comparative approach that relies on 1-D and 2-D STD data acquired at different saturation frequencies on samples with different peptide concentrations and filtration states. This artifact evaluation protocol was applied to the Abeta(12-28) model system, and all three types of artifacts appear to affect the measured STD spectra. In addition, we propose a method to minimize the biases introduced by these artifacts in the Halpha STD distributions used to obtain peptide self-recognition maps at residue resolution. This method relies on the averaging of STD data sets acquired at different saturation frequencies and provides results comparable to those independently obtained through other NMR pulse sequences that probe oligomerization, such as nonselective off-resonance relaxation experiments. The artifact evaluation protocol and the multiple frequencies averaging strategy proposed here are of general utility for the growing family of amyloidogenic peptides, as they provide a reliable analysis of STD spectra in terms of polypeptide self-recognition epitopes.

Interfacial water structure on a polymer surface in water (or surface hydration) is related to the antifouling activity of the polymer. Zwitterionic polymer materials exhibit excellent antifouling activity due to their strong surface hydration. It was proposed to replace zwitterionic polymers using mixed charged polymers because it is much easier to prepare mixed charged polymer samples with much lower costs. In this study, using sum frequency generation (SFG) vibrational spectroscopy, we investigated interfacial water structures on mixed charged polymer surfaces in water and how such structures change while being exposed to salt solutions and protein solutions. The 1:1 mixed charged polymer exhibits excellent antifouling property whereas other mixed charged polymers with different ratios of the positive/negative charges do not. It was found that on the 1:1 mixed charged polymer surface, SFG water signal is dominated by the contribution of the strongly hydrogen bonded water molecules, indicating strong hydration of the polymer surface. The responses of the 1:1 mixed charged polymer surface to salt solutions are similar to those of zwitterionic polymers. Interestingly, exposure to high concentrations of salt solutions leads to stronger hydration of the 1:1 mixed charged polymer surface after replacing the salt solution with water. Protein molecules do not substantially perturb the interfacial water structure on the 1:1 mixed charged polymer surface and do not adsorb to the surface, showing that this mixed charged polymer is an excellent antifouling material.

Many studies have demonstrated that vocabulary size plays a key role in learning English as a foreign language (EFL). In recent years, mobile game-based learning (MGBL) has been considered a promising scheme for successful acquisition and retention of knowledge. Thus, this study applies a mixed methodology that combines quantitative and qualitative approaches to assess the effects of PHONE Words, a novel mobile English vocabulary learning app (application) designed with game-related functions (MEVLA-GF) and without game-related functions (MEVLA-NGF), on learners’ perceptions and learning performance. During a four-week experiment, 20 sophomore students were randomly assigned to the experimental group with MEVLA-GF support or the control group with MEVLA-NGF support for English vocabulary learning. Analytical results show that performance in vocabulary acquisition and retention by the experimental group was significantly higher than that of the control group. Moreover, questionnaire results confirm that MEVLA-GF is more effective and satisfying for English vocabulary learning than MEVLA-NGF. Spearman rank correlation results show that involvement and dependence on gamified functions were positively correlated with vocabulary learning performance.