Density functional theory investigation of mechanisms of degradation reactions of sulfonated PEEK membranes with OH radicals in fuel cells: addition-elimination reactions and acid catalyzed water elimination.

Sulfonated polyether (ether) ketone or sulfonated PEEK (sPEEK) membranes are one possible candidate for proton-transfer membranes in hydrogen fuel cells. Reaction with hydroxy radicals is expected to be a significant source of degradation of these membranes during fuel cell operation. In this work, the reactivity of the sPEEK polymer molecule with OH radicals is studied by M062X hybrid density functional calculations of the energetics of several reaction paths in a water environment as modeled by polarized continuum model calculations. Reactants, products, encounter minima and transition states are optimized for a reaction pathway in which OH addition is followed by acid-catalyzed water elimination which cationizes the polymer, degradation is expected to follow this reaction as the unstable cation then undergoes bond-breaking or other reactions. Two pathways for this acid-catalyzed cationization, one in which a water molecule plays the role of an additional co-catalyst, are reported. Further calculations explore reaction pathways in which addition of OH to the polymer is followed by bond breaking reactions which would break the polymer chain or the bond between the polymer and sulfonyl groups. Examination of the free energy barriers to all these reactions, relative to reactants, suggests that these direct bond-breaking reactions may compete somewhat with acid-catalyzed water elimination following OH addition. Supplementary Information: The online version contains supplementary material available at 10.1007/s00214-023-02981-2.

Perception and Knowledge of Oral and Facial Piercings among Dental Students: Web-based Survey.

AIM: The aim of this web-based questionnaire was to survey dental students to obtain their perception and knowledge of oral and facial piercings. MATERIALS AND METHODS: The participants comprised 240 students enrolled in the dental school who were asked to complete 20 close-ended, yes/no, yes/no/do not know, and multiple responses questions. The questionnaire covers general information concerning oral/facial piercing, triggers why youths and early adults get it, probable complications, their appreciation of the possibility of related health conditions, and their knowledge and perception. The survey was distributed to the students by email. The results were tabulated and statistically analyzed. RESULTS: Dental first year (D1) and dental second year (D2) were substantially more likely to indicate that orofacial piercings as unacceptable and are less expected to have an orofacial piercing compared to D3 and D4 (p < 0.01). About 16.8% of the students reported previous orofacial piercings. There was a definite correlation between previous orofacial piercings and thinking that is appropriate in society (p < 0.05). Males were significantly more likely to have an orofacial piercing (p < 0.01). The Internet was reported as the most common source of information. The most popular cause for piercings is to be unique and different. CONCLUSIONS: Orofacial piercings are relatively frequently used by students in dental school and few students intend on getting one in the future. Knowledge of the hazards of orofacial piercing correlated with the requirement for parental approval. The majority of students think piercings are appropriate in society and know their complications and risks. CLINICAL SIGNIFICANCE: Orofacial piercing has been gaining popularity but its risks/complications may not be known by practitioners. There is a need for research to assist dental/medical practitioners in advising, educating, and safeguarding patients by evaluating of the perception and knowledge of students about orofacial piercings.

Density functional theory investigation of mechanisms of degradation reactions of sulfonated PEEK membranes with OH radicals in fuel cells: Addition-elimination reactions and acid catalyzed water elimination.

Sulfonated polyether (ether) ketone, or sulfonated PEEK (sPEEK) membranes are one possible candidate for proton-transfer membranes in hydrogen fuel cells. Reaction with hydroxy radicals is expected to be a significant source of degradation of these membranes during fuel cell operation. In this work, the reactivity of the sPEEK polymer molecule with OH radicals is studied by M062X hybrid density functional calculations of the energetics of several reaction paths in a water environment as modeled by polarized continuum model (PCM) calculations. Reactants, products, encounter minima and transition states are optimized for a reaction pathway in which OH addition is followed by acid-catalyzed water elimination which cationizes the polymer, degradation is expected to follow this reaction as the unstable cation then undergoes bond-breaking or other reactions. Two pathways for this acid-catalyzed cationization, one in which a water molecule plays the role of an additional co-catalyst, are reported. Further calculations explore reaction pathways in which addition of OH to the polymer is followed by bond breaking reactions which would break the polymer chain or the bond between the polymer and sulfonyl groups. Examination of the free energy barriers to all these reactions, relative to reactants, suggest that these direct bond-breaking reactions may compete somewhat with acid-catalyzed water elimination following OH addition.