Hydration modulates every aspect of protein structure and function. However, studying water structures in hydration shells remains challenging mostly due to overwhelming background from bulk water. We used vibrational sum frequency generation (SFG) spectroscopy to characterize hydrated films of an antiparallel β-sheet peptide (LK7β) adsorbed on glass slides. The hydrated films give chiral SFG response from water only when the peptide self-assembles into antiparallel β-sheets. Experiments of isotopic labeling, isotopic dilution of water, and H2O–D2O exchange kinetics corroborate the assignments of the chiral SFG response to water stretching modes. Because individual water molecules are achiral, the chiral SFG response indicates formation of chiral superstructures of water around the antiparallel β-sheet, implying that a protein secondary structure can imprint its chirality onto the surrounding water. This result demonstrates chiral SFG spectroscopy as a promising tool for probing water structures in protein hydration and addressing fundamental questions of protein structure–function.

Understanding the role of water in biological processes remains a central challenge in the life sciences. Water structures in hydration shells of biomolecules are difficult to study in situ due to overwhelming background from aqueous environments. Biological interfaces introduce additional complexity because biomolecular hydration differs at interfaces compared to bulk solution.Here, we perform experimental and computational studies of chiral sum frequency generation (chiral SFG) spectroscopy to probe chirality transfer from a protein to the surrounding water molecules. This work reveals that chiral SFG probes the first hydration shell around the protein almost exclusively. We explain the selectivity to the first hydration shell in terms of the asymmetry induced by the protein structure and specific protein−water hydrogen-bonding interactions. This work establishes chiral SFG as a powerful technique for studying hydration shell structures around biomolecules at interfaces, presenting new possibilities to address grand research challenges in biology, including the molecular origins of life.

In Spring 2020, we began a study focused on the development of inclusive teaching practices in an undergraduate chemistry lecture course for non-STEM students. In the wake of the COVID-19 pandemic and ensuing educational disruptions, we changed the design of our study to focus on the learning and teaching experiences of students and instructors. Here, we conducted student surveys before and after the emergency transition to remote teaching and analyzed data on student participation in the online setting. We observed that student engagement was likely negatively impacted by the emergency transition. We also found that lectures engaged students less after the transition. By contrast, course activities that did not heavily rely on a physical classroom, such as students blogging about their research of chemistry literature and crafting an independent research paper about a chemical question, were more effective in retaining student engagement after the transition. We also analyze student utilization of synchronous and asynchronous learning opportunities (for example, recorded lectures). We contextualize student engagement in the course relative to policies adopted by the educational institution, notably a mandatory universal pass/fail grading policy. Finally, we communicate thematic reflections from students, undergraduate peer tutors, graduate student teaching fellows, and the course instructor about learning chemistry and teaching non-STEM undergraduates in the time of COVID-19. On the basis of these studies, we recommend seven instructional strategies for teaching chemistry during sustained educational disruptions.

Biomolecular hydration is fundamental to biological functions. Using phase-resolved chiral sum-frequency generation spectroscopy (SFG), we probe molecular architectures and interactions of water molecules around a self-assembling antiparallel β-sheet protein. We find that the phase of the chiroptical response from the O-H stretching vibrational modes of water flips with the absolute chirality of the (l-) or (d-) antiparallel β-sheet. Therefore, we can conclude that the (d-) antiparallel β-sheet organizes water solvent into a chiral supermolecular structure with opposite handedness relative to that of the (l-) antiparallel β-sheet. We use molecular dynamics to characterize the chiral water superstructure at atomic resolution. The results show that the macroscopic chirality of antiparallel β-sheets breaks the symmetry of assemblies of surrounding water molecules. We also calculate the chiral SFG response of water surrounding (l-) and (d-) LK7β to confirm the presence of chiral water structures. Our results offer a different perspective as well as introduce experimental and computational methodologies for elucidating hydration of biomacromolecules. The findings imply potentially important but largely unexplored roles of water solvent in chiral selectivity of biomolecular interactions and the molecular origins of homochirality in the biological world.

A parallel study of protein variants with all (L-), all (D-), or mixed (L-)/(D-) amino acids can be used to assess how backbone architecture versus side chain identity determines protein structure. Here, we investigate the secondary structure and side chain orientation dynamics of the antiparallel β-sheet peptide LK 7 β (Ac-Leu-Lys-Leu-Lys-Leu-Lys-Leu-NH 2 ) composed of all (L-), all (D-), or alternating (L-Leu)/(D-Lys) amino acids. Using interface-selective vibrational sum frequency generation spectroscopy (VSFG), we observe that the alternating (L-)/(D-) peptide lacks a resonant C−H stretching mode compared to the (L-) and (D-) variants and does not form antiparallel β-sheets. We rationalize our observations on the basis of density functional theory calculations and molecular dynamics (MD) simulations of LK 7 β at the air−water interface. Irrespective of the handedness of the amino acids, leucine side chains prefer to orient toward the hydrophobic air phase while lysine side chains prefer the hydrophilic water phase. These preferences dictate the backbone configuration of LK 7 β and thereby the folding of the peptide. Our MD simulations show that the preferred side chain orientations can force the backbone of a single strand of (L-) LK 7 β at the air−water interface to adopt β-sheet Ramachandran angles. However, denaturation of the β-sheets at pH = 2 results in a negligible chiral VSFG amide I response. The combined computational and experimental results lend critical support to the theory that a chiral VSFG response requires macroscopic chirality, such as in β-sheets. Our results can guide expectations about the VSFG optical responses of proteins and should improve understanding of how amino acid chirality modulates the structure and function of natural and de novo proteins at biological interfaces.