The mechanism of ice nucleation at the molecular level remains largely unknown. Nature endows antifreeze proteins (AFPs) with the unique capability of controlling ice formation. However, the effect of AFPs on ice nucleation has been under debate. Here we report the observation of both depression and promotion effects of AFPs on ice nucleation via selectively binding the ice-binding face (IBF) and the non-ice-binding face (NIBF) of AFPs to solid substrates. Freezing temperature and delay time assays show that ice nucleation is depressed with the NIBF exposed to liquid water, whereas ice nucleation is facilitated with the IBF exposed to liquid water. The generality of this Janus effect is verified by investigating three representative AFPs. Molecular dynamics simulation analysis shows that the Janus effect can be established by the distinct structures of the hydration layer around IBF and NIBF. Our work greatly enhances the understanding of the mechanism of AFPs at the molecular level and brings insights to the fundamentals of heterogeneous ice nucleation.antifreeze proteins | ice nucleation | Janus effect | interfacial water | selective tethering A ntifreeze proteins (AFPs) protect a broad range of organisms inhabiting subzero environments. The function of AFPs lies in lowering the freezing point in a noncolligative manner (1, 2). It has been shown that AFPs can adsorb on the ice crystal surface with the ice-binding face (IBF, also termed ice-binding site or icebinding surface) (3, 4). The adsorbed AFPs lead to curvatures on the ice surface between adjacent AFPs, and ice growth is retarded due to the Kelvin effect, which is known as the adsorptioninhibition mechanism (5). However, whether the non-ice-binding face (NIBF) is involved in the function of AFPs and what effect the NIBF exerts are rarely studied (4, 6, 7). On the other hand, the effect of AFPs on ice nucleation (8) is still under intense debate (9-13), although ice nucleation, the formation of a stable nucleus with a critical size, is the control step for ice formation (8). Liu et al. (9) suggested that AFPs could inhibit heterogeneous ice nucleation of water, whereas research on ice nucleation of microdroplets of AFP solutions exhibited no obvious effect of AFPs in inhibiting ice nucleation (10). It was also reported that an AFP solution with high concentration facilitated ice nucleation (11). The contradiction also exists for the research of ice nucleation on solid surfaces immobilized with AFPs (12, 13). Therefore, it is highly desirable to elucidate the exact role of AFPs on ice nucleation and to correlate AFP structures at the molecular level with their function in tuning ice nucleation, which is essential for practical applications in food, pharmaceutical, and chemical industries (14,15).Herein, we investigate the effect of IBF and NIBF of AFPs on ice nucleation via binding AFPs to solid substrates in a way that either IBF or NIBF is exposed to liquid water. This binding method is readily extendable to other AFPs because of the clear distinction...

Scanning tunneling microscopy (STM) has been used to study the chiral molecules (R)/(S)-2-bromohexadecanoic acid at the liquid/solid interface. When adsorbed onto the basal plane of graphite, these molecules segregate on the surface into domains of pure R or S enantiomers. The atomic resolution obtained in the STM images of these species allows a direct assignment of the chirality of individual molecules.

devices, [26,27] to small-scale nano- [28][29][30] and DNA origamis. [31] A common theme in these studies is to exploit the sophisticated shape transformations from folding. For example, an origami robot is typically fabricated in a 2D flat configuration and then folded into the prescribed 3D shape to perform its tasks. The origamis have been treated essentially as linkage mechanisms in which rigid facets rotate around hingelike creases (aka "rigid-folding origami"). Elastic deformation of the constituent sheet materials or the dynamics of folding are often neglected. Such a limitation in scope indeed resonates the origin of this field, that is, folding was initially considered as a topic in geometry and kinematics.However, the increasingly diverse applications of origami require us to understand the force-deformation relationship and other mechanical properties of folded structures. Over the last decade, studies in this field started to expand beyond design and kinematics and into the domain of mechanics and dynamics. Catalyzed by this development, a family of architected origami materials quickly emerged (Figure 1). These materials are essentially assemblies of origami sheets or modules with carefully designed crease patterns. The kinematics of folding still plays an important role in creating certain properties of these origami materials. For example, rigid folding of the classical Miura-ori sheet induces an in-plane deformation pattern with auxetic properties (aka negative Poisson's ratios). [32,33] However, elastic energy in the deformed facets and creases, combined with their intricate spatial distributions, impart the origami materials with a rich list of desirable and even unorthodox properties that were never examined in origami before. For example, the Ron-Resch fold creates a unique tri-fold structure where pairs of triangular facets are oriented vertically to the overall origami sheet and pressed against each other. Such an arrangement can effectively resist buckling and create very high compressive load bearing capacity. [34] Other achieved properties include shape-reconfiguration, tunable nonlinear stiffness and dynamic characteristics, multistability, and impact absorption.Since the architected origami materials obtain their unique properties from the 3D geometries of the constituent sheets or modules, they can be considered a subset of architected cellular solids or mechanical metamaterials. [35][36][37][38][39] However, the origami materials have many unique characteristics. The rich geometries of origami offer us great freedom to tailor targeted Origami, the ancient Japanese art of paper folding, is not only an inspiring technique to create sophisticated shapes, but also a surprisingly powerful method to induce nonlinear mechanical properties. Over the last decade, advances in crease design, mechanics modeling, and scalable fabrication have fostered the rapid emergence of architected origami materials. These materials typically consist of folded origami sheets or modules with intricate 3D geomet...