We present a computer simulation picture of the dynamical behavior, at room temperature, of water in the region close to a protein surface. We analyzed the probability distribution of water molecules diffusing near the surface, and we found that it deviates from a Gaussian, which is predicted for Brownian particles. Consistently, the mean square displacements of water oxygens show a sublinear trend with time. Moreover, the relaxation of hydration layers around the whole protein is found to follow a stretched exponential decay, typical of complex systems, which could as well be ascribed to the non-Gaussian shape of the propagator. In agreement with such findings, the analysis of water translational and reorientational diffusion showed that not only are the solvent molecule motions hindered in the region close to the protein surface, but also the very nature of the particle diffusive processes, both translational and rotational, is affected. The deviations from the bulk water properties, which put into evidence a deep influence exerted by the protein on the solvent molecule motion, are discussed in connection with the presence of spatial (protein surface roughness) and temporal (distribution of water residence times) disorder inherent in the system.

Atomic force spectroscopy (AFS) is one of the most promising and powerful tools to get information on biorecognition processes at single molecule resolution. AFS allows to measure forces acting between biomolecules undergoing biorecognition process with a picoNewton sensitivity in near-physiological conditions and without any labelling. The capability of AFS to provide detailed information about the kinetics and thermodynamics of a single pair of interacting biomolecules, besides complementing traditional biochemical approaches, offers the possibility to elucidate non-conventional aspects of biorecognition processes, such as rare events, transient phenomena, conformational changes and molecular heterogeneity. Despite its enormous capabilities and potentialities, AFS as applied to biomolecular interactions, has provided some ambiguous and controversial results in different experimental contexts. The present critical review describes, after an in-depth introduction to AFS and to the most used experimental and data analysis procedures, the more recent and rewarding ideas and advancements to overcome the main critical aspects faced in the investigation of biorecognition processes. Possible developments of AFS in applicative fields are briefly addressed (150 references).