Biomolecular force fields optimized for globular proteins fail to properly reproduce properties of intrinsically disordered proteins. In particular, parameters of the water model need to be modified to improve applicability of the force fields to both ordered and disordered proteins. Here, we compared performance of force fields recommended for intrinsically disordered proteins in molecular dynamics simulations of three proteins differing in the content of ordered and disordered regions (two proteins consisting of a well-structured domain and of a disordered region with and without a transient helical motif and one disordered protein containing a region of increased helical propensity). The obtained molecular dynamics trajectories were used to predict measurable parameters, including radii of gyration of the proteins and chemical shifts, residual dipolar couplings, paramagnetic relaxation enhancement, and NMR relaxation data of their individual residues. The predicted quantities were compared with experimental data obtained within this study or published previously. The results showed that the NMR relaxation parameters, rarely used for benchmarking, are particularly sensitive to the choice of force-field parameters, especially those defining the water model. Interestingly, the TIP3P water model, leading to an artificial structural collapse, also resulted in unrealistic relaxation properties. The TIP4P-D water model, combined with three biomolecular force-field parameters for the protein part, significantly improved reliability of the simulations. Additional analysis revealed only one particular force field capable of retaining the transient helical motif observed in NMR experiments. The benchmarking protocol used in our study, being more sensitive to imperfections than the commonly used tests, is well suited to evaluate the performance of newly developed force fields.

Fluorination of diamonds modulates their optical and electromagnetic properties and creates surfaces with increased hydrophobicity. In addition, fl uorination of diamonds and nanodiamonds has been recently shown to stabilize fl uorescent nitrogen-vacancy centers, which can serve as extremely sensitive single atomic defects in a vast range of sensing applications from quantum physics to high-resolution biological imaging. Traditionally, fl uorination of carbon nanomaterials has been achieved using harsh and complex experimental conditions, creating hydrophobic interfaces with diffi cult dispersibility in aqueous environments. Here, a mild benchtop approach to nanodiamond fl uorination is described using selective Ag + -catalyzed radical substitution of surface carboxyls for fl uorine. In contrast to other approaches, this highyielding procedure does not etch diamond carbons and produces a highly hydrophilic interface with mixed C−F and C−OH termination. This dual functionalization of nanodiamonds suppresses detrimental hydrophobic interactions that would lead to colloidal destabilization of nanodiamonds. It is also demonstrated that even a relatively low surface density of fl uorine contributes to stabilization of negatively charged nitrogen-vacancy centers and boosts their fl uorescence. The simultaneous control of the surface hydrophilicity and the fl uorescence of nitrogen-vacancy centers is an important issue enabling direct application of fl uorescent nanodiamonds as nanosensors for quantum optical and magnetometry measurements operated in biological environment.

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