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Antimicrobial peptides (AMPs) are widely studied as therapeutic agents due to their broad-spectrum efficacy against infections. However, their clinical use is hampered by the low in vivo bioavailability and systemic toxicity. Such limitations might be overcome by using appropriate drug delivery systems. Here, the preparation of a drug delivery system (DDS) by physical conjugation of an arginine-rich peptide and hydrothermal carbon nanoparticles (CNPs) has been explored, and its antimicrobial efficacy against Eschericia coli ( E. coli ) and Staphylococcus aureus investigated in comparison with the unloaded carrier and the free peptide. The mechanism of interaction between CNPs and the bacteria was investigated by scanning electron microscopy and a combined dielectrophoresis-Raman spectroscopy method for real-time analysis. In view of a possible systemic administration, the effect of proteins on the stability of the DDS was investigated by using albumin as a model protein. The peptide was bounded electrostatically to the CNPs surface, establishing an equilibrium modulated by pH and albumin. The DDS exhibited antimicrobial activity toward the two bacterial strains, albeit lower as compared to the free peptide. The decrease in effectiveness toward E. coli was likely due to the rapid formation of a particle-induced extracellular matrix. The present results are relevant for the future development of hydrothermal CNPs as drug delivery agents of AMPs., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Two epimeric series of foldamers characterized by the presence of a repeating α,ε-dipeptide unit have been prepared and characterized by (1)H NMR and ECD spectroscopies together with X-ray diffraction. The first series contains L-Ala and D-4-carboxy-5-methyl-oxazolidin-2-one (D-Oxd). The other series contains L-Ala and L-Oxd. The L,D series of oligomers forms ordered β-turn foldamers, characterized by a 311 pattern. The L,L series is not ordered. Simulations show that an ordered L,L trimer lies more than 2 kcal/mol higher than the more stable nonfolded extended conformations. Cu(2+) forms complexes with both series but is not able to order the L,L series. Analysis of the EPR spectra shows that the L,D foldamers bear two types of complexation sites that are assigned as a nitrogen donor of the triazole ring and a carboxylate ligand. The L-Ala-D-Oxd-Tri-CO motif may be introduced in any peptide sequence requiring the presence of a stable β-turn conformations, like in the study of protein-protein interactions.

The rapid development of nanotechnology has raised some concerns about the effects of engineered nanoparticles (NPs) on human health and the environment. At the same time, NPs have attracted intense interest because of their potential applications in biomedicine. Hence, the requirement of detailed knowledge of what takes place at the molecular level when NPs get inside living organisms is a necessary step in assessing and likely predicting the behavior of an NP. The elicited effects strongly depend on the early events occurring when NPs reach biological fluids, where the interaction with proteins is the primary process. Whereas the adsorption of proteins on biomaterials has been thoroughly investigated, the mechanisms underlying the interaction of proteins with NPs are still largely unexplored. Here we report a study of the behavior of four model proteins differing in their resistance to conformational changes, net charge, and surface charge distributions, adsorbed on two nanometric silica powders with distinct hydrophilicity. An integrated picture of the adsorption process has been obtained by applying a whole set of techniques: the extent of coverage of the silica surface and the reversibility of the process were evaluated by combining the adsorption isotherms with the changes in the zeta potential and the point of zero charge for NPs at different protein coverages; the occurrence of protein deformation was evaluated by Raman spectroscopy, and EPR spectroscopy of spin-labeled proteins provided insight into their orientation on the silica surface. We have found that the extent of coverage of the nanoparticle surface is strongly influenced by the protein structural stability as well as by the distribution of charges at the protein surface.

The Mn(4)-cluster of photosystem II (PSII) from Synechococcus elongatus was studied by electron paramagnetic resonance (EPR) spectroscopy after a series of saturating laser flashes given in the presence of either methanol or ethanol. Results were compared to those obtained in similar experiments done on PSII isolated from plants. The flash-dependent changes in amplitude of the EPR multiline signals were virtually identical in all samples. In agreement with earlier work [Messinger, J., Nugent, J. H. A., and Evans, M. C. W. (1997) Biochemistry 36, 11055-11060; Ahrling, K. A., Peterson, S., and Styring, S. (1997) Biochemistry 36, 13148-13152], detection of an EPR multiline signal from the S(0) state in PSII from plants was only possible with methanol present. In PSII from S. elongatus, it is shown that the S(0) state exhibits an EPR multiline signal in the absence of methanol (however, ethanol was present as a solvent for the artificial electron acceptor). The hyperfine lines are better resolved when methanol is present. The S(0) multiline signals detected in plant PSII and in S. elongatus were similar but not identical. Unlike the situation seen in plant PSII, the S(2) state in S. elongatus is not affected by the addition of methanol in that (i) the S(2) multiline EPR signal is not modified by methanol and (ii) the spin state of the S(2) state is affected by infrared light when methanol is present. It is also shown that the magnetic relaxation properties of an oxidized low-spin heme, attributed to cytochrome c(550), vary with the S states. This heme then is in the magnetic environment of the Mn(4) cluster.