The knowledge of the phonon coherence length is of great importance for two-dimensional-based materials since phonons can limit the lifetime of charge carriers and heat dissipation. Here we use tip-enhanced Raman spectroscopy (TERS) to measure the spatial correlation length L c of the A1g 1 and A1g 2 phonons of monolayer and few-layer gallium sulfide (GaS). The differences in L c values are responsible for different enhancements of the A1g modes, with A1g 1 always enhancing more than the A1g 2, independently of the number of GaS layers. For five layers, the results show an L c of 64 and 47 nm for A1g 1 and A1g 2, respectively, and the coherence lengths decrease when decreasing the number of layers, indicating that scattering with the surface roughness plays an important role.

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We have performed a biophysical characterization, at single molecule level, of the interaction between the DNA molecule and the biogenic polyamine putrescine. By using force spectroscopy, we were able to monitor the complexes formation as putrescine is added to the sample, determining the mechanical properties of such complexes and the physicochemical (binding) parameters of the interaction for three different ionic strengths. In particular, it was shown that the behavior of the equilibrium binding constant as a function of the counterion concentration deviates from the prediction of the Record-Lohman model. The measured constants were (1.3 ± 0.2) × 10 M for [Na] = 150 mM, (2.1 ± 0.2) × 10 M for [Na] = 10 mM, and (2.2 ± 0.3) × 10 M for [Na] = 1 mM. The cooperativity degree of the binding reaction, on the other hand, increases with the ionic strength. From these analysis, the DNA-putrescine binding mechanisms are inferred, and a comparison with results reported for ordinary bivalent ions like magnesium is performed. Such study provides new insights on the general behavior of the DNA interactions with biogenic polyamines.

Melanoma accounts for only 4% of all skin cancers but is among the most lethal cutaneous neoplasms. Dacarbazine is the drug of choice for the treatment of melanoma in Brazil through the public health system mainly because of its low cost. However, it is an alkylating agent of low specificity and elicits a therapeutic response in only 20% of cases. Other drugs available for the treatment of melanoma are expensive, and tumor cells commonly develop resistance to these drugs. The fight against melanoma demands novel, more specific drugs that are effective in killing drug-resistant tumor cells. Dibenzoylmethane (1,3-diphenylpropane-1,3-dione) derivatives are promising antitumor agents. In this study, we investigated the cytotoxic effect of 1,3-diphenyl-2-benzyl-1,3-propanedione (DPBP) on B16F10 melanoma cells as well as its direct interaction with the DNA molecule using optical tweezers. DPBP showed promising results against tumor cells and had a selectivity index of 41.94. Also, we demonstrated the ability of DPBP to interact directly with the DNA molecule. The fact that DPBP can interact with DNA in vitro allows us to hypothesize that such an interaction may also occur in vivo and, therefore, that DPBP may be an alternative to treat patients with drug-resistant melanomas. These findings can guide the development of new and more effective drugs.