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The pressure-induced transformation of molecular crystals can give rise to new materials characterized by intriguing hardness or energetic properties. Mechanisms regulating these reactions at the molecular level result from a complex interplay among crystal structure, lattice dynamics, and electronic properties. Here, we show that the formation of a three-dimensional amorphous carbon nitride by compressing phase II s-triazine is controlled by the competition between two different mechanisms, one entirely structural and the other electronic, representing the first example where such occurrence is demonstrated. Temperature drives the reactivity below 8 GPa by ruling the lattice dynamics, whereas above 8 GPa the electronic modifications, uniquely governed by pressure, trigger the chemical transformation. The amorphous material synthesized has a bonding structure characterized by a bulk typical of a strongly conjugated three-dimensional carbon nitride with hydrogen atoms migrated to saturate C and N terminations.

The adsorption of isothiazole on silver colloids was studied by surface-enhanced Raman scattering (SERS) spectroscopy in comparison with other five-membered heterocycles. The experimental results coupled with those obtained by density functional theory calculations for molecule/metal complexes evidenced the presence of positively charged active sites on the surface of the silver nanoparticles, along with a close relation between ligand basicity and strong SERS effect.

Surface-enhanced Raman scattering (SERS) of adenine-containing microRNA chains has been obtained by adsorption on roughened silver substrates. The spectral features of all of these samples appear dominated by the bands of adenine. By comparison with the SERS spectra of adenine and adenosine obtained on the same substrates, along with DFT calculations on the interaction sites of adenine and adenosine with silver, inferences are discussed about the structural arrangement of the microRNA chains with respect to the metal surface. This approach gives suitable guidelines in order to investigate the adsorption of complex biomolecules on metal substrates.

The role of surface metal clusters in the surface enhanced Raman scattering (SERS) enhancement mechanism was investigated by coupling Raman measurements and DFT (density functional theory) calculations for pyrazole adsorbed on Ag colloidal nanoparticles. The adsorption process of the ligand can be suitably described by a model system constituted of pyrazolide anions chemically interacting with (Ag4)+2 surface clusters since the DFT approach allows a complete depiction of the SERS profile to be obtained, including both band frequencies and relative intensities.