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How many water molecules are needed to solvate one?
Get PDFThe comprehension at the molecular scale of the processes involved during solvation still remains a challenge in chemistry. Remarkably, the question concerning how many solvent molecules are necessary to solvate a solute one is still open. By exploring several water clusters of increasing size, we employ semiclassical spectroscopy [1-5] to determine on quantum dynamical grounds the minimal number of surrounding water molecules to make the central one display the same vibrational features of liquid water. We find out that the minimal structure eventually responsible of proper solvation is made of 21 water molecules, and that particular care must be reserved to the quantum description of the combination of the central monomer bending mode with network low-frequency librations.[6] The results obtained with the accurate ab initio potential are then compared with the popular Caldeira-Leggett one to rationalize whether a simplified model can qualitatively and quantitatively describe the solvated system behavior.[7] An ongoing study on how genetic algorithms[8] and adiabatically switched trajectories[9] can help to deconstruct the complex spectrum of the formic acid dimer will be also presented.
[1] E. J. Heller, Acc. Chem. Res. 14, 368-375 (1981).
[2] M. F. Herman and E. Kluk, Chem. Phys. 91, 27-34 (1984).
[3] A. L. Kaledin and W. H. Miller, J. Chem. Phys. 119, 3078-3084 (2003).
[4] M. Ceotto, S. Atahan, G. F. Tantardini and A. Aspuru-Guzik, J. Chem. Phys. 130, 234113 (2009).
[5] M. Ceotto, G. Di Liberto and R. Conte, Phys. Rev. Lett. 119, 010401 (2017).
[6] A. Rognoni, R. Conte and M. Ceotto, Chem. Sci. 12, 2060 (2021).
[7] A. Rognoni, R. Conte and M. Ceotto, J. Chem. Phys. 154, 094106 (2021). [8] M. Gandolfi, A. Rognoni, C. Aieta, R. Conte and M Ceotto, J. Chem. Phys. 153, 204104 (2020). [9] R. Conte, L. Parma, C. Aieta, A. Rognoni and M. Ceotto, J. Chem. Phys. 151, 214107 (2019)
How many water molecules are needed to solvate one?
No full textThe comprehension at the molecular scale of the processes involved during solvation still remains a challenge in chemistry. Remarkably, the question concerning how many solvent molecules are necessary to solvate a solute one is still open. By exploring several water clusters of increasing size, we employ semiclassical spectroscopy [1-5] to determine on quantum dynamical grounds the minimal number of surrounding water molecules to make the central one display the same vibrational features of liquid water. We find out that double-acceptor double-donor tetrahedral coordination constituting the standard picture is necessary but not sufficient for solvation, and that particular care must be reserved to the quantum description of the combination band due to the coupling of the central monomer bending mode with network low-frequency modes. The minimal structure eventually responsible of proper solvation is made of a total of 21 water molecules and includes two complete solvation shells, of which the whole first one is tetrahedrally coordinated to the central molecule [6]
How many water molecules are needed to solvate one?
Get PDFTheoretical vibrational spectroscopy provides a practical way to study both isolated (gas-phase) and solvated systems. When dealing with sizeable molecular systems, the main challenge is represented by the large number of degrees of freedom to be considered. Furthermore, an accurate spectroscopical investigation requires a quantum mechanical treatment, which makes the task even harder to achieve.
This key issue involves both the description of the potential energy surface and the molecular dynamics. Semiclassical dynamics allows one to calculate accurate vibrational spectra with inclusion of quantum effects like zero-point energies, overtones, and quantum resonances starting from short-time classical molecular dynamics runs. In this talk I will briefly introduce the divide-and-conquer semiclassical initial value representation technique (DC SCIVR), and then show a batch of applications involving biomolecules and water-based supramolecular systems. I will start by demonstrating the spectroscopic accuracy of the technique on isolated (gas-phase) biomolecules (glycine and thymidine). Then, I will describe an investigation of water clusters aimed at revealing how many water molecules are needed to have the central monomer featuring the spectroscopic properties of bulk water. Finally, some preliminary results of a study of solvated
thymidine will be presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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