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Symmetry
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Symmetry in Acid-Base Chemistry II
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Symmetry in Acid-Base Chemistry II

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Chemistry: Symmetry/Asymmetry".

Deadline for manuscript submissions: 31 December 2024 | Viewed by 1328

Special Issue Editor

Prof. Dr. Ewa Daniela Raczyńska

E-Mail Website
Guest Editor
Emeritus Professor, Department of Chemistry, Warsaw University of Life Sciences, 02-787 Warsaw, Poland
Interests: physical organic chemistry; structural chemistry; computational chemistry; gas-phase and solution acid-base equilibria; HB and metal cation adduct formation; tautomerism; substituent and solvent effects
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Symmetry plays a pivotal role in the permanently moving Univer and also in the continuously progressing life on the Earth. It can be found in the macro- and microworlds of plants, animals, and humans. Symmetry exists in human nature, and it reveals itself in human products of different constructive and artworks, as well as in scientific theories and laws. In acid-base chemistry, the symmetry concept has been introduced in structural studies on chemical compounds possessing an acid, base, or amphoteric character, and additionally in physicochemical, analytical, and spectroscopic investigations on their acid-base properties. Consequently, detailed analyses of internal (structural) and external (solvent) effects on these properties have led to formulating exciting structure–reactivity relationships that are very useful to design new mono- or polyfunctional molecules of desired acidity or basicity. They also help to understand the action of bioactive molecules and drugs in living organisms and to explain the mechanisms of various biochemical processes.

Prof. Dr. Ewa Daniela Raczyńska
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • symmetry in the structure of organic monofunctional and polyfunctional acids and bases, including biomolecules and drugs
  • isomerization from unsymmetrical to symmetrical acid-base forms and vice versa
  • electron and/or charge delocalization in relation to acid-base properties
  • intra- and intermolecular neutral and ionic hydrogen-bonding
  • proton-transfer reactions, including prototropy
  • acid-base adducts formation
  • similarities in substituent and solvent effects

Published Papers (1 paper)

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Research

21 pages, 2060 KiB  
Article
On Analogies in Proton-Transfers for Pyrimidine Bases in the Gas Phase (Apolar Environment)—Cytosine Versus Isocytosine
by Ewa D. Raczyńska
Symmetry 2023, 15(2), 342; https://doi.org/10.3390/sym15020342 - 26 Jan 2023
Cited by 3 | Viewed by 918
Abstract
Inter- and intra-molecular proton-transfers between functional groups in nucleobases play a principal role in their interactions (pairing) in nucleic acids. Although prototropic rearrangements (intramolecular proton-transfers) for neutral pyrimidine bases are well documented, they have not always been considered for their protonated and deprotonated [...] Read more.
Inter- and intra-molecular proton-transfers between functional groups in nucleobases play a principal role in their interactions (pairing) in nucleic acids. Although prototropic rearrangements (intramolecular proton-transfers) for neutral pyrimidine bases are well documented, they have not always been considered for their protonated and deprotonated forms. The complete isomeric mixtures in acid-base equilibria and in acidity–basicity parameters have not yet been examined. Taking into account the lack of literature and data, research into the question of prototropy for the ionic (protonated and deprotonated) forms has been undertaken in this work. For the purposes of this investigation, two isomeric pyrimidine bases (C—cytosine and iC—isocytosine) were chosen. They exhibit analogous (symmetrical) general acid-base equilibria (intermolecular proton-transfers). Being similar polyfunctional tautomeric systems, C and iC possess two labile protons and five conjugated tautomeric sites. However, positions of exo groups are different. Consequently, structural conversions such as prototropy, rotational, and geometrical isomerism of exo groups (=O/−OH and =NH/−NH2) and their intramolecular interactions with endo groups (=N−/>NH) possible in neutral C and iC and in their ionic forms lead to some differences in compositions of isomeric mixtures. By application of quantum–chemical methods to the isolated (in vacuo) species, stability of all possible neutral and ionic isomers has been examined and the candidate isomers selected. The complete isomeric mixtures have been considered for the first time for di-deprotonated, mono-deprotonated, mono-protonated, and di-protonated forms. Protonation–deprotonation reactions have been analyzed in the gas phase that models non-polar environment. The gas-phase microscopic (kinetic) and macroscopic (thermodynamic) acidity–basicity parameters have been estimated for each step of acid-base equilibria. When proceeding from di-anion to di-cation in four steps of protonation–deprotonation reaction, the macroscopic proton affinities for C and iC differ by less than 10 kcal mol−1. Their DFT-calculated values are as follows: 451 and 457, 340 and 339, 228 and 224, and 100 and 104 kcal mol−1, respectively. Differences between the microscopic proton affinities for analogous isomers of C and iC seem to be larger for the exo than endo groups. Owing to variations of relative stabilities for neutral and ionic isomers, in some cases they are even larger than 10 kcal mol−1. Full article
(This article belongs to the Special Issue Symmetry in Acid-Base Chemistry II)
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