SOMO–HOMO Conversion in Triplet Cyclopentane-1,3-diyl Diradicals
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ABSTRACT:
SUBMITTER: Wang Z
PROVIDER: S-EPMC8427779 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Conventionally, the singly occupied molecular orbital (SOMO) of a radical species is considered to be the highest occupied molecular orbital (HOMO), but this is not the case always. In this study, we considered a number of radicals from smallest diatomic anion radicals such as superoxide anion radical to one-electron oxidized DNA related base radicals that show the SOMO is energetically lower than one or more doubly occupied molecular orbitals (MOs) (SOMO-HOMO level inversion). The electronic configurations are calculated employing the B3LYP/6-31++G** method, with the inclusion of aqueous phase via the integral equation formalism of the polarized continuum model solvation model. From the extensive study of the electronic configurations of radicals produced by one-electron oxidation or reduction of natural-DNA bases, bromine-, sulfur-, selenium-, and aza-substituted DNA bases, as well as 20 diatomic molecules, we highlight the following important findings: (i) SOMO-HOMO level inversion is a common phenomenon in radical species. (ii) The more localized spin density in ?-orbital on a single atom (carbon, nitrogen, oxygen, sulfur, or selenium), the greater the gap between HOMO and SOMO. (iii) In species with SOMO-HOMO level inversion, one-electron oxidation takes place from HOMO not from the SOMO, which produces a molecule in its triplet ground state. Oxidation of aqueous superoxide anion producing triplet molecular oxygen is one example of many. (iv) These results are for conventional radicals and in contrast with those reported for distonic radical anions in which SOMO-HOMO gaps are smaller for more localized radicals and the orbital inversions vanish in water. Our findings yield new insights into the properties of free radical systems.
| S-EPMC5767877 | biostudies-literature
Project description:We report relatively persistent, open-shell thiophene-based double helices, radical cations 1•+ -TMS12 and 2•+ -TMS8 . Closed-shell neutral double helices, 1-TMS12 and 2-TMS8 , have nearly identical first oxidation potentials, E +/0 ≈ +1.33 V, corresponding to reversible oxidation to their radical cations. The radical cations are generated, using tungsten hexachloride in dichloromethane (DCM) as an oxidant, E +/0 ≈ +1.56 V. EPR spectra consist of a relatively sharp singlet peak with an unusually low g-value of 2.001-2.002, thus suggesting exclusive delocalization of spin density over π-conjugated system consisting of carbon atoms only. DFT computations confirm these findings, as only negligible fraction of spin density is found on sulfur and silicon atoms and the spin density is delocalized over a single tetrathiophene moiety. For radical cation, 1•+ -TMS12 , energy level of the singly occupied molecular orbital (SOMO) lies below the four highest occupied molecular orbitals (HOMOs), thus indicating the SOMO-HOMO inversion (SHI) and therefore, violating the Aufbau principle. 1•+ -TMS12 has a half-life of the order of only 5 min at room temperature. EPR peak intensity of 2•+ -TMS8 , which does not show SHI, is practically unchanged over at least 2 h.
| S-EPMC8688166 | biostudies-literature
Project description:In the mol-ecule of the title compound, C(14)H(20)N(4)O(3), the five-membered ring adopts an envelope conformation with the O atom displaced by 0.207 (3) Å from the plane of the other ring atoms. Intra-molecular C-H⋯O hydrogen bonds result in the formation of three five-membered rings having envelope conformations. In the crystal structure, inter-molecular N-H⋯O hydrogen bonds link the mol-ecules, forming R(2) (2)(20) ring motifs, which produce two-dimensional polymeric sheets extending along the b axis. There are also two C-H⋯π inter-actions. The H atoms of one of the methyl groups are disordered over two positions and were refined with occupancies of 0.50.
| S-EPMC2967959 | biostudies-literature
Project description:A series of derivatives of the known thromboxane A2 prostanoid (TP) receptor antagonists, 3-(6-((4-chlorophenyl)sulfonamido)-5,6,7,8-tetrahydronaphthalen-1-yl)propanoic acid and 3-(3-(2-((4-chlorophenyl)sulfonamido)ethyl)phenyl) propanoic acid, were synthesized in which the carboxylic acid functional group was replaced with substituted cyclopentane-1,3-dione (CPD) bioisosteres. Characterization of these molecules led to the discovery of remarkably potent new analogues, some of which were considerably more active than the corresponding parent carboxylic acid compounds. Depending on the choice of the C2 substituent of the CPD unit, these new derivatives can produce either a reversible or an apparent irreversible inhibition of the human TP receptor. Given the potency and the long-lasting inhibition of TP receptor signaling, these novel antagonists may comprise promising leads for the development of antithromboxane therapies.
| S-EPMC4160754 | biostudies-literature
Project description:Organic radicals possessing an electronic configuration in which the energy of the singly occupied molecular orbital (SOMO) is below the highest doubly occupied molecular orbital (HOMO) level have recently attracted significant interest, both theoretically and experimentally. The peculiar orbital energetics of these SOMO-HOMO inversion (SHI) organic radicals set their electronic properties apart from the more common situation where the SOMO is the highest occupied orbital of the system. This review gives a general perspective on SHI, with key fundamental aspects regarding the electronic and structural factors that govern this particular electronic configuration in organic radicals. Selected examples of reported compounds with SHI are highlighted to establish molecular guidelines for designing this type of radical, and to showcase the potential of SHI radicals in organic spintronics as well as for the development of more stable luminescent radicals for OLED applications.
| S-EPMC9430691 | biostudies-literature
Project description:Mol-ecules of the title compound, C(17)H(18)N(2)O(4), lie on a twofold rotation axis that passes through the central methyl-ene C atom. The mol-ecules adopt a 'V' shape and the trimethyl-ene unit assumes a gauche-gauche conformation. The amino N atom shows a nonplanar coordination. Adjacent mol-ecules are connected by N-H?O hydrogen bonds into chains running along [001]. Furthermore, N-H?N hydrogen bonds connect these chains into a three-dimensional network.
| S-EPMC3007263 | biostudies-literature
Project description:In the mol-ecule of the title compound, C(20)H(26)N(2)O(2), the 1,3-diazinane ring adopts a slightly distorted chair conformation and the hy-droxy-benzyl substituents occupy equatorial positions on the N atoms of the heterocyclic ring. There are two intra-molecular O-H?N hydrogen bonds between the N atoms of the 1,3-diazinane ring and the hy-droxy groups of the aromatic rings, with an S(6) set-graph motif. However, the two observed intra-molecular hydrogen-bond distances were different. Considering that both N atoms experience the same chemical environment, it is surprising to see the difference in O?N distances [2.6771?(14) and 2.8123?(12)?Å]. The crystal structure is further stabilized by a C-H?? interaction.
| S-EPMC3295478 | biostudies-literature
Project description:The title compound, C(23)H(25)N(3)O(2), was obtained as an inter-mediary in the preparation of non-symmetric tertiary diamines. The mol-ecular structure presents T-shaped spatial form, in which the pyrimidine ring exhibits a chair conformation. The pyridyl ring is almost perpendicular to the phenyl rings with dihedral angles of 80.17 (8) and 76.03 (2)°. The phenol and amine groups are involved in two strong intra-molecular O-H⋯N inter-actions. In the crystal, the mol-ecules are stacked along [010]; however, no inter-molecular inter-actions are observed.
| S-EPMC3435756 | biostudies-literature
Project description:The title compound. C(15)H(14)N(2)O(4), (I), has a gauche-gauche (O/C/C/C-O/C/C/C or GG) conformation and is a positional isomer of propane-1,3-diyl bis-(pyridine-3-carboxyl-ate), (II). The mol-ecule of (I) lies on a twofold rotation axis, which passes through the central C atom of the aliphatic chain, giving one half-mol-ecule per asymmetric unit. There is excellent agreement of the geometric parameters of (I) and (II). The most obvious differences between them are the O/C/C/C-O/C/C/C torsion angles [56.6?(2)° in (I) and 174.0?(3)/70.2?(3)° in (II) for GG and TG conformations, respectively] and the dihedral angle between the planes of the aromatic rings [80.3?(10)° in (I) and 76.5?(3)° in (II)]. The crystal structure is stabilized by weak C-H? N and C-H? O hydrogen bonding.
| S-EPMC2979147 | biostudies-literature
Project description:The title compound, C(15)H(14)N(2)O(4), has a trans-gauche [O/C/C/C-O/C/C/C] (TG) conformation. The angle between the planes of aromatic rings is 76.4 (3)°. The crystal structure is stabilized by van der Waals inter-actions and C-H⋯O hydrogen bonds. The crystal used was a non-merohedral twin with a fractional contribution of the minor component of 0.443 (5).
| S-EPMC2983924 | biostudies-literature