In this article, the proton transfer dynamics along a stable norharmane•(H2O)n (n = 2–4) hydrogen-bonded cluster on conversion from the neutral to cationic form of norharmane (NHM) in water medium was demonstrated experimentally and theoretically. The distinct absorption and emission bands of different prototropic forms of NHM are well-known in the literature. Initially, the conversion from neutral to cationic form of NHM on moving from a polar aprotic (acetonitrile) to a polar protic (water) solvent was ensured by steady-state absorption and fluorescence studies. The analysis of IR spectra and steady-state anisotropy data of NHM confirmed the possibility of the formation of a hydrogen-bonded network in the presence of water. The length of the network was explored and assumed by extensive Density Functional Theory (DFT) calculations. Then, by time-dependent density functional theory (TD-DFT), the excited state proton transfer (ESPT) pathway was established interrogating the NHM-water cluster with different numbers of water molecules. The theoretical analysis assured that the NHM•(H2O)2 cluster was incapable of maintaining the stable hydrogen bonding wire in the course of the ESPT mechanism. Rather, NHM•(H2O)3 and NHM•(H2O)4 clusters were simultaneously involved in operating the ESPT mechanism. The NHM•(H2O)4 cluster was more feasible to carry out the proton transfer than the NHM•(H2O)3 cluster. To the best of our knowledge, this was possibly the first theoretical evidence behind the conversion from neutral to cationic form of NHM via the formation of a hydrogen-bonded network.
We report quantitative details of addition reactions of a strained trans-cyclooctene with a series of oxadiazinones, analogues of the bioorthogonally fruitful tetrazines. Both experimental and computational studies of these ligations reveal their sensitivity to differing electronic character of oxadiazinone substituents. Achieving rate constants up to 9.5 L mol−1 s−1, oxadiazinones demonstrate untapped potential for bioorthogonal applications.
Methyl N22-methylpyropheophorbides-a with chloride or hexafluorophosphate were prepared by chemically modifying chlorophyll-a. The resulting product composed of cationic N-methylated chlorin and chloride anion exhibited visible absorption and fluorescence emission maxima in chloroform at longer wavelengths than those with hexafluorophosphate. Both the absorption and emission spectra of the former were hypsochromically shifted by change of the solvent from chloroform to methanol to give almost the same corresponding spectra of the latter independent of solvents. The apparent counter-anion dependency in chloroform and the specific solvent dependency in the N-methyl-chlorin with chloride are ascribable to the weak solvation of a hard chloride anion over soft hexafluorophosphate in chloroform and strong electrostatic interaction of the cationic chlorin with a chloride anion over hexafluorophosphate in chloroform as well as well solvation of both the anions in methanol. In addition, less emission of N-methyl-chlorin with chloride in chloroform would be due to partial fluorescence quenching based on the heavy atom effect of the adjacent chloride anion.
SF5CF3, commonly recognized as a potent greenhouse gas, has recently emerged as a valuable source of fluoride functional groups. Despite its traditional role, recent studies have highlighted its potential applications beyond its environmental implications. However, investigations into its reactivity remain limited, particularly regarding the activation of its constituent bonds. In this study, we conducted a comprehensive computational analysis to elucidate the competition among C–F, C–S, and S–F bond activations within SF5CF3 utilizing N-heterocyclic olefin derivatives. Our investigations shed light on the underlying mechanisms of bond activation, revealing a preference for the activation of the S–F bond in SF5CF3 by both NHOs and mNHOs. Specifically, we observed a Gibbs free energy barrier (ΔG≠) ranging from 24.90 to 25.77 kcal/mol in the case of mNHOs, indicating a favorable energetics for this process.
The structural, optoelectronic and charge transport properties of porphyrin and its analogues are investigated using the density functional theoretical methods. Most of the above molecules absorb in visible region with high light harvesting efficiency. The small energy gap between the frontier molecular orbitals (FMOs) suggests that porphyrin and its derivatives can be used in organic semiconductors. Electronic properties such as ionization potential, electron affinity, reorganization energy and the charge transfer integral are calculated to obtain their charge transport properties. It is revealed that porphyrin, porphyrazine and phthalocyanine act as hole transporters, whereas corrole and corrolazine act as electron transporters.
A detailed mechanistic investigation of the Zn (II)-catalyzed Csp–Csp2 (Sonogashira-type) cross-coupling reaction is reported herein, using the Density Functional Theory method. The present study unveiled an unconventional non-redox mechanism for Zn-catalyzed cross-coupling reaction, where the oxidation state of Zn remains intact throughout the catalytic cycle. Our study further revealed the significant role of the base in controlling the feasibility of cross-coupling reactions that are catalyzed by electron-deficient metal centers. Our study indicates that K3PO4 acts as an ancillary ligand (Lewis base) for the electron-deficient Zn (II) catalytic center rather than as a proton abstractor for the nucleophilic coupling partner (phenylacetylene) in this reaction. The active catalyst was identified to be a four-coordinate bis-DMEDA Zn (II) complex. The mechanism proceeds via the initial activation of the nucleophilic coupling partner (phenylacetylene), followed by the electrophilic coupling partner (organic halide) activation liberating the cross-coupled product by a concerted nucleophilic substitution pathway. The turn-over limiting step was identified to be the activation of the electrophilic coupling partner. The activation barrier obtained for the reaction, 31.0 kcal/mol concords well with experimental temperature requirements (125°C). The coordination by base is found to stabilize the rate-determining intermediates and transition states involved in the reaction. The mechanistic insights gained from this study could aid in the rational design and development of sustainable cross-coupling reactions using zinc as the catalyst.
Amino acid oxidation is fascinating because different oxidants produce diverse compounds. No research has examined how metal catalysts affect amino acid oxidation by diperiodatocuprate (III) (DPC) in micellar environments. This research is crucial to understanding amino acids in redox processes and identifying active species of Ru(III) and DPC. The study will evaluate how cationic surfactant affects Ru(III)-facilitated L-phenylalanine (L-Pheala) oxidation utilizing DPC in an alkaline medium. The reaction's advancement has been assessed employing the pseudo-first-order condition as a gauge for [OH−], [DPC], ionic strength, [L-Pheala], [Ru(III)], [IO4−], [Surfactant], and temperature. L-Pheala and DPC interact stoichiometrically in a ratio of 1:4. Across the spectrum of concentrations examined, the reported reaction reflects less than unit order kinematics in relation to both [L-Pheala] (0.61 in the aqueous medium and 0.58 in the CPC micellar medium) and [OH−] (0.47 in the aqueous medium and 0.51 in the CPC micellar medium), first-order reliance on the [DPC] and [Ru(III)], and negative fractional-order for [IO4−] (−0.54 in the aqueous medium and −0.56 in the CPC micellar medium). A zero salt effect is suggested by the observed constancy in oxidation rate with the inclusion of electrolytes. The oxidation rate is significantly enhanced by Ru(III) solution (as a catalyst) at ppm concentration. Cetylpyridinium chloride (CPC) micellar media facilitate an additional enhancement (four times) in the rate of the reaction. CPC thus exhibits an excellent compatibility with Ru(III) for the L-Pheala oxidation using (DPC).
The photosensitizer mechanism by the psoralen (PSO) reacts to produce reactive oxygen species has not been thoroughly studied; thus, this work was carried out a study of the reaction and mechanism involved in the photosensitizer activity of PSO, employing M06-2X/6-311++G(d,p) of the density functional theory. There is a competition between the generation of radical anion superoxide (type I mechanism) and the singlet oxygen molecule (type II mechanism) in lipid media; therefore, the ROS anion superoxide and singlet oxygen could be formed as products of the reaction involved in the photosensitizer activity of PSO in lipid media. In aqueous media, the reaction involved in the photosensitizer activity of PSO was only attributed to the type I mechanism; hence, in aqueous media, the photosensitizer activity of PSO yielded the anion superoxide. The present study supports the photosensitizer activity of the PSO in lipid and aqueous media. It enhances the knowledge of these reactions in different media and their application to reactivity, including the physiology media.
Rapid detection of chemical explosives plays a critical role in national security and public safety. An in-depth study of the sensing mechanism is particularly urgent for the development of highly efficient, sensitive, and selective chemical sensors for the precise detection of chemical explosives. Density functional theory (DFT) and time-dependent DFT approaches were used in this work to examine the sensing mechanism of a novel fluorescent probe 1-benzyl-3,5-di (thiophen-2-yl)pyrazin-1-ium bromide (BTPyz) for the detection of 2,4,6-trinitrophenol (TNP). A comprehensive theoretical exploration was carried out, and a different interaction mode between the probe and TNP from that in the original experiment was proposed. The π–π stacking was established to be the recognition interaction between BTPyz and TNP anion, and the active site was determined from the three potential sizes according to the Gibbs free energy analysis results. The rationality of the reaction mode and the π–π stacking product between the BTPyz and TNP (BTN) was further confirmed by the fluorescence properties (absorption and emission spectra). According to the findings of frontier molecular orbitals (FMOs), photoinduced electron transfer (PET) is the intrinsic mechanism through which TNP quenches the probe's fluorescence.
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