Expanding the Range of Force Fields Available for ONIOM Calculations: The SICTWO Interface

Thermo-responsive emission induced by different delocalized excited-states in isomorphous Pd(ii) and Pt(ii) one-dimensional chains

The self-assembly of d8 transition metal complexes is essential for the development of optoelectronic and sensing materials with superior photofunctional properties. However, detailed insight into the electronic delocalization of excited states across multiple molecules, particularly in comparing 5d8 (Pt(ii)) and 4d8 (Pd(ii)) systems, remains ambiguous but important. In this study, we have successfully evaluated the differences in the excited-state delocalization and thermal responses of self-assembled Pt(ii) and Pd(ii) complexes. Although the complexes presented herein, K[M(CN)2(dFppy)]·H2O (M = Pt or Pd, dFppy = 2-(4,6-difluorophenyl)pyridinate), are crystallographically isomorphous with similarly short metal⋯metal contacts, only the Pt(ii) complex exhibited thermal equilibria between delocalized excited states, resulting in a drastic thermochromic luminescence with a red-shift of greater than 100 nm. In contrast, the dimeric localized emission from the Pd(ii) complex showed a significant increase in the quantum yield upon cooling, approaching almost unity.

A systematic mechanistic survey on the reactions between OH radical and CH3OH on ice

A systematic mechanistic survey was performed for the CH3OH + OH reaction on ice. ONIOM(ωB97X-D/Def2-TZVP:AMOEBA09) calculations suggested a range of binding energies for the CH2OH radical (0.29-0.69 eV) and CH3OH (0.15-0.72 eV) molecule on hexagonal water ice (Ih) and amorphous solid water (ASW). Computed average binding energies of CH2OH radical (0.49 eV) and CH3OH (0.41 eV) are relatively stronger compared to the CH3O radical binding energies (0.32 eV, Sameera et al., J. Phy. Chem. A, 2021, 125, 387-393). Thus, the CH3OH molecule, CH2OH and CH3O radicals can adsorb on ice, where the binding energies follow the order CH2OH > CH3OH > CH3O. The multi-component artificial force-induced reaction (MC-AFIR) method systematically determined the reaction mechanisms for the CH3OH + OH reaction on ice, where two reaction paths, giving rise to CH2OH and CH3O radicals, were confirmed. A range of reaction barriers, employing the ωB97X-D/Def2-TZVP level of theory, was found for each reaction (0.03-0.11 eV for CH2OH radical formation, and 0.03-0.44 eV for CH3O radical formation). Based on the lowest energy reaction paths, we suspect that both reactions operate on ice. The computed data in this study evidence that the nature of the binding site or the reaction site has a significant effect on the computed binding energies or reaction barriers. Thus, the outcomes of the present study will be very useful for the computational astrochemistry community to determine reliable binding energies and reaction barriers on ice.

A DFT Study on the Binuclear Copper(I)-Catalyzed Synthesis Mechanism of 1,2,3-Triazolo[1,5-c]Pyrimidine via Interrupted Click and Ketenimine Rearrangement

In this paper, the mechanism of the full catalytic cycle for binuclear Cu(I)-catalyzed sulfonyl azide-alkyne cycloaddition reaction for the synthesis of triazolopyrimidines was rationalized by density functional theoretical (DFT) calculations. The computed reaction route consists of: (a) formation of dicopper intermediates, including C-H activation of terminal alkyne, 3+2 ring cycloaddition and ring-reducing reaction and transmetalation, (b) interrupted CuAAC reaction, including di-copper catalyzed ring-opening of 2H-azirines and C-C bond formation to generate the copper-triazoles and -ketenimines, (c) two-step C-N cross-coupling and following (d) multi-step hydrogen transfer by the hydrogen bonding chain of water to promote the C-N formation and another C-N cleavage through the removal of p-tolyl sulfonamides. Our DFT results indicate that the multi-step hydrogen transfer process is the rate-determining step along the potential energy surface profile. The explicit water model was used for systematic determination of barrier for C-C cross-coupling, C-N bond formation and cleavage, and p-tolylsulfonamide removal. A critical insight in the interrupted CuAAC reaction was proposed. Further prediction interprets H₂ O hydrogen bond chain plays an important role in C-N bond formation and cleavage, and the removal of p-tolylsulfonamide. This may have fundamental guidance on the design of 1, 5-herterocyclic functionalized triazolopyrimidines via interrupted CuAAC rearrangement reaction, as well as hydrogen bond chain of water.

UV-Vis, Raman spectroscopic and density functional theoretical studies on microsolvation 1, 2, 4-triazole-3-thione clusters

Photophysical and photochemical reactions of microsolvation clusters are attracting an increasing attention due to their wide applications in materials science and biology. In this paper, 1, 2, 4-triazole-3-thione (3TT) is investigated in solid, protic, and aprotic solvents using FT-Raman, resonance Raman and electronic absorption spectroscopic experiments. The structures of microsolvation clusters in solvents were confirmed by 488 nm Raman spectroscopy combining with density functional theory (DFT) calculation. Steady-state absorption and resonance Raman spectra of 3TT in different environments indicate that the intermolecular hydrogen bonding may reveal important insights in the photophysical and photochemical process. With the aid of DFT and time-dependent density functional theory (TDDFT) calculations, we assigned the observed Raman spectra to the microsolvation clusters in acetonitrile, water and methanol, and carried out preliminary investigations on spectrum shifts of UV and Raman spectra due to the hydrogen bonding with the solvent molecules. The intermolecular >NH···O and >=S···H hydrogen bonding interactions, which are the key constituents of stable thione structure of 3TT, revealed the obvious spectrum shifts of 3TT, including Raman and absorption shifts in CH₃CN, CH₃OH and H₂O. The hydrogen bond sites were further confirmed to be located on the functional group SCNH of 3TT with CH₃CN, H₂O and CH₃OH.

Synthesis, characterization and biological evaluation of dipicolylamine sulfonamide derivatized platinum complexes as potential anticancer agents

Three new Pt complexes, [PtCl₂(N(SO₂(2-nap))dpa)], [PtCl₂(N(SO₂(1-nap))dpa)] and [PtCl₂(N(SO₂pip)dpa)], containing a rare 8-membered ring were synthesized in good yield and high purity by utilizing the ligands N(SO₂(2-nap))dpa, N(SO₂(1-nap))dpa and N(SO₂pip)dpa, which contain a dipicolylamine moiety. Structural studies of all three complexes confirmed that the ligands are bound in a bidentate mode via Pt–N_(pyridyl) bonds forming a rare 8-membered ring. The intense fluorescence displayed by the ligands is quenched upon coordination to Pt. According to time dependent density functional theory (TDDFT) calculations, the key excitations of N(SO₂(2-nap))dpa and [PtCl₂(N(SO₂(1-nap))dpa)] involve the 2-nap-ligand-centered π → π* excitations. While all six compounds have shown antiproliferative activity against human breast cancer cells (MCF-7), the N(SO₂pip)dpa and N(SO₂(2-nap))dpa ligands and [PtCl₂((NSO₂pip)dpa)] complex have shown significantly high cytotoxicity, directing them to be further investigated as potential anti-cancer drug leads.

Three new Pt complexes, [PtCl₂(N(SO₂(2-nap))dpa)], [PtCl₂(N(SO₂(1-nap))dpa)] and [PtCl₂(N(SO₂pip)dpa)], containing a rare 8-membered ring were synthesized in good yield and high purity by utilizing ligands which contain a dipicolylamine moiety.

CH3O Radical Binding on Hexagonal Water Ice and Amorphous Solid Water

Binding energies of the CH3O radical on hexagonal water ice (Ih) and amorphous solid water (ASW) were calculated using the ONIOM(QM:MM) method. A range of binding energies is found (0.10-0.50 eV), and the average binding energy is 0.32 eV. The CH3O radical binding on the ASW surfaces is stronger than on the Ih surfaces. The computed binding energies from the ONIOM(wB97X-D/def2-TZVP:AMBER) and wB97X-D/def2-TZVP methods agree quite well. Therefore, the ONIOM(QM:MM) method is expected to give accurate binding energies at a low computational cost. Binding energies from the ONIOM(wB97X-D/def2-TZVP:AMBER) and ONIOM(wB97X-D/def2-TZVP:AMOEBA09) methods differ noticeably, indicating that the choice of force field matters. According to the energy decomposition analysis, the electrostatic interactions and Pauli repulsions between the CH3O radical and ice play a crucial role in the binding energy. This study gives quantitative insights into the CH3O radical binding on interstellar ices.

Computational Surface Modelling of Ices and Minerals of Interstellar Interest—Insights and Perspectives

The universe is molecularly rich, comprising from the simplest molecule (H2) to complex organic molecules (e.g., CH3CHO and NH2CHO), some of which of biological relevance (e.g., amino acids). This chemical richness is intimately linked to the different physical phases forming Solar-like planetary systems, in which at each phase, molecules of increasing complexity form. Interestingly, synthesis of some of these compounds only takes place in the presence of interstellar (IS) grains, i.e., solid-state sub-micron sized particles consisting of naked dust of silicates or carbonaceous materials that can be covered by water-dominated ice mantles. Surfaces of IS grains exhibit particular characteristics that allow the occurrence of pivotal chemical reactions, such as the presence of binding/catalytic sites and the capability to dissipate energy excesses through the grain phonons. The present know-how on the physicochemical features of IS grains has been obtained by the fruitful synergy of astronomical observational with astrochemical modelling and laboratory experiments. However, current limitations of these disciplines prevent us from having a full understanding of the IS grain surface chemistry as they cannot provide fundamental atomic-scale of grain surface elementary steps (i.e., adsorption, diffusion, reaction and desorption). This essential information can be obtained by means of simulations based on computational chemistry methods. One capability of these simulations deals with the construction of atom-based structural models mimicking the surfaces of IS grains, the very first step to investigate on the grain surface chemistry. This perspective aims to present the current state-of-the-art methods, techniques and strategies available in computational chemistry to model (i.e., construct and simulate) surfaces present in IS grains. Although we focus on water ice mantles and olivinic silicates as IS test case materials to exemplify the modelling procedures, a final discussion on the applicability of these approaches to simulate surfaces of other cosmic grain materials (e.g., cometary and meteoritic) is given.

Palladium-Catalyzed Regioselective and Stereospecific Ring-Opening Cross-Coupling of Aziridines: Experimental and Computational Studies

Aziridines, i.e., the smallest saturated N-heterocycles, serve as useful building blocks in synthetic organic chemistry. Because of the release of the large ring strain energy accommodated in the small ring, (ca. 27 kcal/mol), aziridines undergo ring-opening reactions with a variety of nucleophiles. Therefore, among the synthetic reactions utilizing aziridines, regioselective ring-opening substitutions of aziridines with nucleophiles, such as heteroatomic nucleophiles (e.g., amines, alcohols, and thiols) and carbonaceous nucleophiles (e.g., carbanions, organometallic reagents, and electron-rich arenes), constitute a useful synthetic methodology to synthesize biologically relevant β-functionalized alkylamines. However, the regioselection in such traditional ring-opening substitutions of aziridines is highly dependent on the substrate combination, and stereochemical control is challenging to achieve, especially in the case of Lewis acid-promoted variants. Therefore, the development of robust catalytic ring-opening functionalization methods that enable precise prediction of regioselectivity and stereochemistry is desirable. In this direction, our group focused on the highly regioselective and stereospecific nature of the stoichiometric oxidative addition elementary step of 2-substituted aziridines into Pd(0) complexes in an S_N2 fashion. In conjunction with the recent advancements in transition-metal-catalyzed cross-coupling reactions of alkyl pseudohalides containing a C(sp³)-Q (Q = O, N, S, etc.) bond, aziridines can be used as nonclassical alkyl pseudohalides in regioselective and stereospecific cross-couplings.In this Account, starting from the background of transition-metal-catalyzed ring-opening functionalization of aziridines, our contributions to the palladium-catalyzed regioselective and stereoinvertive cross-couplings of aziridines with organoboron reagents to form C(sp³)-C, C(sp³)-B, and C(sp³)-Si bonds have been compiled. The developed methods allow the syntheses of medicinally important amine compounds, e.g., enantioenriched β-phenethylamines, β-amino acids, and their boron and silyl surrogates, from readily available enantiopure aziridine substrates. Notably, the regioselectivity of the ring opening can be switched by appropriate selection of the catalyst (i.e., Pd/NHC vs Pd/PR₃ systems). Computational studies rationalized the detailed mechanisms of the full catalytic cycle and the regioselectivity and stereospecificity of the reactions. The computational results suggested that the interactions operating between the Pd catalyst and aziridine substrate play important roles in determining the regioselection of the aziridine ring-opening event (i.e., oxidative addition). Also, the computational results rationalized the role of water molecules in promoting the transmetalation step through the formation of a Pd-hydroxide active intermediate. This Account evidences the benefits of synergistic collaborations between experimental and computational methods in developing novel transition-metal-catalyzed cross-coupling reactions.