Vibronic Coupling and Multiple Electronic States Effect in ABS and ECD Spectra: Three [7]Helicene Derivatives

The Journal of Physical Chemistry A, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 15, 2025

Vibronic coupling and multiple electronic states effect play a pivotal role in the molecular spectroscopy of large systems. Herein, we present detailed theoretical study on absorption (ABS) circular dichroism (ECD) spectra three [7]helicene derivatives chloroform, with particular emphasis significance vibronic spectral simulations. The vertical gradient (VG) Hessian (VH) models, incorporating Franck-Condon (FC) Herzberg-Teller (HT) contribution, are considered calculations. results indicate that simulated vibrationally resolved obtained by VG model combined FC more reliable, showing advantages rationality shapes, accuracy relative heights peaks, correctness positive negative signals. Reliable predictions allowed us to further explore importance spectra, demonstrating high-energy excited states, particularly fifth (S5) sixth (S6) essential for accurately capturing fine structures observed experimental spectra. Our predicts reliable reference family provides fundamental understanding chiral organic molecules states.

Language: Английский

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Chiroptical Spectroscopy, Theoretical Calculations, and Symmetry of a Chiral Transition Metal Complex with Low-Lying Electronic States

Molecules, Journal Year: 2025, Volume and Issue: 30(4), P. 804 - 804

Published: Feb. 10, 2025

Vibrational circular dichroism (VCD) enhancement by low-lying electronic states (LLESs) is a fascinating phenomenon, but accounting for it theoretically remains challenge despite significant research efforts over the past 20 years. In this article, we synthesized two transition metal complexes using tetradentate Schiff base ligands (R,R)- and (S,S)-N,N'-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine with Co(II) Mn(III), referred to as Co(II)-salen-chxn Mn(III)-Cl-salen-chxn, respectively. Their stereochemical properties were explored through combined experimental chiroptical spectroscopic theoretical approach, focus on Co(II)-salen-chxn. Extensive conformational searches in CDCl3 both high- low-spin carried out associated infrared (IR), VCD, ultraviolet-visible (UV-Vis) absorption, (ECD) spectra simulated. A good agreement between simulated data was achieved IR, UV-Vis, ECD, except case of VCD which exhibits intensity monosignate bands, attributed LLESs. Interestingly, detailed comparisons Mn(III)-Cl-salen-chxn previously reported Ni(II)-salen-chxn Cu(II)-salen-chxn suggest that factor predicted current density functional theory simulations. However, signatures observed spectrum not captured theoretically. Based experiment ECD comparison, tentatively suggested exists low- high-spin states, former being dominant, while state. The study indicates LLESs at least partially existing simulation, symmetry consideration vibronic coupling provides further insight into mechanisms behind sign-flip.

Language: Английский

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Assessing Nonbonded Aggregates Populations: Application to the Concentration-Dependent IR O–H Band of Phenol

Journal of Chemical Theory and Computation, Journal Year: 2025, Volume and Issue: unknown

Published: April 14, 2025

In this work, we present two alternative computational strategies to determine the populations of nonbonded aggregates. One approach extracts these from molecular dynamics (MD) simulations, while other employs quantum mechanical partition functions for most relevant minima multimolecular potential energy surfaces (PESs), identified by automated conformational sampling. both cases, adopt a common graph-theory-based framework, introduced in identifying aggregate conformations, which enables consistent comparative assessment methodologies and provides insight into underlying approximations. We apply investigate phenol aggregates, up tetramer, at different concentrations phenol/carbon tetrachloride mixtures. Subsequently, simulate concentration-dependent OH stretching IR region averaging harmonic Infrared (IR) spectra aggregates using predicted each strategy. Our results indicate that extracted MD trajectories yield signals closely follow experimental trends, outperforming obtained systematic searches. Such better performance is attributed description entropic contributions. Moreover, proposed protocol not only successfully addresses very challenging problem but also offers benchmark assess accuracy intermolecular force fields.

Language: Английский

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Stereochemistry of natural products from vibrational circular dichroism

Chemical Communications, Journal Year: 2024, Volume and Issue: 60(76), P. 10439 - 10450

Published: Jan. 1, 2024

Secondary metabolites from land and marine (micro)organisms have been at the focus of drug discovery process for many years. One reasons this success is nature's incredible ability to create intricate molecular scaffolds. Such structural richness, however, makes elucidation, absolute configuration assignment in particular, a challenging process. Vibrational circular dichroism (VCD) has emerged as one most reliable versatile methods unambiguously assign both conformations chiral molecules solution. Although VCD no longer curiosity field spectroscopy after 50 years since its first report, it still underutilized by natural product chemists worldwide varying reasons. Herein, we highlight evolution application chemistry, focusing on strengths well points that need improvement. General guidelines correct stereochemical studies are also provided.

Language: Английский

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Pitfalls in the Optimization of Conformer Populations to Maximize the Similarity between Predicted and Experimental Chiroptical Spectra

The Journal of Physical Chemistry A, Journal Year: 2023, Volume and Issue: unknown

Published: Dec. 28, 2023

The conformational populations of pantolactone, epichlorohydrin, and N-acetyl-tryptophan methyl ester were investigated by using similarity analysis between their calculated experimental chiroptical spectra. By performing the on pantolactone two different methods, namely, vibrational circular dichroism Raman optical activity, it was found that optimal sets conformers do not match indicating obtained optimizing spectra are unlikely to be more accurate than energy-based Boltzmann populations. Also, for would often vary significantly if each populated discarded, one at a time. This observation indicates set can provide acceptable predicted Therefore, correct cannot accurately determined analysis.

Language: Английский

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Revisiting the Absolute Configuration of Peyssonnoside A Using Vibrational Circular Dichroism Spectroscopy

Symmetry, Journal Year: 2024, Volume and Issue: 16(2), P. 133 - 133

Published: Jan. 23, 2024

Peyssonnoside A is an unusual natural product consisting of a diterpene unit and sulfonated monosaccharide. The experimental theoretical comparison Optical Rotatory Dispersion (ORD) quantitative Nuclear Magnetic Resonance (NMR) data provided strong evidence for the stereochemistry unit. However, predicted Vibrational Circular Dichroism (VCD) spectra at B3LYP/6-311++G(2d,2p) level showed poor correlation to corresponding spectra, preventing independent absolute configuration (AC) determination from VCD analysis. New calculations using B3PW91 functional 6-311G(3df,2pd) basis set suggest that we can now independently confidently assign AC through analyses. use f-polarization functions responsible current successful assignment, compared previously failed This study highlights two important points: (a) importance multiple levels theories satisfactorily reproducing (b) comparisons similarity indices, it consider not only but also absorption spectra.

Language: Английский

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