The Journal of Physical Chemistry Letters最新文献

Herein, we present the first experimental observation of isolated progesterone, an endogenous steroid, placed in the gas phase by laser ablation and characterized in a supersonic expansion by Fourier transform microwave techniques. Guided by quantum-chemical calculations, we assigned the rotational spectrum of the most stable structure. The internal rotation of the acetyl methyl group led to the observation of A-E doublets in the spectrum, which were analyzed, resulting in a V₃ barrier of 2.4425 ± 0.0025 kJ mol^-1. By fitting over 250 transitions, we determined accurate rotational constants that enabled us to compare the gas phase geometrical parameters with those of crystalline forms and complexes with progesterone receptors. Our results indicate that the A ring of progesterone that contains the ketone group is surprisingly flexible, despite its rigid appearance. This finding is particularly significant, since this ring is an active biological site that is involved in strong intermolecular interactions. Notably, progesterone C₂₁H₃₀O₂ is the largest molecule investigated using laser ablation rotational spectroscopy.

The Alder-ene reaction is a chemical reaction between an alkene with an allylic hydrogen, and it provides an efficient method to construct the C-C bond. Traditionally, this reaction requires catalysts, high temperatures, or photocatalysis. In this study, we reported a high-pressure-induced solid-state Alder-ene reaction of 1-hexene at room temperature without a catalyst. 1-Hexene crystallizes at 4.3 GPa and polymerizes at 18 GPa, forming olefins. By exploring gas chromatography-mass spectrometry, we discovered that 1-hexene generates dimeric products through the Alder-ene reaction under high pressures. The in situ neutron diffraction shows that the reaction process did not obey the topochemical rule. A six-membered ring transition state including one C-H σ bond and two alkene π bonds was evidenced by the theoretical calculation, whose energy obviously decreased when compressed to 20 GPa. Our work offers a novel and promising method to realize the Alder-ene reaction at room temperature without a catalyst, expanding the application of this important reaction.

Organic electrochromic (EC) materials enabling energy-efficient smart windows, human-friendly displays, and highly transparent medical lenses are key for a future society. However, developing organic EC molecules that change from transparent to pure magenta, one of the three primary colors, had been impossible through simple quantum chemical calculations and experiments alone, as it requires sophisticated spectral optimization involving multiple electronic transitions in neutral and radical states. In this study, we successfully identified structures exhibiting colorless-to-pure-magenta switching from 1.2 million triphenylamine derivatives using electronic state descriptors easily obtained from semiempirical molecular orbital calculations with qualitative accuracy. Subsequent organic synthesis and spectroelectrochemical experiments proved that the identified candidate molecules achieve the desired functionality.

The separation of ethylene glycol (EG) and 1,2-butanediol (1,2-BDO) azeotrope in the synthesis process of EG via coal and biomass is becoming increasingly commercial and of environmental importance. Selective adsorption is deemed as the most promising method because of energy savings and environment favorability. In this study, we developed an interpretable decision tree (DT) model to facilitate high-throughput screening of covalent organic frameworks (COFs) as adsorbents for the separation of EG/1,2-BDO mixtures, achieving an R² value of 0.96. The interpretable decision tree analysis has shown that using the difference in isosteric heat (ΔQ_st) between EG (Q_st-EG) and 1,2-BDO (Q_st-BDO), combined with the largest cavity diameter (LCD), is effective for selecting the optimal COFs for EG/1,2-BDO separation. COFs with ΔQ_st greater than 6.5 kcal/mol and an LCD ranging from 3.6 to 4.8 Å typically exhibit superior performance and can serve as preselection criteria to accelerate the screening process. Six COFs with high EG working capacity and exceptional adsorption selectivity for EG/1,2-BDO were selected using the selection principle. All the selected COFs containing strong electronegative groups. The electronegative groups can significantly amplify the disparity in adsorption strength between EG and 1,2-BDO, thereby boosting separation efficiency. The principles proposed in this work can be used to guide the design of COFs for effective separation of EG and 1,2-BDO.

The closed-shell B₇^3-, B₈^2-, and B₉^- species are recognized recently to be electron-precise molecular wheels with three delocalized π-bonds reminiscent of benzene, giving rise to the concept of "borozene". The B₈^2- borozene is especially stable because the B₇ ring has the right size to host a central boron atom. Replacing a B atom by C yields a highly stable closed-shell CB₇^-, which is isoelectronic to B₈^2-. Here we use high-resolution cryogenic photoelectron imaging to probe B₈^- and CB₇^-, revealing rich vibrational information about B₈ and CB₇ and the vibrational modes responsible for the structure changes from the anions to the neutrals. Surprisingly, a minor isomer is also observed for B₈^- and found to be due to Jahn-Teller splitting, analogous to the Jahn-Teller effect in the C₆H₆⁺ benzene cation. The transformation from the B₈^2- borozene to the CB₇^- carborozene is similar to that from the B₁₂H₁₂^2- borane to the CB₁₁H₁₂^- carborane.

Over the past decades, extensive research on large guest molecules (LGMs) has shown that a given LGM exclusively forms only a single type of clathrate hydrate (sI, sII, or sH). This study challenges this prevailing understanding by revealing that certain LGMs can selectively form sII- or sH-type hydrates depending on the environment. This study presents various experimental evidence demonstrating that cyclohexylamine and cyclohexanol exhibit chameleon-like behavior, forming sII or sH hydrates when mixed with sII or sH formers, respectively. This intriguing structural modification induced by coguest inclusion is expected to broaden the scope of physicochemical investigations into hydrate materials. Furthermore, this study also suggests that shifting from the traditional approach, which has predominantly focused on single LGMs, could potentially drive breakthroughs in the development and application of sustainable hydrate-based technologies.

Elemental phosphorus exhibits a remarkable diversity of allotropes, including black, white, and violet phosphorus, each with unique structural and electronic properties. Recently, phosphorus has experienced a renaissance in scientific interest for its potential applications across various fields. Among these, the red phosphorus (RP) possesses a considerable variety of stacking configurations. By analyzing the preference for the P₂₁ building block in Type II, Type IV, and Type V RP allotropes, we proposed a novel butterfly connected structural scheme. This new structure's stability was well confirmed by ab initio calculations. It is characterized as a semiconductor with a band gap of 1.4 eV, exhibiting a red appearance. Additionally, this structure demonstrates ferroelectric behavior, making it an instance of single-element ferroelectric materials. Furthermore, our investigation of chain-type phosphorus structures within carbon nanotubes (CNTs) revealed that the butterfly type connection scheme represents the lowest energy configuration within specifically sized CNTs.

The iron-catalyzed Belousov-Zhabotinsky (BZ) oscillating reaction was investigated in an unstirred reactor by combining Br K-edge X-ray absorption and UV-vis spectroscopies. The experimental data were analyzed through an integrated approach based on principal component analysis, multivariate curve resolution, and ab initio theoretical X-ray absorption spectroscopy (XAS), providing quantitative insights into the properties of the key reaction bromine species while contextually tracking the Fe²⁺ to Fe³⁺ oscillatory transformation. The high-quality XAS experimental data supported by the multivariate and theoretical analyses provide clear-cut evidence of the conversion of bromate, initially predominant in the reaction mixture, to the brominated derivative of the employed allylmalonic acid substrate. The described interdisciplinary method was proven to be valuable to monitor the fate of the main BZ reaction brominated species, which are silent to conventional spectroscopic methods of detection, and the developed approach may support future mechanistic investigations of other oscillatory systems.

Herein, we present the first experimental observation of isolated progesterone, an endogenous steroid, placed in the gas phase by laser ablation and characterized in a supersonic expansion by Fourier transform microwave techniques. Guided by quantum-chemical calculations, we assigned the rotational spectrum of the most stable structure. The internal rotation of the acetyl methyl group led to the observation of A-E doublets in the spectrum, which were analyzed, resulting in a V₃ barrier of 2.4425 ± 0.0025 kJ mol^–1. By fitting over 250 transitions, we determined accurate rotational constants that enabled us to compare the gas phase geometrical parameters with those of crystalline forms and complexes with progesterone receptors. Our results indicate that the A ring of progesterone that contains the ketone group is surprisingly flexible, despite its rigid appearance. This finding is particularly significant, since this ring is an active biological site that is involved in strong intermolecular interactions. Notably, progesterone C₂₁H₃₀O₂ is the largest molecule investigated using laser ablation rotational spectroscopy.