Modulation of the strength of weak S-H⋯O hydrogen-bond: Spectroscopic study of the complexes of 2-flurothiophenol with methanol and ethanol.

Spectroscopic exploration of sulfur-centered hydrogen bonding involving a thiol group (S-H) as the hydrogen bond donor is scarce in the literature. Herein, we have investigated 1:1 complexes of 2-fluorothiophenol (2-FTP) with methanol (MeOH) and ethanol (EtOH) in the gas phase to examine the physical characteristics and strength of the S-H⋯O hydrogen bond. Structures, conformations, and the strength of the S-H⋯O interaction are investigated by measuring the electronic and Infrared (IR) spectra of the two complexes employing resonant two-photon ionization, UV-UV hole-burning, and IR-UV double resonance spectroscopic techniques combined with quantum chemical calculations. Three conformers of 2-FTP⋯MeOH and two conformers of 2-FTP⋯EtOH have been detected in the experiment. A comparison of the IR spectra obtained from the experiment with those of the low-energy conformers of 2-FTP⋯MeOH and 2-FTP⋯EtOH predicted from the theory confirms that all the observed conformers of the two complexes are primarily S-H⋯O hydrogen bonded. The IR red-shifts found in the S-H stretching frequencies in 2-FTP⋯MeOH and 2-FTP⋯EtOH concerning that in 2-FTP are ∼76 and ∼88 cm-1, respectively, which are much larger than that was reported earlier in the 2-FTP⋯H2O complex (30 cm-1). The strength and physical nature of different noncovalent interactions, including the S-H⋯O hydrogen bond existing in the complexes, are further analyzed using natural bond orbital analysis, quantum theory of atoms in molecules, and localized molecular orbital-energy decomposition analysis. The current investigation reveals that the S-H⋯O hydrogen bond can be strengthened by judicial choices of the hydrogen bond acceptors of higher proton affinities.

Inhibition of TNBC Cell Growth by Paroxetine: Induction of Apoptosis and Blockage of Autophagy Flux.

The strategy of drug repurposing has gained traction in the field of cancer therapy as a means of discovering novel therapeutic uses for established pharmaceuticals. Paroxetine (PX), a selective serotonin reuptake inhibitor typically utilized in the treatment of depression, has demonstrated promise as an agent for combating cancer. Nevertheless, the specific functions and mechanisms by which PX operates in the context of triple-negative breast cancer (TNBC) remain ambiguous. This study aimed to examine the impact of PX on TNBC cells in vitro as both a standalone treatment and in conjunction with other pharmaceutical agents. Cell viability was measured using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, apoptosis was assessed through flow cytometry, and the effects on signaling pathways were analyzed using RNA sequencing and Western blot techniques. Furthermore, a subcutaneous tumor model was utilized to assess the in vivo efficacy of combination therapy on tumor growth. The results of our study suggest that PX may activate the Ca2+-dependent mitochondria-mediated intrinsic apoptosis pathway in TNBC by potentially influencing the PI3K/AKT/mTOR pathway as well as by inducing cytoprotective autophagy. Additionally, the combination of PX and chemotherapeutic agents demonstrated moderate inhibitory effects on 4T1 tumor growth in an in vivo model. These findings indicate that PX may exert its effects on TNBC through modulation of critical molecular pathways, offering important implications for improving chemosensitivity and identifying potential therapeutic combinations for clinical use.

Near-infrared spectroscopy of H3O+⋯Xn (X = Ar, N2, and CO, n = 1-3).

Near-infrared (NIR) spectra of H3O+⋯Xn (X = Ar, N2, and CO, n = 1-3) in the first overtone region of OH-stretching vibrations (4800-7000 cm-1) were measured. Not only OH-stretching overtones but also several combination bands are major features in this region, and assignments of these observed bands are not obvious at a glance. High-precision anharmonic vibrational simulations based on the discrete variable representation approach were performed. The simulated spectra show good agreement with the observed ones and provide firm assignments of the observed bands, except in the case of X = CO, in which higher order vibrational mode couplings seem significant. This agreement demonstrates that the present system can be a benchmark for high precision anharmonic vibrational computations of NIR spectra. Band broadening in the observed spectra becomes remarkable with an increase of the interaction with the solvent molecule (X). The origin of the band broadening is explored by rare gas tagging experiments and anharmonic vibrational simulations of hot bands.

A chemical accident cause text mining method based on improved accident triangle.

BACKGROUND: With the rapid development of China's chemical industry, although researchers have developed many methods in the field of chemical safety, the situation of chemical safety in China is still not optimistic. How to prevent accidents has always been the focus of scholars' attention. METHODS: Based on the characteristics of chemical enterprises and the Heinrich accident triangle, this paper developed the organizational-level accident triangle, which divides accidents into group-level, unit-level, and workshop-level accidents. Based on 484 accident records of a large chemical enterprise in China, the Spearman correlation coefficient was used to analyze the rationality of accident classification and the occurrence rules of accidents at different levels. In addition, this paper used TF-IDF and K-means algorithms to extract keywords and perform text clustering analysis for accidents at different levels based on accident classification. The risk factors of each accident cluster were further analyzed, and improvement measures were proposed for the sample enterprises. RESULTS: The results show that reducing unit-level accidents can prevent group-level accidents. The accidents of the sample enterprises are mainly personal injury accidents, production accidents, environmental pollution accidents, and quality accidents. The leading causes of personal injury accidents are employees' unsafe behaviors, such as poor safety awareness, non-standard operation, illegal operation, untimely communication, etc. The leading causes of production accidents, environmental pollution accidents, and quality accidents include the unsafe state of materials, such as equipment damage, pipeline leakage, short-circuiting, excessive fluctuation of process parameters, etc. CONCLUSION: Compared with the traditional accident classification method, the accident triangle proposed in this paper based on the organizational level dramatically reduces the differences between accidents, helps enterprises quickly identify risk factors, and prevents accidents. This method can effectively prevent accidents and provide helpful guidance for the safety management of chemical enterprises.

Signaling pathways and potential therapeutic targets in acute respiratory distress syndrome (ARDS).

Acute respiratory distress syndrome (ARDS) is a common condition associated with critically ill patients, characterized by bilateral chest radiographical opacities with refractory hypoxemia due to noncardiogenic pulmonary edema. Despite significant advances, the mortality of ARDS remains unacceptably high, and there are still no effective targeted pharmacotherapeutic agents. With the outbreak of coronavirus disease 19 worldwide, the mortality of ARDS has increased correspondingly. Comprehending the pathophysiology and the underlying molecular mechanisms of ARDS may thus be essential to developing effective therapeutic strategies and reducing mortality. To facilitate further understanding of its pathogenesis and exploring novel therapeutics, this review provides comprehensive information of ARDS from pathophysiology to molecular mechanisms and presents targeted therapeutics. We first describe the pathogenesis and pathophysiology of ARDS that involve dysregulated inflammation, alveolar-capillary barrier dysfunction, impaired alveolar fluid clearance and oxidative stress. Next, we summarize the molecular mechanisms and signaling pathways related to the above four aspects of ARDS pathophysiology, along with the latest research progress. Finally, we discuss the emerging therapeutic strategies that show exciting promise in ARDS, including several pharmacologic therapies, microRNA-based therapies and mesenchymal stromal cell therapies, highlighting the pathophysiological basis and the influences on signal transduction pathways for their use.

Pimavanserin tartrate induces apoptosis and cytoprotective autophagy and synergizes with chemotherapy on triple negative breast cancer.

Triple negative breast cancer (TNBC) poses a significant clinical challenge due to its lack of targeted therapy options and the frequent development of chemotherapy resistance. Metastasis remains a primary cause of mortality in late-stage TNBC patients, underscoring the urgent need for alternative treatments. Repurposing existing drugs offers a promising strategy for the discovery of novel therapies. In this study, we investigated the potential of pimavanserin tartrate (PVT) as a treatment for TNBC. While previous studies have highlighted PVT's anticancer effects in various cancer types, its activity in TNBC remains unclear. Our investigation aimed to elucidate the anticancer effects and underlying mechanisms of PVT in TNBC. We evaluated the impact of PVT and combination treatments involving PVT on TNBC cell viability, apoptosis, autophagy, and associated signaling pathways. Our findings revealed that PVT may induce mitochondria-dependent intrinsic apoptosis and caused cytoprotective autophagy via the PI3K/Akt/mTOR pathway in TNBC cells in vitro. Notably, our study demonstrated strong synergistic anti-TNBC effects when combining PVT with doxorubicin. We also found PVT showed some efficacies to inhibit TNBC tumor growth in vivo. These results provided valuable insights into the potential of PVT as an anti-TNBC therapeutic and a possible option for enhancing the sensitivity of TNBC cells to conventional chemotherapy drugs. Further studies are needed to determine the activity and mechanism of PVT in inhibiting TNBC.

Ab initio anharmonic analysis of complex vibrational spectra of phenylacetylene and fluorophenylacetylenes in the acetylenic and aromatic C-H stretching region.

Vibrational spectra in the acetylenic and aromatic C-H stretching regions of phenylacetylene and fluorophenylacetylenes, viz., 2-fluorophenylacetylene, 3-fluorophenylacetylene, and 4-fluorophenylacetylene, were measured using the IR-UV double resonance spectroscopic method. The spectra, in both acetylenic and aromatic C-H stretching regions, were complex exhibiting multiple bands. Ab-initio anharmonic calculations with quartic potential using B97D3/6-311++G(d,p) and vibrational configuration interaction were able to capture all important spectral features in both the regions of the experimentally observed spectra for all four molecules considered in the present work. Interestingly, for phenylacetylene, the spectrum in the acetylenic C-H stretching region emerges due to anharmonic coupling of modes localized on the acetylenic moiety along with the other ring modes, which also involve displacements on the acetylenic group, which is in contrast to what has been proposed and propagated in the literature. In general, this coupling scheme is invariant to the fluorine atom substitution. For the aromatic C-H stretching region, the observed spectrum emerges due to the coupling of the C-H stretching with C-C stretching and C-H in-plane bending modes.

Broadband phase shifter based on SiN-MoS2 integrated racetrack resonator.

As the critical device of microwave photonics and optical communication, the low-loss and high-efficiency optical phase shifter has attracted intense attention in photonic integrated circuits. However, most of their applications are restricted to a particular band. Little is known about the characteristics of broadband. In this paper, an SiN-MoS2 integrated broadband racetrack phase shifter is demonstrated. The coupling region and the structure of the racetrack resonator are elaborately designed to improve the coupling efficiency at each resonance wavelength. The ionic liquid is introduced to form a capacitor structure. Then, the effective index of the hybrid waveguide can be efficiently tuned by adjusting the bias voltage. We achieve a phase shifter with a tunable range covering all the WDM bands and even up to 1900 nm. The highest phase tuning efficiency is measured to be 72.75 pm/V at 1860 nm, and the corresponding half-wave-voltage-length product is calculated as 0.0608 V·cm.

Repurposing fluphenazine to suppress melanoma brain, lung and bone metastasis by inducing G0/G1 cell cycle arrest and apoptosis and disrupting autophagic flux.

Brain metastasis is the main cause of treatment failure and melanoma-related death. Inadequate concentrations of therapeutic drugs in the brain due to the blood-brain barrier (BBB) pose a major challenge in the treatment of brain metastasis. Antipsychotics can cross the BBB to reach the brain. Fluphenazine (FPZ) inhibits the survival of melanoma cells in vitro. However, its efficacy in suppressing the metastasis of melanoma, especially brain metastasis, remains unknown. Therefore, we explored whether fluphenazine (FPZ) can be repurposed for treating melanoma metastasis. A subcutaneous tumor model, and experimental metastasis models that simulate the outgrowth of melanoma cells in the brain, lung, and bone were established to verify the inhibitory effect of FPZ on melanoma cells. FPZ showed potential inhibitory effects against melanoma both in vivo and in vitro. It induced G0/G1 phase arrest and-mitochondrion-mediated intrinsic apoptosis, and inhibited autophagic flux in melanoma cells in vitro. In vivo, subcutaneous tumor, brain, lung, and bone models of metastatic melanoma were established. Intraperitoneal injection of FPZ (8 mg/kg) significantly inhibited melanoma growth in the subcutaneous and experimental metastasis models. In a lung metastasis model, FPZ reduced the proportion of M2 macrophages and increased the proportion of CD8+ T cells and NK cells in vivo, thereby promoting an anticancer immune response. The findings of this study indicate that FPZ is a potential drug candidate for treating metastatic melanoma.

Analysis of Risk Factors of Coal Chemical Enterprises Based on Text Mining.

Coal chemical enterprises have many risk factors, and the causes of accidents are complex. The traditional risk assessment methods rely on expert experience and previous literature to determine the causes of accidents, which has the problems such as lack of objectivity and low interpretation ability. Analyzing the accident report helps to identify typical accident risk factors and determines the accident evolution rule. However, experts usually judge this work manually, which is subjective and time-consuming. This paper developed an improved approach to identify safety risk factors from a volume of coal chemical accident reports using text mining (TM) technology. Firstly, the accident report was preprocessed, and the Term Frequency Inverse Document Frequency (TF-IDF) was used for feature extraction. Then, the K-means algorithm and apriori algorithm were developed to cluster and for the association rule analysis of the vectorized documents in the TF-IDF matrix, respectively to quickly identify the hidden risk factors and the relationship between risk factors in the accident report and to propose targeted safety management measures. Using the sample data of 505 accidents in a large coal chemical enterprise in Western China in the past seven years, the enterprise accident reports were analyzed by text clustering analysis and association rule analysis methods. Through the analysis, six accident clusters and 13 association rules were obtained, and the main risk factors of each accident cluster were further mined, and the corresponding management suggestions were put forward for the enterprise. This method provides a new idea for coal chemical enterprises to make safety management decisions and helps to prevent safety accidents.

OSW-1 induces apoptosis and cyto-protective autophagy, and synergizes with chemotherapy on triple negative breast cancer metastasis.

PURPOSE: Triple-negative breast cancer (TNBC) is the most malignant subtype of breast cancer. As yet, chemotherapy with drugs such as doxorubicin is the main treatment strategy. However, drug resistance and dose-dependent toxicities restrict their clinical use. Natural products are major sources of anti-tumor drugs. OSW-1 is a natural compound with strong anti-cancer effects in several types of cancer, but its effects on the efficacy of chemotherapy in TNBC and its underlying mechanism remain unclear. METHODS: The inhibitory activities of OSW-1 and its combination with several chemotherapy drugs were tested using in vitro assays and in vivo subcutaneous and metastatic mouse TNBC models. The effects of the mono- and combination treatments on TNBC cell viability, apoptosis, autophagy and related signaling pathways were assessed using MTT, flow cytometry, RNA sequencing and immunology-based assays. In addition, the in vivo inhibitory effects of OSW-1 and (combined) chemotherapies were evaluated in subcutaneous and metastatic mouse tumor models. RESULTS: We found that OSW-1 induces Ca2+-dependent mitochondria-dependent intrinsic apoptosis and cyto-protective autophagy through the PI3K-Akt-mTOR pathway in TNBC cells in vitro. We also found that OSW-1 and doxorubicin exhibited strong synergistic anti-TNBC capabilities both in vivo and in vitro. Combination treatment strongly inhibited spontaneous and experimental lung metastases in 4T1 mouse models. In addition, the combination strategy of OSW-1 + Carboplatin + Docetaxel showed an excellent anti-metastatic effect in vivo. CONCLUSIONS: Our data revealed the mode of action and molecular mechanism underlying the effect of OSW-1 against TNBC, and provided a useful guidance for improving the sensitivity of TNBC cells to conventional chemotherapeutic drugs, which warrants further investigation.

Enhanced fire-proofing performance and crystallizability of bio-based poly(L-lactic acid): Dual functions of a Schiff base-containing synergistic flame retardant.

Poly(L-lactic acid) (PLA) is a kind of important bio-macromolecule which can be prepared via fermentation of starch of maize and sweet potato. Flammability and extremely poor crystallizability limited its wide application. In this work, a novel Schiff base derivate (CP) was synthesized and, combined with ammonium polyphosphate (APP) as a synergistic flame retardant and nucleating agent to investigate its effects on LOI, UL-94 rating, thermal stability, combustion behavior and crystallizability of PLA. With loading of 5%CP/10%APP, PLA showed a significantly enhanced LOI and passed V-0 fire-safety rating with self-extinguish effect. PLA/5%CP/10%APP presented the lowest pHRR, THR and TSR, and highest char residue yield, FPI and FRI in cone calorimetry test, indicating an excellent flame retardancy effect, enhanced fire safety and longer escaping time in the fire. A continuous, compact and thick char layer structure formed as a protective barrier in combustion process, to enhance heat-insulating and oxygen resistance property, thermal stability and smoke-suppressing capacity of PLA. Flame retardancy mechanism was proposed and discussed based on comprehensive and in-depth characterization techniques. Also, 5%CP/10%APP presented a good nucleation effect to enormously increase crystallizability and shorten crystallization time of PLA.

Muscle-to-tumor crosstalk: The effect of exercise-induced myokine on cancer progression.

Physical exercise has gradually become a focus in cancer treatment due to its pronounced role in reducing cancer risk, enhancing therapeutic efficacy, and improving prognosis. In recent decades, skeletal muscles have been considered endocrine organs, exerting their biological functions via the endocrine, autocrine, and paracrine systems by secreting various types of myokines. The amount of myokines secreted varies depending on the intensity, type, and duration of exercise. Recent studies have shown that muscle-derived myokines are highly involved the effects of exercise on cancer. Multiple myokines, such as interleukin-6 (IL-6), oncostatin M (OSM), secreted protein acidic and rich in cysteine (SPARC), and irisin, directly mediate cancer progression by influencing the proliferation, apoptosis, stemness, drug resistance, metabolic reprogramming, and epithelial-mesenchymal transformation (EMT) of cancer cells. In addition, IL-6, interleukin-8 (IL-8), interleukin-15 (IL-15), brain-derived neurotrophic factor (BDNF), and irisin can improve obesity-induced inflammation by stimulating lipolysis of adipose tissues, promoting glucose uptake, and accelerating the browning of white fat. Furthermore, some myokines could regulate the tumor microenvironment, such as angiogenesis and the immune microenvironment. Cancer cachexia occurs in up to 80% of cancer patients and is responsible for 22%-30% of patient deaths. It is characterized by systemic inflammation and decreased muscle mass. Exercise-induced myokine production is important in regulating cancer cachexia. This review summarizes the roles and underlying mechanisms of myokines, such as IL-6, myostatin, IL-15, irisin, fibroblast growth factor 21 (FGF21) and musclin, in cancer cachexia. Through comprehensive analysis, we conclude that myokines are potential targets for inhibiting cancer progression and the associated cachexia.

Improvement of the anticancer efficacy of PD-1/PD-L1 blockade via combination therapy and PD-L1 regulation.

Immune checkpoint molecules are promising anticancer targets, among which therapeutic antibodies targeting the PD-1/PD-L1 pathway have been widely applied to cancer treatment in clinical practice and have great potential. However, this treatment is greatly limited by its low response rates in certain cancers, lack of known biomarkers, immune-related toxicity, innate and acquired drug resistance, etc. Overcoming these limitations would significantly expand the anticancer applications of PD-1/PD-L1 blockade and improve the response rate and survival time of cancer patients. In the present review, we first illustrate the biological mechanisms of the PD-1/PD-L1 immune checkpoints and their role in the healthy immune system as well as in the tumor microenvironment (TME). The PD-1/PD-L1 pathway inhibits the anticancer effect of T cells in the TME, which in turn regulates the expression levels of PD-1 and PD-L1 through multiple mechanisms. Several strategies have been proposed to solve the limitations of anti-PD-1/PD-L1 treatment, including combination therapy with other standard treatments, such as chemotherapy, radiotherapy, targeted therapy, anti-angiogenic therapy, other immunotherapies and even diet control. Downregulation of PD-L1 expression in the TME via pharmacological or gene regulation methods improves the efficacy of anti-PD-1/PD-L1 treatment. Surprisingly, recent preclinical studies have shown that upregulation of PD-L1 in the TME also improves the response and efficacy of immune checkpoint blockade. Immunotherapy is a promising anticancer strategy that provides novel insight into clinical applications. This review aims to guide the development of more effective and less toxic anti-PD-1/PD-L1 immunotherapies.

An ab initio anharmonic approach to IR, Raman and SFG spectra of the solvated methylammonium ion.

The methylammonium ion (CH3NH3+, or noted as MA-H+) is one of the smallest organic ammonium ions that play important roles in organic-inorganic halide perovskites. Despite the simple structure, the vibrational spectra of MA-H+ exhibit complicated features in the 3 µm region which are sensitive to the solvation environment. In the present work, we have applied the ab initio anharmonic algorithm at the CCSD/aug-cc-pVDZ level to simulate the IR and Raman spectra of the solvated methylammonium ion, MA-H+⋯X3, where X denotes the solvent molecules, to understand the Fermi resonance mechanism in which the overtones of NH bending modes are coupled with the fundamentals of NH stretching modes. The spectral features of the solvated clusters with proper solvent species resemble those observed in the perovskite crystal, indicating that they have similar solvation environments and hydrogen bond interactions. Therefore, a linkage between the gas-phase cluster models and the condensed-phase materials can be established, and our simulations and anharmonic analyses help in interpreting the spectral assignments of the observed IR and Raman spectra of perovskites reliably. Furthermore, we have extended this approach to the SFG spectra to demonstrate the selective appearance of bands depending on both the beam polarization configurations and the symmetry of vibrational modes.

Infrared Spectroscopy and Anharmonic Vibrational Analysis of (H2O-Krn)+ (n = 1-3): Hemibond Formation of the Water Radical Cation.

The hemibond is a nonclassical covalent bond formed between a radical (cation) and a closed shell molecule. The hemibond formation ability of water has attracted great interest, concerning its role in ionization of water. While many computational studies on the water hemibond have been performed, clear experimental evidence has been hardly reported because the hydrogen bond formation overwhelms the hemibond formation. In the present study, infrared photodissociation spectroscopy is applied to (H2O-Krn)+ (n = 1-3) radical cation clusters. The observed spectra of (H2O-Krn)+ are well reproduced by the anharmonic vibrational simulations based on the hemibonded isomer structures. The firm evidence of the hemibond formation ability of water is revealed.

Understanding Fermi resonances in the complex vibrational spectra of the methyl groups in methylamines.

Vibrational spectra of the methyl groups in mono-methylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA) monomers and their clusters were measured in three experimental set-ups to capture their complex spectral features as a result of bend/umbrella-stretch Fermi resonance (FR). Multiple bands were observed between 2800 and 3000 cm-1 corresponding to the methyl groups for MMA and DMA. On the other hand, the corresponding spectrum of TMA is relatively simple, exhibiting only four prominent bands in the same frequency window, even though TMA has a larger number of methyl groups. The discrete variable representation (DVR) based ab initio anharmonic algorithm with potential energy surface (PES) at CCSD/aug-cc-pVDZ quality is able to capture all the experimentally observed spectral features across all three amines, and the constructed vibrational Hamiltonian was used to analyze the couplings that give rise to the observed FR patterns. It was observed that the vibrational coupling among CH stretch modes on different methyl groups is weak (less than 2 cm-1) and stronger vibrational coupling is found to localize within a methyl group. In MMA and DMA, the complex feature between 2850 and 2950 cm-1 is a consequence of closely packed overtone states that gain intensities by mixing with the stretching modes. The simplification of the spectral pattern of TMA can be understood by the red-shift of the symmetric CH3 stretching modes by about 80 cm-1 relative to MMA, which causes the symmetric CH3 stretch to shift outside the FR window.

Anharmonic Coupling Revealed by the Vibrational Spectra of Solvated Protonated Methanol: Fermi Resonance, Combination Bands, and Isotope Effect.

Intriguing vibrational features of solvated protonated methanol between 2400-3800 cm-1 are recorded by infrared predissociation spectroscopy. Positions of absorption bands corresponding to OH stretching modes are sensitive to changes in solvation environments, thus leading to changes in these vibrational features. Two anharmonic coupling mechanisms, Fermi resonance (FR) contributed by bending overtones and combination band (CB) associated with intermolecular stretching modes, are known to lead to band splitting of OH stretching fundamentals in solvated hydronium and ammonium. Theoretical analyses based on the ab initio anharmonic algorithm not only well reproduce the experimentally observed features but also elucidate the magnitudes of such couplings and the resulting interplay between these two mechanisms, which provide convincing assignments of the spectral patterns. Moreover, while the hydroxyl group plays the leading role in all the above-mentioned features, the role of the methyl group is also analyzed. Through the H/D isotope substitution, we identify overtones of the methyl-hydroxyl rocking modes and their participation in FR.

Vibrational Signature of Dynamic Coupling of a Strong Hydrogen Bond.

Elucidating the dynamic couplings of hydrogen bonds remains an important and challenging goal for spectroscopic studies of bulk systems, because their vibrational signatures are masked by the collective effects of the fluctuation of many hydrogen bonds. Here we utilize size-selected infrared spectroscopy based on a tunable vacuum ultraviolet free electron laser to unmask the vibrational signatures for the dynamic couplings in neutral trimethylamine-water and trimethylamine-methanol complexes, as microscopic models with only one single hydrogen bond holding two molecules. Surprisingly broad progression of OH stretching peaks with distinct intensity modulation over ∼700 cm-1 is observed for trimethylamine-water, while the dramatic reduction of this progression in the trimethylamine-methanol spectrum offers direct experimental evidence for the dynamic couplings. State-of-the-art quantum mechanical calculations reveal that such dynamic couplings are originated from strong Fermi resonance between the stretches of hydrogen-bonded OH and several motions of the solvent water/methanol, such as translation, rocking, and bending, which are significant in various solvated complexes commonly found in atmospheric and biological systems.

Strong Fermi Resonance Associated with Proton Motions Revealed by Vibrational Spectra of Asymmetric Proton-Bound Dimers.

Infrared spectra for a series of asymmetric proton-bound dimers with protonated trimethylamine (TMA-H+ ) as the proton donor were recorded and analyzed. The frequency of the N-H+ stretching mode is expected to red shift as the proton affinity of proton acceptors increases. The observed band, however, shows a peculiar splitting of approximately 300 cm-1 with the intensity shifting pattern resembling a two-level system. Theoretical investigation reveals that the observed band splitting and its extraordinarily large gap of around 300 cm-1 is a result of strong coupling between the fundamental of the proton stretching mode and overtone states of the two proton bending modes, that is commonly known as Fermi resonance (FR). We also provide a general theoretical model to link the strong FR coupling to the quasi-two-level system. Since the model does not depend on the molecular specification of TMA-H+ , the strong coupling we observed is an intrinsic property associated with proton motions.