Two-dimensional Spectroscopy Research Articles

Tuning the Fermi resonance of pyridine using ethanol molecules

The Fermi resonance (FR) phenomenon is prevalent in infrared and Raman spectroscopy, and it can be observed in a variety of molecules. In particular, pyridine is a compound that has two Fermi doublets: ν1 ∼ ν12 and ν1 + ν6 ∼ ν8. To analyze the effect of environmental changes on the FR, this study first investigated the Raman spectra of pyridine mixed with ethanol at different concentrations. Results indicated that the FR parameters exhibited a nonlinear dependence on the pyridine concentration fractions, and changing the concentration fraction of pyridine led to different hydrogen bond strengths. Second, the interaction mechanism of pyridine-ethanol binary solutions was analyzed by two-dimensional correlation Raman spectroscopy (2DCRS). In addition, high-pressure Raman spectra of a 50% pyridine-ethanol binary solution were measured up to a pressure of 19.65 GPa by a diamond anvil cell technique, and the phase transition of the binary solution occurred at 6.35 GPa. Finally, the impact of ethanol on the FR of pyridine was determined by deducing the FR parameters at different pressures. The turning point at 6.35 GPa was consistent with the Raman frequency–pressure relationships. The results demonstrated that changes in the intensity of ν1 did not affect the FR of ν1 + ν6 ∼ ν8, whereas the undisturbed frequency ν1 still played a role in the FR. When the pressure was compressed to 13.36 GPa, the disappearance of the Raman peaks (ν1 and ν1′) was attributed to the tuning of the molecular symmetry by pressure during the phase transition.

Optical two-dimensional coherent spectroscopy of cold atoms.

We report an experimental demonstration of optical two-dimensional coherent spectroscopy (2DCS) in cold atoms. The experiment integrates a collinear 2DCS setup with a magneto-optical trap (MOT), in which cold rubidium (Rb) atoms are prepared at a temperature of approximately 200 µK and a number density of 1010 cm-3. With a sequence of femtosecond laser pulses, we first obtain one-dimensional second- and fourth-order nonlinear signals and then acquire both one-quantum and zero-quantum 2D spectra of cold Rb atoms. The capability of performing optical 2DCS in cold atoms is an important step toward optical 2DCS study of many-body physics in cold atoms and ultimately in atom arrays and trapped ions. Optical 2DCS in cold atoms/molecules can also be a new avenue to probe chemical reaction dynamics in cold molecules.

Two-dimensional spectroscopy of two-dimensional materials: A Mahan-Nozières-De Dominicis model of electron-exciton scattering

In this paper, we provide a systematically convergable and efficient numerical approach to simulate multitime correlation functions in the Mahan-Nozi\`eres-De Dominicis model, which crudely mimics the spectral properties of doped two-dimensional (2D) semiconductors such as monolayer transition metal dichalcogenides. We apply this approach to study the coherent 2D electronic spectra of the model. We show that several experimentally observed phenomena, such as peak asymmetry and coherent oscillations in the waiting-time dependence of the trion-exciton cross peaks of the 2D rephasing spectrum, emerge naturally in our approach. Additional features are also present which find no correspondence with experimentally expected behavior. We trace these features to the infinite hole mass property of the model. We use this understanding to construct an efficient approach which filters out configurations associated with the lack of exciton recoil, enabling the connection to previous work and providing a route to the construction of realistic 2D spectra over a broad doping range in 2D semiconductors.

Impact ionization in low-band-gap semiconductors driven by ultrafast terahertz excitation: Beyond the ballistic regime

Using two-dimensional THz spectroscopy in combination with numerical models, we investigate the dynamics linked to carrier multiplication caused by high-field THz excitation of the low-gap semiconductor InSb. In addition to previously reported dynamics connected with quasiballistic carrier dynamics, we observe other spectral and temporal features that we attribute to impact ionization for peak fields above 60 kV/cm, which continue up to the maximum investigated peak field of 430 kV/cm. At the highest fields we estimate a carrier multiplication factor greater than 10 due to impact ionization, which is well-reproduced by a numerical simulation of the impact ionization process which we have developed.

Hydrogen Transfer Hydrogenolysis of Organosolv Chinese Fir Lignin to Monophenols over NiZnAlOx Catalyst

Lignin is the only naturally renewable aromatized polymer consisting of several phenyl propane structures linked by C–O and C–C bonds, so lignin can be depolymerized into value-added chemicals or liquid fuels. In this study, M5Zn5AlOx (M = Co, Ni and Cu) catalysts were obtained by the co-precipitation method and then were used in organosolv lignin depolymerization. Among these catalysts, the Ni5Zn5AlOx catalyst possessed the largest surface area and abundant surface oxygen vacancies as well as strong acidic sites on the surface, giving the highest yield of monophenols (about 14.49 wt %). The effect of Ni/Zn ratios on the lignin depolymerization was also investigated, and it was found that the surface area and the proportion of surface oxygen vacancies and strong acidic sites of the NiZnAlOx catalysts increased and then decreased with the Ni/Zn ratios increasing. Similarly, the yield of monomeric compounds increased and then decreased with the Ni/Zn ratios increasing. The highest yield of monophenols was 17.18 wt % obtained over the Ni3Zn7AlOx catalyst, a remarkable monomer yield from organosolv lignin. The two-dimensional 1H-13C heteronuclear single-quantum coherence nuclear magnetic resonance spectroscopy of bio-oil revealed that the linkage bonds in lignin could be effectively broken over the Ni3Zn7AlOx catalyst. This study provided an effective route to obtain high-value chemicals from organosolv lignin under nickel-based catalysts.

Development and Implementation of MBR Monitoring: Use of 2D Fluorescence Spectroscopy.

The monitoring of a membrane bioreactor (MBR) requires the assessment of both biological and membrane performance. Additionally, the development of membrane fouling and the requirements for frequent membrane cleaning are still major concerns during MBR operation, requiring tight monitoring and system characterization. Transmembrane pressure is usually monitored online and allows following the evolution of membrane performance. However, it does not allow distinguishing the fouling mechanisms occurring in the system or predicting the future behavior of the membrane. The assessment of the biological medium requires manual sampling, and the analyses involve several steps that are labor-intensive, with low temporal resolution, preventing real-time monitoring. Two-dimensional fluorescence spectroscopy is a comprehensive technique, able to assess the system status at real-time without disturbing the biological system. It provides large sets of data (system fingerprints) from which meaningful information can be extracted. Nevertheless, mathematical data analysis (such as machine learning) is essential to properly extract the information contained in fluorescence spectra and correlate it with operating and performance parameters. The potential of 2D fluorescence spectroscopy as a process monitoring tool for MBRs is, therefore, discussed in the present work in view of the actual knowledge and the authors' own experience in this field.

Energy cascades in donor-acceptor exciton-polaritons observed by ultrafast two-dimensional white-light spectroscopy

Exciton-polaritons are hybrid states formed when molecular excitons are strongly coupled to photons trapped in an optical cavity. These systems exhibit many interesting, but not fully understood, phenomena. Here, we utilize ultrafast two-dimensional white-light spectroscopy to study donor-acceptor microcavities made from two different layers of semiconducting carbon nanotubes. We observe the delayed growth of a cross peak between the upper- and lower-polariton bands that is oftentimes obscured by Rabi contraction. We simulate the spectra and use Redfield theory to learn that energy cascades down a manifold of new electronic states created by intermolecular coupling and the two distinct bandgaps of the donor and acceptor. Energy most effectively enters the manifold when light-matter coupling is commensurate with the energy distribution of the manifold, contributing to long-range energy transfer. Our results broaden the understanding of energy transfer dynamics in exciton-polariton systems and provide evidence that long-range energy transfer benefits from moderately-coupled cavities.

Two-dimensional confocal photoluminescence spectroscopy of nonpolar a-plane InGaN/GaN multiple quantum wells

A nonplanar a-plane (11–20) and c-plane (0001) InGaN/GaN multiple quantum wells (MQWs) structures were grown an r-plane (1–102) and a c-plane (0001) sapphire (Al2O3) substrate, respectively. Using two-dimensional confocal photoluminescence spectroscopy, the spatially resolved optical characteristics of two samples are examined. We found that the integrated PL intensity of a-plane MQWs is 88.4% greater than that of c-plane MQWs based on our analysis of PL spectra taken at room temperature. According to results from two-dimensional confocal PL mapping, the a-plane MQWs have a more uniform distribution of PL intensity according to two-dimensional space than the c-plane MQWs. Compared to typical c-plane InGaN/GaN MQWs, the experimental results of the two-dimensional confocal PL peak position distribution and PL spectrum skewness map of nonpolar a-plane InGaN/GaN MQWs show increased uniformity of the InGaN alloy in two-dimensional space and a decreased proportion of multiple PL peaks buried in the PL spectrum. These findings are ascribed to higher electron and hole wavefunction overlap caused by decreased the quantum-confinement Stark effect and increased the uniformity of InGaN alloy in the two-dimensional space of nonpolar a-plane InGaN QW.

Role of MRSI Major Metabolite Ratios in Differentiating Between Intracerebral Ring-Enhancing Neoplastic and Non-Neoplastic Lesions, High-Grade Gliomas and Metastases, and High-Grade and Low-Grade Gliomas.

Introduction The purpose of this study was to determine whether multi-voxel magnetic resonance spectroscopic imaging (MRSI) can differentiate between intracranial neoplastic and non-neoplastic and between neoplastic ring-enhancing lesions (RELs) based on differences in major metabolite ratios in their enhancing and peri-enhancing regions. Methods In a prospective observational study involving patients with an intracerebral RELs, MRSI using the two-dimensional multi-voxel point-resolved spectroscopy (PRESS) chemical-shift imaging (CSI) sequence at an echo time (TE) of 135 milliseconds (ms) was performed on a total of 38 patients. Of 38 lesions, 23 (60.5%) were neoplastic and 15 (39.5%) were non-neoplastic. Of the 23 neoplastic lesions, 12 were high-grade gliomas (HGGs), seven were metastases, and four were low-grade gliomas (LGGs). Major metabolite ratios, i.e., choline-to-N-acetylaspartate (Cho/NAA), choline-to-creatine (Cho/Cr), and N-acetylaspartate-to-creatine (NAA/Cr), were calculated in the enhancing and peri-enhancing regions of the RELs. A Mann-Whitney U test was run to determine differences in metabolite ratios at different voxel locations between neoplastic versus non-neoplastic lesions, HGGs versus metastatic lesions, and HGGs versus LGGs. A receiver operating characteristic (ROC) curve analysis was performed to derive cut-off values for Cho/NAA and NAA/Cr ratios in the enhancing and peri-enhancing portions of the lesions. Results The sensitivity, specificity, positive predictive value, and negative predictive valuefor categorizing an REL in either neoplastic or non-neoplastic lesions using MRSI with magnetic resonance imaging (MRI) were 91.3%, 73.3%, 84%, and 84.6%, respectively. There was a statistically significant difference between Cho/NAA (p = 0.006) and NAA/Cr (p = 0.021) ratios in the enhancing region of 23 neoplastic and 15 non-neoplastic lesions. In the voxel placed in the peri-enhancing portions, the differences between Cho/Cr ratios were just significant (p = 0.047). A cut-off score of Cho/NAA >1.67 in the enhancing regions gave a sensitivity of 82.6% and specificity of 60%. The cut-off score for NAA/Cr of <0.80 in the enhancing regions showed a sensitivity and specificity of 60.9% and 86.7%, respectively. Of the 23 neoplastic lesions, 12 HGGs and seven metastases were differentiated using the Cho/NAA ratio in the peri-enhancing region with a cut-off value of 1.21, sensitivity of 100%, and specificity of 85%. A cut-off value of Cho/Cr ≥1.45 in the peri-enhancing regions showed a sensitivity of 83% and a specificity of 71.4%. For discriminating between 12 HGGs and four LGGs both from the 23 neoplastic REL group, using the cut-off score for Cho/NAA in the enhancing portions ≥4.16 showed a sensitivity of 0.75 and specificity of 100%. In the peri-enhancing regions, a cut-off score of ≥2.07 provided a sensitivity and specificity of 83% and 100%, respectively. Conclusion Conventional MRI sometimes poses a diagnostic challenge in distinguishing between neoplastic and non-neoplastic lesions and other neoplastic RELs. Interpreting MRSI findings by comparing the major metabolite ratios in the enhancing and peri-enhancing regions of these lesions may enable distinction between the two.

Ultrafast Continuum IR Generation and Its Application in IR Spectroscopy

The spectral range of femtosecond time-resolved infrared spectroscopy is limited by the bandwidth of mid-IR pulses (100~400 cm-1) generated from the combination of Ti:Sapphire amplifier, Optical Parametric Amplifier (OPA), and Difference Frequency Generation (DFG). To overcome this limitation, we implement a compact continuum mid-IR source producing ultrafast pulses that span the frequency range from 1000 to 4200 cm-1 (from 10 to 2.4 μm), which utilize the mixing of fundamental, second-harmonic, and third-harmonic of 800 nm pulse in the air. After building an IR spectrometer with continuum IR and a monochromator, we found that the distortion of the measured IR spectrum originated from the contamination of higher-order diffraction. We used bandpass filters to eliminate the higher-order contributions and correct the measured IR spectrum. We further characterized the spectral properties of fundamental, second-harmonic, and third-harmonic fields after the plasmonic filamentation process, which helps to improve the efficiency of the continuum IR generation. Using the generated continuum IR pulses, we measured the IR absorption spectrum of a water-benzonitrile mixture, which was found to be consistent with the spectrum obtained with a commercial FT-IR spectrometer. The present work will be useful for the efficient generation of continuum IR pulses for IR pump-probe and two-dimensional IR spectroscopy experiments in the future.

An integrated solid-state lithium-oxygen battery with highly stable anionic covalent organic frameworks electrolyte

<h2>Summary</h2> Rechargeable solid-state lithium-oxygen (Li-O₂) batteries are considered promising candidates for next-generation energy storage systems. However, the development of solid-state Li-O₂ batteries has been limited by the lack of solid-state electrolytes (SSEs) with high ionic conductivities and high stability toward air/metal Li. To address this challenge, we report the three-dimensional covalent organic framework (3D COF) CD-COF-Li with a prominent Li-ion conductivity of 2.7 × 10⁻³ S cm⁻¹ as the SSE for Li-O₂ batteries. The ion transport in the porous COFs is clarified through two-dimensional exchange nuclear magnetic resonance spectroscopy (2D-EXSY NMR), which provides a method at the forefront for understanding Li-ion transport in the molecular channel. Solid-state Li-O₂ batteries with CD-COF-Li deliver a high specific capacity (9,340 mAh g⁻¹) and a record cycling life (100 cycles). These findings pave the way for the application of COFs as superior Li-ion conductors in other next-generation solid-state energy storage systems.

High-field ex vivo and in vivo two-dimensional nuclear magnetic resonance spectroscopy in murine brain: Resolving and exploring the molecular environment.

The structural and chemical complexities within the brain pose a challenge that few noninvasive techniques can tackle with the dexterity of nuclear magnetic resonance (NMR) spectroscopy. Still, even with the advent of ultrahigh fields and of cryogenically cooled coils for in vivo research, the superposition of metabolic resonances arising from the brain remains a challenge. The present study explores the potential to tackle this milieu using a combination of two-dimensional (2D) NMR techniques, implemented on murine brains in vivo at 15.2T and ex vivo at 14.1T. While both experiments were affected by substantial inhomogeneous broadenings conveying distinct elongated lineshapes to the cross-peaks, the ability of increased fields to resolve off-diagonal resonances was clear. A comparison between the corresponding conventional and double quantum-filtered correlated spectroscopy traces enabled an improved assignment of in vivo resonances on the basis of more sensitive ex vivo 2D acquisitions, foremost on the basis of homonuclear cross-relaxation-driven correlations for peaks resonating downfield from water, and of heteronuclear correlations at natural abundance for the upfield protons. With the aid of such 2D correlations approximately 29 metabolites could be resolved and identified. This enhanced resolution was used to explore features related to the metabolites' diffusivities, their exposure to water, and their facility to undergo magnetization transfers to amide/amine/hydroxyl resonances. Cross-peaks from main murine brain biomolecules, including choline, creatine, γ-aminobutyric acid, N-acetyl aspartate, glutamine, and glutamate, showed enhancements in several of these various features, opening interesting vistas about metabolite compartmentalization as viewed by these 2D NMR experiments.

Bioabsorbable, elastomer-coated magnesium alloy coils for treating saccular cerebrovascular aneurysms

Cerebral aneurysm embolization is a therapeutic approach to prevent rupture and resultant clinical sequelae. Current, non-biodegradable metallic coils (platinum or tungsten) are the first-line choice to secure cerebral aneurysms. However, clinical studies report that up to 17% of aneurysms recur within 1 year after coiling, leading to retreatment and additional surgery. It would be ideal for the aneurysm coiling material to induce acute thrombotic occlusion, contribute to a tissue development process to fortify the degenerated vessel wall, and ultimately resorb to avoid leaving a permanent foreign body. With these properties in mind, a new fatty amide-based polyurethane urea (PHEUU) elastomer was synthesized and coated on biodegradable metallic (Mg alloy) coils to prepare a bioabsorbable cerebral saccular aneurysm embolization device. The chemical structure of PHEUU was confirmed using two-dimensional nuclear magnetic resonance spectroscopy. PHEUU showed comparable physical properties to elastomeric biodegradable polyurethanes lacking fatty amide immobilization, modest enzymatic degradation profiles in the first 8 wks, inherent antioxidant activity (>70% at 48 h), no cytotoxicity, and better protection for the underlying Mg alloy than poly(lactic-co-glycolic acid) (PLGA) against surface corrosion and cracking. Rat aortic smooth muscle cell attachment and platelet deposition were higher with the PHEUUs compared to bare or PLGA coated Mg alloy in vitro. PHEUU-coated Mg alloy coils showed the potential to design a fully bioabsorbable embolization coil amenable to clinical placement conditions based on computational mechanics modeling and blood-contacting test using an in vitro aneurysm model. In vivo studies using a mouse aneurysm model elicited comparable inflammatory cytokine expression to a commercially available platinum coil.

Synergism between betaine surfactants under high-salt conditions

Foam properties and surface dilational rheology of single and mixed LHSB (lauramidopropyl hydroxyl sulfobetaine)-OAB (oleic amide propyl betaine) surfactants were measured to investigate the synergism between the two components. Experimental results showed obvious synergistic effects in foam stability, dilational modulus, and phase angle between LHSB and OAB. Moreover, interaction parameters were calculated to quantitatively characterize the synergism. The negative interaction parameters between LHSB and OAB demonstrated that there was an attractive interaction between LHSB and OAB, and the attractive interaction contributed to forming the dense surfactant layer at the liquid/air layer, which in turn improved foam stability. The negative values of parameters reached their maximum when the LHSB: OAB molar ratio ranged from 1:1 to 1:2, the same time the foam stability reached its maximum. The interaction between LHSB and OAB was confirmed by 2D NOSEY (two-dimensional nuclear overhauser enhancement spectroscopy) experiments, the interaction between LHSB and OAB could be attributed to the hydrogen bonding or the electrostatic interaction between the hydrophilic groups of the two surfactants.

Spectral, structural, and pharmacological studies of perillaldehyde and myrtenal based benzohydrazides

N-Acylhydrazones have been an interesting scaffold due to their diverse biological activities toward different therapeutic targets. We synthesized seven new N'‐[(E)‐[(4S)‐4‐(prop‐1‐en‐2‐yl)cyclohex‐1‐en‐1‐yl]methylidene]benzohydrazides as well as seven new N'-[(E)-{6,6-dimethylbicyclo[3.1.1]hept-2-en-2-yl}methylidene]benzohydrazides. The structure of synthesized hydrazides has been studied by using X-ray analysis, FT-IR, NMR, and HRMS spectra. Derivatives containing fluorine atoms in position 2 of the phenyl ring display versatile structures in solution and the solid state. The 1H NMR spectra of 3c and 5c measured in DMSO-d6 display at ambient temperature two unequally populated sets of signals. These facts confirm the existence of the two conformers of 3c and 5c of different stability which interconvert by rotation about their C―N bond slowly enough to lead to discrete sets of signals in 1H NMR spectra at room temperature. The kinetics of the conformational interconversion of derivatives 3c and 5c in DMSO-d6 were studied by two-dimensional exchange spectroscopy (2D EXSY). In 1H NMR spectra of 3c and 5c measured in CDCl3 and acetone-d6 was observed the strong splitting of the H-2 signal into a doublet because of H-bond formation between organic fluorine and NH donor. The FT–IR spectra of 3a–g and 5a–g confirmed the presence of the H-bonds N–H···O=C and N–H···N. Hydrazones 3f, 5a, and 5c crystallize in the P1 space group and the asymmetric units contain two pairs of pseudo-centrosymmetric molecules. Hydrazone 5b crystallizes in the P41 space group and the asymmetric units contain only one molecule. In the crystal, the molecules in 3f, 5a and 5b are linked through N―H···O hydrogen bonds, in 5c also N―H···N hydrogen bonds are present. In contrast to the NMR, the X-ray and IR spectra did not give unambiguous evidence of the F···H−N H-bond. The synthesized hydrazones 3c and 3g exhibited excellent antiproliferative effects in Jurkat cells with IC50 values of 3.8 and 4.2 μM, respectively. Our findings indicate that these compounds are promising antitumor agents.

Enzymatic bioconversion of beechwood xylan into the antioxidant 2′-O-α-(4-O-methyl-D-glucuronosyl)-xylobiose

Acidic xylooligosaccharides (XOS), also called aldouronics, are hetero-oligomers of xylose randomly branched with 4-O-methyl-D-glucuronic acid residues linked by α(1 → 2) bonds, which display bioactive properties. We have developed a simple and integrated method for the production of acidic XOS by enzymatic hydrolysis of a glucurono-xylan from beechwood. Among the enzymes screened, Depol 670L (a cellulolytic preparation from Trichoderma reesei) displayed the highest activity (70.3 U/mL, expressed in reducing xylose equivalents). High-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) analysis revealed the formation of a neutral fraction (corresponding to linear XOS, mainly xylose and xylobiose) and a group of more retained products (acidic XOS), which were separated using strong anion-exchange cartridges. The acidic fraction contained a major product, characterized by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry and mono- and two-dimensional nuclear magnetic resonance spectroscopy (NMR) as 2′-O-α-(4-O-methyl-α-D-glucuronosyl)-xylobiose (X2_MeGlcA). Starting from 2 g of beechwood xylan, 1.5 g of total XOS were obtained, from which 225 mg (11% yield) corresponded to the aldouronic X2_MeGlcA. The acidic XOS exhibited higher antioxidant activity (measured by the ABTS·+ discoloration assay) than xylan, whilst neutral XOS displayed no antioxidant activity. This work demonstrates that it is possible to obtain a safe and natural antioxidant by enzymatic biotransformation of hardwood hemicellulose.

Understanding 2D-IR Spectra of Hydrogenases: A Descriptive and Predictive Computational Study

[NiFe] hydrogenases are metalloenzymes that catalyze the reversible cleavage of dihydrogen (H2), a clean future fuel. Understanding the mechanism of these biocatalysts requires spectroscopic techniques that yield insights into the structure and dynamics of the [NiFe] active site. Due to the presence of CO and CN− ligands at this cofactor, infrared (IR) spectroscopy represents an ideal technique for studying these aspects, but molecular information from linear IR absorption experiments is limited. More detailed insights can be obtained from ultrafast nonlinear IR techniques like IRpump-IRprobe and two-dimensional (2D-)IR spectroscopy. However, fully exploiting these advanced techniques requires an in-depth understanding of experimental observables and the encoded molecular information. To address this challenge, we present a descriptive and predictive computational approach for the simulation and analysis of static 2D-IR spectra of [NiFe] hydrogenases and similar organometallic systems. Accurate reproduction of experimental spectra from a first-coordination-sphere model suggests a decisive role of the [NiFe] core in shaping the enzymatic potential energy surface. We also reveal spectrally encoded molecular information that is not accessible by experiments, thereby helping to understand the catalytic role of the diatomic ligands, structural differences between [NiFe] intermediates, and possible energy transfer mechanisms. Our studies demonstrate the feasibility and benefits of computational spectroscopy in the 2D-IR investigation of hydrogenases, thereby further strengthening the potential of this nonlinear IR technique as a powerful research tool for the investigation of complex bioinorganic molecules.

Enantiodetection of Chiral Molecules via Two-Dimensional Spectroscopy.

Enantiodetection of chiral molecules is important to chemical reaction control and biological function designs. Traditional optical methods of enantiodetection rely on the weak magnetic-dipole or electric-quadrupole interactions, and in turn suffer from the weak signal and low sensitivity. We propose a new optical enantiodetection method to determine the enantiomeric excess via two-dimensional (2D) spectroscopy of the chiral mixture driven by three electromagnetic fields. The quantities of left- and right-handed chiral molecules are reflected by the intensities of different peaks on the 2D spectrum, separated by the chirality-dependent frequency shifts resulting from the relative strong electric-dipole interactions between the chiral molecules and the driving fields. Thus, the enantiomeric excess can be determined via the intensity ratio of the peaks for the two enantiomers.

Effect of temperature on Electron-Phonon coupling of carotenoids by Two-Dimensional correlation resonance Raman spectroscopy

Carotenoids, the most prevalent light-absorbing pigments in nature, perform many functions in photosynthetic systems. The Raman and absorption spectra of carotenoids (including lycopene and β-carotene) were measured in the temperature range between 303 K and 83 K. As the temperature decreased, the Huang-Rhys factor and the electron–phonon coupling constant also decreased. Nevertheless, the Raman scattering cross-section increased. The results suggested that lycopene was more sensitive to changes in temperature due to the longer conjugated length and the different open-chain structure as compared to β-carotene. Two-dimensional correlation resonance Raman spectroscopy (2DCRRS) showed a correlation between electron–phonon coupling and changes in temperature. Moreover, the complex mode evolution of lycopene rendered the molecule more sensitive to temperature. Density functional theory (DFT) simulation was used to optimize the geometrical structure, and bond length alternation (BLA) calculation was performed. The result can be applied to investigate the temperature dependence of electron-coupling in π-conjugated molecules.

Triterpene glycosides from the aerial parts of Elsholtzia penduliflora W. W. Smith and their cytotoxic activity

Bio-guided fractionation of the 80% ethanol extract of the aerial parts of Elsholtzia penduliflora W. W. Smith (Lamiaceae) led to the isolation of seven new triterpene glycosides, i.e., pendulosides A–G (1-7), and one known compound (8). Their structures were determined based on extensive spectroscopic analysis, including one- and two-dimensional nuclear magnetic resonance spectroscopy, high-resolution electrospray ionization mass spectroscopy, and the results of hydrolytic cleavage. Compounds 1, 3-5, and 7-8 were tested for cytotoxic activity against two human cancer cell lines in vitro using the MTT assay method. Among them, two compounds (3 and 7) displayed significant cytotoxicities against human lung cancer (A549) cells with IC50 values of 9.01 ± 1.52 μM and 6.18 ± 1.06 μM, respectively, and human breast cancer (MCF-7) cells with IC50 values of 10.98 ± 1.76 μM and 6.82 ± 1.09 μM, respectively. The results suggest that compounds 3 and 7 might be useful for the therapeutic study of cancer.