Search Results (13)

Background/Objectives: Rotigotine is a conformationally flexible chiral dopamine agonist, but its solution-phase chiroptical behavior and conformational heterogeneity have not been systematically assessed. This study characterized its electronic circular dichroism (ECD), optical rotatory dispersion (ORD), and vibrational circular dichroism (VCD) responses and evaluated their consistency with its absolute configuration. Methods: ECD and ORD data were acquired for rotigotine ((S)-1) and its simplified analog (S)-2 in acetonitrile and methanol, and VCD spectra were recorded in appropriate deuterated solvents. Conformational searches, Boltzmann weighting, and density functional theory/time-dependent density functional theory calculations were performed. A principal-component-analysis/torsion (PCA-Tor) workflow selected a compact but structurally representative conformer ensemble for (S)-1. Results: In acetonitrile, (S)-1 exhibited a positive Cotton effect (CE) at 208.5 nm and a negative CE at 194.0 nm. The Boltzmann-weighted ECD spectrum reproduced the intense negative band below 200 nm and the positive band near 210 nm. The calculated VCD spectrum agreed with the signs and positions of the main experimental bands in the 1500–1100 cm⁻¹ region. Experimental ORD curves of both compounds were negative in acetonitrile and methanol. The calculations reproduced the sign and overall trend, although their magnitudes were protocol- and population-sensitive. Ring puckering strongly affected the calculated ECD and ORD data, whereas side-chain flexibility expanded the accessible conformational space. Conclusions: The combined results support the known S configuration of rotigotine and demonstrate the value of representative conformational sampling for flexible chiral pharmaceuticals. This study also defines the practical utility and limitations of simplified molecular models in chiroptical analysis. Full article

Poly(l-lactic acid) or poly(l-lactide) (PLLA) is an optically active polymer derived from renewable sources and fully biodegradable. It is known that PLLA assumes a left-handed helix in the solid state and also in solution it still keeps a certain degree of helical structure. Here, we examine the Optical Rotatory Dispersion (ORD) behavior of two grades of PLLA (medium molecular weight and hexadecyl-terminated or high molecular weight for 3D printing) in 13 different solvents and analyze the experimental ORD data through the Moffitt–Yang equation. Furthermore, the ORD data of PLLA in additional 6 solvents were taken from the literature and analyzed with the Moffitt-Yang approach. The results suggest that, also in solution, PLLA maintains the left-handed helix, and the most structurizing and helicogenic solvents for PLLA are ethyl acetate, acetonitrile, and certain chlorinated solvents. The equilibrium association constant (K) and other thermodynamic parameters (ΔG°, ΔH° and ΔS°) between PLLA and polyphenylacetylene (PPA, another helical polymer in the solid state and in solution) were determined in trichloromethane, dichloromethane, and tetrahydrofuran. The K values found suggest a strong helix-helix interaction between the two polymers. The ORD analysis of the PLLA-PPA solutions shows evidence of the extrinsic Cotton effect and confirms the chiral helicity induction between the two polymers with 1:1 complex formation. Full article

Nine new mycophenolic acid derivatives, penicacids O–W (1–9), two first-time reported natural products (10, 11), and five known compounds (12–16), were isolated from a marine-derived fungus Penicillium senticosum RCDB005 found in a South China Sea sediment sample. Their structures were determined using NMR, HRESIMS, and optical rotatory dispersion (ORD) spectra, electronic circular dichroism (ECD) calculations, X-ray crystallography, and modified Mosher’s methods. Eight of these compounds were evaluated for anti-proliferative effects against nine human cancer cell lines and the IC₅₀ values ranged from nM to μM levels. Compounds 5, 7–9 showed potent inhibition activity against MOLM-13 acute myeloid leukemia cells with IC₅₀ values between 0.13 and 1.13 μM. Full article

A comprehensive theory is developed for the chiral optical response of two configurations of the N-oscillator Born–Kuhn model (NOBK): the helically stacked and the corner stacked models. In the helical NOBK model, there is always a chiral response regardless of the value of N, whereas in the corner NOBK, only configurations with even N demonstrate a chiral response. Generally, the magnitudes of optical rotatory dispersion (ORD) and circular dichroism (CD) increase with N when the parameters of each oscillator are fixed. In cases of weak coupling, the spectral shapes of ORD and CD remain invariant, while strong coupling significantly alters the spectral shapes. For large damping, the spectral amplitude becomes smaller, and the spectral features become broader. In the presence of small damping, strong coupling introduces degeneracy in the coupled oscillator system, leading to multiple spectral features in both ORD and CD across the entire spectral region. This simple model can not only help in the design of tunable chiral metamaterials but also enhance our understanding of chiro-optical responses in structures with different configurations. Full article

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

Cercis glabra is a plant belonging to the legume family, whose flowers and barks are commonly used as food and traditional Chinese medicines. However, its leaves are usually disposed of as wastes. This research comprehensively investigated the bioactive constituents of C. glabra leaves, and two new phenolic, ceroffesters A-B (1–2) and thirteen known compounds (3–15) were isolated. Their structures were elucidated by spectroscopic methods such as nuclear magnetic resonance (1D NMR and 2D NMR), high-resolution electrospray ionization mass spectra (HR-ESI-MS), optical rotatory dispersion (ORD) and electronic circular dichroism (ECD). All of them were assessed for their antioxidant activities through ABTS, DPPH and PTIO methodologies, and evaluated for inhibitory activities against two enzymes (mushroom tyrosinase and acetylcholinesterase). As a result, compounds 3–6, 10 and 13 exhibited evident antioxidant activities. Meanwhile, compounds 5, 10 and 13 showed the most potent tyrosinase inhibitory activities, with IC₅₀ of 0.64, 0.65 and 0.59 mM, and compared with the positive control of 0.63 mM (kojic acid). In the initial concentration of 1 mg/mL, compounds 3, 5 and 6 demonstrated moderate inhibitory activities against acetylcholinesterase with 85.27 ± 0.06%, 83.65 ± 0.48% and 82.21 ± 0.09%, respectively, compared with the positive control of 91.17 ± 0.23% (donepezil). These bioactive components could be promising antioxidants, tyrosinase and acetylcholinesterase inhibitors. Full article

Chemical investigation of the Hainan soft coral Sinularia hirta resulted in the isolation and identification of a library of sixteen structurally diverse terpenoids, including a dinorditerpenoid with an uncommon 17,19-dinorxeniaphyllane skeleton, namely sinuhirtone A (7), six new xeniaphyllane-type diterpenoids (1–6), one new norxeniaphyllanoid (8), two new norcaryophyllene-type sesquiterpenoids (9 and 10), together with six known related compounds (11–16). Compounds 1–3 are three new furanone-containing xeniaphyllane-type diterpenoids. The structures of the new compounds, including their absolute configurations, were determined by extensive spectroscopic analysis and a series of quantum chemical calculations, including quantum mechanical-nuclear magnetic resonance (QM–NMR), time-dependent density functional theory–electronic circular dichroism (TDDFT–ECD), and optical rotatory dispersion (ORD) methods. A plausible biosynthetic connection between new compounds 1–9 was also proposed. New compounds 2–4, 7, and 8 were evaluated for in vitro cytotoxicity against four cancer cell lines. Full article

Endophytic fungi are one of prolific sources of bioactive natural products with potential application in biomedicine and agriculture. In our continuous search for antimicrobial secondary metabolites from Fusarium oxysporum R1 associated with traditional Chinese medicinal plant Rumex madaio Makino using one strain many compounds (OSMAC) strategy, two diastereomeric polyketides neovasifuranones A (3) and B (4) were obtained from its solid rice medium together with N-(2-phenylethyl)acetamide (1), 1-(3-hydroxy-2-methoxyphenyl)-ethanone (2) and 1,2-seco-trypacidin (5). Their planar structures were unambiguously determined using 1D NMR and MS spectroscopy techniques as well as comparison with the literature data. By a combination of the modified Mosher’s reactions and chiroptical methods using time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD) and optical rotatory dispersion (ORD), the absolute configurations of compounds 3 and 4 are firstly confirmed and, respectively, characterized as (4S,7S,8R), (4S,7S,8S). Bioassay results indicate that these metabolites 1–5 exhibit weak inhibitory effect on Helicobacter pylori 159 with MIC values of ≥16 μg/mL. An in-depth discussion for enhancement of fungal metabolite diversity is also proposed in this work. Full article

Chiral materials, which show different optical behaviors when illuminated by left or right circularly polarized light due to broken mirror symmetry, have greatly impacted the field of optical sensing over the past decade. To improve the sensitivity of chiral sensing platforms, enhancing the chiroptical response is necessary. Metasurfaces, which are two-dimensional metamaterials consisting of periodic subwavelength artificial structures, have recently attracted significant attention because of their ability to enhance the chiroptical response by manipulating amplitude, phase, and polarization of electromagnetic fields. Here, we reviewed the fundamentals of chiroptical metasurfaces as well as categorized types of chiroptical metasurfaces by their intrinsic or extrinsic chirality. Finally, we introduced applications of chiral metasurfaces such as multiplexing metaholograms, metalenses, and sensors. Full article

Optical rotatory dispersion (ORD) is a beautiful analytical technique for the study of chiral molecules and polymers. In this study, ORD was applied successfully to follow the degree of polycondensation of l-(+)-lactic acid toward the formation of poly(lactic acid) oligomers (PLAO) and high molecular weight poly(l-lactic acid) (PLLA) in a simple esterification reaction equipment. PLLA is a biodegradable polymer obtainable from renewable raw materials. The racemization of the intrinsically isotactic PLLA through thermal treatment can be easily followed through the use of ORD spectroscopy. Organic or molecular electronics is a hot topic dealing with the combination of π-conjugated organic compounds and polymers with specific properties (e.g., chirality) which can be exploited to construct optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) high efficiency cells, switchable chirality devices, organic field-effect transistors (OFETs), and so on. ORD spectroscopy was applied to study either the gigantic optical rotation of PLLA films, as well as to detect successfully the excitonic coupling, occurring in thin solid PLLA green film loaded with a combination of two dyes: SY96 (a pyrazolone dye) and PB16 (the metal-free phthalocyanine pigment). The latter compound PLLA loaded with SY96 and PB16 shows a really gigantic optical activity in addition to typical ORD signal due to exciton coupling and may be considered as a simple and easily accessible model composite of a chiral polymer matrix combined with π-conjugated dyes for molecular electronics studies. Full article

Radicinin and cochliotoxin (1 and 2) two phytotoxic pyranpyran-4,5-diones were isolated together with their close metabolites 3-epi-radicinin, radicinol, and its 3-epimer (3–5), from the culture filtrates of Cochliobolus australiensis, a fungus proposed as mycoherbcide for biocontrol of buffelgrass, a very noxious and dangerous weed. The absolute configuration of cochliotoxin was determined by chiroptical Optical Rotatory Dispersion (ORD), Electronic Circular Dichroism (ECD), and Vibrational Circular Dichroism (VCD)) and computational methods. The same methods were used to confirm that of radicinin, radicinol and their 3-epimers, previously determined with chemical, spectroscopic and ECD methods. Full article

A series of non-proteinogenic amino acids, most of them found quite commonly in the meteorites known as carbonaceous chondrites, were subjected to solid state radiolysis in vacuum to a total radiation dose of 3.2 MGy corresponding to 23% of the total dose expected to be taken by organic molecules buried in asteroids and meteorites since the beginning of the solar system 4.6 × 10⁹ years ago. The radiolyzed amino acids were studied by FT-IR spectroscopy, Differential Scanning Calorimetry (DSC) and by polarimety and Optical Rotatory Dispersion (ORD). It is shown that an important fraction of each amino acid is able to “survive” the massive dose of radiation, while the enantiomeric excess is partially preserved. Based on the results obtained, it is concluded that it is unsurprising to find amino acids even in enantiomeric excess in carbonaceous chondrites. Full article

Many phenomena, including life itself and its biochemical foundations are fundamentally rooted in chirality. Combinatorial methodologies for catalyst discovery and optimization remain an invaluable tool for gaining access to enantiomerically pure compounds in the development of pharmaceuticals, agrochemicals, and flavors. Some exotic metamaterials exhibiting negative refractive index at optical frequencies are based on chiral structures. Chiroptical activity is commonly quantified in terms of circular dichroism (CD) and optical rotatory dispersion (ORD). However, the linear nature of these effects limits their application in the far and near-UV region in highly absorbing and scattering biological systems. In order to surmount this barrier, in recent years we made important advancements on a novel non linear, low-scatter, long-wavelength CD approach called two-photon absorption circular dichroism (TPACD). Herein we present a descriptive analysis of the optics principles behind the experimental measurement of TPACD, i.e., the double L-scan technique, and its significance using pulsed lasers. We also make an instructive examination and discuss the reliability of our theoretical-computational approach, which uses modern analytical response theory, within a Time-Dependent Density Functional Theory (TD-DFT) approach. In order to illustrate the potential of this novel spectroscopic tool, we first present the experimental and theoretical results obtained in C₂-symmetric, axially chiral R-(+)-1,1'-bi(2-naphthol), R-BINOL, a molecule studied at the beginning of our investigation in this field. Next, we reveal some preliminary results obtained for (R)-3,3′-diphenyl-2,2′-bi-1-naphthol, R-VANOL, and (R)-2,2′-diphenyl-3,3′-(4-biphenanthrol), R-VAPOL. This family of optically active compounds has been proven to be a suitable model for the structure-property relationship study of TPACD, because its members are highly conjugated yet photo-stable, and easily derivatized at the 5- and 6-positions. With the publication of these outcomes we hope to motivate more members of the scientist community to engage in state-of-the-art TPACD spectroscopy. Full article