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Photo-Modification of Melanin by a Mid-Infrared Free-Electron Laser
摘要： Melanin is rigidly constructed by several nitrogen-containing aromatic rings, and its excess accumulation in skin tissue is closely associated with melanosis. Although visible lasers (wavelength: 600–1000 nm) are conventionally used for the photo-thermolysis of melanocyte, several pigmented nevi are difficult to be treated. Here, we propose an alternate method for targeting the molecular structure of melanin using an infrared free electron laser (FEL) tuned to 5.8 μm that corresponds to the stretching vibrational mode of carboxylate group. A drastic morphological change on the black-colored surface of melanin powder were observed after the pulse irradiation with a power of 500 mJ/cm2, and the minimum irradiation time for damage to the morphology was 1.4 seconds. Analyses by mass spectroscopy, infrared spectroscopy, and 13C-nuclear magnetic resonance implied that a pyrrole group was removed by the FEL irradiation. In addition, the FEL irradiation dispersed almost all of the melanoma cells from a culture solution without any influence on other ingredients in the medium, and one-cell analysis by infrared microscopy showed that the structure of melanoma could be substantially damaged by the irradiation. This study proposes the potency of intense mid-infrared laser as novel alternative way to reduce melanin.
关键词： Infrared free electron laser,Melanoma,Vibrational mode,Melanin,Photo-modification
更新于2025-11-21 11:03:13
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Quantumness in light harvesting is determined by vibrational dynamics
摘要： We demonstrate for the multi-level spin-boson (MLSB) Hamiltonian, typically used to describe biological light-harvesting, that the distinction between quantum and classical dynamics is determined entirely by the thermal environment. In particular, any MLSB model featuring classical interactions with a classical bath is exactly equivalent in its absorption and energy transfer dynamics to a classical model involving coupled harmonic oscillators. This result holds in the linear response regime for both pulsed and incoherent excitation. In the biological context, this finding highlights the centrality of vibrational dynamics in determining the 'quantumness' of photosynthetic light-harvesting, particularly in the creation of the photosynthetic energy funnel where excitation energy concentrates near the reaction center via a series of downhill energy transfer events. These findings support the idea that this energy funnel is exclusively quantum-mechanical in origin, although it need not rely on entanglement.
关键词： vibrational dynamics,energy transfer,photosynthesis,quantumness,light harvesting,spin-boson model
更新于2025-09-23 15:23:52
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Structure, Reactivity, Nonlinear Optical Properties and Vibrational Study of 5-Thioxo-1,4-thiazaolidin-3-one and 5-thioxo-1,4,2-thiazasilolidin-3-one (Silicon vs. Carbon). A DFT Study
摘要： The structures and nonlinear optical properties (NLO) of 5-thioxo-1,4-thiazaolidin-3-one(Rhodanine) and 5-thioxo-1,4,2-thiazasilolidin-3-one (silarhodanine) tautomers were studied in gas phase and in solutions using the B3LYP density functional theory and composite CBS-QB3 method. The global minimum at the B3LYP/6-31++G(d,p) and CBS-QB3 levels of theory is tautomer 5 in the gas phase and in solvents for rhodanine, and simiarly, tautomer 13 is the global minimum for silarhodanine. The interconversion among the tautomers is proceeded by an intramolecular proton transfer reaction. An identical solvent effects can be noted for rhodanine and silarhodanine tautomers. The activation barrier towards ring-opening processes (1→2, 9→10) decreases with the increasing dielectric constant of the solvent; on the other hand, the barrier of the ring-closure processes (2→3, 10→11) increases with the increasing dielectric constant. The tautomers are predicted to show significant NLO properties. Also, a number of correlations between the dipole moment and electron densities in bond critical points of the S3-C4 bond and interaction energy as well as vibrational frequencies at the transition states (TS2–3,TS10–11) were examined under different solvents. Finally, the investigation of the heavy atom substitution effects on the properties of silarhodanine is proven to be very weak under these conditions.
关键词： Vibrational assignments,Silarhodanine,Reactivity,Rhodanine,NLO,Ring-opening,Solvent effects
更新于2025-09-23 15:23:52
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Synthesis, crystal structure, vibrational and optical properties of a new Bi(III) halide complex: (C9H13N2O2)2Bi2Cl8
摘要： A new Bi(III) halide complex, (C9H13N2O2)2Bi2Cl8, was successfully grown by slow evaporation method. The structure of this hybrid compound was determinated by single crystal X-ray diffraction and further characterized by IR and RAMAN spectra, UV-Visible, luminescence and DFT calculations. This compound crystallizes in the monoclinic system P21/n space group with the following lattice parameters: a = 10.2036 (4), b = 9.8723 (4), c = 14.5920 (6) ?, ? = 99.899 (4)°, V = 1448.01 (10) ?3 and Z =2. The crystal structure of this compound was solved by direct methods and refined to R = 0.038 (wR = 0.079), based on 4118 unique observed reflections. The crystal structure consists of a 1-(2-furoyl)piperazinium cation and discrete (0D) anion built up of edge-sharing bioctahedra which are linked by bifurcated N-H…Cl and N-H…O hydrogen bonds to build up the whole molecular packing. The optical properties of this compound were studied by UV–Vis, luminescence spectroscopy and by Time Dependent Density Functional Theory studies. The vibrational properties of this compound were investigated by Infrared and Raman spectroscopy and compared with the calculated ones. The nature and amount of contacts in the crystal packing were investigated by means the Hirshfeld surfaces. Ab-initio and DFT calculations were also performed on whole compound and on reduced model: bis(μ2-chloro)-diaqua-hexachloro-di-bismuth.
关键词： luminescence,X-Ray diffraction,Vibrational studies,Bismuthates,DFT calculations
更新于2025-09-23 15:23:52
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Quantifying Double-Layer Potentials at Liquid–Gas Interfaces from Vibrational Sum-Frequency Generation
摘要： Vibrational sum-frequency generation (SFG) spectroscopy is demonstrated as a fast method to quantify variations of the electric double-layer potential ?0 at liquid?gas interfaces. For this, mixed solutions of nonionic tetraethyleneglycol-monodecylether (C10E4) and cationic hexadecyltrimethylammonium bromide (C16TAB) surfactants were investigated using SFG spectroscopy and a thin-film pressure balance (TFPB). Derjaguin?Landau?Verwey?Overbeek analysis of disjoining pressure isotherms obtained with the TFPB technique provides complementary information on ?0, which we apply to validate the results from SFG spectroscopy. By using a single ?0 value, we can disentangle χ(2) and χ(3) contributions to the O?H stretching modes of interfacial water molecules in the SFG spectra. Having established the latter, we show that unknown double-layer potentials at the liquid?gas interface from solutions with different C16TAB/C10E4 mixing ratios can be obtained from an analysis of SFG spectra and are in excellent agreement with the complementary results from the TFPB technique.
关键词： disjoining pressure,Vibrational sum-frequency generation,electric double-layer potential,thin-film pressure balance,liquid?gas interfaces,surfactants
更新于2025-09-23 15:22:29
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Multi-mode heterodyned 5th-order infrared spectroscopy
摘要： Fifth-order multidimensional infrared spectroscopy with heterodyned detection was carried out in the three-beam dual-frequency configuration. Numerous 5th-order cross peaks were detected for the 4-azidobutyrate-N-hydroxysuccinimide ester compound in solution involving several vibrational modes ranging in frequency from 1045 to 2100 cm?1. Cross peaks involving overtones (2X/Z) and combination bands (XY/Z) among the tags, modes X and Y excited by the first two mid-IR laser pulses, and the reporter, modes Z excited by the third laser pulse, were acquired and the factors affecting the amplitude of 5th-order cross peaks are discussed. The 5th-order cross peaks were detected among modes that are spatially close (a few bonds apart) as well as for modes spatially separated by ca. 12 ? (eight bonds apart). In both cases, the waiting time dependences for the 3rd and 5th order cross peaks were found to be different. In particular, the waiting time at which the cross-peak maximum is reached, the decay time, and the value of a plateau at large waiting times were all differing strongly. The differences are explained by reduced sensitivity of the 5th-order signals to modes coupled weakly to the reporter mode and different relaxation dynamics involving overtone state of the tag. The ability of the 5th-order peaks to single out the modes coupled strongly to the reporter can help identifying specific energy relaxation and transport pathways, which will be useful for understanding energy transport dynamics in molecules. The absorptive 5th-order cross peaks were constructed which report on three-point correlation functions. It is shown that in addition to the triple-frequency correlation functions, a correlation of the frequencies with the mode coupling (anharmonicity) can be naturally measured by the 5th-order spectroscopy. The current limit for detecting 5th-order signals was estimated at the level of 1 × 10?3 in reduced anharmonicity, which is determined by the corresponding two-state anharmonicity divided by the reporter mode spectral width. Given the simplicity of recording the 5th-order cross peaks in the three-beam configuration, the approach carries a potential for a broad use.
关键词： vibrational modes,anharmonicity,heterodyned detection,fifth-order,multidimensional infrared spectroscopy,energy transport
更新于2025-09-23 15:22:29
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Bulk-or-interface assignment of heterodyne-detected chiral vibrational sum frequency generation signal by its polarization dependence
摘要： Polarization dependence of heterodyne-detected chiral vibrational sum frequency generation (VSFG) was examined for thin films of polylactic acids and neat limonene liquid far from electronic resonance. The enantiomers of polylactic acid films on silica substrates were successfully distinguished, and their chiral VSFG signals were ascribed not to bulk but to the interfaces by comparing chiral signals observed in reflection in the S-polarized VSFG, P-polarized visible, and P-polarized infrared and P-polarized VSFG, S-polarized visible, and P-polarized infrared polarization combinations with theoretical model calculations. In the same way, the chiral VSFG signal of neat limonene was assigned to bulk, which is consistent with the previous assignment. The method employed for assigning the source of chiral signals to the bulk or the interface may be useful for organic films on substrates with low refractive indices and thick samples.
关键词： limonene,chiral vibrational sum frequency generation,polarization dependence,bulk-or-interface assignment,heterodyne detection,polylactic acid
更新于2025-09-23 15:22:29
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Differentiation of Taxonomically Closely Related Species of the Genus Acinetobacter Using Raman Spectroscopy and Chemometrics
摘要： In recent years, several efforts have been made to develop quick and low cost bacterial identification methods. Genotypic methods, despite their accuracy, are laborious and time consuming, leaving spectroscopic methods as a potential alternative. Mass and infrared spectroscopy are among the most reconnoitered techniques for this purpose, with Raman having been practically unexplored. Some species of the bacterial genus Acinetobacter are recognized as etiological agents of nosocomial infections associated with high rates of mortality and morbidity, which makes their accurate identification important. The goal of this study was to assess the ability of Raman spectroscopy to discriminate between 16 Acinetobacter species belonging to two phylogroups containing taxonomically closely related species, that is, the Acinetobacter baumannii-Acinetobacter calcoaceticus complex (six species) and haemolytic clade (10 species). Bacterial spectra were acquired without the need for any sample pre-treatment and were further analyzed with multivariate data analysis, namely partial least squares discriminant analysis (PLSDA). Species discrimination was achieved through a series of sequential PLSDA models, with the percentage of correct species assignments ranging from 72.1% to 98.7%. The obtained results suggest that Raman spectroscopy is a promising alternative for identification of Acinetobacter species.
关键词： species,bacteria,vibrational spectroscopy,typing,haemolytic clade
更新于2025-09-23 15:22:29
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Enhanced NLO activity of organic 2-methyl-5-nitroaniline crystal: Experimental and computational investigation with and without silver addition
摘要： The nonlinear optical (NLO) material, 2-methyl-5-nitroaniline (M5NA), is synthesized and the crystals are grown by slow evaporation technique. The theoretical vibrational spectral analyses are done for the first time for M5NA using B3LYP computational method with the basis set cc-pVTZ. Natural Bond Orbital (NBO) and Atoms In Molecules (AIM) analyses are carried out for obtaining the charge transfer interactions and the Hirshfeld surface analysis with the fingerprint plot is performed for finding out the intermolecular interaction sites of the molecule. Using the theoretical and experimental IR and Raman spectra, the vibrations of M5NA are estimated. Changes in the linear and nonlinear optical properties with the addition of silver nanoparticles are studied from the UV–vis absorption spectra and the Z-Scan curves. A comparison of the hyperpolarizability values is done with pure and silver-added M5NA.
关键词： NLO,HOMO-LUMO,DFT,Vibrational spectroscopy,Silver nanoparticles
更新于2025-09-23 15:22:29
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<i>l</i> -Stercobilin-HCl and <i>d</i> -Urobilin-HCl. Analysis of Their Chiroptical and Conformational Properties by VCD, ECD, CPL Experiments and MD, DFT Calculations
摘要： Vibrational circular dichroism (VCD) and IR spectra of dichloromethane solutions of l-stercobilin and d-urobilin hydrochlorides have been recorded in the mid-IR region. The spectra are best interpreted by combining molecular dynamics (MD) calculations and DFT calculations within the QM/MM ONIOM-type framework, and the combined predicted results are better and more informative than the more standard analysis provided by DFT calculations. The same approach also sheds light on the Cotton effect sign inversion of room temperature versus low temperature electronic CD (ECD) spectra of the same compounds in methanol-glycerol solution. Finally, circularly polarized luminescence (CPL) spectra for l-stercobilin in chloroform solution provide information on the excited state geometry of this molecule.
关键词： Vibrational circular dichroism,electronic CD,molecular dynamics,IR spectra,QM/MM ONIOM-type framework,Cotton effect,circularly polarized luminescence,DFT calculations
更新于2025-09-23 15:21:21