Vibrational Spectroscopy of Pain Relievers: Traditional and Remote Raman Techniques

The application of vibrational spectroscopy in the pharmaceutical industry is widely investigated, from the quality assurance of the product during the production process control to the final products’ quality control and the authentication of products on the markets. This study focuses on non-contact and noninvasive detection and identification of pain-relievers at 1-5 meters standoff distances. The specimens analyzed include standard laboratory-grade active ingredients and commercially available pain relievers in powder, solid and liquid forms. All the remote measurements captured revealed the Raman signatures of the specimens, with varying peak intensities. To correlate the band intensities captured with the standoff distances between the laser source and the specimens, the intensity ratios of the two prominent peaks of the laboratory grade reference active ingredient (1607 and 1319 cm-1) normalized with 1319 cm-1 are used. The results of the study suggest the viability of standoff Raman spectroscopy for routine monitoring and identification of pharma-ceuticals, including counterfeit pain relievers.

Synthesis,Crystal Structure,Vibrational Spectroscopy,and Thermal Behavior of Y[B_2O_3(OH)]_3

The hydroxy yttrium hexaborate,Y[B2O3（OH）]3,has been synthesized under mild hydrothermal conditions at 458 K.The crystal structure was solved and refined from single-crystal X-ray diffraction.It adopts a trigonal space group R3c（No.161） with a = 8.3942（4）,c = 20.6484（12） ,V = 1260.03（12） 3,YB6H3O12,Mr = 348.79,Z = 6,Dc = 2.758 g/cm3,F（000） = 1008,μ = 7.015 mm-1,R = 0.0321 and wR = 0.0772.Its crystal structure is made up of six-membered rings,alternating three-connected [BO3（OH）] tetrahedra and planar [BO3] trigonal groups,which are interconnected with each other by sharing their common oxygen corners to form a three-dimensional framework structure with six-membered ring channels that are occupied by the yttrium atoms and run along the c axis.FT-IR,Raman,and TG-DTA results are also presented.

Chemical leaching of an Indian bituminous coal and characterization of the products by vibrational spectroscopic techniques

High volatile bituminous coal .was demineralized by a chemical method. The vibrations of the ＂aromatics＂ structure of graphite, crystalline or non-crystalline, were observed in the spectra at the 1600 cm-1 region. The band at 1477 cm-1 is assigned as VR band, the band at 1392 cm-1 as VL band and the band at 1540 cm-1 as GR band. Graphite structure remains after chemical leaching liberates oxygenated functional groups and mineral groups. The silicate bands between 1010 and 1100 cm-1 are active in the infrared （IR） spec^urn but inactive in the Raman spectrum. Absorption arising from C-H stretching in alkenes occurs in the region of 3000 to 2840 cm-~. Raman bands because of symmetric stretch of water molecules were also observed in the spectrum at 3250 cm-1 and 3450 cm-1. Scanning electron microscopy analy- sis revealed the presence of a graphite layer on the surface. Leaching of the sample with hydrofluoric acid decreases the mineral phase and increases the carbon content. The ash content is reduced by 84.5wt% with leaching from its initial value by mainly removing aluminum and silicate containing minerals.

Review： Tip-based vibrational spectroscopy for nanoscale analysis of emerging energy materials

Vibrational spectroscopy is one of the key instrumentations that provide non-invasive investigation of structural and chemical composition for both organic and inorganic materials. However, diffraction of light funda- mentally limits the spatial resolution of far-field vibrational spectroscopy to roughly half the wavelength. In this article, we thoroughly review the integration of atomic force microscopy （AFM） with vibrational spectroscopy to enable the nanoscale characterization of emerging energy materials, which has not been possible with far-field optical techniques. The discussed methods utilize the AFM tip as a nanoscopic tool to extract spatially resolved electronic or molecular vibrational resonance spectra of a sample illuminated by a visible or infrared （IR） light source. The absorption of light by electrons or individual functional groups within molecules leads to changes in the sample＇s thermal response, optical scattering, and atomic force interactions, all of which can be readily probed by an AFM tip. For example, photothermal induced resonance （PTIR） spectroscopy methods measure a sample＇s local thermal expansion or temperature rise. Therefore, they use the AFM tip as a thermal detector to directly relate absorbed IR light to the thermal response of a sample. Optical scattering methods based on scanning near-field optical microscopy （SNOM） correlate the spectrum of scattered near-field light with molecular vibrational modes. More recently, photo-induced force microscopy （PiFM） has been developed to measure the change of the optical force gradient due to the light absorption by molecular vibrational resonances using AFM＇s superb sensitivity in detecting tip-sample force interactions. Such recent efforts successfully breech the diffraction limit of light to provide nanoscale spatial resolution of vibrational spectroscopy,which will become a critical technique for characterizing novel energy materials.

Applications of sum-frequency generation vibrational spectroscopy in friction interface

Sum-frequency generation(SFG)vibrational spectroscopy is a second-order nonlinear optical spectroscopy technique.Owing to its interfacial selectivity,SFG vibrational spectroscopy can provide interfacial molecular information,such as molecular orientations and order,which can be obtained directly,or molecular density,which can be acquired indirectly.Interfacial molecular behaviors are considered the basic factors for determining the tribological properties of surfaces.Therefore,owing to its ability to detect the molecular behavior in buried interfaces in situ and in real time,SFG vibrational spectroscopy has become one of the most appealing technologies for characterizing mechanisms at friction interfaces.This paper briefly introduces the development of SFG vibrational spectroscopy and the essential theoretical background,focusing on its application in friction and lubrication interfaces,including film-based,complex oil-based,and water-based lubricating systems.Real-time detection using SFG promotes the nondestructive investigation of molecular structures of friction interfaces in situ with submonolayer interface sensitivity,enabling the investigation of friction mechanisms.This review provides guidance on using SFG to conduct friction analysis,thereby widening the applicability of SFG vibrational spectroscopy.

Ordering effects of cholesterol on sphingomyelin monolayers investigated by high-resolution broadband sum-frequency generation vibrational spectroscopy

This report investigated the ordering of the alky chain of sphingomyelin （SMs） monolayers induced by cholesterol at the air/water interface using high-resolution broadband sum frequency generation vibrational spectroscopy （HR-BB-SFG-VS）. The SFG spectra of the three nature sphingomyelin/cholesterol mixture monolayers with two concentrations of the cholesterol at the air/water interface are performed under different polarization combination. A new resolved CH2 symmetric stretching （d＋, ~2834 cm-1） and the CH3 symmetric stretching （r＋, ~2874 cm-1） mode are applied to characterize the conformational order in the sphingomyelin/cholesterol mixture monolayers. It was found that the cholesterol make the sphingosine backbones more conformational order. During this process, the conformational order of the N-linked acyl chain remains unaltered. Moreover, the sphingosine backbones of SMs have much larger contributions to gauche defects of SMs than one in the N-linked acyl chain. These results presented here not only shed lights on understanding of the interactions of sphingomyelin molecules with cholesterol molecules at interface but also demonstrates the ability of HR-BB-SFG to probe such complicated molecular systems.

Loss-induced phase transition in mid-infrared plasmonic metamaterials for ultrasensitive vibrational spectroscopy

Metamaterials have proven their ability to possess extraordinary physical properties distinct from naturally available materials,leading to exciting sensing functionalities and applications.However,metamaterial-based sensing applications suffer from severe performance limitations due to noise interference and design constraints.Here,we propose a dual-phase strategy that leverages loss-induced different Fano-resonant phases to access both destructive and constructive signals of molecular vibration.When the two reverse signals are innovatively combined,the noise in the detection system is effectively suppressed,thereby breaking through the noise-related limitations.Additionally,by utilizing loss optimization of the plasmon-molecule coupling system,our dual-phase strategy enhances the efficiency of infrared energy transfer into the molecule without any additional fabrication complex,thereby overcoming the trade-off dilemma between performance and fabrication cost.Thanks to the pioneering breakthroughs in the limitations,our dual-phase strategy possesses an overwhelming competitive advantage in ultrasensitive vibrational spectroscopy over traditional metamaterial technology,including strong signal strength(×4),high sensitivity(×4.2),effective noise suppression(30%),low detection limit(13 ppm),and excellent selectivity among CO_(2),NH_(3),and CH_(4) mixtures.This work not only opens the door to various emerging ultrasensitive detection applications,including ultrasensitive in-breath diagnostics and high-information analysis of molecular information in dynamic reactions,but also gains new insights into the plasmon-molecule interactions in advanced metamaterials.

A machine learning vibrational spectroscopy protocol for spectrum prediction and spectrum-based structure recognition

Vibrational spectroscopy is one of the most commonly applied techniques for determining molecular structures.Conventional applications often involve extensive expertise or expensive first-principles computational effort in order to establish one-to-one spectrum-structure relationships.Here we developed a machine-learning protocol to correlate spectral fingerprints with local molecular structures.Our protocol enables not only quick and accurate prediction of infrared(IR)absorption and Raman vibrational spectra based on molecular structures,but more importantly,also enables structure recognition of chemical groups from vibrational spectral features.IR and Raman spectral features arising from different selection rules were recurrently fed to the model to achieve a nearly zero error rate in structure recognition.Both the spectrum prediction and structure recognition models have good transferability,implying a high possibility of being extended to various spectral or non-spectral characteristics.This machine learning protocol may provide impovements to real-time field applications in many areas of spectroscopy.

Microsecond scale vibrational spectroscopic imaging by multiplex stimulated Raman scattering microscopy

Real-time vibrational spectroscopic imaging is desired for monitoring cellular states and cellular processes in a label-free manner.Raman spectroscopic imaging of highly dynamic systems is inhibited by relatively slow spectral acquisition on millisecond to second scale.Here,we report microsecond scale vibrational spectroscopic imaging by lock-in free parallel detection of spectrally dispersed stimulated Raman scattering signal.Using a homebuilt tuned amplifier array,our method enables Raman spectral acquisition,within the window defined by the broadband pulse,at the speed of 32 μs and with close to shot-noise limited detection sensitivity.Incorporated with multivariate curve resolution analysis,our platform allows compositional mapping of lipid droplets in single live cells,observation of intracellular retinoid metabolism,discrimination of fat droplets from protein-rich organelles in Caenorhabditis elegans,spectral detection of fast flowing tumor cells and monitoring drug diffusion through skin tissue in vivo.The reported technique opens new opportunities for compositional analysis of cellular compartment in a microscope setting and high-throughput spectral profiling of single cells in a flow cytometer setting.

Theoretical studies of vibrationally resolved absorption and emission spectra: From a single chromophore to multichromophoric oligomers/aggregates

Absorption and photoluminescence spectroscopies are useful tools to study the photo-physical properties of materials. The theoretical methods for calculation of the spectra of molecules/supermolecules and aggregates, whose structures can differ significantly, are reviewed from the viewpoint of computational efficiency. Several model compounds/multimers are taken as examples for the spectral calculations. The numerical results achieve a satisfactory agreement between the theory and experiment.

Theoretical Simulation of the Vibrationally Resolved UV Absorption Spectrum of Acryloyl Fluoride

Acryloyl fluoride is an ideal molecule for investigating the phenomenon of hindered internal rotation.In concert with recently acquired high-resolution UV absorption spectrum of acryloyl fluoride,in this study,the absorption spectra of the s-trans and s-cis isomers of acryloyl fluoride were theoretically simulated.The simulated spectra were convoluted by a Gaussian function with displacement,distortion,Franck-Condon,Herzberg-Teller,and Duschinsky effects in the framework of the time-independent model.The statistical vibronic transition analysis reveals the unity of the spectrum transition property,the relevant normal modes,and the primary geometrical variations,enriching the understanding of the experimental observation.The discrepancy between the theoretical and experimental spectra was interpreted clearly.

Vibrational Spectroscopic Study on Ion Solvation and Association of Lithium Perchlorate in 4-Methoxymethyl-ethylene Carbonate

Solvation interaction and ion association in solutions of lithium perchlorate/4-methoxymethyl-ethylene carbonate （MEC） have been studied by using Infrared and Raman spectra as a function of concentration of lithium perchlorate. The splitting of ring deformation band and ring ether asymmetric stretching band, and the change of carbonyl stretching band suggest that there should be a strong interaction between Li^＋ and the solvent molecules, and the site of solvation should be the oxygen atom of carbonyl group. The apparent solvation number of Li^＋ was calculated by using band fitting technique. The solvation number was decreased from 3.3 to 1.1 with increasing the concentration of LiClO4/MEC solutions. On the other hand, the band fitting for the ClO4^- band revealed the presence of contact ion pair, and free ClO4^- anion in the concentrated solutions.

Hierarchically nanostructured Ni O-Co3O4 with rich interface defects for the electro-oxidation of 5-hydroxymethylfurfural

Ni-based electrocatalysts with strong redox abilities are active for the electrochemical oxidation of 5-hydroxymethylfurfural(HMF). Interface engineering is an efficient way to modulate the electronic structure, tune the intermediate adsorption, and expose more active sites. Herein, we increased the concentration of interfacial sites with rich defects in a 3D hierarchical nanostructured NiO-Co3O4 electrocatalyst and investigated its catalytic performance for HMF electro-oxidation. The interface effect created abundant cation vacancies, modulated the electronic properties of Co and Ni atoms, and raised the oxidation state of Ni species. The NiO-Co3O4 catalysts show superb HMF oxidation activities with a low onset potential of 1.28 VRHE.Meanwhile, in-situ surface-selective vibrational spectroscopy of sum-frequency generation was performed to study the reaction pathway during the oxidation process on the electrocatalysts. The current study offers an efficient way to create cation vacancies and proves the decisive role of cation vacancies in catalyzing the HMF electro-oxidation.

Spectroscopic stimulated Raman scattering imaging of highly dynamic specimens through matrix completion

Spectroscopic stimulated Raman scattering(SRS)imaging generates chemical maps of intrinsic molecules,with no need for prior knowledge.Despite great advances in instrumentation,the acquisition speed for a spectroscopic SRS image stack is fundamentally bounded by the pixel integration time.In this work,we report three-dimensional sparsely sampled spectroscopic SRS imaging that measures~20%of pixels throughout the stack.In conjunction with related work in low-rank matrix completion(e.g.,the Netflix Prize),we develop a regularized non-negative matrix factorization algorithm to decompose the sub-sampled image stack into spectral signatures and concentration maps.This design enables an acquisition speed of 0.8 s per image stack,with 50 frames in the spectral domain and 40,000 pixels in the spatial domain,which is faster than the conventional raster laser-scanning scheme by one order of magnitude.Such speed allows real-time metabolic imaging of living fungi suspended in a growth medium while effectively maintaining the spatial and spectral resolutions.This work is expected to promote broad application of matrix completion in spectroscopic laser-scanning imaging.

A Crystallization Study of Nanocrystalline PZT 53/47 Granular Arrays Using a Sol-Gel Based Precursor

In this work,we intend to perform a detailed study on the crystallization process of PZT 53/47 nanostructured powders by starting out with an amorphous precursor synthesized by a sol-gel based solution.Our interests also lie in the feasibility for controlling the average grain size of the final structure in the submicron range on an ab initio basis.Purposely,Fourier transform infrared spectroscopy（FT-IR）,Raman（Stokes and Anti-Stokes）,X-ray diffraction（XRD） and scanning electron microscopy（SEM） are used to examine the microstructural characteristics based on previously reported differential thermal analysis/thermal gravimetric analysis（DTA/TGA） data.The results show a crystallization temperature of 800℃ to attain pure perovskite phase with excellent morphological quality,average grain size 〈DG〉〈 300 nm and with average crystallite size 〈DC〉〈15 nm.