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Dual-prism based terahertz time-domain attenuated total reflection spectroscopy and its application to characterise the hydration state of L-threonine in solution
摘要： To investigate the hydration state of amino acids, terahertz time-domain attenuated total internal reflection (THz TD-ATR) spectroscopy is often adopted to measure the complex permittivity. However, the classical THz TD-ATR spectroscopy system has only a single ATR prism and requires prism cleaning for different measuring modes, increasing the time consumed and easily introducing errors due to the changing environment. To accelerate the measurements and avoid the influence of environmental fluctuations, in this paper, we designed and built a dual-prism based THz TD-ATR spectroscopy: two ATR prisms with and without samples setting on the optical rail can be sequentially switched to optical systems for easily and rapidly collecting both sample and reference ATR spectra. According to the measurements of deionised water, the dual-prism based THz TD-ATR spectroscopy system can measure the sample complex permittivity rapidly and with high accuracy. The complex permittivity of L-threonine in aqueous solution is measured and analysed via the proposed system, and the hydration numbers of L-threonine solutions in different concentrations are quantitatively characterised. It is believed that the dual-prism based THz TD-ATR technique is a powerful tool for quickly and accurately investigating the hydration of amino acids.
关键词： Terahertz spectroscopy,Complex permittivity,Time-domain attenuated total internal reflection,Amino acid hydration
更新于2025-09-23 15:22:29
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Polymers with Exceptional Photoluminescence by Homoconjugation
摘要： Commonly, photoluminescence in organic polymers relies on π-electron delocalization by alternating double and single bonds. Remarkably, however, poly(phenylene methylene) (PPM) and methyl-substituted derivatives, such as those shown in Fig.1a, exhibit fluorescence in the wavelength region of 400–600 nm which cannot be explained by such systems of delocalized electrons. Instead, the results of extended investigations are in line with homoconjugation as the origin of the photoluminescence between 400 nm and 600 nm. Homoconjugation only arises in special chemical structures for which conjugation across individual π-electron systems can occur despite those systems being separated by an electronically insulating group, e.g. a methylene group. Such a conjugation is enabled by the overlap of p-orbitals in PPM (and derivatives), as schematically illustrated in Fig. 1b. DFT calculations for PPM indicate that homoconjugation is indeed energetically favorable. Note that homoconjugation in PPM and its derivatives can only be effective in certain conformations of the polymer chains, such as that displayed in Fig. 1b. For example, it appears that the conformations in the as-synthesized materials, which were finally obtained by rapid precipitation, are frozen in non-optimal geometries for homoconjugation because absorption and fluorescence intensity for such samples markedly increase following annealing above the glass transition temperature (66 °C for PPM; onset of thermal decomposition by TGA at 470 °C). Fluorescence of PPM and its derivatives is observed in the solid (Fig. 1c) as well as in the dissolved states. The polymers were extensively studied by UV-vis absorption spectroscopy, photoluminescence excitation spectroscopy and cyclovoltammetry. The HOMO-LUMO gap of 3.2–3.3 eV corresponds to an onset of optical absorption at approximately 375–390 nm, i.e. at higher wavelengths than expected for isolated phenylene groups. This is in agreement with homoconjugation for which electron delocalization occurs over several phenylene units. Further to this, the observed peak shifts of photoluminescence spectra towards higher wavelengths with increasing degree of polymerization (DP), up to DP ≈ 10, are fully consistent with electron delocalization along the polymer backbone. The photoluminescence lifetime recorded for thin PPM films is remarkably high, namely 8.55 ns. The photoluminescence quantum efficiency in solutions amounts to 69% and in films to 41%; notably the latter value is comparable to those for high-performance π-conjugated polymers. Interestingly, however, the absorption coefficient of PPM, measured for thick films, amounted to 80 cm–1 which, for comparison, is about 2600 times lower than the value of poly(dioctylfluorene). Notably, π-stacking, aggregation/crystallization and impurities were excluded as the origins of fluorescence in the course of the extended investigations. We expect that poly(phenylene methylene) and its derivatives will serve as examples of a new class of fluorescent polymers characterized by homoconjugation along the main chain.
关键词： Optical spectroscopy,Fluorescence,Homoconjugation,Poly(phenylene methylene)s,Light emission
更新于2025-09-23 15:22:29
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Simultaneous quantitative analysis of indomethacin and benzoic acid in gel using ultra-violet-visible spectrophotometry and chemometrics
摘要： BACKGROUND: In order to manufacture pharmaceutical products, real-time monitoring in the manufacturing process is necessary, but large equipment cost is required to achieve it. OBJECTIVE: The aim of this research is to use ultra-violet-visible spectroscopy along with chemometrics procedure to simultaneously quantitative analysis of indomethacin (IMC) and benzoic acid (BA) in the gel during pharmaceutical manufacturing process. METHODS: The gel preparations were contained of 0.1–1.5% IMC, 0.015–0.225% BA, 2% carbopol? 941 and 95% ethanol solution. The calibration models were constructed using the partial least square regression (PLS). RESULTS: The relationships of the measured and predicted concentrations for both IMC and BA had linear plots. The developed PLS calibration models were used to monitor the IMC and BA concentrations during mixing of the gels by the planetary centrifugal and conventional mixers, respectively. IMC and BA were gradually dispersed, dissolved and completely homogeneous within 30 min by the centrifugal mixer. In contrast, IMC and BA were slowly dispersed, dissolved and completely homogeneous at more than 60 min by the conventional mixer. CONCLUSIONS: The ultra-violet-visible spectrophotometric method couples with multivariate chemometric techniques for quantitative data analysis were successfully applied for the simultaneous determination of major component IMC and trace component BA in the gel.
关键词： benzoic acid,indomethacin,partial least square regression,Ultra-violet-visible spectroscopy,process analysis technology,process monitoring
更新于2025-09-23 15:22:29
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Fast Padé Transform for increasing the signal to noise ratio of spectra provided by STEAM pulse sequence
摘要： BACKGROUND/OBJECTIVE: There are two routine pulse-sequences for single voxel spectroscopy (SVS), point resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM). Although STEAM has several advantages in comparison to PRESS, signal/noise ratio (SNR) superiority of PRESS makes it the first choice for SVS. Application of Fast Padé transform (FPT) instead of Fast Furrier transform (FFT) might increase the SNR of the signal produced by STEAM pulse-sequence and therefore allows the benefits of its advantages. We aimed to evaluate and compare the noise root mean square (RMS) and SNR provided by STEAM pulse-sequence using both FPT and FFT. MATERIALS AND METHOD: A gelatin-based phantom was constructed in a 19-cm acrylic cylinder. The phantom had two normal/tumoral parts. The SVS was performed using a 3T MRI scanner. STEAM pulse-sequence were used with the following parameters: TR = 2000 ms, TM = 10 ms, and three TEs of 20, 135 and 270 ms with two data-points of 1024 and 512 and voxel-size of 1 cm3. The raw data were extracted and processed using both FFT and FPT estimators to produce the spectrum. The noise RMS and SNR of Cho and Cr metabolites were assessed. RESULTS: According to the results, noise RMS of spectra provided by FPT were decreased between 3619.01–14252.94% in comparison to FFT (p < 0.00001). The SNR of Cr1 and Cho peaks of the spectra provided by FPT were increased more than 96.80 and 97.18, respectively (0.00006 < p < 0.02). DISCUSSION: The difference of noise RMS’s provided by FPT are thousands percent less than FFT. This enormous decrease in noise provides a good increase of SNR. While the range of Cr1 and Cho SNR by FFT are between 41.55–120.32 the range of SNRs of these peaks provided by FPT are between 1719.99–9744.79, which implies a significant difference between the efficiency of FPT and FFT. CONCLUSION: This study showed that application of FPT in comparison to FFT can increase the spectra SNR and so that its usage can be helpful during the application of STEAM pulse-sequence which results in lower SNR in comparison to PRESS pulse-sequence. Thus, we should make use of the advantages of STEAM pulse-sequence.
关键词： Magnetic resonance spectroscopy,signal to noise ratio,STEAM pulse sequence,Fast Padé Transform,Fast Furrier Transform
更新于2025-09-23 15:22:29
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Effects of selenisation temperature on photoluminescence and photoluminescence excitation spectra of ZnO/CdS/Cu2ZnSnSe4/Mo/glass
摘要： The effect of solar cell processing (including etching in KCN along with deposition of CdS and ZnO) on photoluminescence (PL) spectra and bandgap Eg (measured at 4.2 K by photoluminescence excitation) of Cu2ZnSnSe4 films, produced by selenising metallic precursors at 450°C, 500°C and 550°C, was studied. Temperature and excitation intensity analysis of the P1 dominant band in the PL spectra of solar cells suggests that after processing this band still can be assigned to the free-to-bound recombination of free electrons with holes bound at deep acceptor levels influenced by valence band-tails. However processing increased the intensity of P1 and blue shifted it. The strongest effect was observed for the film selenised at 500°C. For the film selenised at 450°C the blue shift and increase in the intensity were smaller and only a slight intensity rise was found for the film selenised at 550°C. The intensity increase we assign to a reduction in the concentration of non-radiative recombination centers on the surface because of the etching and changes in doping due to inter-diffusion of Cd, S, Se and Zn after the deposition of CdS. Such an inter-diffusion depends on the elemental composition of the films defining the chemistry of defects and influencing Eg which increased in the film selenised at 500°C but decreased in the other films. Processing increased the P1 shift rate (j-shift) with excitation power change in all the films demonstrating a higher compensation degree in the solar cells which is consistent with the formation of an interface layer containing new donors CdCu.
关键词： Optical spectroscopy,Copper zinc tin selenide,Photoluminescence,Solar cells,Selenisation
更新于2025-09-23 15:22:29
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Determination of Pigments in Virgin and Extra-Virgin Olive Oils: A Comparison between Two Near UV-Vis Spectroscopic Techniques
摘要： The colour of olive oil is due to the presence of natural pigments belonging to the class of carotenoids, chlorophylls, and their derivatives. These substances, other than being responsible for the colour, an important qualitative feature of the oil, have antioxidant and, more generally, nutraceutical properties and their quantification can be related to the product’s quality and authenticity. In this work, we have quantified the total amount of carotenoids and chlorophylls’ derivatives in several virgin and extra-virgin olive oils produced in Italy, by using two different methods that are based on near-ultraviolet-visible absorption spectroscopy. The first method defines two indexes, K670 and K470, related to absorbance values of oil at wavelengths of 670 and 470 nm, respectively. The second method is based on the mathematical deconvolution of the whole absorption spectrum of the oil to obtain the concentrations of four main pigments present in olive oils: β-carotene, lutein, pheophytin A, and pheophytin B. The concentrations of the total carotenoids and total chlorophylls’ derivatives, as obtained by the two spectroscopic methods, are compared and the results are discussed in view of the practical usefulness of spectroscopic techniques for a fast determination of pigments in olive oil.
关键词： EVOO,colour,ultraviolet-visible light,extra-virgin olive oil,chlorophylls,pigments,carotenoids,spectroscopy,quality,light absorption
更新于2025-09-23 15:22:29
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Recent Trends in Compressive Raman Spectroscopy Using DMD-Based Binary Detection
摘要： The collection of high-dimensional hyperspectral data is often the slowest step in the process of hyperspectral Raman imaging. With the conventional array-based Raman spectroscopy acquiring of chemical images could take hours to even days. To increase the Raman collection speeds, a number of compressive detection (CD) strategies, which simultaneously sense and compress the spectral signal, have recently been demonstrated. As opposed to conventional hyperspectral imaging, where full spectra are measured prior to post-processing and imaging CD increases the speed of data collection by making measurements in a low-dimensional space containing only the information of interest, thus enabling real-time imaging. The use of single channel detectors gives the key advantage to CD strategy using optical filter functions to obtain component intensities. In other words, the filter functions are simply the optimized patterns of wavelength combinations characteristic of component in the sample, and the intensity transmitted through each filter represents a direct measure of the associated score values. Essentially, compressive hyperspectral images consist of 'score' pixels (instead of 'spectral' pixels). This paper presents an overview of recent advances in compressive Raman detection designs and performance validations using a DMD based binary detection strategy.
关键词： Chemometrics,multivariate data analysis,digital light processor (DLP),digital micromirror device (DMD),optimal binary filters,spatial light modulators (SLM),Raman spectroscopy,chemical imaging,compressive detection
更新于2025-09-23 15:22:29
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Fingerprints of sp1 Hybridized C in the Near-Edge X-ray Absorption Spectra of Surface-Grown Materials
摘要： Carbon structures comprising sp1 chains (e.g., polyynes or cumulenes) can be synthesized by exploiting on-surface chemistry and molecular self-assembly of organic precursors, opening to the use of the full experimental and theoretical surface-science toolbox for their characterization. In particular, polarized near-edge X-ray absorption fine structure (NEXAFS) can be used to determine molecular adsorption angles and is here also suggested as a probe to discriminate sp1/sp2 character in the structures. We present an ab initio study of the polarized NEXAFS spectrum of model and real sp1/sp2 materials. Calculations are performed within density functional theory with plane waves and pseudopotentials, and spectra are computed by core-excited C potentials. We evaluate the dichroism in the spectrum for ideal carbynes and highlight the main differences relative to typical sp2 systems. We then consider a mixed polymer alternating sp1 C4 units with sp2 biphenyl groups, recently synthesized on Au(111), as well as other linear structures and two-dimensional networks, pointing out a spectral line shape specifically due to the presence of linear C chains. Our study suggests that the measurements of polarized NEXAFS spectra could be used to distinctly fingerprint the presence of sp1 hybridization in surface-grown C structures.
关键词： density functional theory,self-assembly,carbynes,on-surface chemistry,near edge X-ray absorption spectroscopy,C 1s absorption
更新于2025-09-23 15:22:29
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Fish oil preparation inhibits leukocyte recruitment and bands that characterize inflamed tissue in a model of phenol-induced skin inflammation: percutaneous penetration of a topically applied preparation demonstrated by photoacoustic spectroscopy
摘要： Fish oil (FO) is a natural source of omega-3 fatty acids, with well-established beneficial effects in inflammatory diseases when FO is orally administered. This study investigated the effects of a topically applied FO preparation (FOP) on phenol-induced ear edema and evaluated the percutaneous penetration of FOP in ear tissue. After applying phenol, groups of mice received FOP on the ear. After 1 h, ear tissue was collected to determine the percent inhibition of edema, myeloperoxidase activity, and to perform photoacoustic spectroscopy (PAS). Treatment with FOP did not reduce edema, but reduced myeloperoxidase activity. The FOP decreased the area of bands that characterize inflamed tissue and penetrated into the tissue. These results indicated an inhibitory effect of FOP on leukocyte recruitment in phenol-induced ear edema. These data support the applicability of PAS as a non-destructive method for evaluating the inflammatory response, percutaneous penetration and antiinflammatory activity of compounds.
关键词： ear edema,Fish oil,inflammation,phenol,skin,photoacoustic spectroscopy
更新于2025-09-23 15:22:29
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Photochromic properties in silver-doped titania nanoparticles
摘要： The Ag-doped TiO2 nanoparticles were synthesized at room temperature using a solution of titanium isopropoxide and silver nitrate as precursors. The inclusion of Ag in the nanocrystalline TiO2 lattice was systematically analyzed both from a morphological and a structural point of view. Raman spectroscopy, electron microscopy, electronic diffraction and x-rays allow us to testify that the dopant Ag does not modify the nanocrystalline anatase tetragonal structure of the nanoparticles, but causes a small distortion of the structure. UV–vis spectroscopy allowed to analyze the optical properties of the obtained nanoparticles. Kubelka Munk’s model allowed the interpretation of diffuse reflectance spectra. We have obtained a very different system from the hetero-system Ag-TiO2 described in the literature, but it shows an interesting photochromic behaviour. Ag-doped TiO2 nanoparticles darken and whiten under UV light and visible light, respectively, in a very fast way. A simple kinetic model has been used to process experimental data and describe the observed photochromic process and to determine the darkening and whitening constants.
关键词： photochromism,electron diffraction,nanoparticles,optical properties,Raman spectroscopy
更新于2025-09-23 15:22:29