Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy最新文献

We report a newly synthesized 7-diethylamino-4-hydroxycoumarin tagged symmetrical azine derivative (SHC), with an interesting color transformation from yellowish green to orange via aggregation induced red shifted emissive (117 nm) feature in THF-H₂O mixture. Interestingly, the single crystal X-ray analysis of this molecule demonstrates that two hydroxycoumarin moieties were present in azine unit, among them one of the coumarin units was exist as enol form and another one transferred to keto form via ground state proton transfer reaction. The optical responses of the compound in different solvents exposed the observation of dual emissive bands which corresponds to the presence of ESIPT phenomenon in SHC molecule. Further, this characteristic was confirmed by absorption, emission, solid state structure and time resolved fluorescence decay measurements. Furthermore, the fluorophore, SHC was exploited as a colorimetric and turn on-off-on fluorescent probe for detection of Cu²⁺ ions and Cysteine (Cys). The 1:1 binding ratio of the probe with Cu²⁺ and Cys with SHC-Cu²⁺, was established via Job plot analysis, mass spectral technique and the DFT calculations. The probe, SHC was employed for the detection of copper ions in the environmental real water samples. Finally, the reversible fluorescent turn on-off-on character of the probe, SHC was established to construct the IMPLICATION logic gate application.

A simple and highly sensitive isatin-based colorimetric sensor ISAT 3(a-d) was synthesized through a single-step reaction. The as-prepared receptor ISAT 3b with carbonate ions (CO₃^2- ions) shows a significant red shift in the UV-visible absorption spectra and a visible color change from pale yellow to pink. Also, the receptor ISAT 3b shows unique solvatochromic behavior with CO₃^2- ions in different aprotic solvents and solvent compositions. Moreover, the receptor's pink coloration (absorption maxima at 544 nm) with CO₃^2- ions could be reversible by adding HSO₄^- ions (attain initial pale-yellow color, absorption maxima at 425 nm), which can be repeatable. The observed color changes with spectral shift and reversibility of the receptor with CO₃^2- ions and HSO₄^- ions provide "ON-OFF" switching for applying molecular logic gates. Receptors exhibited properties, such as reversibility and repeatability, benefit the design of a molecular-scale sequential memory unit with a display of "Writing-Reading-Erasing-Reading". The real sample analysis was also carried out to prove the practical applicability of receptor (ISAT 3b) for detecting CO₃^2- ions.

Carbon dot-based fluorescence sensors have attracted research interest for the selective determination of anti-inflammatory drugs in biological fluids and environments. The overdose and accumulation of anti-inflammatory drugs in tissues can cause chronic side effects including abdominal pain, and renal damage. Herein, we report a new fluorescent probe, bamboo stem waste-derived carbon dots (BS-CDs) for highly sensitive detection of Flufenamic acid (FA), a hazardous anti-inflammatory drug. The UV-vis absorption spectra of BS-CDs show a redshifted absorption peak at 283 nm upon the addition of FA suggesting strong binding interaction between BS-CDs and FA molecule. The BS-CDs showed a fluorescence enhancement (∼2-fold) detection for FA (400 μM) in the linear concentration range (0.40 → 0.65 μM) with a limit of detection (LoD; 17 nM) and binding constant (K_a = 1.33 × 10^-3 M^-1). The time-resolved fluorescence decay analysis showed that the average lifetime of BS-CDs has slightly changed (4.42 → 4.67 ns) by the interaction with FA through the aggregation-induced emission (AIE) process. The interference, pH, and effect of time results suggest that BS-CDs are highly selective probes for FA detection and do not show any interference involvement during FA detection. The confirmation of the structure and morphology changes of BS-CDs after interaction with FA was carried out by XRD, FESEM, HRTEM, FTIR, and Raman spectroscopy. The practicability of the BS-CDs probe was proved by the detection of FA in human urine samples with recovery of 103-109 %. This suggests that the proposed BS-CDs-based 'turn-on' sensor could be used to determine the FA in biological fluids.

With the development of global industry, carbon dioxide emissions surged. The conversion of carbon dioxide from the air results in some CO₃^2-, which can exacerbate environmental disasters like ocean acidification. Therefore, the content of CO₃^2- in seawater is an important indicator of the degree of ocean acidification. In this study, natural fluorescent protein phycocyanin (PC) was used as a fluorescent probe, and a fluorescence detection method was established for quantitative monitoring of CO₃^2- with quick response time (within 50 s), high sensitivity, and selectivity. The fluorescence quenching phenomenon between PC and CO₃^2- was mainly attributed to static quenching. The limit of detection (LOD) was 0.42 μM and the method was successfully applied to monitor CO₃^2- in tap water and seawater, acquiring satisfactory recovery between 99.28 % and 106.40 %. More importantly, paper-based test strips were easily fabricated using PC, enabling the rapid, visual, and on-site detection of CO₃^2- with the aid of a smartphone. The visual detection integrated with the smartphone was converted to data information (RGB value) through a Color Picker APP and successfully used for quantitative identification of CO₃^2-. By capturing fluorescent images and analyzing the corresponding RGB value via a smartphone, the linear calibration ranged from 0.5 μM to 500.0 μM with LOD of 0.11 μM was obtained. Satisfactory recoveries were acquired in tap water (98.00 %-107.50 %) and seawater (97.30 %-101.74 %), respectively. Therefore, integrating the PC fluorescent paper with a smartphone realizes the rapid, visual, and on-site detection of CO₃^2- in the water environment, which is expected to broaden application prospects of monitoring ocean acidification degree.

As a cutting-edge technique, fluorescence imaging in the second near-infrared window (NIR-II) is vital for both biomedical research and clinical applications. However, its intravital imaging capacity has been restricted by the extremely limited brightness of NIR-II fluorophores. To address this challenge, we elucidated the inner mechanism of constructing high-performance NIR-II chromophores based on molecular isomer engineering from detailed computational investigations. Herein, three pairs of cis-trans isomers (cis-1, 2, 3 and trans-1, 2, 3) are designed by attaching amino, methoxyl and nitro moieties to different positions on the donor-acceptor-donor molecular skeleton with benzobisthiadiazole as the acceptor and triphenylamine as the donor. All the compounds feature efficient NIR-II emission ranging in 1000-1164 nm, and the photophysical characterizations are regulated by molecular isomer manipulation. Interestingly, fluorescence quantum yields of cis-isomers are higher than those of their trans-counterparts. These enhancements can be attributed to the significant reduction in non-radiative transition, as evidenced by the non-adiabatic excitation energy, non-adiabatic electron coupling and electron-vibration coupling. Meanwhile, fluorophores with nitro terminal group exhibit superior performance facilitated by the prominently intramolecular charge transfer. As a result, cis-3 achieves an optimal brightness maxima of 196.36 M^-1 cm^-1 at 632 nm. Notably, the energy gap and the hole-electron related H index are respectively identified as strongly relevant to the emission wavelength and brightness, making them capable of evaluating the feasibility of fluorophores as effective NIR-II candidates. These findings highlight the correlations between molecular geometry and luminescent properties, which will inspire more insights into the development of highly efficient NIR-II fluorophores through rational isomer engineering for biomedical applications.

The development and design of a novel, uniform and highly active local electromagnetic field enhanced structure is crucial for expanding Surface-enhanced Raman Scattering (SERS) applications. In this study, we developed Ag ring-coupled nanoarrays (Ag RCNAs) with controllable nanogaps using a substrate rotary evaporation coating technique with self-assembled polystyrene (PS) microspheres as templates. This straightforward and cost-effective method efficiently prepares plasma-coupled nanoarrays. Ag RCNAs demonstrated high sensitivity in detecting organic dyes, our prepared Ag RCNAs showed high sensitivity (with the limit of detection of 10^-8 M), high signal reproducibility (with the relative standard deviation of 6.73 %). Furthermore, Ag RCNAs showed remarkable sensitivity to a broad spectrum of dyes in river water, indicating the large-area uniform and highly active circular-ring-shaped nanogaps can realize highly sensitive detection of various pollutants. This approach offers advantages in electromagnetic field enhancement, tunable nanogaps, uniformity, reproducibility, and recyclability, making it promising for applications in environmental monitoring, bioassays, food safety, and medical diagnostics.

Nickel foam (NF) was evaluated as a medium for the capture of polyethylene (PE) particles in water. NF is a hydrophobic and porous material with a large surface area, making it a promising candidate for attracting PE particles. However, the particle-capturing efficiency using bare NF was only 69.5%. To increase capturing efficiency, a circular polydimethylsiloxane (PDMS)-coated NF (PDMS@NF, diameter: 6 mm) was employed to enhance the hydrophobicity. The capturing efficiency using the PDMS@NF was substantially increased to 97.6 % owing to the increase in hydrophobicity. To quantify the captured PE particles on/in the PDMS@NF using Raman spectroscopy, a wide area illumination (WAI) scheme providing 6 mm-diameter laser illumination was adopted to fully cover the PDMS@NF for representative spectroscopic sampling and accurate quantification. The intensity ratios of PE to PDMS peaks in the collected spectra clearly increased with the quantity of dispersed PE particles (0.1 ∼ 4.0 mg range, R²: 0.992) in the water samples, and the limit of detection was 0.08 mg. Moreover, the capturing efficiencies for polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) particles (1 mg of each) using the PDMS@NF were also superior, ranging from 96.4 to 98.2 %. Therefore, the proposed scheme incorporating the PDMS@NF as a particle-capturing and Raman measurement platform has potential as a method for on-line detection of microplastics in water.

In view of the significant role of reactive sulfur species (RSS) and reactive oxygen species (ROS) in maintaining the redox homeostasis of organisms, we proposed a colorimetric fluorescent probe (HTN) for reversible detection of HSO₃^-/H₂O₂ and effective discrimination of HSO₃^-/ClO^-. C = C is the active site for the Michael addition of HSO₃^- and the oxidation of ClO^-. When HTN interacts with HSO₃^- and ClO^-, it exhibits fluorescence quenching. The addition of oxidizing H₂O₂ to the system can restore the conjugate structure of the addition product of HSO₃^- (HTN-HSO₃^-) and the fluorescence recovery, but it cannot restore the structure of the oxidation product of ClO^- (HTN-ClO^-). By studying the change of the reversibility/non-reversibility of the probe structure with the addition of H₂O₂, the purpose of reversible detection of HSO₃^-/H₂O₂ and distinguishing HSO₃^-/ClO^- is achieved. In addition, HTN can not only be used as a fluorescent ink to detect HSO₃^- on the test paper, but also has excellent detection effect on HSO₃^- and ClO^- in real food samples and water samples. Meantime, HTN has good biocompatibility and can target mitochondria to achieve reversible detection of HSO₃^-/H₂O₂ and effective discrimination of HSO₃^-/ClO^- in living cells. Therefore, HTN has great potential as a molecular tool for studying redox homeostasis in the interaction network of complex living systems.

It has been established that near infrared (NIR) spectroscopy has the potential of estimating sensory traits given the direct spectral responses that these properties have in the NIR region. In sweetpotato, sensory and texture traits are key for improving acceptability of the crop for food security and nutrition. Studies have statistically modelled the levels of NIR spectroscopy sensory characteristics using partial least squares (PLS) regression methods. To improve prediction accuracy, there are many advanced techniques, which could enhance modelling of fresh (wet and un-processed) samples or nonlinear dependence relationships. Performance of different quantitative prediction models for sensory traits developed using different machine learning methods were compared. Overall, results show that linear methods; linear support vector machine (L-SVM), principal component regression (PCR) and PLS exhibited higher mean R² values than other statistical methods. For all the 27 sensory traits, calibration models using L-SVM and PCR has slightly higher overall R² (x¯ = 0.33) compared to PLS (x¯ = 0.32) and radial-based SVM (NL-SVM; x¯= 0.30). The levels of orange color intensity were the best predicted by all the calibration models (R² = 0.87 - 0.89). The elastic net linear regression (ENR) and tree-based methods; extreme gradient boost (XGBoost) and random forest (RF) performed worse than would be expected but could possibly be improved with increased sample size. Lower average R² values were observed for calibration models of ENR (x¯ = 0.26), XGBoost (x¯ = 0.26) and RF (x¯ = 0.22). The overall RMSE in calibration models was lower in PCR models (X = 0.82) compared to L-SVM (x¯ = 0.86) and PLS (x¯ = 0.90). ENR, XGBoost and RF also had higher RMSE (x¯ = 0.90 - 0.92). Effective wavelengths selection using the interval partial least-squares regression (iPLS), improved the performance of the models but did not perform as good as the PLS. SNV pre-treatment was useful in improving model performance.

On the basis of first-principles electronic structure calculations, crystallographic parameters have been refined for calcium hydroxozincate (Qatranaite mineral), and the vibration properties (frequencies and eigenvectors) calculated. A detailed analysis of vibration modes is done, in the context of comparison with infrared and Raman spectra previously available. Special attention is paid to a posteriori symmetry analysis of vibration modes, discussing the latters' attribution to four irreducible representations of the P2₁/c space group, and to identifying stretchings and bendings of particular chemical bonds, pronounced in different vibrations. It turns out that high-frequency (>700 cm^-1) vibrations of hydroxyl groups bridging the Ca or Zn cations differ quite considerably for crystallographically distinct hydroxyl positions. It is shown that the vibrations involving hydroxyl groups and crystalline water typically come about in quadruplets at very close frequencies, whereby different irreducible representations reflect different combinations of similar "molecular" vibrations of four identical entities (of each hydroxyl or water) present in the unit cell. However, some vibrations show exceptions from this rule. In addition to interpretation of earlier experimental investigations, our study indicates that the low-frequency (<700 cm^-1) vibrations within the cation-hydroxyl connected skeleton are of more "solid-state-like" character and cannot be reasonably interpreted in terms of "molecular" vibrations within ZnO₄ or CaO₆ units.