查看更多>>摘要：The taste of different flavor liquor is multifarious, but the same brand liquor with different quality is truth. The essence of supramolecular ethanol-water clusters and their intrinsic structural differences in three kinds of Fenjiu are studied by two-dimensional correlation spectra (2D-COS) of fluorescence and Raman. The 2D-COS of fluorescence reveals the prominent emission peaks of three Fenjiu are apparently different. The central fluorescence peak of Fenjiu (a) is located at 330 nm, corresponding to the cluster of (H2O)(m)(EtOH)(n). In Fenjiu (b), the emission peak appears near 310 nm, while those of Fenjiu (c) appear mainly near 310 and 373 nm, corresponding to the clusters of (H2O)(EtOH)(n) and (H2O)(m)(EtOH), respectively. Based on 2D-COS of Raman, the peak of Fenjiu (b) at 3440 cm(-1) changes initially, indicating its disorder degree is getting higher with continuous dilution with water. However, along with the dilution of Fenjiu (a) and Fenjiu (c), the peak located near 3200 cm(-1) changes in priority, indicating that the degree of association between ethanol and water is high, and the clusters formed there are stable. Therefore, this work provides the combined methods to distinguish different supramolecular sets in Fenjiu, applying liquor differentiation in the future. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Aqueous solutions of salts composed from monovalent ions are explored using temperature-dependent FT-IR spectroscopy in transmission. Water combination band, being extremely sensitive to the network of hydrogen bonds due to the contribution of water librations (rho LH2O), is analyzed in uni- and multivariate fashion. Univariate analysis of the combination band maximum (nu(max)) reveals that perturbation of water hydrogen bond network by ions is primary driven by electrostatic interactions between water and ions. Using multivariate curve resolution with alternating least squares and evolving factor analysis this band is separated into two components that represent low- and high-density water. The observed asymmetry in their behavior is interpreted in terms of fluctuations of a hydrogen bond network of two water components. The significance of the found phenomenon is unambiguously confirmed by performing analogous analysis in the spectral range that contains partial signature of water linear bending (delta HOH) and is free from rho LH2O, in which the asymmetry is absent. Additionally, we show that this phenomenon, namely ion-invariant behavior of water fluctuations, persists even in the regime of high ionic strengths. Although ions indeed participate in shaping of water hydrogen bond network, this straightforward approach shows that its temperature-dependent fluctuations are ion-independent. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
Richter, Wagner E.Duarte, Leonardo J.Bruns, Roy E.
7页
查看更多>>摘要：Population analyses based on point charge approximations accurately estimating the equilibrium dipole moment will systematically fail when predicting infrared intensities of out-of-plane vibrations of planar molecules, whereas models based on both charges and dipoles will always succeed. It is not a matter of how the model is devised but rather how many degrees of freedom are available for the calculation. Population analyses based on point charges are very limited in terms of the amount of meaningful chemical information they provide, whereas models employing both atomic charges and atomic dipoles should be preferred for molecular distortions. A good model should be able to correctly describe not only static, equilibrium structures but also distorted geometries in order to correctly assess information from vibrating molecules. The limitations of point charge models also hold for distortions much larger than those encountered vibrationally. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Black phosphorus has important applications in many fields such as optics, optoelectronics and thermals. Many of its excellent properties are related to its special anisotropy. In this work, we adopted Raman spectroscopy, which can obtain fast response optical signals without destroying the structure of the sample, to identify its crystal orientation and explore its thermal and SERS properties. We successfully distinguished the armchair and zigzag directions of black phosphorus by angle-resolved polarized Raman spectroscopy of A(g) mode in a less studied orthogonal polarization configuration. Then we used temperature dependent Raman spectroscopy to study its thermal properties. It is found that the first order temperature coefficients of its three Raman vibration modes A(g)(1), B-2g, and A(g)(2) are -0.0133 cm(-1) K-1, -0.0232 cm(-1) K-1 and -0.0229 cm(-1) K-1, respectively for the 3.2 nm sample. Furthermore, we studied the surface enhancement effect of black phosphorus with different thicknesses as SERS substrates. We found that few-layer black phosphorus has better enhancement effects and its limit of detection for MB and CV are both 10(-6)M. The analytical enhancement factor of black phosphorus substrates on CV can achieve 1.2 x 10(3) by calculation. These methods can be extended to other similar two-dimensional materials. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Transition dipole moment orientation is one of the crucial factors, which can enhance the performance of organic light-emitting diodes (OLEDs). In this work, the transition dipole moment orientation of the host-guest emission layers (EMLs) prepared by solution method annealed at different temperatures were systematically studied by analyzing the angle-dependent PL spectrum. When the EMLs of 2DPAc-MPM (20 wt%): DPEPO was annealed at the temperature of 115 degrees C, the photoluminescence quantum yield (PLQY) was enhanced to 78%+/- 3.5%, and the vertical dipole ratio was reduced to 0.34. The lower vertical orientation of transition dipoles is conducted to improve the electron and hole mobility, which was testified by the hole and electron only devices. The lower vertical dipole ratio, higher PLQY and carrier mobility together enhanced the performance of solution processed OLEDs. (C) 2022 Published by Elsevier B.V.
查看更多>>摘要：Selective detection of nitroaromatic compounds such as Picric acid (PA), those being explosive materials and hazardous pollutants of environmental and biological concern is highly desirable. With the operational advantages of the chemosensing approach, a pyrene-rhodamine-B couple (1) was explored in this investigation as a ratiometric molecular probe for selective and sensitive detection of picric acid. The bifluorophoric probe displayed absorption and fluorescence enhancements along with colourless to reddish-brown colour transition as signaling responses in the selective presence of PA among all the nitro aromatic analyte investigated. The signaling module relies on PA-mediated modulation of various operational photo-physical processes such as (a) inhibition of photo-induced electron transfer (PET) operative from amino-donor to excited pyrene (b) a conformational translation through spiro-ring opening of rhodamine-B segment, and (c) initiation of Fluorescence Resonance Energy Transfer (FRET) between excited pyrene donor and ring-opened rhodamine acceptor. The ratio of fluorescence from both fluorophores (pyrene and Rhodamine) as output channel displayed sensitive signaling performance (LOD = 13.8 nM) in the detection of PA. The investigation that inferred to the PA-induced selectivity in signalling, higher binding affinity (log K-a approximate to 11), a faster response time, and reversibility in signalling with a counter analyte and an operational pH range established the probe's efficacy as a chemosensor for PA detection. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The dissociation constant is an important physicochemical parameter of a molecule. The protonation state of a molecule reflects its reactivity, solubility or ability to chemically interact with other molecules. In the present study, dissociation constants (pK(a)) values of 2,5-dihydroxy-1,4-benzoquinone (DHBQ) were determined by UV-Vis, fluorescence and ATR-FTIR spectroscopy at 25 degrees C. The resulting pK(a) values for DHBQ were 2.95 and 5.25. We have also experimentally found out that the monoanionic form (HBQ(-)) provides weak fluorescence in the pH range of about 3-6. This allowed us to determine not only the pK(a) in the ground but also the excited state of the molecule (pK(a1)* = 4.38 and pK(a2)* = 5.27). (C) 2022 Elsevier B.V. All rights reserved.
Elsonbaty, AhmedMadkour, Ahmed W.Abdel-Raoof, Ahmed M.Abdel-Monem, Ahmed H....
14页
查看更多>>摘要：Nowadays, the analytical community is focusing on developing new analytical methods that incorporate principles of green analytical chemistry to reduce adverse impacts on the environment and humans. In this study, we focused specifically on establishing a correlated connection between theoretical and experimental applications via developing green, and eco-friendly visible spectrophotometric methods. These methods were relied on charge-transfer complexation (CTC) between ledipasvir and 2,3-dichloro-5,6-d icyano-1,4-benzoquinone (DDQ), or chloranilic acid (CA) for sensitive colorimetric analysis of ledipasvir in the presence of sofosbuvir (Sofolanork plus (R)). The results were evaluated as modern computational chemistry using molecular modeling technology. At ambient temperature, the reactions for DDQ and CA took 15 and 10 min, respectively, to produce a purple red-colored solution with DDQ absorbing maximally at 588 nm and a purple-colored solution with CA absorbing maximally at 522 nm. Linearity was achieved for ledipasvir utilizing DDQ and CA in the concentration ranges of 8-80 mu g.mL(-1) and 40-400 mu g.mL(-1), respectively. The precision and accuracy of the methods mentioned were determined. Finally, the results were statistically compared to a previously published spectrophotometric technique, and no significant differences were found. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The stability of biological drugs with protein as an active substance depends heavily on the retention of natural protein structure during freeze-drying. Stabilizers have become important substances in the process of protein freeze-drying. In order to further understand the mechanism of the interaction between protein and stabilizers, human serum albumin (HSA) and simple hydroxyl compound ethanol were used as models. Infrared (IR) spectroscopy combined with chemometrics was implemented to investigate the changes of secondary structure and hydration of HSA when different concentrations of ethanol were considered as interference. Through the analysis of the protein secondary structure and hydrated layer, we found that the addition of ethanol-d6 increased the alpha-helix of HSA and reduced the disordered structure. The hydrogen bond structure around HSA was enhanced and intermolecular aggregation was reduced through the action of the water molecules. The hypothesis was verified by circular dichroism (CD) and transmission electron microscopy (TEM) observation by adding different concentrations of ethanol-d6. It was found that a small amount of ethanol could protect the native conformation of HSA. In conclusion, this study revealed the mechanism of ethanol as a protein protector, provided a new idea for protein purification process and a theoretical basis for biomolecular interaction. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：A simple and green method for the synthesis of fluorescent carbon nanospheres (CNs) was proposed using chrysanthemum as a natural precursor and ethylenediamine as the co-reagent. The prepared CNs show strong blue fluorescence in water with quantum yield of 13.7 %, and distinguished fluorescent stability against photobleaching and ion strength. Meanwhile, the fluorescence signal of CNs is reversible and sensitive to temperature in the range of 20-80 degrees C, which makes CNs useful as a temperature sensor. More importantly, the CNs can serve as excellent fluorescent sensors for detecting MnO4 and He2+ with the detection limit of 0.72 and 0.26 mu M, respectively. MnO4 quenches the fluorescence of CNs through inner filter effect and static quenching mechanism, while He2+ forms a stable complex with the amino group on the surface of CNs, resulting in the fluorescence quenching of CNs. However, the stronger affinity between He2+ and captopril (Cap) results in the fluorescence quenched by He2+ recovery after the addition of Cap. Thus, the CNs-He2+ system is employed as a novel sensitive and selective fluorescence "turn-on" sensor for Cap in the range of 0-75 mu M. Inspired by the sensing results, the developed sensors were successfully used for the determination of MnO4 , He2+ in river water samples and Cap in the pharmaceutical and urine samples. (C) 2022 Elsevier B.V. All rights reserved.
NSTL
Elsevier