The influence of matrix concentration and solvent composition on the results of MALDI MSI,with the aid of wet-interface matrix deposition

Imaging mass spectrometry is a powerful technique for the molecular analysis of tissue sections. As in many analytical methods, sample preparation is one of the main and most important steps to obtain results of good quality. Usually, the matrix concentration and solvent composition in different studies are taken for granted without any further consideration. In our studies, we aimed to find how matrix concentration and a type of solvent influence the signal. Moreover, we also aimed to find the relationship between these parameters, how they influence the spectra, and how they influence obtained ion maps. In our experiments, we used SunCollect®, which is a commercially available wet-interface system for matrix deposition. We decided to choose two matrix concentrations (2,5-dihydroxybenzoic acid [DHB]: 15 and 25 mg/mL; 9-aminoacridine [9AA]: 7 and 5 mg/mL) and two different water solutions of solvents in two different percentages for the matrices (DHB: 50% and 70% of methanol [MeOH] and acetonitrile [ACN]; 9AA 70% and 50% of ethanol [EtOH] and MeOH). In the end, the influence of these parameters on obtained spectra and ion maps was assessed.     

Solvent effects on the electronic absorption spectra and acid strength of some substituted pyridinols.

The electronic absorption spectra of some substituted pyridinols in organic solvents of different polarities are studied. Also, the solvent effects on the intramolecular charge transfer bands are discussed using various solvent parameters. The acid-base equilibria of the compounds used are studied spectrophotometrically in various mixed aqueous solvents at 25 degrees C and 0.1 M ionic strength (NaClO4). Furthermore, the influence of the solvents on the dissociation constants and tautomeric equilibria of a pyridinol derivatives are discussed. The effect of molecular structure of the pyridinols on the pK's is also examined.     

Reflectance spectra of organic matrices on the basis of photonic crystals formed of polystyrene microspheres with a particle size of 230 nm

The specular and diffuse reflectance spectra of organic matrices on the basis of photonic crystals formed of polystyrene microspheres with a particle size of 230 nm and polydimethylsiloxane layers, which are both applied on substrates made of quartz glass and acrylic plates, are recorded. Part of the organic matrix changes color from green to red-yellow 2 to 5 min after contact with a nonpolar solvent. The kinetics of structural changes occurring in the organic matrix under the influence of non-polar organic solvents, such as toluene, benzene, and n-hexane, is studied by diffusion reflectance spectroscopy. The equilibria in the organic matrix are achieved in 15–20 min.     

Solvent selection for matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometric analysis of synthetic polymers employing solubility parameters

The principle relating to the selection of a proper matrix, cationization reagent, and solvent for matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) of synthetic polymers is still a topic of research. In this work we focused on the selection of a suitable MALDI solvent. Polystyrene PS7600 and poly(ethylene glycol) PEG4820 were analyzed by MALDI‐TOF MS using various solvents which were selected based on the Hansen solubility parameter system. For polystyrene (PS), dithranol was used as the matrix and silver trifluoroacetate as the cationization reagent whereas, for poly(ethylene glycol) (PEG), the combination of 2,5‐dihydroxybenzoic acid and sodium trifluoroacetate was used for all experiments. When employing solvents which dissolve PS and PEG, reliable MALDI mass spectra were obtained while samples in non‐solvents (solvents which are not able to dissolve the polymer) failed to provide spectra. It seems that the solubility of the matrix and the cationization reagent are less important than the polymer solubility. Copyright © 2010 John Wiley & Sons, Ltd.     

Tautomerism phenomenon of pyrazolo[3,4-b]quinoline: spectroscopic and quantum mechanical studies

Tautomerism of pyrazolo[3,4-b]quinoline (PQ) was studied using electronic absorption and emission spectroscopies in various polar and nonpolar solvents. The absorption spectra of the tautomers were modeled, and the respective bands were assigned using ab initio quantum mechanical calculations. Temperature-dependent absorption spectra showed the dynamic equilibrium of the two species, which were observed only in aliphatic solvents. The anomalous relative populations of the tautomers were explained by the stabilizing effect of the specific PQ-hydrocarbon interactions. Excited-state intramolecular proton transfer (ESIPT) was proposed to explain the measured fluorescence spectra. Hydrogen bonds that are formed in methanol and benzene were shown to strongly influence the nature of both the absorption and emission spectra.     

Anwendung von Klassifikationsverfahren zur Interpretation von Lösungsmitteleinflüssen auf EPR-Spektren

Use of Classification Methods to Interpret the Influence of Solvents on Parameters of EPR Spectra The influence of solvents on EPR spectra of Cu^II-Acetylacetonate (registered at room temperature) was investigated. The classification of mean values of the g-tensors and coupling constants using different clustering methods lead to groups of solvents which are related to the respective substance classes. The analysis of the relationship between EPR data and solvent parameters showed, that there exists a close relation between Lewis basicity of solvents and classification found by using clustering methods.     

光异构化反应的研究——水杨醛缩芳胺席夫碱的吸收光谱与分子结构的关系

<正> 具有光致变色现象的席夫碱在过去几十年里一直为人们所感兴趣。一般认为,水杨醛上的邻羟基是这类席夫碱发生光致变色的必要条件。光致变色的过程就是邻羟基的质子转移到亚氨基的氮原子上,随后发生分子内的几何异构,但对此机理仍存在争执。本文主要报道一些席夫碱的电子吸收光谱与分子结构的关系,以及溶剂对电子吸收光谱的影响。     

Analysis of charge-transfer absorption and emission spectra on an absolute scale: evaluation of free energies, matrix elements, and reorganization energies

The relationship between the absorption and emission spectra of the charge-transfer complexes formed between a series of methyl-substituted benzene donors with 1,2,4,5-tetracyanobenzene as acceptor in 1,2-dichloroethane was examined in detail. The association constants for charge-transfer complex formation and the emission quantum yields for these complexes were used to place the experimental absorption and emission spectra on absolute scales. The simultaneous analysis of these spectra is valid only when the Mulliken two-state model is justified. For several of the complexes included in this study the electron-transfer parameters, including the electronic coupling matrix elements, obtained from the analysis of the individual absorption and emission spectra are in close agreement. The simultaneous analysis of the combined absorption and emission spectra leads to a well-defined set of electron-transfer parameters for these complexes. In other complexes, where the two-state model does not apply because of the influence of localized excited states on the absorption spectrum, analysis of the absorption and emission spectra led to significantly different sets of electron-transfer parameters. It is demonstrated that the electronic coupling matrix elements are a very sensitive indicator of the influence of localized excited states on these spectra.     

Solvent effect in polymer analysis by MALDI-TOF mass spectrometry

Solvent effect is one of the important factors in sample preparation which may affect matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra of synthetic polymers. MALDI imaging, a useful imaging tool for discovering biomarkers in tissues, is applied here for better comprehension of solvent effect in polymer analysis by MALDI-TOF mass spectrometry. Nylon-6 was chosen as a model polymer for the study of solvent effect. Its MALDI mass spectra in different solvents were performed. MALDI imaging analysis was performed for studying the incorporation of analytes into matrix crystals in different solvent combinations. Specifically, the colocalization of matrix and analyte was obtained through Pearson’s correlation (PC) coefficient analysis of their MALDI images. The results demonstrated that satisfactory spectra were obtained in higher PC value conditions. PC decreased along with an increase in the ratio of poor solvent, which suggested that we should minimize the poor solvent ratio to obtain better MALDI spectra.     

Internal Conversion Process of Chlorophyll a in Solvents in Femtosecond Pump-Probe Laser Fields

The internal conversion (IC) processes of chlorophyll a (chl-a) in solvents are studied based on the reduced density matrix theory. The IC times can be obtained by simulating the experimental fluorescence depletion spectra (FDS). The calculated IC times of chl-a in ethyl acetate, tetrahydrofuran and dimethyl formamide are 141, 147, and 241 fs, respectively. The oscillation feature of the FDS results from the forward and backward transfer of the population between coupled electronic states. The effects of diabatic coupling between two electronic states on the IC time and the FDS are described. The influence of molecule-reservoir coupling on the IC time is also investigated.     

Covalently bonded polysaccharide derivatives as chiral stationary phases in high-performance liquid chromatography

Polysaccharide derivatives have been extensively used as chromatographic chiral selectors in chiral stationary phases (CSPs) for the separation of enantiomers by HPLC. When coated onto a silica matrix, they represent nowadays one of the most popular type of CSPs. However, they are only compatible with a limited choice of solvents. The main drawback of these CSPs is related to the solubility of the chiral selector in a number of solvents, which limits their applicability. The different attempts which have been described up to now to overcome this problem by covalently fixing the chiral selector to a matrix are reviewed in this paper.     

Dynamics of intramolecular electron transfer in dinitrodibenzodioxin radical anions

The activation energy for intramolecular electron transfer in radical anions of 2,7-dinitrodibenzodioxin and 2,8-dinitrodibenzodioxin, obtained by simulation of their temperature-dependent EPR spectra, are well predicted by the values calculated by the two-state Marcus-Hush model from the optical charge-transfer bands using quartic-adjusted energy surfaces. The electronic coupling is higher in the 2,8-dinitrodibenzodioxin (H(ab) = 485 cm(-1)) than in the 2,7-dinitrodibenzodioxin radical anion (H(ab) = 250 cm(-1)), but for each solvent the reorganization energy, taken as the maximum of the optical band, is only slightly higher in the latter. These values are consistent with the fact that the reaction is faster in the 2,8-dinitrodibenzodioxin radical anion isomer, as determined by EPR spectroscopy. The pre-exponential factors obtained combining the EPR-derived rate constants and the activation energies calculated from the optical bands fit well the theoretical (modified) nonadiabatic values in the less viscous solvents. However, for the more viscous solvents, the trend of the pre-exponential values with solvent can only be explained if dynamical solvent effects increasingly influence their value. The influence of solvent dynamics in the 2,8-dinitrodibenzodioxin radical anion starts in the less viscous solvents DMF and DMSO, but in the 2,7-dinitrodibenzodioxin isomer this is only fully evident for the more viscous PhCN and HMPA. The influence of solvent dynamics is higher in the radical with the lowest activation barrier.     

Excitation wavelength and solvent dependent emission spectra in weakly polar aprotic solvents at room temperature and 77 K

Excitation wavelength-dependent emission spectra of 4-methyl-2,6-diformylphenol (MFOH) and o-hydroxybenzaldehyde (OHBA) have been examined both in pure weakly polar aprotic solvents and in the presence of a base at room temperature and 77 K. It is shown that fluorescence quantum yield shape, position of the spectra, and number of conformers are dependent upon the excitation energy and also on the proton-accepting ability of the solvents. Fluorescence spectra cannot be correlated with the solvent dielectric properties. At 77 K, deactivation occurs via phosphorescence only at a particular experimental condition in all the solvents studied here. The decay rates are relatively slower in an environment where the probability of hydrogen bonding interaction is stronger.     

Temperature and high pressure effects on the spin-hamiltonian parameters in solutions of copper and vanadyl compounds

The temperature dependence of the spin-Hamiltonian (s-H) parameters of the ESR spectra of liquid and glassy solutions of some copper and vanadyl compounds has been investigated.It is shown that in the case of non-coordinating solvents the temperature dependence is not affected by such factors as viscosity, molecular geometrical dimensions and free ligand concentration in solution that strongly influence intermolecular exchange in coordinating solvents.The temperature variations of s-H parameters in the liquid and crystal states of copper diethyldithiocarbamate have been compared.The influence of pressure on the ESR parameters of copper and vanadyl in liquid solutions has been investigated.The measurements show that temperature variations of the s-H parameters of the ESR spectra of solutions of copper and vanadyl in non-coordinating solvents are the results of intramolecular heat effects.     

Several Organic Salts with High Two‐Photon Active

Several organic salts with D‐A molecular structure and different counterion have been prepared and experimentally investigated. The two‐photon induced frequency‐upconverted spectra and two‐photon pumped lasing are measured for the organic salt solutions in various solvents. The results indicate that counterions have influence on their stability and lasing property.     

Dual fluorescence of syringaldazine

The absorption and fluorescence spectra of syringaldazine (SYAZ) has been recorded in solvents of different polarity, pH and beta-cyclodextrin (beta-CD) and compared with syringaldehyde (SYAL). The inclusion complex of SYAZ with beta-CD is investigated by UV-vis, fluorimetry, AM 1, FT-IR, (1)H NMR and scanning electron microscope (SEM). DeltaG value suggests the inclusion process is an exothermic and spontaneous. In all solvents a dual fluorescence is observed for SYAZ, whereas, SYAL shows a dual luminescence only in polar solvents. The excitation spectra for the 410 nm is different from 340 nm indicate two different species present in this molecule. In pH solutions: (i) a large red shifted maxima is observed in the dianion and is due to large interactions between the aromatic ring and (ii) the large blue shift at pH approximately 4.5, is due to dissociation of azine group and formation of aldehyde. beta-CD studies reveal that, SYAZ forms a 1:2 complex from 1:1 complex with beta-CD.     

Solvent effects on the resonance Raman and hyper-Raman spectra and first hyperpolarizability of N,N-dipropyl-p-nitroaniline

Linear absorption spectra, resonance Raman spectra and excitation profiles, and two-photon-resonant hyper-Rayleigh and hyper-Raman scattering hyperpolarizability profiles are reported for the push-pull chromophore N,N-dipropyl-p-nitroaniline in seven solvents spanning a wide range of polarities. The absorption spectral maximum red shifts by about 2700 cm(-1), and the symmetric -NO2 stretch shifts to lower frequencies by about 11 cm(-1) from hexane to acetonitrile, indicative of significant solvent effects on both the ground and excited electronic states. The intensity patterns in the resonance Raman and hyper-Raman spectra are similar and show only a small solvent dependence except in acetonitrile, where both the Raman and hyper-Raman intensities are considerably reduced. Quantitative modeling of all four spectroscopic observables in all seven solvents reveals that the origin of this effect is an increased solvent-induced homogeneous broadening in acetonitrile. The linear absorption oscillator strength is nearly solvent-independent, and the peak resonant hyperpolarizability, beta(-2omega;omega,omega), varies by only about 15% across the wide range of solvents examined. These results suggest that the resonant two-photon absorption cross sections in this chromophore should exhibit only a weak solvent dependence.     

4—甲基—7—羟基香豆素的发光特性研究

对比考察了多种溶剂介质中不同浓度４－甲基－７－羟基香豆素溶液的荧光光谱特性，发现其谱形状与峰位不仅随溶剂性质而异，且随浓度而变，在某些氢键溶剂中，激发光谱随浓度有很大变化，且发射光谱间存在某种内在联系。基于溶剂本身的性质及４－甲基－７－羟基香豆素在氢键溶剂中的二聚作用讨论了这种现象，本文还考察了这种香豆素衍生物在滤纸及聚酰胺膜基质上，以Ｐｂ（Ａｃ）２或Ｐｂ（ＮＯ３）２作重原子微扰剂时的室温磷光特性     

Quality control in residual solvent analysis: the static headspace gas chromatographic method

 Residual solvent testing of raw materials and drug products constitutes part of a quality control programme. Static headspace gas chromatography (HS/GC) is suggested in current pharmacopoeias as a general tool for residual solvent testing. But the main obstacles to using HS/GC procedures are the absence of performance tests, suitable reference solvents and matrix standards, and reference methods. Harmonized regulations for residual solvent testing allow the use of a cumulative approach to estimate the residual solvent content in drug products. The supplier data may be appropriate. Therefore, in a quality control programme the main accent is put on the definition of specification limits (in accordance with toxicological data, and the influence of residual solvents on the physical properties and stability of the product) and supplier qualification. This paper focuses on two main problems linked to supplier qualification: system performance and matrix effect. HS/GC of a mixture containing solvents of different volatility and polarity is proposed as a performance test. The test can be done in three ways in accordance with the residual solvents characteristics, the test sample solubility and the specification levels required. The use of the test as a diagnostic tool is demonstrated and sources of uncertainty of the recovery determination are discussed. Received: 12 December 1998 · Accepted: 25 January 1999     

水杨酸及其酯类化合物在不同溶剂中吸收光谱和荧光光谱的研究

本工作测定了水杨酸和水杨酸甲酯在不同溶剂中的吸收光谱和荧光光谱,并按在不同温度下测得的结果计算出它们在不同溶剂中平衡过程的函变△H.数据表明,在质子溶剂中,上述化合物有较小的△H值,即形成的分子内氢键只有较低的稳定性.根据这些结果可对该类化合物在不同溶剂中形成内氢键的能力作出恰当的评价.