Rationalization of the Color Properties of Fluorescein in the Solid State: A Combined Computational and Experimental Study

Fluorescein is known to exist in three tautomeric forms defined as quinoid, zwitterionic, and lactoid. In the solid state, the quinoid and zwitterionic forms give rise to red and yellow materials, respectively. The lactoid form has not been crystallized pure, although its cocrystal and solvate forms exhibit colors ranging from yellow to green. An explanation for the observed colors of the crystals is found using a combination of UV/Vis spectroscopy and plane‐wave DFT calculations. The role of cocrystal coformers in modifying crystal color is also established. Several new crystal structures are determined using a combination of X‐ray and electron diffraction, solid‐state NMR spectroscopy, and crystal structure prediction (CSP). The protocol presented herein may be used to predict color properties of materials prior to their synthesis.     

The Isothiocyanato Moiety: An Ideal Protecting Group for the Stereoselective Synthesis of Sialic Acid Glycosides and Subsequent Diversification

The preparation of a crystalline, peracetyl adamantanyl thiosialoside donor protected by an isothiocyanate group is described. On activation at ?78 °C in the presence of typical carbohydrate acceptors, this donor gives high yields of the corresponding sialosides with exquisite α‐selectivity. The high selectivity extends to the 4‐O‐benzyl‐protected 3‐OH acceptors, which are typically less reactive and selective than galactose 3,4‐diols. Treatment of the α‐sialosides with tris(trimethylsilyl)silane or allyltris(trimethylsilyl)silane results in replacement of the C5? N5 bond by a C? H or a C? C bond. The reaction of the isothiocyanate‐protected sialosides with thioacids generates amides, while reaction with an amine gives a thiourea, which can be converted into a guanidine. The very high α‐selectivities observed with the new donor and the rich chemistry of the isothiocyante function considerably extend the scope for optimization at the sialoside 5‐position.     

异硫氰酸荧光素标记尿激酶的制备与性能研究

用异硫氰酸荧光素(FITC)对溶栓蛋白药物尿激酶(uPA)进行了荧光标记, 制备了荧光素标记的尿激酶(FITC-uPA), 经核磁谱及红外谱表征证实了反应能有效进行, 其荧光素/蛋白值(F/P)值为0.45. 尿激酶经荧光素标记后, 具有良好的荧光性质, 其荧光检测下限低达10-6 g?mL-1. 在1~100 ?g?mL-1范围内, 荧光强度与溶液浓度具有很好的线性关系, 可用于微/痕量蛋白质的定量/定性检测和跟踪标记. 荧光素标记后的尿激酶, 其流体力学直径与未标记的尿激酶基本一致, 其体外溶栓能力也与未标记的尿激酶相当, 说明FITC标记基本不影响尿激酶的生物活性, 是一种简单、有效的溶栓药物标记方法.     

The Acid-Base/Deprotonation Equilibrium Can Be Studied with a MicroScale Thermophoresis (MST)

MicroScale thermophoresis (MST) is a rapidly developing bioanalytical technique used routinely for the examination of ligand-target affinity. It has never been used so far for the analysis of acid-base dissociation and the determination of pK_a constant. This work is the-proof-of-concept of this new idea. It demonstrates that the pK_a values obtained from the thermophoretic data are consistent with the reference methods. As a result, the analytical potential and utility of the MST technology can become even greater, especially if the new detection system of thermophoretic movement will be developed in the future. Even now, taking into account the necessity to use fluorescence, the proposed method may be useful in many respects.     

Fluorescein Hydrazide-Appended Metal–Organic Framework as a Chromogenic and Fluorogenic Chemosensor for Mercury Ions

In this work, we prepared a fluorescein hydrazide-appended Ni(MOF) (Metal–Organic Framework) [Ni₃(BTC)₂(H₂O)₃]·(DMF)₃(H₂O)₃ composite, FH@Ni(MOF). This composite was well-characterized by PXRD (powder X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy), N₂ adsorption isotherm, TGA (thermogravimetric analysis), XPS (X-ray photoelectron spectroscopy), and FESEM (field emission scanning electron microscopy). This composite was then tested with different heavy metals and was found to act as a highly selective and sensitive optical sensor for the Hg²⁺ ion. It was found that the aqueous emulsion of this composite produces a new peak in absorption at 583 nm, with a chromogenic change to a pink color visible to the naked eye upon binding with Hg²⁺ ions. In emission, it enhances fluorescence with a fluorogenic change to green fluorescence upon complexation with the Hg²⁺ ion. The binding constant was found to be 9.4 × 10⁵ M⁻¹, with a detection limit of 0.02 μM or 5 ppb. This sensor was also found to be reversible and could be used for seven consecutive cycles. It was also tested for Hg²⁺ ion detection in practical water samples from ground water, tap water, and drinking water.     

激光光源-在线荧光光谱检测中的光强度比较研究

基于激光光源和氙灯光源在线荧光光谱法测定罗丹明B、维生素B₂、荧光素和异硫氰酸荧光素含量比较研究激光光源产生的荧光强度和氙灯光源产生的荧光强度。罗丹明B、维生素B₂、荧光素和异硫氰酸荧光素浓度均为10 μg·mL-1,积分时间100 ms,测定3次得其平均值。在线荧光光谱法最大吸收波长分别为580,450,488和510 nm;最大发射波长依次为594,530,525和524 nm。紫外-可见分光光度法测得其最大吸收波长为557,441,481和490 nm;荧光分光光度法测得其最大发射波长为586,520,519和520 nm。通过测定药物,发现激光光源产生的荧光光强度较强于氙灯光源产生的荧光光强度,原因不仅跟光源有关,而且与药物分子的共轭体系大小、共轭大π键的共平面性及其刚性程度、分子母体上取代基的种类有关,分子所处的外界环境如温度、溶剂、溶液酸碱度、激发光的照射等因素也会影响荧光效率。激光光源和氙灯光源产生的荧光光强度大小顺序为罗丹明B>荧光素>异硫氰酸荧光素>维生素B₂。激光光源在线荧光光谱法在一定程度上填补了在线荧光光谱仪在食品、药品痕量检测方面应用的空白。     

几种荧光素酯的自然水解和脂酶催化水解反应的研究

本文研究了荧光素的发光条件以及浓度、温度、pH对四种荧光素酯(荧光素二乙酸酯、荧光素二丙酸酯、荧光素二丁酸酯、荧光素二己酸酯)水解反应的影响,讨论了在脂酶存在下荧光素酯的分解反应机理,确定了每种荧光素酯的最佳酶反应条件.实验结果表明,脂酶对荧光素二丙酸酯(FDP)的酶反应效率最好,有应用前景.     

Fluorescence spectroscopic studies on the multicomponent system coumarin 1/fluorescein/rhodamine B in ethanol

The steady-state fluorescence spectra of the three-component system coumarin 1/fluorescein/rhodamine B in 95% ethanol were studied at room temperature. In the appropriate concentration ranges, upon the excitation of coumarin 1 at 377 nm, the ternary dye mixture solution emitted simultaneously with three bands centered at 443, 528, and 575 nm, respectively. The analysis of the data seems to indicate that there is significant energy transfer between these three dyes and that the main contribution corresponds to the Förster nonradiative mechanism. The critical transfer distances between each two of the three components were calculated to be 48.4 Å for the coumarin 1/fluorescein pair, 42.2 Å for the coumarin 1/rhodamine B pair, and 65.5 Å between fluorescein and rhodamine B dyes. The system can potentially be used to obtain three primary outputs at different wavelengths in a dye laser system.     

Centrifugal distortion analysis of the microwave spectrum of allyl isothiocyanate (C-gauche conformer)

The ground state microwave rotational spectrum of the C-gauche conformer of allyl isothiocyanate has been reinvestigated by extending the frequency range up to 37.0 GHz. A detailed centrifugal distortion analysis has been carried out with previously reported and newly assigned microwave rotational transition frequencies. The evaluated rotational and centrifugal distortion constants are presented.     

双(N-糖基-硫代氨基脲-2-基)硫代磷酸芳基酯的合成(Ⅱ)

芳氧基硫代磷酰二氯(1a，lb)肼解后得到芳氧基硫代磷酰二肼(2a，2b)，将它们分别与糖基异硫氰酸酯(3a～3c)在苯中回流．生成相应的双(N-糖基-硫代氨基脲-2-基)硫代磷酸芳基酯(4a～4c，5a～5c)．它们的结构经IR．^1H NMR,^31P NMP,MS和元素分析加以确证．