交联剂含量对憎水改性缔合型增稠剂性能的影响

以甲基丙烯酸、丙烯酸乙酯和功能单体二十二烷基聚氧乙烯醚甲基丙烯酸酯为原料,过硫酸铵为引发剂,变化交联剂邻苯二甲酸二烯丙酯(DAP)的量,采用半连续乳液聚合方法合成了DAP含量不同的憎水改性缔合型增稠剂乳液.测定了乳液的黏度和乳胶粒粒径及其分布等性能.考察了乳液运动黏度和透光率随pH的变化.随着pH值的增加,乳液的透光率...     

烷烃中碳氢键离解能的估算及其应用

将烷烃中的C－H键看成氢原子H与烷基Ri相连接而成的Ri－H键，以烷基的 HOMO能级和氢原子的轨道能来关联Ri－H键的离解能BDE。研究表明，烷烃分子中 Ri－H键的离能BDE与烷基Ri的极化效应指数PEI（Ri）有良好的线性关系：BDE＝ c+dPEI(Ri)。所得方程具有良好的估算精度。烷基Ri极化效应指数PEI（Ri）在羟 基自由基与烷烃反应速度常数的定量相关中，也得到良好的应用。     

有机磷化合物的研究 Ⅷ.酸性有机磷化合物的气相色谱

酸性磷(膦)酸酯与四甲基氢氧化铵的甲醇溶液反应制得的四甲基铵盐溶液,热解转化成O-甲基化产物用气相色谱鉴定。分离与鉴定了磷酸二烷基酯、磷酸单烷基酯、烷基膦酸单烷基酯和二烷基膦酸等,并讨论了烷基碳原子数和烷基的空间效应对校正保留时间(t′_R)及保留指数(I)的影响。     

烷基极化效应与X=O键伸缩振动频率

烷基取代物R’X=0的X=0键伸缩振动频率ν与烷基R的极化效应指数PEI(R)的关系可表示为:ν=a bPEI(R)。研究结果表明,烷基的极化效应使X=0键的伸缩振动频率降低。     

用诱导效应指数讨论烷基在气相有机化合物中的诱导效应

应用诱导效应指数讨论了烷基的诱导效应方向，解释了低级脂肪醇在气相中酸性、碱性强弱次序一致的原因。     

含氟丙烯酸酯-苯乙烯共聚物的制备及其表面性能的研究

研究了聚合工艺、含氟丙烯酸酯类单体种类和用量、苯乙烯和自由基引发剂用量及硅烷偶联剂、催化剂等因素对含氟丙烯酸酯-乙烯共聚物表面性能的影响。结果表明：聚合工艺、含氟丙烯酸酯类单体种类和用量对共聚物表面的憎水性能有显著的影响;采用延时滴加含氟丙烯酸酯类单体可提高共聚物膜表面的憎水性;随含氟丙烯酸酯类单体侧链含氟烷基的链长和氟原子数及含氟单体用量的增加,共聚物水接触角增大,吸水率下降;共聚物薄膜的硬度则与含氟丙烯酸酯类单体中α-取代基、侧链含氟烷基的链长和用量、苯乙烯用量、引发剂浓度等相关;硅烷偶联剂和催化交联剂的加入可提高共聚物薄膜的强度。     

分子结构与化学活性间的定量关系——Ⅲ.脂肪腈与甲醇的加成反应

在甲醇钠的作用下,进行了脂肪腈类与甲醇的加成反应。实验结果表明:加成反应百分率与腈分子中烷基的诱导效应指数形成一正 S 型曲线,而反应的平衡常数及速度常数的对数则分别与烷基的诱导效应指数形成直线关系。根据转化率 S 型曲线上 I_(50)点的位置(10~3I_(50)=10),可以肯定所有烷基腈在这个反应中的转化率都很低,而且反应速度很慢;在卤素、羧基及氰基取代烷基腈中,α-取代物反应迅速且转化率高,但取代基在γ-位置以外,则情况与简单烷腈相近。蒋化率曲线的正 S 走向及速度常数与平衡常数对数的直线的正倾斜度,均表明这个反应是甲醇对腈的亲核子加成反应。     

反相高效液相色谱法测定酚类化合物的保留指数

以3种ODS柱分别测定了10种酚类化合物的保留值,以烷基甲酮类作为标准参照物计算保留指数及校正保留指数。结果表明,采用校正保留指数系统,可获得比常规保留指数系统更好的精密度和准确性。     

由烷基吡啶和喹啉同系物的保留指数推算结构参数的探讨

随着人们对化合物的色谱保留及其物化性质、结构参数间关系的研究,为色谱法推测化合物的物化性质及分子结构提供了可能性。我们曾把烷基喹啉、苯氧烷基吡啶类等同系列化合物的保留指数(I_R)与其分子量(M),分子中碳原子数(N),分子连通性指数(X)等作了关联,得到了I_R与M、N间的近似线性关系和I_R与X间的良好线性关系。本文根据该关系对15种烷基吡啶和6种烷基喹啉化合物的M、N和X进行计算,获得了较好的结果。     

有效碳链长度与脂肪醇的沸点

脂肪醇沸点(b.p.)变化规律可用下述关系式表示:ln(800.386-T~b)=6.64919-2.94828×10^-^2N~E~C~C+0.150955ΔPEI。式中N~E~C~C为醇中烷基的有效碳链长度, ΔPEI是具有相同碳原子数目的支链烷基与直链烷基的极化效应指数的差值, 它表示羟基对醇的沸点的影响。     

Two-photon-induced intramolecular excited-state proton transfer process and nonlinear optical properties of HBI in ethanol solution

The two-photon-induced excited state intramolecular proton transfer (ESIPT) process of 2-(2′-hydroxyphenyl) benzimidazole (HBI) in ethanol solution has been investigated. We focused on the calculation of TPA coefficient and nonlinear refraction index of HBI, and found that the theoretical calculated results were in good agreement with the experimental ones. By establishing the two-photon-induced ESIPT kinetic model for HBI, the TPA cross section was determined to be 2.09 × 10⁴ GM. For their large TPA cross section, HBI is a promising TPA candidate material for their potential application in many fields.     

Isomeric structures of benzimidazole, benzoxazole, and benzothiazole derivatives, their electronic properties and transformations

The optimized structures of all isomers of HBI, HBO, HBT, HPyBI, HPyBO, and HPyBT compounds were obtained using the potential energy surface method at the B3LYP/6-311++G(d,p) level of theory. Four isomers and three transition states of their transformations for each compound of HBO, HBT, HPyBO, and HPyBT and two isomers and one transition state for each HBI and HPyBI compounds were found. Energetics, thermodynamic properties, rate constants, and equilibrium constants of their transformations were determined. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

QSPR Modeling of Complex Stability by Optimization of Correlation Weights of the Hydrogen Bond Index and the Local Graph Invariants

The hydrogen bond index (HBI) is the global invariant of a molecular graph and equals the number of vertices representing hydrogen and nitrogen atoms. This index was considered a measure of the capability of a complex to form hydrogen bonds. Optimization of the correlation weights of the HBI and local graph invariants was used for the QSPR modeling of the stability of 110 biometal M²⁺ complexes with -amino acids and phosphate derivatives of adenosine. The statistical parameters of the best model are n = 55, r = 0.9921, s = 0.279, and F = 3328 (learning sample) and n = 55, r = 99.35, s = 0.248, and F = 4027 (control sample).     

A Multicolor Large Stokes Shift Fluorogen-Activating RNA Aptamer with Cationic Chromophores

Large Stokes shift (LSS) fluorescent proteins (FPs) exploit excited state proton transfer pathways to enable fluorescence emission from the phenolate intermediate of their internal 4-hydroxybenzylidene imidazolone (HBI) chromophore. An RNA aptamer named Chili mimics LSS FPs by inducing highly Stokes-shifted emission from several new green and red HBI analogues that are non-fluorescent when free in solution. The ligands are bound by the RNA in their protonated phenol form and feature a cationic aromatic side chain for increased RNA affinity and reduced magnesium dependence. In combination with oxidative functionalization at the C2 position of the imidazolone, this strategy yielded DMHBO⁺, which binds to the Chili aptamer with a low-nanomolar K_D. Because of its highly red-shifted fluorescence emission at 592 nm, the Chili–DMHBO⁺ complex is an ideal fluorescence donor for Förster resonance energy transfer (FRET) to the rhodamine dye Atto 590 and will therefore find applications in FRET-based analytical RNA systems.     

Bond selection in the photoisomerization reaction of anionic green fluorescent protein and kindling fluorescent protein chromophore models

The chromophores of the most widely known fluorescent proteins (FPs) are derivatives of a core p-hydroxybenzylidene-imidazolinon-5-one (HBI) motif, which usually occurs as a phenolate anion. Double bond photoisomerization of the exocyclic bridge of HBI is widely held to be an important internal conversion mechanism for FP chromophores. Herein we describe the ground and excited-state electronic structures and potential energy surfaces of two model chromophores: 4- p-hydroxybenzylidiene-1,2-dimethyl-imidazolin-5-one anion (HBDI), representing green FPs (GFPs), and 2-acetyl-4-hydroxybenylidene-1-methyl-imidazolin-5-one anion (AHBMI), representing kindling FPs (KFPs). These chromophores differ by a single substitution, but we observe qualitative differences in the potential energy surfaces which indicate inversion of bond selection in the photoisomerization reaction. Bond selection is also modulated by whether the reaction proceeds from a Z or an E conformation. These configurations correspond to fluorescent and nonfluorescent states of structurally characterized FPs, including some which can be reversibly switched by specific illumination regimes. We explain the difference in bond selectivity via substituent stabilization effects on a common set of charge-localized chemical structures. Different combinations of these structures give rise to both optically active (planar) and twisted intramolecular charge-transfer (TICT) states of the molecules. We offer a prediction of the gas-phase absorption of AHBMI, which has not yet been measured. We offer a hypothesis to explain the unusual fluorescence of AHBMI in DMF solution, as well as an experimental proposal to test our hypothesis.     

QSPR Modeling of Complex Stability by Correlation Weighing of the Topological and Chemical Invariants of Molecular Graphs

The concept of modeling of the complex stability based on optimization of the correlation weights of the nearest neighborhood codes (NNC), the hydrogen bond index (HBI), and the cyclicity code (CC) is described. The NNC is a local topochemical invariant of a vertex of the molecular graph whose numerical value is a function of the total number and the composition of vertices adjacent to the given vertex. The HBI is a global chemical invariant of the molecular graph calculated from the number of oxygen and nitrogen atoms. The CC is a global topological invariant of the graph equal to the number of rings present in the ligand structure. The statistical characteristics of the best model of the stability constants of the complexes are as follows: n = 75, r = 0.9738, s = 0.457, F = 1337 (training sample); n = 75, r = 0.9795, s = 0.461, F = 1724 (test sample).     

Excited-state intramolecular proton transfer in 2-(3'-hydroxy-2'-pyridyl)benzoxazole. Evidence of coupled proton and charge transfer in the excited state of some o-hydroxyarylbenzazoles

The influence of solvent, temperature, and viscosity on the phototautomerization processes of a series of o-hydroxyarylbenzazoles was studied by means of ultraviolet-visible (UV-vis) absorption spectroscopy and steady-state and time-resolved fluorescence spectroscopy. The compounds studied were 2-(2'-hydroxyphenyl)benzimidazole (HBI), 2-(2'-hydroxyphenyl)benzoxazole (HBO), 2-(2'-hydroxyphenyl)benzothiazole (HBT), 2-(3'-hydroxy-2'-pyridyl)benzimidazole (HPyBI), and the new derivative 2-(3'-hydroxy-2'-pyridyl)benzoxazole (HPyBO), this one studied in neutral and acid media. All of these compounds undergo an excited-state intramolecular proton transfer (ESIPT) from the hydroxyl group to the benzazole N3 to yield an excited tautomer in syn conformation. A temperature- and viscosity-dependent radiationless deactivation of the tautomer has been detected for all compounds except HBI and HPyBI. We show that this radiationless decay also takes place for 2-(3-methyl-1,3-benzothiazol-3-ium-2-yl)benzenolate (NMeOBT), the N-methylated analog of the tautomer, whose ground-state structure has anti conformation. In ethanol, the radiationless decay shows intrinsic activation energy for HPyBO and HBO; however, it is barrierless for HBT and NMeOBT and controlled instead by the solvent dynamics. The relative efficiency of the radiationless decay in the series of molecules studied supports the hypothesis that this transition is connected with a charge-transfer process taking place in the tautomer, its efficiency being related to the strength of the electron donor (dissociated phenol or pyridinol moiety) and electron acceptor (protonated benzazole). We propose that the charge transfer is associated with a large-amplitude conformational change of the tautomer, the process leading to a nonfluorescent charge-transfer intermediate. The previous ESIPT step generates the structure with the suitable redox pair to undergo the charge-transfer process; therefore, an excited-state intramolecular coupled proton and charge transfer takes place for these compounds.     

Radiationless decay of red fluorescent protein chromophore models via twisted intramolecular charge-transfer states

We use CASSCF and MRPT2 calculations to characterize the bridge photoisomerization pathways of a model red fluorescent protein (RFP) chromophore model. RFPs are homologues of the green fluorescent protein (GFP). The RFP chromophore differs from the GFP chromophore via the addition of an N-acylimine substitution to a common hydroxybenzylidene-imidazolinone (HBI) motif. We examine the substituent effects on the manifold of twisted intramolecular charge-transfer (TICT) states which mediates radiationless decay via bridge isomerization in fluorescent protein chromophore anions. We find that the substitution destabilizes states associated with isomerization about the imidazolinone-bridge bond and stabilizes states associated with phenoxy-bridge bond isomerization. We discuss the results in the context of chromophore conformation and quantum yield trends in the RFP subfamily, as well as recent studies on synthetic models where the acylimine has been replaced with an olefin.     

Group Additive Values for the Gas‐Phase Standard Enthalpy of Formation,Entropy and Heat Capacity of Oxygenates

A complete and consistent set of 60 Benson group additive values (GAVs) for oxygenate molecules and 97 GAVs for oxygenate radicals is provided, which allow to describe their standard enthalpies of formation, entropies and heat capacities. Approximately half of the GAVs for oxygenate molecules and the majority of the GAVs for oxygenate radicals have not been reported before. The values are derived from an extensive and accurate database of thermochemical data obtained by ab initio calculations at the CBS‐QB3 level of theory for 202 molecules and 248 radicals. These compounds include saturated and unsaturated, α‐ and β‐branched, mono‐ and bifunctional oxygenates. Internal rotations were accounted for by using one‐dimensional hindered rotor corrections. The accuracy of the database was further improved by adding bond additive corrections to the CBS‐QB3 standard enthalpies of formation. Furthermore, 14 corrections for non‐nearest‐neighbor interactions (NNI) were introduced for molecules and 12 for radicals. The validity of the constructed group additive model was established by comparing the predicted values with both ab initio calculated values and experimental data for oxygenates and oxygenate radicals. The group additive method predicts standard enthalpies of formation, entropies, and heat capacities with chemical accuracy, respectively, within 4 kJ mol^?1 and 4 J mol^?1 K^?1 for both ab initio calculated and experimental values. As an alternative, the hydrogen bond increment (HBI) method developed by Lay et al. (T. H. Lay, J. W. Bozzelli, A. M. Dean, E. R. Ritter, J. Phys. Chem.­ 1995 , 99, 14514) was used to introduce 77 new HBI structures and to calculate their thermodynamic parameters (Δ_fH°, S°, C_p°). The GAVs reported in this work can be reliably used for the prediction of thermochemical data for large oxygenate compounds, combining rapid prediction with wide‐ranging application.     

Group additive values for the gas phase standard enthalpy of formation of hydrocarbons and hydrocarbon radicals

A complete and consistent set of 95 Benson group additive values (GAV) for the standard enthalpy of formation of hydrocarbons and hydrocarbon radicals at 298 K and 1 bar is derived from an extensive and accurate database of 233 ab initio standard enthalpies of formation, calculated at the CBS-QB3 level of theory. The accuracy of the database was further improved by adding newly determined bond additive corrections (BAC) to the CBS-QB3 enthalpies. The mean absolute deviation (MAD) for a training set of 51 hydrocarbons is better than 2 kJ mol(-1). GAVs for 16 hydrocarbon groups, i.e., C(C(d))(3)(C), C-(C(d))(4), C-(C(t))(C(d))(C)(2), C-(C(t))(C(d))(2)(C), C-(C(t))(C(d))(3), C-(C(t))(2)(C)(2), C-(C(t))(2)(C(d))(C), C-(C(t))(2)(C(d))(2), C-(C(t))(3)(C), C-(C(t))(3)(C(d)), C-(C(t))(4), C-(C(b))(C(d))(C)(H), C-(C(b))(C(t))(H)(2), C-(C(b))(C(t))(C)(H), C-(C(b))(C(t))(C)(2), C(d)-(C(b))(C(t)), for 25 hydrocarbon radical groups, and several ring strain corrections (RSC) are determined for the first time. The new parameters significantly extend the applicability of Benson's group additivity method. The extensive database allowed an evaluation of previously proposed methods to account for non-next-nearest neighbor interactions (NNI). Here, a novel consistent scheme is proposed to account for NNIs in radicals. In addition, hydrogen bond increments (HBI) are determined for the calculation of radical standard enthalpies of formation. In particular for resonance stabilized radicals, the HBI method provides an improvement over Benson's group additivity method.