Control of Circularly Polarized Luminescence by Using Open‐ and Closed‐Type Binaphthyl Derivatives with the Same Axial Chirality

The solution‐dispersed‐state and polymer‐dispersed‐state circular dichroism (CD) and circularly polarized luminescence (CPL) properties of chiral binaphthyl fluorophores could be controlled by the choice of open‐ or closed‐type substituents on the binaphthyl units and by the axial chirality of the binaphthyls.     

Circularly Polarized Absorption Property of Tetra-4[4''''-(2-methylbutoxy)benzoyloxy]phenyl Porphyrin by Introducing Optical Pendant Groups

Circularly polarized luminescent(CPL) materials possess special dissymmetric optical property, i.e. luminescent light having different intensities for left (L) and right(R) circularly polarized components. Recently, these materials have been applied in colour-image projection, stereoscopic displays and light-emitting diodes(LEDS)1-7. We have synthesized a new porphyrin derivative, tetra-4[4'-(2-methylbutoxy)benzoyloxy] phenyl porphyrin [T(MBBP)P], by introducing a chiral group, which p…     

Molecular Chirality in Meteorites and Interstellar Ices,and the Chirality Experiment on Board the ESA Cometary Rosetta Mission

Life, as it is known to us, uses exclusively L ‐amino acid and D ‐sugar enantiomers for the molecular architecture of proteins and nucleic acids. This Minireview explores current models of the original symmetry‐breaking influence that led to the exogenic delivery to Earth of prebiotic molecules with a slight enantiomeric excess. We provide a short overview of enantiomeric enhancements detected in bodies of extraterrestrial origin, such as meteorites, and interstellar ices simulated in the laboratory. Data are interpreted from different points of view, namely, photochirogenesis, parity violation in the weak nuclear interaction, and enantioenrichment through phase transitions. Photochemically induced enantiomeric imbalances are discussed more specifically in the topical context of the “chirality module” on board the cometary Rosetta spacecraft of the ESA. This device will perform the first enantioselective in situ analyses of samples taken from a cometary nucleus.     

Thioflavin T: Electronic Circular Dichroism and Circularly Polarized Luminescence Induced by Amyloid Fibrils

The circularly polarized luminescence (CPL) spectrum of thioflavin T (ThT) bound to insulin amyloid fibrils has been measured for the first time. It has been found that the samples exhibiting induced circular dichroism (CD) retain the optical activity in the CPL spectra, with the same sign of the rotatory strength. The fluorescence dissymmetry factor is substantial (of the order of magnitude 10^?2). Unlike in the corresponding CD and absorption spectra, there is no shift of the CPL band with respect to the fluorescence band. It has been verified that the measured CPL spectra are free from artifacts from circularly polarized scattering of emitted light by conducting additional measurements in a medium with a refractive index similar to insulin (methylsalicylate). The CD and CPL spectra have been interpreted by means of density functional calculations carried out for ThT in its ground and first excited states in different dielectric environments and for ThT interacting with an aromatic ring. It has been found that the presence of an aromatic ring close to the ThT molecule induces Cotton effects of the same order of magnitude as the stabilization of one enantiomeric conformer. Thus, it is expected that both mechanisms contribute to the induced CD and CPL effect to a similar degree.     

Detection of Circularly Polarized Luminescence of a Cs‐EuIII Complex in Raman Optical Activity Experiments

Circularly polarized luminescence (CPL) spectra are extremely sensitive to molecular structure. However, conventional CPL measurements are difficult and require expensive instrumentation. As an alternative, we explore CPL using Raman scattering and Raman optical activity (ROA) spectroscopy. The cesium tetrakis(3‐heptafluoro‐butylryl‐(+)‐camphorato) europium(III) complex was chosen as a model as it is known to exhibit very large CPL dissymmetry ratio. The fluorescent bands could be discriminated from true Raman signals by comparison of spectra acquired with different laser excitation wavelengths. Furthermore, the ROA technique enables fluorescence identification by measuring the degree of circularity. The CPL dissymmetry ratio was measured as the ROA circular intensity difference of 0.71, the largest one ever reported. The alternative CPL measurement enhances applications of lanthanides in analytical chemistry and chemical imaging of biological objects.     

Circularly Polarized Luminescence of Chiral Pt(pppb)Cl (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene) Aggregate in the Excited State

We prepared enantiomers of chiral Pt^II complexes, Pt(pppb)Cl and Pt(pppb)CN (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene), and measured their CPL (circularly polarized luminescence) spectra for excimer and trimer emission. The contribution of the pinene moiety to CPL was considerably low for the π–π* emission of the monomer but large for MMLCT (metal‐metal‐to‐ligand charge‐transfer) of the excimer and trimer which had a helical structure induced in a face‐to‐face stacking fashion. The trimer CPL for (+)‐Pt(pppb)Cl was larger in intensity than that of excimer CPL; on the other hand, that for (+)‐Pt(pppb)CN was opposite in sign compared with that of excimer CPL. We conclude that differences in the excited‐state structure of the aggregate between Pt(pppb)Cl and Pt(pppb)CN account for the variation in the CPL spectra. By the aid of TD‐DFT calculations it was predicted that the dihedral angle θ(Cl‐Pt‐Pt‐Cl) was 50–60° or 110–140° for Pt(pppb)Cl aggregates and 160° for Pt(pppb)CN aggregates.     

Chiral Sensing of Various Amino Acids Using Induced Circularly Polarized Luminescence from Europium(III) Complexes of Phenanthroline Dicarboxylic Acid Derivatives

Circularly polarized luminescence (CPL) was observed from [Eu(dppda)₂]^? (dppda=4,7‐diphenyl‐1,10‐phenanthroline‐2,9‐dicarboxylic acid) and [Eu(pzpda)₂]^? (pzpda=pyrazino[2,3‐f][1,10]phenanthroline‐7,10‐dicarboxylic acid) in aqueous solutions containing various amino acids. The selectivity of these complexes towards amino acids enabled them to be used as chiral sensors and their behavior was compared with that of [Eu(pda)₂]^? (pda=1,10‐phenanthroline‐2,9‐dicarboxylic acid). As these Eu^III complexes have achiral D_2d structures under ordinary conditions, there were no CPL signals in the emission assigned to f–f transitions. However, when the solutions contained particular amino acids they exhibited detectable CPL signals with g_lum values of about 0.1 (g_lum=CPL/2 TL; TL=total luminescence). On examining 13 amino acids with these three Eu^III complexes, it was found that whether an amino acid induced a detectable CPL depended on the Eu^III complex ligands. For example, when ornithine was used as a chiral agent, only [Eu(dppda)₂]^? exhibited intense CPL in aqueous solutions of 10^?2 mol dm^?3. Steep amino acid concentration dependence suggested that CPL in [Eu(dppda)₂]^? and [Eu(pzpda)₂]^? was induced by the association of four or more amino acid molecules, whereas CPL in [Eu(pda)₂]^? was induced by association of two arginine molecules.     

Photoreaction of rac‐Leucine in Ice by Circularly Polarized Synchrotron Radiation: Temperature‐Induced Mechanism Switching from Norrish Type II to Deamination

The delivery of extraterrestrial organics to primitive Earth is considered to have triggered the origin and subsequent evolution of life. Indeed, enantiomerically enriched amino acids of nonterrestrial origin have been found in carbonaceous meteorites, and enantioselective photodecomposition by circularly polarized light (CPL) in outer space has been proposed to have played some role in the initial enantiomeric bias. To experimentally examine this possibility and elucidate the photoreaction mechanisms, we have studied the photolysis of racemic leucine (rac‐Leu) in acidic and neutral ice/water media at 21–298 K with left‐ and right‐CPL in an attempt to detect enantiomerically enriched D ‐ and L ‐Leu, respectively. Comprehensive product analyses revealed that the CPL‐induced deracemization of Leu proceeds in both acidic and neutral ice matrices even at 21 K, and that the main mechanism switches from Norrish‐type II γ‐hydrogen abstraction to S_Ni deamination on lowering the temperature. The potential role of the CPL‐induced photodecomposition of amino acids as a source of the enantiomer imbalance in meteorites is discussed.     

Three‐Way‐Switchable (Right/Left/OFF) Selective Reflection of Circularly Polarized Light on Solid Thin Films of Helical Polymer Blends

Two poly(quinoxaline‐2,3‐diyl) copolymers bearing miscibility‐enhancing 8‐chlorooctyloxy and (S)‐2‐methylbutoxy or n‐butoxy side chains were synthesized. After annealing in CHCl₃ vapor, a polymer‐blend film of these copolymers exhibited selective reflection of right‐handed circularly polarized light (CPL) in the visible region. The handedness of the CPL reflected was completely inverted upon annealing of the film in THF vapor. Annealing in n‐hexane vapor resulted in the phase separation of the polymer blend, which turned the selective reflection off. This three‐way‐switchable reflection, that is, reflection of right‐handed or left‐handed CPL, together with an OFF state, could be observed visually through right‐ and left‐handed CPL filters.     

在气液界面上压缩诱导聚(L-乳酸)膜的结构变化

聚乳酸(PLA)是一种环境友好及生物可降解的聚合物, 其界面性质受到了广泛关注. 本文以Langmuir-Blodgett (LB)膜天平、原子力显微镜(AFM)研究了聚(L-乳酸) (PLLA)在气液界面上的性质. 表面压-面积(π-A)等温曲线的结果表明, 在膜压缩的初始阶段, 表面压逐渐增大; 当膜压为9.0 mN·m^-1时, 曲线出现了一个平台,其重复单元的面积大约在0.11-0.17 nm²之间. 原子力显微镜的结果发现, 在压缩过程中, 膜结构发生了明显的变化: 平台刚出现时, 膜内出现了大量的纤维结构; 在平台区内, 界面上出现了多层膜结构. 特别地, 当表面压为20.0 mN·m^-1时, PLLA在界面上可形成约6.0 nm厚的薄膜. 由此可见, PLLA等温线中的平台与其膜结构的变化紧密相关. 这有别于普通双亲分子的性质, 即这类双亲分子π-A等温线中的平台通常表示它们在二维空间上发生了单分子膜的相转变.     

Control of Induced Chirality in Optically Active Poly(N‐propargylcarbamate) Films by Solvent Vapor

Chiral polyethyne derivatives with lyotropic liquid‐crystalline properties are found to be able to self‐assemble, forming two chiral organizations with opposite handedness in solid thin films by selection of the casting solvent and its concentration. After the film preparation, chiral organization could also be induced by simple exposure to an appropriate organic solvent's vapor for several minutes without thermal treatment. Furthermore, irreversible inversion of the handedness of the chiral organization in the film could be achieved by exposure to solvent vapor.

     

聚苯乙烯-丙烯酸纳米粒子的制备及共振光散射性质

聚苯乙烯-丙烯酸纳米粒子的制备及共振光散射性质;无皂乳液聚合;超声辐射     

聚二烯丙基二甲基氯化铵与核酸相互作用的共振光散射光谱及分析应用

实验基于核酸与聚阳离子聚二烯丙基二甲基氯化铵(PDDA)的相互作用导致共振光散射(RLS)增强的现象来测定核酸。考察了pH值、PDDA浓度和离子强度对体系共振光散射强度的影响。在优化条件下,建立了用RLS光谱测定微量核酸的新方法。方法的抗干扰能力较强,可允许大部分的常见金属离子、核苷酸、氨基酸、糖、蛋白质等干扰物质的存在。同时用于合成样品的分析,结果令人满意。     

Optical Properties and Photopolymerization of Liquid Crystalline (Acetyl) (Ethyl) Cellulose/Acrylic Acid System

The structure and properties of a chiral nematic phase, which reflects one hand of circularly polarized light in a narrow region of wavelength, of fully acetylated (ethyl) cellulose [(acetyl) (ethyl) cellulose, AEC] in acrylic acid (AA) were studied in comparison with (ethyl) cellulose (EC). AEC mesophase formed right-handed chiral nematic structure while EC formed left-handed one. AEC mesophase showed higher birefringence and reflection intensity. The relationship between the reflection wavelength and the polymer concentration was negatively correlated for both AEC and EC mesophases. The relationship between the reflection wavelength and the molecular weight was also negative for AEC mesophase whereas positive for EC mesophase. AEC mesophase was solidified by photopolymerization of AA moiety. It was revealed that the optical properties of AEC mesophase could be preserved by photopolymerization, since the resulting solid material reflects selectively one hand of circularly polarized light.     

[IrBr6]2-的反对称极化率与圆偏振激光诱导的ESR谱频移

在理论上研究了顺磁性粒子体系的圆偏振激光诱导的ＥＳＲ谱频移效应。给出磁场中分子反对称极化率的公式，并以［ＩｒＢｒ６］＾２－离子为例讨论了吸收带半高宽的影响。计算了［ＩｒＢｒ６］＾２－的ＥＳＲ谱在圆偏振激光作用下的频移。结果发现：在光学共振区附近，ＥＳＲ频移可达１ＭＨｚ的量级，与钠原子体系结果类似。