导致旋光性根本原因的探讨

旋光性是由结构决定的，手性是一种抽象概念，抽象概念不能决定旋光性，旋光性具有明确的方向性，它必然是由具有明确方向性的结构特征所决定。螺旋结构是具有明确方向性的结构，它是实体不是抽象概念，它与旋光方向和旋光度大小可以联系在一起，螺旋结构才是导致旋光性的根本原因。     

螺旋结构与旋光性 4.螺旋理论对旋光度大小的预测

本文分析了影响旋光度的各种因素,并列举了各类型的大量化合物的旋光数据,证明螺旋理论可以预测旋光度大小。     

How many chiral centers can Raman optical activity spectroscopy distinguish in a molecule?

To study the capabilities and limitations of Raman optical activity, (-)-(M)σ-[10]helicene and (-)-(M)σ-[4]helicene serve as scaffold molecules on which new chiral centers are introduced by substitution of hydrogen atoms with other functional groups. These functional groups are deuterium atoms, fluorine atoms, and methyl groups. Multiply deuterated species are compared. Then, results of singly deuterated derivatives are compared against results obtained from singly fluorinated and methylated derivatives. The analysis required the calculation of a total of 2433 Raman optical activity spectra. The method we propose for the comparison of the various Raman optical activity spectra is based on the total intensity of squared difference spectra. This allows a qualitative comparison of pairs of Raman optical activity spectra and the extraction of the pair of most similar Raman optical activity spectra for each group of stereoisomers. Different factors were accounted for, such as the spectral resolution (modeled by line broadening) and the range of vibrational frequencies considered. In the case of σ-[4]helicene all generated stereoisomers in each group can be distinguished from one another by Raman optical activity spectroscopy. For σ-[10]helicene this holds except for the lower one of the two resolutions considered. Here, the group consisting of stereoisomers with five chiral centers contains at least one pair of derivatives whose Raman optical activity spectra cannot be distinguished from one another. This indicates that an increased molecular size has a negative effect on the number of chiral centers which can be distinguished by Raman optical activity spectroscopy. Regarding the different substituents, stereoisomers are the better distinguishable in Raman optical activity spectroscopy, the more distinct the signals of the substituent are from the rest of the spectrum.     

Aggregative optical activity of colloidal surfactants

The discovery of the aggregative optical activity for solutions of different colloid surfactants (anionic sodium dodecyl sulfate, cationic hexadecyltrimethylammonium bromide, and nonionic Brij 30) is reported. The optical activity develops only above the Kraft point, and, in the concentration plot, it is characterized by a distinct maximum in the vicinity of critical micelle concentration. The concentration at which the optical activity disappears corresponds to the formation of spherical micelles and is a new important parameter in the colloid chemistry of surfactants.     

Measurement of the optical activity of some stereoregular vinyl polymers in the crystalline state

The general problems presented by the determination of the optical activity of polymers in the crystalline state are considered. The necessity of using unoriented samples, if the polarimetric data are to be compared with analogous data measured in solution, is emphasized. The optical activity in the crystalline state of a number of stereoregular vinyl polymers has been measured by employing either suspensions of fine powders or thin plates with no detectable orientation. The results of optical rotatory dispersion studies in the crystalline state suggest that, at least in the case of the poly-α-olefins investigated, the same chromophores are responsible for the optical activity in the crystalline state and in solution.     

Vibrational raman optical activity as a mean for revealing the helicity of oligosilanes: a quantum chemical investigation

Using theoretical simulations based on Hartree-Fock and density-functional theory calculations, the simulated vibrational Raman optical activity spectra of helical conformers of heptasilane are shown to present signatures sensitive to the helicity. These signatures are associated with collective wagging, twisting, and rocking motions. These simulated spectra have been obtained by combining analytical and numerical differentiation procedures to evaluate the geometry derivatives of the optical tensors entering into the expressions of the vibrational Raman optical activity intensities. From an investigation of basis set and electron correlation effects, it is shown that, like for local vibrations, diffuse functions are compulsory for evaluating the vibrational Raman optical activity intensities of collective vibrational motions.     

Semiclassical theory of “Optical activity” in the asymmetric top: off resonance

Earlier work on optical activity in pure rotational spectroscopy is generalized to the more realistic model of the asymmetric top. The analog of the Rosenberg dispersion formula for the optical activity parameter, β, is given for the J = 0 state of an asymmetric top. It involves only the coupling to the J = 1 manifold of states. The molecular parameters which determine the presence or absence of optical activity in pure rotational spectroscopy are displayed. These provide a reasonable alternate definition of chirality in the pure rotational region of the spectrum.     

Silicate Xerogels with Dopant-Induced Chirality

A series of silicate xerogels with entrapped chiral amino acids have been obtained via sol-gel technology. The transparent, glassy samples obtained exhibit chirality in the bulk due to the presence of the entrapped asymmetric molecules. Measurements of the optical activity of the doped xerogel samples revealed that the entrapment did not significantly influence the optical activity observed for liquid solutions of the amino acids. Thus, the sol-gel method enables the preparation of amorphous optical materials exhibiting properties of strictly spatially defined molecular systems. Apart from the obvious optical applications, such porous materials with asymmetric centers might find interesting applications in chiral chemical syntheses and separations.     

Circular dichroism of crude oil and its derivatives. Role of permolecular structures

Petrols with different octane numbers, diesel fuel and solutions of crude oil in toluene have been studied by the methods of absorption spectroscopy, circular dichroism spectroscopy and correlation spectroscopy of scattered light. Circular dichroism signal was registered for crude oil solutions in the spectral ranges corresponding to the measured earlier resonance absorption of asphaltene solutions in toluene. We show that the optical activity of crude oil solutions is due to the aggregation of asphaltene molecules in one spectral range and is intensified with the aggregation of asphaltene molecules in another spectral range. Petrols have no optical activity. The optical activity registered for diesel fuel is possibly due to the aggregation of asphaltene molecules.     

胆色素类化合物光学活性及其立体化学研究进展

本文综述了20 年来胆色素光学活性及其立体化学的研究进展, 着重讨论了分子内和分子间相互作用对色素构象的选择性及其光活性的影响。对研究前景进行了展望。     

Monolayer Filaments versus Multilayer Stacking of Bent‐Core Molecules

Bent‐core materials exhibiting lamellar crystals (B4 phase), when dissolved in organic solvents, formed gels with helical ribbons made of molecular monolayers and bilayers, whereas strongly deformed stacks of 5–6 layers were found in the bulk samples. The width and pitch of the helical filaments were governed by molecular length; they both increased with terminal‐chain elongation. It was also found that bulk samples were optically active, in contrast to the corresponding gels, which lacked optical activity. The optical activity of samples originated from the internal structure of the crystal layers rather than from the helicity of the filaments. A theoretical model predicts a strong increase in optical activity as the number of layers in the stack increases and its saturation for few layers, thus explaining the smaller optical activity for gels than for bulk samples. A strong increase and redshift in fluorescence was detected in gels as compared to the sol state.     

Two-dimensional nonlinear optical activity spectroscopy of coupled multi-chromophore system

Most biomolecules are chiral. A variety of optical activity measurement techniques have been extensively used to study chiral natures of complicated biological molecules such as proteins and nucleic acids. Recently, coherent two-dimensional (2D) spectroscopic techniques have been developed and widely used to study structures and dynamics of biomolecules via measuring couplings between chromophores. However, such 2D optical spectroscopic methods utilizing linearly polarized beams do not provide information on the molecular chirality. Thus, we have theoretically shown that novel 2D optical activity measurement techniques based on three- and four-wave-mixing schemes are of use to obtain the 2D spectrum of a chiral molecule. Particularly, we carried out numerical simulations of 2D optical activity spectra of polypeptides and a light-harvesting complex. These methods utilizing circularly polarized beams and related spectroscopic techniques will be of great use in understanding and elucidating the underlying mechanisms of ultrafast chemical and conformational changes of chiral biomolecules in the future.     

Effect of nonelectrostatic interactions on the macromolecular behavior of polyelectrolytes. III. Optical rotatory dispersion of PLL in water and aqueous-organic mixtures

We have investigated the optical rotatory dispersion of a stereo-irregular polyelectrolyte when neutralized with alkaline and N-tetraalkylammonium hydroxides, both in water and aqueousacetone mixtures. The variations of the optical activity properties during the neutralization can be well related to potentiometric and viscosity measurements. They are interpreted by assuming two kinds of solvation of the chiral centers located on the main chain, to which two partial optical rotary dispersions (ORD) of opposite signs are associated. The observed optical activity changes and specifically the discontinuity occurring in the neutralization range where a conformational transition between a compact structure and a more extended one is initiated, are thus accounted for in terms of the corresponding changes in the state of solvation of chains.     

Optically active electrochromism in polyanilines

The electrochemically driven control of the natural optical activity of polyanilines bearing chiral camphorsulfonic acid is reported. Aniline was polymerized in the presence of camphorsulfonic acid by oxidative electrochemical polymerization in water to afford polyanilines containing (+)- or (−)-camphorsulfonic acid. This research elucidated that the polymerization, with cyclic voltammetry scanning up to 1.1 V, produced consistent optically active polyanilines. The polyaniline films thus prepared showed intense and tunable optical activity based on electrochemical reduction/oxidation in a 0.1 M sulfuric acid aqueous solution. The circular dichroism and optical rotation angle of the polymer were tunable by the appropriate adjustment of an externally applied potential as a form of optical modulation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2085–2090, 2007     

pH Switchable Electrochemical and Optical Properties of Polyoctylthiophene – Pyrene Composites

Polyoctylthiophene electrochemical and optical properties are dependent on the polymer oxidation state, generally requiring presence of doping ions. In this work polyoctylthiophene composites with pyrene or aminopyrene have been prepared and studied using optical and electrochemical methods. It is shown that in the composite formed pyrene molecules act as molecular dopant for the conducting polymer, resulting in a system of partially oxidized polythiophene backbone, yet of high lipophilicity. On the other hand, composite of aminopyrene with polyoctylthiophene is characterized with pH dependent electrochemical and optical properties. The difference arises mostly from the protonation/ deprotonation reaction occurring for aminopyrene embedded in polyoctylothiophene. Nanoparticles of polythiophene‐aminopyrene show turn‐on emission dependence on increase of hydrogen ions concentration in solution in a wide pH range from 12 to 5. For low pH high emission activity is observed for nanoparticles, whereas for films high lipophilicity and low electrochemical activity pointing to presence of semiconducting polymer in the system for protonated aminopyrene. For high pH, when deprotonation of aminopyrene is observed, the system is characterized with low optical, yet high electrochemical activity and low lipophilicity. The electrochemical activity of polyoctylthiophene‐aminopyrene composite can be reversibly switched simply by solution pH change.     

Reply to “Fundamental symmetry aspects of optical activity”

Confusion exists between the notion of a single molecule interacting with its environment, and the theoretical notion of an isolated molecule having no interaction with its environment. The space-inversion properties of the isolated-molecule model preclude optical activity: the model is therefore inadequate, leading to the idea that the environment provides the mechanism for generating optical activity.     

Quantitative determination of linear and second-harmonic generation optical effective responses of achiral or chiral materials in planar structures: theory and materials

A theoretical formalism designed to quantify linear optical and second-order nonlinear optical responses of achiral or chiral anisotropic materials in planar structure is presented. In particular, the theory includes linear optical activity that is governed by the gyrotropic components and second-harmonic generation optical rotatory dispersion, the magnitude of which depends on the ratio of chiral and achiral chi((2)) components. Examples are given which reproduce complex interference effects and other subtle optical effects that are encountered in layered structures. Detailed experimental second harmonic generation studies of quartz and dihydrogen phosphate that quantify linear and nonlinear optical activities of these materials are reported.     

Optical activity of alternating copolymers of chiral α-olefins with alkyl acrylates

The synthesis of high-molecular-weight substantially alternating copolymers of alkyl acrylates with optically active α-olefins is reported. “Induced optical activity” on the side-chain ester chromophores, depending on the chemical structure of the chiral α-olefin, is indicated by CD measurements. Data are reported supporting the conclusion that this induced optical activity is related to a preferential chiral conformation of the macromolecules due to a cooperative effect.