Selective Monitoring of Stern-Volmer Quenching of Chiral Molecules Via Fluorescence Detected Circular Dichroism

Abstract

The use of fluorescence detected circular dichroism (FDCD) for monitoring the quenching of chiral molecules is described. This technique combines the specificity for chiral centers of circular dichroism (CD), the sensitivity and selectivity of the fluorescence measurement with the additional chemical information provided by fluorescence quenching. Spectra are acquired using a multidimensional FDCD spectrometer which obtains a FDCD matrix of spectral data as a function of multiple excitation wavelengths (CD information) and multiple fluorescence emission wavelengths. This combination of FDCD and fluorescence quenching produces a very selective monitor for chiral fluorophores.     

Circular dichroism and theoretical studies on the inclusion of the antimalarian drug Licochalcone-A in β-cyclodextrin

The Induced Circular Dichroism of the complex formed by inclusion of Licochalcone-A (a powerful antimalarian of natural origin) and β-cyclodextrin was measured and calculated. The association constant was determined by titration experiments of ICD and fluorescence. The lowest energy conformations of the complex were obtained through docking procedures and their Circular Dichroism was evaluated within the Tinoco framework. The geometry of the complex was found to be consistent with the main experimental features.     

圆二色谱法研究碱基错配对G-quadruplex稳定性的影响

通过将参与形成四链结构G-quadruplex的G(鸟嘌呤)碱基分别替换为T(胸腺嘧啶),C(胞嘧啶)和A(腺嘌呤),用圆二色光谱系统地研究了不同位置的G对G-quadruplex结构稳定性的贡献.结果表明,(1)替换G-quadruplex结构中间层的G对其稳定性的影响最大;(2)该序列及其错配序列大多数情况下在钾离子溶液中比钠离子溶液中稳定;(3)某些特定位置的G被替换为C或A后序列的熔点与原始序列接近甚至高于原始序列.     

Synthesis,chiral resolution and optical properties of amphiphilic oxa[9]helicene derivatives

A new class of amphiphilic oxa[9]helicene derivatives were synthesized in excellent-to-fair yields, and successfully characterized by different analytical techniques (e.g., FT-IR, ¹H and ¹³C NMR, and HRMS). The compounds were enantiomerically separated by chiral HPLC and the absolute configurations of the enantiomers were confirmed by circular dichroism spectroscopy. Other optical properties (e.g., UV, photoluminescence, specific optical rotation and molecular optical rotation) of the newly synthesized compounds were also examined.     

Exciton Chirality. (A) Origins of and (B) Applications from Strongly Fluorescent Dipyrrinone Chromophores

Summary. (A) The origin of exciton interaction and examples of its application to organic stereochemistry are presented. (B) N,N-Carbonyl-bridged dipyrrinones constitute a new class of highly fluorescent chromophores suitable for investigations of stereochemistry and absolute configuration. N,N-Carbonylxanthobilirubic acid esters are strongly fluorescent, with a fluorescence quantum yield (_F) 0.8, but produce only weak exciton CD from the trans-1,2-cyclohexanediol template. The ester of an analog with benzoic acid replacing propionic, N,N-carbonyl-8-(4-carboxyphenyl)-3-ethyl-2,7,9-trimethyl-(10H)-dipyrrin-1-one, exhibits strong fluorescence (_F=0.68, _em=493nm, _ex=422nm in CHCl₃) and UV-Vis absorption (21000 at 424nm) in organic solvents. Its diester with (1S,2S)-cyclohexanediol is fluorescent and exhibits exciton circular dichroism (=+15dm³·mol^–1·cm^–1, =432nm; =–4dm³·mol^–1cm^–1, =380nm) that correlates with the Exciton Chirality Rule.     

Synthesis of optically active amphiphilic tetrathiafulvalene derivatives

The synthesis and characterization of novel chiral tetrathiafulvalenes bearing two long alkyl chains at one end of the π-electron rich unit and different functional groups—ester, acid or thiolate—at the other extreme is described. The synthetic method requires the preparation of 1,3-dithiol derivatives with two stereogenic centers. Different routes and reaction conditions were explored to form these compounds, whose optimized synthesis involved the nucleophilic substitution of a chiral bromo methylene derivative with tetrabutylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolate)zincate. The tetrathiafulvalenes were prepared by coupling the 1,3-dithiol derivative with 4,5-bis(methoxycarbonyl)-1,3-dithiol-2-one or 4,5-bis(2-cyanotehylthio)-1,3-dithiol-2-thione. The products were fully characterized, including by circular dichroism spectroscopy, which confirmed their optical activity. They are promising candidates to be used as building blocks in supramolecular materials for molecular electronics, to produce systems with unique electrical, magnetic or optical properties that stem from their chirality.     

Synthesis and Absolute Configuration of Novel Mono- and Dinuclear Cobalt(III) Complexes Containing S-Phenylalanine

Two diastereomers of bis(1,3-diaminopropane)(S-phenylalaninato)cobalt(III) were prepared by reaction of S-phenylalanine with carbonatobis(1,3-diaminopropane)cobalt(III). The diastereomers were separated on an optically active Sephadex QAE column and their absolute configurations assigned by means of circular dichroism. In addition, ¹HNMR spectra of the diastereomers were analyzed in terms of the population of the three predominant rotamers of the coordinated S-phenylalaninato ligand. One out of 24 theoretically possible diastereomers of the dinuclear species di- µ -hydroxo- tetrakis(S-phenylalaninato)dicobalt(III) was obtained by direct synthesis and its absolute configuration deduced from CD spectra.     

Circular Dichroism and Optical Rotatory Dispersion — Principles and Application to the Investigation of the Stereochemistry of Natural Products

The principles of circular dichroism and of optical rotatory dispersion are described. Examples are given to illustrate the use of these methods for the determination of the configurations and conformations of natural and synthetic products. Some limitations of the octant rule are mentioned.     

Sandwich structure of a ruthenium porphyrin and an amino acid hydrazide for probing molecular chirality by circular dichroism

Owing to the strong Lewis acidity of ruthenium porphyrins, a commercial carbonyl ruthenium porphyrin and an amino acid hydrazide can assemble into a sandwich structure. The nature of such a structure is diagnostic of the absolute configuration of the amino acid by circular dichroism.     

Corroborating study on the absolute configurations of trigochinins A–C

Trigochinins A–C (1–3) are three highly oxygenated daphnane-type diterpenes isolated from Trigonostemon chinensis. Their structures with the absolute configurations were initially assigned by a combination of spectroscopic data, X-ray crystallography (Mo Kα radiation) study and CD analysis. In the current study, the absolute configurations of trigochinins A–C were confirmed by single crystal X-ray diffraction (Cu Kα radiation) study, CD spectral analogy, and theoretical ECD study by using quantum chemical TDDFT calculations.