NMR spectroscopic detection of chirality and enantiopurity in referenced systems without formation of diastereomers

Enantiomeric excess of chiral compounds is a key parameter that determines their activity or therapeutic action. The current paradigm for rapid measurement of enantiomeric excess using NMR is based on the formation of diastereomeric complexes between the chiral analyte and a chiral resolving agent, leading to (at least) two species with no symmetry relationship. Here we report an effective method of enantiomeric excess determination using a symmetrical achiral molecule as the resolving agent, which is based on the complexation with analyte (in the fast exchange regime) without the formation of diastereomers. The use of N,N′-disubstituted oxoporphyrinogen as the resolving agent makes this novel method extremely versatile, and appropriate for various chiral analytes including carboxylic acids, esters, alcohols and protected amino acids using the same achiral molecule. The model of sensing mechanism exhibits a fundamental linear response between enantiomeric excess and the observed magnitude of induced chemical shift non-equivalence in the 1H NMR spectra

Undergraduate Conductors’ and Conducting Teachers’ Perceptions of Basic Conducting Efficacy

basic conducting, nonverbal conducting behaviors, conducting effectivenessThe purpose of this study was to examine undergraduate conductors’ and conducting teachers’ perceptions about basic conducting efficacy. At the beginning and end of the semester, undergraduate students (N = 19) enrolled in a basic conducting course (a) were surveyed about the importance of certain skills necessary for being an effective conductor and (b) viewed and rated their first videotaped conducting episode. Results indicated very few significant differences in participants’ ratings of important conducting skills or their own self-evaluation of nonverbal conducting skills. In addition, university conducting teachers (N = 9) evaluated videos of 10 conductors (five who had participated in the basic conducting course and five nonconductors who had not) who led a university concert band in an identical 1-minute excerpt of band music. No significant differences were found between the basic conductors and the nonconductors’ nonverbal conducting behaviors. Implications for conducting teachers, undergraduate conducting students, and preservice teachers are discussed.YesReviewed and accepted for publication in "Update: Applications of Research in Music Education" http://upd.sagepub.com/content/early/2014/10/23/8755123314554809.abstrac

Amphiprotism-Coupled Near-Infrared Emission in Extended Pyrazinacenes Containing Seven Linearly Fused Pyrazine Units

International audiencePeripherally substituted tetradecaazaheptacene (NHp) compounds, exhibiting amphiprotism-coupled emission, have been synthesized. X-ray crystallography reveals a planar acene-like chromophore, and electronic absorption and emission occur in the near-infrared biological transparency window (650-900 nm). The compounds exhibit long-wavelength emission with photoluminescence quantum yields Φ up to ∼0.61 at 686 nm, with the monodeprotonated state Φ ≈ 0.58 at 712 nm. This unprecedented highly nitrogenous chromophore illustrates the stability and utility of the pyrazinacenes for different applications based on their photophysical properties and chemical structures

Enantiomeric Excess Dependent Splitting of NMR Signal through Dynamic Chiral Inversion and Coligand Exchange in a Coordination Complex

Nuclear magnetic resonance (NMR) spectroscopy cannot be used to discriminate enantiomers, and NMR resonances of enantiomeric mixtures are generally not affected by enantiomeric excess (ee). Here, we report that a coordination complex (L·2Zn·3C), where L is a salen-like prochiral ligand and C is an exchangeable acetate coligand, exhibits symmetrical splitting of one of the 1H NMR resonances of L with the degree of splitting linearly proportional to ee of the chiral guest coligand C, 2-phenoxypropionic acid. Despite the well-defined chirality in the crystal structure of L·2Zn·3C, concurrent fast chiral inversion and coligand exchange in solution renders L·2Zn·3C the primary example of prochiral solvating agent (pro-CSA) based on a coordination complex. Notably, the NMR resonances remain split even in dilute solution due to the lack of chiral guest dissociation in the coligand exchange system. This work provides new insights into chiral transfer events in metal–ligand complexes

Pyrazinaceny vykazují konformační a samoorganizující se chování závislé na povrchovém oxidačním stavu.

Acenes and azaacenes lie at the core of molecular materials' applications due to their important optical and electronic features. A critical aspect is provided by their heteroatom multiplicity, which can strongly affect their properties. Here we report pyrazinacenes containing the dihydro-decaazapentacene and dihydro-octaazatetracene chromophores and compare their properties/functions as a model case at an oxidizing metal substrate. We find a distinguished, oxidation-state-dependent conformational adaptation and self-assembly behaviour and discuss the analogies and differences of planar benzo-substituted decaazapentacene and octaazatetracene forms. Our broad experimental and theoretical study reveals that decaazapentacene is stable against oxidation but unstable against reduction, which is in contrast to pentacene, its C-H only analogue. Decaazapentacenes studied here combine a planar molecular backbone with conformationally flexible substituents. They provide a rich model case to understand the properties of a redox-switchable pi-electronic system in solution and at interfaces. Pyrazinacenes represent an unusual class of redox-active chromophores. Acenes are a promising class of organic materials with distinctive electronic and optical properties. Here decaazapentacene and octaazatetracenes are prepared and their self-assembly behaviour at different oxidation states is analysed.Práce se zabývá studiem pyrazinacenů obsahujících dihydro-dekaazapentacenové a dihydro-oktaazatetracenové chromofory a porovnáním jejich vlastností při modelovém chování na oxidačním kovovém substrátu. Byla nalezena odlišná, na oxidačním stavu závislá konformační adaptace a samouspořádající se chování. Byly připraveny dekaazapentaceny a oktaazatetraceny a analyzováno jejich samoorganizující se chování v různých oxidačních stavech