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Computational spectroscopy has recently evolved from a field reserved for specialists toward a general tool allowing interpretations and analyses of experimental results. However, the current practice of providing tables of transitions for rigid geometries, possibly tuned by phenomenological broadening, is by far too naive. In order to improve this situation in the last few years we have been developing...
The design and synthesis of chiral cyclophanes containing signaling functional groups as an integral part of the macrocyclic framework offer promising possibilities for chiral sensing, molecular recognition, and chiral supramolecular architectures. Our research group has been involved in the construction and study of chiroptical properties of several allenic meta‐ and para‐cyclophanes bearing anthracene...
(1R,2S)‐Dodecyl(2‐hydroxy‐1‐methyl‐2‐phenylethyl)dimethylammonium bromide (DMEB) aggregates dispersed in carbon tetrachloride have been investigated by Fourier transform infrared (FT‐IR), vibrational circular dichroism (VCD) and 1H nuclear magnetic resonance (NMR) spectroscopy at various surfactant concentration and water‐to‐surfactant molar ratio. Experimental data indicate that, even at the lowest...
A time‐dependent Density Functional Theory (TDDFT) computational simulation of the electronic circular dichroism (ECD) spectrum of the phytotoxin scytalone (1), produced by different plant pathogenic fungi and involved in melanin production, was undertaken with the aim to establish a nonempirical correlation between the spectrum and the absolute configuration of this compound. In fact, very low optical...
To elucidate the hitherto unknown absolute configuration of (−)–O‐desmethylangolensin ((−)–O‐DMA), an intestinal bacterial metabolite produced from daidzein, chiroptical study, including specific optical rotation and electronic circular dichroism (ECD), of (R)–O‐DMA was carried out by Time‐Dependent Density Functional Theory (TD‐DFT) calculations. Intramolecular hydrogen bonding between 2’–OH and...
While heme alone does not exhibit circular dichroism (CD) spectrum, it exhibits a prominent positive CD band in the Soret region when incorporated into apoglobin of myoglobin (Mb) and hemoglobin (Hb). The appearance of this optical activity is widely accepted to arise from the interactions between the heme and aromatic residues of the globin. However, the reversed heme orientation in Hb was found...
A series of 13 enantiopure aryl benzyl sulfoxides (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j, 1k, 1l, 1m) with different substituents on the two aromatic rings has been previously analyzed by means of electronic circular dichroism (CD) spectroscopy. Most of these compounds are crystalline and their X‐ray structure is established. For almost one‐half of the series, CD spectra measured in the solid state...
Linear electrogyration (electric field‐induced optical activity) and electro‐optic effects in x‐cut and z‐cut right‐handed (RH) α‐quartz were measured using a complete Mueller matrix polarimeter. The polarimeter used in the analysis was equipped with four photoelastic modulators operating at different frequencies. This configuration is especially sensitive due to the fidelity of the modulators and...
Here we present for the first time the experimental and theoretical (DFT/B3LYP/6‐311++G**) Raman optical activity (ROA) spectra of (−)‐R‐mevalonic acid as the δ‐lactone form in neat liquid and in the aqueous solution. Quantum chemical calculations show the conformational diversity of (−)‐R‐mevalonolactone originated from small energy differences between the various conformation of the six‐membered...
A chiral tetralin norsesquiterpenoid, ligukangtinol, was isolated from the plant Ligularia kangtingensis. Its planar structure was determined by extensive analysis of spectroscopic data (MS, IR, and NMR), and (1S,3R) absolute configuration of the tetralin ring was established by TDDFT‐ECD calculations of the solution conformers. Conformational analysis and ECD calculations proved that the semiempirical...
We present a detailed analysis of the molecular origin of the chiral sum frequency generation (SFG) signals of proteins and peptides at interfaces in the N‐H stretching vibrational region. The N‐H stretching can be a probe for investigating structural and functional properties of proteins, but remains technically difficult to analyze due to the overlapping with the O‐H stretching of water molecules...
Changes in vibrational circular dichroism (VCD) were recorded on‐line during a chemical reaction. The chiral complex nickel‐(–)‐sparteine chloride was hydrolyzed to free (–)‐sparteine base in a biphasic system of sodium hydroxide solution and chloroform (CHCl3). Infrared (IR) and VCD spectra were iteratively recorded after pumping a sample from the CHCl3 phase through a lab‐built VCD spectrometer...
For nuclear magnetic resonance (NMR)‐based protein structure determinations, the random coil chemical shifts are very important because the secondary and tertiary protein structure predictions become possible by examining deviations of measured chemical shifts from those reference chemical shift values. In addition, neighboring residue effects on chemical shifts and J‐coupling constants are crucial...
For three different chiroptical spectroscopic methods, namely, vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and Raman optical activity (ROA), the measures of similarity of the experimental spectra to the corresponding spectra predicted using quantum chemical theories are summarized. In determining the absolute configuration and/or predominant conformations of chiral molecules,...
Recent Raman and Raman optical activity (ROA) results have demonstrated that dimethyl sulfoxide (DMSO) induces the selective conversion of α‐helix motifs into the poly(L‐proline) II (PPII) helix conformation in an array of proteins, while β‐sheets remain mostly unaffected. Human serum albumin (HSA), a highly α‐helical protein, underwent the most dramatic changes and, therefore, was selected as a model...
The versatility and applicability of a time‐perturbed density functional method implemented within the SIESTA program package to calculate electronic circular dichroism of diverse nanoparticles is discussed. Results for nanostructures, such as fullerenes, single‐wall carbon nanotubes, as well as metallic nanoparticles composed of up to hundreds of atoms were examined by comparison with previously...
The chirality of stacked weakly interacting π‐systems was interpreted in terms of Frenkel exciton states and the formation of excitonic circular dichroism (CD) bands was monitored for ethylene stacks of varying sizes. Convergence of CD bands with respect to the system size was observed for stacks involving around 10 molecules. By means of rotation around the C–C double bond in ethylene, chirality...
An unprecedented complementarity of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopic techniques is demonstrated by showing that each technique reveals the structure of a different molecular segment. Using a flexible molecule of biological significance we show that the synergetic use of ECD and VCD yields more complete structural characterization as it provides...
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