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The absolute configuration of semisynthetic (−)‐3α,6β‐acetoxytropane 1, prepared from (−)‐6β‐hydroxyhyoscyamine 2, has been determined using vibrational circular dichroism (VCD) spectroscopy. The vibrational spectra (IR and VCD) were calculated using DFT at the B3LYP/DGDZVP level of theory for the eight more stable conformers which account for 99.97% of the total relative abundance in the first 10...
The optical spectroscopic characterization of γ‐turns in solution is uncertain and their distinction from β‐turns is often difficult. This work reports systematic ECD and vibrational circular dichroism (VCD) spectroscopic studies on γ‐turn model cyclic tetrapeptides cyclo(Ala‐β‐Ala‐Pro‐β‐Ala) (1), cyclo(Pro‐β‐Ala‐Pro‐β‐Ala) (2) and cyclo(Ala‐β‐Ala‐Ala‐β‐Ala) (3). Conformational analysis performed...
In this article, the most advanced extensions of solvation models to chiroptical properties of solvated systems will be reviewed. The main aspects determining the complex phenomenon of solvation will be first discussed in terms of the physical interactions beyond them and successively translated in a computational language introducing the specific models. A particular attention will be devoted to...
Fourier transform infrared vibrational circular dichroism (FTIR‐VCD) measurements have gone through major advances in the last decade. A major thrust in these advances was to find ways that can minimize the VCD spectral artifacts and obtain the VCD signals at enhanced signal quality. However, all these advances are not incorporated in FTIR‐VCD instruments manufactured by some commercial manufacturers...
Stabilization energies of the electron donor–acceptor sulfinimine···BF3 complexes calculated at either the B3LYP/aug‐cc‐pVTZ or the MP2/aug‐cc‐pVTZ level do not allow to judge, whether the N‐ or O‐atom in sulfinimine is stronger electron‐donor to BF3. The problem seems to be solvable because chirality transfer phenomenon between chiral sulfinimine and achiral BF3 is expected to be vibrational circular...
Chiroptical spectroscopy is being widely used for determining the three‐dimensional molecular structures (i.e., absolute configurations and conformations) of chiral molecules. The general procedure used with any of the chiroptical spectroscopic methods is to analyze the experimental data using corresponding quantum chemical predictions. Such analysis involves multiple steps, including consideration...
The absolute configurations (AC) of azaheterocylic compounds resulting from the cascade rearrangement of enediynes involving only light atoms were unambiguously assigned by the joint use of vibrational circular dichroism (VCD) and copper radiation single crystal X‐ray diffraction (XRD). These AC determinations proved that the rearrangements of enediynes proceeded with memory of chirality and retention...
The continuously growing interest in the understanding of peptide folding led to the conformational investigation of methylamides of N‐acetyl‐amino acids as diamide models. Here we report the results of detailed conformational analysis on Ac‐Pro‐NHMe and Ac‐β‐HPro‐NHMe diamides. These compounds were analyzed by experimental and computational methods, the conformational distributions obtained by Density...
A series of lanthanide tris(β‐diketonates) functioned as useful chirality probes in the vibrational circular dichroism (VCD) characterization of biological amino alcohols. Various chiral amino alcohols induced intense VCD signals upon ternary complexation with racemic lanthanide tris(β‐diketonates). The VCD signals observed around 1500 cm−1 (β‐diketonate IR absorption region) correlated well with...
Analysis of the calculated and measured optical rotation (OR) together with other calculated chiroptical properties such as electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) of the prodigiosin alkaloid streptorubin B shows that these are dominated by the pseudoenantiomeric atropisomers anti‐(S)‐streptorubin B (1A) and syn‐(S)‐streptorubin (1B). Atropisomerism is a dynamic...
Three alkyl vinylethers from our collection of chiral samples were investigated through VCD spectroscopy, in combination with Density Functional Theory (DFT) calculations. Despite the simplicity of the compounds, reproducing all the spectral features is an involved task, since the many significantly populated conformers contribute to the total VCD spectrum with bands which often have opposite signatures...
The diastereomer diketopiperazine (DKP) peptides built on phenylalanine, namely, cyclo diphenylalanine LPhe‐LPhe and LPhe‐DPhe, were studied in the solid phase by vibrational circular dichroism (VCD) coupled to quantum chemical calculations. The unit structure of cyclo LPhe‐LPhe in KBr pellets is a dimer bridged by two strong NH…O hydrogen bonds. The intense bisignate signature in the CO stretch region...
The racemic pterocarpanquinone LQB‐118 is active, in mice and hamsters, against tegumentary and visceral leishmaniasis. This compound also presents antiinflammatory and antineoplastic activity in mice. The low level of toxicity observed in these studies makes LQB‐118 a promising drug candidate. In order to conduct further biological testing to investigate enantioselectivity in the above‐mentioned...
The absolute configurations of the separated enantiomers of fluralaner, a racemic animal health product used to prevent fleas and ticks, have been assigned using vibrational circular dichroism (VCD). The crystallographic structure of the active enantiomer (+)‐fluralaner has previously been shown to have the (S) configuration using small molecule crystallography. We sought a faster analytical method...
In this paper, we have studied the chiroptical properties of a family of o‐oligo(phenyleneethynylene) (o‐OPE) derivatives with different steric hindrance. Experimental results show high dissymmetry factors (gabs and glum up to 1.1 × 10−2) and very similar electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) for all the derivatives that make this basic o‐OPE scaffold a robust...
In 1,1,2,2‐tetrachloroethane‐d2, the 129Xe NMR spectrum of the Xe@cryptophane‐223 complex bearing seven acetate groups (Xe@1 complex) shows an unusually broad signal compared with that of its congeners (Chapellet, LL. et al. J. Org. Chem. 2015;80:6143–6151). To interpret this unexpected behaviour, a 1H NMR analysis and a thorough study of the chiroptical properties of 1 as a function of the nature...
Peptide models built from cis‐ and trans‐2‐aminocyclobutane‐1‐carboxylic acids (ACBCs) are studied in the solid phase by combining Fourier‐transform infrared spectroscopy (FTIR) absorption spectroscopy, vibrational circular dichroism (VCD), and quantum chemical calculations using density functional theory (DFT). The studied systems are N‐tert‐butyloxycarbonyl (Boc) derivatives of 2‐aminocyclobutanecarboxylic...
Dirhodium complexes bearing N‐substituted chiral amino acid ligands are investigated. These complexes have an unusual twisted paddlewheel structure, showing inherent chirality. We would like to demonstrate that parallel application of chiroptical spectroscopic methods (ECD and VCD) and NMR spectroscopy combined with quantum chemical calculations constitutes a powerful tool to determine the configuration...
The chiroptical response in the form of vibrational circular dichroism (VCD) in the midinfrared region is found to be enhanced when a hydrogen of amino group of l‐tryptophan is substituted with acetyl, acryloyl, or maleyl group. The order of preference for VCD enhancement is found to be acryloyl > acetyl > maleyl group. The resulting experimental VCD spectra are also found to be satisfactorily...
The vibrational circular dichroism (VCD) spectra of dicarvone (1), dipinocarvone (2), and dimenthol (3) have been recorded in the range 900–3200 cm−1, encompassing the mid‐infrared (mid‐IR), the CO stretching, and the CH‐stretching regions. For compound 3 also, the fundamental and the first overtone OH stretching regions have been investigated by IR/NIR absorption and VCD. Density functional theory...
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