La Ruse de Bacchis et le Chant du Rossignol (Plaute, Bacchides 37-38)

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The interplay between conformation and absolute configuration in chiral electron dynamics of small diols

A competition between chiral characteristics alternatively attributable to either conformation or to absolute configuration is identified. Circular dichroism associated with photoexcitation of the outer orbital of configurational enantiomers of 1,3- and 2,3-butanediols has been examined with a focus on the large changes in electron chiral asymmetry produced by different molecular conformations. Experimental gas phase measurements offer support for the theoretical modelling of this chiroptical effect. A surprising prediction is that a conformationally produced pseudoenantiomerism in 1,3-butanediol generates a chiral response in the frontier electron dynamics that effectively outweighs the influence of the permanent configurational handedness established at the asymmetrically substituted carbon. Induced conformation, and specifically induced conformational chirality, may thus be a dominating factor in chiral molecular recognition in such systems

Diastereo-specific conformational properties of neutral, protonated and radical cation forms of (1R,2S)-cis- and (1R,2R)-trans-amino-indanol by gas phase spectroscopy

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Chirality effects on the intramolecular interactions strongly depend on the charge and protonation states. Here, the influence of chirality on the structure of the neutral, protonated, and radical cation forms of (1R,2S)-cis- and (1R,2R)-trans-1-amino-2-indanol diastereomers, prototypical molecules with two chiral centers, is investigated in a molecular beam by laser spectroscopy coupled with quantum chemical calculations. The neutral systems are structurally characterised by double resonance IR-UV spectroscopy, while IR-induced dissociation spectroscopy is employed for the charged molecules. The sterical constraints due to the cyclic nature of the molecule emphasise the chirality effects, which manifest themselves by the formation of an intramolecular hydrogen bond in neutral or protonated (1R,2S)-cis-amino-indanol. In contrast, this interaction is not possible in (1R,2R)-trans-amino-indanol. In the protonated species, chirality also influences the spectroscopic probes in the NH/OH stretch range by fine-tuning subtle effects such as the hyperconjugation between the sigma(OH) orbital and sigma* orbitals localised on the alicyclic ring. The radical cation undergoes opening of the alicyclic ring, which results in an ionisation-induced loss of the chirality effects.EC/FP7/600209/EU/International Post-Doc Initiative of the Technische Universität Berlin/IPODIEC/FP7/312284/EU/Coordinated Access to Lightsources to Promote Standards and Optimization/CALIPS

Metallic bonding due to correlations: A quantum chemical ab-initio calculation of the cohesive energy of mercury

Solid mercury in the rhombohedral structure is unbound within the self-consistent field (Hartree-Fock) approximation. The metallic binding is entirely due to electronic correlations. We determine the cohesive energy of solid mercury within an ab-initio many-body expansion for the correlation part. Electronic correlations in the $5d$ shell contribute about half to the cohesive energy. Relativistic effects are found to be very important. Very good agreement with the experimental value is obtained.Comment: 4 pages, 1 figur

Spectroscopic Studies Of Chirality

Chirality is pervasive in Nature and describes the property of an object not to be superimposable on its mirror image. To differentiate between the two mirror images of a chiral molecule, called enantiomers, one must probe them with a probe that is itself chiral. The probe can be of chemical nature, for example another chiral molecule, or of physical nature, for example a chiral light. I will give examples of these two approaches. I will describe how laser spectroscopy at low temperature sheds light on the structural differences between the homochiral and heterochiral complexes of chiral biomolecules, such as amino acids or sugars.\footnote{Hirata, K.; Mori, Y.; Ishiuchi, S. I.; Fujii, M.; Zehnacker, A. Physical Chemistry Chemical Physics 2020, 22 (43), 24887-24894} \footnote{Tamura, M.; Sekiguchi, T.; Ishiuchi, S.-I.; Zehnacker-Rentien, A.; Fujii, M. The Journal of Physical Chemistry Letters 2019, (10), 2470-2474} Then I will illustrate the sensitivity of chiroptical spectroscopy to conformational isomerism and molecular interactions on the example of 1-indanol studied by Vibrational Circular Dichroism (VCD) in the condensed phase \footnote{Le Barbu-Debus, K.; Scherrer, A.; Bouchet, A.; Sebastiani, D.; Vuilleumier, R.; Zehnacker, A. Physical Chemistry Chemical Physics 2018, 20 (21), 14635-14646} and PhotoElectron Circular Dichroism (PECD) under jet-cooled conditions

Vibrational circular dichroism of a 2,5-diketopiperazine (DKP) peptide: Evidence for dimer formation in cyclo LL or LD diphenylalanine in the solid state

International audienc

Boundaries: A Boundary Setting and Social Competence Program for Parents and Youth

Learning to set age-appropriate boundaries is an integral element of positive youth development. Both parents and youth need guidance in rule-rsetting and negotiating boundaries. North Dakota State University Extension created Boundaries, a program using parent-youth relationships to teach the importance of setting and following rules or boundaries in various environments. Boundaries was written for 7th- through 12th-grade youth and their parents. This study provides an overview of the program’s objectives and curriculum and shares findings from evaluation efforts conducted with over 60 youth and adults during the program’s pilot phase. In six pilot sessions, respondents completed single-session retrospective questionnaires and answered open-ended questions, which were analyzed using descriptive statistics, paired t-tests, and thematic review. Adults reported higher satisfaction than youth with program content and instruction. Both youth and adults increased their knowledge of program-specific content related to boundaries and relationships. Open-ended responses offered positive feedback and suggestions for program improvement. Results suggested the program was perceived positively and increased youth and adult knowledge of boundary setting and social competence in family life and other settings. Key recommendations include increased rigorous evaluation to measure program impacts and focus on effective implementation strategies for the program

Effect of puckering motion and hydrogen bond formation on the vibrational circular dichroism spectrum of a flexible molecule: the case of ( S )-1-indanol

International audienceThe influence of flexibility and hydrogen bond formation on the IR absorption and vibrational circular dichroism (VCD) spectrum of a floppy protic molecule, namely, (S)-1-indanol, is studied in both non-polar CCl 4 and polar DMSO solvents. The experimental IR absorption and VCD spectra obtained by Fourier transform spectroscopy are interpreted using both static density functional theory (DFT) calculations and first principles molecular dynamics (FPMD) within DFT, using the nuclear velocity perturbation theory (NVPT). Simulation of the spectra based on static optimised geometries is not sufficient in CCl 4 and going beyond static calculations is mandatory for satisfactorily reproducing the VCD spectra. The FPMD results obtained in DMSO indicate that (S)-1-indanol is hydrogen-bonded to one DMSO molecule. As a result, static "cluster-in-the-bulk" DFT calculations in which the solute-solvent interaction is modeled as the most stable (S)-1-indanol:DMSO-d6 complexes in a DMSO continuum yield satisfactory agreement with the experiment. Correspondence between experimental and simulated spectra is slightly improved when the VCD spectrum is calculated as the summed contributions of snapshots extracted from FPMD trajectories, due to better sampling of the potential-energy surface. Finally, NVPT calculations further improve the description of experimental spectra by taking into account higher-energy structures, which are not necessary local minima

Conformer-selective photoelectron circular dichroism: Experimental development and application to nitrogen chirality

Here, we describe recently developed upgrades to our experimental scheme for obtaining the photoelectron spectrum, the anisotropy parameter, and the photoelectron circular dichroism (PECD) of jet-cooled flexible molecules with conformer selectivity. The one-color resonance-enhanced multiphoton ionization process used allows ionizing selectively the different conformers present in the supersonic expansion by selecting their S0-S1 transition. We first describe the experimental setup with emphasis on the data acquisition and processing. Then, we apply this ionization scheme to a flexible molecule, 1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM). This molecule shows two stereogenic centers, namely, an asymmetric carbon and a nitrogen atom. It exists in two conformers, THIQMI and THIQMII, which differ by the direction of the intramolecular hydrogen bond and the absolute configuration of the nitrogen atom. Therefore, these two conformers are also diastereomers, endowed with slightly different ionization energies. The ionization energy of THIQMI, which shows an OH…N hydrogen bond, is slightly higher than that of THIQMII. Their PECD spectra, although of identical signs, differ in shape and magnitude. Surprisingly, the anisotropy parameter is more sensitive than the PECD to the conformational isomerism at play in this system