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1.
Angew Chem Int Ed Engl ; 57(40): 13344-13348, 2018 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-30004162

RESUMO

We demonstrate that molecular vibrations with originally low or zero intensity in a vibrational circular dichroism (VCD) spectrum attain chirality in molecular crystals by coordinated motion of the atoms. Ab initio molecular dynamics simulations of anharmonic solid-state VCD spectra of l-alanine crystals reveal how coherent vibrational modes exploit the space group's chirality, leading to non-local, enhanced VCD features, most significantly in the carbonyl region of the spectrum. The VCD-enhanced signal is ascribed to a helical arrangement of the oscillators in the crystal layers. No structural irregularities need to be considered to explain the amplification, but a crucial point lies in the polarization of charge, which requires an accurate description of the electronic structure. Delivering a quantitative atomic conception of supramolecular chirality induction, our ab initio scheme is applicable well beyond molecular crystals, for example, to address VCD in proteins and related compounds.

2.
Phys Chem Chem Phys ; 19(21): 13882-13894, 2017 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-28513754

RESUMO

We investigated the red absorbing, dark stable state (Pr state) of the second GAF domain of the cyanobacteriochrome AnPixJ (AnPixJg2) by a molecular dynamics simulation of 1 µs duration. Our results reveal two distinct conformational isoforms of the chromophore, from which only one was known from crystallographic experiments. The interconversion between both isoforms is accompanied by alterations in the hydrogen bond pattern between the chromophore and the protein and the solvation structure of the chromophore binding pocket. The existence of sub-states in the Pr form of AnPixJg2 is supported by the results from experimental 13C MAS NMR spectroscopy. Our finding is consistent with the observation of structural heterogeneity in other cyanobacteriochromes and phytochromes.

3.
J Chem Phys ; 144(6): 064305, 2016 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-26874486

RESUMO

The established quantum cluster equilibrium (QCE) approach is refined and applied to N-methylformamide (NMF) and its aqueous solution. The QCE method is split into two iterative cycles: one which converges to the liquid phase solution of the QCE equations and another which yields the gas phase. By comparing Gibbs energies, the thermodynamically stable phase at a given temperature and pressure is then chosen. The new methodology avoids metastable solutions and allows a different treatment of the mean-field interactions within the gas and liquid phases. These changes are of crucial importance for the treatment of binary mixtures. For the first time in a QCE study, the cis-trans-isomerism of a species (NMF) is explicitly considered. Cluster geometries and frequencies are calculated using density functional theory (DFT) and complementary coupled cluster single point energies are used to benchmark the DFT results. Independent of the selected quantum-chemical method, a large set of clusters is required for an accurate thermodynamic description of the binary mixture. The liquid phase of neat NMF is found to be dominated by the cyclic trans-NMF pentamer, which can be interpreted as a linear trimer that is stabilized by explicit solvation of two further NMF molecules. This cluster reflects the known hydrogen bond network preferences of neat NMF.

4.
Dalton Trans ; 44(43): 18760-8, 2015 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-26243459

RESUMO

The two highly flexible ligands 1,1'-bis(4-phospholanobutyl)ferrocene (5a) and 1,1'-bis(5-phospholanopentyl)ferrocene (5b) reacted with [PtCl2(cod)] (cod = 1,5-cyclooctadiene), [AuCl(tht)] (tht = tetrahydrothiophene) and [{RhCl(CO)2}2] to give the respective chelate complexes cis-[PtCl2(5a,b-κ(2)P,P')] (7a,b), [AuCl(5a,b-κ(2)P,P')] (8a,b) and trans-[RhCl(CO)(5b-κ(2)P,P')] (9b). Treatment of 5a,b with selenium gave the corresponding selenides 6a,b. All compounds have been fully characterised by NMR ((1)H, (13)C, (31)P) and IR spectroscopy and mass spectrometry. In addition, crystal structures of 6a, 7b, 8a,b and 9b were determined by X-ray crystallography. Furthermore, the rhodium-catalysed hydroformylation of 1-octene has been studied with ligand 5b.

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