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- 검색키워드
- 저자 : Nicu, Valentin Paul (검색결과 5 건)
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Nicu, Valentin Paul,Baerends, Evert Jan,Polavarapu, Prasad L. American Chemical Society 2012 The Journal of physical chemistry A Vol.116 No.32
<P>We present a combined experimental and computational investigation of the vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra of [1,1′-binaphthalene]-2,2′-diol. First, the sensitive dependence of the experimental VA and VCD spectra on the solvent is demonstrated by comparing the experimental spectra measured in CH<SUB>2</SUB>Cl<SUB>2</SUB>, CD<SUB>3</SUB>CN, and DMSO-<I>d</I><SUB>6</SUB> solvents. Then, by comparing calculations performed for the isolated solute molecule to calculations performed for molecular complexes formed between solute and solvent molecules, we identify three main types of perturbations that affect the shape of the VA and VCD spectra when going from one solvent to another. These sources of perturbations are (1) perturbation of the Boltzmann populations, (2) perturbation of the electronic structure, and (3) perturbation of the normal modes.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcafh/2012/jpcafh.2012.116.issue-32/jp303891x/production/images/medium/jp-2012-03891x_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp303891x'>ACS Electronic Supporting Info</A></P>
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Nicu, Valentin Paul,Baerends, Evert Jan Royal Society of Chemistry 2011 Physical chemistry chemical physics Vol.13 No.36
<P>The concept of <I>robustness</I> of rotational strengths of vibrational modes in a VCD spectrum has been introduced as an aid in assignment of the absolute configuration with the help of the VCD spectrum. The criteria for robustness have been based on the distribution around 90° of the angles <I>ξ</I>(<I>i</I>) between electric and magnetic transition dipoles of all the modes <I>i</I> of a molecule. The angles <I>ξ</I>(<I>i</I>) (not, of course, the rotational strengths) are, however, dependent on the choice of origin. The derived criteria are for the center of mass chosen as the origin of the coordinate system. We stress in this note that application of the derived criteria assumes that excessive translation of the coordinate origin is not applied. Although the <I>ξ</I>(<I>i</I>) angles are not very sensitive to the position of the origin, very small displacements (a few Å) are not a problem, excessive translation of the origin does have considerable effect on the <I>ξ</I>(<I>i</I>) angles. In this note we quantify this effect and demonstrate how the distribution of <I>ξ</I>(<I>i</I>) angles is affected. Although it is possible to recalibrate the robustness criteria for the angles for a specific (large) displacement, we recommend that such displacement simply be avoided. It is to be noted that some modeling software does yield output with excessively displaced coordinate origin; this should be checked and corrected.</P> <P>Graphic Abstract</P><P>The origin dependence of the angle between the electric and magnetic dipole transition moment vectors of fundamental vibrational transitions is investigated using cinchona as example. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1cp21442j'> </P>
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A VCD robust mode analysis of induced chirality: The case of pulegone in chloroform
Nicu, Valentin Paul,Debie, Elke,Herrebout, Wouter,Van der Veken, Benjamin,Bultinck, Patrick,Baerends, Evert Jan Wiley Subscription Services, Inc., A Wiley Company 2009 Chirality Vol.21 No.e1
<P>Vibrational modes in an achiral molecule may acquire rotational strength by complexation to a chiral molecule, as happens for achiral solvent molecules complexed to a chiral solute. We investigate this transfer of chirality in vibrational circular dichroism for the pulegone molecule in CDCl<SUB>3</SUB> solvent from the point of view of the robustness concept introduced recently. It turns out that the transfer of chirality yields nonrobust modes, which means that, although they are observed in vibrational circular dichroism (VCD) experiments, the sign of these modes cannot be predicted reliably with standard (Density Functional Theory) VCD calculations. This limits the usefulness of the induced chirality phenomenon for obtaining information on the intermolecular interactions that give rise to it. Chirality 21:E287–E297, 2009. © 2010 Wiley-Liss, Inc.</P>
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Heshmat, Mojgan,Nicu, ValentinPaul,Baerends, Evert Jan American Chemical Society 2012 The Journal of physical chemistry A Vol.116 No.13
<P>We study systematically the vibrational circular dichroism (VCD)spectra of the conformers of a simple chiral molecule, with one chiralcarbon and an “achiral” alkyl substituent of varyinglength. The vibrational modes can be divided into a group involvingthe chiral center and its direct neighbors and the modes of the achiralsubstituent. Conformational changes that consist of rotations aroundthe bond from the next-nearest neighbor to the following carbon, andbond rotations further in the chain, do not affect the modes aroundthe chiral center. However, conformational changes within the chiralfragment have dramatic effects, often reversing the sign of the rotationalstrength. The equivalence of the effect of enantiomeric change ofthe atomic configuration and conformational change on the VCD sign(rotational strength) is studied. It is explained as an effect ofatomic characteristics, such as the nuclear amplitudes in some vibrationalmodes as well as the atomic polar and axial tensors, being to a highdegree determined by the local topology of the atomic configuration.They reflect the local physics of the electron motions that generatethe chemical bonds rather than the overall shape of the molecule.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcafh/2012/jpcafh.2012.116.issue-13/jp212545z/production/images/medium/jp-2011-12545z_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp212545z'>ACS Electronic Supporting Info</A></P>
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