4th EucheMs chemistry congress

tuesday, 28-Aug 2012
s816
chem. Listy 106, s587–s1425 (2012)
Physical, theoretical and Computational Chemistry
theoretical Chemisry – ii
o - 2 3 8
theoretiCAL Study for LithiuM diffuSion in
SoLid StAte MAteriALS
M. M. iSLAM 1 , t. Bredow 1
1 University of Bonn, Mulliken Center for Theoretical Chemistry,
Bonn, Germany
Lithium diffusion in lithium containing transition element
disulphide and fluoride is investigated theoretically with periodic
quantum-chemical methods. The calculated lithiation energies for
the hexagonal titanium disulphide (h-Li TiS , x = 0.88,1.0)
x 2
confirm that Li preferentially occupies the octahedral site rather
than the tetrahedral site. Among the considered point defects, V , Li
V , and Ti , Li point defects are thermodynamically preferred in
Ti i
h-Li TiS . Competing pathways for Li diffusion in
x 2
h-Li TiS are investigated using the climbing-image
x 2
Nudged-Elastic-Band (cNEB) approach. Li + ions can migrate
within the crystallographic ab plane either in a direct pathway
through shared edges of neighboring octahedra or via vacant
tetrahedral sites. The possibility of three-dimensional Li + diffusion
along the c direction is investigated via inclusion of Ti point
defects and Ti Frenkel defects. The calculated energetic properties
show that ferromagnetic phase is more stable than the
anti-ferromagnetic phase of lithium vanadium fluoride (α-Li VF ). 3 6
Three different inequivalent Li sites (Li(1), Li(2) and Li(3)) are
observed where Li(1) occupies the middle position of the triplet
Li(2)–Li(1)–Li(3). The calculated Li vacancy formation energy
shows that vacancy formation at the Li(1) and Li(3) sites are easier
than that in Li(2) site. The Li exchange processes between Li(1)
to Li(3), Li(1) to Li(2) and Li(2) to Li(3) are studied by calculating
the Li + migration between various sites. It is observed that Li
exchange in α-Li VF may take place in the following order: Li(1)
3 6
to Li(3) > (Li(1) to Li(2) > Li(2) to Li(3). This is in well accord
with the available experiment.
Keywords: Lithium titanium disulphide; Lithium vanadium
fluoride; Defects; Li Ion Diffusion; Activation energy;
theoretical Chemisry – iii
4 th EucheMs chemistry congress
o - 2 3 9
theoretiCAL StudieS of enzyMAtiC
reACtionS
w. thieL 1
1 Max-Planck-Institut für Kohlenforschung, Theory,
Mülheim an der Ruhr, Germany
Combined quantum mechanical/molecular mechanical
(QM/MM) approaches have emerged as the method of choice for
treating local electronic events in large molecular systems, for
example, chemical reactions in enzymes or photoinduced
processes in biomolecules. The lecture will outline the theoretical
background and commonly chosen strategies for QM/MM studies
of biomolecular reactions. [1–3] It will then describe some of our
recent work on biocatalysis by enzymes which includes
mechanistic studies on cytochrome P450cam, [4, 5] xanthine
oxidases [6, 7] , cyclohexanone monooxygenase (CHMO) [8] , and
glycosyltransferases (LgtC) [9] . These studies have addressed,
inter alia, the competition between coupling and uncoupling
reactions in the wild-type P450cam enzyme and its mutants, the
crucial role of active-site residues in the reductive half-reaction
of xanthine oxidases, the origin of enantioselectivity in
CHMO-catalyzed reactions, and the favored reaction mechanism
in LgtC. The examples presented will illustrate the chemical
insights and the improved mechanistic understanding of
enzymatic reactions that can be provided by QM/MM
calculations.
references:
1. H. M. Senn, W. Thiel, Angew. Chem. Int. Ed. 48,
1198–1229 (2009).
2. H. M. Senn, J. Kästner, J. Breidung, W. Thiel,
Can. J. Chem. 87, 1322–1337 (2009).
3. T. Benighaus, W. Thiel, J. Chem. Theory Comput. 7,
238–249 (2011).
4. M. Altarsha, T. Benighaus, D. Kumar, W. Thiel, J. Am.
Chem. Soc. 131, 4755–4763 (2009).
5. S. Shaik, S. Cohen, Y. Wang, H. Chen, D. Kumar,
W. Thiel, Chem. Rev. 110, 949–1017 (2010).
6. S. Metz, D. Wang, W. Thiel, J. Am. Chem. Soc. 131,
4628–4640 (2009).
7. S. Metz, W. Thiel, J. Am. Chem. Soc. 131, 14885–14902
(2009).
8. I. Polyak, M. T. Reetz, W. Thiel, J. Am. Chem. Soc. 134,
2732–2741 (2012).
9. H. Gomez, I. Polyak, W. Thiel, J. M. Lluch, L. Masgrau,
J. Am. Chem. Soc. (2012); doi:10.1021/ja210490f.
Keywords: QM/MM; reaction mechanisms; enzymes;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc