Ferreira M. M. C., Kiralj R., “A Combined Structural, Quantum Chemical and Chemometric Study on Aromatic Bond Lengths in Crystals of Nucleosides”. Kraków, Poland, 25-31/08/2001: 20th European Crystallographic Meeting, Book of Abstracts, 314 (2001). Poster S9.M3.P2. Section: S9.M3. Data Bases.
POSTERS
|S9.M3.P2.| A
Combined Structural, Quantum
Chemicaland
ChemometricStudy on
Aromatic
Bond Lengths in Crystals
of Nucleosides. M.M.C.
Ferreira, R.
Kiralj,
Instituto de Quìmica,
UNICAMP,
Campinas, SP, Brazil.
Keywords:
aromatic bonds, nucleosides,
che-
mometrics
The rapid
growth of life sciences concerning modifi-
cations of nucleicacids
at atomic level [1], and also
the exponential
increase of number of nucleobase
containing crystal
structures necessarily
implicate
various studies
on both standard [2],
non-standard
and modified
nucleobases. In general, nucleobases
are heteroaromatic
systems whose intrinsic proper-
ties change due to
intermolecular or non-boded in-
tramolecular
interactions, especially stacking. The
aromaticity aspect
studied here are experimental
carbon-carbon, carbon-nitrogenand
carbon-oxygen
bond lengths d
of seven standard [2], more
than
thirty non-standard
and modified nucleobases in
nucleosides. The
best X-ray and neutron crystal
structures (R
< 6.0%, e.s.d.’s < 0.005 Å, publication
year 1975 and after, no
disorder) were retrieved from
Cambridge Structural
Database [3]. Structural vari-
ables to describe
the bond lengths were generated:
Pauling p-bond
order pP,
weighted p-bond
order pw
obtained from
the HOSE (Harmonic Oscillator Sta-
bilization Energy)
approach [4], p-bond
order in-
cluding maximal packing
effects on bond lengths pcr,
number of non-hydrogen
atoms around the bond n,
and the sum of
atomic numbers Q. Principal Com-
ponent Analysis
(PCA) and Hierarchical
Cluster
Analysis (HCA) [5]
were peformed to study the rel-
ationships among the
bonds and the variables. Par-
tial Least Squares
(PLS) and Multiple Linear
Re-
gression (MLR) [5]
were used to calculate and pre-
dict the bond
lengths from the structural variables.
As alternative methods of
bond length calculation and
prediction, Pauling
potential curves, semi-empirical
PM3 and ab initio
HF 6-31G** were employed. PCA
shows that bond lengths
of nucleobases are three-
dimensional phenomena.There
is a clear clustering of
the bonds both in PCA andHCA
due to the bond type
and other
structural characteristics. All
regression mod-
els arefailygood(r>0.9),among
which PLSand the
ab
initio shows to be
the best ones.
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Ren, R. X -F., Kool, E. T. "C-Nucleosides
Derived from Simple
Aromatic Hydrocarbons", Synlett, (1997):
341 - 347.
[2] Clowney L., Jain
S. C., Srinivasan A. R., Westbrook J., Olson
W. K., Berman H. M.
"Geometric Parameters in Nucleic Acids:
Nitrogenous Bases", J. Am. Chem.
Soc., (1996), 118: 509 – 518.
[3] Alen F. H.,
Kennard O. "3D Search and Research Using the
Cambridge Structural Database",
Chem. Design Autom. News,
(1993), 8: 31 - 37.
[4] Krygowski T.
M., Anulewicz R., Kruszewski J.
"Crystallo-
graphic Studies and
Physicochemical Properties of p-Electron
Compounds. III. Stabilization
Energy and Kekulé Structure Con-
tributions Derived
from Experimental Bond Lengths",
Acta
Cryst.; B39: 732 – 739.
[5] Beebe K. R.,
Pell R. J., Seasholtz M. B. "Chemometrics: A
Practical Guide", Wiley&Sons,
New York, 1998.
PAGE 314 20TH EUROPEAN CRYSTALLOGRAPHIC MEETING,KRAKÓW,AUGUST 25-31,2001, BOOK OF ABSTRACTS