XI Simpósio Brasileiro de Química Teórica
Caxambu, 18 a 21 Novembro de 2001
 
 
 
 

P228

A COMBINED QUANTUM CHEMICAL, CHEMOMETRIC AND
STRUCTURAL STUDY ON AROMATIC BONDS IN NUCLEOSIDES

Márcia M. C. Ferreira (PQ) and Rudolf Kiralj (PQ), Instituto de Química, Universidade
Estadual de Campinas, Campinas, SP, 13083-970, Brazil. marcia@iqm.unicamp.br
 

Rapid growth  of  life sciences  including  modifications  of  nucleic acids  at  atomic level¹,
and also  the  exponential increase of number  of nucleobase containing crystal structures
necessarily is followed by various studies on both standard²,   non-standard and modified
nucleobases.  This work studies aromatic C-C,  C-N  and  C-O  bonds of seven standard²,
and   more   than   forty   non-standard   and   modified  nucleobases.   The   best   crystal
structures  (crystallographic R  <  6.0%,  e.s.d.'s  <  0.005  Å,  published   after  1974,  no
disorder) were retrieved from  Cambridge Structural Database³  as source  of  high-quality
experimental bond lengths d.   Bond descriptors were calculated:   Pauling p-bond  order
p_P,   weighted  p-bond  order   p_w (HOSE  approach⁴),  p-bond  order   with  maximal  and
overall  packing  effects  p_cr and p_cm,  number  of non-hydrogen atoms around the bond n,
and   the   sum   of   atomic   numbers   Q.    Principal   Component   Analysis  (PCA)  and
Hierarchical Cluster Analysis  (HCA)  were  performed  to  study  relationships among  the
bonds and variables.   Partial Least Squares  (PLS)  were used to model  and  predict the
bond lengths based upon  the variables.   Pauling potential curves,  semi-empiricial   PM3
and  ab initio  HF 6-31G**  were  employed also for bond length calculation.  PCA  shows
that  the  bond lengths of nucleobases  are  three-dimensional  phenomena.   There  is  a
clear clustering of the bonds both   in  PCA  and  HCA  due  to  the  bond type  and  other
structural characteristics. PLS (r > 0.9)  and ab initio shows to predict/calculate d's better
than PM3 and Pauling potential curve.  Detailed results will be discussed.
1 N. C. Chaudhuri, R. X.-F. Ren, E. T. Kool, Synlett (1997) 341 - 347.
2 L. Clowney,  S. C. Jain,  A. R. Srinivasan, J. Westbrook, W. K. Olson, H. M. Berman, J.
Am. Chem. Soc. 118 (1996) 509 - 518.
3 F. H. Allen, O. Kennard, Chem. Design. Autom. News 8 (1993) 31 - 37.
4 T. M. Krygowski, R. Anulewicz, J. Kruszewski, Acta Cryst. B39 (1983) 732 - 739.

(FAPESP