QUANTUM COMPUTATIONAL STUDIES ON PORPHYCENE - Theoretical and Computational Research in the 21st Century - page 158

porphyrias are inherited, whereas others are acquired. Recently, the anti-
cancer drugs are synthesized using several gold-porphyrin complexes [5].
The porphyrins are biologically handy compounds. Their functions can be
varied by changing the metal, its oxidation state, or the nature of the or-
ganic substituents on the porphyrin structure. It is a general principle that
the evaluation tends to proceed by modifi cation structures and functions
that are already present on the organism rather than producing new ones
de novo [6]. As evidenced by the host of expanded, reshuffl ed, inverted,
contracted, and otherwise modifi ed porphyrins brought to light in recent
years, the quest for this concept has proven to be highly successful.
The interdisciplinary interests on the porphyrins induced scientists to
introduce a new research line relating to the development of novel porphy-
rin-like molecules. The molecules are designed by the structural variation
of the tetrapyrrolic macrocycle while maintaining a (4 n +2) π main conju-
gation pathway anticipated to exhibit special properties. During the devel-
opment of the quantum-chemical method, many of the empirical chemical
concepts were derived rigorously and it has provided a method for the
calculation of the properties of chemical systems and the bonding that is
involved in the formation of molecular systems. Computational theoreti-
cal chemistry is a branch of chemistry that uses theoretical studies to assist
in solving chemical problems. It uses the results of theoretical chemistry,
incorporated into effi cient computer programs, to calculate the structures
and properties of molecules and solids. While its results normally comple-
ment the information obtained by chemical experiments, it can in some
cases predict hitherto unobserved chemical phenomena. Quantum-chemi-
cal (QC) calculations are a key element in biological research. When con-
stantly tested for their range of validity QC methods, provide a description
of how molecules interact and form their three-dimensional shape, which
in turn determines molecular function. They can aid the formulation of
hypotheses that provide the connecting link between experimentally deter-
mined structures and biological function. QC calculations can be used to
understand enzyme mechanisms, hydrogen bonding, polarization effects,
spectra, ligand binding, and other fundamental processes both in normal
and aberrant biological contexts. The power of parallel computing and
progress in computer algorithms are enlarging the domain of QC applica-
tions to ever more realistic models of biological macromolecules.
The key insight of chemistry is the relationship between molecular
structure and molecular function. We use the details of molecular structure