organic compounds
Acta Crystallographica Section C
Crystal Structure
such as the oxidation of 1,2-phenylenediamine (o-PD) by
horseradish peroxidase (Jiao et al., 1998).
Communications
Synthetically, DAP is prepared by the catalysed auto-
sensitized or photochemical oxidation cyclization of o-PD. The
oxidation has been catalysed by various oxidants, including
silver oxide, lead(IV) oxide, ferric chloride, cupric chloride
and perchlorate and by cobalt perchlorate (Crank & Makin,
ISSN 0108-2701
Phenazine-2,3-diamine
1
989). The oxidation takes place in two one-electron transfer
a
a
a
Robert P. Doyle, Paul E. Kruger, * Philip R. Mackie and
steps, a mechanism which may have relevance when studying
the biological functions of metal-containing proteins (Loveless
et al., 1981). The fact that the heterocycle is produced in high
yield in neutral or acid conditions, but not under basic
conditions, perhaps explains why only structures of the
protonated molecule (as its chloride or perchlorate salts) have
been published previously (Brownstein & Enright, 1995; Peng
& Liaw, 1986). These studies have shown that the heterocycle
is protonated at the phenazine nitrogen although spectro-
scopic evidence suggests that the more basic amine N atoms
are protonated in solution. When one of the phenazine N
atoms is protonated the cation may exist in six resonance
forms which, when the individual ꢀ bond strengths are
considered, explains the lack of symmetry of the bond lengths
in the structures of protonated DAP. In contrast, the structure
of DAP (Fig. 1) shows a high degree of symmetry both in bond
b
Mark Nieuwenhuyzen
a
Department of Chemistry, University of Dublin, Trinity College, Dublin 2, Ireland,
b
and School of Chemistry, The Queens University of Belfast, Belfast BT9 5AG,
Northern Ireland
Received 21 August 2000
Accepted 19 October 2000
The planar electron-rich heterocyclic diamine 2,3-diamino-
phenazine (DAP), C H N , is of particular interest to both
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2
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chemists and biochemists because of its rich organic chemistry
and intense luminescence. In this paper, we report the ®rst
structure of DAP in its non-protonated form and describe the
intriguing crystal packing, which features ꢀ±ꢀ, hydrogen- and
T-bonded interactions.
lengths and angles on each side of the molecular C axis (Table
2
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). In the solid state, the structure of DAP is essentially planar,
Comment
however a small degree of bending is discernible. This
curvature may be attributed to the geometry of the central
pyrazine ring which displays some distortions from that of an
ideal aromatic ring (Table 1).
The crystal packing of DAP (Fig. 2) is particularly inter-
esting and as the molecule is replete with numerous ꢀ-bonding
and hydrogen-bond donor and acceptor sites it may be
expected that it can act as a particularly versatile supramole-
cular tecton. Indeed, it is found that DAP forms in®nite ꢀ±ꢀ
stacks in the x and z directions, a feature which is a conse-
quence of the orthorhombic crystal system. The average
The planar electron-rich heterocyclic diamine 2,3-diamino-
phenazine (DAP) is a compound which has long been of
interest, initially because of its chemical and physical prop-
erties and more recently because of its mutagenic and geno-
toxic behaviour. The fact that DAP has a rich and varied
chemistry is demonstrated by the vast number of organic
transformations that have been published in the literature. In
addition, the compound has been well characterized spectro-
scopically by NMR, absorption and most notably by emission
techniques, where the remarkable luminescence of DAP has
been intensively studied and exploited in analytical and
biochemical applications.
Ê
arene±arene non-bonded distance is 3.64 A. The in®nite ꢀ
stacks are connected in three dimensions by way of inter-
molecular hydrogen bonds (Table 2). The hydrogen bonds
connect the amine H1A and H16A and the aromatic H3 and
H14 atoms of one molecule and the pyrazine N atoms (N5 and
N12) of its nearest neighbour. In addition, there are T-bonded
interactions which feature the terminal benzene ring
DAP is known to luminesce strongly both in polar organic
solvents (Zheng et al., 1997) and in aqueous buffer solutions,
especially when embedded within a micelle structure (Mekler
&
Bystryak, 1992). Indeed, it is the luminescence of DAP that
sparked our interest in the molecule, especially as probes
containing phenazine have shown potential in the exploration
of nucleic acid structure. Further, DAP has been shown to
damage DNA (Watanabe et al., 1996) and so may have some
role to play as a chemotherapeutic agent. The compound has
found useful application in analytical chemistry as a cataly-
metric analyte, where it is used as a marker in ¯uorimetric
determinations of laccase activity (Huang et al., 1998) and in
immunoassay determination of enzyme-catalysed reactions
Figure 1
The molecular structure of DAP showing 50% probability displacement
ellipsoids.
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04 # 2001 International Union of Crystallography ꢀ Printed in Great Britain ± all rights reserved
Acta Cryst. (2001). C57, 104±105
Doyle, Robert P.
