The crystal structure of 8-aza-2,6-diaminopurine sulfate monohydrate

Abstract

The crystal and molecular structure of 8-aza-2,6-diaminopurine sulfate monohydrate, (CaN7H6)2SOa.H20, has been determined from three-dimensional diffractometer X-ray data. The material crystallizes in space group P1 of the triclinic system with two formula units in a cell of dimensions a=6.813 (5), b=15-117 (11), c=8.182 (5)/~, e=91.71 (1), fl= 106.21 (1), and y=93.57 (1) °. The observed and calculated densities are 1"71 and 1.72 gcm -a, respectively. The structure has been refined by full-matrix least-squares techniques to a final value of the conventional R value (on F) of 0.039 for 2706 independent intensities. The two independent 8-aza-2,6-diaminopurine cations (ADPH) are very similar, and the sites of protonation are at N(3) and N(8); this result is similar to that observed in the 8-azaguaninium cation (AGH) but different from that found in the protonated form of natural purines. The hydrogen bonding in the crystal is extremely complicated, with all hydrogen atoms and all acceptor atoms except N(1) of one ADPH cation participating. The bond lengths and angles in the cations are normal, showing the anticipated effects of the protonation at N(3) and N(8).

Refinement of the crystal structure of kröhnkite

“…The azapurine ring is not quite planar, but comprises a planar five-membered triazole ring [C(4), C(5), N(7), N(8), N(9)] and a planar pyrimidine ring [N(1), C(2), N(3), C(4), C(5), C(6)] which are inclined to each other at an angle of 0.92°; this slight pucker along the C(4)-C(5) bond is commonly found in purine structures (Bugg, 1972) and is very similar to that reported for the similar 8-aza-2,6-diaminopurine cation (Singh, Lewis & Hodgson, 1974;Singh & Hodgson, 1975). The hydrogen bonding is, as expected, quite complex, and the probable intermolecular hydrogen bonds are listed in Table 4; the criterion for inclusion of an interaction in the table was that of Hamilton & Ibers (1968).…”

pH‐Switchable Helicity of DNA‐Templated Assemblies

“…N‐1 being occupied in H‐bonding to the thymines, protonation is most likely to occur at N‐3 23. Further evidence was taken from the lower p K a value determined for P (p K a ≈4.8), when compared to other 2,6‐diaminopurine derivatives (p K a ≈5.1),23 which can be explained by stabilization of P +H + through H‐bonding with the ethylene glycol unit at the N‐9 position,24 as shown in Figure 3 b. Interestingly, related N‐9‐glycol‐substituted 2,6‐diaminopurine derivatives also show a small decrease in p K a value (p K a ≈4.9) 21.…”

4,6-Diphenyl-2-methylthieno[3,4-d]-1,2,3-triazole

“…Does the presence of a non-classical thiophene ring alter the geometry of the fused triazole? Crystal structures of nine compounds containing a (2H)-I,2,3-triazole moiety have been reported (ManottiLanfredi, Tiripicchio & Tiripicchio-Camellini, 1977;Harlow, Brown, Dewar & Simonsen, 1977;K~n~m, P~rk~nyi & Schawartz, 1977;K/dman, P~rk~nyi, Schawartz & Simon, 1976;Lopez de Lerma, Cano, Garcia-Blanco & Martinez-Ripoll, 1976;Singh & Hodgson, 1975;Foces-Foces, Cano & Garcia-Blanco, 1975a, b;Kozlowski, Singh & Hodgson, 1974). Although the substituents vary widely and six of the compounds involve a six-membered ring fused to the five-membered ring, the mean geometries of the triazole rings are quite similar; the overall average distances and angles for the nine structures are: N--N = 1.332, C-N = 1.338, C-C --1.394 /~; N--N--N = 116.6, C--N--N = 102.7, C-C-N = 109.0 °.…”