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Crystal structure resolution of two different chlorhexidine salts

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ABSTRACT

Two salts of the chlorhexidine di-cation (H2CHx2+) – (H2CHx)(SO4)·3H2O and (H2CHx)(CO3)·4H2O – have been synthesised and characterised crystallographically.

No MeSH data available.


A view along the a-axis of a) (H2CHx)(SO4)·3H2O and b) (H2CHx)(CO3)·4H2O, showing the structural similarities between the two compounds.
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fig1: A view along the a-axis of a) (H2CHx)(SO4)·3H2O and b) (H2CHx)(CO3)·4H2O, showing the structural similarities between the two compounds.

Mentions: Crystals were prepared by reaction of neutral chlorhexidine and sodium sulfate or potassium carbonate in aqueous ethanol, as part of a series of attempts to generate chlorhexidine-containing coordination complexes. Full crystallographic details of both salts are presented in Table 1. Structurally, the two salts are very similar to one another (Fig. 1), with small variations in the conformation of the hexyl chains and intermolecular hydrogen-bonding due to the different arrangement of oxygen atoms between the tetrahedral SO42− and the trigonal planar CO32− anions, and different protonation sites along the chlorhexidine moiety. The differences in protonation site may be seen by a comparison of Fig. 2a and 2b: in (H2CHx)(SO4)·3H2O, one biguanidine moiety is doubly protonated, whilst the other remains unprotonated; in (H2CHx)(CO3)·4H2O, both biguanidine moieties are singly protonated in an asymmetrical manner. In both instances, the C—N bond lengths within the biguanidine units (1.307 Å to 1.379 Å) indicate that some delocalisation of the double and single bonds is occurring. The protonation of the biguanidine moieties of the chlorhexidine was unexpected, given the alkaline nature of the reaction solution. Chlorhexidine di-cations in both salts adopt a spiral conformation and are arranged into U-shaped ‘coils’ that extend parallel to the a-axis. In the labelling scheme in Fig. 2, the biguanidine moiety N1 to N5 lies at the open end of the U-shaped coils. Within the coils, adjacent H2CHx2+ cations alternate between left- and right-handed conformations, so that each coil is not helical overall (Fig. 3). The coils are held together by hydrogen bonds to the sulfate or carbonate anions and water molecules that occupy the spaces between coils.


Crystal structure resolution of two different chlorhexidine salts
A view along the a-axis of a) (H2CHx)(SO4)·3H2O and b) (H2CHx)(CO3)·4H2O, showing the structural similarities between the two compounds.
© Copyright Policy - CC BY
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4920644&req=5

fig1: A view along the a-axis of a) (H2CHx)(SO4)·3H2O and b) (H2CHx)(CO3)·4H2O, showing the structural similarities between the two compounds.
Mentions: Crystals were prepared by reaction of neutral chlorhexidine and sodium sulfate or potassium carbonate in aqueous ethanol, as part of a series of attempts to generate chlorhexidine-containing coordination complexes. Full crystallographic details of both salts are presented in Table 1. Structurally, the two salts are very similar to one another (Fig. 1), with small variations in the conformation of the hexyl chains and intermolecular hydrogen-bonding due to the different arrangement of oxygen atoms between the tetrahedral SO42− and the trigonal planar CO32− anions, and different protonation sites along the chlorhexidine moiety. The differences in protonation site may be seen by a comparison of Fig. 2a and 2b: in (H2CHx)(SO4)·3H2O, one biguanidine moiety is doubly protonated, whilst the other remains unprotonated; in (H2CHx)(CO3)·4H2O, both biguanidine moieties are singly protonated in an asymmetrical manner. In both instances, the C—N bond lengths within the biguanidine units (1.307 Å to 1.379 Å) indicate that some delocalisation of the double and single bonds is occurring. The protonation of the biguanidine moieties of the chlorhexidine was unexpected, given the alkaline nature of the reaction solution. Chlorhexidine di-cations in both salts adopt a spiral conformation and are arranged into U-shaped ‘coils’ that extend parallel to the a-axis. In the labelling scheme in Fig. 2, the biguanidine moiety N1 to N5 lies at the open end of the U-shaped coils. Within the coils, adjacent H2CHx2+ cations alternate between left- and right-handed conformations, so that each coil is not helical overall (Fig. 3). The coils are held together by hydrogen bonds to the sulfate or carbonate anions and water molecules that occupy the spaces between coils.

View Article: PubMed Central - PubMed

ABSTRACT

Two salts of the chlorhexidine di-cation (H2CHx2+) – (H2CHx)(SO4)·3H2O and (H2CHx)(CO3)·4H2O – have been synthesised and characterised crystallographically.

No MeSH data available.