The Complexation of Tetracycline and Anhydrotetracycline with Mg2+ and Ca2+: A Spectroscopic Study

Autor:	W. E. Ford, and W. Szymczak, J. M. Wessels, S. Schneider
Rok vydání:	1998
Předmět:	Circular dichroism Aqueous solution Ligand Hydrogen bond Chemistry Inorganic chemistry Surfaces Coatings and Films Crystallography Deprotonation Materials Chemistry Titration Qualitative inorganic analysis Chelation Physical and Theoretical Chemistry
Zdroj:	The Journal of Physical Chemistry B. 102:9323-9331
ISSN:	1520-5207 1520-6106
Popis:	Steady-state absorption and emission, circular dichroism (CD), and time-of-flight secondary-ion-mass-spectroscopic (TOF−SIMS) measurements were performed to study the complexation of tetracycline (TC) and anhydrotetracycline (AHTC) with Mg2+ and Ca2+ ions, respectively, in aqueous solutions at pH 8.02. The results obtained suggest that Ca2+ forms a 1:2 ligand:metal complex with TC via chelation through O10−O11 and O12−O1 and induces thereby the extended conformation A of TC, which is stabilized through hydrogen bonding between the deprotonated dimethylamino nitrogen, N4, and OH12a. pH titrations provide evidence that N4 deprotonates in the presence of a 164-fold molar excess of Ca2+ at approximately pH ⩾ 7.7 (cTC = 2.1 × 10-5 M). In contrast to Ca2+, Mg2+ binds to N4−O3 and thereby stabilizes the twisted conformation B of TC. TOF−SIMS measurements indicate that a 1:2 ligand:metal complex is formed in addition to the 1:1 complex. The Mg2+-induced increase in the fluorescence intensity and the observed chan...
Databáze:	OpenAIRE
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