Abstract. The bulk modulus, Ko, and its pressure derivative/Co, of 7-(Mgo.6, Feo.4)2SiO4 have been accurately determined to 50.0 GPa under hydrostatic conditions at room temperature in a diamond cell using synchrotron radiation. Our results agree with Brillouin and ultrasonic measurements on 7-M~g2SiO4 at low pressure, indicating normal elastic behaviour in the metastable pressure range of this high pressure mineral. Our values of Ko and K; are 183.0 GPa and 5.4, respectively.
Functionalized xanthine derivatives bearing a nitroxide moiety at the 3- or 8-position were synthesized as electron paramagnetic resonance (EPR) probes. The 8-cyclopentyl-1-propylxanthine derivative 4, spin-labeled at N3 by substitution with a nitroxide-bearing dihydropyrrole moiety, was a potent and selective A(1) adenosine receptor antagonist (K(i) for A(1) 5.5 nM, 1600-fold selectivity vs A(2A), >200-fold vs A(2B), and 310-fold vs A(3) adenosine receptors). 8-(1-Oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)-1,3-dipropylxanthine 10 (K(i) for A(1) 8.2 nM) was similarly potent and selective, while 8-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-1,3-dipropylxanthine 11 (K(i) for A(1) 160 nM) exhibited significantly lower affinity for A(1) adenosine receptors. 8-[4-(((1-Oxyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-2-oxoethoxy)phenyl]-1-propylxanthine14, a 3-unsubstituted xanthine derivative, was found to be a potent A(2B) adenosine receptor antagonist (K(i) for A(2B) 48 nM) but also exhibited high affinity for A(1) receptors (K(i) for A(1) 15.7 nM). An X-ray structure of compound 10 was obtained, confirming the proposed structure. The novel spin-labeled A(1)-selective or A(1)/A(2B)-nonselective adenosine receptor antagonists may become useful probes for biophysicochemical investigations of adenosine receptors in their membrane environment.
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