Molecular mechanical calculations and molecular dynamics simulations, based on the AMBER force field, were used to examine the molecular structures and stabilities of nine multidentate ligands and their Gd(III) ion complexes. The magnitude of various factors determining the stability of multidentate Gd(III) complexes, including the energy loss due to change of ligand conformation by complexation, the energy gain from cation-ligand attraction, and effects of intramolecular hydrogen bonding, were calculated by molecular mechanics. The fit between the Gd cation and the binding cavity in the ligands was examined by molecular graphics techniques. Intramolecular hydrogen bonds in free ligands with amide or hydroxyl as H-bond donors usually disfavor complex formation, due to disruption of hydrogen bonds during complex formation. Intramolecular hydrogen bonds may contribute to enhance complex stability if they make the desolvation energy of the free ligands smaller. The calculated complex stabilities were in reasonable agreement with experimental log K values which were available for five of the compounds. The calculated complex stabilities of two hitherto unsynthesized covalently constrained DTPA-derivatives and a DOTA-derivative bearing phenoxy groups as pendant arms indicate that these may form Gd(III) complexes with sufficient stability for use in magnetic resonance imaging techniques.
Perioperative mortality in coronary artery bypass grafting is usually caused by reduced left ventricular function due to regional myocardial ischemia or infarction. Post-operative graft occlusion is a well-known problem in coronary surgery. A sensitive tool to detect graft occlusion and monitor myocardial function may give the opportunity to revise malfunctioning grafts before departure from the hospital. This paper describes how a new method can detect cardiac ischemia using a 3-axis piezoelectric accelerometer. In three anesthetized pigs, a 3-axis piezoelectric accelerometer was sutured on the lateral free wall of the left ventricle. The left anterior descending (LAD) was occluded for different time periods and the accelerometer data were sampled with a PC. Short-time Fourier transform was calculated based on the accelerometer time series. The results were visualized using a 2D color-coded time–frequency plot. In the area of occlusion, a change to stronger power of higher harmonics was observed. Consequently, a difference value between the instant frequency pattern and a reference frequency pattern showed a rise in absolute value during the occlusion period. The preliminary results indicate that early recognition of regional cardiac ischemia is possible by analyzing accelerometer data acquired from the three animal trials using the prototype 3-axis accelerometer sensor.
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