Abstract
ABSTRACT Today MRI imagining techniques are capable of discerning between abnormal and normal complex tissues by providing contrasting images of these tissues. One drawback of using MRI imagining is its low sensitivity. However, this sensitivity can be greatly enhanced by introducing contrasting agents who can provide a new pathway for water molecules to significantly relax faster and hence generate the desired “contrast” between healthy and unhealthy tissues. We report the first ever recorded fluorescence emission spectrum of Gd3N@C80(OH)20; where -(OH)20 is the average number of hydroxyl groups. Our emission data indicates that the H2O- Gd3N@C80(OH)20 interactions lead to fluorescence quenching via a static quenching mechanism. The binding constant, Kb, on the other hand, was found to be of the same magnitude as interactions between human serum albumin and small organic acid but quite different, several orders of magnitude smaller, than protein nanoparticle complexes. Interestingly, the binding number, n, was found to be approximately 0.5, which in cases like this, is rounded to a whole number of one. The data also indicated an extremely fast rate constant on the order of 1012 L mol-1 s-1 which is outside of the diffusion-control regime. These results are presented within this report.
Highlights
Modern imagining techniques, such as MRI, are able to discriminate between normal and abnormal tissues by generating contrasting images of these organs and/or tissues
Various types of molecular interactions including collisions, molecular rearrangements, excited state reactions, ground-state complex formation, and energy transfer can lead to fluorescence quenching.21The rate constant, binding constant and binding number can be determined in a straight forward manner by fitting the fluorescence decay as a function of the H2O concentration; [H2O]
The main reason for the limited number of contrasting agents is that these contrasting agents must be able to pass the blood-brain barrier (BBB) which places a limit on the molecular size to a range of about 400 – 500 Da or a molecular surface cross section (MSCS) limit of less than 80 Å2
Summary
Modern imagining techniques, such as MRI, are able to discriminate between normal and abnormal tissues by generating contrasting images of these organs and/or tissues. 4-20Gadolinium complexes are ideal contrasting agents and their water solubility is frequently generated by functionalizing these complexes with groups ranging from –(OH)n, -(COOH)n, and poly(ethylene glycol)n with n =8 – 114, have been reported.11-15Due to the almost spherical shape of Gd3N@C80(OH)[20], one of the objectives of this study was to determine the average number of water molecules interacting with this complexes to determine if Gd3N@C80(OH)20-H2O possess the physical dimensions to cross the blood-brain-barrier allowing for imaging of brain tissues.This research project has the potential of introducing a non-radioactive contrasting agent with the ability to penetrate the blood-brain-barrier This compound will allow patients to receive a contrasting agent via an accessible vein which will permit the contrasting agent to differentiate between healthy brain tissue and potentially dangerous brain tumors
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