There are some tricks to optimize your spectrum once recorded but I think you should concentrate first on running an experiment with a better signal to noise ratio. A solution of 10 mg/ml should be sufficient wrt signal to noise. What A mixing timne of 1.5 sec is the mixing time used? much too long. For my experience you can use 250 – 500 msec as an initial delay, again depending on molecule and the interaction you want to observe. Do not start You can always optimize the delay but in this range you should be able to record a spectrum with too short or too long delays. a good signal to noise.
However, depending on your solvent, field strength and your molecule, you need to choose between a NOESY or ROESY, since the NOE effect will disappear and no cross-peaks will be observed in a NOESY spectrum when w*tc=1.
Back to your problem. You can do two three simple things;
1) run the experiment with a mixing time of 500 msec.
1) try a ROESY using a 300 500 msec spinlock
2) change the tumbling rate by changing solvent, e.g. CDCl3 <-> DMSO.
Good luck
ps; like one of my friends always tells me when I am struggling to record good data: it is easier to optimize a signal then to find a signal ;-)
