Hi, I doubt you have a TaBr cluster bound in your soaks.
You'd expect a strong anomalous signal from cluster compounds (that's what they are made for) and you can easily get a low resolution anomalous signal from a few dislocated HA in the solvent channels, especially if you don't counter soak the crystals (expose them to HA free buffer briefly prior to freezing to leech the solvent channels from excess HA). I wouldn't collect MAD data on cluster compound soaks anyway. If they are present, you should be able to solve it with SAD. Alternatively, try the LIII and LII edges at the respective peak wavelength instead of collecting data at wavelength around the same edge. I don't think that's your problem because I don't think the TaBr bound at all in your crystals. In your case, I'd recommend trying a different HA soak first. If you cannot express your protein with selenium but you can get your hands on xenon derivatization equipment, try xenon!! Mercury is always worth a try IMHO. Non-isomorphous data from various soaks is not very helpful, that single SAD dataset with that little bit of extra signal IS very helpful. Optimize your cryo protectant and data collection strategy (inverse wedges, kappa goni, etc.). If you want to try MAD, try collecting all wavelength data from the same crystal. Don't do MAD if you have radiation sensitive non-isomorphous crystals. An non interpretable MR solution will help you locate the HA sites as long it is correct. So, if you have one, try to use it to phase an anomalous difference map. You indicated that you have several datasets from two compounds. Try merging the 'identical' datasets and see if that works better. SHARP is really good for MAD data, but you need to collect and process the data right, which is difficult. SHELX is great for low resolution/low signal SAD/SIR. I'd always use SHELX first because it was the only thing working for me below 5A so far (sample size=1, anecdotal evidence, handle with care!). good luck, S.
