Wednesday, March 10, 2010

Updated Chemistry Web Services - now with Density

I mentioned a while back the web services that Rajarshi Guha had set up for us. We are often in need of molecular weight and density data for both solutes and solvents since we rely on an assumption of volume additivity when calculating concentration.

Since Rajarshi moved to the NIH, the location of the services has changed. We now have the CDK installed on a Drexel server so some of the simple services like MW and SMILES generation are still available there.

However density has been challenging to provide as a service. Experimental density values for solvents are commonly available but the calculated densities of solids is hard to find. ChemSpider is one of the few sources where calculated densities of solids and liquids are freely available. Unfortunately there are currently no ChemSpider density web services.

As an interim solution for the UsefulChem and ONSChallenge projects we have set a look-up table as a Google Spreadsheet (SolventLookUp) for most solvents of potential interest. Solutes added to our SolubilitiesSum sheet are automatically added to a SoluteLookUp SQL database running at Oral Robert University and the ChemSpider densities are added there via an automated but slow process.

Andrew Lang has used these resources to provide web services returning densities and other properties or descriptors. These data sources are especially important for the nearly automated production of new editions of the ONS Challenge Solubility Book. This is not a general solution since it only includes compounds of interest to our group and would not scale (at least for licensing reasons) to millions of compounds.

But it does come in handy for us because we can quickly call these services within a Google Spreadsheet to do a variety of useful calculations, minimizing the possibility of error by copy and pasting.

As an example see the following ChemServices sheet. Enter the common name for a solvent or solute and the number of millimoles and the sheet will automatically calculate the corresponding number of milligrams or microliters. [Note that Google Spreadsheets can only handle a maximum of 50 web service calls at a time - a useful trick is to highlight cells after the calculations then copy and "paste as values". Make sure to keep some cells with the web service calls in case you need to do more calculations in the future]

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