Procedure

1. ONS Challenge: Solubility Determination of Carboxylic Acids in Chloroform using 1H NMR and External Water Standard David Bulger 1, Andrew Lang, Ph. D. 2, Jean-Claude Bradley, Ph. D. 3, Robert Stewart, Ph. D. 1 1 Department of Chemistry, Oral Roberts University,2 Department of Mathematics, Oral Roberts University, 3 Department of Chemistry, Drexel University Calculations Introduction NMR, Sample Vial, Sonicator, External Reference Setup Two solute peaks were chosen based on how clear (how distinct and separate from other peaks - complete Lorentzian tails) the peak is and what the peak corresponds to. The spectra were converted to J-CAMPDX for JSpecViewer analysis. The solute peaks' integrals as found using the JSpecViewer as shown to the left in the example spectrum (green line is the integration) with screenshots of the manually obtained start and end points of the integral analyzed against the external water reference integral per hydrogen as follows: (area / # H's) / (water area / 2 H's).Integral ratios were calculated for each of the solute's unsaturated reference spectrum as follows: Integral Ratio = g solute from unsaturated reference / unsaturated solute peak against water peakThe observed mass of the solute is calculated as follows: g solute observed = Integral Ratio of unsaturated reference * saturated solute peak against water peak Solubilities were reported as g solute per 100 g solution. Analysis of saturated solutions of carboxylic acids in chloroform using 1H NMR with an external standard effectively and efficiently provided solubility data. Calibration proton NMR spectra were acquired with a known concentration of solute in the presence of an external water standard in a capillary tube. Proton NMR spectra were then acquired on a saturated solution using the same external water standard. This research won the February 2009 Open Notebook Science Challenge (ONSC), which involved collaboration with over 20 scientists and their students in 2 different countries in an open notebook crowdsourcing endeavor to measure the solubility of organic compounds in non-aqueous solvents; part of a larger cheminformatic anti-malarial drug discovery program, a research program sponsored by Submeta, Nature, and Sigma Aldrich. Procedure Conclusion Fourier transform proton NMR experiments were conducted on a JEOL 300 MHz equipped with a 5 mm NMR tube capped with a single seal cap. All experiments were carried out at approximately 23 °C. The proton spectra were acquired using a 45-degree pulse with a relaxation delay of 5 seconds, JEOL automatic zero filling and autogaining, and 8 scans with a resolution of 77.97 mHz. Shimming of spectra used JEOL automatic gradient shimming with deuterated solvent (chloroform) spinning at 15 Hz. Mass determinations were performed using a 0.1 mg accuracy Sortorius balance. A saturated solution was made by adding solute (various carboxylic acids) to approximately 6 mL solvent until a layer at least 1 cm thick was observed in the vial after equilibration achieved following at least ten minutes of sonication. The supernatant was then transferred to the NMR tubes using a Pasteur pipet followed by addition of capillary tubes filled with 94 µL water using a Microsyringe. Samples were sonicated with a thermometer. Reference NMR runs performed with protonated chloroform. Experimental data was posted online through googledocs spreadsheets, wikispace experiments with critiques from ONSC judges, and JSpecViewer spectrum analysis. Solubility determination using 1H NMR and external water standard presents an alternative to conventional methods, such as weighing evaporated residue. The NMR method takes less time, avoids loss of solute during evaporation of solvent, and is less prone to experimental error. As qualitative and quantitative analysis are performed simultaneously, sample identity and quality can be assured. NMR solubility determination could be applied to many solutes other than carboxylic acids in solvents other than chloroform. This experiment could also be improved by taking volume measurements, using deuterated chloroform as a solvent, and placing less water in the capillary tube. Example 1H NMR Spectrum of Benzoic acid Hf He References Hd Hc Lin, M., Tesconi, M., Tischler, M., Use of 1HNMR to Facilitate Solubility Measurement for Drug Discovery Compounds, International Journal of Pharmaceutics (2008), doi:10.1016/j.ijpharm.2008.10.038 (http://onschallenge.wikispaces.com/list+of+experiments) Hb Ha