In this study ten different sulfonamide derivatives were studied. Sulfa drugs are commonly used in aquaculture as agricultural herbicides and in the treatment of respiratory and urinary tract infections in humans. The aim of the work was to use Raman spectroscopy as well as density functional (DFT) calculations to characterize ten sulfa drugs. The ten derivatives were sulfisoxazole, sulfamethizole, sulfamethoxazole, sulfathiazole, sulfachloropyridazine, sulfadimethoxine, sulfamerzine, sulfameter, sulamethazine and sulfadiazine. The first four mentioned sulfa drugs have a five membered ring attached to a sulfonamide group while the last six mentioned have a six membered ring attached to a sulfonamide group. This difference and the functional group each of the sulfa drug possesses were analyzed in terms of vibrational bands that are both unique and common to the sulfa drugs. Once the results were obtained experimentally through Raman Spectroscopy and theoretical using the program Gaussian, they were compared and it was observed that the experimental data was very similar to the theoretical data. The ten different derivatives exhibited peaks at common areas and unique areas, which I will discuss further in detail.
When observing the graphs of the Raman spectra it was observed that there were similar peaks in the 10 different drugs. At about the wave region of 630 cm-1 – 790 cm-1 where the carbon-sulfur bond exhibits stretching there was a peak in all ten derivatives. They all exhibited peaks at the 800 cm-1 – 1300 cm-1 wave region as well that is characteristically due to the carbon-nitrogen bond stretching. Another feature they had in common is the fact that they all exhibit ring stretching in the wave region of 900 cm-1 – 1100 cm-1. This is supported by the theoretical data that was obtained and is expected due to the fact that all of the derivatives contain a ring. Due to the fact that they are all sulfonamide derivatives, they all contain sulfonamide groups and therefore all showed peaks in the wave region 1000 cm-1 – 1200 cm-1. This is typically where sulfonamides exhibit symmetrical stretching. These peaks were also present in the theoretical data. All of the experimental spectra showed peaks at about 1600 cm-1. which was concluded to have been caused by the stretching of the aromatic carbon-carbon bonds. Since all of the derivatives contain a ring that has carbon nitrogen double bonds, all of the spectra showed peaks at about 1610 cm-1 – 1680 cm-1.
Although there were many similar peaks that are shown in the spectra of all ten derivatives, there are also some unique characteristics shown. For example, all of the structures that contain methyl groups on the substituent, such as sulfamethazine, sulfamerazine, sulfamethoxazole, sulfamethizole, and sulfasoxazole, all show peaks in the wave region of about 1380 cm-1 where the methyl group undergoes bending. Sulfamethazine has the peak at the wavenumber of 1347 cm-1, sulfamerazine has the peak at 1335 cm-1, sulfamethizole has the peak at 1310 cm-1, sulfisoxazole has the peak at 1391 cm-1, and sulfamethoxazole at 1310 cm-1.
Sulfadimethoxine and sulfameter both contain ethers on the pyrimidine structure. Sulfadimethoxine’s had a peak at 1282 cm-1 and sulfameter had a peak at 1280 cm-1 and 1319 cm-1. These peaks are in the region of 1150 cm-1 – 1300 cm-1 that can be attributed to the ether. The only derivative that contains a thiazole shows distinguishing vibrations. There is out of plane bending of the carbon hydrogen bonds on the thiazole ring that can be seen at the wavenumbers 637 cm-1 and 726 cm-1. The thiazole ring also undergoes vibrations. The regions are from 930 cm-1 – 1160 cm-1, 1175 cm-1 – 1340 cm-1, and 1480 cm-1 – 1690 cm-1. In the spectrum it can be seen that sulfathiazole has peaks at 930 cm-1, 1159 cm-1, 1350 cm-1, and 1502 cm-1 that can all be attributed to this ring stretching.
Sulfadiazine contains only the pyrimidine and didn’t have any distinguishing peaks. As for sulfachloropyridazine, the data obtained was did not provide much information as the spectrum did not exhibit many peaks. This was concluded to be due to the color of the solid form being yellow when it was tested.
When trying to determine which spectrum belongs to which derivative, it will be necessary to look at the differing substituents. However, for the derivatives like sulfadiazine, which have only a pyrimidine ring, or such as sulfamerzine and sulfamethazine, whose only differences are the number of methyl groups attached, determining which spectrum belongs to which derivative will be much more challenging.
There is a slight shift observed in the Raman peaks when the ten sulfonamide antibiotics were mixed in their solid form together. It was observed that there is a very distinct peak seen at a wavenumber of 1593 cm-1, which is likely due to the aromatic ring structure that all ten derivatives have. It can also be seen that they have a very intense peak at 1148 cm-1 that is probably due to the sulfonamide functional group stretching.
Overall I learned a lot during this study. I learned how to properly assign vibrational bond modes using the computer program Gaussian and how to analyze Raman spectra. Not only did I learn how to trouble shoot issues that came up as the experiment went on but I have gained valuable lab experience that will help me in my future career. I had the amazing opportunity to present my research at the American Chemical Society’s National convention in San Francisco. Being at a national convention, presenting, and making connections with all of the other scientists was an experience like no other. Doing research as an undergraduate has really made my time here at Pace University so much more valuable. I would not have been able to do any of this without the help and guidance of my wonderful mentor Elmer-Rico E. Mojica. I have learned so much during my time in his research group and I hope in the future I have the opportunity to impact young minds in the same way he has impacted me.