Table 1. The vibrational frequencies of C = O, NH and PO− 2 (FTIR, KBr cm−1) bands of free DNA, free drugs and DNA-drug complexes.
| Functional Groups | Free DNA (cm−1) | Free Drugs (cm−1) | DNA-X1 (cm−1) | DNA-X2 (cm−1) | DNA-X3 (cm−1) | ||
| X1 | X2 | X3 | |||||
| NH | 3350–2900 | 3121 | 3113 | 3111 | 3600–2600 | 3650–2650 | 3450–2700 |
| C = O | 1694.4 | 1718, 1666.8 | 1691.7 | 1699.8, 1658.7 | 1702.7 | 1691.7 | 1693.35 |
| PO− 2 (υas) | 1238.9 | — | — | — | 1250, 1240.9 | 1223.83, 1205 | 1238.42, 1210 |
| PO− 2 (υs) | 1099 | — | — | — | 1090 | 1070.95 | 1098 |
X1 = theophylline, X2 = theobromine and X3 = caffeine.
DNA-X1 = DNA-theophylline complex, DNA-X2 = DNA-theobromine complex and DNA-X3 = DNA-caffeine complex.