Raman and infrared spectroscopy of WHO essential antibiotics.

Antimicrobial resistance (AMR) poses a critical global health challenge, driving the need for improved molecular-level understanding of antibiotic function. The World Health Organization's Essential Medicines List (EML) highlights six antibiotic classes - β-lactams, aminoglycosides, glycopeptides, lipopeptides, quinolones, and ansamycins - as clinical priorities While vibrational spectroscopy, including infrared (IR) and Raman techniques, has emerged as a powerful tool in AMR research and diagnosis, detail spectral characterisation of these antibiotics remains incomplete. This study presents a comparative vibrational analysis of representative EML antibiotics using both IR and Raman spectroscopy (1064, 633, 532 and 488 nm excitation) alongside density functional theory (DFT)-based calculations, (ωB97X-D3/6-31+G*). Experimental and computational spectra were aligned to identify and assign key vibrational modes and function groups for each antibiotic class. Distinct signatures include the ν(CO) stretches (1779-1750 cm-1) (β-lactams), carbohydrate ν(CO)/ν(CC) envelopes between 1200 and 900 cm-1 (aminoglycosides), amide I-III and aromatic δ(CH) signatures (glyco- and lipopeptides), strong keto/carboxyl vibrations (1710-1650 cm-1) (quinolones), and intense ν(COC)/ν(CO) bands at 1240-1160 cm-1 (rifampicin). The high degree of agreement between experimental and theoretical spectra provides a validated spectral fingerprint for these compounds. These results serve as a reference framework for antibiotic identification and classification and offer a foundation for mechanistic interpretation of spectral changes observed in bacteria under antibiotic pressure, supporting future applications of vibrational spectroscopy in drug monitoring, resistance profiling, and high-throughput screening within AMR research.