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 (C O) stretches (1779–1750 cm −1 ) (β-lactams), carbohydrate ν(C O)/ν(C C) envelopes between 1200 and 900 cm −1 (aminoglycosides), amide I–III and aromatic δ(C H) signatures (glyco- and lipopeptides), strong keto/carboxyl vibrations (1710–1650 cm −1 ) (quinolones), and intense ν (C O C)/ν(C O) 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.