Spectroscopic investigation of hydrogen bond network stability and microplastic leaching in ethanol-based potentised medicines at extreme dilutions during prolonged plastic storage

The quality and efficacy of pharmaceutical products stored under proper conditions are critical. This study examined the effects of long-term plastic storage on extremely diluted ethanol-based potentised (EP) medicines using advanced spectroscopic techniques. Four medicines, Arnica montana, Rhus toxicodendron, Conium maculatum, and Belladonna, at ultra-high (200C, 1 M) and moderate-high (30C, 200C) potencies, were stored in glass and plastic containers for one month. Post-storage, antioxidant activity (DPPH assay), pH, and spectroscopic analyses (ATR-FTIR, Raman and DLS) were conducted. Glass-stored medicines showed increased antioxidant activity and zeta potential with higher potency, while plastic-stored samples showed a decreasing trend. Conductivity was inversely correlated with zeta potential, with glass-stored medicines showing a ∼ 41.91 % reduction, while plastic-stored samples showed a ∼ 36.29 % increase. Mid-IR spectra revealed a blue shift (∼4–14 cm⁻¹) in O–H stretching and a red shift (∼2–3 cm⁻¹) in H–O–H bending for glass-stored medicines, showing weaker inter-molecular H-bonds at higher potencies. In contrast, plastic-stored medicines showed opposite shifts (∼2–17 cm⁻¹), implying more constrained H-bonding due to carbonyl-water interaction in presence of microplastics, disrupting the native ethanol-water H-Bond network. Far-IR spectra showed an enthalpic gain (∼45.34 %) in glass-stored medicines, while plastic-stored samples showed an enthalpic loss (∼56.60 %), confirming structural destabilisation of native water-network due to microplastic leaching. Our findings show that plastic containers compromised the efficacy of studied medicines by altering H-bond network stability and electrical properties. Further studies on different plastic grades and storage durations are needed to validate these findings and explore cost-effective alternatives for long-term storage of such medicines.