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Molecules 2014, 19(6), 7497-7515; doi:10.3390/molecules19067497
Article

Effect of Structure on the Interactions between Five Natural Antimicrobial Compounds and Phospholipids of Bacterial Cell Membrane on Model Monolayers

1
,
2,†
,
3
 and
1,*
1 Institute for Global Food Security, School of Biological Sciences, Queen's University Belfast, David Keir Building, Stranmillis Road, Belfast BT9 5AG, UK 2 School of Biological Sciences, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK 3 Agricultural Research Service, United States Department of Agriculture, Western Regional Research Center, Albany, CA 94710, USA Present address: The Sonochemistry Centre, Faculty of Health and Life Sciences, Coventry University, Priory Street, Coventry CV1 5FB, UK.
* Author to whom correspondence should be addressed.
Received: 19 April 2014 / Revised: 29 May 2014 / Accepted: 3 June 2014 / Published: 6 June 2014
(This article belongs to the Section Natural Products)
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Abstract

Monolayers composed of bacterial phospholipids were used as model membranes to study interactions of the naturally occurring phenolic compounds 2,5-dihydroxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde, and the plant essential oil compounds carvacrol, cinnamaldehyde, and geraniol, previously found to be active against both Gram-positive and Gram-negative pathogenic microorganisms. The lipid monolayers consist of 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE), 1,2-dihexa- decanoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), and 1,1',2,2'-tetratetradecanoyl cardiolipin (cardiolipin). Surface pressure–area (π-A) and surface potential–area (Δψ-A) isotherms were measured to monitor changes in the thermodynamic and physical properties of the lipid monolayers. Results of the study indicated that the five compounds modified the three lipid monolayer structures by integrating into the monolayer, forming aggregates of antimicrobial –lipid complexes, reducing the packing effectiveness of the lipids, increasing the membrane fluidity, and altering the total dipole moment in the monolayer membrane model. The interactions of the five antimicrobial compounds with bacterial phospholipids depended on both the structure of the antimicrobials and the composition of the monolayers. The observed experimental results provide insight into the mechanism of the molecular interactions between naturally-occurring antimicrobial compounds and phospholipids of the bacterial cell membrane that govern activities.
Keywords: natural antimicrobials; phospholipid monolayers; langmuir balance; isotherm; surface potential; antimicrobial mechanisms natural antimicrobials; phospholipid monolayers; langmuir balance; isotherm; surface potential; antimicrobial mechanisms
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Nowotarska, S.W.; Nowotarski, K.J.; Friedman, M.; Situ, C. Effect of Structure on the Interactions between Five Natural Antimicrobial Compounds and Phospholipids of Bacterial Cell Membrane on Model Monolayers. Molecules 2014, 19, 7497-7515.

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