Molecular Organization of Nalidixate Conjugated Calixarenes in Bacterial Model Membranes Probed by Molecular Dynamics Simulation and Langmuir Monolayer Studies

Functionalized Calixarenes as Promising Antibacterial Drugs to Face Antimicrobial Resistance

Since the discovery of polyphenolic resins 150 years ago, the study of polymeric compounds named calix[n]arene has continued to progress, and those skilled in the art perfectly know now how to modulate this phenolic ring. Consequently, calix[n]arenes are now used in a large range of applications and notably in therapeutic fields. In particular, the calix[4]arene exhibits multiple possibilities for regioselective polyfunctionalization on both of its rims and offers researchers the possibility of precisely tuning the geometry of their structures. Thus, in the crucial research of new antibacterial active ingredients, the design of calixarenes finds its place perfectly. This review provides an overview of the work carried out in this aim towards the development of intrinsically active prodrogues or metallic calixarene complexes. Out of all the work of the community, there are some excellent activities emerging that could potentially place these original structures in a very good position for the development of new active ingredients.

Congo Red as a Supramolecular Carrier System for Doxorubicin: An Approach to Understanding the Mechanism of Action

The uptake and distribution of doxorubicin in the MCF7 line of breast-cancer cells were monitored by Raman measurements. It was demonstrated that bioavailability of doxorubicin can be significantly enhanced by applying Congo red. To understand the mechanism of doxorubicin delivery by Congo red supramolecular carriers, additional monolayer measurements and molecular dynamics simulations on model membranes were undertaken. Acting as molecular scissors, Congo red particles cut doxorubicin aggregates and incorporated them into small-sized Congo red clusters. The mixed doxorubicin/Congo red clusters were adsorbed to the hydrophilic part of the model membrane. Such behavior promoted transfer through the membrane.

The Molecular Bases of the Interaction between a Saponin from the Roots of Gypsophila paniculata L. and Model Lipid Membranes

In view of the possible medical applications of saponins, the molecular structure of a GOTCAB saponin from the roots of Gypsophila paniculata L. was determined by NMR. The biological activity of saponins may depend on the interaction with cell membranes. To obtain more insight in the mechanism of membrane-related saponin function, an experimental and theoretical study was conducted. Ternary lipid systems composed of sphingomyelin, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, and cholesterol were used as models of mammalian cell membranes. The membrane–saponin interaction was studied experimentally by monitoring surface pressure in the monomolecular films formed at the air–aqueous subphase interface. The behavior of GOTCAB saponin in a water box and model monolayer systems was characterized by molecular dynamics simulations. The results obtained showed that, in the systems used, cholesterol had a decisive effect on the interaction between GOTCAB and phosphocholine or sphingomyelin as well as on its location within the lipid film.

The antibacterial activity of p-tert-butylcalix[6]arene and its effect on a membrane model: molecular dynamics and Langmuir film studies

The antibacterial activity of a calixarene derivative, p-tert-butylcalix[6]arene (Calix6), was assessed and was shown not to inhibit the growth of E. coli, S. aureus and B. subtilis bacteria. With the aim of gaining more insights into the absence of antibacterial activity of Calix6, the interaction of this derivative with DPPG, a bacterial cell membrane lipid, was studied. Langmuir monolayers were used as the model membrane. Pure DPPG and pure Calix6 monolayers, as well as binary DPPG:Calix6 mixtures were studied using surface pressure measurements, compressional modulus, Brewster angle and fluorescence microscopies, ellipsometry, polarization-modulation infrared reflection absorption spectroscopy and molecular dynamics simulations. Thermodynamic properties of the mixed monolayers were additionally calculated using thermodynamic parameters. The analysis of isotherms showed that Calix6 significantly affects the DPPG monolayers, modifying the isotherm profile and increasing the molecular area, in agreement with the molecular dynamics simulations. The presence of Calix6 in the mixed monolayers decreased the interfacial elasticity, indicating that calixarene disrupts the strong intermolecular interactions of DPPG hindering its organization into a compact arrangement. At low molar ratios of Calix6, the DPPG:Calix6 interactions are preferentially attractive, due to the interactions between the hydrophobic tails of DPPG and the tert-butyl groups of Calix6. Increasing the proportion of calixarene generates repulsive interactions. Calix6 significantly affects the hydrophobic tail organization, which was confirmed by PM-IRRAS measurements. Calix6 appears to be expelled from the mixed films at a biologically relevant surface pressure, π = 30 mN m-1, indicating a low interaction with the cell membrane model related to the absence of antibacterial activity.

Two novel colorimetric probes (5-HMBA-FH and 3-HMBA-FH) based on fluorescein for copper(II) ion detection

Two novel isomeric colorimetric probes are established for simultaneous determination of copper ions using 2-hydroxy-5-methoxybenzaldehyde fluorescein hydrazone (5-HMBA-FH) and 2-hydroxy-3-methoxybenzaldehyde fluorescein hydrazone (3-HMBA-FH). They are synthesized by reacting fluorescein hydrazide with 2-hydroxy-5-methoxybenzaldehyde and 2-hydroxy-3-methoxybenzaldehyde, respectively, and then characterized by 1H-NMR, 13C-NMR, and infrared spectrum. The addition of copper ions to the solutions of two novel colorimetric probes can generate the obviously peaks at 498 nm in UV–vis absorption spectra along with a rapid colour change from colourless to dark yellow. The detection limits of the method for Cu2+ ion were 3.442 × 10−6 mol/L and 3.682 × 10−6 mol/L separately for 5-HMBA-FH and 3-HMBA-FH, respectively. The additions of other metal ions hardly affect the determination of copper ions. The proposed method was successfully applied to the analysis of Cu2+ ions in various samples. This method possesses high sensitivity, high simplicity, and minimized interference and will provide a great advantage in detecting copper ions in the environment, food, and medical applications.

Two antibacterial nalidixate calixarene derivatives in cholesterol monolayers: Molecular dynamics and physicochemical effects

The interaction of two antibacterial calixarene derivatives with cholesterol, a eukaryotic cell membrane lipid, was investigated with the aim to get more insight in the potential advers effects on our cells. The derivatives used had one or two nalidixic acid arms grafted on the lower rim of the calixarene aromatic crown. Monomolecular films spread at the air-water interface were used as model lipid membranes. Pure cholesterol and pure calixarene derivatives, as well as binary cholesterol - calixarene derivative mixtures were studied using surface pressure measurements, polarization-modulation infrared reflection absorption spectroscopy and molecular dynamics simulations. The properties of the mixed monolayers were described quantitatively using thermodynamic models. The analysis of surface pressure-area isotherms of mixed monolayers shows that cholesterol may form homogenous but metastable domains with both nalidixate derivatives. This phenomenon is more clearly observed with mono-substituted calixarene. A detailed modeling analysis indicates that cholesterol favors dehydration of the calixarene polar headgroups and transfer of the derivatives from the aqueous to the gas phase. This effect, more pronounced in the case of the monosubstituted calixarene, can be linked to the hydrophobic interaction with cholesterol. This observation may be useful for developing new calixarene derivatives allowing us to control disease-causing bacteria without harming our own cells.

The selective interactions of cationic tetra-p-guanidinoethylcalix[4]arene with lipid membranes: theoretical and experimental model studies

Behavior of cationic tetra-p-guanidinoethylcalix[4]arene (CX1) and its building block, p-guanidinoethylphenol (mCX1) in model monolayer lipid membranes was investigated using all atom molecular dynamics simulations and surface pressure measurements. Members of two classes of lipids were taken into account: zwitterionic 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and anionic 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine sodium salt (DMPS) as models of eukaryotic and bacterial cell membranes, respectively. It was demonstrated that CX1 and mCX1 accumulate near the negatively charged DMPS monolayers. The adsorption to neutral monolayers was negligible. In contrast to mCX1, CX1 penetrated into the hydrophobic part of the monolayer. The latter effect, which is possible due to a flip-flop inversion of the CX1 orientation in the lipid layer compared to the aqueous phase, may be responsible for its antibacterial activity.

A Study of the Interaction between a Family of Gemini Amphiphilic Pseudopeptides and Model Monomolecular Film Membranes Formed with a Cardiolipin

The interaction between five gemini amphiphilic pseudopeptides (GAPs) differing by the length of the central spacer and a model membrane lipid, 1,3-bis[1,2-dimyristoyl-sn-glycero-3-phospho]-sn-glycerol (cardiolipin) were studied with the aim to evaluate their possible antimicrobial properties. To this end, monomolecular films were formed at the air/water interface with pure cardiolipin or cardiolipin/GAPs mixtures; film properties were determined using surface pressure and surface potential measurements, as well as polarization-modulation infrared reflection-absorption spectroscopy. Moreover, to better understand the GAPs-phospholipid interaction at the molecular level, molecular dynamics simulations were performed. The results obtained indicate that the length of the central spacer has an effect on the interaction of GAPs with cardiolipin and on the properties of the lipid film. The GAPs with the longer linkers can be expected to be useful for biological membrane modification and for possible antimicrobial applications.