Azacrown Ethers as Amphiphile Headgroups: Formation of Stable Aggregates from Two- and Three-Armed Lariat Ethers

Antimicrobial and Adjuvant Potencies of Di-n-alkyl Substituted Diazalariat Ethers

Lariat ethers are macrocyclic polyethers-crown ethers-to which sidearms are appended. 4,13-Diaza-18-crown-6 having twin alkyl chains at the nitrogens show biological activity. They exhibit antibiotic activity, but when co-administered at with an FDA-approved antibiotic, the latter's potency is often strongly enhanced. Potency enhancements and resistance reversals have been documented in vitro for a range of Gram-negative and Gram-positive bacteria with a variety of antimicrobials. Strains of E. coli and Staphylococcus aureus having resistance to a range of drugs have been studied and the potency enhancements (checkerboards) are reported here. Drugs included in the present study are ampicillin, cefepime, chlortetracycline, ciprofloxacin, doxycycline, kanamycin, minocycline, norfloxacin, oxycycline, penicillin G, and tetracycline. Enhancements of norfloxacin potency against S. aureus 1199B of up to 128-fold were observed. The properties of these lariat ethers have been studied to determine solubility, their membrane penetration, cytotoxicity and mammalian cell survival, and their effect on bacterial efflux pumps. It is shown that in some cases, the lariat ethers have complex antimicrobials with considerable selectivity. Based on these observations, including 1:1 complexation between lariat ethers and antimicrobials and the cytotoxicity of the MeI salts showing a separation index of 32-fold, they hold significant potential for further development.

Effect of Alkali Metal Cations on the Unilamellar Vesicle of a Squalene Bearing 18-Crown-6

Squalene bearing 18-crown-6 was synthesized and formed unilamellar vesicles with a membrane thickness of about 6 nm and a diameter of about 0.32 μm. In the wake of the recognition of alkali metal cations, squalene unilamellar vesicles become larger as multilamellar vesicles or smaller while maintaining unilamellar vesicles depending on cations.

Influence of the Hydro/Fluorocarbon Chain Length on CMC and HLB of Surface-Active Nonionic Surfactants Containing Polyethylene Glycol Groups

Series of cyclic polyethylene glycol succinates based surfactants bearing a hydro- or fluorocarbon group was synthesized and characterized. Evaluation of the surface-active properties of the obtained compounds reveals, (i) the surface tension decreases gradually when is the length of the lipophilic chain increased (ii) the critical micelle concentration (CMC) increases with the number of ethylene oxide unit present in the polar head and (iii) surface tension follows the increasing pattern of hydrophilic-lipophilic balance (HLB) number.

Hydraphiles: a rigorously studied class of synthetic channel compounds with in vivo activity

Hydraphiles are a class of synthetic ion channels that now have a twenty-year history of analysis and success. In early studies, these compounds were rigorously validated in a wide range of in vitro assays including liposomal ion flow detected by NMR or ion-selective electrodes, as well as biophysical experiments in planar bilayers. During the past decade, biological activity was observed for these compounds including toxicity to bacteria, yeast, and mammalian cells due to stress caused by the disruption of ion homeostasis. The channel mechanism was verified in cells using membrane polarity sensitive dyes, as well as patch clamping studies. This body of work has provided a solid foundation with which hydraphiles have recently demonstrated acute biological toxicity in the muscle tissue of living mice, as measured by whole animal fluorescence imaging and histological studies. Here we review the critical structure-activity relationships in the hydraphile family of compounds and the in vitro and in cellulo experiments that have validated their channel behavior. This report culminates with a description of recently reported efforts in which these molecules have demonstrated activity in living mice.

Spontaneous formation of vesicles by sodium 2-dodecylnicotinate in water

The surface activity and aggregation behavior of a synthesized nicotinic acid based anionic surfactant, sodium 2-dodecylnicotinate, were studied in aqueous solution. The self-assembly formation was investigated by use of a number of techniques, including surface tension and conductivity measurements, fluorescence spectroscopy, dynamic light scattering measurement, gel permeation chromatography, and microscopy. The amphiphile exhibits two breaks in the surface tension vs concentration plot, indicating stepwise aggregate formation and thus producing two values of the aggregation concentration. Stepwise aggregation of the amphiphile was further confirmed by steady-state fluorescence spectroscopy using pyrene as a probe molecule, and also the micropolarity of the aggregates was determined. The rigidity of the microenvironment was estimated by determining steady-state fluorescence anisotropy using 1,6-diphenyl-1,3,5-hexatriene as a fluorescence probe molecule. The average hydrodynamic radius and size distribution of the aggregate suggest formation of larger aggregates in aqueous solution. The formation of vesicles in water was established by conductivity measurement and a dye entrapment experiment. The entrapment of a small solute and the release capability have also been examined to demonstrate these bilayers form enclosed vesicles. Transmission electron micrographs revealed the existence of closed vesicles and closed tubules in aqueous solution. Therefore, for the first time, it has been observed that this simple single-chain nicotinic acid based amphiphile spontaneously assembles to vesicles in aqueous solution.

Vesicle and stable monolayer formation from simple "click" chemistry adducts in water

Click chemistry has been successfully extended into the field of molecular design of novel amphiphatic adducts. After their syntheses and characterizations, we have studied their aggregation properties in aqueous medium. Each of these adducts forms stable suspensions in water. These suspensions have been characterized by dynamic light scattering (DLS) studies and transmission electron microscopy (TEM). The presence of inner aqueous compartments in such aggregates has been demonstrated using dye (methylene blue) entrapment studies. These aggregates have been further characterized using X-ray diffraction (XRD), which indicates the existence of bilayer structures in them. Therefore, the resulting aggregates could be described as vesicles. The temperature-induced order-to-disorder transitions of the vesicular aggregates and the accompanying changes in their packing and hydration have been examined using high-sensitivity differential scanning calorimetry, fluorescence anisotropy, and generalized polarization measurements using appropriate membrane-soluble probe, 1,6-diphenylhexatriene, and Paldan, respectively. The findings of these studies are consistent with each other in terms of the apparent phase transition temperatures. Langmuir monolayer studies confirmed that these click adducts also form stable monolayers on buffered aqueous subphase at the air-water interface.

Complexation of metal ions in Langmuir films formed with two amphiphilic dioxadithia crown ethers

The two new crown ethers presented in this study were synthesized in order to investigate two important features of ionophores, namely metal cation complexation and interfacial properties, and the way in which they interrelate. The two derivatives were conceived as analogs of membrane phospholipids with respect to their amphiphilicity and geometry. They contain a hydrophilic 1,1'-dioxo-3,3'-dithio-14-crown ether headgroup and bear two myristoyl or stearoyl lateral chains. The length of the myristoyl and stearoyl derivatives in an extended conformation is comparable with the thickness of the individual leaflets of cell membranes. The membrane-related and complexation properties of the two crown ether derivatives were studied in monomolecular films spread on pure water and on aqueous solutions of mono-, di-, and trivalent metal salts. The properties of the monolayers are described quantitatively using thermodynamic models. The compression isotherms of the monolayers formed on different subphases show a clear-cut differentiation of the monovalent and di- or trivalent cations with both ligands. This differentiation was interpreted in terms of conformational changes occurring in the crown ether derivatives upon complexation. Molecular modeling indicates that the mono- and divalent cations are coordinated differently by the ligands, yielding complexes with different conformations. The differences of the conformations of the mono- and di- or trivalent cation complexes may be important from the point of view of the interactions with lipid membranes and the biological activity of these potential ionophores.

Mixed monolayers of alkylated azacrown ethers and palmitic acid at the air-water surface

The Langmuir films of two alkylated azacrown ethers at the air-water surface were characterized using surface pressure-area isotherms, ellipsometry, Brewster angle microscopy, and constant-area surface pressure relaxation. The azacrown ether molecules aggregate in the monolayer, which significantly stabilizes the film against dissolution. Mixed azacrown ether-palmitic acid monolayers were also characterized; results suggest that at high compression the two molecules interact repulsively. The influence of Cu(II) ions present in the aqueous subphase on the single components and mixed monolayer characteristics was also studied.

Correlation of bilayer membrane cation transport and biological activity in alkyl-substituted lariat ethers

Dialkyldiaza-18-crown-6 lariat ethers having twin n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl, 1-oxodecyl and 1-oxododecyl side arms were prepared and studied. Cation transport in liposomes mediated by these compounds showed discontinuous activity that correlated with toxicity to the bacteria E. coli and B. Subtilis, and the yeast S. Cerevisiae. Transport, toxicity and membrane depolarization studies all suggest that side chain length affords very different interactions in a bilayer membrane compared with bulk phases. An explanation for activity in terms of carrier transport and restricted transverse relaxation is proposed.

Hydraphile channels: models for transmembrane, cation-conducting transporters

A completely synthetic, non-peptide channel has been prepared and shown to conduct cations across a phospholipid bilayer membrane. Studies have been undertaken to assess the compound's location within the bilayer and to better understand its function. These studies are described along with background on the design and concept of the channel.