Calixarenes in a Membrane Environment: A Monolayer Study on the

J. Phys. Chem. B 2007, 111, 13231-13242

13231

Calixarenes in a Membrane Environment: A Monolayer Study on the Miscibility of Three p-tert-Butylcalix[4]arene β-Lactam Derivatives with 1,2-Dimyristoyl-sn-glycero-3-phosphoethanolamine Beata Korchowiec,†,‡ Adel Ben Salem,§,⊥ Yohann Corvis,† Jean-Bernard Regnouf de Vains,§ Jacek Korchowiec,| and Ewa Rogalska*,† Groupe d’Etude des Vecteurs Supramole´ culaires du Me´ dicament UMR 7565 CNRS/UniVersite´ Henri Poincare´ Nancy 1, Faculte´ des Sciences, BP 239, 54506 VandoeuVre-le` s-Nancy Cedex, France and Faculte´ de Pharmacie, 5, rue Albert Lebrun, BP 80403, 54001 Nancy Cedex, France, Department of Physical Chemistry and Electrochemistry, Faculty of Chemistry, Jagiellonian UniVersity, and Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian UniVersity, ul. R. Ingardena 3, 30-060 Krakow, Poland ReceiVed: February 4, 2007; In Final Form: September 1, 2007

Literature data indicate that some calixarene derivatives with antimicrobial activities may be useful as drugs; one of the aspects of the biological activity of different classes of antibiotics concerns interactions with lipid membranes. Here, the possibility of incorporation and/or translocation of three amphiphilic p-tert-butylcalix[4]arene derivatives across membranes was studied using lipid monolayers. The derivatives used have 6-aminopenicillanic acid or benzylpenicillin moieties grafted in alternate positions at the calixarene lower rim; 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), a model bacterial membrane lipid, was used to prepare the monolayers. The miscibility of calixarene-antibiotic conjugates with lipid films was studied using surface pressure and surface potential measurements, as well as Brewster angle microscopy. The results obtained show that the miscibility is significantly different for the 6-aminopenicillanic acid and the two benzylpenicillin derivatives. Molecular modeling allowed the assessment of the lowest energy conformations of the calixarene derivatives and gave more insight into the interactions with the DMPE films.

1. Introduction Staying one step ahead of resistance with new antibiotics and treatments for infections is a huge challenge because bacteria evolve quickly to counter them.1 Indeed, use or misuse of antibiotics may result in the development of antibiotic resistance by the infecting organisms. For example, nearly all strains of Staphylococcus aureus, which could be treated successfully with penicillin in the 1940s and 1950s, are at present resistant to it.2 Therefore, there is an urgent need for new antibiotics and new strategies to combat bacteria, particularly those showing multidrug resistance. Calixarenes, a class of polyphenolic macrocycles, are receiving increased attention due to their great fundamental and practical importance.3-6 The calix[n]arenes (Scheme 1) can be tailored synthetically by altering the R moieties. Literature data indicate that some calixarene derivatives with antimicrobial activities7 may be useful as drugs in the treatment of tuberculosis and mycobacterioses.8 It was shown as well that calixarenebased vancomycin antibiotic mimics were active against Grampositive bacteria.9 Other calixarene derivatives, of which synthesis and applications are covered by patents, showed activities against bacteria,10 fungi, cancerous cells, viruses,11,12 enveloped viruses,13 but also against thrombosis14 or fibrosic * Corresponding author. E-mail: [email protected]. † Faculte ´ des Sciences, Universite´ Henri Poincare´ Nancy 1. ‡ Department of Physical Chemistry and Electrochemistry, Jagiellonian University. § Faculte ´ de Pharmacie, Universite´ Henri Poincare´ Nancy 1. | Department of Theoretical Chemistry, Jagiellonian University. ⊥ Current address: Institut Supe ´ rieur des Sciences Applique´es et de Technologie de Gabe`s, Rue Omar, El Khattab 6072, Gabes, Tunisie.

diseases. Our group demonstrated recently that some ionic calixarene derivatives were active against Gram-positive, as well as Gram-negative bacteria.15,16 In our group, different synthetic methods have been developed to prepare calixarene derivatives.17-22 The derivatives bearing antibiotic moieties were conceived as possible drug carriers, releasing the antibiotic upon hydrolysis. Indeed, the release of the antibiotics from this kind of derivative occurs upon hydrolysis in vitro (results not published), and the same process could be expected to take place in physiological conditions. Along this line, 6-aminopenicillanic acid was grafted via amide bonds on the 1,3-bis(O-acetyl)-p-tert-butylcalix[4]arene cone conformer in alternate positions (Calix I).21 On the other hand, different penicillins (Calix II and III), as well as an antibiotic from the quinolone group, the nalidixic acid, were grafted on the p-tert-butylcalix[4]arene via ester bonds.22 One of the aspects of the biological activity of different classes of antibiotics are interactions with lipid membranes.23-29 The derivatives used in this study are liposoluble amphiphiles; their structures might allow incorporation into the bilayer or translocation across the lipid membrane. The length of Calix I, Calix II, and Calix III in a fully extended conformation is, respectively, 20.0, 18.9, and 21.9 Å. These values are significantly lower compared to the thickness of a phosphoglyceride bilayer and the thickness of the bilayer hydrocarbon core, which are around 35-4030 and 32 Å,23,31 respectively. As a result of this difference in thickness, the orientation and structure of these calixarene-based molecules within the bilayer is currently under investigation using molecular modeling techniques. On the other

10.1021/jp070970+ CCC: $37.00 © 2007 American Chemical Society Published on Web 11/01/2007

13232 J. Phys. Chem. B, Vol. 111, No. 46, 2007

Korchowiec et al.

SCHEME 1: Calixarene Structure and Derivatives Used in This Studya

a (A) General calixarene structure. In the molecules used here R ) N-acetyl-pivaloyloxymethyl-6-aminopenicillanic acid (6-pivAPA, in Calix I), benzylpenicillin (penicillin G or PG) ethyl ester (in Calix II), or propyl ester (in Calix III); (B) numbering of the atoms in the antibiotic substituents; (C) derivative Calix I; (D) derivative Calix II; (E) derivative Calix III.

hand, an impact of calixarene-based antibiotics on the activity of surface-active enzymes, lipases and phospholipases was observed in vivo.8 The latter effect might be linked to the modification of the structure and physicochemical properties of lipid aggregates by the incorporated drug molecules. Indeed, we showed recently that the presence of an antifungal agent, griseofulvin, in phospholipid monolayers stimulates phospholipase A2 (PLA2) activity.32 Other literature data indicate that PLA2 is sensitive to the lipid aggregate morphology.33-36 Taking the above considerations into account, we decided to proceed with a study on the calixarene-antibiotic conjugatelipid systems. This study aimed to evaluate the capacity of the three new derivatives to interact with biological membranes; to this end, the Langmuir technique was used. Indeed, we showed recently that different amphiphilic calixarene derivatives formed stable monomolecular films at the air-water interface.37 First, the interfacial behavior of the pure calixarene derivatives was examined in the monolayers formed at the air-water interface. Second, mixed 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE)/calixarene derivative films were studied. Surface pressure-molecular area (Π-A) isotherms, surface potential-molecular area (∆V-A) isotherms, Brewster angle microscopy (BAM), and molecular modeling were used to characterize the monolayers. The results obtained gave us an insight into the inter- and intramolecular interactions of these molecules and showed that the calixarenes studied differ significantly in their interfacial behavior and in the interactions with DMPE. In the case of Calix II and Calix III, disorganizing of the lipid monolayer was observed. The disorganizing effect was more pronounced in the case of Calix II compared to Calix III, albeit the only structural difference between these two derivatives is the one methylene-different length of the linkers

by which the benzylpenicillin is attached to the aromatic crown. The results obtained in this study prepare the ground for further research on the biological activity of calixarene-antibiotic conjugates. 2. Experimental Section Characterization. Melting points (°C, uncorrected) were determined on an Electrothermal 9100 in capillary apparatus. 1H and 13C NMR spectra were recorded on a Bruker DRX 400 (400.130 and 100.612 MHz, respectively; CDCl3, TMS as internal standard, chemical shifts in ppm). Mass spectra (electrospray, ES) were recorded on a Platform Micromass apparatus at the Service Commun de Spectrome´trie de Masse, Nancy. Infrared spectroscopy was performed on a Bruker Vector 22 apparatus (KBr, ν in cm-1), and UV spectra were recorded on a SAFAS UV mc2 apparatus, λmax in nm, in L mol-1 cm-1. Elemental analyses were performed on a Thermofinnigan FlashEA 1112 apparatus, at the Service Commun de Microanalyse, Nancy. All chemicals were used without further purification unless otherwise specified. Synthesis. Calix I, bearing an amide-linked 6-pivAPA derivative was synthesized as described previously.21 Calix II and Calix III were obtained by attaching PG to the calixarene moiety via a bifunctional ester-ether alkyl linkage. 1,3-Bis(bromoalkyl)-calixarene calixarene derivatives were esterified using PG sodium salt (PGNa). To this end, bromoethyl and bromopropyl derivatives 3 and 4 (Scheme 2) were prepared as described in the literature.38 Subsequently, 3 and 4 were reacted with 2 equiv of PGNa in DMF to give Calix II (47%) and Calix III (32%), respectively. An alternative synthetic route, with the β-lactam used as an alkylating agent, was explored as well; this approach was aimed

Calixarenes in a Membrane Environment

J. Phys. Chem. B, Vol. 111, No. 46, 2007 13233

SCHEME 2: Synthetic Pathway Used to Prepare the Calixarene Derivatives

at a regioselective functionalization of the calixarene.20,39-42 The reaction of PGNa with 1,2-dibromoethane or 1,3-dibromopropane in DMF gave the bromoester 1 (70% yield) or 2 (50% yield), respectively. Unfortunately, in the next step, compounds 1 and 2 underwent degradation. The new derivatives Calix II and Calix III were characterized using infrared, UV-vis, mass spectrometry, elemental analyses, and 1D and 2D NMR methods. IR analyses showed in both cases the presence of amide, ester, and lactam CdO bonds in the 1685-1709, 1745-1752, and 1786-1792 cm-1 regions, respectively. The UV-vis spectrometry performed in CHCl3 showed a transition at around 284 nm. The electrospray mass spectrometry performed in the positive mode using MeOH with trace amounts of H2O as solvent yielded base peaks attributed to the monocharged, monosodio derivatives and to the dicharged, disodio derivatives. Elemental analyses were in accordance with the molecular formulas; some amount of CH2Cl2 detected in Calix III with NMR was probably due to its complexation within the calixarene cavity, as already observed for other calixarene species.17 Structural and conformational analysis of Calix II and Calix III in CDCl3 solution was done using 1H and 13C NMR; COSY, HSQC, and HMBC experiments (results not shown). The ArCH2-Ar resonance signals observed with 13C NMR between 31 and 32 ppm showed that both derivatives were in a cone conformation.43,44 It is worth noticing that Calix II bearing ethyl linkers exhibits two very close resonance signals for the ArCH2-Ar protons, suggesting that the proximity of the penicillin chiral centers induces distortion of the calixarene crown. The 1H NMR spectra of Calix II and Calix III display all characteristic signals of both penicillin and calixarene moieties. The influence of the chiral penicillin moiety on the calixarene conformation was evidenced by the presence of two or more Ar-CH2-Ar AB systems and, in the ethyl derivative Calix II

(Figure 1), of two strong AX systems for the aromatic protons. In the intermediate 1, the ester methylene group appears as a decuplet at around 4.50 ppm, whereas in 2 it gives a well-defined ABm resonance signal at around 4.32 ppm. This difference suggests that, in the absence of steric or other constraint due to the calixarene moiety, the influence of the pename chirality on the ester methylene group through the carboxylic function is more pronounced in the propyl intermediate 2. The study of the ethyl and propyl linkers in the calixarene derivatives showed that the ether methylene group appears as an ABm system at around 4.20 ppm in Calix II (ethyl) and as a triplet (J ) 6 Hz) at around 4.10 ppm in Calix III (propyl), while the ester methylene groups appear as a broad multiplet

Figure 1. Partial 1H NMR spectra of the (A) propyl linker analog Calix III and (B) PG ethyl linker Calix II (CDCl3, 400 MHz, room temperature).


Figure 2. ROESY correlations between β-lactam and aromatic protons in Calix II (CDCl3; 400 MHz, room temperature).

at around 4.65 ppm in Calix II and as a well-defined ABm system at around 4.72 ppm in Calix III (Figure 1). It can be concluded that increasing the length of the linker decreases the influence of the calixarene moiety on the penicillin substituent. This influence is absent in Calix III, while it is clearly seen in the ethyl derivative Calix II, as shown in the diastereotopic differentiation of the ether methylene protons. At low temperatures, the ester multiplet of Calix II can be seen to be a spread out and poorly resolved ABm system; it is also the case with the ether ABm signal (results not shown). A similar diastereotopic differentiation observed in tensed helicoidal calixarene-based bipyridyl Cu(I) complexes18 suggests that the ethyl penicillin substituent in Calix II is blocked in a specific conformation relative to the calixarene main axis. The AX resonance signals of the calixarene aromatic protons observed in Calix II, which result from a twisting of the macrocycle around its main axis, support the suggestion of the conformational hindrance. Moreover, the penicillin H(6) and H(5) protons in the ethyl derivative Calix II are shifted upfield around 0.35 and 0.1 ppm, respectively, compared to the penicillin bromoethyl ester 1 and, as shown in Figure 1, to Calix III. This phenomenon can be interpreted in terms of shielding due to a short distance between these protons and the calixarene aromatic cycle and the consequent steric constraints. A ROESY (rotational frame nuclear Overhauser effect spectroscopy) experiment performed with Calix II (Figure 2) showed that H(5) and H(6) were correlated to the aromatic and hydroxyl protons of the unsubstituted and, to a lesser extent, to the substituted phenolic units. This observation suggests that in CDCl3 solution the penicillin substituents are oriented parallel relative to the calixarene core axis. This result is in accordance with the results of molecular modeling (Figure 3). Finally, the residual phenolic -OH groups appear at around 7.00 and 7.50 ppm in Calix II and Calix III, respectively. This effect may be due to H bonding,45 as already observed in other carboxylated calixarenes.19 Compound 1. A solution of PGNa (0.2 g, 5.6 10-4 mol) and 1,3-dibromoethane (2 mL, 23.1 10-3 mol) in dry DMF (10 mL) was stirred at 50 °C during 18 h under Ar. The solvent was evaporated to dryness, and the residue was dissolved in CH2Cl2, washed with water, then dried over Na2SO4. The solution was concentrated and chromatographed (SiO2, CH2Cl2/Et20 10: 1) to give 1 (0.17 g, 70%) as an oily solid. 1H NMR (CDCl3): 1.498 (s, 3 H, CH3), 1.502 (s, 3 H, CH3), 3.546 (t, J ) 5.7 Hz,

Korchowiec et al. 2 H, OCH2CH2Br), 3.649 (s, 2 H, CH2C6H5), 4.418 (s, 1 H, H(2)), 4.476 (dec, 2 H, OCH2CH2Br), 5.330 (d, J ) 4.2 Hz, 1 H, H(5)), 5.677 (dd, J1 ) 4.2 Hz, J2 ) 9 Hz, 1H, H(6)), 6.151 (d, J ) 9 Hz, 1 H, NH), 7.250, 7.420 (m, 5 H, HC6H5). 13C NMR (CDCl3): 27.35 (CH3), 28.47 (OCH2CH2Br), 32.05 (CH3), 43.78 (CH2C6H5), 59.16 (C(6)), 64.92 (C(3)), 65.40 (OCH2CH2Br), 68.49 (C(5)), 70.70 (C(2)), 128.06, 129.54, 129.95 (Cp,m,o of C6H5), 134.24 (Ci of C6H5), 167.60 (COester), 170.73 (COamide), 173.94 (COlactam). Compound 2. A solution of PGNa (0.2 g, 5.6 10-4 mol) and 1,3-dibromopropane (2 mL, 19.6 10-3 mol) in dry DMF (20 mL) was stirred at 35 °C during 30 h under Ar. The solvent was evaporated to dryness, and the residue was dissolved in CH2Cl2, washed with water, then dried over Na2SO4. The solution was concentrated and chromatographed (SiO2, CH2Cl2) to give 2 (0.13 g, 50%) as an oily solid. UV (CHCl3): 326.0 (675.4). 1H NMR (CDCl3): 1.438 (s, 3 H, CH3), 1.453 (s, 3 H, CH3), 2.204 (quint, J ) 6.3 Hz, 2 H, CH2CH2CH2), 3.465 (t, J ) 6.3 Hz, 2 H, OCH2CH2CH2Br), 3.639 (s, 2 H, CH2C6H5), 4.306 (ABm, 2 H, OCH2CH2CH2Br), 4.386 (s, 1 H, H(2)), 5.503 (d, J ) 4.2 Hz, 1 H, H(5)), 5.646 (dd, J1 ) 4.2 Hz, J2 ) 9 Hz, 1 H, H(6)), 6.214 (d, J ) 9 Hz, 1 H, NH), 7.240, 7.407 (m, 5 H, HC6H5). 13C NMR (CDCl3): 27.14 (CH3), 29.39 (OCH2CH2CH2Br), 31.53 (OCH2CH2CH2Br), 32.54 (CH3), 43.73 (CH2C6H5), 59.35 (C(6)), 63.69 (OCH2CH2CH2Br), 64.79 (C(3)), 68.59 (C(5)), 70.69 (C(2)), 128.04, 129.52, 129.96 (Cp,m,o of C6H5), 134.28 (Ci of C6H5), 167.77 (COester), 170.77 (COamide), 173.78 (COlactam). Calix II. A solution of PGNa (0.455 g, 1.27 10-3 mol) and 1,3-bis(bromoethyl)calixarene 3 (0.5 g, 5.8 10-4 mol) in dry DMF (20 mL) was stirred under argon at 50 °C during 27 h. The solvent was evaporated to dryness, and the residue dissolved in CH2Cl2, then washed with H2O. The organic phase was dried over Na2SO4, concentrated, then chromatographed (SiO2, CH2Cl2/Et2O 10:1) to give Calix II (0.37 g, 46%) as a white powder. Mp: 123 °C. IR (KBr): 1686.46 cm-1 (CO amide), 1751.61 cm-1, 1787.22 cm-1 (CO lactam, CO ester). UV-vis (CHCl3): 284 (7360). 1H NMR (CDCl3): 0.959 (s, 18 H, 2 Me3C A), 1.307 (s, 18 H, 2 Me3C B), 1.451 (s, 6 H, 2 CH3), 1.549 (s, 6 H, 2 CH3), 3.308, 4.250 (AB, JAB ) 13.2 Hz, 4 H, Ar-CH2-Ar), 3.331, 4.327 (AB, JAB ) 13.2 Hz, 4 H, Ar-CH2-Ar), 3.614 (s, 4 H, C6H5CH2), 4.200 (ABm, 4 H, OCH2CH2OCO), 4.499 (s, 2 H, H(2)), 4.590 (m, 4 H, OCH2CH2OCO), 5.263 (dd, J1 ) 9 Hz, J2 ) 4.2 Hz, 2 H, H(6)), 5.442 (d, J ) 4.2 Hz, 2 H, H(5)), 6.04 (d, J ) 9 Hz, 2 H, NH), 6.780, 6.808 (AX, JAX ) 2.4 Hz, 4 H, ArH A), 7.031 (s, 2 H, OH), 7.050, 7.097 (AX, JAX ) 2.3 Hz, 4 H, ArH B), 7.24-7.40 (m, 10 H, Hm,p,o of C6H5).13C NMR (CDCl3): 27.27 (CH3), 31.37 (Me3C A), 31.73 (CH3), 32.06 (Me3C B), 31.73, 31.87 (Ar-CH2-Ar), 34.25 (Me3C B), 34.34 (Me3C A), 43.81 (CH2C6H5), 58.86 (C(6)), 64.85 (C(3)), 64.85 (OCH2CH2OCO), 68.26 (C(5)), 70.87 (C(2)), 73.51 (OCH2CH2OCO), 125.61, 125.77 (C(H) of Ar B), 125.94, 126.22 (C(H) of Ar A), 127.71, 128.18 (Co of Ar B), 127.98 (Cp,(C6H5)), 129.49, 129.92 (Co,m (C6H5)), 132.62, 132.94 (Co of Ar A), 134.34 (Ci,(C6H5)), 142.22 (Cp of Ar B), 147.75 (Cp of Ar A), 149.63 (Ci of Ar A), 150.69 (Ci of Ar B), 168.03 (COO), 170.45 (CONH), 173.96 (CONH). Anal. Calcd for C80H96N4O12S2 (1369.77): C, 70.15; H, 7.06; N, 4.09. Found: C, 70.06; H, 7.05; N, 4.01. ES-MS (positive mode): 1391.33 [Calix II + Na]+; 707.25 [Calix II + 2Na]2+/2. Calix III. A solution of 1, 3-bis(bromopropyl)calix[4]arene 4 (1 g, 1.12 10-3 mol) and PGNa (0.9 g, 0.25 10-3 mol) in dry DMF (100 mL) was heated at 40 °C under argon. The reaction was monitored by chromatography (SiO2; CH2Cl2/Et2O 5:1).



Figure 3. Optimized structures of Calix I (A), Calix II (B), and Calix III (C). Left and middle column, side view; right column, top view. Hydrogen bonds are not shown.

After 72 h, the solvent was evaporated to dryness at room temperature; the residue was dissolved in CH2Cl2, washed with H2O, and then dried over Na2SO4. The solvent was evaporated, and the final solid residue was chromatographed (SiO2; CH2Cl2/Et2O 5:1) to give Calix III (0.5 g, 32%) as a white solid. Mp: 142 °C. IR (KBr): 1685.81 cm-1 (CO amide), 1747.54 cm-1 (CO lactam), 1786.62 cm-1 (CO ester). UV-vis (CHCl3): 285 (6950). 1H NMR (CDCl3): 1.020 (s, 18 H, Me3C A), 1.297 (s, 18 H, Me3C B), 1.431 (s, 6 H, CH3), 1.465 (s, 6 H, CH3), 2.359 (quint, J ) 6.0 Hz, 4 H, OCH2CH2CH2OCO), 3.331, 4.210 (AB, JAB ) 13.0 Hz, 4 H, ArCH2Ar), 3.342, 4.192 (AB, JAB ) 13.0 Hz, 4 H, ArCH2Ar), 3.658 (s, 4 H, CH2C6H5), 4.074 (t, J ) 6 Hz, 4 H, OCH2CH2CH2OCO), 4.436 (s, 2 H, H(2)), 4.703 (ABm, 4 H, OCH2CH2CH2OCO), 5.507 (d, J ) 4.2 Hz, 2 H, H(5)), 5.621 (dd, J1 ) 9.0 Hz, J2 ) 4.2 Hz, 2 H, H(6)), 6.145 (d, J ) 9 Hz, 2 H, NH), 6.870 (s, 4 H, ArH A), 7.062 (s, 4 H, ArH B), 7.26-7.42 (m, 10 H, C6H5), 7.549 (s, 2 H, OH). 13C NMR (CDCl3): 27.05 (CH3), 29.76 (OCH2CH2-

CH2OCO), 31.43 (Me3C A), 32.08 (Me3C B), 32.18 (ArCH2Ar), 32.48 (CH3), 34.24 (Me3C B), 34.42 (Me3C A), 43.83 (CH2C6H5), 59.24 (C(6)), 62.95 (OCH2CH2CH2OCO), 64.79 (C(3)), 68.52 (C(5)), 70.74 (C(2)), 72.49 (OCH2CH2CH2OCO), 125.61 (Cm of Ar B), 126.11 (Cm of Ar A), 128.10 (Cp of C6H5), 129.54 (Cm of C6H5), 129.99 (Co of C6H5), 127.81, 127.83 (Co of Ar B), 132.94, 132.94 (Co of Ar A), 134.28 (Ci of C6H5), 142.16 (Cp of Ar B), 147.73 (Cp of Ar A), 149.64 (Ci of Ar A), 150.87 (Ci of Ar B), 167.88 (COO), 170.68 (CONH), 173.80 (COlactam). Anal. Calcd for C82H100N4O12S2‚0.5CH2Cl2 (1440.29): C, 68.80; H, 7.07; N, 3.89. Found: C, 69.12; H, 7.05; N, 3.84. ES-MS (positive mode): 1420.22 [Calix III + Na]+; 721.37 [Calix III + 2Na]2+/2. Compression Isotherms and Brewster Angle Microscopy. Monolayer experiments were carried out with a KSV 5000 Langmuir balance (KSV, Helsinki). A Teflon trough (15 cm × 58 cm × 1 cm) with two hydrophilic Delrin barriers (symmetric compression) was used in all experiments. The system was

13236 J. Phys. Chem. B, Vol. 111, No. 46, 2007 equipped with an electrobalance and a platinum Wilhelmy plate (perimeter 39.24 mm) as a surface pressure (Π) sensor. Surface potential was measured using KSV Spot 1 with a vibrating plate and a stainless steel counter electrode. The apparatus was closed in a Plexiglas box, and temperature was kept constant at 20 °C. Before each utilization, the trough and the barriers were cleaned using cotton soaked in chloroform, gently brushed with ethanol, then with tap water, and finally rinsed with water purified by reverse osmosis (Millipore, France). All solvents used for cleaning the trough and the barriers were of analytical grade. Pure water (Millipore Milli-Q system, 18 MΩ‚cm), surface tension (γ) of 72.75 mN m-1 at 20 °C, was used as a subphase in all experiments. Any residual surface-active impurities were removed before each experiment by sweeping and suction of the surface. Monolayers were spread on pure water using calibrated solutions (concentration ∼0.5 mg mL-1) of pure calixarenes, pure 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE; 99%, Sigma) and DMPE/calixarene mixtures. Calixarene solutions were prepared with spectrophotometric grade chloroform (Aldrich, ACS). DMPE and DMPE/calixarene mixtures were dissolved in chloroform/methanol 4:1 v/v. After the equilibration time of 20 min, the films were compressed at the rate of 2.5 mm min-1 barrier-1 (750 mm2 min-1). A PC was used with KSV software to control the surface pressuremolecular area (Π-A) compression isotherm experiments. The standard deviation obtained from compression isotherms repeated systematically at least three times for each system studied was (0.5 Å2 on molecular area, (0.01 V on surface potential, and (0.2 mN m-1 on surface pressure. The morphology of the films was imaged with a computerinterfaced KSV 2000 Langmuir balance combined with a Brewster angle microscope (KSV Optrel BAM 300, Helsinki). The light source was a standard HeNe laser, 10 mW, 633 nm; the spatial resolution of the device is 2 µm. The Teflon trough dimensions were 6.5 cm × 58 cm × 1 cm; other experimental conditions were as described above. Computational Details. The geometrical structure of investigated calixarenes was initially optimized at the semiempirical level of theory (AM1). The conelike shape of the calixarene part was taken into account, according to NMR experiments. The other possible structures, namely, partial cone, 1,2-alternate, and 1,3-alternate, were excluded from the optimization process. The conelike calixarene crown and the penicillin moieties were optimized independently. The entire Calix I, II, and III systems were assembled from these smaller fragments, with the terminating hydrogen atoms removed. Since all three calixarene derivatives have several single bonds in both substituents, a large number of local minima exist on the hyperenergy surfaces; the full search on the energy surfaces is practically impossible. We have performed a limited search on the energy hypersurface with restricted (C2) and unrestricted (C1) symmetries, respectively. In the former case, the surface was scanned by simultaneously changing two selected dihedral angles using C2 symmetry. In the latter case, both rotation angles were independent. It was found that for the reduced, C1 symmetry of the molecules, the located conformers were less stable compared to those for C2. For this reason, the C2 symmetry was assumed in more extended ab initio calculations at the Hartree-Fock (HF) level of theory with 6-31G basis set.46,47 The Gamess48,49 and Gaussian50 program packages were used in the calculations.

Korchowiec et al. TABLE 1: Total Energies, Dipole Moments, and Surface Areas Computed at Hartree-Fock Level of Theory with 6.31G Basis Set for the Most Stable Conformers of Calixarene Derivatives Calix I Calix II Calix III a

E (au)

µ (D)

S (Å2)a

-5144.98313 -4994.79176 -5072.83142

9.11 14.04 12.24

149 158 160

Surface areas were integrated to 0.0001 contour.

stretch along the long molecule axis below the aromatic crown. The lowest energy conformers are depicted in Figure 3. Hydrogen bonds form between the free hydroxyl groups and the oxygen atoms of the substituted hydroxyl groups on the lower calixarene rim. In Calix I, the two amide linkers are hydrogen bonded via the nitrogen and oxygen atoms of the amide groups. These hydrogen bonds rigidify the molecule skeleton and favor the column-like shape. An alternative, propeller-like structure of Calix I (structure not shown) is around 20.5 kcal mol-1 less stable. The column-like conformation is favored as well in the case of Calix II and Calix III; these conformations are stabilized by the intersubstituent hydrogen bonds, namely, the two β-lactam carbonyl oxygens hydrogen bond to the amide linker nitrogens. In Table 1 the total energies, dipole moments, and calculated molecular areas of the three derivatives are listed. The molecular areas were computed by integrating the density plot in the plane perpendicular to the long molecule symmetry axis. The same plane, cutting through the most rigid part of the molecule at the level of the t-butyl moieties of the calixarene upper rim, was taken into account with the three derivatives. Calixarene One-Component Monolayers. The properties of the monolayers formed with the calixarene derivatives were characterized using surface pressure-area (Π-A) isotherms, surface potential-area (∆V-A) isotherms, and BAM. Surface pressure-area isotherms recorded on pure water subphase at 20 °C are shown in Figure 4. All derivatives form stable monolayers at the air-water interface. The monolayers have limiting areas, A0, of 175, 180, and 181 Å2 with Calix I, Calix II, and Calix III, respectively. The experimental limiting area values were determined by a linear fitting of the upper part of the isotherm corresponding to the most condensed film and extrapolating to zero surface pressure. The comparison of the experimental, A0exp, and

3. Results and Discussion Calixarene Modeling. The located structures have a columnlike shape. The substituents are brought closely together and

Figure 4. Surface pressure isotherms of Calix I (solid line), Calix II (dotted line), and Calix III (dashed line) spread on pure water at 20 °C.



Figure 5. Surface potential-area (A) and surface dipole moment-area (B) isotherms of Calix I (solid line), Calix II (dotted line), and Calix III (dashed line) spread on water at 20 °C.

TABLE 2: Characteristic Parameters of Pure Calixarene Isotherms Πcoll (mN m-1) Calix I Calix II Calix III

36.1 39.1 37.4

(Å2

Acoll molecule-1) 113 133 116

Cs-1 (mN m-1)

A0 (Å2 molecule-1)

∆Vmax (V)

µ⊥ (D)

82.7 129 87.9

175 180 181

0.795 0.442 0.554

2.39 1.56 1.71

theoretical, A0theor, values shows that the latter are lower (Tables 1 and 2); note that the computed surface areas were obtained by integrating the electron density contour plot. The similar values of A0exp/A0theor (1.174, 1.139, and 1.131, for Calix I, Calix II, and Calix III, respectively) indicate that a quantitative agreement between the experimental and theoretical results can be obtained by choosing an adequate molecule contour for the calculations. The maximum values of the compressibility modulus, Cs-1, corresponding to the highest packing of molecules in the monolayer are given in Table 2. It can be seen that the monolayer formed with Calix II is more condensed compared to those formed with Calix I and Calix III. Indeed, the Cs-1 values with the Calix I and Calix III monolayers are situated between the liquid expanded and condensed phase, whereas that of Calix II can be considered as condensed phase.51 The Π-A

isotherms of Calix II and Calix III bearing similar substituents exhibit similar phase characteristics. However, the slope of the isotherm can be seen to decrease upon introduction of an additional methylene group between the phenolic unit and benzylopenicillin moiety. Indeed, with an increased length of the linker in Calix III, the monolayer becomes more compressible and less stable. The lower stability of the monolayer, which shows in the lower collapse pressure values (Table 2), may result from a higher conformational mobility and lower ordering of the Calix III polar head groups in the monolayer. These results are in accordance with the NMR results on the conformational mobility of these two derivatives. However, the highest compressibility and the lowest stability of the monolayer are observed in the case of Calix I. This effect may be due to the presence of alkyl moieties in the penicillin substituents compared to Calix II and Calix III, bearing benzyl moieties. Indeed, in

Figure 6. Π-A and ∆V-A isotherms of binary mixtures DMPE/Calix I spread on water at 20 °C. Solid lines correspond to pure components; dashed lines, xDMPE ) 0.75; dotted lines, xDMPE ) 0.50; dashed-dotted lines, xDMPE ) 0.25.

Figure 7. Π-A and ∆V-A isotherms of binary mixtures DMPE/Calix II spread on water at 20 °C. Solid lines correspond to pure components; dashed lines, xDMPE ) 0.75; dotted lines, xDMPE ) 0.50; dashed-dotted lines, xDMPE ) 0.25.


Korchowiec et al.

∆V ) µ⊥/0A where A is the area per molecule, 0 is the vacuum permittivity, and is the relative permittivity of the monolayer, which is assumed to be 1.52

µ ⊥ ) µR + µω

Figure 8. Π-A and ∆V-A isotherms of binary mixtures DMPE/Calix III spread on water at 20 °C. Solid lines correspond to pure components; dashed lines, xDMPE ) 0.75; dotted lines, xDMPE ) 0.50; dashed-dotted lines, xDMPE ) 0.25.

the latter case the π-π stacking could contribute to the monolayer stabilization. It is worth noticing that the obtained values of the molecular areas at the collapse of the monolayers (Acoll) compare well with those reported for other amphiphilic calixarene derivatives.37 The surface potential of the investigated calixarenes plotted as a function of the molecular area is shown in Figure 5A. The difference between the ∆V-A isotherm of Calix I and Calix II or Calix III is more pronounced compared to the difference between Calix II and Calix III. As indicated by the ∆V values, Calix I is oriented more vertically relative to the water surface compared to Calix II and Calix III. In the case of Calix I the surface potential increases smoothly with the decreasing monolayer area. The ∆V-A isotherm shows a liquid expanded phase even for the highest measured molecular area of 468 Å2 molecule-1 (data not shown). In the case of Calix II, ∆V is close to zero for the areas larger than 240 Å2 molecule-1 showing that the monolayer is in a gas phase. Upon compression, ∆V sharply increases at 240 Å2 molecule-1 indicating a reorientation of the molecules and an LE-G phase transition. The highest value of ∆V corresponds to the maximum packing of molecules in the monolayer (∆Vmax values are reported in Table 2). Calix III, having one additional methylene unit in the linker, is in a liquid expanded phase at the molecular areas at which gas phase is observed with Calix II, and its orientation relative to the water surface is more vertical. On the basis of the ∆V values, the effective dipole moment of molecules at the interface, µ⊥, was calculated. As follows from the Helmholtz equation

where µR represents the change in the effective dipole moment in the hydrated polar group region, including the effective dipole moment of the hydrophilic group and changes in the dipole moment due to the reorientation of the water dipoles, whereas µω corresponds to the hydrophobic region of the monolayer.53,54 The plots µ⊥-A are presented in Figure 5B. The calixarenes studied here have an identical hydrophobic calixarene crown. The contribution to the total effective dipole moment of the hydrophobic part being identical for all three molecules, the differences between the effective dipole moments of Calix I, Calix II, and Calix III reflect different contributions of the polar head groups and the associated water molecules. The maximum dipole moments (Table 2) indicate reducing of the tilt angle of the head group in the order Calix II, Calix III, Calix I. It can be noticed that in the case of Calix II and Calix III the slopes of the surface potential-area (Figure 5A) and surface dipole moment-area (Figure 5B) isotherms, as well as the ∆Vmax and µ⊥ values (Table 2) are similar. We propose that the hydrogen bonding to the penicillin heteroatoms may be responsible for structuring a water layer around the polar side chains; the water layer contribution would have an equalizing effect on the surface potential results, masking the small structural difference between Calix II and Calix III. Phospholipid/Calixarene Binary Mixtures. The surface pressure and surface potential-area isotherms of mixed DMPE/ calixarene monolayers at the air-water interface are shown in Figures 6-8 for DMPE/Calix I, DMPE/Calix II, and DMPE/ Calix III, respectively. The characteristic parameters of the isotherms are given in Table 3. The DMPE monolayer shows a typical first-order transition from the liquid expanded to liquid condensed phase (LE-LC) at around 5 mN m-1 and 0.330 V.55 The isotherms of the mixed films are situated between those corresponding to the pure monolayers. The decrease of the calixarene molar fraction results in a shift of the isotherm toward smaller molecular areas. The only exception is the Π-A isotherm corresponding to the highest calixarene content in DMPE/Calix I system, which is shifted to higher molecular areas compared to that of the pure calixarene monolayer. This effect may be due to the disrupting of the Calix I network by DMPE. The profiles of the isotherms corresponding to the mixed films (Figures 6-8) as well as compressibility modulus (Cs-1) values (Table 3) indicate that the properties of the mixed systems are dominated by the calixarene derivatives (for pure DMPE

TABLE 3: Characteristic Parameters of DMPE/Calixarene Isotherms xDMPE

Πcoll (mN m-1)

Acoll (Å2 molecule-1)

Cs-1 (mN m-1)

A0 (Å2 molecule-1)

∆Vmax (V)

µeff (D)

Calix I

0.25 0.50 0.75

35.9 35.7 35.5

118 101 80

88.3 86.4 226

179 153 106

0.764 0.741 0.677

2.40 1.99 1.44

Calix II

0.25 0.50 0.75

38.6 39.0 38.9

114 88 62

127 147 194

156 118 80

0.455 0.462 0.492

1.37 1.08 0.81

Calix III

0.25 0.50 0.75

37.2 37.0 36.8

102 80 60

78.3 82.0 107

169 129 91

0.540 0.539 0.536

1.47 1.15 0.86



Figure 9. Miscibility analysis of DMPE/Calix I (A and B), DMPE/Calix II (C and D), and DMPE/Calix III (E and F) monolayers at 10 (dotted lines), 15 (dashed lines), and 20 mN m-1 (solid lines). The straight lines represent the additive mixing.

Cs-1 ) 873.3 mN m-1). The fact that the collapse pressure for all the mixed monolayers is close to that of the corresponding calixarene might suggest phase separation in the two-component films.56-58 However, the surface potential at the collapse (∆Vmax) gradually evolves from the value corresponding to the pure calixarene film to that of the pure DMPE (Table 3). It has to be noted that surface potential is usually considered as a more sensitive tool for providing information about the orientation and organization of the molecules in monolayers compared to surface pressure. Consequently, on the basis of the surface potential measurements, it may be supposed that the calixarenes studied are miscible with DMPE. Moreover, all mixed monolayers undergo a phase transition, which occurs at the same

molecular areas with both types of isotherms. The increase of the phase transition surface pressure and surface potential with the increasing calixarene molar fraction could be considered as a supplementary indication of the surface miscibility of the two components. To clarify the miscibility properties of the three calixarene derivatives, mean molecular area (MMA) and ∆V dependencies versus molar fraction of DMPE (xDMPE) were plotted for arbitrarily chosen surface pressures (10, 15, and 20 mN m-1) (Figure 9). Positive deviations from linearity in the MMA of mixed films are observed for all three derivatives and surface pressures investigated (Figure 9, parts A, C, and E). These deviations, which imply polar or steric interactions in the mixed


Figure 10. Gibbs energy of mixing as function of xDMPE, calculated at Π ) 20 mN m-1. Solid line, DMPE/Calix I; dotted line, DMPE/Calix II; dashed line, DMPE/Calix III.

films, are low in the case of Calix II and Calix III, and increase in the order Calix II, Calix III, and Calix I. This observation is in accordance with the results of modeling, showing that the antibiotic substituents in Calix I are hydrogen bonded via the amide linkers beneath the calixarene crown, compared to hydrogen bonding via β-lactam rings in Calix II and Calix III. A higher conformational liberty of the substituent extremities

Korchowiec et al. in Calix I would make the Calix I and DMPE packing looser compared to the derivatives Calix II and Calix III. ∆V-xDMPE dependencies show as well that the miscibility behavior of Calix I is different compared to that of Calix II and Calix III. The negative excess ∆V (∆V ex) observed with Calix I for xDMPE ) 0.00-0.25 indicates that the ordering of the Calix I molecules decreases in the presence of DMPE; inversely, the positive ∆V ex observed at 15 and 20 mN m-1 for xDMPE ) 0.75-1.00 indicates that Calix I has an ordering effect on DMPE at these surface pressures; at 10 mN m-1 the ordering effect is observed only for xDMPE ) 0.50. In the case of Calix II/DMPE and Calix III/DMPE, the negative ∆V ex indicates a decreased ordering of the molecules forming the film in the whole range of compositions, compared to pure substances. From another point of view, Calix I, contrary to Calix II and Calix III, contributes to a more vertical average orientation of the dipoles in the mixed films; along this line, dipoles are oriented more vertically in the mixed films containing Calix III, compared to Calix II; obviously, the longer linker in Calix III allows for an easier ordering of molecules in the mixed film compared to Calix II. These observations may be relevant for further studies on the biological activity of the three calixarene derivatives. The miscibility of the three calixarenes with phospholipid monolayers can be analyzed59 in terms of Gibbs energy of

Figure 11. BAM images of calixarene, DMPE, and DMPE/calixarene monolayers. Line A-C: pure Calix II; line D-F: pure DMPE; line G-I: mixed films. (A) Π ∼ 0 mN m-1; A ) 240 Å2 molecule-1; (B) Π ) 6 mN m-1, A ) 185.6 Å2 molecule-1; (C) collapse point; (D) Π ∼ 0 mN m-1, A ) 90 Å2 molecule-1; (E) Π ) 6 mN m-1; A ) 57.8 Å2 molecule-1; (F) collapse point; (G) DMPE/Calix I; (H) DMPE/Calix II; (I) DMPE/Calix III. The G, H, and I images were taken at 12, 13, and 14 mN m-1 and 110.9, 82.5, and 87.5 Å2 molecule-1, respectively. The composition of all the mixed films was xDMPE ) 0.75. Scale: the width of the snapshots corresponds to 400 µm.

Calixarenes in a Membrane Environment mixing, ∆Gex, expressed for the two-component system as follows:

∆Gex )

∫0Π[A12 - (x1A1 + x2A2)] dΠ

where A12 is the mean molecular area in the mixture, A1 and A2 are the mean molecular areas of the pure components 1 and 2, and x1 and x2 are the molar fractions of the components in the mixed film. The Gibbs energy of mixing for all investigated systems, obtained from the integration of the Π-A isotherms from 0 to 20 mN m-1, is shown in Figure 10. It can be seen that the energy of the formation of the mixed films, ∆G ex, is higher compared to pure films. Assuming that the enthalpy of film formation is comparable for Calix II and Calix III due to their structural similarities, the differences in the ∆G ex values can be attributed to entropic effects. Therefore, the DMPE/Calix III films, having a higher ∆G ex, would form more ordered systems than those formed with DMPE/Calix II. These results are in accordance with those obtained with ∆V-A isotherms (Figures 6-9). This reasoning cannot be used in the case of structurally different Calix I. A BAM study was carried out to obtain complementary information about the monolayer properties (Figure 11). The images of the Calix I and Calix III monolayers are not presented, as these monolayers are isotropic all along compressions. In the pure Calix II monolayer formation of a foam is observed at the molecular area of 240 Å2 molecule-1 and surface pressures close to zero (Figure 11A);37 at this point LE-G phase transition is observed in the corresponding ∆V-A isotherms. At higher surface pressures this monolayer is isotropic (Figure 11, parts B and C), which is in accordance with the Π-A and ∆V-A isotherm characteristics. BAM images of the pure DMPE monolayer show formation of a foam in the LE-G phase transition (Figure 11D) and large condensed domains in the LELC phase transition (Figure 11E). Upon compression the DMPE monolayer becomes isotropic and breaks down at the collapse point (Figure 11F). All mixed films go, at different surface pressures, through an LE-LC phase transition manifested in BAM images by domain structure. The BAM images corresponding to the LELC region in the mixed xDMPE ) 0.75 monolayers are presented in Figure 11G-I. The shape of the domains resembles that of the pure lipid only in the case of the DMPE/Calix I film (Figure 11G). The domains in the DMPE/Calix III and DMPE/Calix II mixtures (Figure 11, parts H and I, respectively) are significantly smaller compared to the pure DMPE. These results suggest that the mechanism of the LE-LC phase transition is different in the DMPE/Calix I compared to the DMPE/Calix II and DMPE/Calix III films. The formation of small, numerous domains in the latter two mixtures may be attributed to the disorganizing effect of these calixarene derivatives observed with the ∆V-A isotherms. 4. Conclusions The results obtained show that the miscibility properties of the 6-pivAPA derivative, Calix I, are different compared to the two benzylpenicillin derivatives, Calix II and Calix III. This effect is obviously linked to the aliphatic pivaloyl terminal moieties present in Calix I substituents, which decrease the molecule packing in the mixed films compared to the benzyl moieties present in Calix II and Calix III; the decreased molecule packing in the case of Calix I is accompanied by an increased ordering of the DMPE molecules in the lipid-rich phase. On the other hand, the higher ∆G ex obtained with Calix

J. Phys. Chem. B, Vol. 111, No. 46, 2007 13241 III compared to Calix II indicates that a higher conformational flexibility of the former facilitates the interactions with DMPE. The results obtained suggest that the incorporation of Calix II and Calix III into biological membranes can be expected, whereas Calix I could be more easily translocated across the membrane compared to the benzylpenicillin derivatives. A study of the biological effects of the calixarene derivatives in lipid membranes is underway in our laboratory. Acknowledgment. The Ministe`re de la Recherche et de l’Enseignement Supe´rieur and the Centre National de la Recherche Scientifique are acknowledged for their financial support. A.B.S. acknowledges the Ministe`re de l’Enseignement Supe´rieur de Tunisie for a 6 month Ph.D. fellowship. Part of the calculation was performed at CYFRONET (MNiSW/ SGI3700/UJ/161/2006 and MNiSW/SGI4700/UJ/061/2007). We thank Dr. J.-M. Ziegler for mass spectroscopy, Ms. E. Eppiger for NMR measurements, and Jean-Louis Vaucher and Alexis Martin from Service Technique de l’UHP for technical assistance. We thank Ms. N. Marshall for proof-reading the manuscript. References and Notes (1) Leeb, M. Nature 2004, 431, 892-893. (2) Chambers, H. F. Emerging Infect. Dis. 2001, 7, 178-182. (3) Gutsche, C. D., Stoddart, F. J., Eds. Calixarenes; The Royal Society of Chemistry: Cambridge, U.K., 1989. (4) Bo¨hmer, V., Vicens, J., Eds. Calixarenes. A Versatile Class of Macrocyclic Compounds; Kluwer Academic Publications: Dordrecht, The Netherlands, 1991. (5) Gutsche, C. D. Calixarenes ReVisited; Monographs in Supramolecular Chemistry; Royal Society of Chemistry: Cambridge, U.K., 1998. (6) Azfari, Z., Bo¨hmer, V., Harrowfield, J., Vicens, J., Eds. Calixarenes 2001; Kluwer Academic Publishers: Dordrecht, The Netherlands, 2001. (7) Cornforth, J. W.; D’Arcy Hart, P.; Nicholls, G. A.; Rees, R. J. W.; Stock, J. A. Br. J. Pharmacol. Chemother. 1955, 10, 73-86. (8) D’Arcy Hart, F.; Armstrong, J. A.; Brodaty, E. Infect. Immun. 1996, 64, 1491-1493. (9) Casnati, A.; Fabbi, M.; Pelizzi, N.; Pochini, A.; Sansone, F.; Ungaro, R.; Di Modugno, E.; Tarzia, G. Bioorg. Med. Chem. Lett. 1996, 6, 26992704. (10) Yo, T.; Fujiwara, K.; Otsuka, M. Jpn. Patent 10203906, 1998. (11) Harris, S. J. WO Patent 9519974, 1995. (12) Harris, S. J. WO Patent 0244121, 2002. (13) Hwang, K. M.; Qi, Y. M.; Liu, S. Y.; Choy, W.; Chen, J. WO Patent 9403164, 1994. (14) Hwang, K. M.; Qi, Y. M.; Liu, S. Y.; Lee, T. C.; Choy, W.; Chen, J. WO Patent 9403165, 1994. (15) Mourer, M.; Duval, R. E.; Finance, C.; Regnouf de Vains, J.-B. Bioorg. Med. Chem. Lett. 2006, 16, 2960-2963. (16) Grare, M.; Mourer, M.; Regnouf de Vains, J.-B.; Finance, C.; Duval, R. E. Pathol. Biol. 2006, 54, 470-476. (17) Dalbavie, J.-O.; Regnouf de Vains, J.-B.; Lamartine, R.; Lecocq, S.; Perrin, M. Eur. J. Inorg. Chem. 2000, 4, 683-691. (18) Regnouf de Vains, J.-B.; Lamartine, R.; Fenet, B.; Bavoux, C.; Thozet, A.; Perrin, M. HelV. Chim. Acta 1995, 78, 1607-1619. (19) Molard, Y.; Bureau, C.; Parrot-Lopez, H.; Lamartine, R.; Regnouf de Vains, J.-B. Tetrahedron Lett. 1999, 40, 6383-6387. (20) Regnouf de Vains, J.-B.; Lamartine, R. HelV. Chim. Acta 1994, 77, 1817-1825. (21) Ben Salem, A.; Regnouf de Vains, J.-B. Tetrahedron Lett. 2001, 42, 7033-7036. (22) Ben Salem, A.; Regnouf de Vains, J.-B. Tetrahedron Lett. 2003, 44, 6769-6771. (23) Lee, A. G. Biochim. Biophys. Acta 2003, 1612, 1-40. (24) Neves, P.; Berkane, E.; Gameiro, P.; Winterhalter, M.; De Castro, B. Biophys. Chem. 2005, 113, 123-128. (25) Malewicz, B.; Borowski, E. Nature 1979, 281, 80-82. (26) Fa, N.; Ronkart, S.; Schanck, A.; Deleu, M.; Gaigneaux, A.; Goormaghtigh, E.; Mingeot-Leclercq, M. P. Chem. Phys. Lipids 2006, 144, 108-116. (27) Chen, X.; Tang, H.; Even, M. A.; Wang, J.; Tew, G. N.; Chen, Z. J. Am. Chem. Soc. 2006, 128, 2711-2714. (28) Berquand, A.; Fa, N.; Dufrene, Y. F.; Mingeot-Leclercq, M. P. Pharm. Res. 2005, 22, 465-475. (29) Zhang, L.; Dhillon, P.; Yan, H.; Farmer, S.; Hancock, R. E. Antimicrob. Agents Chemother. 2000, 44, 3317-3321.

13242 J. Phys. Chem. B, Vol. 111, No. 46, 2007 (30) Pasenkiewicz-Gierula, M.; Murzyn, K.; Rog, T.; Czaplewski, C. Acta Biochim. Pol. 2000, 47, 601-611. (31) Wiener, M. C.; White, S. H. Biophys. J. 1992, 61, 434-447. (32) Corvis, Y.; Barzyk, W.; Brezesinski, G.; Mrabet, N.; Badis, M.; Hecht, S.; Rogalska, E. Langmuir 2006, 22, 7701-7711. (33) Corvis, Y.; Korchowiec, B.; Brezesinski, G.; Follot, S.; Rogalska, E. Langmuir 2007, 23, 3338-3348. (34) Halperin, A.; Mouritsen, O. G. Eur. Biophys. J. 2005, 34, 967971. (35) Honger, T.; Jorgensen, K.; Biltonen, R. L.; Mouritsen, O. G. Biochemistry 1996, 35, 9003-9006. (36) Mouritsen, O. G.; Andresen, T. L.; Halperin, A.; Hansen, P. L.; Jakobsen, A. F.; Jensen, U. B.; Jensen, M. O.; Joergensen, K.; Kaasgaard, T.; Leidy, C.; Simonsen, A. C.; Peters, G. H.; Weiss, M. J. Phys.: Condens. Matter 2006, 18, S1293-S1304. (37) Van der Heyden, A.; Regnouf de Vains, J.-B.; Warszynski, P.; Dalbavie, J.-O.; Zywocinski, A.; Rogalska, E. Langmuir 2002, 18, 88548861. (38) Li, Z.-T.; Ji, G.-Z.; Zhao, C.-X.; Yuan, S.-D.; Ding, H.; Huang, C.; Du, A.-L.; Wei, M. J. Org. Chem. 1999, 64, 3572-3584. (39) Ferguson, G.; Gallagher, J. F.; Giunta, L.; Neri, P.; Pappalardo, S.; Parisi, M. J. Org. Chem. 1994, 59, 42-53. (40) Pappalardo, S.; Giunta, L.; Foti, M.; Ferguson, G.; Gallagher, J. F.; Kaitner, B. J. Org. Chem. 1992, 57, 2611-2624. (41) Pappalardo, S.; Caccamese, S.; Giunta, L. Tetrahedron Lett. 1991, 32, 7747-7750. (42) Bottino, F.; Giunta, L.; Pappalardo, S. J. Org. Chem. 1989, 54, 5407-5409. (43) Jaime, C.; De Mendoza, J.; Prados, P.; Nieto, P. M.; Sanchez, C. J. Org. Chem. 1991, 56, 3372-3376. (44) Oriol Magrans, J.; de Mendoza, J.; Pons, M.; Prados, P. J. Org. Chem. 1997, 62, 4518-4520. (45) Gu¨nther, H. La Spectroscopie de RMN; Masson: Paris, 1993. (46) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J. Chem. Phys. 1971, 54, 724-728. (47) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56, 2257-2261.

Korchowiec et al. (48) GAMESS, version 14, Jan. 2003 (R2), Iowa State University. (49) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M. S.; Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su, S.; Windus, T. L.; Dupuis, M.; Montgomery, J. A., Jr. J. Comput. Chem. 1993, 14, 1347-1363. (50) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision D.01; Gaussian, Inc.: Wallingford, CT, 2004. (51) Davies, J. T.; Rideal, E. K. Interfacial Phenomena, 2nd ed.; Academic Press: New York, 1963. (52) Demchak, R. J.; Fort, T., Jr. J. Colloid Interface Sci. 1974, 46, 191-202. (53) Vogel, V.; Mo¨bius, D. J. Colloid Interface Sci. 1988, 126, 408420. (54) Vogel, V.; Mo¨bius, D. Thin Solid Films 1988, 159, 73-81. (55) Weidemann, G.; Vollhardt, D. Thin Solid Films 1995, 264, 94103. (56) Crisp, D. J. Research 1949, 17-22. (57) Crisp, D. J. Research 1949, 23-35. (58) Gaines, G. L. Insoluble Monolayers at Liquid-Gas Interfaces; Interscience Publishers: New York, 1966. (59) Korchowiec, B.; Paluch, M.; Corvis, Y.; Rogalska, E. Chem. Phys. Lipids 2006, 144, 127-136.

Calixarenes in a Membrane Environment: A Monolayer Study on the

Recommend Documents