Induced chirality of supramolecular assemblies of some amphiphiles with beta-cyclodextrin through the interaction at the air/water interface

4-(N-Stearoylamino)-2-amino-azobenzene (AzoNH2C18) and 4-(N-stearoylamino)-azobenzene (AzoC18) have been synthesized. The inclusion complex formation of AzoNH2C18 and beta-cyclodextrin (beta-CyD) at the air/water interface was investigated and compared to that of AzoC18. It has been found that both the amphiphiles can form stable monolayer films on water surface. When the amphiphiles were spread on the aqueous solution of beta-CyD, AzoNH2C18 can form inclusion complexes with the beta-CyD molecules at the interface while AzoC18 cannot. The inclusion complex formation was confirmed by the changes in the isotherms and the circular dichroism (CD) and Fourier transform infrared (FT-IR) spectra of the transferred LS films. Atomic force microscopy (AFM) observation found morphological changes in the course of complex formation. It was suggested that the additional amino group in the azobenzene ring plays an important role in forming the inclusion complex in situ at the air/water interface.     

The miscibility of poly(D,L-lactide-co-glycolide) with amphiphilic molecules and the interaction of their mixtures with DNA at air/water interface

The miscibility of poly(D,L-lactide-co-glycolide) (PLG) with three amphiphilic molecules and the interaction of the PLG/surfactant mixtures with DNA at air/water interface are investigated by pi-A isotherms, Brewster angle microscopy (BAM) and atomic force microscopy (AFM) techniques. The pi-A isotherms of the PLG mixtures with cationic C(12)AzoC(6)PyBr, and C(12)AzoC(6)N(CH(3))(3)Br, are quite different from the pi-A isotherm of pure PLG on water subphase. In contrast to the case, the pi-A isotherm of PLG mixed with nonionic C(12)AzoC(6)OPy is almost identical to the pure PLG except some increasing of molecular area. Similar phenomena are observed on DNA subphase. The in situ BAM and ex situ AFM observations demonstrate that the dispersion of PLG at air/water interface becomes good when it mixes with the two cationic surfactants, whereas quite poor due to the phase separation when it mixes with the nonionic amphiphilic molecule. Based on these results we conclude that the cationic surfactants can affect the conformation change of PLG at air/water interface and figure a well miscibility with polymer whereas the nonionic amphiphilic molecule presents poor miscibility. In addition, the even mixing of the PLG and the cationic surfactants is favorable for the adsorption to DNA more effectively.     

Photoreversible DNA condensation using light-responsive surfactants

A means to control DNA compaction with light illumination has been developed using the interaction of DNA with a photoresponsive cationic surfactant. The surfactant undergoes a reversible photoisomerization upon exposure to visible (trans isomer, more hydrophobic) or UV (cis isomer, more hydrophilic) light. As a result, surfactant binding to DNA and the resulting DNA condensation can be tuned with light. Dynamic light scattering (DLS) measurements were used to follow lambda-DNA compaction from the elongated-coil to the compact globular form as a function of surfactant addition and light illumination. The results reveal that compaction occurs at a surfactant-to-DNA base pair ratio of approximately 7 under visible light, while no compaction is observed up to a ratio of 31 under UV light. Upon compaction, the measured diffusion coefficient increases from a value of 0.6 x 10(-8) cm2/s (elongated coil with an end-to-end distance of 1.27 microm) to a value of 1.7 x 10(-8) cm2/s (compact globule with a hydrodynamic radius of 120 nm). Moreover, the light-scattering results demonstrate that the compaction process is completely photoreversible. Fluorescence microscopy with T4-DNA was used to further confirm the light-scattering results, allowing single-molecule detection of the light-controlled coil-to-globule transition. These structural studies were combined with absorbance and fluorescence spectroscopy of crystal violet in order to elucidate the binding mechanism of the photosurfactant to DNA. The results indicate that both electrostatic and hydrophobic forces are important in the compaction process. Finally, a DNA-photosurfactant-water phase diagram was constructed to examine the effects of both DNA and surfactant concentration on DNA compaction. The results reveal that precipitation, which occurs during the latter stages of condensation, can also be reversibly controlled with light illumination. The combined results clearly show the ability to control the interaction between DNA and the complexing agent and, therefore, DNA condensation with light.     

Spectrofluorimetric study on the inclusion interaction between lomefloxacin and p-sulfonated calix[4]arene and its analytical application

The characteristics of host-guest complexation between p-sulfonated calix[4]arene (SC4A) and lomefloxacin (LMFX) were investigated by fluorescence spectrometry. A 1:1 stoichiometry for the complexation was established and an association constant of 6.48x10(4) l mol-1 at 25 degrees C was calculated by applying a deduced equation. The interaction mechanism of the inclusion complex was discussed and the various factors affecting the inclusion process were examined in detail. It was found that an appropriate amount of cationic surfactant cetyltrimethylammonium bromide (CTAB) can remarkably enhance the fluorescence intensity of the supramolecular complex system. Based on the obtained results, a novel sensitive spectrofluorimetric method for the determination of lomefloxacin based on supramolecular complex was developed with a linear range of 0.01-3.0 microg ml-1 and a detection limit of 0.008 microg ml-1, for the first time. The method was applied for the determination of lomefloxacin in pharmaceutical preparations successfully.     

DNA condensation induced by cationic surfactant: a viscosimetry and dynamic light scattering study

The compaction of DNA induced by two simple amphiphiles, cetyltrimethylammonium bromide [CTAB] and dodecyldimethylamine oxide [DDAO], has been investigated by means of combined viscosity and dynamic light scattering measurements, to demonstrate the formation of soluble DNA/surfactant complexes, undergoing a coil-globule transition, upon the increase of the amphiphile concentration. In both of the two systems investigated, the complexation process reaches a maximum for a value of the surfactant to DNA phosphate groups molar ratio of about X = 1. Below this critical concentration, the coil and the globule state coexist in the solution, as clearly shown by the bimodal size distribution obtained from the light scattering intensity correlation functions. Some suggestions are given to support a molecular mechanism responsible for the complex formation, both in the case of a cationic surfactant (CTAB) and of a pH-dependent neutral or cationic amphiphile (DDAO), where the hydrophobic interactions play an important role.     

Molecular mechanism and thermodynamics study of plasmid DNA and cationic surfactants interactions

The molecular mechanism and thermodynamics of the interactions between plasmid DNA and cationic surfactants were investigated by isothermal titration calorimetry (ITC), dynamic light scattering, surface tension measurements, and UV spectroscopy. The cationic surfactants studied include benzyldimethyldodecylammonium chloride, benzyldimethyltetradecylammonium chloride, cetylpyridinium chloride, and cetyltrimethylammonium chloride. The results indicate a critical aggregation concentration (cac) of a surfactant: above the cac the surfactant forms aggregates with plasmid DNA; below the cac, however, there is no detectable interaction between DNA and surfactant. Surfactants with longer hydrocarbon chains have smaller cac, indicating that hydrophobic interaction plays a key role in DNA-surfactant complexation. Moreover, an increase in ionic strength (I) increases the cac but decreases the critical micellization concentration (cmc). These opposite effects lead to a critical ionic strength (I(c)) at which cac = cmc; when I < I(c), cac < cmc; when I > I(c), DNA does not form complexes with surfactant micelles. In the interaction DNA exhibits a pseudophase property as the cac is a constant over a wide range of DNA concentrations. ITC data showed that the reaction is solely driven by entropy because both deltaH(o) (approximately 2-6 kJ mol(-1)) and deltaS(o) (approximately 70-110 J K(-1) mol(-1)) have positive values. In the complex, the molar ratio of DNA phosphate to surfactant is in the range of 0.63-1.05. The reaction forms sub-micrometer-sized primary particles; those aggregate at high surfactant concentrations. Taken together, the results led to an inference that there is no interaction between surfactant monomers and DNA molecules and demonstrated that DNA-cationic surfactant interactions are mediated by the hydrophobic interactions of surfactant molecules and counterion binding of DNA phosphates to the cationic surfactant aggregates.     

DNA and surfactants in bulk and at interfaces

Recent investigations of the DNA interactions with cationic surfactants and catanionic mixtures are reviewed. Several techniques have been used such as fluorescence microscopy, dynamic light scattering, electron microscopy, and Monte Carlo simulations.

The conformational behaviour of large DNA molecules in the presence of cationic surfactant was followed by fluorescence microscopy and also by dynamic light scattering. These techniques were in good agreement and it was possible to observe a discrete transition from extended coils to collapsed globules and their coexistence for intermediate amphiphile concentrations. The dependence on the surfactant alkyl chain was also monitored by fluorescence microscopy and, as expected, lower concentrations of the more hydrophobic surfactant were required to induce DNA compaction, although an excess of positive charges was still required.

Monte Carlo simulations on the compaction of a medium size polyanion with shorter polycations were performed. The polyanion chain suffers a sudden collapse as a function of the concentration of condensing agent, and of the number of charges on the polycation molecules. Further increase in the concentration increases the degree of compaction. The compaction was found to be associated with the polycations promoting bridging between different sites of the polyanion. When the total charge of the polycations was lower than that of the polyanion, a significant translational motion of the compacting agent along the polyanion was observed, producing only a small-degree of intrachain segregation, which can explain the excess of positive charges necessary to compact DNA.

Dissociation of the DNA–cationic surfactant complexes and a concomitant release of DNA was achieved by addition of anionic surfactants. The unfolding of DNA molecules, previously compacted with cationic surfactant, was shown to be strongly dependent on the anionic surfactant chain length; lower amounts of a longer chain surfactant were needed to release DNA into solution. On the other hand, no dependence on the hydrophobicity of the compacting agent was observed. The structures of the aggregates formed by the two surfactants, after the interaction with DNA, were imaged by cryogenic transmission electron microscopy. It is possible to predict the structure of the aggregates formed by the surfactants, like vesicles, from the phase behaviour of the mixed surfactant systems.

Studies on the interactions between DNA and catanionic mixtures were also performed. It was observed that DNA does not interact with negatively charged vesicles, even though they carry positive amphiphiles; however, in the presence of positively charged vesicles, DNA molecules compact and adsorb on their surface.

Finally Monte Carlo simulations were performed on the adsorption of a polyelectrolyte on catanionic surfaces. It was observed that the mobile charges in the surface react to the presence of the polyelectrolyte enabling a strong degree of adsorption even though the membrane was globally neutral. Our observations indicate that the adsorption behaviour of the polyelectrolyte is influenced by the response given by the membrane to its presence and that the number of adsorbed beads increases drastically with the increase of flexibility of the polymer. Calculations involving polymers with three different intrinsic stiffnesses showed that the variation is non-monotonic. It was observed also that a smaller polyanion typically adsorbs more completely than the larger one, which indicates that the polarisation of the membrane becomes less facilitated as the degree of disruption increases.     

Gemini表面活性剂(12-6-12)和DNA的相互作用

应用紫外光谱、荧光探针、zeta 电位、动态光散射和凝胶电泳等方法探讨了阳离子gemini 表面活性剂C₁₂H₂₅N⁺(CH₃)₂―(CH₂)₆―(CH₃)₂N⁺C₁₂H₂₅·2Br^-(12-6-12)与DNA之间的相互作用. 研究结果表明, 与传统表面活性剂相比, 偶联表面活性剂特殊的分子结构使其与DNA的作用更强烈. DNA引导表面活性剂在其链周围形成类胶束结构, 开始形成类胶束时对应的表面活性剂临界聚集浓度(CAC)比纯表面活性剂临界胶束浓度(CMC)低两个数量级. CAC与DNA的浓度无关, 而与表面活性剂之间的疏水作用以及表面活性剂与DNA之间的静电吸引作用密切相关. Zeta 电位和凝胶电泳结果显示了DNA链所带负电荷逐渐被阳离子表面活性剂中和的过程. 借助原子力显微镜(AFM)成功观察到了松散的线团状DNA, 球状体随机地分散在DNA链上形成类似于串珠的结构、尺寸较大的球形复合物以及其由于吸附多余的表面活性剂重新带正电而被溶解得到的较小DNA/12-6-12聚集体. 圆二色(CD)光谱结果显示, 12-6-12可以诱导DNA的构象发生改变.     

Spectrofluorimetric study on the inclusion interaction between vitamin K3 with p-(p-sulfonated benzeneazo)calix[6]arene and determination of VK3

The characteristics of host-guest complexation between p-(p-sulfonated benzeneazo) calix[6]arene (SBC6A) and vitamin K3 (VK3) were investigated by fluorescence spectrometry. A 1:1 stoichiometry for the complexation was established and was verified by Job's plot. An association constant of 4.95 x 10(3)L mol(-1) at 20 degrees C was calculated by applying a deduced equation. The interaction mechanism of the inclusion complex was discussed. It was found that the fluorescence of SBC6A could be remarkably quenched by an appropriate amount of VK3 especially when non-ionic surfactant Triton X-100 existed. According to the obtained results, a novel sensitive spectrofluorimetric method for the determination of VK3 based on supramolecular complex was developed with a linear range of 5.0 x 10(-7) -3.0 x 10(-5)mol L(-1) and a detection limit of 2.0 x 10(-7)mol L(-1). The proposed method was used to determine VK3 in commercial preparations with satisfactory results.     

Evidence of higher complexes between cucurbit[7]uril and cationic surfactants

The host-guest assembly of CB7 with a series of alkyl(trimethyl)ammonium (C(n)TA(+)) surfactants of different chain lengths (n=6-18) has been studied. The complexation behaviour was investigated by NMR spectroscopy, isothermal titration calorimetry and kinetics measurements. The combined results of these techniques provided evidence for the formation of 1:1 inclusion and 2:1 external complexes in the cases of C(n)TA(+) with n=12-18. The binding constants for the 1:1 complexes are independent of the alkyl chain length of the surfactant, whereas a relationship between K(2:1) and the chain length of the surfactant was found for the 2:1 complexes.     

DNA‐Surfactant Interactions. Compaction,Condensation, Decompaction and Phase Separation

Recent investigations of the interaction between DNA and alkyltrimethylammonium bromides of various chain lengths are reviewed. Several techniques have been used such as phase map determinations, fluorescence microscopy, and electron microscopy. Dissociation of the DNA‐surfactant complexes, by the addition of anionic surfactant, has received special attention. Precipitation maps for DNA‐cationic surfactant systems were evaluated by turbidimetry for different salt concentrations, temperatures and surfactant chain lengths. Single‐stranded DNA molecules precipitate at lower surfactant concentrations than double‐helix ones. It was also observed that these systems precipitate for very low concentrations of both DNA and surfactant, and that the extension of the two‐phase region increases for longer chain surfactants; these observations correlate well with fluorescence microscopy results, monitoring the system at a single molecule level. Dissociation of the DNA‐cationic surfactant complexes and a concomitant release of DNA was achieved by addition of anionic surfactants. The unfolding of DNA molecules, previously compacted with cationic surfactant, was shown to be strongly dependent on the anionic surfactant chain length; lower amounts of a longer chain surfactant were needed to release DNA into solution. On the other hand, no dependence on the hydrophobicity of the compacting agent was observed. The structures of the aggregates formed by the two surfactants, after the interaction with DNA, were imaged by cryogenic transmission electron microscopy. It is possible to predict the structure of the aggregates formed by the surfactants, like vesicles, from the phase behaviour of the mixed surfactant systems. The compaction of a medium size polyanion with shorter polycations was furthermore studied by means of Monte Carlo simulations. The polyanion chain suffers a sudden collapse as a function of the condensing agent concentration and of the number of charges on the molecules. Further increase of the concentration gives an increase of the degree of compaction. The compaction was found to be associated with the polycations promoting bridging between different sites of the polyanion. When the total charge of the polycations was lower than that of the polyanion, a significant translational motion of the compacting agent along the polyanion was observed, producing only a small‐degree of intrachain segregation. However, complete charge neutralization was not a prerequisite to achieve compacted forms.     

Photosensitive Surfactants with Various Hydrophobic Tail Lengths for the Photocontrol of Genomic DNA Conformation with Improved Efficiency

We report the synthesis and characterisation of photosensitive cationic surfactants with various hydrophobic tail lengths. These molecules, called AzoCx, are used as photosensitive nucleic acid binders (pNABs) and are applied to the photocontrol of DNA conformation. All these molecules induce DNA compaction in a photodependent way, originating in the photodependent polarity of their hydrophobic tails. We show that increasing hydrophobicity strongly enhances the compaction efficiencies of these molecules, but reduces the possibility of reversible photocontrol of a DNA conformation. Optimal performance was achieved with AzoC5, which allowed reversible control of DNA conformation with light at a concentration seven times smaller than previously reported.     

Thermodynamics of the molecular and chiral recognition of cycloalkanols and camphor by modified beta-cyclodextrins possessing simple aromatic tethers

The complex stability constants (K(S)) and thermodynamic parameters (DeltaG degrees, DeltaH degrees, and TDeltaS degrees ) for 1:1 inclusion complexation of beta-cyclodextrin (beta-CD) derivatives, 6-O-phenyl-beta-CD (2) 6-O-(4-formyl-phenyl)-beta-CD (3), 6-O-(4-nitrophenyl)-beta-CD (4), 6-O-(4-bromophenyl)-beta-CD (5), 6-O-(4-chlorophenyl)]-beta-CD (6), and 6-O-(4-hydroxybenzoyl)-beta-CD (7) with representative guest molecules, cyclic alcohols (cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol), (+/-)-borneol, and (+/-)-camphor, have been determined by means of titration microcalorimetry in an aqueous phosphate buffer solution (pH = 7.20) at 298.15 K. The results obtained indicate that the introduction to beta-CD of an aromatic ring bearing different substituent groups significantly enhances the molecular binding ability and moderately alters the chiral discrimination ability for the guests examined here, displaying the highest enantioselectivity of up to 4.01 for the inclusion complexation of 6 with (+/-)-camphor. The enhanced molecular/chiral discrimination ability caused by derivatization is attributed solely to increased positive entropy changes due to the expanding hydrophobic interaction and desolvation effects. The binding modes of host-guest interactions derived from ROESY spectroscopy data show that the resulting complex of 4 and (+)-borneol possesses better induced-fit interaction as compared to (-)-borneol, which is responsible for the enhanced molecular/chiral recognition ability.     

Interaction between tetramethylcucurbit[6]uril and some pyridine derivates

Interaction between tetramethylcucurbit[6]uril (TMeQ[6], host) with hydrochloride salts of 2-phenylpridine (G1), 2-benzylpyridine (G2), and 4-benzylpyridine (G3) (guests) have been investigated by using 1H NMR spectroscopy and electronic absorption spectroscopy and theoretical calculations. The 1H NMR spectra analysis established an interaction model in which the host selectively included the phenyl moiety of the HCl salt of the above three guests, and formed inclusion complexes with a host-guest ratio of 1:1. Absorption spectrophotometric analysis allowed quantitative measurement of the stability of these host-guest inclusion complexes. Particularly, we have established a competitive interaction in which one host-guest inclusion complex pair is much more stable than another host-guest inclusion complex pair. The stability constants for the three host-guest inclusion complexes of TMeQ[6]-G1, TMeQ[6]-G2, and TMeQ[6]-G3 are approximately 2x10(6), 60.7, and 19.9 mol-1.L, respectively. To understand how subtle differences in the structure of the title guests lead to a significant difference in the stability of the corresponding host-guest inclusion complexes with the TMeQ[6], ab initio theoretical calculations have been performed, not only for the gas phase but also the solution phase (water as solvent) in all cases. The calculation results revealed that when the phenyl moiety of the three pyridine derivate guests was included, the host-guest complexation reached the minimum, and the corresponding energy differences for the formation of the title host-guest inclusion complexes are qualitatively consistent with the experimental results.     

Highly photoresponsive monolayer-protected gold clusters by self-assembly of a cyclodextrin-azobenzene-derived supramolecular complex

Reversibly-photoswitchable gold nanoparticles containing azobenzene and exhibiting a light response "virtually identical" to that of the free chromophore were achieved by self-assembling a host-guest inclusion complex between alpha-cyclodextrin and an azobenzene-terminated alkanethiol in an aqueous medium.     

Enhancement of DNA compaction by negatively charged nanoparticles: effect of nanoparticle size and surfactant chain length

We study the compaction of genomic DNA by a series of alkyltrimethylammonium bromide surfactants having different hydrocarbon chain lengths n: dodecyl-(DTAB, n=12), tetradecyl-(TTAB, n=14) and hexadecyl-(CTAB, n=16), in the absence and in the presence of negatively charged silica nanoparticles (NPs) with a diameter in the range 15-100 nm. We show that NPs greatly enhance the ability of all cationic surfactants to induce DNA compaction and that this enhancement increases with an increase in NP diameter. In the absence of NP, the ability of cationic surfactants to induce DNA compaction increases with an increase in n. Conversely, in the presence of NPs, the enhancement of DNA compaction increases with a decrease in n. Therefore, although CTAB is the most efficient surfactant to compact DNA, maximal enhancement by NPs is obtained for the largest NP diameter (here, 100 nm) and the smallest surfactant chain length (here, DTAB). We suggest a mechanism where the preaggregation of surfactants on NP surface mediated by electrostatic interactions promotes cooperative binding to DNA and thus enhances the ability of surfactants to compact DNA. We show that the amplitude of enhancement is correlated with the difference between the surfactant concentration corresponding to aggregation on DNA alone and that corresponding to the onset of adsorption on nanoparticles.     

DNA compaction onto hydrophobic surfaces by different cationic surfactants

DNA compaction by alkyltrimethylammonium surfactants at hydrophobized silica surfaces and the effect of the counterion, as well as the hydrocarbon chain length, was investigated by in situ null-ellipsometry. In addition, DNA compaction in the presence of a gemini surfactant, hexyl-alpha,omega-bis(dodecyldimethylammonium bromide), was studied. The type of cationic amphiphile used was found not to have a pronounced effect on the mixed DNA-cationic surfactant adsorbed layer thickness, although the surface concentration excess for the mixed layers seemed to follow the same trend as that for DNA-free surfactant layers. Interestingly, it was also found that the stability of the mixed adsorbed layer largely depends on the cationic surfactant used.     

基于β-环糊精与偶氮苯衍生物的基因传递体系构筑

通过β-环糊精修饰聚乙烯亚胺(HPEI-CDs)与偶氮苯修饰聚乙二醇(Azo-PEG)的主客体作用,制备了HPEI-CDs/Azo-PEG/DNA自组装体,并对其生理盐溶液稳定性、粒径形貌及光控特性进行了研究。结果表明,对比HPEI-CDs/DNA自组装体,PEG的引入显著提高了其生理盐稳定性,借助PEG壳层的电荷屏蔽和CD氢键的协同作用,自组装体表面电位仅为+3mV,粒径分布均匀,呈现球形结构。在365nm波长光照下,HPEI-CDs/Azo-PEG/DNA的表面电位迅速增加,随着光照时间的延长,其ζ电位最终增大到与HPEI-CDs/DNA相近水平,这表明偶氮苯(Azo)空间结构发生转变,PEG层成功从组装体脱离。     

Effect of headgroup on DNA-cationic surfactant interactions

The interaction behavior of DNA with different types of hydroxylated cationic surfactants has been studied. Attention was directed to how the introduction of hydroxyl substituents at the headgroup of the cationic surfactants affects the compaction of DNA. The DNA-cationic surfactant interaction was investigated at different charge ratios by several methods like UV melting, ethidium bromide exclusion, and gel electrophoresis. Studies show that there is a discrete transition in the DNA chain from extended coils (free chain) to a compact form and that this transition does not depend substantially on the architecture of the headgroup. However, the accessibility of DNA to ethidium bromide is preserved to a significantly larger extent for the more hydrophilic surfactants. This was discussed in terms of surfactant packing. Observations are interpreted to reflect that the surfactants with more substituents have a larger headgroup and therefore form smaller micellar aggregates; these higher curvature aggregates lead to a less efficient, "patch-like" coverage of DNA. The more hydrophilic surfactants also presented a significantly lower cytotoxicity, which is important for biotechnological applications.     

Identification of face-to-face inclusion complex formation of cyclodextrin bearing an azobenzene group by electrospray ionization mass spectrometry

The solution-based self-assembly of native and permethylated cyclodextrins (CD) bearing an azobenzene substituent has been studied by electrospray ionization mass spectrometry (ESI-MS). The results revealed that the CD molecules form either a contact or a face-to-face inclusion complex depending on the interaction of their substituents. The mass spectrometric study further demonstrated that the inclusion complex is formed through the interaction between the host CD cavity and the guest-substituent and that a contact complex is formed by hydrogen-bonding of the hydroxyl functions at the rims of the CD molecule. We also found that in order to detect the face-to-face inclusion complex by ESI-MS, the following conditions have to be met: (1) The CD moieties must be permethylated to avoid formation of the contact complex, (2) they must possess a guest-substituent of suitable length, such as an azobenzene moiety, and (3) they must possess an NH(2) or OH group at the substituent terminals for protonation and for detection as cations by ESI-MS. Formation of the inclusion complexes was further confirmed by the synthesis of a capped inclusion dimer and a capped monomer. Collision-induced dissociation (CID) experiments have been carried out for the contact, the host-guest inclusion, and the capped inclusion dimers, and the contact complexes are found to be the most stable among them.