Interdigitation Of Alkyl Chains Research Articles

Direct Observation of Alkyl Chain Interdigitation in Conjugated Polyquarterthiophene Self‐Organized on Graphite Surfaces

AbstractA solution processible polymer—poly(3,3‴‐didodecylquaterthiophene) (PQT‐12) is investigated at the liquid/solid interface using the scanning tunneling microscopy (STM). Two‐dimensional ordered films made up of self‐assembled domains, with dimensions of 100 nm × 50 nm adsorbed on highly oriented pyrolytic graphite (HOPG) were formed. These domains consist of parallel lamellar polymer chains, with the alkyl chains forming interdigitated structures, along with U‐shaped and closed ring segments of the polymer chains. A polymer chain packing model is proposed herein, which attempts to propose a correlation between the packing of long chains and charge mobilities. These STM results could help in understanding the relationship between the extended conjugation and molecular organization of the PQT‐12 chains.magnified image

Investigation into liquid crystalline smectic-C*subphase stability using chiral and achiral dopants

In this paper we investigate the influence of chiral and achiral dopants on a chiral smectic liquid crystal material, which exhibits a rich phase sequence, including the antiferroelectric phase and the three-layer intermediate smectic (SmC*FI1) phase. Using polarized optical microscopy, differential scanning calorimetry, and x-ray diffraction we find that small amounts of achiral dopant have the ability to significantly broaden the SmC*FI1 phase, whereas an oppositely-handed dopant (otherwise identical to the host material) destabilizes the phase. This work clearly indicates that bulk chirality strongly influences SmC*FI1 phase formation and that steric effects also play an important role. Interestingly, addition of the shorter achiral molecule (8CB) was observed to increase the smectic layer spacing, most likely by suppressing interdigitation of alkyl chains between adjacent smectic layers. Control of the SmC*FI1 phase width using mixtures in this way is clearly important for effective phase characterization, and could potentially lead to commercially viable materials with a stable SmC*FI1 phase over a large temperature range.

Synthesis of Dehydrobenzo[18]annulene Derivatives and Formation of Self-Assembled Monolayers: Implications of Core Size on Alkyl Chain Interdigitation

The synthesis of a series of dodecadehydrotribenzo[18]annulene ([18]DBA) derivatives is reported, together with their steady-state absorption and fluorescence properties. The main focus, though, is on the self-assembly of these compounds at the liquid-solid interface as investigated with scanning tunneling microscopy (STM), highlighting the effect of alkyl chain orientation and alkyl chain length on the molecular ordering. Owing to the large triangular pi-electron system of the [18]DBAs, two different types of alkyl chain orientation are observed. The observed changes in the monolayer networks upon elongation of the alkyl chains are attributed to the increased van der Waals interactions between molecules and substrate. The effect of the core size on the alkyl chain orientation and, as a result, the monolayer structure is discussed in relation to the results obtained previously for triangularly-shaped dehydrobenzo [12]annulene ([12]DBA) derivatives and triphenylene derivatives. A guideline for substituent spacing allowing control of molecular alignment for large planar pi-electron systems utilizing directional alkyl chain interdigitation is also discussed.

Self-assembly of bipyridine derivatives at solid/liquid interface: Effects of the number of peripheral alkyl chains and metal coordination on the two-dimensional structures

Self-assembled two-dimensional structures of bipyridine derivatives ( bpys) were observed by scanning tunneling microscopy at HOPG/1-phenyloctane interface. Two types of bpy molecules were used in this study. One is bpy 1, which has two alkyl chains on each end, and the other is bpy 2, which holds single alkyl chain on each end. The bpy 1 formed a monolayer, which is composed of a bent molecular structure with interdigitated alkyl chains. In the case of bpy 2, the structure exhibited pm plane group symmetry. A pair of molecules formed a columnar structure, and the alkyl chains aligned in a tail-to-tail orientation. Metal coordination of both bpy samples increased the intermolecular distance at the π-conjugated units, resulting in the formation of lamellar structure. Although both bpys showed straight form, the alkyl chain unit of complexed bpy 1 was not interdigitated, whereas that of complexed bpy 2 was interdigitated. Thus, the metal–metal distances could be tuned by changing the number of alkyl chain unit.

Variable temperature Hirshfeld surface analysis of interdigitated calix[6]arene bearing O-alkyl C18 linear chains

Calix[6]arene bearing linear C18 alkyl chains crystallises in the inverted double cone conformation with three chains on either side forming a side of a hexagon in an hexagonal close packed array of interdigitated alkyl chains. The nature of the interactions has been probed over different temperatures using Hirshfeld surfaces.

Elasticity and Phase Behavior of DPPC Membrane Modulated by Cholesterol, Ergosterol, and Ethanol

Giant vesicles formed of 1,2-dipalmitoylphosphatidylcholine (DPPC) and sterols (cholesterol or ergosterol) in water and water/ethanol solutions have been used to examine the effect of sterol composition and ethanol concentration on the area compressibility modulus ( K a), overall mechanical behavior, vesicle morphology, and induction of lipid alkyl chain interdigitation. Our results from micropipette aspiration suggest that cholesterol and ergosterol impact the order and microstructure of the gel (L β ′) phase DPPC membrane. At low concentration (10–15 mol%) these sterols disrupt the long-range lateral order and fluidize the membrane ( K a ∼ 300 mN/m). Then at 18 mol%, these sterols participate in the formation of a continuous cohesive liquid-ordered (L o) phase with a sterol-dependent membrane density ( K a ∼ 750 for DPPC/ergosterol and K a ∼ 1100 mN/m for DPPC/cholesterol). Finally at ∼40 mol% both cholesterol and ergosterol impart similar condensation to the membrane ( K a ∼ 1200 mN/m). Introduction of ethanol (5–25 vol.) results in drops in the magnitude of K a, which can be substantial, and sometimes individual vesicles with lowered K a reveal two slopes of tension versus apparent area strain. We postulate that this behavior represents disruption of lipid-sterol intermolecular interactions and therefore the membrane becomes interdigitation prone. We find that for DPPC vesicles with sterol concentrations of 20–25 mol%, significantly more ethanol is required to induce interdigitation compared to pure DPPC vesicles; ∼7 vol. more for ergosterol and ∼10 vol. more for cholesterol. For lower sterol concentrations (10–15 mol%), interdigitation is offset, but by <5 vol.. These data support the idea that ergosterol and cholesterol do enhance survivability for cells exposed to high concentrations of ethanol and provide evidence that the appearance of the interdigitated (L β I) phase bilayer is a major factor in the disruption of cellular activity, which typically occurs between ∼12 and ∼16 vol. ethanol in yeast fermentations. We summarize our findings by producing, for the first time, “elasticity/phase diagrams” over a wide range of sterol (cholesterol and ergosterol) and ethanol concentrations.

Structural characterization of dimethyldioctadecylammonium-encapsulated terbium-substituted heteropolyoxotungatates in solid, Langmuir–Blodgett and solvent-casting films

We synthesized a series of dimethyldioctadecylammonium (DODA)-encapsulated terbium-substituted heteropolyoxotungstates: (DODA) 11[Tb(PW 11O 39) 2]·4H 2O (SEC-1), (DODA) 13[Tb(SiW 11O 39) 2]·5H 2O (SEC-2) and (DODA) 13H 2[Tb(BW 11O 39) 2]·11H 2O (SEC-3). Their structures were characterized by elemental analysis, thermogravimetric analysis (TGA), X-ray diffraction, transmission, reflection–absorption (RA) and polarized Fourier transform infrared (FT-IR) spectroscopy. These hybrids can form stable Langmuir monolayers at air–water interface and the molecular areas at collapsed point increase according to the order of SEC-1 < SEC-2 ≈ SEC-3, which corresponds to the numbers of DODA adsorbed on the surfaces of POM-1, POM-2 and POM-3, respectively. The polyoxometalates (POMs) in surfactant-encapsulated clusters (SECs) are organized with their long-axis parallel to the substrate in Langmuir–Blodgett (LB) films, as well as in casting films. DODA alkyl chains are well-ordered in solid and oriented to the normal of substrate with tilting angles of 29° and 32° in LB and casting films, respectively. The calculated layer distances of the LB and casting films according to the IR spectra are well consistent with the experimental data obtained by their X-ray diffraction. In addition, the short layer spacing in casting film is proposed to derive from interdigitation of DODA alkyl chains comparing with the long one in LB film. These layer spacings are in good agreement with the two structures in bulk solid, respectively. Furthermore, we found that the percentage of the interdigitiation structure in solid is related to the numbers of DODA covered on the POM surface.

Solid-state phase behaviour of dodecylglycosides

The solid-state phase behaviour of lyophilised n-dodecyl-β- d-glucoside (β-C 12G 1), n-dodecyl-β- d-maltoside (β-C 12G 2) and n-dodecyl-β- d-maltotrioside (β-C 12G 3) has been investigated by differential scanning calorimetry (DSC) and X-ray techniques. For β-C 12G 1, lyophilisation results in a formation of a crystalline anhydrate. The lamellar spacing (37 Å) is consistent with an alkyl chain packing in which the chains are not interdigitated. At 80 °C, the material melts into a lamellar liquid crystal with a lamellar spacing of 32 Å, which suggests that the non-interdigitated chain packing of the crystalline state is retained in the liquid crystal. In contrast, lyophilisation of β-C 12G 2 and β-C 12G 3 results in the formation of a glassy state, best described as a frozen version of the lamellar liquid crystal. For β-C 12G 2, the lamellar spacing in the glass and liquid crystal suggests interdigitation of the alkyl chains. The glass transition temperature was found to be 65 °C for β-C 12G 2 and 100 °C for β-C 12G 3, which compares favourably with the glass transition of the parent carbohydrates. A second crystalline modification of β-C 12G 1 was prepared by precipitation from an aqueous solution at temperatures below the Krafft point (38 °C). For this modification, the lamellar distance (24 Å) is consistent with interdigitated alkyl chains. At 50 °C, the crystalline material melts into a liquid crystalline phase. The material also readily loses water and rapidly re-crystallises to the anhydrate. The amount of water lost upon drying is consistent with the idea that the material is a monohydrate of β-C 12G 1. The drying and re-crystallisation processes give rise to ‘pre-transitions’ in the DSC thermograms and illustrate the importance of careful control of water in any analysis of the phase behaviour of alkylglycosides.

Methods of preparation of novel composites of poly(ϵ‐caprolactone) and a modified Mg/Al hydrotalcite

Abstract12‐Hydroxydodecanoate (HD) anions were intercalated, via an ion‐exchange procedure, onto a Mg/Al hydrotalcite‐like compound with the formula [Mg0.65Al0.35(OH)2](NO3)0.35·0.56H2O. The obtained intercalate, characterized by chemical and thermal analyses, X‐ray powder diffraction, and Fourier transform infrared spectroscopy, had the formula [Mg0.65Al0.35(OH)2](NO3)0.08(HD)0.28·0.56H2O and an interlayer distance of 2.27 nm. Structural considerations indicated that the charge‐balancing HO(CH2)11COO− anions were accommodated in the interlayer region as a monofilm of partially interdigitated alkyl chains in a trans planar conformation and bearing the alcoholic group. The organically modified hydrotalcite was used to prepare novel composites based on poly(ϵ‐caprolactone) (PCL) with different procedures: (1) solvent casting, (2) ring‐opening polymerization of ϵ‐caprolactone, and (3) blending of precursors consisting of a PCL intercalated oligomer with a high‐molecular‐weight PCL. Microcomposites were obtained by the solvent casting of a mixture of a high‐molecular‐weight PCL and the modified hydrotalcite. The ring‐opening polymerization of ϵ‐caprolactone initiated by the OH groups of the alkyl chains intercalated in the hydrotalcite led to hybrid materials in which a low‐molecular‐weight PCL was in part intercalated into the modified hydrotalcite. Nanocomposites containing exfoliated hydrotalcite were obtained through the mixing, in different weight ratios, of hybrids consisting of PCL oligomers and modified hydrotalcite with a commercial high‐molecular‐weight PCL. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2281–2290, 2005

Amide−Ligand Hydrogen Bonding in Reverse Micelles

One approach to modeling the second coordination shell of metalloproteins is to pair amide-containing counterions with metal complexes to form hydrogen bonds in the solid state. In a more general approach, we have designed a surfactant counterion that can sustain hydrogen bonding interactions with metal complexes in solution. The surfactant is cationic and incorporates an amide as part of its headgroup to form hydrogen. The surfactant forms hydrogen bonding reverse micelles that accommodate anionic metal complexes in their polar core. In reverse micelles containing an iron(III) hexacyanide complex, spectroscopic evidence suggests that the anion is confined to the polar core region in solution. Single-crystal X-ray diffraction data on the surfactant ferricyanide system reveals a layered structure with interdigitated alkyl chains and an extensive network of hydrogen bonds that link amide groups to the cyanide ligands and to neighboring headgroups.

Hydrogen bonding, alkyl chain crystallization and constitutional isomerism in solid-state self-assembly of dodecyloxyisophthalic acid complexes

Self-assembly of the molecular complexes of O-alkoxy isophthalic acid (5-C12 and 4-C12) with 4,4′-bipyridine (bipy) in the crystal lattice is described. Complexes 5-C12ISA·bipy and 4-C12ISA·bipy exhibit 3-D supramolecular structures through and interplay of H-bonding, alkyl chain interdigitation, π⋯π and C–H⋯π interactions. The former forms a unique triple helix which further assembles into a 2D network stabilized via π⋯π stacking interactions. The latter forms hydrogen bonded supramolecular sheets.

Lipid-Based Nanotubes as Functional Architectures with Embedded Fluorescence and Recognition Capabilities

A limited combinatorial strategy was used to synthesize a small library of soft lipid-based materials ranging from structurally unordered fibers to highly uniform nanotubes. The latter nanotubes are comprised of a bilayer structure with interdigitated alkyl chains associated through hydrophobic interactions. These tubes contain accessible 2,6-diaminopyridine linkers that can interact with thymidine and related nucleosides through multipoint hydrogen bonding, thereby quenching the intrinsic fluorescence of the aromatic linker. These results are the first example of a systematic strategy to design functional lipid nanotubes with precise structural and functional features.

Surfactant-encapsulated polyoxometalloeuropate: polarized Eu 3+ emission in the highly ordered self-organizing film

An organic/inorganic composite, (DODA) 9EuW 10O 36·9H 2O, can form a highly ordered self-organizing film with a layered structure and almost fully interdigitated alkyl chains at solid supports. EuW 10O 36 9− is deduced to be oriented in its self-organizing film, resulting in its polarized emission, which offers an accessible approach to fabricating the functional thin films containing polyoxometalates.

Switching of spin states triggered by a phase transition: spin-crossover properties of self-assembled iron(II) complexes with alkyl-tethered triazole ligands.

Iron(II) complexes of triazole derivatives having two C12 and C16 long alkyl chains, (C12trz)FeII and (C16trz)FeII, serve as novel spin-crossover materials, which display a spin-state transition in response to a phase transition. In contrast, a triazole complex with two C8 alkyl chains ((C8trz)FeII) exhibits only a poor response. EXAFS and XRD analyses of (C16trz)FeII indicate an interdigitating self-assembled structure of polynuclear iron(II) species. According to DSC, VT-IR, and VT-XRD profiles, the spin-state transition is triggered by melting of the interdigitating alkyl chains, which is likely responsible for the "lock-and-release" feature of the spin state. By virtue of the thermoreversibility of the phase transition, the spin crossover could be repeated without deterioration.

Application of Complementary Experimental Techniques to Characterization of the Phase Behavior of [C16mim][PF6] and [C14mim][PF6

A range of analytical techniques (DSC, conductivity measurement, Raman spectroscopy, small- and wide-angle X-ray diffraction (S-WAXS), quasi-elastic neutron scattering (QENS), and single-crystal X-ray diffraction) are applied to the characterization of the phase behavior of the low-melting-point liquid crystalline salts 1-hexadecyl-3-methylimidazolium hexafluorophosphate ([C16mim][PF6]) and 1-methyl-3-tetradecylimidazolium hexafluorophosphate [C14mim][PF6]. This is the first time that QENS has been applied to the structural analysis of this type of ionic liquid crystal. For the first time in this class of salts, a low-temperature phase transition is identified, which is assigned to a crystal−crystal transition. Conductivity and QENS data for [C16mim][PF6] suggest that the higher-temperature crystalline phase (CII) has greatly increased freedom in its long alkyl chain and anion than the lower-temperature crystalline phase (CI). This conclusion is supported by single-crystal X-ray diffraction results for [C14mim][PF6]. In both crystalline phases, as well as in the higher-temperature mesophase, the structure maintains a monodispersed layer structure with interdigitated alkyl chains. The structure of the mesophase is confirmed as smectic A by the S-WAXS and Raman spectroscopy results. Detailed analysis suggests that in this phase the alkyl chains undergo complete conformational melting.

The influence of short strong hydrogen bonding on the structure and the physicochemical properties of alkyl-N-iminodiacetic acids in solid state and aqueous systems.

Alkyl-N-iminodiacetic acids with varying alkyl chain lengths have been prepared and characterized with respect to structure, acidic properties, and ability to form aggregates in water. The alkyl-N-iminodiacetic acids are the group of ligands with the lowest molecule weight which can be characterized as chelating surfactants, compounds with surface chemical properties which at the same time have a high ability to bind metal ions. The solid alkyl-N-iminodiacetic acids have a unique structure with neutral zwitterionic units linked together to polymer chains through a short strong hydrogen bond, d(O(-H)...O) approximately 2.46 A, and where the nu(O-H) stretching vibration at ca. 720 cm(-1) supports the presence of such a hydrogen bond. The polymer chains are cross-linked together to bilayers through relatively strong hydrogen bonds between ammonium and carboxylate groups, and where the parallel alkyl groups are interdigitating each other; the bilayer surface consists of hydrophilic iminodiacetic acid groups. The acidic properties of monomeric alkyl-N-iminodiacetic acids in water are in the expected ranges with pK(a) values of about 1.7, 2.3, and 10.3. n-Octadecyl-N-iminodiacetic acid, present as aggregates in water, displays very acidic properties of the first proton, and a substantially weakened acidity of the second proton, pK(a2) = 5.5-7.5, depending on ionic strength, and pK(a3) = 9.5-10.5. This pattern of the acidic constants strongly indicates that the polymer structure with short strong hydrogen bonds is maintained in the aggregates and that such bonds can exist in aqueous systems if they are supported by a strong and rigid backbone structure, as the bilayers of well-organized long interdigitating alkyl chains in the studied systems. Hydrogenbis(methyl-N-iminodiacetic acid) perchlorate precipitates from perchloric acidic solutions of methyl-N-iminodiacetic acid. The structure is built up of dimers of zwitterionic methyl-N-iminodiacetic acid units linked together by an extra proton in a short strong hydrogen bond, d(O(-H)...O) approximately 2.456(6) A, and nu(O-H) = 789 cm(-1).

Monohelical self-assembly of 5-alkoxyisophthalamides

The solid state self-assembly of 5-alkoxyisophthalamides (1 and 2) shows monohelical structures formed through an interplay of intermolecular hydrogen bonds, interdigitation of alkyl chains, a large head-to-tail volume ratio and 1,3,5-functionalization of the central benzene ring.

Aromatic Side Chain-Functionalized Long Chain Acid Salts: Structural Factors Influencing Their Lyotropic Liquid-Crystalline Behavior

The structural factors influencing the self-assembly of aromatic side chain functionalized long chain acid salts into lyotropic liquid crystal (LLC) phases were examined. Two sets of amphiphiles were synthesized containing two different ionic headgroups (i.e., sodium carboxylate and sodium sulfonate) and four different aromatic side chains (i.e., 4-styryl ether, 4-ethylphenyl ether, 1-naphthyl ether, and 4-phenylazophenyl ether) positioned at various locations along the amphiphile backbone. Systematic variation of the type of the aromatic side chain and its relative position on the amphiphile as a function of the two headgroups revealed that the position of the side chain on the amphiphile is the most important structural factor influencing the type and stability of the LLC phases formed. The nature of the aromatic side chain and the nature of the anionic headgroup play much more subtle roles in the LLC behavior of this particular amphiphile structural motif. Noncovalent aromatic−aromatic interactions are known to play important roles in the aggregation behavior of amphiphiles containing aromatic units along the alkyl chains; however, such interactions could not be detected spectroscopically in the LLC phases of our aromatic side chain amphiphiles. We speculate that the differences in alkyl chain interdigitation and packing efficiency arising from having the aromatic unit as a side chain rather than along the alkyl chains are responsible for this discrepancy. Control experiments with aliphatic ether side chain amphiphiles also corroborate the fact that aromatic interactions do not play a significant role in the aggregation behavior of these side chain amphiphiles. Side chain amphiphiles lacking an aromatic unit are still able to form the inverted hexagonal LLC phase, so long as the extent of branching and volume of the aliphatic side chain are sufficient.

Helical polymeric network of [ZnCl 2(4′-aryl-4,2′-6′,4″-terpyridine)] n

The coordination polymer formed by the addition of zinc(II)chloride to 4′-(4‴-octyloxyphenyl)-4,2′-6′,4″-terpyridine (readily prepared using green chemistry principles) has been structurally authenticated using single crystal X-ray diffraction and microanalysis techniques. The polymeric network adopts a layered helical zigzag arrangement about a distorted tetrahedral Zn(II) centre, forming channels of inter-digitated alkyl chains.

Liquid-Crystalline Compounds Consisting of Two Mesogenic Cores in Parallel Conformation

Behaviors and organization of novel liquid-crystalline compounds 1 and 2, which have an iminodicarbonyl moiety as a curved central junction and consist of two mesogenic units in parallel conformation, were investigated. Compound 2a showed a nematic phase which has extremely small transition enthalpy (0.045 kcal/mol) and a broad temperature range of pressure-induced nematic phase. The smectic A phase of 1b and 2b showed interdigitation of alkyl chains which originates in the molecular structure which has two cores with three alkyl chains in parallel conformation.