Polymerization of the 12-methacryloyloxydodecanoic acid and a corresponding phospholipid in monolayers at the liquid/gas interfaces

The following surface-active monomers with methacrylic group at the end of hydrophobic tail: 12-methacryloyloxydodecanoic acid (12-MAODA) and 12-(methacryloyloxydodecanoyl)-glycerophosphatidylcholine 12-MAODPC) were synthesized and investigated. Both monomers are forming monolayers at the liquid/gas interfaces with liquid-expanded and liquid-condensed states at low and high surface pressures, respectively. These monomers have been polymerized in the monolayers just by soft UV-irradiation (254 nm). Dependences of polymerization rate vs. surface pressure for both monomers have maxima (3.33^*10⁻⁴ s⁻¹ for 12-MAODPC and 4.89^*10⁻⁴ s⁻¹ for 12-MAODA) at about 8–10 mN/m. The higher polymerization rate of 12-MAODA polymerization as compared to 12-MAODPC is due to the more dense packing of the acid molecules in monolayers as compared to the lipid. Areas per monomer unit in the obtained polymeric monolayers are much smaller than those for the monomer one. The collapse pressures increase after monomer polymerization that evidences the increase of the monolayer stability in case of polymer as compared to monomer.     

New mesogens with a fluoro-substituted bent core

Ferroelectric properties in liquid crystals are no longer restricted to materials with a chiral molecular structure; ferroelectricity has been observed in a smectic phase formed by bent achiral molecules. Accordingly, two homologous series possessing a central biphenyl methane core have been synthesized, the central core having two lateral fluoro substituents. Both the series have six-ring structures and exhibit smectic mesophases of high thermal stability. The flexible biphenyl methane core imparts a slight curve to the molecules, giving them a bent shape.     

New mesogens with a fluoro-substituted bent core

Ferroelectric properties in liquid crystals are no longer restricted to materials with a chiral molecular structure; ferroelectricity has been observed in a smectic phase formed by bent achiral molecules. Accordingly, two homologous series possessing a central biphenyl methane core have been synthesized, the central core having two lateral fluoro substituents. Both the series have six-ring structures and exhibit smectic mesophases of high thermal stability. The flexible biphenyl methane core imparts a slight curve to the molecules, giving them a bent shape.     

Two crystal forms of mesogenic bis(4′‐cyanobiphenyl‐4‐yl) butanedioate

The title compound, C₃₀H₂₀N₂O₄, exhibits a nematic phase in the wide temperature range between 498.5 and 538.6 K, in spite of the short linker moiety. Two crystal forms have been found. In both forms, the molecule is centrosymmetric. Form I has a planar biphenyl group, while form II has a twisted biphenyl group with a twist angle of 34.75 (6)°. The packing modes are also different. In form I the long molecular axes are tilted with respect to each other at about 30°, while in form II the long molecular axes have an almost parallel arrangement.     

Grazing incidence X-ray diffraction studies of condensed double-chain phospholipid monolayers formed at the soft air/water interface

The use of highly brilliant synchrotron light sources in the middle of the 1980s for X-ray diffraction has revolutionized the research of condensed monolayers. Since then, monolayers gained popularity as convenient quasi two-dimensional model systems widely used in biophysics and material science. This review focuses on structures observed in one-component phospholipid monolayers used as simplified two-dimensional models of biological membranes. In a monolayer system the phase transitions can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction. Competing interactions between the different parts of the molecule are responsible for the different monolayer structures. These forces can be modified by chemical variations of the hydrophobic chain region, of the hydrophilic head group region or of the interfacial region between chains and head groups. Modifications of monolayer structures triggered by changes of the chemical structure of double-chain phospholipids are highlighted in this paper.     

Synthesis and polymerization reactions of cyclic imino ethers. VI. Polymers with biphenyl structure

A monomer of the AB‐type and a bifunctional comonomer of the AA‐type containing two 2‐oxazoline rings and a biphenyl structural unit were prepared from the corresponding carboxylic acids via their esterification and subsequent amidation with an aminoalcohol. The cyclization of an amide to 2‐oxazoline structure was achieved by treatment with thionyl chloride followed by liberation of the free base with sodium hydrocarbonate in an aqueous solution. The prepared monomers were used for the polyaddition polymerization of the AB‐type monomer having a 2‐oxazoline and phenol group bound on adjacent rings of the biphenyl structure in solution. The monomer of the AA‐type was used for AA+BB‐type polyaddition reactions with aliphatic dicarboxylic acids. Both types of polymerizations have been performed in melt and in solution. The structures of the polymers were determined, and the thermal properties of the polymers were evaluated. Liquid‐crystalline (LC) structures of the prepared polymers were observed by DSC measurements and optical microscopy. The polyaddition reactions of the monomers containing a 2‐oxazoline ring and a biphenyl unit represent a new efficient way for the preparation of a biphenyl unit containing poly(ether amide)s and poly(ester amide)s. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Multiple transmission-reflection infrared spectroscopy for high-sensitivity measurement of molecular monolayers on silicon surfaces

A new infrared spectroscopic measurement involving multiple transmissions and reflections for molecular monolayers adsorbed on silicon surfaces has been established. Compared to the well-known multiple internal reflection (MIR) method, the distinctive advantage of multiple transmission-reflection infrared spectroscopy (MTR-IR) is the convenient measurement using standard silicon wafers as samples, while in the MIR setup special fabrication of geometric shapes such as 45 degrees bevel cuts on an attenuated total reflection silicon crystal is needed. Both p- and s-polarized spectra can be obtained reproducibly with the same order of sensitivity as by the MIR spectroscopy. Optimal conditions for spectral acquisition have been obtained from theoretical calculations. The ability of this methodology to gather high quality infrared spectra of adsorbed monolayers is demonstrated and the analysis of the surface packing and molecular orientation is discussed.     

The pressure dependence of the low-frequency Raman spectra of crystalline biphenyl and p-terphenyl

Raman spectra as a function of hydrostatic pressure are presented for crystalline biphenyl and p-terphenyl. The observed changes in the low-frequency Raman spectra of crystalline biphenyl indicate that there are probably some changes in the crystal or molecular structure with increasing pressure. The Raman spectra of p-terphenyl have no evident anomalies at pressures up to 33 kbar.     

Hydrodynamic and conformational properties of cellulose valerate molecules in dilute solution

Using the methods of molecular hydrodynamics, structural-conformational studies have been performed for a number of cellulose valerate and acetovalerate samples in the molecular-mass range M = (58.1–464.3) × 10³ and with a mean degree of substitution of 182.4 with respect to valeric acid isomers. The conformations of valerate-substituted cellulose molecules are characterized by an increased local packing density of monomer units. The molecular conformations are quantitatively described in terms of the helix formed by the succession of vectors connecting glycoside oxygens of a chain. The molecular-hydrodynamic and conformational characteristics of cellulose valerate are compared with the corresponding characteristics of cellulose myristate.     

Block copolymers of polystyrene and poly(dimethyl siloxane). I. Synthesis and characterization

The block copolymers of the ABA type, poly(dimethyl siloxane-b-styrene-b-dimethyl siloxane), were synthesized by the anionic polymerization of styrene and cyclic siloxane monomer, hexamethyl cyclotrisiloxane (D₃) or octamethylcyclotetrasiloxane (D₄), with lithium or sodium biphenyl as initiator. The effect of initiator concentration, gegenion, and the polymerization temperature for styrene on molecular weight distribution (MWD) was investigated. Gel permeation chromatography (GPC) data show broader MWD of polystyrene prepared by sodium biphenyl in comparison to that produced by lithium biphenyl. The block copolymers have been characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectra. The influence of dimethylsiloxy units on thermal stability of the copolymers has also been discussed.     

The effect of halogen substitution in self-assembled monolayers of 4-mercaptobiphenyls on noble metal substrates

Self-assembled monolayers (SAMs) formed from 4'-substituted 4-mercaptobiphenyls X-(C6H4)2SH (X-BPT, with X = I, Cl, and F) on polycrystalline (111) gold and silver substrates have been characterized by synchrotron-based high-resolution X-ray photoelectron spectroscopy and angle-resolved near-edge X-ray absorption fine structure spectroscopy. The X-BPT molecules were found to form highly oriented and densely packed SAMs on both substrates, with a smaller molecular inclination in the case of Ag. The experimental data show clear evidence for the charge transfer between the 4'-substituent and biphenyl moieties with the direction and extent of the transfer depending on the electronegativity of the halogen substituent. At the same time, no direct evidence of the charge transfer between the 4'-substituent and the thiolate group was observed. However, the substitution of the 4'-hydrogen by a halogen atom seems to affect the detailed packing arrangements of the SAM constituents.     

Brewster angle microscopy: A preferential method for mesoscopic characterization of monolayers at the air/water interface

Knowledge of the mesoscopic morphology of condensed phase domains formed after the main phase transition in the two-phase coexistence region of Langmuir monolayers progressed rapidly with the development of the highly-sensitive imaging techniques, particularly by Brewster angle microscopy (BAM). Latest developments of commercial BAM instruments have been developed to a high technical level and allow upgrading to imaging ellipsometers which combine optical microscopy and ellipsometry and make the assessment of small layered structures or patterned thin films possible. A large variety of condensed phase domains different in mesoscopic sizes and shapes as well as their textural features has been observed which depend sensitively on the chemical structure of the amphiphilic monolayer and the system conditions, such as surface pressure and temperature. This unsuspected morphological variety of condensed phase domains has been proven not only in Langmuir monolayers but also in adsorbed monolayers (Gibbs monolayers), in Langmuir monolayers penetrated by dissolved surfactants or in adequate molecular recognition systems. The inner textures of domains can be explained on the basis of their geometry and the two-dimensional lattice in dependence of the tilt angle of the alkyl chains and gave rise to the development of a geometric concept on the basis of the molecular packing. New knowledge has been gained about non-equilibrium structures and their transition kinetics into the equilibrium state. Combined results obtained recently by BAM have enhanced the understanding of molecular organization in phase diagrams and binary mixtures. Recent advances in model studies about chiral discrimination effects and of the highly specific structural changes of host-monolayers by recognition of non-surface active guest-components have made progress. Semi-empirical quantum chemical methods have been used to gain insight into the role of different types of interactions involved in the main characteristics of mesoscopic length scale aggregates of mimetic systems.     

Rapulasides A and B: two novel intermolecular rearranged biiridoid glucosides from the roots of Heracleum rapula

Two novel intermolecular rearranged biiridoid glucosides, rapulasides A and B (1 and 2), have been isolated from the roots of Heracleum rapula. Their structures were identified by extensive spectral analysis especially different NMR techniques. NOESY experiment, with the help of Dreiding molecular model, was used to elucidate their relative stereochemistry. Both compounds were tested for their inhibitory effects on rabbit platelet aggregation induced by PAF, ADP, or AA, respectively. Only trends of inhibition were observed for them.     

Packing of molecules of poly-<Emphasis Type="Italic">p</Emphasis>-phenylenebenzo-bis-oxazole in crystalline structures: Calculation by the molecular mechanics method

The mutual packing of trans- and cis-stereoisomeric molecules of poly-p-phenylenebenzo-bisoxazole is calculated by the molecular mechanics method. By varying all intramolecular and intermolecular parameters, energetically favorable structures are found. Calculation is performed both for molecules with uniform rotational isomeric composition (only TRANS or CIS mutual orientation of heterocycles along the polymer chain) and for molecules with random alternation of rotational isomers. In ordered structures, all molecules are shown to have a flat conformation and they are packed so that their planes are shifted along and perpendicular to the direction of molecular axes. The shifts can be similar [towards one (Δ) or another (?Δ) side] and alternating (±Δ). For trans-TRANS molecules with a homogeneous rotational isomeric composition, longitudinal shifts Δ and ?Δ are not equivalent because, in one case, similar heteroatoms of neighboring molecules appear to be the most closely positioned, whereas in the other case, this is true of different heteroatoms. As a result, different types of molecular packing develop: in the first case, structures with parallel mutual orientation of molecular planes form and, in the second case, the structures are characterized by parquet arrangement. When trans-TRANS molecules are packed with an alternating longitudinal shift, the mutual packing of molecules shows the parquet pattern. At the same time, for cis-stereoisomeric molecules with homogeneous or arbitrary rotational isomeric composition, only the parquet pattern in their mutual arrangement is observed. This conclusion disagrees with experimental evidence according to which, in crystalline structures, the planes of molecules are parallel to each other. For the above structures, the packing energy calculated with allowance for the experimental values of cell parameters appears higher than that for the structures under study. The difference in energy exceeds 80 kJ/mol (per one monomer unit). The experimentally observed type of crystalline structure is assumed to be conceived even at the stage of nucleation of crystal-solvate phases.     

Organic monolayers chemisorbed on gold observed by scanning probe microscopy

Scanning force (SFM) and scanning tunneling (STM) microscopies are suitable techniques for the investigation of the structure of organic monolayers. Results are presented on thioalkane monolayers and thiolipid monolayers on gold. Both molecules attach covalently to the gold surface. STM images of the self assembled dodecanethiol layer display the molecular order of the film and reveal the presence of defects at the molecular scale. Moreover, domains and domain boundaries can be distinguished. Thiolipid layers on gold have been observed by SFM. The monolayer separates in solid-analogous star shaped domains and fluid-analogous domains. Imaging under water demonstrates the stability of the layer.     

Polymers with advanced structural and supramolecular features synthesized through topochemical polymerization

Polymers are an integral part of our daily life. Hence, there are constant efforts towards synthesizing novel polymers with unique properties. As the composition and packing of polymer chains influence polymer''s properties, sophisticated control over the molecular and supramolecular structure of the polymer helps tailor its properties as desired. However, such precise control via conventional solution-state synthesis is challenging. Topochemical polymerization (TP), a solvent- and catalyst-free reaction that occurs under the confinement of a crystal lattice, offers profound control over the molecular structure and supramolecular architecture of a polymer and usually results in ordered polymers. In particular, single-crystal-to-single-crystal (SCSC) TP is advantageous as we can correlate the structure and packing of polymer chains with their properties. By designing molecules appended with suitable reactive moieties and utilizing the principles of supramolecular chemistry to align them in a reactive orientation, the synthesis of higher-dimensional polymers and divergent topologies has been achieved via TP. Though there are a few reviews on TP in the literature, an exclusive review showcasing the topochemical synthesis of polymers with advanced structural features is not available. In this perspective, we present selected examples of the topochemical synthesis of organic polymers with sophisticated structures like ladders, tubular polymers, alternating copolymers, polymer blends, and other interesting topologies. We also detail some strategies adopted for obtaining distinct polymers from the same monomer. Finally, we highlight the main challenges and prospects for developing advanced polymers via TP and inspire future directions in this area.

This perspective showcases the potential of topochemical polymerization as an effective tool for synthesizing polymers with advanced molecular and supramolecular structures.     

Triangle-shaped polycyclic aromatics based on tribenzocoronene: facile synthesis and physical properties

A series of triangle-shaped polycyclic aromatics have been developed according to a facile synthetic protocol with high yields. As revealed by X-ray single crystal data, their molecular conformation and packing arrangement are significantly influenced by the electronic properties and steric bulk of peripheral subunits. The ‘saddle’-shaped hexahalotribenzocoronenes (ClTBC and FTBC) possess C₂ symmetric structures and can self-assemble into well-defined columnar structures, dramatically different from hexabutyoxytribenzocoronene (TBC), which adopts a C₃ symmetric ‘double-concave’ structure and less efficient packing arrangement. In the compound trithiophenocoronene (TTC), the five-membered corner rings produce a more open bay-region periphery alleviating intramolecular steric congestion. As a result, the molecule adopts an almost planar conformation.     

Pulse radiolysis study of formation of poly(4-vinylbiphenyl) anions in 2-methyltetrahydrofuran solution at 100–120 K

The reactions of poly(4-vinylbiphenyl) (denoted as PVB) polymers and biphenyl molecules with solvated electrons in the 2-methyltetrahydrofuran (MTHF) solvent have been studied at 100–120 K by electron-pulse radiolysis. The formation of PVB polymer anions as well as biphenyl anions was observed by the electron-pulse irradiation of the MTHF-PVB(or biphenyl) solution. The anions are formed by two processes; a rapid formation during the pulse irradiation (<20 ns) and a slow formation after the pulse irradiation. The slow formation is due to a diffusion-controlled reaction between solutes, such as PVB and biphenyl, and solvated electrons. It was found that the reaction efficiency, expressed in monomer unit, of PVB polymers is 1/27 of that of biphenyl molecules. The reaction radius for the electron capture reaction of PVB polymers is estimated as 200–370 A, which is much larger than the gyration radius (107 A) of polymer coils in MTHF solution.     

Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects

Smirnova, N.A., 1978. Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects. Fluid Phase Equilibria, 2: 1–25.A multilayer lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects is developed. The system is treated in the grand canonical ensemble on the basis of the quasi-chemical approximation. The results relate to the mixtures of monomers + flexible r-mers, where all r segments of r-mer may be different and the surface of monomer molecules and r-mer segments may be inhomogeneous (thus, the systems with polar components, associated solutions among them, are in the range of applicability of the model). The monomer + r-mer system is described based on the modified model for the multicomponent system formed by monomeric particles with strong directed interactions. Equations for the concentration profile and for the average molecular orientations, with respect to the surface, are derived; the formulae for the adsorption and surface tension are given. The surface properties calculated on the basis of the model for three monomer + dimer systems are in satisfactory agreement with the experimental data. The entropy contribution to the surface tension of pure r-mer composed of identical segments is reported for r = 2, 4, 6, 8, 12 and for different lattice parameters. The model can be generalized to mixtures of r-mers + l-mers.