Terminal Methoxy Group Research Articles

Dendritic surface functionalization of biodegradable polymer assemblies

The functionalization of nanomaterials with dendritic surface moieties was recently demonstrated to be an effective means of displaying biological ligands and potentially modulating the biological properties of these materials. With the aim of extending this surface functionalization approach to biodegradable polymer assemblies, poly(ethylene oxide)-polycaprolactone (PEO-PCL) block copolymers with terminal azide or methoxy groups were prepared and were assembled to form micelles or vesicles with varying loadings of surface azides. Dendrons bearing peripheral amines, guanidines, or hydroxyls were prepared and conjugated to the assemblies, and the conjugation yields were measured and compared as a function of azide loading and assembly type (micelle versus vesicle). A small molecule rhodamine derivative was also conjugated, allowing the effect of sterics to be studied. The effects of the surface functionalization on the aggregation state of the assemblies were studied by light scattering and transmission electron microscopy. Overall, the results revealed interesting differences between the two systems with respect to both the reaction yields and the stabilities. Furthermore, micelles functionalized with dendrons bearing peripheral guanidines were found to exhibit enhanced cell uptake relative to control micelles, demonstrating that this approach can be used to modulate the biological properties of the materials. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis of new schiff base ester liquid crystals with a benzothiazole core

A series of new calamitic liquid crystals, 6-methoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, comprising a benzothiazole core, terminal methoxy group and a Schiff base linkage were synthesised and characterised. This series comprises 12 members wherein members differ by the length of the alkanoyloxy chain (C n-1H2n-1COO-, where n = 2–8, 10, 12, 14, 16, 18). Their mesomorphic properties were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. The short chain derivatives (n = 2 and 3) were non-mesogenic compounds, while an enantiotropic nematic phase was present throughout the remaining members of the series. The smectic C phase emerged from the decanoyloxy derivative onwards.

Theoretical study of the mechanisms of the hydrolysis and condensation reactions of silicon and titanium alkoxides: similarities and differences

Stationary states for hydrolysis reactions in M(OCH(3))(4) + nH(2)O (M = Si, Ti; n = 1-3) systems are optimized at the B3LYP and MP2 levels with the Wachters basis set for titanium and the cc-pVDZ set for other atoms. Geometries of these states for M = Ti are characterized by trigonal bipyramidal (water molecules in front-side position) and octahedral coordination (for back-side position). Barrier heights for hydrolysis and condensation are substantially lower than those for silicon in keeping with experimental results. The lowering of the barrier heights on the addition of water molecules in the front-side position (reduction of hydrogen bond strain) exceeds that of the back-side addition (catalytic effect) for both M = Si and Ti, but the difference diminishes with n. The influence of oligomerization of titanium alkoxides on the rate of hydrolysis is studied on the model of the interaction of a Ti(2)(OCH(3))(8) dimer with one and two water molecules. It was shown that only terminal methoxy groups are exposed to hydrolysis and therefore the dimeric structure is retained in the process of the substitution of terminal methoxy groups. Barrier heights for terminal hydrolysis do not differ significantly from those of monomers. Barrier heights for condensation reactions obtained for the 2M(OMe)(n)(OH)(4-n) + H(2)O model system, are substantially (by ca. 10 kcal mol(-1)) lower for M = Ti and in both silicon and titanium species demonstrate a steady growth with n.

Raman spectroscopy of unbranched hexenyl methyl ethers containing a terminal methoxy group

The Raman spectra of six isomeric hexenyl methyl ethers in which the alkenyl chain is unbranched and has a terminal methoxy group are reported and discussed. A well-defined and analytically useful correlation is found between the stereochemistry of the double bond and the wavenumber of the ν(C C) stretching vibration. Confirmation of the stereochemistry of the double bond and its location within the alkyl chain is accessible from the number and wavenumber of the ν(sp 2C H) stretching bands. In addition, the nature of the double bond in the hexenyl chain is observed to exert an influence on several deformation and skeletal modes. These trends allow the assignment of Raman bands to vibrational modes to be refined or corrected. The implications of this study on model compounds for larger molecules of biological significance in which an alkenyl group is present are considered.

Synthesis, crystal structures, mesomorphic and photo-luminescent properties of 1,3,4-thia(oxa)diazole-based compounds with a terminal methoxy or methylthio group

A series of aromatically 2,5-disubstituted 1,3,4-thia(oxa)diazoles with a terminal methoxy or methylthio group were synthesized and characterized by means of 1H NMR, 13C NMR, MS and elemental analysis. The X-ray crystal structures of compounds 1a and 3b revealed that both of them adopted layered arrangement without short intermolecular interactions. The liquid crystal properties have been investigated by means of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), variable temperature X-ray diffraction (VXRD) and thermogravimetric analysis (TGA). All compounds (except 2a and 2b) exhibited various mesophases (nematic, smectic C and/or smectic A) with wide temperature ranges and good thermal stability. In CH 2Cl 2 solution, all these compounds displayed a room temperature emission with λ max at 371–425 nm and quantum yields of 0.25–0.83. The effect of the sulfur and oxygen atoms on mesomorphic and photo-luminescent properties was discussed according to the positions in the central heterocyclic rings and the terminal groups.

A novel type of optically active helical liquid crystalline polymers: Synthesis and characterization of poly(p‐phenylene)s containing terphenyl mesogen with different terminal groups

AbstractSeries of poly(p‐phenylene)s (PPPs) containing terphenyl mesogenic pendants with cyano and methoxy terminal groups by flexible COO(CH2)6O bridge [P(CN) and P(OCH3)] are synthesized through Yamamoto polycondensation with Ni‐based complex catalysts. The effects of the structural variation on their properties, especially their mesomorphism, ultraviolet–visible (UV), and photoluminescence behaviors, are studied. All of the polymers are stable, losing little of their weights when heated to ≥340 °C. The polymers show good solubility and can be dissolved in common solvents. P(CN) with cyano terminal group shows enantiotropic SmAd phase with bilayer packing arrangement, while P(OCH3) with methoxy terminal group readily forms nematic and SmAd phase when heated and cooled. Photoexcitation of their solutions induces strong blue light emission. Compared with P(OCH3), the light‐emitting bands of polymer P(CN) is slightly redshifted to 428 nm and the emission intensity of P(CN) is much stronger, due to the existence of donor–acceptor pairs. More interestingly, both of the polymers exhibit obvious Cotton effect on the CD spectra, resulting from the predominant screw sense of the backbone. This indicates that the bulky mesogenic pendant orientating around the backbone will force the main chain with helical conformation in the long region due to steric crowdedness. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4723–4735, 2009

Alkyl Peroxides Reveal the Ring Opening Mechanism of Verdoheme Catalyzed by Heme Oxygenase

Heme oxygenase (HO) catalyzes heme catabolism through three successive oxygenation steps where the substrate heme itself activates O2. Although a rate-determining step of the HO catalysis is considered as third oxygenation, the verdoheme degradation mechanism has been the least understood in the HO catalysis. In order to discriminate three possible pathways proposed for the verdoheme ring-opening, we have examined reactions of the verdoheme-HO-1 complex with alkyl peroxides, namely MeOOH. Under reducing conditions, the MeOOH reaction afforded two novel products whose absorption spectra are similar to but slightly different from that of biliverdin. HPLC, ESI-MS, and NMR analysis show that these products are 1- and 19-methoxy-deoxy-biliverdins. The addition of a methoxy group at one end of the linear tetrapyrrole unambiguously indicates transient formation of the Fe-OOMe intermediate and rearrangement of its terminal methoxy group to the alpha-pyrrole carbon. The corresponding OH transfer of the Fe-OOH species is highly probable in the H2O2-dependent verdoheme degradation and is likely to be the case in the O2-dependent reaction catalyzed by HO as well.

Chemical Pathways in the Interactions of Reactive Metal Atoms with Organic Surfaces: Vapor Deposition of Ca and Ti on a Methoxy-Terminated Alkanethiolate Monolayer on Au

In situ time-of-flight secondary ion mass spectrometry, infrared spectroscopy, and X-ray photoelectron spectroscopy measurements have been used to characterize the interfacial chemistry that occurs upon physical vapor deposition of Ti and Ca atoms onto a -OCH(3) terminated alkanethiolate self-assembled monolayer (SAM) on Au{111}. While the final result for both metals is near-exhaustive degradation of the methoxy terminal group and partial degradation of the alkyl chains to inorganic products such as carbides, hydrides, and oxides, the reaction mechanisms differ significantly. Titanium reacts in parallel with the -OCH(3) and -CH(2)- units, extensively degrading the latter until a metallic overlayer forms preventing further degradation. At this point, there is a cessation of the Ti-SAM reactions. In contrast, Ca is initially consumed by the -OCH(3) terminal group via a reaction mechanism involving two -OCH(3) groups; subsequent depositions lead to alkyl chain degradation, but at a rate slower than that for Ti deposition. These results demonstrate the subtle differences in chemistry that can arise in the vapor deposition of reactive metals, and have important implications for the behavior of electrical interfaces in organic and molecular devices made with Ti or Ca top contacts.

Ionic conductivities of the LiCF3SO3 complexes with liquid crystalline aromatic polyesters having oligo(oxyethylene) pendants

We have synthesized new aromatic polyesters (DiPEG-HQ and DiPEG-BP) by condensation polymerization of a terephthalic acid derivative bearing a pendant oligo(oxyethylene) (195-1,195-2), which has a methoxy terminal group, and two different aromatic diols, hydroquinone and 4,4′-biphenol. The synthesized polymers were characterized by differential scanning calorimetry (DSC), polarizing microscopy, and X-ray diffractometry for their liquid crystallinity (LC), thermal transitions, and structural morphologies in mesophases. The morphology of the LC phases depends strongly on the length of the rigid backbone repeating unit. The DiPEG-BP polymer having a longer repeating unit exhibits both layered and nematic structures before isotropization, whereas the DiPEG-HQ polymer having a shorter repeating unit shows only the layered structure in the mesophase. We found that the layer spacing for DiPEG-HQ is larger than that for DiPEG-BP. Both polymers easily form complexes with LiCF3SO3; we studied this complex formation by FT-IR spectroscopy. The layer spacing of the polymer-electrolyte composites increases upon increasing the amount of the lithium salt. The polymer/salt electrolyte mixtures we investigated at molar ratios of EO: salt in the range of 5–20 exhibit electrical conductivity values at 40 °C of 2.4 × 10−5 and 1.1 × 10−5 S/cm for DiPEG-HQ/LiCF3SO3 andDiPEG-BP/LiCF3SO3, respectively. At 80 °C, these values are higher: 4.6 × 10−4 and 2.5 × 10−4 S/cm, respectively. The activation energy of conductivity depends strongly on the salt concentration.

Supramolecular side chain liquid crystalline polymers assembled via hydrogen bonding between carboxylic acid-containing polysiloxane and azobenzene derivatives

Supramolecular side chain liquid crystalline polymers were prepared from poly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene derivatives through intermolecular hydrogen bonding (H-bonding) between the carboxylic acid groups in the PSI100 and the imidazole rings in the azobenzene derivatives. The existence of H-bonding has been confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline (LC) polymers and exhibit stable mesophases. The LC behaviour of these H-bonded polymeric complexes was investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The complexes exhibit nematic LC phases identified on the basis of Schlieren optical textures. On increasing spacer length or the concentration of the H-bonded mesogenic unit in the complex, the clearing temperature and the temperature range of the LC phase of the polymeric complex increase. The terminal group plays a critical role in determining the LC properties of the polymeric complexes. A terminal methoxy group is more efficient than a nitro group in increasing the clearing temperature. The electron donor-acceptor interactions between the H-bonded mesogenic units containing methoxy and nitro terminal groups in supramolecular 'copolymeric' complexes lead to an increase in the clearing temperature and a wider temperature range for the LC phase.

Electronically asymmetric triphenylmethane dyes. Half-methoxy analogues of Malachite Green

A series of derivatives of 4-dimethylamino-4′-methoxytriphenylmethanol has been prepared and the electronic absorption spectra and lightfastness properties of the derived cationic dyes determined. The introduction of one terminal methoxy group results in an electronically unsymmetrical system, to which PMO treatment appears inapplicable. The effects of substitution on the values of λ max x and λ max y are accounted for in terms of bond rotation about essential double or single bonds in an unsymmetrical cyanine chromophoric system and by restoration of electronic symmetry.

Bistable Memory Switching of (Liquid Crystalline Copolymer/ Low Molecular Weight Liquid Crystal) Composite Systems

Bistable electro-optical switching characteristics have been investigated for composite systems in a smectic phase induced by mixing a side chain type nematic liquid crystalline polymer (nematic LCP) or its copolymer with weak polar methoxy terminal groups in the side chains and low molecular weight nematic liquid crystals (nematic LCs) with strong polar cyano end groups. The liquid crystalline copolymer (LCcoP) with weak polar methoxy terminal groups in the side chains attaching to a polysiloxane main chain was used in order to improve the response speed of the bistable light switching for the binary composite system. Although the LCcoP with 52.5 mol% substituted mesogenic side chains did not exhibit any mesophase characteristics at any temperature, this LCcoP induced a smectic state by mixing nematic LCs. A reversible and bistable electro-optical switching with a short response time (∽100 ms) was realized for the induced smectic binary composite system upon the application of an appropriate electric field at room temperature.

The effect of electrostatic fields on an oligo(ethylene glycol) terminated alkanethiol self-assembled monolayer

Static energy minimization and Monte Carlo simulation are used to study the effect of external electrostatic fields on the structure of a self-assembled monolayer (SAM) formed by methoxytri(ethylene glycol) terminated alkanethiol molecules. It is found that fields of the order of 1 V Å−1 in strength can substantially change the equilibrium configuration of the SAM, making the oxygen atoms of the terminal methoxy groups buried or exposed depending on the field polarity, which is qualitatively similar to what was found in our previous ab initio calculations with a single molecule. This finding implies a potential possibility of developing SAM-coated surfaces with electrically controlled (switchable) properties.

Terminal and bridging methoxyls on zeolites detected by13C magic angle spinning NMR spectroscopy

Pure silicalites, synthesized without any heteroatoms and treated with [13C]methanol vapour, exhibit in the 13C magic angle spinning NMR spectrum signals at 48, 49 and 50 ppm with respect to tetramethylsilane (TMS) after desorption at 200 °C. The signals at 48 and 49 ppm were assigned to terminal methoxy groups at the defects of the lattice. Similar signals were detected also on modified Cs-exchanged faujasite by impregnation with caesium acetate after calcination in air and also on samples of hydrotalcite. The basicity (nucleophilicity) of the zeolitic lattice oxygen controls the carbon deshielding of chemisorbed methylium ions at bridging positions so that methoxy carbon signals increase linearly from 53 to 60 ppm (TMS) with increasing intermediate electronegativity of the lattice oxygen. On the other hand, terminal methoxy species exhibit signals from 48 to 51 ppm. Terminal and bridging methoxy species on silicalite, LSX, CsNaX/Cs2O and hydrotalcite are discussed. Copyright © 1999 John Wiley & Sons, Ltd.

Spacer Length Dependence of Mesomorphic Characteristics and Bistable Electro-Optical Effects for Smectic (Liquid Crystalline Copolymer/Liquid Crystals) Composite Systems

Mesomorphic characteristics and bistable electro-optical switching effects of smectic composite systems composed of side chain liquid crystalline copolymer (LCcoP) with a weak polar methoxy terminal group in a side chain and low molecular weight nematic liquid crystals (nematic LCs) with each strong polar cyano end group have been investigated. The spacer length of the mesogenic side chain in LCcoP has strongly affected the mesomorphic characteristics and the electro-optical effects of the (LCcoP/LCs) composite systems. The response speed of the binary composite systems became faster with a decrease of the spacer length. The binary composite systems showed reversible and bistable electro-optical switching characteristics with response time of ∼100 ms, that is, a light scattering state and a transparent one upon the application of ac electric fields with low frequency (up to - Hz) and high one (10–105 Hz), respectively. However, a light scattering state was also observed due to the sign reversal of dielectric anisotropy upon the application of an ac electric field above ∼105 Hz.

Side-Chain Liquid-Crystalline Polymers from the Alternating Copolymerization of Maleic Anhydride and 1-Olefins Carrying Biphenyl Mesogens

Side-chain liquid-crystalline copolymers (SCLCPs) were synthesized from the alternating copolymerization of maleic anhydride with mesogenic 1-olefins. These SCLCPs showed high glass transition temperatures and highly ordered smectic mesophases. The mesophase width increased with spacer length. The terminal alkyl group length determined the degree of order in the hexatic mesophase that was present just above the glass transition temperature. A terminal methoxy group induced a hexatic smectic B mesophase, intermediate terminal alkyl groups induced a smectic E mesophase, and long terminal alkyl groups induced a crystal smectic B mesophase. If the spacer was shorter than the terminal alkyl group, an interdigitated smectic A mesophase was found in which the terminal alkyl groups overlap. A strong correlation was found between the glass transition temperature and the temperature at which the hexagonal or orthorhombic ordered mesophase disappears. Introduction of an ester linkage between the spacer and biphenyl mesogen or replacing the terminal alkoxy group by a cyano terminal group induced a lowering of transition temperatures and a lower degree of order in the mesophase.

Synthesis of side-chain liquid crystalline polyurethanes via ester type attachment

A series of side-chain liquid crystalline polyurethanes was prepared by reacting a COOH functionalized polyurethane with monomers based on a biphenyl core with a methoxy terminal group and spacers of different lengths (α-bromo-ω-(4'-methoxybiphenyl-4-oxy)alkanes) in the presence of triethylamine. FTIR and NMR spectroscopic analysis of the products revealed that the monomers were attached to the polymer backbone as side chains by covalent, ester bonds. Thermotropic liquid crystalline behaviour of the ester type derivatives was analysed by differential scanning calorimetry and polarizing optical microscopy. All products exhibited smectic mesophases of highly ordered focal-conic structures.

Bistable Electro-optical Fast Switching for Induced Smectic (Liquid Crystalline Polymer/Liquid Crystals) and (Pseudo Liquid Crystalline Copolymer/Liquid Crystals) Composite Systems

Reversible and bistable electro-optical switching characteristics of induced smectic composite systems composed of a side chain nematic liquid crystalline polymer (nematic LCP) and its copolymer with weak polar methoxy terminal groups in the side chains and low molecular weight nematic liquid crystals (nematic LCs) with each strong polar cyano end have been investigated. The liquid crystalline copolymer (LCcoP) with weak polar methoxy terminal groups in the side chains was used to improve the response speed at room temperature for the bistable and reversible light switching of the binary composite system. Since LCcoP with 52.5 mol % substituted mesogenic side chains did not exhibit mesophase characteristics, this LCcoP was named as pseudo LCcoP in the present study. The (pseudo LCcoP/nematic LCs) composite system showed an induced smectic phase over a wide range of mixing concentration and temperature. A reversible and bistable electro-optical switching with a short response time (∼100 ms) was realized for the induced smectic binary composite system upon the application of an appropriate electric field at room temperature. Also, the binary composite system showed a reversible and bistable electro-optical switching based on the sign reversal of the dielectric anisotropy upon the application of ac electric fields with high (∼kHz) and higher (∼100 kHz) driving frequencies.

Opposite electrorheological effects between urethane-based polymers having different terminal groups

Electrorheological (ER) measurements have revealed that a solution of a urethane-based polymer having a cyanoethoxy terminal group exhibits an increase in the elastic modulus under an electric field. In contrast, the elasticity of a similar polymer with a methoxy terminal group is decreased by the field. The opposite ER effects are discussed in terms of the induced segmental behaviour of the polymers.

Polar polymeric Langmuir-Blodgett films containing nitrobiphenyl groups

Side-chain liquid crystalline copolymers containing nitrobiphenyl were used to fabricate polar Langmuir multilayers. (Methoxyethoxy)methoxy terminal groups were incorporated in the copolymers to enhance the spreadability and monolayer formation of the copolymers. X-ray diffraction, second harmonic measurements, and pyroelectric studies all support the existence of a noncentrosymmetric structure for the polymeric multilayers. Thus, the possibility of using polymeric monolayers to prevent molecular turnaround upon X-type horizontal deposition was demonstrated. The molecular susceptibility for nitrobiphenyl was measured to be (9.8±1.0)×10 -30 esu