Polar Terminal Groups Research Articles

Synthesis and photochromic reaction kinetics of unsaturated spiropyran derivatives

Abstract The absorption spectra and decay kinetics of the ground and triplet states of merocyanine (MC) form of spiropyran vinylogs have been investigated by nanosecond laser flash photolysis techniques in toluene and ethanol. The 3 MC decays to the ground state MC either by quenching with O 2 or due to the intersystem crossing. Relative quantum yield of both 3 MC and MC drastically decreases when the terminal polar group is separated from the indoline moiety by the C C-linker. In the presence of the C C-linker the replacement of terminal CN by CHO has no effect. The yield of 3 MC and corresponding MC in ethanol is 5 times smaller than that in toluene solution.

Structural Characterization and Molecular Order of Rodlike Mesogens with Three- and Four-Ring Core by XRD and 13C NMR Spectroscopy

Structural characterizations using XRD and (13)C NMR spectroscopy of two rodlike mesogens consisting of (i) three phenyl ring core with a polar cyano terminal and (ii) four phenyl ring core with flexible dodecyl terminal chain are presented. The three-ring-core mesogen with cyano terminal exhibits enantiotropic smectic A phase while the four-ring mesogen reveals polymesomorphism and shows enantiotropic nematic, smectic C, and tilted hexatic phases. The molecular organization in the three-ring mesogen is found to be partial bilayer smectic Ad type, and the interdigitation of the molecules in the neighboring layers is attributed to the presence of the polar terminal group. For the four-ring mesogen, the XRD results confirm the existence of the smectic C and the tilted hexatic mesophases. A thermal variation of the layer spacing across the smectic C phase followed by a discrete jump at the transition to the tilted hexatic phase is also observed. The tilt angles have been estimated to be about 45° in the smectic C phase and about 40° in tilted hexatic phase. (13)C NMR results indicate that in the mesophase the molecules are aligned parallel to the magnetic field. From the (13)C-(1)H dipolar couplings determined from the 2D experiments, the overall order parameter for the three-ring mesogen in its smectic A phase has been estimated to be 0.72 while values ranging from 0.88 to 0.44 have been obtained for the four-ring mesogen as it passes from the tilted hexatic to the nematic phase. The orientations of the different rings of the core unit with respect to each other and also with respect to the long axis of the molecule have also been obtained.

Wear durability study on self-lubricating SU-8 composites with perfluoropolyther, multiply-alkylated cyclopentane and base oil as the fillers

Though SU-8 has become a useful material for micro-fabrication of MEMS/NEMS components using the micro-fabrication route, its poor tribological properties limit its wider applications. From our previous study [1], it was observed that adding PFPE lubricant to SU-8 possibly promoted chemical reaction between the molecules and helped in the boundary lubrication enhancing the wear durability of SU-8 by more than four orders of magnitude. For further investigation, another two different lubricants, a base oil and a multiply-alkylated cyclopentane (MAC) oil, were also added to SU-8. Both lubricants are hydrocarbons, chemically inert and have no polar reactive terminal groups unlike PFPE which has –OH polar terminal groups. SU-8+PFPE composite exhibited higher wear life than all SU-8 composites at all wt% of the lubricant content. Proper dispersion and possible chemical bonding of PFPE molecules with SU-8 are responsible for the superior tribological properties of SU-8+PFPE composite when compared with other SU-8 composites.

Synthesis and Liquid-crystal Properties of New Amphiphilic Long-chain Derivatives of Meso-arylporphyrins with Terminal Polar Groups

New amphiphilic alkoxyarylporphyrins with long-chain substituents bearing carboxy, methoxycarbonyl and hydroxy groups, and their metal complexes, were synthesized. Those of them having mesogenic properties were identified by optical polarisation microscopy, and their liquid-crystal properties were studied.

Superhydrophobic Alkanethiol-Coated Microsubmarines for Effective Removal of Oil

We demonstrate the use of artificial nanomachines for effective interaction, capture, transport, and removal of oil droplets. The simple nanomachine-enabled oil collection method is based on modifying microtube engines with a superhydrophobic layer able to adsorb oil by means of its strong adhesion to a long chain of self-assembled monolayers (SAMs) of alkanethiols created on the rough gold outer surface of the device. The resultant SAM-coated Au/Ni/PEDOT/Pt microsubmarine displays continuous interaction with large oil droplets and is capable of loading and transporting multiple small oil droplets. The influence of the alkanethiol chain length, polarity, and head functional group and hence of the surface hydrophobicity upon the oil-nanomotor interaction and the propulsion is examined. No such oil-motor interactions were observed in control experiments involving both unmodified microengines and microengines coated with SAM layers containing a polar terminal group. These results demonstrate that such SAM-Au/Ni/PEDOT/Pt micromachines can be useful for a facile, rapid, and efficient collection of oils in water samples, which can be potentially exploited for other water-oil separation systems. The integration of oil-sorption properties into self-propelled microengines holds great promise for the remediation of oil-contaminated water samples and for the isolation of other hydrophobic targets, such as drugs.

Molecular dynamics simulation of a polysorbate 80 micelle in water

The structure and dynamics of a single molecule of the nonionic surfactant polysorbate 80 (POE (20) sorbitan monooleate; Tween 80®) as well as a micelle comprising sixty molecules of polysorbate 80 in water have been investigated by molecular dynamics simulation. In its free state in water the polysorbate 80 molecule samples almost its entire conformational space. The micelle structure is compact and exhibits a prolate ellipsoid shape, with the surface being dominated by the polar terminal groups of the POE chains. The radius of gyration of the micelle was 26.2 Å. The physical radius, determined from both the radius of gyration and atomic density, was about 35 Å. The estimated diffusion constants for the free molecule (1.8 × 10−6 cm2s−1) and the micelle (1.8 × 10−7 cm2s−1) were found to be remarkably close to the respective experimental values. The lateral diffusion of the molecules on the micelle surface was estimated to be 1.7 × 10−7 cm2s−1, which confirms the highly dynamic nature of the micelle structure.

Experimental and Theoretical Examination of Surface Energy and Adhesion of Nitrifying and Heterotrophic Bacteria Using Self-Assembled Monolayers

Biofilm-based systems, including integrated fixed-film activated sludge and moving bed bioreactors, are becoming increasingly popular for wastewater treatment, often with the goal of improving nitrification through the enrichment of ammonia and nitrite oxidizing bacteria. We have previously demonstrated the utility of self-assembled monolayers (SAMs) as tools for studying the initial attachment of bacteria to substrata systematically varying in physicochemical properties. In this work, we expanded these studies to bacteria of importance in wastewater treatment systems and we demonstrated attachment rates were better correlated with surface energy than with wettability (water contact angle). Toward the long-term goal of improving wastewater treatment performance through the strategic design of attachment substrata, the attachment rates of two autotrophic ammonia-oxidizing bacteria (Nitrosomonas europaea and Nitrosospira multiformis) and a heterotroph (Escherichia coli) were evaluated using SAMs with a range of wettabilities, surface energies, and functional properties (methyl, hydroxyl, carboxyl, trimethylamine, and amine terminated). Cell attachment rates were somewhat correlated with the water contact angles of the SAMs with polar terminal groups (hydroxyl, carboxyl, trimethylamine, and amine). Including all SAM surfaces, a better correlation was found for all bacteria between attachment rates and surface free energy, as determined using the Lewis Acid-Base approach. The ammonia-oxidizers had higher adhesion rates on the SAMs with higher surface energies than did the heterotroph. This work demonstrated the successful application of SAMs to determine the attachment surface preferences of bacteria important to wastewater treatment, and it provides guidance for a new area of research aimed at improving treatment performance through rational attachment surface design.

Effect of terminal branching on mesomorphism of a homologous series of Schiff base ethers

A lot of studies have been focused on the Schiff base’s alkyl and alkyloxy possessing polar terminal group. Yet, the thermotropic properties of Schiff base’s ether (alkyloxy) with dialkylamino terminal group remained less studied. A series of 4-(dialkylamino)benzylidene-4’-alkyloxyanilines were prepared and all the members are differed by the alkyloxy chain length, CnH2n+1O, where n = 6, 8, 10, 12, 14, 16 and 18. Their transition temperatures and mesophase characteristics were studied by differential scanning calorimetry and optical polarizing microscopy techniques. DSC thermograms exhibited direct isotropization and recrystallization during heating and cooling cycles, respectively. The crystal phase texture changed to dark region isotropic without displaying any mesophase. Lengthening of dialkylamino terminal branch has caused depression of mesomorphic property in the compounds studied. Key words: Schiff base, dialkylamino group, terminal branching, mesophase.

Molecular volumes of phospholipids and glycolipids in membranes

Data on the molecular volumes of phospholipids and glycolipids in membranes are collected together in order to determine the contributions from the component groups, for as wide a range of lipids as possible, including sphingolipids. Wherever possible, the volumes of the methylene groups in the lipid chains are established from the dependence on chain length at fixed temperature in a given phase. In this way, it is also possible to determine the constant contribution from cis double bonds in the chains of monoenoic unsaturated phosphatidylcholines, and the volume of the branched methyl groups in isoacyl phosphatidylcholines. Issues concerning separation of contributions from the polar head groups from those of the chain terminal methyl groups are discussed. Molecular volumes of lipids in crystals are also analysed to provide information on head-group packing that can be compared with the situation in membranes, and used to set limits on the relative contributions from polar groups and terminal methyl groups. Comparisons are made with volumetric analyses based on diffraction studies of bilayers of single lipids. The parameters derived can be used to estimate molecular volumes of lipids for which dilatometric or densitometric data are lacking. Lipid volumes are determining parameters for lipid dynamics, membrane partitioning and permeation of solutes, and are essential quantities for the structural analysis of lipid membranes.

Occurrence of a transition between two polar orthogonal smectic phases in a new homologous series of novel bent-core compounds

Two new homologous series of isomeric achiral five-ring bent-core compounds containing 3,4-disubstituted biphenyl moiety have been synthesised and the mesophases that they exhibit characterised. Compounds of series A are obtained from 4-hydroxybiphenyl-3-carboxylic acid while those in series B are prepared by reversing the position of the hydroxyl and carboxylic groups. This change seems to have a profound effect on the mesophase properties. Interestingly, for compounds of series A containing the long terminal chain, a transition between two polar orthogonal smectic phases has been observed. The observed mesophases have been characterised using a combination of polarised light optical microscopy, differential scanning calorimetry, X-ray diffraction studies and electro-optical measurements. This is the first example of a transition between two partial bilayer polar orthogonal smectic phases. In addition, the effect of a fluoro substituent ortho to the strongly polar terminal cyano group on the mesophase has also been examined.

New Mesogenic Schiff Base Esters with Polar Chloro Substituent: Synthesis, Thermotropic Properties and X-Ray Diffraction Studies

Problem statement: Many studies have been conducted on the Schiff base’s alkyl and alkyloxy possessing terminal halogen substituent. However, the thermotropic properties of Schiff base’s ester (or alkanoyloxy) with chloro terminal group remained unstudied. Approach: Synthesis a series of new Schiff base ester possessing polar chloro group and investigate its mesomorphic properties. The title compounds were prepared via condensation and esterification reactions. The molecular structures were confirmed using spectroscopic techniques. All the members are differed by the length of alkanoyloxy chain, Cn-1H2n-1COO, where n = 2-8, 10, 12, 14, 16 and 18. The mesomorphic properties were studied using differential scanning calorimetry, polarizing optical microscopy and temperature-dependent X-ray diffractometry. Results: Whilst short members (n = 2-5) were not mesogenic compounds, n-hexanoyloxy and n-heptanoyloxy derivatives exhibited monotropic SmA and SmB phases. Enantiotropic smectogenic A and monotropic smectogenic B were observed in n-octanoyloxy to n-hexadecanoyloxy derivatives. Highest member of the series, n-octadecanoyloxy derivatives exhibited monotropic SmA phase. Conclusion: The ester linkage and polar terminal group in the present series are essential for the formation of liquid crystal phase in Schiff bases.

Parameterization and validation of an accurate force-field for the simulation of alkylamine functionalized silicon (111) surfaces

The stretching, bending, and torsional force-field parameters for modelling Si (111) surfaces functionalized with alkylamines have been derived from energies, optimized geometries and harmonic frequencies obtained by accurate quantum mechanical calculations. Addition of inter-chain non-bonded parameters from a literature force field leads to computed energies in good agreement with their quantum mechanical counterparts for a large set of geometrical arrangements. The overall force-field was tested through molecular dynamics simulations performed on several models of Si functionalized surfaces, with different coverage percentages. Preliminary results indicate that the presence of a polar terminal amine group yields a surface coating of around 50%.

Influence of spacer chain lengths and polar terminal groups on the mesomorphic properties of tethered 5-phenylpyrimidines

Based on 5-(4-hydroxyphenyl)-2-octylpyrimidine 8, 5-phenylpyrimidine derivatives 3–7, 9 with different spacer chain lengths (C2 up to C6) and different terminal polar groups (Br, Cl, N3, OH, CN) were synthesized by etherification and nucleophilic substitution. The mesomorphic behaviour of these compounds was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS and SAXS) and revealed smectic A mesophases for bromides, chlorides and azides 3, 4 and 6. For these compounds a maximum phase width was observed for the C5 spacer regardless of the terminal group, whereas the hydroxy- and cyano-substituted derivatives 5 and 7, respectively, were non mesomorphic and showed only melting transitions.

Molecular organization and aggregation in Langmuir and Langmuir-Blodgett films of azo dye/liquid crystal mixtures

AbstractA study of azo dye/liquid crystal mixtures in monolayers formed at air-water (Langmuir films) and air-solid substrate (Langmuir-Blodgett films) interfaces was performed. Three azo dyes with various molecular structure and two liquid crystal materials: 4-octyl-4′-cyanobiphenyl (8CB) and trans-4-octyl(4′-cyanophenyl)-cyclohexane (8PCH) were used. The morphology of Langmuir films was monitored by means of a Brewster angle microscope (BAM). Moreover, a surface pressure and electronic absorption spectra of the monolayer spread on the water surface of dye/liquid crystal mixtures as a function of a mean molecular area were simultaneously recorded. In addition, the absorption for Langmuir-Blodgett films deposited on quartz plates was measured. Information about intermolecular interactions in the mixtures of the nonamphiphilic dye and the liquid crystal with polar terminal group was obtained. Conclusions about the formation of self-aggregates between dye molecules have been drawn. The influence of the dye molecular structure and its concentration on aggregates’ geometry was found.

Acidic heterocycles as novel hydrophilic pharmacophore of androgen receptor ligands with a carborane core structure

A novel series of androgen receptor (AR) ligands bearing an acidic heterocycle with hydrogen-bonding ability as the terminal polar group was developed. Since most non-steroidal AR ligands so far known are structurally limited to nitro- or cyanobenzanilide as the polar pharmacophore, development of alternative hydrogen-bonding components is required to obtain novel AR ligands. Various acidic heterocycles were introduced into a hydrophobic phenylcarborane (1-phenyl-1,12-dicarba- closo-dodecaborane) core structure to provide a moiety that could interact effectively with the critical basic arginine residue of the AR ligand binding domain. The most potent compounds, 1,2,4-oxadiazole-5-thione derivatives 21a and 21b, exhibited higher affinity for hAR than did the well-known anti-androgen hydroxyflutamide. The results suggest that this heterocyclic functionality is potential bioisoster of the nitro and cyano groups forming the polar pharmacophores of known non-steroidal AR ligands.

Pretransitional behaviour in the vicinity of the isotropic–nematic transition of strongly polarcompounds

The isotropic–nematic transition, being weakly first order, exhibits pretransitional effectssignifying the appearance of the nematic-like regions in the isotropic phase. In the isotropicphase, strongly polar liquid crystals, such as the popular alkyl and alkoxy cyano biphenylbehave in a non-standard fashion: whereas far away from the transition the dielectric constantεiso hasa 1/T dependence (a feature also commonly seen in polar liquids), on approachingthe nematic phase the trend reverses resulting in a maximum inεiso, at a temperature slightly above the transition, an effect explained on the basisof short-range correlations with an antiparallel association of the neighbouringmolecules. Recently, there has been a revival in studies on this behaviour to possiblyassociate it with the order of transition. Here we report dielectric measurementscarried in the vicinity of this transition for a number of compounds having differentmolecular structures including a bent core system, but with a common featurethat the molecules possess a strong terminal polar group, nitro in one case andcyano in the rest. Surprisingly, the convex shape of the thermal variation ofεiso wasmore an exception than the rule. In materials that exhibit such an anomaly we find a linear correlationbetween δε = (εpeak−εIN)/εIN and δT = Tpeak−TIN,where εpeak is the maximum value of the dielectric constant in the isotropic phase,εIN the value at thetransition, and Tpeak and TIN the corresponding temperatures.

Local forms of molecular mobility in copolymethacrylates containing side‐chain nonlinear optical chromophores

AbstractLocal forms of molecular mobility of comb‐like random copolymethacrylates, containing side‐chain nonlinear optical chromophores and amyl‐ or octafluoroamyl‐groups, are studied. In the glassy state, two relaxation processes are found, which are due to reorientation of terminal polar groups (γ2‐process) and rotation of chromophore groups about their long axes (β‐process). For octafluoroamyl‐containing copolymers, the γ2‐process is superposition of the two molecular motions due to reorientation of terminal chromophore groups and CF2H groups. The intensity and relaxation times in the range of the γ2‐process depend on the chemical structure and concentration of chromophores in a copolymer. For the β‐process, the molecular mobility weakly depends on the chromophore structure, being mainly determined by the relative lengths of the rigid chromophore and flexible side chains. On the global spectrum of depolarization current it was observed the γ1‐process due to reorientation of (CH2)n spacers between chromophore groups and copolymer backbone. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1488–1496, 2008

Synthesis and Physical Properties of Novel Dimesogenic Compounds Possessing both Lateral and Terminal Polar Groups

We prepared a homologous series of non-symmetric dimesogenic compounds 1-(4- fluorophenyl)-4-{ω -{4-[4-(4-hexylphenyl)-2,3-difluorophenyl]phenyloxy}alkyloxy} benzene ( I-n ) and investigated the physical properties. For comparison, we also prepared a compound ( II-6 ) possessing a 4-(4-cyanophenyl)benzene unit instead of the 4-(4- fluorophenyl)benzene unit. All the compounds exhibited an enantiotropic nematic phase. When an electric AC field was applied, a striped pattern that was similar to Williams domain appeared in the nematic phases of compounds I-n , whereas such a pattern was not observed in the nematic phase of II-6 . We discuss structure-property correlations of the polar liquid crystal oligomers.

Substrate Specificity of Platypus Venom L-to-D-Peptide Isomerase

The L-to-D-peptide isomerase from the venom of the platypus (Ornithorhyncus anatinus) is the first such enzyme to be reported for a mammal. In delineating its catalytic mechanism and broader roles in the animal, its substrate specificity was explored. We used N-terminal segments of defensin-like peptides DLP-2 and DLP-4 and natriuretic peptide OvCNP from the venom as substrates. The DLP analogues IMFsrs and ImFsrs (srs is a solubilizing chain; lowercase letters denote D-amino acid) were effective substrates for the isomerase; it appears to recognize the N-terminal tripeptide sequence Ile-Xaa-Phe-. A suite of 26 mutants of these hexapeptides was synthesized by replacing the second residue (Met) with another amino acid, viz. Ala, alpha-aminobutyric acid, Ile, Leu, Lys, norleucine, Phe, Tyr, and Val. It was shown that mutant peptides incorporating norleucine and Phe are substrates and exhibit L- or D-amino acid isomerization, but mutant peptides that contain residues with shorter, beta-branched or long side chains with polar terminal groups, viz. Ala, alpha-aminobutyric acid, Ile, Val, Leu, Lys, and Tyr, respectively, are not substrates. It was demonstrated that at least three N-terminal amino acid residues are absolutely essential for L-to-D-isomerization; furthermore, the third amino acid must be a Phe residue. None of the hexapeptides based on LLH, the first three residues of OvCNP, were substrates. A consistent 2-base mechanism is proposed for the isomerization; abstraction of a proton by 1 base is concomitant with delivery of a proton by the conjugate acid of a second base.

Intermolecular Interactions in Langmuir and Langmuir-Blodgett Films of Azo Dye/Liquid Crystal Mixtures

Binary mixtures of the dichroic azo dye with the liquid crystal as Langmuir and Langmuir-Blodgett films have been studied. Four azo dyes with various molecular structure and liquid crystal materials: 4-octyl-4′-cyanobiphenyl (8CB) and trans-4-octyl(4′-cyanophenyl)-cyclohexane (PCH8) were used. The surface pressure as a function of the mean molecular area for Langmuir films were measured and the organization of molecules at the air-water interface was determined. Absorption spectra in situ for Langmuir films and absorption spectra by using both natural and linearly polarized light for Langmuir-Blodgett films were recorded and information about intermolecular interactions in the mixtures of the nonamphiphilic dye and the liquid crystal with polar terminal group was obtained. Conclusions about the formation of self-aggregates between dye molecules have been drawn.