Polar Side Groups Research Articles

Poly(2-thiophen-3-yl-malonic acid), a Polythiophene with Two Carboxylic Acids Per Repeating Unit

A new substituted polythiophene derivative bearing malonic acid, poly(2-thiophen-3-yl-malonic acid), has been prepared and characterized using a strategy that combines both experimental and theoretical methodologies. The chemical structure of this material has been investigated using FTIR and (1)H NMR, and its molecular conformation has been determined using quantum mechanical calculations. Interestingly, the arrangement of the inter-ring dihedral angles was found to depend on the ionization degree of the material, that is, on the pH, which has been found completely soluble in aqueous base solution. Thus, the preferred anti-gauche conformation changes to syn-gauche when the negatively charged carboxylate groups transforms into neutral carboxylic acid. UV-vis experiments and quantum mechanical calculations on model systems with a head-to-tail regiochemistry showed that the lowest pi-pi* transition energy is 2.25 and 2.39 eV for the negatively charged and the neutral polymer, respectively. These values are slightly larger than those previously reported for other polythiophenes with bulky polar side groups. The polymer presents a good thermal stability with a decomposition temperature above 215 degrees C and an electrical conductivity of 10(-5) S/cm, which is characteristic of semiconductor materials. Scanning electron microscopy micrographs showed that, after doping, the surface of this material displays regular distribution pores with irregular sizes. This surface suggests that poly(2-thiophen-3-yl-malonic acid) is a candidate for potential applications such as selective membranes for electrodialysis, wastewater treatment, or ion-selective membranes for biomedical uses.

Impact of ligands on CO2 adsorption in metal-organic frameworks: First principles study of the interaction of CO2 with functionalized benzenes. II. Effect of polar and acidic substituents

Intermolecular interactions between the CO(2) molecule and a range of functionalized aromatic molecules have been investigated using density functional theory. The work is directed toward the design of linker molecules which could form part of new metal-organic framework materials with enhanced affinity for CO(2) adsorption at low pressure. Here, the focus was on the effect of introducing polar side groups, and therefore functionalized benzenes containing -NO(2), -NH(2), -OH, -SO(3)H, and -COOH substituents were considered. The strongest types of intermolecular interactions were found to be: (i) between lone pair donating atoms (N,O) of the side groups and the C of CO(2) (enhancement in binding energy of up to 8 kJ mol(-1) compared to benzene); and (ii) hydrogen bond interactions between acidic protons (of COOH and SO(3)H groups) and CO(2) oxygen (enhancement of 3-4 kJ mol(-1)). Both of these types of interaction have the effect of polarizing the CO(2) molecule. Weaker types of binding include hydrogen-bond-like interactions with aromatic H and pi-quadrupole interactions. The strongest binding is found when more than one interaction occurs simultaneously, as in C(6)H(5)SO(3)H and C(6)H(5)COOH, where simultaneous lone pair donation and H-bonding result in binding energy enhancements of 10 and 11 kJ mol(-1), respectively.

Electrical response and functionality of polymer matrix-titanium carbide composites

The dielectric response and conductivity of polymer matrix-titanium carbide composites was examined by means of Broadband Dielectric Spectroscopy in the frequency range of 10-1-107 Hz and over the temperature range of 40-150°C, varying the filler content. Dielectric data were analyzed via the electric modulus formalism. Recorded relax- ations were attributed to interfacial polarization, glass to rubber transition and local motions of polar side groups. Alternat- ing current conductivity varies up to seven orders of magnitude with both frequency and temperature. Direct current conductivity increases with temperature, although the rate of its alteration does not remain constant in the examined tem- perature range. In the low temperature region (up to 60°C) increases at a higher rate, while right afterwards approaches rather constant values. Finally, in the high temperature range (above 90°C) conductivity raises again but at a lower rate. This behaviour adds functionality to the composites' performance and could be exploited in developing self-current regulators.

Synthesis and antiplasmodial activity of novel 2,4-diaminopyrimidines

Two sets of diaminopyrimidines, totalling 45 compounds, were synthesized and assayed against Plasmodium falciparum. The SAR was relatively shallow, with only the presence of a 2-(pyrrolidin-1-yl)ethyl group at R(2) significantly affecting activity. A subsequent series addressed high LogD values by introducing more polar side groups, with the most active compounds possessing diazepine and N-benzyl-4-aminopiperidyl groups at R(1)/R(2). A final series attempted to address high in vitro microsomal clearance by replacing the C6-Me group with CF(3), however antiplasmodial activity decreased without any improvement in clearance. The C6-CF(3) group decreased hERG inhibition, probably as a result of decreased amine basicity at C2/C4.

Novel Recognition Sign of DNA-binding α-Helix in Complexes of Transcription Factors from Different Families with Operator DNA

Binding sites of 75 protein domains from 65 complexes of transcription factors with fragments of double-chained operator B-DNA in the major groove region were considered for known spatial structures at a resolution higher than 2.5 Å. The DNA-binding protein domains belong to various structural families and differ greatly in the molecular structure and size. However, in all cases mainly polar residues of the only recognizing a-helix of protein factor ensured the binding. We have shown that binding helical residues have a very clear novel recognition sign. For 95.8% of total protein domains the binding polar residues of the recognizing α-helix were localized within one of the two largest clusters of polar side groups on the protein surface. In fact, we have seen a unique recognition sign of the DNA-binding a-helix of transcription factors to be inherent to different structural families. This enables determining the binding helical residues of transcription factor due to its known spatial structure. The observed regularity on the localization of contact polar residues is general both in DNA and RNA-binding proteins as shown earlier. It contributes seriously to further understanding of a complex formation on the way to exact identification of binding helical residues of transcription factors.

All solid polymer electrolytes based on polar side group rotation for rechargeable lithium batteries

AbstractA novel polymer matrix with a polar carbonyl group was designed and used to prepare an all‐solid polymer electrolyte in lithium rechargeable batteries. The ionic conductivity of this type of polymer electrolyte was examined. The relationship between the lithium salt concentration and ionic conductivity was investigated by Fourier transform infrared (FTIR) spectroscopy. The carbonyl groups in the polymer matrix effectively interacted with the lithium salt, which improved the ionic conductivity at a large range of temperatures. The ionic conductivity of this type of polymer electrolyte was approximately 10−4 S cm−1 at room temperature. The stability of the interface between electrode and electrolyte was evaluated by measuring the alternating current (AC) impedance. Copyright © 2009 John Wiley & Sons, Ltd.

Interaction of nano-TiO2 with lysozyme: insights into the enzyme toxicity of nanosized particles

Nanomaterials have been used increasingly in industrial production and daily life, but their human exposure may cause health risks. The interactions of nanomaterial with functional biomolecules are often applied as a precondition for its cytotoxicity and organ toxicity where various proteins have been investigated in the past years. In the present study, nano-TiO(2) was selected as the representative of nanomaterials and lysozyme as a representative for enzymes. By investigating their interaction by various instrumentations, the objective is to identify the action sites and types, estimate the effect on the enzyme structure and activity, and reveal the toxicity mechanism of nanomaterial. Laboratory-scale experiments were carried out to investigate the interactions of nano-TiO(2) with lysozyme. The interaction of nano-TiO(2) particles with lysozyme has been studied in the analogous physiological media in detail by UV spectrometry, fluorophotometry, circular dichroism (CD), scanning electron microscope, zeta-potential, and laser particle size. The interaction accorded with the Langmuir isothermal adsorption and the saturation number of lysozyme is determined to be 580 per nano-TiO(2) particle (60 nm of size) with 4.7 x 10(6) M(-1) of the stability constant in the physiological media. The acidity and ion strength of the media obviously affected the binding of lysozyme. The warping and deformation of the lysozyme bridging were demonstrated by the conversion of its spatial structure from alpha-helix into a beta-sheet, measured by CD. In the presence of nano-TiO(2), the bacteriolysis activity of lysozyme was subjected to an obvious inhibition. The two-step binding model of lysozyme was proposed, in which lysozyme was adsorbed on nano-TiO(2) particle surface by electrostatic interaction and then the hydrogen bond (N-H...O and O-H...O) formed between nano-TiO(2) particle and polar side groups of lysozyme. The adsorption of lysozyme obeyed the Langmuir isothermal model. The binding of lysozyme is dependent on the acidity and ion strength of the media. The bigger TiO(2) aggregate was formed in the presence of lysozyme where lysozyme may bridge between nano-TiO(2) particles. The coexistence of nano-TiO(2) particles resulted in the transition of lysozyme conformation from an alpha-helix into a beta-sheet and a substantial inactivation of lysozyme. The beta-sheet can induce the formation of amyloid fibrils, a process which plays a major role in pathology. Lysozyme was adsorbed on the nano-TiO(2) particle surface via electrostatic attraction and hydrogen bonds, and they also bridged among global nano-TiO(2) particles to form the colloidal particles. As a reasonable deduction of this study, nano-TiO(2) might have some toxic impacts on biomolecules. Our data suggest that careful attention be paid to the interaction of protein and nanomaterials. This could contribute to nanomaterial toxicity assessment. Our results strongly suggest that nano-TiO(2) has an obvious impact on biomolecules. Our data suggest that more attention should be paid to the potential toxicity of nano-TiO(2) on biomolecules. Further research into the toxicity of nanosized particles needs to be carried out prior to their cell toxicity and tissue toxicity. These investigations might serve as the basis for determining the toxicity and application of nanomaterials.

Specific interactions in complexes formed by polythiophene derivatives bearing polar side groups and plasmid DNA

The interaction between plasmid DNA and polythiophene derivatives bearing substituents with polar groups has been examined using electrophoresis assays, and both UV–Vis and CD spectroscopies. Results clearly indicate that such conducting polymers form stable adducts with DNA, even although the interactions strongly depend on the chemical constitution of the polymers. Furthermore, digestion assays with EcoRI and BamHI evidence that the polymers form specific interactions with the DNA, protecting the target nucleotide sequences of these restriction enzymes. On the other hand, UV–Vis and CD spectra show that the interactions induce a fast and very significant exposition of the nitrogen bases, which is consequence of the structural alterations induced in the circular DNA. These results have been compared with those previously reported for polypyrrole, poly(3,4-ethylenedioxythiophene) and poly(3-methylthiophene). Finally, a model based on the intercalation of the conducting polymer between the two DNA strands has been proposed.

Structure-related lower surface resistivity and faster doping of poly(thiophene-3-acetic acid- co-3-hexylthiophene) compared with poly(thiophene-3-acetic acid)

Two types of electrically active polymers, namely poly(thiophene-3-acetic acid- co-3-hexylthiophene) or poly(TAA- co-HT), and poly(thiophene-3-acetic acid) or PTAA were synthesized by oxidizing polymerization, and compared in terms of structure, surface resistivity and doping rate. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy data revealed that there is a smaller content of acetic acid functional groups in poly(TAA- co-HT) than in PTAA. Importantly, poly(TAA- co-HT) showed lower surface resistivity and higher doping rate when doped with iodine vapor in comparison with PTAA. The different surface resistivities and doping rates of the two polymers are related with the differences in their relative abundance of polar side groups and packing density of the polymer chains.

Mechanical spectroscopy of laser deposited polymers

Pulsed laser deposition (PLD) at 248 nm in ultra high vacuum was used to produce thin poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) films. The ablation and deposition mechanisms were found to be similar in both systems. Having the same backbone, these polymers differ in the size of their polar side groups leading to changes in their dynamics. Studies of the relaxation processes were performed using mechanical torsion and bending spectroscopy by means of a double-paddle oscillator (DPO) and an in-situ plasma plume excited reed (PPXR), respectively. A strong increase of the mechanical damping was observed during annealing of the polymer films well above the glass transition temperature T g, while in-situ X-ray measurements did not reveal any structural changes. For PEMA, the glass transition temperature T g=335 K and the main absorption maximum appear at lower temperatures compared to PMMA (T g=380 K), allowing one to measure the mechanical properties in a much wider range above T g.

Dielectric behaviour and functionality of polymer matrix – ceramic BaTiO3 composites

Dielectric properties of polymer matrix - ceramic BaTiO3 composites were examined by means of Broadband Dielectric Spectroscopy (BDS) in the frequency range of 10 -1 -10 7 Hz and over the temperature range of 30-160°C, vary- ing the content of ferroelectric particles. Experimental results provide evidence that the recorded relaxation phenomena include contributions from both the polymeric matrix and the presence of the reinforcing phase. Obtained results are analysed via the electric modulus formalism. Polymer matrix exhibits two distinct relaxation processes attributed, with ascending relaxation rate, to glass/rubber transition, and local motions of polar side groups. Interfacial polarization or Maxwell-Wagner-Sillars process is present in the low frequency range and at high temperatures. Finally, in the vicinity of the characteristic Curie temperature (TC) an abrupt variation of the real part of dielectric permittivity with temperature is recorded. This peak is probably related to the ferroelectric to paraelectric phase transition of the employed ceramic inclu- sions.

Photoinduced chirality in achiral liquid crystalline azobenzene polymers containing different polar side groups

Circular dichroism (CD) was induced in the films of two achiral liquid crystalline polymers, poly[(4′-(6-(methacryloyloxy)hexyl)oxy)-(4-X)azobenzene] (PM6X, X = C and N for cyano and nitro, respectively), by irradiation with one handed circularly polarized light (CPL) at 442 nm. The CD and UV spectra of the polymeric films suggest that left-CPL induces a left helical structure and right-CPL reverses the resulting structure into a right helix. For PM6C, the photoinduced CD values of the nematic film are much higher than in the casting and isotropic film. The photoinduced chirality of PM6C films is higher than PM6N due to a higher polarity of nitro groups in PM6N. The PM6N’s CD intensity around 450 nm is increased with the irradiation time of linearly polarized light (LPL) followed by left-CPL irradiation. The correlation between azobenzene chromophores and circularly polarized light will be discussed in the paper.

Relaxation phenomena in rubber/layered silicate nanocomposites

Broadband Dielectric Spectroscopy (BDS) is employed in order to investigate relaxation phenomena occurring in natural rubber (NR), polyurethane rubber (PUR) and PUR/NR blend based nanocomposites, reinforced by 10 parts per hundred (phr) Layered Silicates (LS). Nanocomposites and matrices were examined under identical conditions in a wide frequency (10-1 to 106 Hz) and temperature (-100 to 50°C) range. Experimental data are analyzed in terms of electric mod- ulus formalism. The recorded relaxation phenomena include contributions from both the polymer matrices and the nano- filler. Natural rubber is a non-polar material and its performance is only slightly affected by the presence of layered silicates. Polyurethane rubber exhibits four distinct relaxation processes attributed, with ascending relaxation rate, to Inter- facial Polarization (IP), glass/rubber transition (α-mode), local motions of polar side groups and small segments of the polymer chain (β, γ-mode). The same processes have been detected in all systems containing PUR. IP is present in all nanocomposites being the slowest recorded process. Finally, pronounced interfacial relaxation phenomena, occurring in the PUR+10 phr LS spectra, are attributed to nanoscale effects of intercalation and exfoliation.

Electrical relaxation dynamics in TiO2 – polymer matrix composites

Polymer matrix-TiO2 composites were prepared in three different filler concentrations. The electrical relaxation dynamics as well as the electrical conductivity of all samples were examined by means of Broadband Dielectric Spec- troscopy (BDS) over a wide frequency and temperature range. The recorded relaxation response includes contributions from both the polymer matrix and the reinforcing phase. Two relaxation modes (β and γ) are observed in the low tempera- ture region, which are attributed to the re-orientation of polar side groups of the matrix and rearrangement of small parts of the polymeric chain respectively. The α-relaxation and the Maxwell-Wagner-Sillars effect (MWS), attributed to the glass- rubber transition of the polymeric matrix and to interfacial polarization phenomena respectively, are observed in the high temperature region. These two mechanisms are superimposed, thus a computer simulation procedure was followed in order to distinguish them. MWS effect becomes more pronounced with increasing concentration of the filler following an Arrhe- nius behaviour. The relaxation frequencies corresponding to α-mode follow the Vogel-Tamann-Fulcher (VTF) equation. An additional relaxation mode is recorded at relatively high temperatures and high frequencies. Its occurrence and dynam- ics are related to the presence and the concentration of the filler. Finally, the Direct Current (DC) conductivity follows the VTF equation.

Study on reconstruction mechanism at the surface of a glassy polymer

The introduction of hydrophilic functional groups at various depths in the functionalized interfacial region of poly(4-methylstyrene) (P4MS) provided a system for studying the surface reconstruction mechanism of this glassy polymer. The degree of surface reconstruction (RD) and the rate of surface reconstruction (1/ t 1/2) were employed to compare the surface reconstruction behavior for various samples. The results showed that 1/ t 1/2 decreased with increase of the depth in the functionalized interface region at a temperature below T g of poly(4-methylstyrene). By studying the relation of water contact angles and the surface free energy of the samples with temperature, it was found that surface reconstruction of surface-oxidized P4MS samples took place in two steps when the samples were heated in air. The first step took place below 80 °C, in which polar side groups turned into the bulk, leaving a relatively nonpolar backbone projecting out of the surface to form a “hydrophobic conformation”. The second step occurred above the P4MS T g (110 °C), in which P4MS molecular chains migrated to the surface in order to minimize the interfacial free energy between surface-oxidized P4MS film and air, since oxidized P4MS molecules containing carbonyl groups have higher surface free energy than the unmodified P4MS molecules. As the depth of the functionalized interfacial region increases, a longer time is needed for the polar side groups to reorient (the first step) and for unoxidized P4MS molecules to migrate to the surface (the second step), which resulted in the sample with deeper functionalized region having lower reconstruction rate and RD using the same treatment condition.

Thermal stability of refractive index of polymethylmethacrylate layers prepared under electrical field

Thin films of polymethylmethacrylate (PMMA) were prepared by spin-coating with and without assistance of electrical field. Refractive index of the films was studied as a function of PMMA molecular weight and the time of specimen aging proceeding at different temperatures. The PMMA aging rate was modified by addition of non-polar polystyrene (PS). Refractive index and the aging rate of the films prepared under electrical field are inversely proportional to PMMA molecular weight. From calculated activation energy it is speculated that observed reorientation of PMMA macromolecules at elevated temperature is mostly due to a movement of side polar groups. Thermal stability of films composed of PMMA and PS increases with increasing fraction of PS. No measurable change of refractive index of the PMMA films with 4–10 wt.% PS admixture was observed even after 330 h of aging at 363 K, so that in these films no reorientation of PMMA dipoles occurs. Such films are considered as prospective materials for fabrication of planar optical waveguides.

Dielectric and conductivity processes in poly(ethylene terephthalate) and poly(ethylene naphthalate) homopolymers and copolymers

AbstractElectrical relaxation and conductivity processes in amorphous and semicrystalline poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) homopolymers and certain PET/PEN copolymers have been studied by means of dielectric spectroscopy. Homopolymers and copolymers able to crystallize were subjected to successive thermal runs to investigate the influence of the thermal history upon the morphology and the electrical behavior of the polymeric systems. The morphology of the untreated as well as the heat‐treated specimens was determined by means of Differential Scanning Calorimetry (DSC). All samples exhibit β‐relaxation process, due to local motions of the CO polar side groups, and α‐relaxation process associated to the glass/rubber transition. In the PEN spectrum an additional, subglass, mode was recorded, most probably attributed to cooperative motions of the naphthalene groups. Finally, the dynamic nature of the crystallization process is expressed via the over glass transition mode and the temperature dependence of dc conductivity recorded in amorphous PET, PEN, and PET/PEN (85/15) (wt/wt) samples. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3078–3092, 2006

Polyurethane latex/water dispersible boehmite alumina nanocomposites: Thermal, mechanical and dielectrical properties

Boehmite aluminas that become nanosize-dispersed in water were mixed with polyurethane (PU) latex. The produced nanocomposites were investigated upon their mechanical performance, thermal stability, water uptake and dielectric response as a function of the nominal nanoparticle size of the boehmites. The stiffness, determined by tensile experiment and dynamic mechanical thermal analysis (DMTA), was enhanced with decreasing particle size at the same filler content. The 25 nm alumina caused the highest modulus improvement, however, at cost of the thermal stability compared to the 90 nm and 220 nm boehmite aluminas. The water uptake increased by filling, however, decreased with increasing size of the alumina particles. The dielectric response of the nanocomposites was examined by means of broadband dielectric spectroscopy in the frequency range 10 −3–10 7 Hz, at ambient temperature. Three distinct relaxation modes were recorded in the spectra of all systems. They were attributed to interfacial polarization, glass transition (α-relaxation) and movement of polar side groups (β-relaxation). The intensity and position of these relaxations varied as a function of the size of the water dispersible boehmite.

Synthesis of silk fibroin‐insulin bioconjugates and their characterization and activities in vivo

The regenerated liquid silk fibroin with an average molecular mass of about 60 kDa consists of 18 kinds of amino acids containing approximately 10% of polar amino acids with hydroxyl and amino groups such as serine and lysine. The liquid silk fibroin is coupled covalently with insulin molecules through these strongly polar side groups by using glutaraldehyde. The physicochemical properties of the silk fibroin-insulin (SF-Ins) bioconjugates were investigated by enzyme-linked immunosorbent assay for the quantitative measurement of insulin. The biological activities of the insulin bioconjugates were characterized in vitro and in vivo. The SF-Ins constructs obtained by 5 h of covalent crosslinking showed much higher recovery (about 70%) and in vitro stability in human serum than bovine serum albumin-insulin (BSA-Ins) derivatives. The results in human serum indicated that the half-life in vitro of the biosynthesized SF-Ins derivatives was 2.1 and 1.7 times more than that of BSA-Ins conjugates and native insulin, respectively. The immunogenicity of the regenerated silk fibroin and the antigenicity of silk fibroin-modified insulin were not observed in both rabbits and rats. The pharmacological activity of the SF-Ins bioconjugates in diabetic rats evidently lengthened and was about 3.5 times as long as that of the native insulin, nearly 21 h. The bioconjugation of insulin with the regenerated silk fibroin greatly improved its physicochemical and biological stability.

Tannic acid‐stabilized pericardium tissue: IR spectroscopy, atomic force microscopy, and dielectric spectroscopy investigations

Infrared (IR) spectroscopy, atomic force microscopy (AFM), and dielectric spectroscopy methods were employed to study structural and dynamic changes in the tannic acid (TA)-stabilized pericardium tissue. Chemically stabilized pericardium tissue is widely used in construction of the tissue derived bioprostheses. IR spectra recorded in the range 400-4000 cm-1 allowed us to recognize different types of TA-collagen interactions. Formation of hydrogen bonds between amine as well as amide NH groups from collagen and hydroxyl groups of TA was analyzed. The AFM imaging showed that the stabilization procedure with TA introduces considerable changes in both surface topography and thickness of collagen fibrils as well as in fibril arrangement on the tissue surface. It was found, that these structural changes have an impact on the dielectric behavior of the TA-stabilized tissue. The dielectric spectra for the native and TA-stabilized tissues were measured in the frequency and temperature ranges of 10(-1) -10(7) Hz and 120-270 K, respectively. The dielectric spectra revealed the relaxation process due to orientation of bound water supplemented by the fluctuation of collagen polar side groups. At the temperatures above approximately 210 K, the relaxation due to ion migration process was observed. It was found that both relaxation processes were influenced by the TA-collagen interaction.