Interchain Packing Research Articles

2-(hydroxymethyl)pyridinium dihydrogenphosphate.

The title compound, C(6)H(8)NO(+).H(2)PO(4)(-), consists of 2-(hydroxymethyl)pyridinium and dihydrogenphosphate ions. The dihydrogenphosphate moieties are linked into chains by pairs of P-O-H.O-P hydrogen bonds. The 2-(hydroxymethyl)pyridinium cations are connected to the dihydrogenphosphate units by O-H.O and N-H.O hydrogen bonds. Weak pi-pi interactions help to determine the interchain packing.

Polyolefin Miscibility: Solid-State NMR Investigation of Phase Behavior in Saturated Hydrocarbon Blends

Chain-level mixing in polyolefins is investigated for blends of polyisobutylene (PIB) and polyethylene-co-1-butene (PEB). Previous reports suggest that PIB exhibits unusual mixing behavior in certain saturated blends relative to other polyolefins, even though it is immiscible with most. Variable-temperature 1H, 2H, 13C, and 129Xe NMR experiments are used to characterize local PIB chain dynamics in blends with PEB in which the concentration of 1-butene comonomer units is 23 or 66 wt %. Results from 1D and 2D solid-state 13C exchange experiments, 1H relaxation measurements, and 2H line shape analysis indicate that local conformational dynamics of the PIB CH2 group in the polymer backbone increase significantly in blends with PEB copolymers containing 66 wt % butene comonomer (PEB-66). Even though the PEB-66 is a higher Tg polymer than PIB, PIB exhibits a lower effective Tg when the blend is formed relative to its pure state. Similar perturbations are not observed in the PIB/PEB-23 blend, indicating that this blend is not miscible at the chain level. These results are directly relevant to the length scale of glass transitions in polyolefins, indicating that local interchain packing plays an important role in the conformational dynamics that occur within a chain, and are suggestive of local configurational entropy contributions to mixing. Although 1H spin-diffusion experiments could not reveal quantitative length scales of mixing in the these blends due to insufficient contrast between the constituents, 129Xe NMR experiments showed that the PIB/PEB-66 blend was homogeneous on a 50 nm length scale. In agreement with the heterogeneous morphology indicated by the dynamic NMR experiments, 129Xe NMR showed two resolved peaks for the PIB/PEB-23 blend, indicative of phase separation on a 50 nm length scale. The compilation of all the data, most of which was obtained at natural abundance, indicates that the PIB/PEB-66 blend exhibits intimate chain-level mixing on a length scale much shorter than Rg (ca. 8 nm). More importantly, the data show that reduced chain packing constraints occur in the miscible blend and suggest that local entropic contributions are the driving force for miscibility.

On the dynamic mechanical behavior of polyimides based on aromatic and alicyclic dianhydrides

AbstractA series of polyimides has been synthesized based on different dianhydrides and diamines. The microstructure of polyimide films has been analyzed by performing density measurements, X‐ray diffraction and UV‐visible spectrophotometry. The dynamic mechanical behavior was investigated according to both chemical and microstructural aspects. Thus, it was pointed out that the broadness of the β subglass transition is dependent not only on dianhydride flexibility but also on para‐ or meta‐diamine links. Such behavior is discussed in terms of intra‐charge transfer complex. On the contrary, the temperature location of the γ‐transition appears to be controlled by interchain packing. Based on a statistical approach, a correlation between microstructural data and gamma relaxation temperature is established.

INTERACTION OF CISPLATIN WITH CELLULAR MACROMOLECULES: A FOURIER TRANSFORM INFRARED SPECTROSCOPY STUDY

Platinum is a metallic element, which may react with our cellular component through its involvement in cancer chemotherapy medications. Cisplatin is one of the most useful antineoplastic drugs against human ovarian carcinoma, which has the central element of platinum in its structure. The nature of chemical interaction between platinum and cellular macromolecules is yet to be understood. We examined the interactions of platinum with human ovarian OV 2008 cancer cells by infrared spectroscopy, through the exposure of this cell line to cisplatin. These studies showed that there was an interaction between cisplatin and DNA and proteins. Nature of these interactions and their possible effects are discussed in this paper. In summary, it has caused denaturation of proteins and modification of the interchain packing of the DNA. Our results show that infrared spectroscopy is a potentially useful technique for monitoring the interaction of elements and drugs with cell components.

Gas transport in modified polysulfones with trimethylsilyl groups: effect of substitution site

Trimethylsilyl (TMS) groups were chemically introduced on to the phenylene group of bisphenol-A polysulfone (PSf) at sites ortho to ether (EM3) or to sulfone (SM3) linkages. Gas permeabilities increased by substitution of TMS and especially oxygen permeability increased from 1.1 barrer for PSf to 4.2 barrer for SM3 and to 7.1 barrer for EM3. Perm-selectivity of oxygen to nitrogen decreased from 5.8 to 5.5 and therefore substitution of TMS on polysulfone resulted in improved gas transport properties. In addition, it was found that EM3 is more effective in enhancing the gas transport properties than SM3. In order to interpret the effect substitution site on gas transport, d-spacing was investigated in terms of interchain packing. Furthermore, the effect of substitution site on chain motion was investigated through dynamic mechanical analyzer (DMA), dielectric analyzer (DEA), and solid-state NMR. DMA and DEA experiments showed that motions of unsubstituted phenylene and sulfonyl linkage are much more hindered in SM3 than in EM3. NMR experiments showed that motion of TMS is more mobile in EM3 than in SM3. These results revealed that chain motions of SM3 are more hindered than those of EM3 and substitution site affects chain motions. Therefore, we can conclude that these changes in chain motion also gas transport in modified polysulfones with silyl side group.

Anisotropic Polythiophene Films with High Conductivity and Good Mechanical Properties via a New Electrochemical Synthesis

A new electrochemical route to polythiophene (PT) films with an electrical conductivity between 800 and 1300 S cm–1 and a mechanical strength of 135 MPa is reported. The PT polymerization was performed in a BF3-ethyl ether solvated Lewis acid solution in the presence of the proton scavenger 2,6-di-tert-butylpyridine. The prepared PT films are shown to possess relatively regular molecular structure and inter-chain packing. The resulting microscopic structure enhances the macroscopic properties of the PT films.

Chain Packing in Ethoxyphenyl−Polycarbonate by 13C{2H} REDOR

Rotational-echo double-resonance 13 C{ 2 H} NMR has been used to characterize the chain packing in a 13 C, 2 H-labeled ethoxyphenyl-substituted bisphenol A polycarbonate. Approximately 36% of the repeat units are locally ordered, and between 85% and 95% of carbonate linkages are trans. The local order in interchain packing is correlated with the local order of intrachain conformations of the carbonate linkages.

Chain Packing in Linear Phenol−Polycarbonate by 13C{2H} REDOR

Interchain packing in [carbonyl-13C, phenol-2H]phenol-substituted bisphenol A polycarbonate (a totally amorphous polymer by X-ray powder diffraction) has been characterized by 13C{2H} rotational-echo double-resonance (REDOR) NMR measurements on a 10 A distance scale. Differences in the REDOR dephasing rates of the centerband and spinning sidebands of the carbonyl carbon resonance prove the presence of local orientational order. Approximately 70% of the repeat units are locally ordered. For the most tightly packed pairs of chains, the phenol 2H of one chain is 4−5 A from the carbonate 13C of the other chain, and the interchain 2H−13C dipolar vector has an orientation of approximately 30° (azimuthal) and 70° (polar) in the carbonyl carbon chemical shift tensor reference frame. The REDOR determination of these packing parameters is model-independent. Both random and chain-pair models were generated to describe the chain packing, but only the chain-pair model was consistent with the REDOR distance and orienta...

The structure of polypyridine

X-ray diffraction on samples in the form of a deposited thin layer, a crushed powder and a flake were used to deduce models for the crystalline structure of polypyridine ((C5H3N)n), a conjugated polymer of great interest for applications. A monoclinic unit cell with lattice parameters a=7.47Å, b=5.83Å, c=4.25Å, γ=108.7° containing two chains running along the c-axis and with the molecular plane normal to the a-axis gives a good fit with the observations. The interchain packing distance is about 3.6Å, i.e. in the same range as intermolecular distances found in conductive charge transfer salts. The deposited layer is highly anisotropic, with the a–c-plane parallel to the substrate.

Structure of Chlorotrifluoroethylene/Vinylidene Fluoride Random Copolymers and Homopolymers by Molecular Dynamics Simulations

We perform molecular dynamics simulations of chlorotrifluoroethylene (CTFE)/vinylidene fluoride (VDF) copolymers over a wide range of compositions and temperatures including the volumetric glass transition. Structural features of the polymers and copolymers were characterized using pair correlation functions and wide-angle X-ray scattering (WAXS) spectra. Calculated WAXS spectra for the CTFE/VDF copolymer known as Kel-F 800 are compared with experimental results and are found to compare well. The X-ray peak associated with interchain spacing is found to shift to larger scattering angles (smaller d spacings) as the concentration of the CTFE comonomer decreases, suggesting a transition between CTFE and VDF homopolymer interchain packing structures, consistent with earlier experiments. The strong compositional dependence is traced to packing involving the CF2 moiety. The calculated WAXS were further deconvoluted into atom−atom contributions in an attempt to explain the origin of the peak positions found in t...

A direct correlation function for mesomorphic polymers and its application to the ‘smectic’ phase of isotactic polpropylene

A general model to calculate the structure of a smectic to nematic-like order in polymer systems is proposed. The model is limited to well-aligned molecules with respect to each other. It is especially suited for systems where the packing between neighboring chains is described by liquid-like disorder with axial registration in the chain-axis direction. In such a case the diffraction pattern from the oriented structure exhibits broad liquid-like reflections on the equatorial but sharper reflections on the layer lines. An Ornstein–Zernike approach is adopted to calculate the inter-chain packing and inter-chain registration, where the direct correlation function of packing and registration are decoupled. The model is applied to quantify the structure of the smectic phase of isotactic polypropylene (i-PP).

X-ray diffraction and UV-Vis absorption studies of poly(di-n-hexylsilane) and poly(di-n-octylsilane) after quenching

Poly(di-n-hexylsilane) (PdHexSi) and poly(di-n-octylsilane) (PdOctSi) polymers have been studied using X-ray diffraction and UV-Vis absorption on warming after thermal quenching. These σ-conjugated conducting polymers exhibited qualitative similarities in their overall behavior. Quenching led to low temperature, ordered structures which retained the hexagonal interchain packing of the high temperature mesophase. This rapid cooling also suppressed the development of three-dimensional interchain ordering. In most other respects the behavior of PdHexSi was similar to that of slowly cooled samples. PdOctSi exhibited pronounced variations in both the X-ray diffraction and the UV absorption in comparison to its slowly cooled counterpart. These changes were found to be somewhat sample dependent. The diversity in PdOctSi behavior appears to stem from systematic changes in the side chain packing on passing from the n-hexyl to the n-octyl moiety.

Spiroalkanedithiol-Based SAMs Reveal Unique Insight into the Wettabilities and Frictional Properties of Organic Thin Films

Self-assembled monolayers (SAMs) were prepared by the adsorption of a series of 2,2-dialkylpropane- 1,3-dithiols (1-5) and 2-pentadecylpropane-1,3-dithiol (6) onto the surface of gold. These SAMs were characterized by ellipsometry, contact angle goniometry, X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and atomic force microscopy (AFM). The studies demonstrate that a systematic variation in the structure of RRC(CH2SH)2 from symmetrical (1 ;R ' ) R) to progressively more unsymmetrical (2-6 ;R ' * R) can be used to provide control over the conformational order and interchain packing of the hydrocarbon tail group assembly. The tail group conformation and packing were found to influence profoundly both the wettability and the tribological properties of the SAMs. Assemblies of well-ordered, well-packed hydrocarbon tail groups yielded interfaces that exhibited low wettabilities and low frictional responses when compared to assemblies of disordered, loosely packed hydrocarbon tail groups. The trends in wettability and friction were rationalized by considering the magnitude of the van der Waals interactions between the hydrocarbon film and the contacting probe liquid and AFM tip, respectively.

Infrared Spectroscopic and Modulated Differential Scanning Calorimetric Study of Physical Aging in Bisphenol A Polycarbonate

FT-IR spectroscopy was used to examine conformational changes in the quenched Bisphenol A Polycarbonate (BPAPC) films during physical aging. It was observed that the amount of energy favored trans-trans conformers increased, while energy less favored trans-cis conformers decreased upon sub-Tg annealing. Since the trans-trans conformers allow closer local packing of the polymer chains than the trans-cis conformers do, the results may indicate that sub-Tg annealing will lead to closer interchain packing. In situ FT-IR studies on the conformational changes of BPAPC films with different thermal histories, i.e., quenched from the rubbery and sub-Tg annealed for different time, were carried out while increasing the temperature through the glass transition region. The temperature dependencies of the infrared spectra show that incremental changes of the population of trans-cis conformers in the quenched sample are gradual, while rather abrupt changes occur in the sub-Tg annealed samples. The magnitude and temperature of the abrupt changes of trans-cis conformers are related with the time of the sub-Tg annealing. The energy absorbed during the abrupt conformational change represents only part of the energy of the endothermic peak observed by modulated differential scanning calorimetry. The results are explained in terms of the formation of new cohesional entanglements during sub-Tg annealing.

Conformation and Monolayer Assembly Structure of a Pentiptycene-Derived α,ω-Alkanedithiol

The synthesis, conformation, and monolayer assembly structure of a pentiptycene-derived α,ω-alkanedithiol (1) are reported. The results of MM2 modeling, the scanning tunneling microscopy (STM), and the surface plasmon resonance (SPR) suggest that 1 favors a folded conformation, corresponding to a looped monolayer assembly structure, on the Pt(111) and Au(111) surfaces. Nonetheless, the conformation of 1 in the crystals might be an extended form according to the crystal structure of an analogous compound 4. The relative interchain interactions and packing densities can account for the choice between a folded and an extended conformation for 1 in the condensed phases.

Conservation of cys–cys trp structural triads and their geometry in the protein domains of immunoglobulin superfamily members

In almost all members of the immunoglobulin superfamily (IgSF) for which an experimental structure has been determined, a triad (C–CW) consisting of two cysteine residues that form a disulfide bond and a neighboring tryptophan can be found in the core of the protein fold. We analyzed the geometry of these C–CW triads among a database of 60 Fab crystal structures and found it to be remarkably conserved. We identified C–CW triads of a similar configuration in other members of the IgSF such as T cell receptor (TCR), major histocompatibility complex antigens (MHC), cell surface antigens CD4 and CD8, and cell-adhesion molecules. We used this C–CW pattern to search a database of non-IgSF proteins, and identified several proteins that contain a disulfide bridge associated with a tryptophan in a similar configuration. Examination of the distances and orientations between triads found in adjacent domains in Fab fragments and TCR also reveal a high degree of conservation, which reflects the invariance of the inter-chain domain packing. This high degree of conservation of the geometry of the C–CW triad in IgSF structures suggests that the Trp may contribute significantly to the stability of the disulfide bond. Knowledge of these geometric parameters may prove useful in the construction and validation of theoretical models of Ig, TCR, and other IgSF members.

Nearly pure α2 form crystals obtained by melt crystallization of high tacticity isotactic polypropylene

The effect of tacticity on the formation of the most ordered from of α2 modification of crystals of isotactic polypropylene (iPP) during melt crystallization at atmospheric pressure has been investigated. It was found that melt crystallization of iPP with 99.5% isotacticity at 150°C resulted in nearly 100% pure α2 form crystals, i.e. fraction of α2(ƒ(α2)) = 1. At temperatures higher than 150°C, ƒ(α2) was found to decrease from unity. The present study on the two different molecular weight samples showed that molecular weight does not influence the α2 formation. The results are explained on the basis of the effect of chain mobility and thermal expansion on the regularity of interchain packing.

Subglass-transition-temperature annealing of poly(ethylene terephthalate) studied by FTIR

Using FTIR spectroscopy we have examined conformational changes in the quenched and slowly cooled amorphous PET films during physical aging process. It was observed that the amount of trans conformers for quenched sample decreased upon sub-Tg annealing. For the slowly cooled sample that corresponds to a state closer to equilibrium, the amount of trans conformers hardly decreased, but increased gradually during sub-Tg annealing process. The conformational populations of these two samples tend to be identical with annealing time. These results demonstrate that sub-Tg annealing will lead to closer interchain packing and result in the formation of new cohesional entanglements along the chains. In situ FTIR studies on the conformational changes of these samples were also carried out during heating up of the sample through the glass transition region. The results showed that incremental changes of the amount of trans conformers in Samples Q and SC were gradual, while an abrupt change of trans conformers occurred in the sub-Tg annealed samples. These results were in agreement with the formation of the interchain cohesional entanglement due to sub-Tg annealing. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 783–788, 1998

Liquid-State Theory of Semidilute and Concentrated Polymer Solutions

We present a theory for thermodynamic and equation-of-state properties of polymer solutions over the entire concentration range, and for homopolymer melts, based on analytic polymer reference interaction site model (PRISM) methods. A single polymer is modeled as either an effectively Gaussian thread, or as a Gaussian string which approximately accounts for the effects of a nonzero chain thickness. Both good (athermal) and ϑ solvent conditions are considered within a molecular closure approximation scheme. Good agreement is found with experimentally measured second and third virial coefficients, and with the osmotic pressure and screening length, in dilute and semidilute athermal solutions. Experimentally observed deviations from the power law dependence on chain length (N) of the athermal second and third virial coefficients is interpreted in terms of finite segmental hard core interchain packing effects at low molecular weights; these finite size effects are predicted to vanish in the limit N → ∞. For lo...

Characterization of the interaction of Ca2+ with hydroxy and non-hydroxy fatty acid species of cerebroside sulfate by Fourier transform infrared spectroscopy and molecular modeling.

Ca2+-mediated interactions between the carbohydrate groups of glycolipids, including that of cerebroside sulfate (galactosylceramide I3-sulfate), have recently been implicated as a basis of cell recognition and adhesion. Hydroxylation of the fatty acid of this lipid has an effect on these interactions. Therefore, FT-IR spectroscopy was used to study the interaction of Ca2+ with semisynthetic hydroxy (HFA) and non-hydroxy fatty acid (NFA) species of cerebroside sulfate (CBS). Ca2+ caused partial dehydration of the sulfate group and reduced hydrogen bonding of the sugar hydroxyls of both species. The amide I and II bands of the lipids in the absence of Ca2+ (NH4+ salt forms) suggested that the N-H of the HFA species is involved in a bent intramolecular hydrogen bond, probably with the fatty acid hydroxyl group and the glycosidic oxygen, while that of the NFA species is involved in a linear intermolecular hydrogen bond with the C=O and/or other oxygens. Ca2+ caused a rearrangement of the hydrogen-bonding network in the interfacial region of the HFA species involving the amide group. The results suggested increased hydrogen bonding of the C=O and a shift in hydrogen bonding of the N-H of the Ca2+ salt form of the HFA species from a bent intramolecular hydrogen bond to a linear intermolecular hydrogen bond, probably with the C=O of neighboring molecules, similar to the NFA species. The involvement of the fatty acid alpha-hydroxyl group in the rearranged network was indicated by a reduction in mobility of the alpha-CH group of the HFA species, in contrast to that of the NFA species. Participation of the alpha-OH group in hydrogen-bonding networks in the interfacial region of both the NH4+ and Ca2+ salt forms caused a significant increase in the interchain packing, as evident from correlation field splitting of the HFA-CBS methylene scissoring mode, while this did not occur for the NFA species. The absence of intramolecular hydrogen bonding of the N-H with the glycosidic oxygen for both salt forms of the NFA species and for the Ca2+ salt form of the HFA species may destabilize the "bent shovel", bilayer planar conformation of the sugar and cause it to be in the extended, bilayer perpendicular conformation. Calculations of the three-dimensional interaction energy of Ca2+ with CBS showed strong binding around the sulfate and the surface of galactose facing the bilayer in the bent shovel conformation. Ca2+ binding at this surface would disrupt intra- and intermolecular hydrogen-bonding interactions of the head group, thus accounting for its effect in inducing a transition to the extended conformation.