Synapse-Mimicking Memristors Based on 3,6-Di(tpy)-9-Phenylcarbazole Unimer and Its Copolymer with Cobalt(II) Ions.

The title compound, unimer U (tpy stands for 2,2':6',2″-terpyridin-4'-yl end-group), by itself shows the memristor effect with a retention time of 18 h and persistence of 11 h. Its coordination copolymer with Co(II) ions, [CoU]n, exhibits multimodal resistance changes similar to the synaptic responses observed in biological systems. More than 320 cycles of potentiation and depression measured in continuous sequence occurred without observing a significant current change, confirming the operational stability and reproducibility of the device based on the [CoU]n polymer. The synaptic effect of a device with an indium tin oxide (ITO)/[CoU]n/top-electrode (TE) configuration is more pronounced for the device with TE = Au compared to devices with TE = Al or Ga. However, the latter TEs provide a cost-effective approach without any significant compromise in device plasticity. The detected changes in the synaptic weight, about 12% for pair-pulse facilitation and 80% for its depression, together with a millisecond trigger and reading pulses that decay exponentially on the time scale typical of neurosynapses, justify the device's ability to learn and memorize. These properties offer potential applications in neuromorphic computation and brain-inspired synaptic devices.

Antifouling Microparticles To Scavenge Lipopolysaccharide from Human Blood Plasma.

Currently, one of the most promising treatments of lipopolysaccharides (LPS)-induced sepsis is based on hemofiltration. Nevertheless, proteins rapidly adsorbed on the artificial surface of membranes which leads to activation of coagulation impairing effective scavenging of the endotoxins. To overcome this challenge, we designed polymer-brush-coated microparticles displaying antifouling properties and functionalized them with polymyxin B (PMB) to specifically scavenge LPS the most common endotoxin. Poly[( N-(2-hydroxypropyl) methacrylamide)- co-(carboxybetaine methacrylamide)] brushes were grafted from poly(glycidyl methacrylate) microparticles using photoinduced single-electron transfer living radical polymerization (SET-LRP). Notably, only parts-per-million of copper catalyst were necessary to achieve brushes able to repel adsorption of proteins from blood plasma. The open porosity of the particles, accessible to polymerization, enabled us to immobilize sufficient PMB to selectively scavenge LPS from blood plasma.

Structural insight into the physical stability of amorphous Simvastatin dispersed in pHPMA: enhanced dynamics and local clustering as evidenced by solid-state NMR and Raman spectroscopy.

New drug formulations are sought for poorly water-soluble substances because there is a risk of compromised bioavailability if such substances are administered orally. Such active pharmaceutical ingredients can be reformulated as solid dispersions with suitable water-soluble polymers. In this contribution, formulation of a novel and physically stable dispersion of Simvastatin in poly(2-hydroxypropyl) methacrylamide (pHPMA) is demonstrated. Due to the limited water sorption of pHPMA and a high Tg, the prepared dispersion is more suited for oral administration and storage compared with neat amorphous Simvastatin. Surprisingly, the rate of global reorientation and the internal motion of Simvastatin molecules were enhanced and exhibited dynamical heterogeneities when incorporated into the pHPMA matrix. As revealed by solid-state nuclear magnetic resonance combined with Raman spectroscopy exploiting the fluorescence phenomenon the mobility of the ester and lactone components increased considerably, whereas the naphthalene ring remained rigid. Furthermore, the solid dispersion was found to be nano-heterogeneous with nanometer-sized Simvastatin domains. The presence of these clusters had no impact on the dynamics of the rigid pHPMA chains. Thus, the diffusion of Simvastatin molecules through the glassy pHPMA walls and the subsequent transformation of the clusters into larger crystallites were prevented. No crystallization was detected for more than two years.

Self-assembly thermodynamics of pH-responsive amino-acid-based polymers with a nonionic surfactant.

The behavior of pH-responsive polymers poly(N-methacryloyl-l-valine) (P1), poly(N-methacryloyl-l-phenylalanine) (P2), and poly(N-methacryloylglycyne-l-leucine) (P3) has been studied in the presence of the nonionic surfactant Brij98. The pure polymers phase-separate in an acidic medium with critical pHtr values of 3.7, 5.5, and 3.4, respectively. The addition of the surfactant prevents phase separation and promotes reorganization of polymer molecules. The nature of the interaction between polymer and surfactant depends on the amino acid structure in the side chain of the polymer. This effect was investigated by dynamic light scattering, isothermal titration calorimetry, electrophoretic measurements, small-angle neutron scattering, and infrared spectroscopy. Thermodynamic analysis revealed an endothermic association reaction in P1/Brij98 mixture, whereas a strong exothermic effect was observed for P2/Brij98 and P3/Brij98. Application of regular solution theory for the analysis of experimental enthalpograms indicated dominant hydrophobic interactions between P1 and Brij98 and specific interactions for the P2/Brij98 system. Electrophoretic and dynamic light scattering measurements support the applicability of the theory to these cases. The specific interactions can be ascribed to hydrogen bonds formed between the carboxylic groups of the polymer and the oligo(ethylene oxide) head groups of the surfactant. Thus, differences in polymer-surfactant interactions between P1 and P2 polymers result in different structures of polymer-surfactant complexes. Specifically, small-angle neutron scattering revealed pearl-necklace complexes and "core-shell" structures for P1/Brij98 and P2/Brij98 systems, respectively. These results may help in the design of new pH-responsive site-specific micellar drug delivery systems or pH-responsive membrane-disrupting agents.

The effect of micellization-induced deprotonation on the associative behavior of a carboxyl modified Pluronic P85.

Thermoresponsive polymeric surfactant CAE85 is a telechelic carboxyl group derivative of Pluronic P85 and its carboxyl end-groups undergo deprotonation into carboxylate groups upon micellization. Micelle formation and disintegration were studied here by means of small angle X-ray scattering, FTIR and Raman spectroscopy, quantum mechanical calculations and dynamical mechanical analysis. The deprotonation was observed in aqueous solutions of CAE85 for concentrations from 5 wt% to 30 wt% at temperatures above the corresponding critical micellization temperature (CMT). The most likely cause is a difference between the proton dissociation constant of the micelle (pK(m)) and the proton dissociation constant of the unimers in solution (pK(a)); our observations indicate that pKm < pK(a). For concentrations up to 15 wt%, the presence of carboxylate groups in CAE85 lowered the CMT in comparison with P85. In addition, the behavior of CAE85 was generally not thermo-reversible and reproducible upon cooling. Quantum chemical calculations showed that, in the dense micelle corona, the deprotonated states were more stable than hydrogen-bonded states of neutral molecules, which is likely to affect the equilibrium processes in the micelle. In contrast to the unmodified P85, no gelation was observed in the case of CAE85. By studying the processes at all the levels of organization from nanoscale charge formation through micellization to the macroscale process of gelation, our understanding of polymeric micelle formation may be advanced.

Characterizing crystal disorder of trospium chloride: a comprehensive,(13) C CP/MAS NMR, DSC, FTIR, and XRPD study.

Analysis of C cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and X-ray powder diffraction data of trospium chloride (TCl) products crystallized from different mixtures of water-ethanol [φ(EtOH) = 0.5-1.0] at various temperatures (0°C, 20°C) and initial concentrations (saturated solution, 30%-50% excess of solvent) revealed extensive structural variability of TCl. Although (13) C CP/MAS NMR spectra indicated broad variety of structural phases arising from molecular disorder, temperature-modulated DSC identified presence of two distinct components in the products. FTIR spectra revealed alterations in the hydrogen bonding network (ionic hydrogen bond formation), whereas the X-ray diffraction reflected unchanged unit cell parameters. These results were explained by a two-component character of TCl products in which a dominant polymorphic form is accompanied by partly separated nanocrystalline domains of a secondary phase that does not provide clear Bragg reflections. These phases slightly differ in the degree of molecular disorder, in the quality of crystal lattice and hydrogen bonding network. It is also demonstrated that, for the quality control of such complex products, (13) C CP/MAS NMR spectroscopy combined with factor analysis (FA) can satisfactorily be used for categorizing the individual samples: FA of (13) C CP/MAS NMR spectra found clear relationships between the extent of molecular disorder and crystallization conditions. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:1235-1248, 2013.

Structure of cellulose microfibrils in primary cell walls from collenchyma.

In the primary walls of growing plant cells, the glucose polymer cellulose is assembled into long microfibrils a few nanometers in diameter. The rigidity and orientation of these microfibrils control cell expansion; therefore, cellulose synthesis is a key factor in the growth and morphogenesis of plants. Celery (Apium graveolens) collenchyma is a useful model system for the study of primary wall microfibril structure because its microfibrils are oriented with unusual uniformity, facilitating spectroscopic and diffraction experiments. Using a combination of x-ray and neutron scattering methods with vibrational and nuclear magnetic resonance spectroscopy, we show that celery collenchyma microfibrils were 2.9 to 3.0 nm in mean diameter, with a most probable structure containing 24 chains in cross section, arranged in eight hydrogen-bonded sheets of three chains, with extensive disorder in lateral packing, conformation, and hydrogen bonding. A similar 18-chain structure, and 24-chain structures of different shape, fitted the data less well. Conformational disorder was largely restricted to the surface chains, but disorder in chain packing was not. That is, in position and orientation, the surface chains conformed to the disordered lattice constituting the core of each microfibril. There was evidence that adjacent microfibrils were noncovalently aggregated together over part of their length, suggesting that the need to disrupt these aggregates might be a constraining factor in growth and in the hydrolysis of cellulose for biofuel production.

Role of hydration and water coordination in micellization of Pluronic block copolymers.

Raman, attenuated total reflectance FTIR, near-infrared spectroscopy, and DFT calculations have been used in a study of aqueous solutions of three tri-block copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) or PEO-PPO-PEO with commercial names Pluronic PE6200, PE6400 and F68. It is shown that the process of micellization as a response to increased temperature is reflected in the hydroxyl stretching region of infrared and Raman spectra, which contains information both about restructuring of water and changes of polymer chains in polymer/water aggregates. Raman spectra exhibit differences between individual Pluronics even at temperatures below the critical micellization temperature (CMT). According to the attenuated total reflection (ATR) FTIR spectra, the same five water coordination types defined by the number of donated/accepted hydrogen bonds are present in interacting water as in bulk water. It indicates that models considering mixed states of water with different hydrogen bonding environments provide appropriate descriptions of bound water both below and above the CMT. Above the CMT, aggregate hydration increases in the order PE6400 < PE6200 < F68, although that does not fully correspond to the EO/PO ratio, and points to the differences in microstructure of aggregates formed by each copolymer. This study relates nanoscale phenomena (hydrophobic and hydrophilic hydration) with the mesoscale phenomenon of micellization.

Vibrational spectroscopy of biopolymers under mechanical stress: processing cellulose spectra using bandshift difference integrals.

Mechanical stretching of covalent bonds, for example when a fibrous polymer is loaded in tension, results in their stretching vibrational bands in the infrared or Raman spectrum being shifted to lower frequency. Conversely stretching a hydrogen bond shifts the stretching vibrational mode of the donor covalent X-H bond to higher frequency. These band shifts are small and difficult to detect in complex regions of the spectrum where differently affected bands overlap. This paper describes a method of integrating the difference spectra (spectrum under tensile strain minus spectrum at zero tensile strain) to recover the shape of the bands that are shifted and the spectral variation in bandshift. The application of this method to two sets of vibrational spectra of cellulose under tension is described. In one example, C-O-C stretching bands of highly crystalline tunicate cellulose were observed to shift to lower frequency under axial strain. In the other example, a group of overlapping O-D stretching bands in partially deuterated cellulose showed varied bandshifts under axial strain, some bandshifts being positive as expected due to extension of axially oriented hydrogen bonds while others were negative. The possibility of constructing spectral plots of bandshift has the potential to clarify the interpretation of overlapped, shifting bands in the vibrational spectra of polymers under tension.

Cell-wall structure and anisotropy in procuste, a cellulose synthase mutant of Arabidopsis thaliana.

In dark-grown hypocotyls of the Arabidopsis procuste mutant, a mutation in the CesA6 gene encoding a cellulose synthase reduces cellulose synthesis and severely inhibits elongation growth. Previous studies had left it uncertain why growth was inhibited, because cellulose synthesis was affected before, not during, the main phase of elongation. We characterised the quantity, structure and orientation of the cellulose remaining in the walls of affected cells. Solid-state NMR spectroscopy and infrared microscopy showed that the residual cellulose did not differ in structure from that of the wild type, but the cellulose content of the prc-1 cell walls was reduced by 28%. The total mass of cell-wall polymers per hypocotyl was reduced in prc-1 by about 20%. Therefore, the fourfold inhibition of elongation growth in prc-1 does not result from aberrant cellulose structure, nor from uniform reduction in the dimensions of the cell-wall network due to reduced cellulose or cell-wall mass. Cellulose orientation was quantified by two quantitative methods. First, the orientation of newly synthesised microfibrils was measured in field-emission scanning electron micrographs of the cytoplasmic face of the inner epidermal cell wall. The ordered transverse orientation of microfibrils at the inner face of the cell wall was severely disrupted in prc-1 hypocotyls, particularly in the early growth phase. Second, cellulose orientation distributions across the whole cell-wall thickness, measured by polarised infrared microscopy, were much broader. Analysis of the microfibril orientations according to the theory of composite materials showed that during the initial growth phase, their anisotropy at the plasma membrane was sufficient to explain the anisotropy of subsequent growth.

Elastic modulus and stress-transfer properties of tunicate cellulose whiskers.

Experimental deformation micromechanics of natural cellulose fibers using Raman spectroscopy and X-ray diffraction have been widely reported. However, little has been published on the direct measurements of the mechanical properties, and in particular the elastic modulus, of the highly crystalline material in the native state. Here we report on measurements of the elastic modulus of tunicate cellulose using a Raman spectroscopic technique. A dispersed sample of the material is deformed using a four-point bending test, and a shift in a characteristic Raman band (located at 1095 cm(-1)) is used as an indication of the stress in the material. Relatively little intensity change of the Raman band located at 1095 cm(-1) is shown to occur for samples oriented parallel and perpendicular to the polarization direction of the laser, as compared to a highly oriented flax sample. This indicates that the tunicate sample is a two-dimensional in-plane random network of fibers. By use of this result, the Raman shift, and calibrations with strain from other materials, it is shown that the modulus of the material is very high, at about 143 GPa, and a lack of Raman band broadening is thought to be due to the fact that there is pure crystalline deformation occurring without the effect of crystalline/amorphous fractions. A strain sensitivity of the shift in the 1095-cm(-1) Raman peak for this specimen is shown to be -2.4 +/- 0.2 cm(-1)/%. A molecular mechanics approach, using computer simulation and an empirical force field, was used to predict the modulus of a highly oriented chain of the material, and this is found to be 145 GPa, which is in agreement with the experimental data. However, by use of a normal-mode analysis, it is found that a number of modes have positions close to the central positions of the experimental Raman band. One in particular is found to shift at a rate of 2.5 cm(-1)/%, but due to the complex nature of the structure, it is not entirely conclusive that this band is representative of the experimental findings.

Structural details of crystalline cellulose from higher plants.

It is commonly assumed that cellulose from higher plants contains the Ialpha and Ibeta crystalline allomorphs together with surface and disordered chains. For cellulose Ialpha, the evidence for its presence in higher plants is restricted to the C-4 signals in the solid-state (13)C NMR spectrum, which match those of crystalline cellulose Ialpha from algal sources. Algal cellulose Ialpha can be converted to the Ibeta form by high-temperature annealing. We used this approach to generate cellulose samples differing in Ibeta content from flax fibers and celery collenchyma, which respectively are representative of textile (secondary-wall) and primary-wall cellulose. It was then possible to isolate the detailed spectral contributions of the surface, Ibeta and Ialpha-like phases from linear combinations of the observed (13)C NMR and FTIR spectra. The (13)C NMR spectra resembled those of highly crystalline tunicate or algal cellulose Ibeta and Ialpha, with slight differences implying increased disorder and minor conformational discrepancies. The FTIR spectrum of the Ibeta form was closely similar to its more crystalline counterparts, but the FTIR spectrum of the Ialpha form was not. In addition to increased bandwith indicative of lower order, it showed substantial differences in the profile of hydroxyl stretching bands. These results confirm that higher plants synthesize cellulose Ibeta but show that the Ialpha-like chains, although conformationally quite similar to crystalline algal cellulose Ialpha, sit in a different hydrogen-bonding environment in higher plants. The differences are presumably occasioned by the small diameter of the crystallites and the influence of the crystallite surface on chain packing.

Polarized vibrational spectroscopy of fiber polymers: hydrogen bonding in cellulose II.

Vibrational spectroscopy using polarized incident radiation can be used to determine the orientation of X-H bonds with respect to coordinates such as crystallographic axes. The adaptation of this approach to polymer fibers is described here. It requires spectral intensity to be quantified around a 180 degrees range of polarization angles and not just recorded transversely and longitudinally as is normal in fiber spectroscopy. Mercerized cellulose II is used as an example. The unit cell of the cellulose II lattice contains six distinct hydroxyl groups engaged in a complex network of hydrogen bonds that hold the cellulose chains laterally together. A formalism is described to relate the variation in intensity of each O-H stretching mode to the angle between its transition moment and the chain axis as the polarization axis is rotated with respect to the fiber axis. It was necessary to include the effect of dispersion in chain orientation around the mean and the averaging of all rotational positions of the chains round their axis. The two crystallographically distinct O(2)-H groups, which are each hydrogen-bonded to only one acceptor oxygen, show a close match in orientation between the transition moments of their stretching bands and the O-H bond axis. The two O(3)-H groups each have a three-centered hydrogen bond to O-5 and O-6 of the next residue in the same chain. The transition moments of their stretching modes lay between the acceptor oxygens. Hydrogen bonding from the O(6)-H groups is still more complex but again the transition moment of each O-H bond lay within the cone of orientations described by the acceptor oxygens, provided that one additional acceptor oxygen excluded from the published crystal structure was considered. The transition moments for the O-H stretching modes were approximately aligned with the O-H bond axes, but the alignment was not necessarily exact. This approach is not restricted to hydroxyl groups, but it is particularly useful for the elucidation of hydrogen bonding in fibrous polymers for which crystallographic data on proton positions are not available.

Structure of cellulose-deficient secondary cell walls from the irx3 mutant of Arabidopsis thaliana.

In the Arabidopsis mutant irx3, truncation of the AtCesA7 gene encoding a xylem-specific cellulose synthase results in reduced cellulose synthesis in the affected xylem cells and collapse of mature xylem vessels. Here we describe spectroscopic experiments to determine whether any cellulose, normal or abnormal, remained in the walls of these cells and whether there were consequent effects on other cell-wall polysaccharides. Xylem cell walls from irx3 and its wild-type were prepared by anatomically specific isolation and were examined by solid-state NMR spectroscopy and FTIR microscopy. The affected cell walls of irx3 contained low levels of crystalline cellulose, probably associated with primary cell walls. There was no evidence that crystalline cellulose was replaced by less ordered glucans. From the molecular mobility of xylans and lignin it was deduced that these non-cellulosic polymers were cross-linked together in both irx3 and the wild-type. The disorder previously observed in the spatial pattern of non-cellulosic polymer deposition in the secondary walls of irx3 xylem could not be explained by any alteration in the structure or cross-linking of these polymers and may be attributed directly to the absence of cellulose microfibrils which, in the wild-type, scaffold the organisation of the other polymers into a coherent secondary cell wall.