Intermolecular Association Research Articles

Slowly digestible starch in fully gelatinized material is structurally driven by molecular size and A and B1 chain lengths

The objective of this study was to obtain structure-digestion relationships of fully gelatinized starch. Twelve starch samples with marked fine structural differences (HPLC-SEC) were studied for their retrogradation behavior (thermal and rheological properties of starch gels) and in vitro digestibility. A reduction in the digestion rate during storage for 7 days was observed in all samples and, interestingly, this reduction was particularly evident in sago (64.7%), potato (57.3%), pea (55.1%) and acid-converted maize (ACM, 51.6–51.8 %) starches. Results indicated two potential interactions that may result in slowly digestible supramolecular structures: 1) double helices between external A and B1 chains of DP at peak maximum ≥ 15.5 Glucose Units (perhaps involving internal long chains) that also are prone to forming intermolecular associations [high relative drop in the storage modulus (G’) during heating of 7 days-stored gels] and; 2) interactions of small molecular size acid-hydrolyzed starch molecules that may be more mobile and easily aligned.

Magnetism and EPR Studies of Binuclear Ruthenium Hydride Binuclear Species Bearing Redox-Active Ligands.

The binuclear complex {[N3]Ru(H)}2(μ-η1:η1-N2) ([N3] = 2,6-(ArylN═CMe)2C5H3N and Aryl = mesityl or xylyl) contains two formally Ru(I), d7 centers linked by a bridging dinitrogen ligand, although the odd electrons are substantially delocalized onto the redox non-innocent pincer ligands. The complex exhibits paramagnetic behavior in solution, but is diamagnetic in the solid state. This difference is attributed to intermolecular "π-stacking" observed in the solid state, which essentially couples unpaired electrons on each half of the complex to form delocalized 22-center-2-electron covalent bonds. Introduction of a bulky t-butyl group on the ligand pyridine ring prevents this intermolecular association and allows further investigation of the magnetic behavior and electronic structure of the binuclear species. The interaction of the unpaired electrons in the two halves of the complex has been probed with magnetic susceptibility and perpendicular and parallel mode EPR measurements, revealing a weakly antiferromagnetically coupled system with a thermally accessible triplet excited state. In addition, the mixed valent, S = 1/2, {[N3]Ru(H)}(μ-η1:η1-N2){[N3]Ru} system has also been observed via perpendicular mode EPR and was used to quantify the growth of the thermally accessible triplet state of the dihydride complex using parallel mode EPR.

Structural and Intermolecular Associations Between Connexin36 and Protein Components of the Adherens Junction–Neuronal Gap Junction Complex

Intimate structural and functional relationships between gap junctions and adherens junctions have been demonstrated in peripheral tissues, but have not been thoroughly examined in the central nervous system, where adherens junctions are often found in close proximity to neuronal gap junctions. Here, we used immunofluorescence approaches to document the localization of various protein components of adherens junctions in relation to those that we have previously reported to occur at electrical synapses formed by neuronal gap junctions composed of connexin36 (Cx36). The adherens junction constituents N-cadherin and nectin-1 were frequently found to localize near or overlap with Cx36-containing gap junctions in several brain regions examined. This was also true of the adherens junction-associated proteins α-catenin and β-catenin, as well as the proteins zonula occludens-1 and AF6 (aka, afadin) that were reported constituents of both adherens junctions and gap junctions. The deployment of the protein constituents of these junctions was especially striking at somatic contacts between primary afferent neurons in the mesencephalic trigeminal nucleus (MesV), where the structural components of adherens junctions appeared to be maintained in connexin36 null mice. These results support emerging views concerning the multi-molecular composition of electrical synapses and raise possibilities for various structural and functional protein–protein interactions at what now can be considered the adherens junction–neuronal gap junction complex. Further, the results point to intracellular signaling pathways that could potentially contribute to the assembly, maintenance and turnover of this complex, as well as to the dynamic nature of neuronal communication at electrical synapses.

Molecular association of small amphiphiles: Origin of ionic liquid properties in dibutyl phosphate/propylamine binary mixtures

Binary mixtures of liquid surfactants, owing to the amphiphilic nature of the molecules involved, can exhibit nano-segregation and peculiar transport properties. The amphiphilicity, and consequently the resulting self-assembly, can be tuned by changing the length of the alkyl chains and the nature of the polar head group. So, in the present study, the structural and dynamic properties of dibutyl phosphate/propylamine liquid mixtures at various compositions have been investigated by Wide Angle X-ray Scattering (WAXS), FT-IR, rheometry and dielectric spectroscopy in order to study the intermolecular association taking place when alkylphosphates and alkylamines with a small apolar part are mixed together. It was found that a proton transfer from the dibutyl phosphate PO4H group to the propilamine NH2 one takes place, due to the acidic and basic nature of the two molecules involved. This triggers the formation of charged species and an intermolecular association typical of ionic liquid systems and causing an increase in viscosity of two orders of magnitude with respect to the two pure components. Effects due to the different amine isomers have been highlighted since the steric hindrance of the amine alkyl chain can significantly contribute to the molecular slippage thus affecting the overall mixture viscosity. Surprising dielectric properties have also been observed at a specific composition: a strikingly enhanced proton conductivity and a negative value of the dielectric constant in the MHz frequency range, as a result of the local self-assembly and the competition between the mechanism of jump of “free” protons among neighboring polar headgroups and the molecularly-assisted mechanism of charge transport. This work shows news potentialities of such systems as specialized solvent media and proton conducting water-free organic-based liquid systems and, from a more general prospect, the comprehension of the molecular mechanism involved in their transport properties is pivotal for the piloted design of smart materials for specific applications.

Utilization of steric hindrance of alkyl lithium-based initiator to synthesize high 1,4 unit-containing hydroxyl- terminated polybutadiene.

A novel alkyl lithium-based initiator with relatively large steric hindrance, tert-butyldimethylsiloxydimethylpropyl lithium (TBDMSODPrLi), was designed and synthesized. By using TBDMSODPrLi, hydroxyl-terminated polybutadiene (HTPB) was prepared via anionic polymerization. The macromolecular structure of HTPB was characterized and verified by FTIR and 1H-NMR. It was found that 1,4 unit content in HTPB initiated by TBDMSODPrLi was significantly higher (over 90%) compared to a HTPB (1,4 unit content of 70%) initiated with another initiator possessing smaller steric hindrance. The possible mechanism, which was based on initiator steric hindrance affecting monomer chain addition behaviour, was deduced. It was that the initiator's larger steric hindrance blocked lithium's intermolecular association during anionic polymerization; as a result, it could effectively increase the 1,4 unit content in HTPB. To further study how to obtain higher and stable 1,4 unit content, the optimal anionic polymerization technique for HTPB was explored including polymerization temperature, time and the amount of initiator used. The study concluded that utilization of an initiator with larger steric hindrance and reducing the polymerization temperature were two important factors to raise the 1,4 unit content in HTPB.

Synergistic Amyloid Switch Triggered by Early Heterotypic Oligomerization of Intrinsically Disordered α-Synuclein and Tau

Amyloidogenic intrinsically disordered proteins, α-synuclein and tau are linked to Parkinson's disease and Alzheimer's disease, respectively. A body of evidence suggests that α-synuclein and tau, both present in the presynaptic nerve terminals, co-aggregate in many neurological ailments. The molecular mechanism of α-synuclein-tau hetero-assembly is poorly understood. Here we show that amyloid formation is synergistically facilitated by heterotypic association mediated by binding-induced misfolding of both α-synuclein and tau K18. We demonstrate that the intermolecular association is largely driven by the electrostatic interaction between the negatively charged C-terminal segment of α-synuclein and the positively charged tau K18 fragment. This heterotypic association results in rapid formation of oligomers that readily mature into hetero-fibrils with a much shorter lag phase compared to the individual proteins. These findings suggested that the critical intermolecular interaction between α-synuclein and tau can promote facile amyloid formation that can potentially lead to efficient sequestration of otherwise long-lived lethal oligomeric intermediates into innocuous fibrils. We next show that a well-known familial Parkinson's disease mutant (A30P) that is known to aggregate slowly via accumulation of highly toxic oligomeric species during the long lag phase converts into amyloid fibrils significantly faster in the presence of tau K18. The early intermolecular interaction profoundly accelerates the fibrillation rate of A30P α-synuclein and impels the disease mutant to behave similar to wild-type α-synuclein in the presence of tau. Our findings suggest a mechanistic underpinning of bypassing toxicity and suggest a general strategy by which detrimental amyloidogenic precursors are efficiently sequestered into more benign amyloid fibrils.

Preparation and evaluation of supramolecular fracturing fluid of hydrophobically associative polymer and viscoelastic surfactant

A novel fracturing fluid (NAF) comprising of self-synthesized β-cyclodextrin-functionalized hydrophobically associative polymer (HMPAM) and viscoelastic surfactant (VES) was developed. The apparent viscosity of NAF was several times more than that of HMPAM and VES alone. The supramolecular complex gel was achieved by weak physical attractive forces, including intermolecular hydrophobic association, host-guest inclusion, and self-assembly between hydrophobic chains and wormlike micelles. NAF possessed favorable temperature tolerance, shearing resistance, and proppant suspension ability due to its multiple supramoelcular behaviors and high viscoelasticity. Moreover, the gel could be completely broken with no residue, and the broken fluid was easy to flow back. The results indicated that NAF is an effective fracturing fluid and might have favorable application during hydraulic fracturing.

Self‐assembly behavior of amphiphilic linear‐block‐dendritic copolymers with long subchains: Dependences on dendron generation and mixing dynamics

ABSTRACTBlock copolymers composed of acrylic acid and methyl methacrylate with three topologies of double linear blocks, poly(acrylic acid) (PAA) linear block/poly(methyl methacrylate) (PMMA) G1‐dendron and PAA linear block/PMMA G2‐dendron have been prepared by the combination of atom transfer radical polymerization and azide–alkyne click reaction. Proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography have been adopted thoroughly to identify the chemical structure of those block copolymers with expected topologies. The self‐assembly of those block copolymers in the selective solvent has been performed through two mixing routes of gentle and abrupt variation in solvent selectivity, and the morphology of the obtained self‐assemblies/aggregates was observed by transmission electron microscopy. Because the abrupt variation route altered sharply the solvent quality during the mixing, the intermolecular association of polymer chains resulted in the smaller self‐assemblies but the further growth of smaller self‐assemblies was not observed. On the contrary, the gentle variation route changed gradually the solvent quality during the mixing, favoring not only the intermolecular association but also the further growth of self‐assemblies to result in larger aggregates. The final morphology of those assemblies/aggregates also exhibited the dependence of PMMA dendron generation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1446–1456

Nanoparticles from Amphiphilic Heterografted Macromolecular Brushes with Short Backbones

Heterografted macromolecular brushes are highly grafted macromolecules with two different side chains attached to a backbone. When endowed with an amphiphilic character, these can serve as unique stabilizers of biphasic systems and solute carriers and yield interesting self-assembled structures. Herein, we report on the solution structure of amphiphilic double-brush copolymers with short backbones—i.e., comparable to the length of the side-chains—in a selective solvent for one of the grafted blocks. As determined by small-angle neutron scattering measurements, poly(ethylene glycol)/poly(d,l-lactide) double brushes adopt a cylindrical structure with highly extended backbones in DMSO. In contrast, brushes undergo intermolecular self-assembly into spherical nanoparticles in water, with aggregation numbers that vary inversely with backbone degree of polymerization. While considerably less susceptible to intermolecular association than linear diblocks of similar hydrophobic and hydrophilic block lengths, the i...

Temperature and Recognition Dual Responsive Poly(N-Isopropylacrylamide) and Poly(N,N-Dimethylacrylamide) with Adamantyl Side Group.

A series of copolymers with an adamantyl side group (poly(NIPAM-co-AdMA) and poly(DMAM-co-AdMA)) were prepared by radical copolymerization of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMAM) with a 2-methyl-2-adamantylmethacrylate (AdMA) monomer. The structure and composition of the as-synthesized copolymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), and elemental analysis. Temperature and recognition dual responsivity of the copolymers was investigated by cloud point (Tcp) and dynamic light scattering (DLS), respectively. The results show that the as-synthesized copolymers are a kind of temperature-responsive polymer with a lower critical solution temperature (LCST). Tcp was approximately consistent with the critical temperature of intermolecular copolymer association (Tass) from DLS. For these copolymers, Tcp decreases with increasing content of AdMA unit in the copolymers. After the addition of β-cyclodextrins (β-CD), Tcp increases, and the increment of Tcp values gradually became large with increasing content of AdMA in the copolymers. It is host-guest molecular recognition of β-CD and adamantyl groups that endows the as-synthesized copolymers with recognition-tunable thermosensitivity.

Reactive processing preparation of sustainable composites from canola meal reinforced by chemical modification

Canola meal (CM), a by-product of canola oil extraction, was modified by poly (styrene-co-glycidyl methacrylate) (PSG) and could potentially be used as a sustainable natural composite. Infrared analysis indicated that PSG could efficiently react with the proteins in CM and become covalently bonded. DSC results revealed that the modified CM composites showed new glass transition temperatures (Tg) decreasing with the introduction of PSG, which were attributed to the disruption of intermolecular association. Torque curves and melt flow index tests showed the flow property of the modified CM composites increased due to interference by PSG of the hydrogen and disulfide bonding among the protein species. DMA results showed greater amorphous character for the modified CM composites and new glassy plateaus with increased storage moduli, indicating a change in molecular structure and enhancement in mechanical property and usability below Tg. Furthermore, the thermostability, the tensile strength, and the elastic moduli of the modified CM composites increased because of the formation of cross-linked proteins in the CM composites, which will potentially increase the application value in some fields, such as single-use agricultural planting containers replacing high-impact polystyrene (HIPS) containers, and food or coffee trays.

Competing Hydrogen-Bond Polarities in a Dynamic Oligourea Foldamer: A Molecular Spring Torsion Balance.

Symmetrical oligourea foldamers were made from meso cyclohexane-1,2-diamine and desymmetrised by incorporating terminal functional groups (carbamates, ureas or thioureas) with differing hydrogen-bonding capacities. Irrespective of solvent, the foldamers populate a dynamic equilibrium of two alternative screw-sense conformers whose relative population is determined by the competing hydrogen-bonding properties of the terminal groups, dictating the foldamer's global hydrogen-bond directionality. Intermolecular association of these dynamic foldamers with achiral anionic guests (acetate or phosphate, but not neutral hydrogen-bonding solvents) leads to inversion of the conformational preference, as strong intermolecular hydrogen bonding induces reorganization of the intramolecular hydrogen-bond network. The foldamers behave as a molecular torsion balance whose conformational preference is governed by competing hydrogen-bond pairing.

Durable pectin/chitosan membranes with self-assembling, water resistance and enhanced mechanical properties

Processing water-soluble polysaccharides, like pectin (PT), into materials with desirable stability and mechanical properties has been challenging. Here we report a new method to create water stable and mechanical resistant polyelectrolyte complex (PEC) membranes from PT and chitosan (CS) assemblies, without covalent crosslinking. This new method overcomes challenges of obtaining stable and durable complexes, by performing the complexation at low pH, enabling complex formation even when using an excess of PT, and when using PT with high degree of O-methoxylation. By performing the complexation at low pH, the complexes form with a high degree of intermolecular association, instead of forming by electrostatic complexation. This method avoids precipitation, and overcomes the aqueous instability typical of PT/CS complexes. After neutralization, the PEC membranes display features characteristic of a high degree of intermolecular association because of the self-assembling of polymer chains. The PT/CS ratio can be tuned to enhance the mechanical strength (σ = 39 MPa) of the membranes. These polysaccharide-based materials can demonstrate advantages over synthetic materials for technological applications.

Influence of gas injection on viscous and viscoelastic properties of Xanthan gum

Xanthan gum is widely used as a model fluid for sludge to mimic the rheological behaviour under various conditions including impact of gas injection in sludge. However, there is no study to show the influence of gas injection on rheological properties of xanthan gum specifically at the concentrations at which it is used as a model fluid for sludge with solids concentration above 2%.In this paper, the rheological properties of aqueous xanthan gum solutions at different concentrations were measured over a range of gas injection flow rates. The effect of gas injection on both the flow and viscoelastic behaviour of Xanthan gum (using two different methods - a creep test and a time sweep test) was evaluated. The viscosity curve of different solid concentrations of digested sludge and waste activated sludge were compared with different solid concentrations of Xanthan gum and the results showed that Xanthan gum can mimic the flow behaviour of sludge in flow regime.The results in linear viscoelastic regime showed that increasing gas flow rate increases storage modulus (G’), indicating an increase in the intermolecular associations within the material structure leading to an increase in material strength and solid behaviour. Similarly, in creep test an increase in the gas flow rate decreased strain%, signifying that the material has become more resistant to flow. Both observed behaviour is opposite to what occurs in sludge under similar conditions.The results of both the creep test and the time sweep test indicated that choosing Xanthan gum aqueous solution as a transparent model fluid for sludge in viscoelastic regime under similar conditions involving gas injection in a concentration range studied is not feasible. However Xanthan gum can be used as a model material for sludge in flow regime; because it shows a similar behaviour to sludge.

Study on thermo physical properties of binary mixture containing aromatic alcohol with aromatic, substituted aromatic amines at different temperatures interms of FT-IR, 1H NMR spectroscopic and DFT method

The densities (ρ) of binary mixtures of benzyl alcohol (BA) with aniline (A), N-methylaniline (NMA), N,N-dimethylaniline (NNDMA), o-chloroaniline (o-CA) and m-chloroaniline (m-CA) have been analysis at different temperatures. Further, the speeds of sound (u) were measured at 303.15 K and 313.15 K temperatures of the above said systems. The excess molar volumes (VE) and excess isentropic compressibilities (κSE) calculated by using experimental data. The measured thermo physical properties were fitted in terms of R.K & HW equations. The measured u values were compared with Jacobson's free length theory (FLT) and Schaff's collision factor theory (CFT). The experimental and theoretical investigations have been playing a dominant role in the elucidation of hydrogen bond in solute, solvent and solute-solvent of the mixture. The results has been further confirmed by the existence of solvent-solute interactions of hydrogen bonding between benzyl alcohol and amines through Fourier transform Infrared and Nuclear Magnetic Resonance data at equimolar composition. The analysis of intermolecular hydrogen bond association through electron density, natural bond orbital analysis using density functional theory (DFT). The position and design of intensity of –OH and –NH2 bands as per Nuclear Magnetic Resonance and Fourier transform Infrared spectroscopic data strongly supported by the conclusion that molecular association of inter molecular hydrogen bonding through excess properties have been observed. Further, the molecular dynamics (MD) simulations have been performed in liquid phase used to calculate the radial distribution functions of the pure components and mixtures with equimolar mole fractions at 298.15 K and 1 atm. From the molecular dynamics simulation and quantum calculations it has been confirmed the existence of H-bond between component molecules.

Mechanistic Insights into Hydrogen Activation by Frustrated N/Sn Lewis Pairs.

The mechanism of H2 activation by recently reported N/Sn Lewis pairs is unravelled using the representative iPr3 SnOTf/DABCO combination. Computations provide evidence for weak intermolecular associations between Lewis acid and Lewis base (LA/LB) in which the counteranion to cationic LA fragment plays a critical role. Two frustrated Lewis pairs (FLPs) are observed; an unprecedented counteranion-mediated noncovalent LA/LB association is characterised along with the usual FLP structure. Both the FLPs are shown to be capable of H2 activation through cooperative electron transfer processes involving the LA/LB centres. Overall, computed results are in good agreement with the experimental findings and account for the observed reactivity. Insights obtained in this study are fundamentally important for the rational design of Sn-based alternative FLP LAs. The present findings could also provide a general mechanistic framework for H2 activation by FLPs having an ion pair LA component.

The effect of pulsed electric fields on the rheology and microstructure of chitosan-poly(vinyl alcohol) composites

Colloidal matrices of chitosan (CS) and poly(vinyl alcohol) (PVOH), 0.18 weight fraction CS (wiCS), were subjected to pulsed electric fields (PEF) at specific energy 95 - 465 kJ/kg. The influence of pH was examined at various pHs 4.1, 4.8 (control), 5.2, 5.6 and 6.1. The treated samples were subsequently analysed for particle size and size distributions, surface zeta potential and viscoelastic behaviour. PEF at specific energy ≥275 kJ/kg resulted in larger particles and a wider range of particle size distribution (PSD). The zeta potential decreased with increasing pH, which corresponded with an increase in particle size. High pH of the inter-mixed blends of CS and PVOH resulted in higher viscosity, but weaker intermolecular associations as depicted by the rapidly declining viscosity. These findings demonstrated the potentials of PEF in the microstructural modification of macromolecular systems.

Synthesis and characterization of carboxymethylcellulose grafted with thermoresponsive side chains of high LCST: The high temperature and high salinity self-assembly dependence

Graft copolymers based on carboxymethylcellulose (CMC) and thermosensitive polyetheramines (ethylene oxide/propylene oxide = 33/10 and 1/9) were prepared in water, at room temperature, by using a carbodiimide and N-hydroxysuccinimide as activators. SLS was applied to obtain Mw, A2 and Rg of CMC and its derivatives. Amide linkages were evidenced by FTIR and grafting percentage was determined by 1H NMR. TGA demonstrated that copolymers were thermally more stable than their precursors. DLS, UV-vis and rheological measurements revealed that properties were salt- and thermo-responsive and linked to the polysaccharide/polyetheramine ratio and the hydrophobicity of the graft. None of the copolymers showed cloud point temperature (Tcp) in water, but they turned turbid in saline media when heated. Copolymers exhibited thermothickening behaviour at 60 °C (>Tcp) in saline media. Below their Tcp, they showed the ability of keeping constant viscosity or even slight increase it, which was interpreted in terms of intermolecular hydrophobic associations.

Liposomal Circular Dichroism (L-CD) of Arenoyl Derivatives of Sphingolipids. Amplification of Cotton Effects in Ordered Lipid Bilayers.

Liposomal circular dichroism (L-CD) of acyclic amino alcohols exhibit amplification of Cotton effects when measured in highly uniform, unilamellar liposomes. The effect is likely due to intermolecular associations—H-aggregates—that self-assemble spontaneously within the lipid bilayer, and persists over long time scales. L-CD spectra of N,O,O′-tri-(6′methoxy-2′-naphthoyl)-d-erythro-sphingosine, or the corresponding dihydro-derivative (sphinganine), shows ~10-fold amplification of magnitudes of Cotton effects over conventional CD spectra recorded in isotropic solution.

Time- and Composition-Dependent Evolution of Distinctive Microstructures in Bitumen

Bitumen’s chemistry often results in complicated intermolecular associations, which are manifested by the diverse microstructures as observed by atomic force microscopy (AFM). These microstructures largely contribute to bitumens’ bulk mechanical properties; therefore, it is essential to understand the chemical–microstructural–mechanical relationships for optimal design of bitumen-related applications. However, the complex nature of bitumen and the various influencing factors often lead to practical challenges in investigation of bitumens’ microstructures and their chemical origins. This study aims at addressing some of the main concerns related to AFM characterization of bitumens’ microstructures, namely the dependence of bitumens’ microstructures on such factors as sample preparation methods, annealing conditions and durations, and chemical composition. Our results suggest that microstructures of bitumen films of a few micrometers or thicker (i.e., the thickness of the asphalt-coating layer over the aggr...