Changes In Supramolecular Structure Research Articles

Geometric isotope effect of deuteration in a hydrogen-bonded host\u2013guest crystal

Deuteration of a hydrogen bond by replacing protium (H) with deuterium (D) can cause geometric changes in the hydrogen bond, known as the geometric H/D isotope effect (GIE). Understanding the GIEs on global structures and bulk properties is of great importance to study structure–property relationships of hydrogen-bonded systems. Here, we report a hydrogen-bonded host–guest crystal, imidazolium hydrogen terephthalate, that exemplifies striking GIEs on its hydrogen bonds, phases, and bulk dielectric transition property. Upon deuteration, the donor–acceptor distance in the O–H···O hydrogen bonds in the host structure is found to increase, which results in a change in the global hydrogen-bonded supramolecular structure and the emergence of a new phase (i.e., isotopic polymorphism). Consequently, the dynamics of the confined guest, which depend on the internal pressure exerted by the host framework, are substantially altered, showing a downward shift of the dielectric switching temperature.

OBTAINING NEW FLOCCULANTS BASED ON HIGH-SUBSTITUTED CATIONIC STARCHES

In this work synthesis of the high-substituted cationic starches by reaction of starches of different botanical origin with 3-chloro-2-hydroxypropyltrimetylammonium chloride in the presence of the alkaline catalyst was carried out by semi-dry way. The assessment of their flocculating properties on the model systems of kaolinic dispersions was carried out. It was established that the efficiency of a starch cationization substantially depends on its nature. This is due to various initial supermlecular structure and morphology of starch granules. The largest rate and degree of a cationization was characteristic for potato starch, and the least – for corn. The offered heterogeneous method of synthesis allows to receive the high-substituted cationic starches with preservation their granular and minimum changes in supramolecular structure. At achievement of particular extent of high-substituted (DScat> 0.1) cationic starches form the transparent colloid dispersions in cold water. Cationization of starches to higher DScat. demands increase in a consumption of cationic reagent and the catalyst. Formation of cationic bonds in starch was confirmed with results of element and IR-spectroscopical analyses. When carrying out a cationization of starch in an alkaline condition there can be changes of the supramolecular structure of a polysaccharide depending on a temperature and type of starch. Unessential decrease in a degree of crystallinity of all types of starches after their cationization at ambient temperature was demonstrated by the diffractograms received in work. Despite slight amorphicity of starch after their cationization it should be noted that all cationic starches having DScat> 0.1, easily disperse in cold water with formation of the homogeneous transparent pastes. The kinetics and efficiency of a flocculation of model kaolinic suspensions with synthesized cationic starches was investigated. Kaolinic suspensions for lack of flocculant are rather stable for a long time. Introduction to the system of cationic starch leads to fast destabilization of kaolinic dispersions. At the same time for all cationic starches with increase in a dose in the range of 0.5 – 7.5 mg/g(kaolin) the flocculation rate of particles of kaolin dispersions increases. The most efficiently a flocculation of dispersions of kaolin happens to the largest rate in the presence of cationic potato starch. It was established that the efficiency of a flocculation of mineral kaolinic systems is defined not only by a molecular mass of polymer, but also the sizes of non-draining chains which in the strong degree depend on a charge of microions and a rigidity of a polymeric chain. It was shown that the synthesized flocculants are not inferior in efficiency to the polyacrylamide derivants which are applied now.Forcitation:Butrim S.M., Bildyukevich T.D., Butrim N.S., Yurkshtovich T.L., Kaputskiy F.N. Obtaining new flocculants based on high-substituted cationic starches. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 1. P. 89-95

Examining a change in the properties of coarse wool fiber under the influence of electrical discharge treatment

Modification of coarse wool fibre is a basic condition for improving quality of the manufactured woolen textile products while reducing their cost. Traditional methods of modification of wool are expensive, that is why the implementation of these methods into existing technological modes is not always economically justified. The obtained effect of modification is often associated with undesirable damage of protein structure of fiber. A solution to this problem is the application of electric discharge treatment, accompanied by the emergence of electric discharge non-linear bulk cavitation. It is shown that the influence of electrohydrolic shock and products of water cleavage on wool does not cause profound destruction of keratin, in contrast to enzymatic and plasmochemical methods of treatment. Based on the performed experimental studies, it was determined that during electric discharge treatment of coarse wool there occurs the compaction of fiber cuticles and a change in supramolecular structure of keratin. This fact predetermines a decrease in felting ability of wool fibre, an increase in sorption properties, as well as in resistance to hydrolysis and influence of oxidants and reductants. It was established that the application of electric discharge treatment as a method of coarse wool modification would contribute to a decrease in shrinking and improvement of optimized dyeing of woolen textile material. Thus, the proposed technology of wool improvement will make it possible to use less expensive raw materials for the production of textile materials for different purposes.

From Two, to Three, to Multi‐Color Switches: Developing AIEgen‐Based Mechanochromic Materials

AbstractA multi‐color switching mechanochromic aggregation‐induced emission luminogen (AIEgen) whose fluorescence spectra nearly covers the whole visible region was obtained from attaching spiropyran (SP) moiety on tetraphenylethylene (TPE). The covalent attachment of SP to TPE is crucial. It enables the tuning of the fluorescence of SP‐TPE dyads from no color change, to two‐color switching, to three‐color switching under grinding, based on the amorphization of TPE moiety and isomerization of spiropyran moiety. Under quantifiable hydrostatic pressures, the multi‐color switch with wide spectral response region was obtained resulting from distinct pressure thresholds for supramolecular and chemical structural changes. The attached spiropyran helped to enhance the response of the mechanochromic AIEgens to show more fantastic and obvious responses. The multi‐color changes and obvious responses in a wider visible region and an enhancement of fluorescence intensity give this molecule great potential for applications in visual pressure sensors, pressure calibration, etc.

Radiation-Modification Impact on the Filled Polytetrafluoroethylene Structure and Mechanical Strength

The article studies the structure and properties, regularities of their change with the introduction of various fillers and under the influence of gamma – irradiation (γ-radiation). PCM structure study was performed using electron microscopy with scanning electron microscope BS -350 (TESLA) and with X-ray structural analysis method using X-ray diffractometer DRON-3. Shooting of wide-angle X-ray patters was performed in the range of Bragg angles reflection 2Q=5° - 96°. We selected the following properties to study: tensile strength, static tensile modulus. The findings allowed determining: firstly, we determined that based on electron microscopy the supramolecular structural organization depends on the type and percentage of filler in PTFE matrix. Changes take place from lamellar (pure PTFE) to a defective spherulitic (20% of coke) structure. Secondly, we completed X-ray structural analysis (we determined the degree of crystallinity, crystallite size, with parameters а = b in the hexagonal cell, interlayer distance of amorphous area) showed the nature of supramolecular structure changes according to the nature of the filler and subsequent radiation dose. Thirdly there was conducted connection between changes in mechanical strength (tensile strength, statical module of elasticity) and structural changes; the depth of these changes depends on the original supramolecular structure, type and percentage of the filler and the dose of the absorbed radiation energy. The studies will allow change purposefully the supramolecular structure of polymer composite materials to improve the performance properties.

Structural and enzyme kinetic studies of retrograded starch: Inhibition of α-amylase and consequences for intestinal digestion of starch

Retrograded starch is known to be resistant to digestion. We used enzyme kinetic experiments to examine how retrogradation of starch affects amylolysis catalysed by porcine pancreatic amylase. Parallel studies employing differential scanning calorimetry, infra red spectroscopy, X-ray diffraction and NMR spectroscopy were performed to monitor changes in supramolecular structure of gelatinised starch as it becomes retrograded. The total digestible starch and the catalytic efficiency of amylase were both decreased with increasing evidence of retrogradation. A purified sample of retrograded high amylose starch inhibited amylase directly. These new findings demonstrate that amylase binds to retrograded starch. Therefore consumption of retrograded starch may not only be beneficial to health through depletion of total digestible starch, and therefore the metabolisable energy, but may also slow the rate of intestinal digestion through direct inhibition of α-amylase. Such physiological effects have important implications for the prevention and management of type 2 diabetes and cardiovascular disease.

Digestibility and supramolecular structural changes of maize starch by non-covalent interactions with gallic acid.

The effects of non-covalent interactions between gallic acid (GA) and starch on starch digestibility and supramolecular structural changes (short-range ordered molecular structure, crystalline structure, lamellar structure and fractal structure) were investigated. The results indicated that the digestibility of both starches was substantially reduced in the rapidly digestible starch (RDS) content, but resistant starch (RS) was increased after interacting with GA. The RS content of starch-GA complexes ranged from 17.70 to 50.02%, which is much higher than that of high amylose starch (G50) (11.11%) and normal maize starch (NMS) (4.46%). Compared with native starches, starch-GA complexes possess more ordered and compact structures; furthermore, G50-GA complexes possessed more compact scattering objects, thicker crystalline lamellae and thinner amorphous lamellae than those of NMS-GA complexes. This revealed that more ordered multi-scale structures promote the RS formation. Docking studies were conducted to reveal the mechanism of digestibility variations. It showed that GA would non-covalently interact with starch molecules and contribute to ordered structure formation to somewhat extent; meanwhile, GA had higher binding affinities to α-amylase than to starch chains; during the hydrolytic process, GA could be released from the complex and was more likely to occupy the active sites of Asp197, Asp300, His299 and Glu233 by hydrogen bonds and van der Waals forces, which kept starch out of the active site pocket and reduced starch digestibility. These results demonstrate that the non-covalent interactions between GA and starch could be a promising method of controlling starch structures and starch digestion behaviors.

Cyclic Voltammetry Studies of a Redox-Responsive 4 H-Bond Ureidopyrimidinone Alkyl-Pyridinium Capable of Self-Dimerization

The design of stimuli-responsive systems in which supramolecular structure changes in response to external signals, such as the change in voltage of an electrode, is important for many applications, for example, self-healing polymers and gels, triggered release of entrapped molecules for drug delivery, and “smart” materials. In this study, a four H-bond ureidopyrimidinone (UPy) array with an alkyl-pyridinium, (RP), redox center has been synthesized, UPy(RP), shown below. This array prefers the tautomer that presents an ADAD H-bond motif in the starting oxidation state. Due to electrostatic repulsions and unfavorable secondary H-bond interactions, this motif would form a dimer with relatively weak H-bonding. Upon 2e- reduction, where 1e-is gained per R-pyridinium redox center, the H-bond strength should increase due to the loss of the repulsive charges, making the nitrogen a stronger hydrogen acceptor. Because the nitrogen is now a better hydrogen acceptor, there could be a possibility of an intermolecular proton transfer. This would encourage the tautomer to have an AADD motif that will make the H-bonding stronger by increasing the favorable secondary H-bond interactions. UPy dimers can exist in two tautomeric forms called pyrimidinol and pyrimidinone. In order to more efficiently study the electrochemistry of the two forms, two compounds, 4-acetylpyridinium (AcP) and N-methyl-4,4’-bipyridinium (MeV+), were used as model compounds. AcP resembles the pyrimidinone tautomer and MeV+ resembles the pyrimidinol tautomer. The cyclic voltammetry (CV) scans for the two model compounds in CH2Cl2 and CH3CN show two widely spaced, reversible redox waves. UPy(RP) is insoluble in CH2Cl2, but soluble in CH3CN. The concentration dependent NMR spectra suggest that UPy(RP) is a monomer in acetonitrile. The CV’s of UPy(RP) in CH3CN show three reductions. The first occurs at a potential very similar to that seen with simple model compounds. The second is considerably positive of that observed for the model compounds and the third is very close to the second reduction peak of the model compounds. The first reduction is reversible if the scan direction is switched immediately after the peak, but irreversible if the scan direction is switched after the second reduction peak. As the scan rate increases, the second and the third reduction peaks disappear and a new peak emerges in between. Going through the second and third reductions also leads to the appearance of new oxidation waves at more positive potentials. DFT calculations suggest the preferred tautomer changes upon reduction, and this may explain the unexpected voltammetry observed in acetonitrile where the compound is not dimerized. Further studies to help elucidate what is actually happening in this system will include using a new counter anion in the electrolyte to help the solubility of the compound in CH2Cl2. Figure 1

Transformation of the lamellar structure into nanofibrillar structure in the bulk oriented ultra high molecular weight polyethylene: mechanical and tribological properties

The possibility of a change in supramolecular structure of ultra high molecular weight polyethylene and its influence on the polymer mechanical and tribological properties has been demonstrated.

Investigation of a Redox-Responsive 4 H-Bond Array Capable of Strong Self-Dimerization

The design of stimuli-responsive systems in which supramolecular structure changes in response to external signals, such as the change in voltage of an electrode, is important for many applications, for example, self-healing polymers and gels, triggered release of entrapped molecules for drug delivery, and “smart” materials. In this study, a four H-bond ureidopyrimidinone (UPy) array with an alkyl-pyridinium, (RP), redox center has been synthesized, UPy(RP), shown below. This array prefers the tautomer that presents an ADAD H-bond motif in the starting oxidation state. Due to electrostatic repulsions and unfavorable secondary H bond interactions, this motif would form a dimer with relatively weak H-bonding. Upon 2e- reduction, where 1e- is gained per R-pyridinium redox center, the H-bond strength should increase due to the loss of the repulsive charges, making the nitrogen a stronger hydrogen acceptor. Because the nitrogen is now a better hydrogen acceptor, there could be a possibility of an intermolecular proton transfer. This would encourage the tautomer to have an AADD motif that will make the H-bonding stronger by increasing the favorable secondary H-bond interactions. UPy dimers can exist in two tautomeric forms called pyrimidinol and pyrimidinone. In order to more efficiently study the electrochemistry of the two forms, two compounds, 4-acetylpyridinium (AcP) and N-methyl-4,4’-bipyridinium (MeV+), were used as model compounds. AcP resembles the pyrimidinone tautomer and MeV+ resembles the pyrimidinol tautomer. The cyclic voltammetry (CV) scans for the two model compounds in CH2Cl2 and CH3CN show two widely spaced, reversible redox waves. In contrast, CV’s of UPy(RP) in these solvents show two closely spaced reductions. The first occurs at a potential very similar to that seen with simple model compounds. The second is considerably positive of that observed for the model compounds, consistent with strong stabilization of the doubly reduced form by H-bonding. However, the voltammetry is complex. The first reduction is partially reversible if the scan direction is switched immediately after the peak, but irreversible if the scan direction is switched after the second reduction peak. Going through the second reduction also leads to the appearance of new oxidation waves at more positive potentials. This behavior suggests, not surprisingly, that the second reduction induces proton transfer and tautomerization. It is possible that the new oxidation peaks are due to oxidation of a more strongly H-bonded dimer. Further studies to help elucidate what is actually happening in this system will include concentration dependent CV’s and analysis of binding strength using NMR. Figure 1

Supramolecular structural evolutions of maize starch hydrothermally treated in excess water

Supramolecular structural changes of maize starch as affected by hydrothermal treatment in excess water were investigated. At a temperature slightly higher than the onset (To) of gelatinization endotherm (G), an increase in the size of the cavity at the granule core and a sharp decrease in the ordering degree of the semi‐crystalline lamellae occurred, together with the scattering objects apparently becoming looser. When the temperature approached close to the peak temperature (Tp) of endotherm G (70°C), the semi‐crystalline lamellae disappeared, accompanied by the emergence of a dual fractal structure. This suggests that the molecules of swollen maize starch displayed inhomogeneity on nanoscale, with a mass fractal structure at a higher scale level constituted by the scattering objects at a lower scale level. Additionally, it is proposed that a reduction in starch crystallites could enhance the degree of mixing between the crystalline and amorphous materials. The results enable a better understanding of starch supramolecular structural evolutions during the hydrothermal treatment in excess water.

Spiropyran-based multi-colored switching tuned by pressure and mechanical grinding

The multi-colored mechanochromic materials based on a spiropyran and pyrene derivative were realized through a combination of supramolecular and chemical structural changes.

Unraveling the Structural Modifications in Lignin of Arundo donax Linn. during Acid-Enhanced Ionic Liquid Pretreatment.

Solid acid-enhanced ionic liquid (IL) pretreatment is of paramount importance for boosting the yield of sugars from biomass cost-effectively and environmentally friendly. To unravel the chemical and supramolecular structural changes of lignin after pretreatment, IL-acid lignin (ILAL) and subsequent residual cellulolytic enzyme lignin (RCEL) were isolated from Arundo donax Linn. The structural features were compared with those of the corresponding milled wood lignin (MWL). Results indicated that the pretreatment caused loss of β-O-4', β-β', β-1' linkages and formation of condensed structures in lignin. A preferential breakdown of G-type lignin may have occurred, evidenced by an increased S/G ratio revealed by 2D HSQC NMR analysis. It was determined that the depolymerization of β-O-4' linkage, lignin recondensation, and cleavage of ferulate-lignin ether linkages took place. Moreover, a simulation module was first developed to define morphological changes in lignin based on AFM and TEM analyses. Briefly, tree branch like aggregates was destroyed to monodisperse particles.

Changes in the properties of water during the germination of marrow seeds

In this research the changes in the supramolecular structure of distilled water during the germination of a seed in water were studied. We used three methods: gravimetry, precision thermal analysis, and electron work-function measurements. In the first stage of seed germination, viz., seed swelling, the seed extracts coherent domains from the water; here, due to the transition of coherent domains that are adsorbed in nanocavities into a stable state, the flow of electromagnetic energy occurs. In the second stage of the experiment, viz., the appearance of the shoot, the flow of biophotons occurs, as shown by the increased electron work function of the water. A hypothetical model of the process of marrow-seed germination is suggested.

The rheology of gelatin hydrogels modified by κ-carrageenan

We studied the impact of anionic polysaccharide (κ-carrageenan) as a co-gelator of gelatin at different physico-chemical and by varying the κ-carrageenan/gelatin ratio. It has been shown that increasing κ-carrageenan concentration accelerates the gelation and leads to significant increase in the viscoelastic parameters of the modified gels. Non-linearity of viscoelastic properties becomes evident in much lower deformations in comparison with those of native gelatin gels. The strength of gels characterized by the yield stress also increases along with κ-carrageenan concentration. The deformation (but not flow) of gels happens along the rupture surfaces appearing at the apparent yield stress. The melting temperature increases until 45 °C for high κ-carrageenan/gelatin ratio. The suggested explanation of the observed changes in properties of modified gels relates these effects with formation of complexes of gelatin and polysaccharide. FT-IR spectroscopy data show that (bio)polyelectrolyte complex formation is due to electrostatic interaction between positively charged groups in gelatin and negatively charged sulfate groups in κ-carrageenan that leads to conformation changes of gelatin macromolecules. Micrographs (scanning electron microscopy) show that addition of even a small quantity of polysaccharide leads to radical changes in supramolecular structure of modified gels.

Structural Plasticity of Helical Nanotubes Based on Coiled-Coil Assemblies

Numerous instances can be seen in evolution in which protein quaternary structures have diverged while the sequences of the building blocks have remained fairly conserved. However, the path through which such divergence has taken place is usually not known. We have designed two synthetic 29-residue α-helical peptides, based on the coiled-coil structural motif, that spontaneously self-assemble into helical nanotubes in vitro. Using electron cryomicroscopy with a newly available direct electron detection capability, we can achieve near-atomic resolution of these thin structures. We show how conservative changes of only one or two amino acids result in dramatic changes in quaternary structure, in which the assemblies can be switched between two very different forms. This system provides a framework for understanding how small sequence changes in evolution can translate into very large changes in supramolecular structure, a phenomenon that may have significant implications for the de novo design of synthetic peptide assemblies.

Thermodynamics of Aging and Heredity

A brief review of the author’s works in the sphere of thermodynamic theory of aging is presented. Particular attention is given to justification of the methods of classical and near-equilibrium “dynamic” thermodynamics used to assess the direction and extent of ontogenesis. It is noted that discovery of the law of temporal hierarchies and the substance stability principle made it possible to use quasi-equilibrium thermodynamics to describe aging of organisms and evolution of the living world. The review contains certain examples confirming thermodynamic direction of the origin of life and its development. The author states that supramolecular thermodynamics is the foundation of modern epigenetics. The review shows that the environment affects the composition and structure of the genetic apparatus as well as gene expression through the mechanisms of hierarchical thermodynamics. The author discusses the influence of “nutritive molecules” and other biological substances on tissue composition. It is noted that “nutritive molecules” can have an epigenetic influence on DNA and genetic apparatus as a whole. The author gives recommendations regarding nutrition and use of medicines from the perspective of the thermodynamic theory of aging. Though the author used simplifications and approximations when developing the thermodynamic theory of living beings’ aging, the theory is in agreement with the detected correlation between changes in the specific Gibbs free energy of supramolecular structure formation and changes in the chemical composition of body tissues during aging. The author believes that hierarchical thermodynamics is the foundation of Darwinian natural selection.

Insights into the Coassembly of Hydrogelators and Surfactants Based on Aromatic Peptide Amphiphiles

The coassembly of small molecules is a useful means of increasing the complexity and functionality of their resultant supramolecular constructs in a modular fashion. In this study, we explore the assembly and coassembly of serine surfactants and tyrosine-leucine hydrogelators, capped at the N-termini with either fluorenyl-9-methoxycarbonyl (Fmoc) or pyrene. These systems all exhibit self-assembly behavior, which is influenced by aromatic stacking interactions, while the hydrogelators also exhibit β-sheet-type arrangements, which reinforce their supramolecular structures. We provide evidence for three distinct supramolecular coassembly models; cooperative, disruptive, and orthogonal. The coassembly mode adopted depends on whether the individual constituents (I) are sufficiently different, such that effective segregation and orthogonal assembly occurs; (II) adhere to a communal mode of self-assembly; or (III) act to compromise the assembly of one another via incorporation and disruption. We find that a greater scope for controllable coassembly exists within orthogonal systems; which show minimal relative changes in the native gelator's supramolecular structure by Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), and fluorescence spectroscopy. This is indicative of the segregation of orthogonal coassembly constituents into distinct domains, where surfactant chemical functionality is presented at the surface of the gelator's supramolecular fibers. Overall, this work provides new insights into the design of modular coassembly systems, which have the potential to augment the chemical and physical properties of existing gelator systems.

Preparation and characterization of chitosan coatings onto regular cellulose fibers with ultrasound technique

Regenerated cellulose fibers—viscose fibers—were coated with chitosan using an ultrasound technique to improve their accessibility, reactivity and sorption properties. The main purpose of our research was to study the modification of viscose fibers and to determine the effect of the application of chitosan onto viscose fibers. Samples were obtained by treating the fibers with chitosan in a dilute acetic acid solution in an ultrasonic bath. The influences of the chitosan coating on the changes in morphology, supramolecular structure, sorption and tensile properties were studied. The spectra (FTIR analysis) of the treated viscose fibers showed changes and new absorption bands that revealed the existence of the chemical interactions with the chitosan. The scanning electron microscope images confirmed that the surface of the fibers was covered with the chitosan. A decrease in the water retention value and increase in the absorption and moisture content with an increasing concentration of chitosan was noted. Furthermore, the differences in tensile behavior were analyzed using an Instron tensile testing machine. The chitosan coating had no effect on the tensile strength of the viscose fibers, but influenced the tensile strain. Some changes, though not significant, were noted in the structure (crystallinity, orientation) of the treated viscose fibers.

Entropy-Controlled 2D Supramolecular Structures of N,N′-Bis(n-alkyl)naphthalenediimides on a HOPG Surface

The two-dimensional supramolecular structures of a series of N,N'-bis(n-alkyl)naphthalenediimides (NDIs), whose chain lengths span from C3 to C18, at a liquid-HOPG surface interface, studied by STM and FM-AFM, are assigned with the help of molecular dynamics/molecular mechanics calculations to demonstrate that the C3- and C4-NDIs show lamellar structures, the C4- to C12-NDIs show honeycomb (KAGOME) structures, and the C14- to C18-NDIs show lamellar structures again. The change in supramolecular structure depending on chain length can be explained semiquantitatively by the balance of entropy and enthalpy terms to show the importance of "self-avoiding walk" of the alkyl chain in entropy terms.