Unordered State Research Articles

Curcumin amorphous solid dispersions benefit from hydroxypropyl methylcellulose E50 to perform enhanced anti-inflammatory effects

The solubility and permeability enhancement of curcumin (Cur) is crucial for its manufacture and application in medical field. Herein, Cur amorphous solid dispersions (ASDs) with enhanced drug solubility and permeability was formulated by Eudragit EPO (EuD) and biological macromolecules of hydroxypropyl methylcellulose E50 (HPMC), and significant functions of HPMC for Cur ASDs were mainly studied. The results showed that the mean particle size of Cur decreased from more than 300 nm to less than 200 nm with the addition of HPMC in excipient aqueous solution evidenced by dynamic light scattering result, confirming that HPMC had the ability to inhibit crystallization by lowering drug-rich droplets in the initial mixing process. Innovatively for molecular dynamic modeling study, crystalline Cur molecules in EuD medium trended to aggregate while not for EuD/HPMC 1:1 and EuD/HPMC 3:1 medium. HPMC functioned as surfactant converted the arrangement of phospholipid bilayers to un-ordered, and un-ordered state of phospholipids lead to the enhancement of Cur transmembrane using HPMC as auxiliary excipient. Cur-EuD/HPMC 3:1 contributed greatly to the Cur permeability, leading to obtain superior relative oral bioavailability and anti-inflammatory effect. Cur ASDs with proper amount of HPMC can be rendered as outstanding therapeutic strategy for medical application.

Framework for formation control of jet-propelled unmanned surface vehicles

This study focuses on the research of spray-pump type unmanned surface vehicles (USVs). Based on the analysis of the dynamics and motion characteristics of USVs, a method combining Dubins curves and the particle swarm optimization algorithm is proposed to find the optimal or suboptimal solution for the formation path. The research goal is to switch multiple USVs from an unordered state to a formation state, taking the speed of USVs and the formation endpoint as dynamic variables and integrating Dubins curve theory into the particle swarm optimization algorithm. A theoretical framework for the formation of spray-pump type USVs is proposed. Finally, the formation of three USVs is realized in a simulation platform.

ХАЛДЕЙНОВСКИЕ ЦЕПОЧКИ

In a number of quasi-one-dimensional magnets, transition metal ions obeying the motives of the crystal lattice can form chains of integer spins that are distant from each other, named Haldane chains. This paper provides a brief overview of the magnetic properties of Haldane chains and considers some compounds containing such chains. The main features of the S=1 spin chain are that it has an unordered ground state with a finite correlation length and a spin gap in the magnetic excitation spectrum. In this paper, the manifestation of these properties is considered on the example of some compounds containing chains of Ni2+ ions (S=1). The disappearance of the spin gap and the establishment of antiferromagnetic ordering can lead to inter-chain interaction (as is the case in CsNiCl3), as well as an external magnetic field (in the case of Ni(C5H14N2)2N3(ClO4)), in which the Zeeman splitting of the Haldane triplet state occurs. To date, PbNi2V2O8 is the only known compound, in which the long-range magnetic order is induced by non-magnetic dilution of S=1 chains. In contrast to the above-listed compounds, Y2BaNiO5 remains disordered down to 0.1 K. When the non-magnetic Y3+ ion in Y2BaNiO5 is replaced by the rare earth ion R3+, a three-dimensional magnetic ordering occurs in the system. However, the Haldane gap in the spectrum of magnetic excitations of nickel is preserved both in the paramagnetic region and in the ordered state. In the ordered state, there is a paradoxical coexistence of the Haldane phase and spin waves, and the ordering occurs in the rare-earth subsystem, while the nickel subsystem remains internally disordered.

Comparative Analysis of the Structure and Fibrillogenesis of Aβ11-28 Peptide and the Inverse Sequence

The inverse sequences of naturally occurring proteins display different folding and structural properties and fail to retain the functions of native proteins despite identical fundamental features, such as the amino acid composition, hydrophobicity, etc. To gain insight into the physical mechanisms underlying secondary structure formation and aggregation of direct and retro sequences of amyloidogenic peptides, we probed the fibrillogenesis and accompanying structural changes of amyloid β peptide fragment Aβ11-28 (EVHHQKLVFFAEDVGSNK) and its inverse sequence, Aβ28-11. These peptides are of interest because the aggregation of both Aβ11-28 or Aβ28-11 into parallel, in-register β-sheet (characteristic structure of Aβ fibrils) will be hampered by electrostatic repulsion between amino acids of like charges. Therefore, each peptide is expected to form antiparallel intermolecular β-sheet structure and their combination would form parallel β-sheet stabilized by ionic interactions between juxtaposed side chains with opposite charges. Circular dichroism data identified α-helical structure for both peptides and their equimolar combination in hexafluoroisopropanol and in dry state. Addition of aqueous buffer caused transition into unordered state, followed by formation of β-sheet/β-turn structure, faster for Aβ11-28. Thioflavin-T fluorescence showed fibril formation by Aβ11-28 and Aβ28-11, starting around 200 and 250 h, respectively. For the combination, ThT fluorescence stayed at low level for 360 h. FTIR data confirmed formation of β-sheet/β-turn structure in Aβ11-28 and Aβ28-11 and identified α-helix propensity of the retro sequence. The combination slowly transitioned from unordered to mostly β-turn structure. Amide I spectral features characteristic of antiparallel β-sheet were not detected for any of the peptide samples. These data suggest that ionic interactions between side chains play a minor role in amyloid peptide structure and aggregation, and the structural propensity of the inverse sequence is distinctly different from that of the parent peptide.

Caesalpinia bonduc serine proteinase inhibitor CbTI–2: Exploring the conformational features and antimalarial activity

Seeds of tropical legumes posses a repertoire of proteinase inhibitors (PI) and the current study highlights some structural/functional features of a strong serine PI from the seeds of Caesalpinia bonduc (CbTI–2). Following purification, N-terminal sequence of CbTI–2 revealed over 40% similarity with a few serine PIs of Caesalpinioideae subfamily. Upon exposure to metal ions and ionic/non ionic surfactants, CbTI–2 showed immense variation in the levels of antitryptic activity. Exposure of CbTI–2 to 1,4-Dithiothreitol, Guanidinium HCl, H2O2 and Dimethyl sulfoxide led to a steady loss of inhibitory activity. Chemical modification of amino acids suggested an arginine as the active site residue. Circular Dichroism spectrum of native CbTI–2 revealed an unordered state. Secondary structure composition of CbTI–2 following exposure to extreme conditions (heat, acidic/alkaline environment, Guanidine hydrochloride and DTT) showed considerable perturbations that caused severe loss of antiproteolytic activity. DLS studies yielded a hydrodynamic radius of ∼2.2nm for CbTI–2 and also reconfirmed 1:1 stoichiometry for the trypsin-CbTI–2 complex. Initial studies indicated CbTI–2 to be a potent antiplasmodial agent by being highly toxic towards growth, schizont rupture process and erythrocytic invasion of Plasmodium falciparum.

Influence of grafting with acrylate compounds on the conformational rearrangements of silk fibroin upon electrospinning and treatment with aqueous methanol

Silk fabrics from Bombyx mori silkworm were grafted with 2‐hydroxyethyl methacrylate (HEMA) as well as a binary system of HEMA and 4‐hydroxybutyl acrylate (HBA) and then analysed by Raman and infrared (IR) spectroscopy to elucidate the interactions between the components and their possible conformational changes. The samples were then dissolved in trifluoroacetic acid and electrospun; the influence of the grafted polymers on the silk fibroin rearrangements upon these treatments was investigated by vibrational spectroscopy. Upon grafting, the fabrics underwent conformational rearrangements towards a more unordered state, although they kept their prevailing β‐sheet conformation; also the polymeric component underwent hydrogen bonding and backbone rearrangements upon interaction with silk fibroin and the occurrence of strong covalent bonds cannot be excluded. By immersing the as‐electrospun grafted and pure fibroin nanofibres (prevalently unordered) in aqueous methanol, they partially recovered the β‐sheet content observed in the corresponding starting fabrics; the percentage of recovery decreased along the series: pure silk > HEMA‐grafted silk > HEMA and HBA‐grafted silk. This trend suggests that the presence of the polyHEMA grafted component hinders the silk fibroin recrystallization into β‐sheet upon aqueous methanol treatment; moreover, the addition of the more sterically hindered HBA monomer in the grafting system further prevented this process. Copyright © 2016 John Wiley & Sons, Ltd.

Structural study on methacrylamide-grafted Tussah silk fibroin fibres

Tussah silk fibroin fibres were modified by grafting with methacrylamide (MAA), with weight gains ranging between 2.6% and 71.4%. Raman and IR spectroscopic analyses showed that upon grafting the fibres underwent slight conformational changes towards a more unordered state, due to the covalent and hydrogen bonds interactions occurring between the polymer (polyMAA) and the amorphous domains of silk fibres.To test the stability towards alkaline hydrolysis, the untreated and MAA-grafted silk fibres (weight gain of 71.4%) were immersed in NaOH 5% at 50°C for different times; the IR and Raman spectroscopic techniques were utilized to elucidate the degradation mechanism as well as the rearrangements of the fibres induced by the treatment.Upon hydrolysis, both the untreated and grafted fibres underwent an enrichment in β-sheet conformation, due to the preferential removal of the unordered domains. As a result of the covalent interactions with silk fibroin, the polymer increased its stability towards alkaline hydrolysis, since its complete solubilization was avoided and the transformation of its CONH2 groups into COO⿿ and COOH was delayed. Vibrational spectroscopy proved to be a valid technique to investigate the mechanism and the effects of the hydrolytic attack, which are both fundamental to design new-generation silk-based materials.

Stability toward alkaline hydrolysis ofB.morisilk fibroin grafted with methacrylamide

Bombyx mori silk fibroin fibers were grafted with methacrylamide (MAA) and characterized by Raman and infrared (IR) vibrational spectroscopy before and after hydrolysis in NaOH 5% to elucidate the possible interactions between the two components and the stability of the fibers toward alkaline hydrolysis. Upon grafting, the fibers underwent conformational rearrangements toward a more unordered state and lost orientation at weight gains higher than 60%. Vibrational spectroscopy disclosed the occurrence of intermolecular interactions (mainly hydrogen bonds) between B. mori silk fibroin and polyMAA in the grafted fibers, and the formation of covalent bonds has been explored. These strong interactions made the grafted fibers as a whole more stable toward alkaline hydrolysis because they prevented the solubilization of the polymer upon hydrolysis and made slower the transformation of its CONH2 groups into COOH and COO− groups. Upon hydrolysis, silk fibroin underwent an enrichment in the β-sheet crystalline domains, because of the preferential removal of the unordered domains, which were more prone to the OH− attack. IR and Raman spectroscopy proved valid techniques to investigate the degradation mechanism and kinetics of grafted silk fibroin fibers and so for designing high-performing silk-based materials. The A731/A1004 Raman intensity ratio was proposed to spectroscopically evaluate the composition of the grafted samples; its value was found to linearly increase with weight gain (R2 = 0.998), envisaging the possibility of using Raman spectroscopy as a routine analytical technique for qualitative and quantitative characterization of grafted industrial samples. Copyright © 2016 John Wiley & Sons, Ltd.

Quantum oscillations and magnetic reconstruction in the delafossitePdCrO2

Quantum oscillations measurements on PdCrO${}_{2}$ show that the Fermi surface of the antiferromagnetically ordered state is a consequence of reconstruction of the Fermi surface of the unordered state.

Folding and Unfolding of pH Sensitive Peptides: The Role of Interfaces

GALA is a 30 amino acid synthetic peptide consisting of a Glu-Ala-Leu-Ala repeat, known to undergo a reversible structural transition from an unordered to an α-helical structure when changing the pH from 7 to 5. In its helical state GALA is amphiphilic and can insert into and permeabilize membranes. This effect has generated much interest because of potential applications for pH triggered targeted drug delivery. GALA also serves as a well-defined model system to understand cell penetration mechanisms and protein folding triggered by external stimuli. The structural reconfiguration of GALA in solution has been studied extensively. However, cell penetration is an interfacial effect and occurs at the membrane surface. Owing to experimental challenges in determining peptide confirmation at an interface, GALAs interaction with surfaces is still unknown. A key question is: What is the secondary structure of GALA specifically at interfaces such as the air-water or water-lipid interfaces? In other words: how does the presence of an interface affect the intricate balance of forces governing folding and unfolding of GALAs Glu-Ala-Leu-Ala motive? We have used sum frequency generation vibrational spectroscopy to probe the structural response of GALA at the air-water interface. SFG is highly interface specific and only probes peptides directly, i.e. within a few Angstrom, at the water-air or water-lipid surface. The data reveal that a large fraction of the GALA population at the water-air interface remains helical above pH 5, while a complete reconfiguration into the unordered state was observed in solution by transmission infrared and circular dichroism spectroscopy. We attribute this effect to the stabilizing interactions of hydrophobic leucine side chains with air. Molecular dynamics simulations support the view that the surface plays a key role in the balance of structure-building forces at the interface.

Pressure–Temperature Stability, Ca2+ Binding, and Pressure–Temperature Phase Diagram of Cod Parvalbumin: Gad m 1

Fish allergy is associated with IgE-mediated hypersensitivity reactions to parvalbumins, which are small calcium-binding muscle proteins and represent the major and sole allergens for 95% of fish-allergic patients. We performed Fourier transform infrared and tryptophan fluorescence spectroscopy to explore the pressure-temperature (p-T) phase diagram of cod parvalbumin (Gad m 1) and to elucidate possible new ways of pressure-temperature inactivation of this food allergen. Besides the secondary structure of the protein, the Ca(2+) binding to aspartic and glutamic acid residues was detected. The phase diagram was found to be quite complex, containing partially unfolded and molten globule states. The Ca(2+) ions were essential for the formation of the native structure. A molten globule conformation appears at 50 °C and atmospheric pressure, which converts into an unordered aggregated state at 75 °C. At >200 MPa, only heat unfolding, but no aggregation, was observed. A pressure of 500 MPa leads to a partially unfolded state at 27 °C. The complete pressure unfolding could only be reached at an elevated temperature (40 °C) and pressure (1.14 GPa). A strong correlation was found between Ca(2+) binding and the protein conformation. The partially unfolded state was reversibly refolded. The completely unfolded molecule, however, from which Ca(2+) was released, could not refold. The heat-unfolded protein was trapped either in the aggregated state or in the molten globule state without aggregation at elevated pressures. The heat-treated and the combined heat- and pressure-treated protein samples were tested with sera of allergic patients, but no change in allergenicity was found.

Pairing, ferromagnetism, and condensation of a normal spin-1 Bose gas

We theoretically study the stability of a normal, spin disordered, homogenous spin-1 Bose gas against ferromagnetism, pairing, and condensation through a Random Phase Approximation which includes exchange (RPA-X). Repulsive spin-independent interactions stabilize the normal state against both ferromagnetism and pairing, and for typical interaction strengths leads to a direct transition from an unordered normal state to a fully ordered single particle condensate. Atoms with much larger spin-dependent interaction may experience a transition to a ferromagnetic normal state or a paired superfluid, but, within the RPA-X, there is no instability towards a normal state with spontaneous nematic order. We analyze the role of the quadratic Zeeman effect and finite system size.

Randomization of Amyloid‐β‐Peptide(1‐42) Conformation by Sulfonated and Sulfated Nanoparticles Reduces Aggregation and Cytotoxicity

The amyloid-β peptide (Aβ) plays a central role in the mechanism of Alzheimer's disease, being the main constituent of the plaque deposits found in AD brains. Aβ amyloid formation and deposition are due to a conformational switching to a β-enriched secondary structure. Our strategy to inhibit Aβ aggregation involves the re-conversion of Aβ conformation by adsorption to nanoparticles. NPs were synthesized by sulfonation and sulfation of polystyrene, leading to microgels and latexes. Both polymeric nanostructures affect the conformation of Aβ inducing an unordered state. Oligomerization was delayed and cytotoxicity reduced. The proper balance between hydrophilic moieties and hydrophobic chains seems to be an essential feature of effective NPs.

Acetonitrile‐induced unfolding of the photosystem II manganese‐stabilizing protein studied by electrospray mass spectrometry

In this paper an acetonitrile-induced unfolding of the manganese-stabilizing protein (MSP) of photosystem II was discovered. More distinct unfolding states of MSP were identified than previously by using mainly electrospray ionization mass spectrometry (ESI-MS), together with fluorescence spectra and far-UV circular dichroism (CD) at pH 2.0, 6.2 or 11.6, and with acetonitrile concentrations from 0 to 50%. At pH 6.2 with acetonitrile concentration changing from 0 to 10%, relatively broad charge-state distributions and poor intensity were observed in ESI-MS, indicating the presence of coexisting conformers. It was concluded that the structure of the MSP protein is unlikely to be a tightly folded form. When the concentration of acetonitrile was 20-40%, simulating the state in the biological membrane, changes in the state of unfolding of MSP were observed to a certain extent using ESI-MS, fluorescence and CD spectroscopy. The charge-state distribution in ESI-MS was found to move toward high states (from 13+ to 27+ to 15+ to 31+) with increasing acetonitrile concentration. At pH 2.0, the MSP structure is rearranged into an unfolded state, and at pH 11.6 the MSP structure is induced to assume another unordered state by deprotonation of appropriate residues. An interesting observation was that a second peak envelope emerged with 20-50% acetonitrile in the medium at pH 11.6.

Purification and Characterization of a Vaterite-Inducing Peptide, Pelovaterin, from the Eggshells ofPelodiscussinensis(Chinese Soft-Shelled Turtle)

Proteins play a crucial role in the biomineralization of hard tissues such as eggshells. We report here the purification, characterization, and in vitro mineralization studies of a peptide, pelovaterin, extracted from eggshells of a soft-shelled turtle. It is a glycine-rich peptide with 42 amino acid residues and three disulfide bonds. When tested in vitro, the peptide induced the formation of a metastable vaterite phase. The floret-shaped morphology formed at a lower concentration ( approximately 1 microM) was transformed into spherical particles at higher concentrations (>500 microM). The solution properties of the peptide are investigated by circular dichroism (CD), fluorescence emission spectroscopy, and dynamic light scattering (DLS) experiments. The conformation of pelovaterin changed from an unordered state at a low concentration to a beta-sheet structure at high concentrations. Fluorescence emission studies indicated that the quantum yield is significantly decreased at higher concentrations, accompanied by a blue shift in the emission maximum. At higher concentrations a red-edge excitation shift was observed, indicating the restricted mobility of the peptide. On the basis of these observations, we discuss the presence of a peptide concentration-dependent monomer-multimer equilibrium in solution and its role in controlling the nucleation, growth, and morphology of CaCO(3) crystals. This is the first peptide known to induce the nucleation and stabilization of the vaterite phase in solution.

Effect of Metal Ions and EGTA on the Optical Properties of Concanavalin A at Alkaline pH

In our earlier communications, we reported the effect of salts and alcohols on alpha-chymotrypsinogen [1] and the existence of stable intermediates at low pH in bromelain [2] and glucose oxidase [3]. In the present study, the role of metal ions and EGTA on the conformation of concanavalin A at alkaline pH was studied by near- and far-UV circular dichroism, fluorescence emission spectroscopy and binding of a hydrophobic dye, 1-anilino-8-naphthalene sulfonate (ANS). Far-UV CD spectra showed the transition from an ordered secondary structure at pH 7 with a trough at 223 nm to a relatively unordered state at pH 12. Near-UV CD spectra showed the loss of signal at 290 nm, thereby indicating the disruption of native three dimensional structure. Maximum ANS binding occurred at pH 12 suggesting the presence of an intermediate or molten globule-like state at alkaline pH.

Effect of ethylene glycol and polyethylene glycol on the acid-unfolded state of trypsinogen.

Effect of increasing concentrations of two of the polyols, ethylene glycol (EG) and polyethylene glycol (PEG), was studied by near and far circular dichroism (CD), fluorescence emission spectroscopy, and binding of hydrophobic dye, 1-anilino-8-naphthalene sulfonic acid (ANS). Far-UV CD spectra show the transition of acid-unfolded trypsinogen from an unordered state to an intermediate state having ordered secondary structure. Interestingly, near-UV CD spectra show some amounts of stabilizing effect on the tertiary structure of the protein also. Tryptophan fluorescence studies indicate the change in the environment of the tryptophan residues on addition of EG and PEG. Maximum ANS binding occurs in presence of 80% EG and 90% PEG (v/v), suggesting the presence of an intermediate or molten globule-like state at high concentrations of the two polyols.

Nucleation-dependent conformational conversion of the Y145Stop variant of human prion protein: structural clues for prion propagation.

One of the most intriguing disease-related mutations in human prion protein (PrP) is the Tyr to Stop codon substitution at position 145. This mutation results in a Gerstmann-Straussler-Scheinker-like disease with extensive PrP amyloid deposits in the brain. Here, we provide evidence for a spontaneous conversion of the recombinant polypeptide corresponding to the Y145Stop variant (huPrP23-144) from a monomeric unordered state to a fibrillar form. This conversion is characterized by a protein concentration-dependent lag phase and has characteristics of a nucleation-dependent polymerization. Atomic force microscopy shows that huPrP23-144 fibrils are characterized by an apparent periodicity along the long axis, with an average period of 20 nm. Fourier-transform infrared spectra indicate that the conversion is associated with formation of beta-sheet structure. However, the infrared bands for huPrP23-144 are quite different from those for a synthetic peptide PrP106-126, suggesting conformational non-equivalence of beta-structures in the disease-associated Y145Stop variant and a frequently used short model peptide. To identify the region that is critical for the self-seeded assembly of huPrP23-144 amyloid, experiments were performed by using the recombinant polypeptides corresponding to prion protein fragments 23-114, 23-124, 23-134, 23-137, 23-139, and 23-141. Importantly, none of the fragments ending before residue 139 showed a propensity for conformational conversion to amyloid fibrils, indicating that residues within the 138-141 region are essential for this conversion.

Optical tweezing electrophoresis of isolated, highly charged colloidal spheres

We report on a novel optical tweezing experiment measuring the electrophoretic mobility μ of highly charged spherical particles suspended in water at volume fractions Φ≤2×10 −7. At deionised conditions μ=2.5×10 −8 m 2 V −1 s −1, it decreases further upon increasing the salt concentration c. We compare our data to measurements at larger Φ, where generally much larger μ and a qualitatively different dependence on the salt concentration are observed. To characterise the dependence on Φ we performed measurements at no added salt. There the mobility increases in the unordered state but stays constant at μ=6.8×10 −8 m 2 V −1 s −1 as the system develops fluid order. In the ordered regime the salt concentration dependence becomes very pronounced for c≤10 −5 M. None of the presently observed trends can be understood in terms of the standard electrokinetic model.

Archaebacterial lipids: high surface activity of polyisoprenoid surfactants in water

The surface tension of aqueous solutions of the amphiphiles, (3RS, 7R, 11R)-3,7,11,15-tetramethylhexadecyl-X where X is SO 4 −Na +, PO 4H −Na +, N +(CH 3) 3Br −, N +(C 2H 5) 3Br −, etc., was studied at 25–75°C. The polyisoprenoid surfactants provided the surface tension of 26–31 mN m −1, which was lower by 10–15 mN m −1 than that of corresponding straight chain-analogues. The results were discussed in conjunction with an unordered fluid state of the highly branched hydrocarbon chains at an air-water interface.