Chizuru Hongo

High-resolution structures of collagen-like peptides [(Pro-Pro-Gly)4-Xaa-Yaa-Gly-(Pro-Pro-Gly)4]: implications for triple-helix hydration and Hyp(X) puckering.

Structures of (Pro-Pro-Gly)4-Xaa-Yaa-Gly-(Pro-Pro-Gly)4 (ppg9-XYG) where (Xaa, Yaa)=(Pro, Hyp), (Hyp, Pro) or (Hyp, Hyp) were analyzed at high resolution using synchrotron radiation. Molecular and crystal structures of these peptides are very similar to those of the (Pro-Pro-Gly)9 peptide. The results obtained in this study, together with those obtained from related compounds, indicated the puckering propensity of the Hyp in the X position: (1) Hyp(X) residues involved in the Hyp(X):Pro(Y) stacking pairs prefer the down-puckering conformation, as in ppg9-OPG, and ppg9-OOG; (2) Hyp(X) residues involved in the Hyp(X):Hyp(Y) stacking pairs prefer the up-puckering conformation if there is no specific reason to adopt the down-puckering conformation. Water molecules in these peptide crystals are classified into two groups, the 1st and 2nd hydration waters. Water molecules in the 1st hydration group have direct hydrogen bonds with peptide oxygen atoms, whereas those in the 2nd hydration group do not. Compared with globular proteins, the number of water molecules in the 2nd hydration shell of the ppg9-XYG peptides is very large, likely due to the unique rod-like molecular structure of collagen model peptides. In the collagen helix, the amino acid residues in the X and Y positions must protrude outside of the triple helix, which forces even the hydrophobic side chains, such as Pro, to be exposed to the surrounding water molecules. Therefore, most of the waters in the 2nd hydration shell are covering hydrophobic Pro side chains by forming clathrate structures.

Unexpected Puckering of Hydroxyproline in the Guest Triplets, Hyp-Pro-Gly and Pro-alloHyp-Gly Sandwiched between Pro-Pro-Gly Sequence

One of the major aims of studying collagen structure is to understand stabilization factors for triple-helical structures. Despite the efforts spent, the results do not provide an unambiguous answer. One obstruction is the fibrous nature of native collagen, and consequently model peptides have been used to study and define the features of the collagen triple helix. In the early stages, homopeptides with repeating sequences of a given triplet unit were studied, but recently host–guest peptides, in which the central region of a stable host peptide was substituted by a particular guest triplet, have been examined to investigate the physical properties of the guest sequence. In this study, (Pro-Pro-Gly)9, one of the best studied triple-helix peptides, serves as the reference host for guest tripeptide units with Hyp and allo-Hyp, to provide new structural data on the effect of environment on the puckering of hydroxyproline. Collagen is a major structural protein in the extracellular matrix of skin, tendons, bones, and other connective tissues. The presence of glycine as every third residue and a high content of imino acids are characteristics of collagen sequences, and its sequence may be designated as the repetition of X-YGly, in which X and Y are often occupied by proline (Pro) and 4R-hydroxyproline (Hyp), respectively. These restrictive sequence features enable the assembly of three chains into a stable triple-helical conformation. The presence of hydroxyproline leads to significant enhancement of the thermal stability of collagen. 4] The mechanism of this additional stability has

Solvent effects on isotactic poly(methyl methacrylate) crystallization and syndiotactic poly(methacrylic acid) incorporation in porous thin films prepared by stepwise stereocomplex assembly.

The solvent effects on the crystallization of porous isotactic (it) poly(methyl methacrylate) (PMMA) thin films as well as the incorporation behavior of syndiotactic (st) poly(methacrylic acid) (PMAA) into the porous films were investigated. The porous it-PMMA thin films were prepared by the extraction of st-PMAA from a stepwise layer-by-layer (LbL) assembly composed of it-PMMA and st-PMAA. The X-ray diffraction pattern of the it-PMMA thin films after immersion in acetonitrile/water (4/6, v/v) showed two characteristic peaks of a crystalline it-PMMA double-stranded helix (2theta = 9 degrees and 14 degrees , d = 0.96 and 0.62 nm). This suggested that acetonitrile promoted the crystallization of the thin films, because water is a nonsolvent for PMMA. The surface structural change of the it-PMMA films was also analyzed by atomic force microscopy. The it-PMMA conformation was maintained after crystallization as observed by infrared spectroscopy. The incorporation percentages of st-PMAA into the porous it-PMMA thin films under various solvent conditions were estimated using a quartz crystal microbalance. The incorporation of st-PMAA decreased as the it-PMMA films crystallized or with growing thickness of the porous it-PMMA films. This suggested that the polymer-polymer interactions and the entanglement of the it-PMMA chains played an important role. The incorporation was promoted as the acetonitrile content in the st-PMAA solution increased, indicating that it was necessary for st-PMAA incorporation to solvate it-PMMA.

Heat Treatment Strengthens Human Dentin

The flexural strength of Type I collagen, the major organic component of human dentin, increases with heat. We hypothesized that human dentin can be strengthened by heating, which may help prevent fracture of non-vital teeth after restoration. Beam-shaped dentin specimens were obtained from the crowns of human third molars. The dentinal tubular orientations were arranged to run parallel or perpendicular to loading surfaces. The flexural and microtensile strengths of dentin in the parallel specimens were 2- to 2.4-fold greater after being heated between 110°C and 140°C for 1 hr. The stress intensity factors at fracture also increased after specimens were heated. The x-ray diffraction analyses suggested that shrinking of the lateral packing of the collagen triple-helices from 14 Å to 11 Å was the probable cause of the strengthening of heated dentin. We conclude that heat treatment strengthens human dentin.

Effect of ultrasonic pretreatment on emulsion polymerization of styrene

This study investigated the effect of pretreatment of ultrasonic irradiation on emulsion polymerization of styrene to propose a process intensification method which gives high conversion, high reaction rate, and high energy efficiency. The solution containing styrene monomer was irradiated by a horn mounted on the ultrasonic transducer with the diameter of 5mm diameter and the frequency of 28 kHz before starting polymerization. The pretreatment of ultrasound irradiation as short as 1 min drastically improved monomer dispersion and increased reaction rate even under the agitation condition with low rotational speed of impeller. Furthermore, the ultrasonic pretreatment resulted in higher monomer concentration in polymer particles and produced larger polymer particles than conventional polymerization without ultrasonic pretreatment.

On-demand easy peeling of acrylic adhesives containing ionic liquids through a microwave irradiation stimulus

AbstractWe prepared microwave-responsive “on-demand-peeling” adhesives simply by mixing second-generation acrylic adhesives with ionic liquids. A rapid response (<30 s for adhesive failure) to microwave irradiation was achieved using a microwave oven. This “on-demand-peeling” was attributed to local heating of the ionic liquid in the adhesive by microwave irradiation. In addition, the adhesive strength was not influenced by the ionic liquid additives without microwave irradiation. We revealed that the local heating and the plasticizing effect of the ionic liquid were the cause of the “on-demand-peeling”. Our preparation method for these microwave-responsive adhesives is simple, conventional, and attractive for the fundamental and industrial fields.We prepared microwave-responsive adhesives from second-generation acrylic adhesives and ionic liquids, and performed microwave-responsive “on-demand-peeling”. The response depended on the types and quantity of the ionic liquids. While the adhesive strength were maintained irrespective of the contents of ionic liquid in the adhesives, with/without microwave irradiation. The peeling of the adhesives was observed in less than 30 s after microwave irradiation. In this study, we proposed simple, conventional, and attractive preparation of microwave-responsive adhesives by adding ionic liquids.