Yuji Jinbo’s research while affiliated with Yamagata University and other places

Ionic hydration and electrostriction are very important phenomena in various fields such as medical science, biochemistry, and chemical engineering. The present study is the first to focus on these parameters at infinite dilution. Limiting partial molar volumes (V 23∞) in a solvent (1) − [solute (2) + solute (3)] system were measured at several solute compositions x3 [= n3/(n2 + n3)] at 30.00 ± 0.05 °C. When the mixed solutes (2 and 3) only slightly ionized, V 23∞ were observed on the additivity line. This result was attributed to the fact that only solvent (1) molecules can exist around an isolated solute (2) molecule or an isolated solute (3) molecule at infinite dilution. However, V 23∞ in water − [pyridine + fatty acid (acetic acid, propionic acid, or butyric acid)] systems negatively deviate from the additivity line. By measuring electrical conductivity (κ) and mixing enthalpy (ΔHmix), the negative deviations of V 23∞ from the additivity line were attributed to the ionic hydration of pyridine and the fatty acid. As a result, by measuring V 23∞ at several solute compositions, the electrostriction in water − [pyridine + fatty acid] systems was observed. Conversely, V 3∞ in all 14 [solvent (1) + solvent (2)] − solute (3) systems deviated in complicated ways from the additivity line. Unfortunately, we could not clarify the reason behind this deviation because numerous factors had to be considered. Thus, it was confirmed that the behavior of $V_{3}^{\infty }$ is much more complicated than that of V 23∞. The solvents used to study V 23∞ and $V_{3}^{\infty }$ are as follows: water, pyridine, acetic acid, propionic acid, butyric acid, benzene, acetone, chloroform, methanol, ethanol, DMF, carbon tetrachloride, isobutylamine, isobutyl alcohol, n-heptane, and n-octane.

We have succeeded in preparing various water-soluble metal phthalocyanine (MPc)–polymer complexes, wherein the metal moiety is lithium, iron, cobalt, copper, zinc, or tin, and the polymer is one of the following water-soluble polymers: polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), or polyvinyl alcohol (PVA). Among all MPc–polymer complexes, the iron phthalocyanine (FePc)–PVP complex in water showed the largest and sharpest absorption peak at ∼700 nm in UV–Vis absorption spectrum, which indicates that FePc–polymer complexes in water are easily prepared and the degree of stacking of FePc in the complexes, very small, such as that of a monomer or a similar structure. Conversely, the polymer chains including those of PEG, PVP, and dextran have high biological affinity as well as flexibility. Speculatively, the FePc–polymer (e.g., PEG, PVP, and dextran) complexes adsorbed onto the surface of a cancer cell might break it via the irradiation of near-infrared light having a wavelength of ∼700 nm. Furthermore, chlorophyll a–polymer complexes, previously prepared by our group, might similarly break a cancer cell because these complexes showed a large and sharp absorption peak at ∼700 nm in UV–Vis spectrum. Keywords: Materials science, Materials chemistry, Cancer research, Pharmaceutical chemistry

The main chain stiffness parameter (λM-1) of cylindrical rod brushes consisting of a flexible polymethacrylate (PMA) main chain and poly(n-hexyl isocyanate) (PHIC) rod side chains has been determined in tetrahydrofuran (THF) at 25 °C by static light and small-angle X-ray scattering measurements. Furthermore, we have rationalized λM-1 as a function of the degree of polymerization of HIC, Ns. The λM-1 values were compared to those of rod brushes consisting of a flexible polystyrene (PSt) main chain [ Macromolecules 2008, 41, 6564 ] to reveal how the molecular conformation of the rod brush is influenced by the difference in the primary structure or chemical nature of the main chain. A series of rod brushes, poly(MA-HIC-Ns-Ac) with different side chain lengths, where Ns ranged from 26 to 82, were prepared by radical homopolymerization of α-methacryloyloxyethoxy-ω-acetyl ended PHIC macromonomers (MA-HIC-Ns-Ac) in n-hexane at 60 °C. The mean-square cross-section radius of gyration ( ) of poly(MA-HIC-Ns-Ac) was essentially consistent with those of the rod brushes consisting of a PSt main chain, poly(VB-HIC-Ns-H), and could be quantitatively described by the wormlike comb model. The z-averaged mean-square radius of gyration ( z) of the brush, determined as the function of molecular weight, was analyzed with the aid of the cylindrical wormlike chain model theory to determine the λM-1 value. The scattering form factor of poly(MA-HIC-Ns-Ac) was also quantitatively described by the wormlike chain model, and the corresponding λM-1 parameter was determined. The λM-1 value of poly(MA-HIC-Ns-Ac) was much greater than that of poly(VB-HIC-Ns-H) having the same Ns and increased in proportion with increasing side chain length (λM-1 Ns1.5). The chemical nature of the main chain, which is the minor component in the brush polymers, was found to play an essential role in the overall conformation of the rod brushes.

Limiting partial molar volumes V ∞ of nine solutes [water, methanol, carbon disulfide, acetic acid, acetone, dimethyl sulfoxide, pyridine, benzene, and carbon tetrachloride] dissolved in various solvents have been measured using a pycnometer at 30.00 ± 0.05 °C. The V ∞ of water apparently decreases with increasing volume-% of void, i.e. empty space, in a solvent. From this result, we were able to experimentally demonstrate that small water molecules can easily enter into the voids existing in various solvents; however, the other larger solute molecules cannot enter easily into them. On the other hand, V ∞ of all the nine solutes increases with increasing mixing enthalpy, ΔH mix, for each solute (mole fraction after mixing x 2 = 0.05) with various solvents. Generally, the repulsive solute-solvent interaction increases as ΔH mix increases. Therefore, we were able to experimentally demonstrate that V ∞ tends to increase with increasing repulsive solute-solvent interaction. It is considered that the repulsive interaction may lengthen the average neighboring solute-solvent distance and play an important role in affecting V ∞ as well as the void effect.

The graft density dependence of main chain stiffness in rod brushes composed of a flexible linear polystyrene (PS) main chain and poly(n-hexyl isocyanate) (PHIC) rod side chains has thoroughly been investigated by static light (LS) and small-angle X-ray scattering (SAXS) measurements in tetrahydrofuran (THF) at 25 °C. A series of statistical graft copolymers having different graft densities (σ) and graft chain lengths (PS-g-HIC-Ns-lg, where Ns is the weight-averaged degree of polymerization of HIC and lg is the average distance (spacing) of the main chain between the side chain joints) were prepared by the nearly azeotrope radical copolymerizations of styrene (M1) with PHIC macromonomers (M2) (r1 = 0.84 ± 0.1 and r2 = 1.1 ± 0.3) in n-hexane or the bulk at 60 °C. The compositional heterogeneities of the graft copolymers were carefully characterized by the ratio of the UV to RI signal in the SEC traces and the comparison with those predicted from the theory by Stejskal and Kratochvil [ Macromolecules1987, 20, 2624], implying that they were sufficiently small enough to allow one to study their dimensional characterizations. The graft density dependence of the root-mean-square cross-section radius of gyration (⟨Sc2⟩1/2) and the z-averaged root-mean-square radius of gyration (⟨S2⟩z1/2) of PS-g-HIC-Ns-lg was studied and rationalized as the function of σ and Ns. The σ-dependence of ⟨Sc2⟩1/2 could be quantitatively described by the theory for the semiflexible comb whose main and side chains have different chain stiffness. The weight-averaged degree of polymerization of the main chain (NM) dependence of ⟨S2⟩z1/2 was also quantitatively described by the cylindrical wormlike chain model. It was found that the change in the main chain stiffness (λb–1) resulting from the interactions among the side chains increases in proportion to the scaling law of λb–1 ∝ Ns1σ1.

Calmodulin (CaM) binds to the FERM domain of 80 kDa erythrocyte protein 4.1R (R30) independently of Ca(2+) but, paradoxically, regulates R30 binding to transmembrane proteins in a Ca(2+)-dependent manner. We have previously mapped a Ca(2+)-independent CaM-binding site, pep11 (A(264)KKLWKVCVEHHTFFR), in 4.1R FERM domain and demonstrated that CaM, when saturated by Ca(2+) (Ca(2+)/CaM), interacts simultaneously with pep11 and with Ser(185) in A(181)KKLSMYGVDLHKAKD (pep9), the binding affinity of Ca(2+)/CaM for pep9 increasing dramatically in the presence of pep11. Based on these findings, we hypothesized that pep11 induced key conformational changes in the Ca(2+)/CaM complex. By differential scanning calorimetry analysis, we established that the C-lobe of CaM was more stable when bound to pep11 either in the presence or absence of Ca(2+). Using nuclear magnetic resonance spectroscopy, we identified 8 residues in the N-lobe and 14 residues in the C-lobe of pep11 involved in interaction with CaM in both of presence and absence of Ca(2+). Lastly, Kratky plots, generated by small-angle X-ray scattering analysis, indicated that the pep11/Ca(2+)/CaM complex adopted a relaxed globular shape. We propose that these unique properties may account in part for the previously described Ca(2+)/CaM-dependent regulation of R30 binding to membrane proteins.

The S100A3 homotetramer assembles upon citrullination of a specific symmetric Arg51 pair on its homodimer interface in human hair cuticular cells. Each S100A3 subunit contains two EF-hand-type Ca2 +-binding motifs and one (Cys)3His-type Zn2 +-binding site in the C-terminus. The C-terminal coiled domain is cross-linked to the presumed docking surface of the dimeric S100A3 via a disulfide bridge. The aim of this study was to determine the structural and functional role of the C-terminal Zn2 +-binding domain, which is unique to S100A3, in homotetramer assembly. The binding of either Ca2 + or Zn2 + reduced the α-helix content of S100A3 and modulated its affinity for the other cation. The binding of a single Zn2 + accelerated the Ca2 +-dependent tetramerization of S100A3 while inducing an extensive unfolding of helix IV. The Ca2 + and Zn2 + binding affinities of S100A3 were enhanced when the other cation bound in concert with the tetramerization of S100A3. Small angle scattering analyses revealed that the overall structure of the S100A3 tetramer bound both Ca2 + and Zn2 + had a similar molecular shape to the Ca2 +-bound form in solution. The binding states of the Ca2 + or Zn2 + to each S100A3 subunit within a homotetramer appear to be propagated by sensing the repositioning of helix III and the rearrangement of the C-terminal tail domain. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

Protein 4.1G (4.1G) is a widely expressed member of the protein 4.1 family of membrane skeletal proteins. We have previously reported that Ca(2+)-saturated calmodulin (Ca(2+)/CaM) modulates 4.1G interactions with transmembrane and membrane-associated proteins through binding to Four.one-ezrin-radixin-moesin (4.1G FERM) domain and N-terminal headpiece region (GHP). Here we identify a novel mechanism of Ca(2+)/CaM-mediated regulation of 4.1G interactions using a combination of small-angle X-ray scattering, nuclear magnetic resonance spectroscopy, and circular dichroism spectroscopy analyses. We document that GHP intrinsically disordered coiled structure switches to a stable compact structure upon binding of Ca(2+)/CaM. This dramatic conformational change of GHP inhibits in turn 4.1G FERM domain interactions due to steric hindrance. Based upon sequence homologies with the Ca(2+)/CaM-binding motif in protein 4.1R headpiece region, we establish that the 4.1G S(71)RGISRFIPPWLKKQKS peptide (pepG) mediates Ca(2+)/CaM binding. As observed for GHP, the random coiled structure of pepG changes to a relaxed globular shape upon complex formation with Ca(2+)/CaM. The resilient coiled structure of pepG, maintained even in the presence of trifluoroethanol, singles it out from any previously published CaM-binding peptide. Taken together, these results show that Ca(2+)/CaM binding to GHP, and more specifically to pepG, has profound effects on other functional domains of 4.1G.