Syntheses and magnetic properties of iron(III) complexes with imidazole groups

Iron(III) complexes with the general formula of [Fe (R-Himap)₂]X and [Fe(R-Himat)₂]X (Himap = shiff-base prepared from the condensation of 4-formylimidazole and 2-aminophenol, Himat = shiff base prepared from the condensation of 4-formylimidazole and 2-aminobenzenethiol, and R = H, Me, Ph; X = ClO₄, NO₃, BPh₄) have been synthesized. The complexes have an N₄O₂ donor set or an N₄S₂ donor set. These complexes have 5 and 5 member rings around an iron(III) atom per one chelate ring, that is, "5-5 member rings". The crystal structure, Mössbauer spectra, magnetic properties and absorption spectra of the complexes were examined. In addition, [Fe (Himsa)₂]ClO₄ having "5-6 member rings" of an N₄O₂ donor set and [Fe (Ph-Himap)(Ph-imap)] obtained by the deprotonation of [Fe (Ph-Himap)₂]ClO₄ have been also synthesized, and the Mössbauer spectra and magnetic properties of those complexes were examined. The X-ray structure of a single crystal of [Fe (Himap)₂]BPh₄ was determined: C₄₄H₃₆N₆BO₂Fe, triclinic, space group P(# 2), a = 12.452(2) Å, b = 12.748(2) Å, c = 11.996(2) Å, = 103.97(1)°, = 90.78(1)°, = 84.70(1)° and Z = 2. The moiety of an iron atom of [Fe(Himap)₂]BPh₄ was a pseudo octahedron with an FeN₄O₂ geometry. [Fe(R-Himap)₂]X was in high-spin state (about 5.9 B.M. at 80 K in solid state), and [Fe(R-Himat)₂]X was in low-spin state (about 2.0 B.M. at 293 K). The complex [Fe(Himsa)₂]ClO₄ with "5-6 member rings" and the deprotonated complex [Fe(Ph-Himap)(Ph-imap)] were in the high-spin state (6.0 B.M. at 80 K). It is concluded that the ligand field strength of an N₄S₂ donor set is stronger than that of an N₄O₂ donor set.     

Kinetics of Iterative Carbohydrate Transfer to Polysaccharide Catalyzed by Chondroitin Polymerase on a Highly Sensitive Flow‐Type 27 MHz Quartz‐Crystal Microbalance

Using a highly sensitive flow‐type 27 MHz quartz crystal microbalance, we could detect a small mass change during stepwise and alternating one‐sugar transfer of glucuronic acid (GlcA) and N‐acetylgalactosamine (GalNAc) to an acceptor, catalyzed by chondroitin polymerase from Escherichia coli strain K4 (K4CP), and analyze the elongation mechanism of K4CP. K4CP was found to bind strongly to a chondroitin acceptor (K_d=0.97 μM ). Although the binding affinity and the catalytic rate constant for each monomer were considerably different, the apparent catalytic efficiency (k_cat/K_m) was similar (6.3×10⁴ M ^?1 s^?1 for GlcA transfer and 3.4×10⁴ M ^?1 s^?1 for the GalNAc transfer). This is reasonable for the smooth alternating elongation of GlcA and GalNAc on the acceptor. This is the first study to report the determination of kinetic parameters for enzymatic, alternated, sugar elongation.     

Resazurin as an electron acceptor in glucose oxidase-catalyzed oxidation of glucose

The behavior of resazurin (1) as an electron acceptor in glucose oxidase (GOD)-catalyzed oxidation of glucose under anaerobic conditions is described. When a mixture of 1, glucose, and GOD in phosphate buffer (pH 7.4, 0.1 M) was incubated at 25 degrees C, the resulting solution turned purple to fluorescent pink due to the deoxygenated product, resorufin (2). On incubation of 1 with GOD alone or with H2O2 under essentially the same conditions, no color change was seen, indicating that generation of 2 in the enzymatic reaction is brought about through reduction of 1 by the reduced form (GODred) of GOD, which was also supported by the voltammetric behavior of 1. However, it was found that the enzymatic transformation of 1 to 2 is of no practical use as an indicator reaction for glucose determination using only GOD due to a slow reaction of 1 with GODred. Based on a ping-pong type mechanism with a steady-state approximation, KM and kcat for 1 as an electron acceptor from GODred were estimated to be 15+/-1.3 microM and (5.0+/-0.5) x 10(-2) s(-1), respectively.     

Rationally Designed Semisynthetic Natural Product Analogues for Stabilization of 14‐3‐3 Protein–Protein Interactions

The natural product family of fusicoccanes are stabilizers of 14‐3‐3 mediated protein–protein interactions (PPIs), some of which possess antitumor activity. In this study, the first use of molecular dynamics (MD) to rationally design PPI stabilizers with increased potency is presented. Synthesis of a focused library, with subsequent characterization by fluorescence polarization, mutational studies, and X‐ray crystallography confirmed the power of the MD‐based design approach, revealing the potential for an additional hydrogen bond with the 14‐3‐3 protein to lead to significantly increased potency. Additionally, these compounds exert their action in a cellular environment with increased potency. The newly found polar interaction could provide an anchoring point for new small‐molecule PPI stabilizers. These results facilitate the development of fusicoccanes towards drugs or tool compounds, as well as allowing the study of the fundamental principles behind PPI stabilization.     

Biphenyl ether and biphenyl quinolizidine lactone alkaloids from Heimia salicifolia

Three new biphenyl ether quinolizidine lactone alkaloids (1–3) and 13 new biphenyl quinolizidine lactone alkaloids (4–16) were isolated from Heimia salicifolia (Lythraceae) together with seven known alkaloids. Their structures were determined by spectroscopic analyses and chemical conversions.     

A new Zn(II) coordination polymer with 4-pyridylthioacetate: assemblies of homo-chiral helices with sulfide sites

A coordination polymer [Zn(pyta)(OH)] (pyta = 4-pyridylthioacetate), was synthesized and structurally characterized; it is constructed by an alternating assembly of two types of homo-chiral helices, [Zn-OH] and [Zn-pyta], in which the sulfide moieties are fastened in the latter columns.     

Increased viscosity of erythrocyte suspension upon hemolysis

Viscous properties of partially hemolyzed erythrocyte suspensions were studied with a cone-plate viscometer. A Casson plot was successfully applied for analysis of the viscous properties. When the degree of hemolysis was increased, Casson viscosity ( _c) of the partially hemolyzed erythrocyte suspensions increased, but the substitution of hemoglobin solution with the same O₂-carrying capacity of hemolyzed fraction (containing ghost) reduced the _c remarkably. The yield stress (f _c) of the intact erythrocyte suspension increased with increasing hematocrit, but thef _c of partially hemolyzed erythrocyte suspension was dependent on both hematocrit and the degree of hemolysis. The apparent viscosity ( _a) of erythrocyte suspension was drastically increased with the slight hemolysis, and became maximum at a certain degree of hemolysis which was dependent on both total hemoglobin concentration and shear rate. Such influence of hemolysis on the _a was also evident in the mixture of erythrocyte suspension and hemoglobin solution. These results suggest that the hemoglobin molecule plays a certain role in erythrocyte-erythrocyte interaction in their suspension, which modifies the viscosity.