Self-assembled hetero-bimetallic coordination cage and cation-clusters with micro(2)-Cl bridging using a flexible two-arm ferrocene amide linker.

One flexible, discrete coordination cage [Cu(2)(3-BPFA)(4)(H(2)O)(2)](ClO(4))(4).4CH(3)OH (), and two cation-clusters with micro(2)-Cl bridging [Ni(2)(micro-Cl)(3-BPFA)(4)(H(2)O)(2)](ClO(4))(3) () and [Co(2)(micro-Cl)(3-BPFA)(4)(H(2)O)(2)](ClO(4))(4).4CH(3)OH (), containing the ferrocenyl functionality were prepared via coordination-driven self-assembly and Cl-anion template from Cu(II), Ni(II) and Co(II) salts and a flexible two-arm molecule 1,1-bis[(3-pyridylamino)carbonyl]ferrocene (3-BPFA).

Metal-ion- and pH-induced conformational changes of acutolysin D from Agkistrodon acutus venom probed by fluorescent spectroscopy.

Acutolysin D isolated from the venom of Agkistrodon acutus is a protein of 44 kDa with marked hemorrhagic and proteolytic activities. The metal-ion- and pH-induced conformational changes of acutolysin D have been studied by following fluorescence and activity measurements. Here we provide evidence for the fact that native holo-acutolysin D adopts two different conformations, native state a, stable in the weak acidic pH range from 5.5 to 7.0 with low activity, and native state b, stable in the weak alkaline pH range from 8.0 to 9.0 with high activity. Holo-acutolysin D has an optimum pH of 9.0 for caseinolytic activity and a maximum fluorescence at pH 9.0. The protein adopts the most stable conformation at pH 9.0. The addition of 1 mM Zn(2+) shifts both the alkali-induced unfolding transition curve and the alkali-induced inactivation curve toward higher pH value but has little effect on the acid-induced unfolding transition curve. No obvious effects on the pH-induced unfolding transition curve and the pH-dependent activity curve have been observed after the addition of 1 mM Ca(2+) to holo-acutolysin D. The results indicate that Zn(2+) is essential for its CA, while Ca(2+) is not essential for its CA. Removal of Ca(2+) and Zn(2+) from the protein enhances its sensitivity to pH and significantly reduces its overall stability during acid-induced denaturation. The kinetic results of the demetalization of holo-acutolysin D show that the demetalization rate constant K(1) for a slower reaction linearly decreases with the pH increase from 5.0 to 9.0, while K(2) for the faster reaction linearly increases with the pH change from 5.0 to 7.0. It is also evident from the present work that the free Zn(2+)-induced inactivation in the pH range from 8.0 to 9.0 should be attributed to the effect of Zn(OH)(2) precipitation on the protein.

[Study on the interaction of cystine and polyphenol oxidase from nicotian tobaccum].

The interaction of cystine and polyphenol oxidase (PPO) from nicotian tobaccum has been studied. The results show that cystine has an inhibitory effect on the enzymatic activity, the mechanism of which might be that the thiolether in cystine coordinates with Cu2+ in the active site of PPO, and the inactivation constant value of PPO by cystine is 0.633 min(-1), while the substrates or the products inhibit their combination. Cystine can also be combined with the products of enzymatic reaction to form a colourless compound. Cystine can inhibit the enzymatic activity completely when the molar ratio of cystine to PPO approaches 16,000:1. The effect of cystine on the fluorescence changes with the molar ratio of cystine to the PPO. However, when the molar ratio gets to 75:1, cystine has no longer the effect on either the fluorescence spectra or the synchronous spectra. Microenvironment of trp residue in PPO is more hydrophobic than that of free trp in water.

[Fluorescence study on the interaction of salicylic acid and bovine serum albumin].

The interaction between salicylic acid and bovine serum albumin has been studied by fluorescence spectroscopy. The results show that the quenching mechanism of the combination of bovine serum albumin with salicylic acid is a static quenching procedure, the quenching constant K(sv) is 1.097 x 10(4) (mol x L(-1))(-1), and the equilibrium constant is 7.377 x 10(4). The number of binding sites is 1 and it is a strong one. When the ratio of molar concentration of salicylic acid to bovine serum albumin is lower than 1:1, it binds to Trp residue first but it doesn't result in any microenvironment changes of Trp residue. The binding distance between salicylic acid and bovine serum albumin and the energy transfer efficiency were obtained based on the theory of Förester spectroscopy energy transfer.

Effects of terbium and pH on structure of anticoagulation factor II from Agkistrodon acutus venom probed by fluorescent spectroscopy and equilibrium dialysis.

Anticoagulation factor II (ACF II) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X-binding protein with marked anticoagulant activity. Present studies show that the pH has a marked effect on the fluorescence intensity of holo-ACF II; however, no appreciable shift of the emission maximum of holo-ACF II was observed in the pH range of 3-10. It was deduced from a relatively weak fluorescence emission of holo-ACF II at a neutral pH (6-7) that native holo-ACF II assumes a compactly folded structure in which the most interior Trp residues and quenchers are adjacent. Terbium ions can completely replace both Ca2+ ions in holo-ACF II as determined by equilibrium dialysis. Two Tb3+-binding sites with different apparent Tb3+ association constant values, (2.1 +/- 0.2) and (1.0 +/- 0.1) x 10(7) M(-1), were identified through Tb3+ fluorescence titration. In addition, it was confirmed from the titration of holo-ACF II and Tb3+-ACF II with N-bromosuccinimide (NBS) that only interior Trp residues are involved in the energy transfer to Tb3+ ions and all accessible Trp residues located in the surface of holo-ACF II have a similar affinity to NBS while those located in the surface of Tb3+-ACF II have two different kinds of affinity to NBS, which suggests a conformational change of holo-ACF II on the substitution of Tb3+ for Ca2+.

N-(ferrocenecarbonyl)-N'-(quinolin-8-yl)thiourea.

In the title compound, [Fe(C5H5)(C16H12N3OS)], the 8-aminoquinoline and acylthiourea moieties are almost planar. There are two perpendicular arrangements of the molecules in the crystal with slightly different conformations. The two cyclopentadienyl rings in each molecule are parallel and eclipsed.