Time delay as a key to apoptosis induction in the p53 network

A feedback mechanism that involves the proteins p53 and mdm2, induces cell death as a controlled response to severe DNA damage. A minimal model for this mechanism demonstrates that the response may be dynamic and connected with the time needed to translate the mdm2 protein. The response takes place if the dissociation constant k between p53 and mdm2 varies from its normal value. Although it is widely believed that it is an increase in k that triggers the response, we show that the experimental behaviour is better described by a decrease in the dissociation constant. The response is quite robust upon changes in the parameters of the system, as required by any control mechanism, except for few weak points, which could be connected with the onset of cancer. Received 8 May 2002 / Received in final form 9 July 2002 Published online 17 September 2002     

Extraction of Americium(III) and Europium(III) with Two Open-Chain Crown Ethers of Amide Type

The extraction of Am³⁺ and Eu³⁺ from aqueous picric acid solution by N, N-dinaphthyl-N, N-diphenyl-3,6-dioxaoctanediamide (L^I) and 1, 1-(3, 6, 9-trioxaundecanedionyl)diphenothiazine (L^II) was investigated by a radioactive tracer technique. Extraction distribution ratios of Am³⁺ and Eu³⁺ have been measured as a function of pH, picric acid concentration, extractant concentration, diluent and temperature. The extraction of Am³⁺ is preferred to that of Eu³⁺ for both L^I and L^II, and the latter gives larger separation factor than the former. The equilibrium constants and thermodynamic parameters of extraction reactions were also calculated.     

Labile rhizosphere soil solution fraction for prediction of bioavailability of heavy metals and rare earth elements to plants

A labile rhizosphere soil solution fraction has been recommended to predict the bioavailability of heavy metals and rare earth elements to plants. This method used moist rhizosphere soil in combination with a mixture of 0.01 mol L(-1) of low-molecular-weight organic acids (LMWOAs) as extractant. The extracted soil solutions were fractionated into two colloidal fractions of <0.45 microm (F(3)) and <0.2 microm (F(2)), and one truly dissolved fraction including free metal ions and inorganic and organic complexes (fractionr(0.2 microm, LMWOAs) approximately r(0.45 microm, LMWOAs). In the case of rare earth elements the good correlation was obtained for both the wheat roots and shoots. Generally, the correlation coefficients obtained by LMWAOs were better than that obtained by the first step of BCR method. Therefore, LMWAOs and F(lrss) were strongly recommended to predict the bioavailability of metals in soil pools to plants.     

PhenNO—TTA—乳化剂OP荧光光度法测定微量铕

研究了Ｅｕ（Ⅲ）－ＰｈｅｎＮＯ－ＴＴＡ－乳化剂ＯＰ体系的荧光性质及其用于微量铕的测定。该体系具有良好的分析特性，最低检测限可达７．０×１０＾－１４ｍｏｌ／Ｌ．     

四足配体铽配合物-蒙脱土超分子复合发光材料的插层组装、表征和性质研究

用两种方法分别将四足配体铽配合物[TbL（NO3）]^2＋和[TbL]^3＋插层组装到了蒙脱土（MT）层板间，制备出超分子复合发光材料[TbL（NO3）^2＋-MT和[TbL]^3＋-MT。方法一：通过离子交换反应让配离子[TbL（NO3）]^2＋取代钠＋基蒙脱土（Na-MT）中的Na^＋离子，插层组装到蒙脱土层板间。方法二：用配体L与铽基蒙脱土（Tb-MT）反应，使配体插入蒙脱土层板间与Tb^3＋离子配位。用元素分析、XRD，FT-IR,UV-vis和热分析对材料进行了表征，并对其荧光性质进行了研究。结果表明，复合材料保持了蒙脱土良好的层柱结构特征，其层间距d001值与插层配离予的直径吻合较好，配离子以单层形式分布于蒙脱土层板间，复合材料中配合物的热稳定性有明显提高。在紫外光激发下，复合材料发出较强的Tb^3＋特征荧光，其发射光谱与相应配合物的发射光谱很相似；复合材料中配合物的相对荧光强度较相应纯配合物有明显提高。荧光寿命较长；配合物的激发波长向可见光区发生位移，说明插层组装实现了对配合物激发波长的调制作用。     

Crystal structures of the complexes of rare earth picrates with N, N, N′, N′-tetraphenyl-3, 6-dioxaoctanediamide

The complexes of rare earth picrate with N, N, N′, N′-tetraphenyl-3, 6-dioxaoctanediamide (TDD), [Eu(pic)₃(TDD)]-2CH₃CN and [Y(pic)₃(TDD)], have been synthesized. The crystal structures reveal that TDD acts as a tetradentate ligand, forming a ring-like coordination structure with its oxygen atoms together with one oxygen atom of the bidentate picrate. In the Eu (III) complex, the europium ion with a larger ionic radius lies out of the ring, while in the Y (III) complex, the yttrium ion with a smaller ionic radius enters the cavity of the ligand. The structures of the complexes are greatly affected by the ionic radii due to participation of the picrates in coordination. Project supported by the National Natural Science Foundation of China, the Doctoral Foundation of the State Education Commission of China, and the Climb Plan Foundation of the State Science and Technology Commission of China.     

Design and coordination behavior of the first selective recognition ligand of 147Pm(III)

A new amide tripodal ligand, 6-[2-(2-diethylamino-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa-6,12-diazatetradecanamide (4) has been designed and synthesized for the recognition of rare earth ions. Three representative complexes of trivalent lighter (La), middle (Gd), and heavier (Er) rare earth ions with 4 were synthesized and characterized by X-ray crystallography. In the complex, the heptadentate forms a cup-like coordination cavity encapsulating the central ion. Different supramolecular complex dimers are constructed by pi-pi interaction and van der Waals forces in accordance with the lanthanide contraction. The differences of the cavity and dimer structures were investigated further by assessing the separation efficiency of in multitrace solvent extraction of rare earth ions from picrate acid solution and the ligand has the best separation factor for 147Pm(III).     

Synthesis and characterization of complexes of lanthanide nitrates with N,N′-dinaphthyl-N,N′-diphenyl-3,6-dioxaoctanediamide

Solid complexes of lighter lanthanide nitrates with N,N′-dinaphthyl-N,N′-diphenyl-3,6-dioxaoctanediamide (DDD), Ln(NO₃)₃(DDD) (Ln = La---Nd, Sm) have been prepared in non-aqueous media. These complexes have been characterized by elemental analysis, conductivity measurements, IR spectra, electronic spectra and TG-DTA techniques. In all the complexes, DDD and NO₃⁻ are coordinated to the lanthanide ions as tetradentate and bidentate ligands, respectively. The differences in the IR and electronic spectra between these complexes and lanthanide nitrate complexes with N,N,N′,N′-tetraphenyl-3,6-dioxaoctanediamide (TDD) are discussed.     

Trinuclear to dinuclear: a radii dependence lanthanide(III) self-assembly coordination behavior of an amide-type tripodal ligand

Lanthanide nitrate complexes with the heptadentate ligand L (6-[2-(2-(diethylamino)-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa-6,12-diazatetradecanamide), [Ln(2)L(NO(3))(6)] (Ln = La, Nd, Sm, Eu, Ho), have been prepared and characterized. The X-ray crystallographic studies show that, in [La(2)L(NO(3))(6)(H(2)O)].H(2)O (1), two complex cations [LaL(H(2)O)](3+) are linked by a hexanitrato anion [La(NO(3))(6)](3)(-) and form a trinuclear cation. In [Nd(2)L(NO(3))(6)(H(2)O)].CHCl(3).1/2CH(3)OH.1/2H(2)O (2), one complex cation [NdL(H(2)O)](3+) and a hexanitrato complex anion [Nd(NO(3))(6)](3)(-) are linked by a bridging NO(3)(-) to form a dinuclear complex. In both complexes, the bridging nitrate is an unusual tetradentate ligand. The metal ions are 12-coordinated in hexanitrato anions and 10-coordinated in complex cations. The chainlike supramolecular structures of La(3+) complex are parallel and have no hydrogen bonds in between, while, in the Nd(3+) complex, a chiral cavity is formed by hydrogen bonds between two adjacent supramolecular chains. These influences are further investigated by assessing the separation efficiency of L and (1)H NMR spectra of its lanthanide nitrate mixtures in solution.     

Synthesis,self-assembly,and photomechanical actuator performance of a sequence-defined polyviologen crosslinker

ABSTRACT

Although it is well known that viologen radical cations can self-assemble into stacks or complexes on account of radical-radical pairing interactions, it has only recently been demonstrated that reduction of main-chain polyviologens integrated into hydrogel networks can trigger actuation. In these earlier examples, hydrogels comprising oligoethylene glycol-based polyviologens and poly(ethylene glycol) were functionalized with terminal azide groups to prepare ‘click’-based gels. Here, we report a new structural design for the functional polyviologen that consists of main-chain viologen subunits separated by hexamethylene groups instead of glycols and is capped at each end with styrene groups. Activation of this viologen-based macrocrosslinker was achieved using chemical- and photoreduction methods and its ability to undergo intramolecular chain-folding was monitored by absorption spectroscopy. Acrylate-based organogels and hydrogels were also prepared and a comparison was carried out to assess the actuator performance in each gel in terms of the rate of contraction and changes in stiffness.