Unfreezing of molecular motions in protein-polymer conjugates: a calorimetric study

Journal of Thermal Analysis and Calorimetry - Protein-polymer conjugates are a promising class of biohybrids. In this work, the dynamics of a set of biodegradable conjugates myoglobin-poly(ethyl...     

Abstract Logical Constants

A possibility of defining logical constants within abstract logical frameworks is discussed, in relation to abstract definition of logical consequence. We propose using duals as a general method of applying the idea of invariance under replacement as a criterion for logicality.     

三种六元瓜环与Sr(Ⅱ)离子的配位及超分子自组装

本文以六元瓜环及两种部分甲基取代六元瓜环(统称为Q[6]s)为构筑元件,合成了4个Q[6]s-Sr(Ⅱ)离子的配合物,用X射线单晶衍射方法测定了配合物的晶体结构。结果表明,Q[6]s-Sr(Ⅱ)离子配合物自组装形成不同结构的分子链,体系中存在Cl-离子时,Q[6]s-Sr(Ⅱ)离子形成配位聚合链,而只有NO3-离子存在时,形成水分子配位桥连的超分子链。     

Novel Approach to Fabricate Carbon Molecular‐Sieve Membranes Based on Consideration of Interpenetrating Networks

Summary: Carbon molecular‐sieve membranes (CMSMs) have shown great potential for gas separation. They exhibit high selectivity by permitting effective size‐ and shape‐separation between gas molecules of similar molecular dimensions. Hence, the control of their pore size is very important. While previous studies have focused on the conditions of pyrolysis and its effect on CMSM properties, a novel approach is reported here whereby the precursor polymer is chemically modified prior to pyrolysis and the resultant CMSM was investigated for its gas separation properties. Pyrolysis of chemically crosslinked and uncrosslinked Matrimid® resulted in a change in d‐spacing from 5.6 to 3.6 and 3.7 Å, respectively. The crosslinked CMSM also exhibited greater ordering in its packing. The Matrimid‐derived CMSMs exhibited excellent separation properties for CO₂/CH₄.

Mechanism of chemical crosslinking modification.     

Effect of temperature on self-assembly of an ionic tetrapeptide

The self-aggregation of the ionic tetrapeptide RWDW (R = arginine, W = tryptophan, D = aspartic acid) was studied at three temperatures (15, 25 and 35 °C) by different experimental techniques such as atomic force microscopy (AFM), isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). AFM was used to investigate the morphology of the aggregates; the AFM images at 15 °C showed the presence of a dense network of entangled fibres, while at 35 °C the peptide assembled into sparse globular and fibrillar structures. Moreover, the calorimetric experiments showed that in all cases the disaggregation process is endothermic and dependent on the investigated temperature. Both the enthalpy of disaggregation and the cac change with temperature. In particular, at 35 °C, we obtained the lower enthalpy of disaggregation and higher cac, showing that the disaggregation process is favoured at high temperature. The DSC scans strengthen the hypothesis that the RWDW aggregation is a rather complex phenomenon.     

Mechanism of indium(III) exchange between NTA and transferrin: a kinetic approach

The equilibria and kinetics for the process of In(3+) exchange between nitrilotriacetic acid (NTA) and bovine serum transferrin (T) have been investigated in aqueous solution containing sodium bicarbonate. The metal exchange equilibria have been measured by difference ultraviolet spectroscopy at 25 degrees C, pH=7.4, and I=0.2 M (NaClO4). The acid dissociation constants of NTA and the binding constants of In(III) to NTA have also been measured. Kinetic experiments revealed that the process of In(3+) uptake by transferrin from [In(NTA)2](3-) is biphasic, the fast phase being completed in a few seconds, the slow phase lasting for hours. The fast phase has been investigated by the stopped-flow method and results in monoexponential kinetics. It involves rapid interaction of the 1:1 complex ML (M=In, L=NTA) with TB (T=transferrin, B=CO3(2-)) to give a quaternary intermediate MLTB which then evolves to an "open" MTB* ternary complex complex with expulsion of L. In turn, this complex interconverts to a "closed", more stable, form MTB. Neither the prevailing complex M2L nor the TB2 form of transferrin are directly involved in the exchange process but act as metal and protein reservoirs. The pH dependence of the reaction has been also investigated. The slow phase has not been investigated in detail; it takes several hours to go to the completeness, its slowness being ascribed to metal redistribution between the C-site and N-site of the protein, and/or metal release from polynuclear In(III) species.     

Coordination features of ditopic oxa-azamacrocycles toward Ni(II) and Co(II). Dioxygen uptake by their dinuclear Co(II) complexes

The coordination properties of the ditopic oxa-aza macrocycles L1-L3 toward Ni(II) and Co(II) have been investigated by means of potentiometric and UV-vis spectrophotometric measurements. L1-L3 contain two triamine and/or tetraamine chains separated by two dioxa chains and form both mono- and dinuclear complexes in aqueous solution. In the [ML]2+ complexes, the metal ion is coordinated by one of the two polyamine moieties, while the other does not participate in the coordination. In the dinuclear complexes each metal ion is coordinated, almost independently, to a single polyamine moiety. Under aerobic conditions the binuclear Co(II) complexes of the ligands L1-L3 are able to bind molecular oxygen, with a bridging coordination of O2 between the two metals.     

A simple,water-soluble,Fe3+-selective fluorescent probe and its application in bioimaging

A simple,water-soluble,Fe³⁺-selective fluorescent probe,derived from rhodamine B,was synthesized and characterized.The probe exhibits a fluorescence response toward Fe³⁺ with acceptable sensitivity and selectivity and even facilitates visual or naked-eye detection of Fe³⁺.The experiment results show that the response of the probe to Fe³⁺ is pH-independent over a wide range of 4.0-10.0.In addition,fluorescence microscopic imaging experiments have proven that the probe is cell permeable and can be used for monitoring intracellular Fe³⁺ in living cells.     

Thermodynamic study of inclusion complexes of zaleplon with natural and modified cyclodextrins

The thermodynamics and stoichiometry of zaleplon (ZAL) complexation with different cyclodextrin derivatives [β-CD, hydroxypropyl-β-cyclodextrin (HP-β-CD), randomly methylated-β-cyclodextrin (RAMEB), sulphobutylether-β-cyclodextrin (SBE-β-CD)] in aqueous solution was studied by spectrofluorimetry and ¹H NMR spectroscopy in order to obtain a more general understanding of the driving forces behind the inclusion phenomena. Job’s plot derived from the NMR spectral data and statistical analysis of spectrofluorimetric titration data confirmed the formation of equimolar complexes in all systems tested, excluding the possibility of higher order complex formation. Furthermore, thermodynamic parameters obtained by both techniques gave similar and negative values of ΔG° for all complexes, indicating spontaneous inclusion of drug into CDs. From a thermodynamic point of view, two types of inclusions were determined. One is enthalpy driven ZAL complexation with β-CD, HP-β-CD and RAMEB, while the other is entropy driven complexation observed in the case of SBE-β-CD. The mechanisms behind each type of inclusion were discussed in detail.