Solvent‐Dependent Cation Exchange in Metal–Organic Frameworks

We investigated which factors govern the critical steps of cation exchange in metal–organic frameworks by studying the effect of various solvents on the insertion of Ni²⁺ into MOF‐5 and Co²⁺ into MFU‐4l. After plotting the extent of cation insertion versus different solvent parameters, trends emerge that offer insight into the exchange processes for both systems. This approach establishes a method for understanding critical aspects of cation exchange in different MOFs and other materials.     

Activation of sepharose withN,N′-disuccinimidyl carbonate

A method is described for the activation of Sepharose withN,N′-disuccimidyl carbonate. The activated carbonate reacts smoothly with amine-containing ligands yielding stable carbamate derivatives.     

Immobilization of protein on aldehyde-containing gels—II. Activation of pyridine rings with cyanogen bromide

Cyanogen bromide was used to convert pyridine rings in polymers to polyaldehyde. By reaction with NH₂-containing substances, the rings are rebuilt, resulting in a pyridinium compound. Thus proteins and other NH₂-containing substances can be covalently bound. This method provides a new means for a immobilization technique. Pyridine-gels based on polysaccharide and polyacrylamide matrices, as well as pyridine glass beads, were synthesized and used to study the conditions necessary for coupling. Trypsin and — chymotrypsin were used as test substances for immobilization of proteins. Some properties of the bound protein were studied and compared to native enzyme. Some general results on the applicability of these gels for affinity chromatography are also presented.     

Temperature Effect on the Phase Behavior of the Systems Water/TritonX-100,114,405/n-Butanol/n-Hexane

We have investigated the effect of temperature on the phase behavior and the partition coefficients of nonionic surfactants in water/n-hexane systems. We found that the composition of the conjugate single and two phase solution in the pseudoternary diagram is continuously transformed from one state to other by increasing the temperature. We also demonstrated that the partition coefficient of a nonionic surfactant is a measure of the relative hydrophilic-lipophilic nature of the surfactant, if the measurement is performed at low concentration.     

Preparation and properties of insoluble forms of bacteriophage T4 lysozyme and chicken egg white lysozyme

Bacteriophage T4 lysozyme and chicken egg white lysozyme were covalently bound to cyanogen bromide activated Sepharose and to glutaraldehyde activated polyacrylhydrazido-Sepharose. The latter method seemed less favorable for T4 lysozyme, since the poly-acrylhydrazido-agarose conjugate exhibited low activity compared to the agarose conjugate. Whole bacteria (M.luteus and chloroform-treatedE. coli B cells) and the soluble uncross-linked peptidoglycan polymer fromM. luteus were used as substrates. Both types of conjugates exhibited low specific activity (lytic activity) toward insoluble substrates (cells), but surprisingly high specific activity toward the soluble substrate (hydrolytic activity). Product analysis showed that the enzyme conjugates retained their specificity of action, i.e., the same products were formed, and their rates of production were the same as those observed with the soluble (native) enzyme. The cell wall disaccharide-tetrapeptide GlcNAc-MurNAc-L-ala-D-gIu-(A₂pm-D-Ala) (C₆) inhibits the hydrolytic activity of both the native and the agarose bound T4 lysozyme. Only a slightly increased thermal stability was observed upon immobilization of T4 lysozyme, whereas the stability of the enzyme during storage and handling was greatly improved. The pH optimum of the lytic activity of Sepharose-T4 lysozyme was shifted about 1 pH unit to the alkaline side, compared to that found for the soluble enzyme, whereas no pH shift was observed for the polyacrylhydrazido-Sepharose conjugate. The optimum of the hydrolytic activity of Sepharose-T4 lysozyme was shifted to the acidic side. The pH optima of the lytic activity of the various lysozymes toward the bacterial cells were all very similar (>7), and differed greatly from the pH optima (<6) observed for their hydrolytic activities toward the negatively charged soluble peptidoglycan polymer. It is proposed that the observed differences in pH optima primarily reflect the basically different properties measured, i.e., the β(1–4) cleaving activity (hydrolytic activity), and dissolution process of the damaged cells (lytic activity).     

Percolation,morphogenesis, and burgers dynamics in blood vessels formation

Experiments of in vitro formation of blood vessels show that cells randomly spread on a gel matrix autonomously organize to form a connected vascular network. We propose a simple model which reproduces many features of the biological system. We show that both the model and the real system exhibit a fractal behavior at small scales, due to the process of migration and dynamical aggregation, followed at large scale by a random percolation behavior due to the coalescence of aggregates. The results are in good agreement with the analysis performed on the experimental data.     

Mechanism of activation of hydroxyl-containing polymers with N-hydroxysuccinimide and carbodiimides: Reason for leakage

The carbodiimide-mediated reaction of N-hydroxysuccinimide with carboxyl groups immobilized to hydroxyl-containing polymers (such as Sepharose or Trisacryl) leads to N-hydroxysuccinimide ester and N-hydroxysuccinimide derivatives of β-alanine which react subsequently with the hydroxyl group of the polymer via ester and carbamate bonds. These derivatives are formed upon interaction of dicyclohexyl carbodiimide with three equivalents of N-hydroxysuccinimide followed by a Lossen rearrangement. The amount of β-alanine thus coupled is very high compared to the number of carboxyl groups present on the resin. The β-alanine bound through the ester bond comprises about 90% of the β-alanine bound. Alkaline treatment of the ester bonded β-alanine containing polymers (prior to coupling of amino-containing ligands) causes a rearrangement yielding β-alanine with a free carboxyl group coupled through a stable carbamate linkage. After coupling of amino-containing ligands, the above-described rearrangement cannot occur, and the β-alanine-linked ligand leaks from the polymer via hydrolysis of the ester bond. The newly formed carboxyl groups (derived from the rearrangement) can be used to prepare active esters (e.g. nitrophenyl). Upon coupling with amino-containing ligands, these esters yield resins bearing chemically stable bonds.     

Reduced 1-cohomology and relative property (T)

Shalom characterized property (T) in terms of the vanishing of all reduced first cohomology for compactly generated groups. We characterize group pairs having the property that the restriction map on all first reduced cohomology vanishes. We show that, in a strong sense, this is inequivalent to relative property (T), even for compactly generated group-pairs.