Complexation Equilibria of Zn(II), Pb(II) and Cd(II) with Reduced Glutathione (GSH) and Biologically Important Zwitterionic Buffers

The interaction of zinc(II), lead(II), and cadmium(II) with Glutathione (S‐L‐glutamyl‐Lcysteinylglycine) as primary ligand and zwitterionic buffers (N‐[2‐Hydroxyethyl]piperazine‐N′‐[2‐ethanesulfonic acid]) (HEPES) and (N‐Hydroxyethyl]piperazine‐N′‐[2‐hydroxy‐propanesulfonic acid]) (HEPPSO) as secondary ligands were studied by potentiometric‐pH titration in 1:1:1 ratio at 25.0 °C and I = 0.1 mol.dm^?3 (KNO₃). The formation constants of different normal and protonated binary and ternary complex species were calculated. Formation constants for the monohydroxy, and dihydroxy complexes for the binary systems M(II) + HEPES and M(II) + HEPPSO have been evaluated. The distribution curves for the various complex species as a function of pH were constructed.     

Hexa­methyl­enetetra­mine–4‐nitro­catechol–water (1/2/1)

In the title adduct, 1,3,5,7‐tetra­aza­tri­cyclo[3.3.1.1^3,7]dec­ane–4‐nitro­benzene‐1,2‐diol–water (1/2/1), C₆H₁₂N₄·2C₆H₅NO₄·H₂O, the hexa­methyl­ene­tetra­mine mol­ecule acts as an acceptor of intermolecular O—H?N hydrogen‐bonding interactions from the water mol­ecule and the hydroxy groups of one of the two symmetry‐independent 4‐nitro­catechol mol­ecules. The structure is built from molecular layers which are stabilized by three intermolecular O—H?O, two intermolecular O—H?N and four intermolecular C—H?O hydrogen bonds. The layers are further interconnected by one additional intermolecular O—H?N and two intermolecular C—H?O hydrogen bonds.     

Effect of thermal treatment on the structure and texture of differently impregnated NiO/SiO2 catalysts

NiO/SiO₂ catalysts were prepared with Ni contents ranging from 2–15% using a microporous silica support at pH ~11.5. The role of the method of preparation on the resulting catalyst is also investigated. Structural and textural changes were followed using X-ray diffraction, TG and DTA techniques—the surface area measurements were carried out on the parent catalysts and those produced in the temperature range 250–1000°C.Impregnation of the silica gel in the nickel ammine complex solution (catalyst series 1N–4N) with subsequent drying at 80°C overnight produced crystalline catalysts with two distinct peaks at d-spacings of 2.035 and 2.349 Å resulting from a surface silicate. This is easily destroyed by thermal treatment at 250°C for Ni contents ? 10% but is stable to this temperature for the higher Ni content. Drying the catalyst at room temperature (3N_b) gives rise to an amorphous product. A non-crystalline catalyst is also obtained when concentrated ammonia solution is added to the adsorbed nickel salt (3N_c). At high Ni content, the hydroxo ligand becomes significant and results in a surface compound in which one silanol group is attacked. This gives rise to a crystalline product at 500°C with characteristic d-spacings at 2.201 and 2.049 Å which, subsequently, produces a poorly crystalline NiO product at 1000°C. The presence of this hydroxo ligand is manifested by a small endotherm at 260°C.At Ni contents below 15% but greater than 2% a small exotherm is observed at ~ 500°C resulting from a reduction process. Entrained SO₄^2? ions present as an impurity are evolved at temperatures & > 750°C and can be estimated by TG analysis.The specific surface area decreases with Ni contents ? 5% but increases for higher Ni contents. Catalyst samples containing 15% Ni possess the highest specific area at all temperatures.Pore structure analysis showed that microporosity increased with increase in Ni content for the catalyst series 1N–4N. Samples from preparations 3N_b and 3N_c showed more mesoporosity than that of 3N. Thermal treatment causes widening of the pores for catalysts 1N–3N becoming predominantly mesoporous, co-existing with some micropores. Catalyst samples with 15% Ni remained predominantly microporous-mesoporosity increasing only at 1000°C.     

Resolution of crystalline ribonuclease by paper electrophoresis

1. Crystalline ribonuclease samples obtained from different commercial sources in addition to one prepared in the laboratory were resolved into their components, RNases I, II, III and IV, by a new two-dimensional electrophoretic technique 2. RNase I and RNase II liberated more uridyhc acid and cytidylic acid from yeast nbonucleic acid, and demonstrated a greater enzymic activity on undine-2', 3'-phosphate and cytidine-2',3'-phosphate, than either RNase III or RNase IV RNase III and RNaso IV liberated more adenylic acid and guanylic acid from yeast ribonucleic acid, and showed a greater enzymic activity on adenosine-2',3'-phosphate and guanosine-2', 3 '-phosphate than cither RNase I and RNase II 3. The degree of heterogeneity of the RNase samples studied revealed the age of the preparation 4. It is thus demonstrated, that certain of the activities of “crystalline nbonucleasc” reside in four different protein entities, and some activity toward punne nucleotidc esters existed in two of the four protein entities     

Bis­[hydrogen 1,1′‐bis­(di­phenyl­phos­phinato)­ferrocenium] octa­chloro­diantimony(III)

In the title compound, [Fe(C₃₄H₂₉O₂P₂)]₂[Sb₂Cl₈], the discrete centrosymmetric [Sb₂Cl₈]^2? anions are formed from two edge‐shared square pyramids of Cl atoms about each Sb atom. Within the cation, the two di­phenyl­phosphinate groups share one H atom and the ferrocene cyclo­penta­dienyl rings are in a staggered conformation, with the average value of the twist angle being 46°. In the crystal, each [Sb₂Cl₈]^2? anion is involved in eight C—H?Cl interactions with four surrounding cations and these interactions interconnect the ions to form molecular columns along the a direction.     

Selective role of oxidants in the presence of cation-exchange resins in Na(+)-form for the detection and differentiation of acidic, basic and neutral amino-acids

A test for detection and differentiation of acidic, basic and neutral amino-acids is based on use of a sulphonic acid cation-exchange resin in Na(+)-form, in the presence of various oxidants (permanganate, dichromate, chromate, iodate, peroxide) and final detection with Nessler's reagent.     

Diacetatobis­(tri­methyl­ene­thio­urea)­zinc(II) monohydrate

In the title compound, [Zn(CH₃COO)₂(C₄H₈N₂S)₂]·H₂O, the Zn atom is tetrahedrally coordinated in the ZnO₂S₂ form. N—H?O and O—H?O intramolecular and intermolecular hydrogen bonds are formed by the four N atoms and the water mol­ecule. N—H?O intermolecular hydrogen bonds and C—H?S and C—H?O intermolecular interactions interconnect columns formed by the mol­ecules into layers. Adjacent layers are then linked by other N—H?O and O—H?O intermolecular hydrogen bonds to form a three‐dimensional framework throughout the structure. The orientations of the acetate planes are such that the Zn atom lies within them.     

Structural Refolding and Thermal Stability of Myoglobin in the Presence of Mixture of Crowders: Importance of Various Interactions for Protein Stabilization in Crowded Conditions

The intracellular environment is overcrowded with a range of molecules (small and large), all of which influence protein conformation. As a result, understanding how proteins fold and stay functional in such crowded conditions is essential. Several in vitro experiments have looked into the effects of macromolecular crowding on different proteins. However, there are hardly any reports regarding small molecular crowders used alone and in mixtures to observe their effects on the structure and stability of the proteins, which mimics of the cellular conditions. Here we investigate the effect of different mixtures of crowders, ethylene glycol (EG) and its polymer polyethylene glycol (PEG 400 Da) on the structural and thermal stability of myoglobin (Mb). Our results show that monomer (EG) has no significant effect on the structure of Mb, while the polymer disrupts its structure and decreases its stability. Conversely, the additive effect of crowders showed structural refolding of the protein to some extent. Moreover, the calorimetric binding studies of the protein showed very weak interactions with the mixture of crowders. Usually, we can assume that soft interactions induce structural perturbations while exclusion volume effects stabilize the protein structure; therefore, we hypothesize that under in vivo crowded conditions, both phenomena occur and maintain the stability and function of proteins.     

Maghemite nanocrystal impregnation by hydrophobic surface modification of mesoporous silica

Here, we report the design of a hybrid inorganic/organic mesoporous material through simultaneous pore engineering and hydrophobic surface modification of the intramesochannels to improve the uptake of superparamagnetic maghemite nanocrystals via impregnation techniques. The mesoporous material of the SBA-15 type was functionalized in situ with thiol organo-siloxane groups. Restricting the addition of the thiol organo-siloxane to 2 mol % yielded an inorganic/organic hybrid material characterized by large pores and a well-ordered hexagonal p6mm mesophase. The hydrophobic surface modification promoted the incorporation of 7.5 nm maghemite (gamma-Fe2O3) nanocrystals, prepared through temperature-controlled decomposition of iron pentacarbonyl in organic solvents. The hydrophobic, oleic acid capped superparamagnetic maghemite nanocrystals were incorporated into the porous network via wet impregnation from organic suspensions. Combining diffraction, microscopy, and adsorption data confirmed the uptake of the nanocrystals within the intramesochannels of the silica host. Magnetization dependencies on magnetic field at different temperatures show a constriction in the loop around the origin, which indicates immobilization of maghemite nanocrystals inside the thiol-functionalized silica host.     

Studies with pyridazines and condensed pyridazines: Routes for synthesis of 3‐amino‐5‐aryl‐2,5‐dihydro‐pyridazine, 10aH‐pyridazino[1,6‐a]quinazoline and thieno[3,4‐d]pyridazinone

Novel routes to 3‐aminopyridazines, 10aH‐pyridazino[1,6‐a]quinazoline and, thieno[3,4‐d]pyridazine utilizing the reaction of 2‐oxobutanal‐1‐arylhydrazones 3a,b with α,β‐unsaturated nitriles are described. Condensation of 3 with ethyl cyanoacetate afforded pyridazinones that reacted with sulphur yielding thienopyradazinone 10 . Reaction of 10 with maleic anhydride and acrylonitrile afforded products of addition and hydrogen sulphide elimination. On other hand reacting 10 with enaminone and ethyl propionate afforded the product of addition of the amino function to activated double bond.