Homogeneous Dimers Research Articles

Extraction of metals by bis-(2-ethylhexyl) phosphoric acid in 2-ethylhexanoic acid as monomerizing diluent from an aqueous chloride phase: Th(IV) and U(VI)

The extraction of Th 4+ and UO 2 2+ from an aqueous phase into a solution of bis 2-ethylhexyl phosphoric acid, (2-C 2H 5·C 6H 12O) 2PO(OH), HDEHP, in the monomerizing diluent 2-ethylhexanoic acid has been studied in terms of the concentration of hydrogen ion in the equilibrated aqueous phase and of HDEHP in the opposing equilibrated organic phase. The extraction stoichiometries, with the corresponding expression for K in terms of F (the formality of HDEHP in the organic phase), [H +] (the concentration of hydrogen ion in the aqueous phase), and K s , for a 1.00 F (NaCl + HCl) aqueous phase, are: Th A 4++ 5HY O⇄ Th(HYO O+ 4H A + K = K sF 5 [H +] 4 UO 2A 2+ + 3HY O ⇄ UO 2( HY 3) O+ 2H A + K = K sF 3 [H +] 2 where HY represents the monomer of HDEHP and the formulations of extracted species are non committal with respect to structure. With HZ representing the monomer of 2-ethylhexanoic acid, suggested formulations of the extracted species in terms of homogeneous and heterogeneous dimers are: Th(HY 2)(HYZ) 3 and UO 2(HY 2)(HYZ). The K s values are: Th 4+ (7 × 10 4) and UO 2 2+ (2 × 10 2). Comparison of the extraction of Th 4+ and UO 2 2+ with the extraction, previously reported, of Am 3+, Eu 3+, Tm 3+ and Y 3+ in the same system is made. Application (patented) of this liquid-liquid extraction system to the purification of thorium from contaminant rare earths and yttrium is demonstrated.

Polymerization of penicillins : IV. Separation, isolation and characterization of ampicillin polymers formed in aqueous solution

Polymeric substances formed from amplicillin sodium in aqueous solution have been separated according to charge by anion-exchange chromatography on a column of DEAE-Sephadex A-25 using a linear sodium chloride gradient at a constant pH of 7.4. The separated materials, ranging in size from the monomer to the octamer, have been characterized by various functional-group analyses. A homogeneous well-defined ampicillin dimer, tetramer and hexamer have been isolated from the effluent in high yields. The separation and isolation of the ampicillin polymers permit a conclusive establishment of their structures, which in turn has confirmed previous suggestions that the polymers are formed through a chain process involving aminolysis of ampicillin at the β-lactam carbonyl moiety by the amino group of the side-chain of a second ampicillin molecule.

Proteinase inhibitor II from potatoes: isolation and characterization of its protomer components

Proteinase inhibitor II, an inhibitor of chymotrypsin and trypsin, is a heat-stable protein with a dimeric molecular weight of 21 000 that is a component of Russet Burbank potato tubers. Four monomeric isoinhibitor species of molecular weight 10 500 comprise inhibitor II and were isolated by chromatography on phosphocellulose in 8 M urea. Upon removal of the urea, each monomeric species dimerized to yield homogeneous dimers. The three major protomer species, called B, C, and D, and their homogeneous dimers were further characterized. They have similar molecular weights and amino acid compositions, and each has an N-terminal alanine residue. Dimers of purified protomers B, C, and D exhibited full cross-reactivities with each other in immunological double-diffusion assays. Reconstituted dimers possess two binding sites for bovine alpha-chymotrypsin, indicating that each monomer possesses one binding site for this enzyme. Significant differences were noted among the reconstituted dimers in their isoelectric points, immunoelectrophoretic mobilities, ion-exchange properties, and their inhibitory reactivities against trypsin. The properties of the inhibitor II dimeric species are similar but not identical to inhibitors IIa and IIb reported from Japanese potatoes (variety "Danshaku-Imo"), indicating the existence of intervarietal, as well as intravarietal, differences among potato tuber inhibitor II isoinhibitors.

A kinetic study of propylene dimerization catalyzed by cobalt dinitrogen complexes

The kinetics of homogeneous propylene dimerization with the dinitrogen complexes of cobalt CoH(N 2)(PPh 3) 3 or Co(N 2)(PPh 3) 3 as catalysts under mild conditions can be described by the following rate equation ▪ The possible mechanism of the reaction is discussed.

Bacillus megaterium, KM β-galactosidase: Purification by affinity chromatography and characterization of the active species

The enzyme β-galactosidase from Bacillus megaterium, strain KM has been purified by affinity chromatography. The enzyme was found to have a dimeric subunit structure, with the monomer having a molecular weight of 120,000. The K eq of the monomer-dimer equilibrium was strongly shifted towards dissociation in the isolated state. Inclusion of 5% sucrose in the buffer (and maintenance of the temperature at 5 °) minimized this dissociation. Molecularly homogeneous monomer and dimer could be prepared on sucrose gradients. The dimer was determined to have an S 20,w of 8, while the monomer had an S 20, w of 3. The amino acid composition was found to be similar to that of the E. coli β-galactosidase although significant differences occur. The activity of the monomer was studied by both urea-denaturation experiments and by immobilization of the monomer on Sepharose-4B. The monomer, bound to Sepharose-4B, was found to be inactive but still capable of binding the inhibitor thio-methyl galactoside. Activity was reconstituted by adding free monomer, in 8 M urea, to the Sepharose-bound monomer, followed by removal of the urea by dialysis. In addition, free monomers from E. coli β-galactosidase were found to form active hybrids with Sepharose-bound B. megaterium β-galactosidase monomers. We conclude on the basis of these studies that the free monomer is inactive, and that the dimer is the active species, in marked contrast to E. coli β-galactosidase where only the tetrameric form is active.

The hemoglobin of the holothurian echinoderm, Molpadia oölitica pourtales

1. 1. The hemoglobin of the holothurian, Molpadia oölitica, in the carbonmonoxy-, oxy- and cyanmet-ligand states has an apparent molecular weight on Sephadex G-75 (superfine) of about 40,000. 2. 2. The hemoglobin is a homogeneous dimer which can be cleaved into identical monomeric subunits by reaction with excess potassium ferricyanide. 3. 3. The purified hemoglobin has an amino acid composition per heme of: Lys 10, His 6, Arg 15, 1 2 Cys 0 , Asp 20, Thr 1, Ser 11, Glu 20, Pro 3, Gly 11, Ala 20, Val 10, Met 6, Ileu 9, Leu 16, Tyr 3, Phe 9, Trp 1. 4. 4. Preliminary studies indicate a pH independent sigmoid oxygen dissociation curve with n = 1·6. The heat of oxygenation is −8·8 kcal/mole. 5. 5. The structure and oxygen equilibrium of M. oölitica hemoglobin are compared with those of other holothurian hemoglobins.

Reactions of group III metalalkyls in the gas phase. Part 4.—Kinetics of the homogeneous dimerization of ethylene to 1-butene, catalyzed by gaseous triethylaluminium

The kinetics of the homogeneous dimerization of ethylene into but-1-ene, catalyzed by triethyl-aluminium (Alet3) in the gas phase was studied in Teflon coated reactors for temperatures ranging between 160 and 233°C. The only significant side reaction is the isomerization of but-1-ene to but-2-ene. The reaction is second order in ethylene pressure and the catalyst Alet3, can practically quantitatively be recovered from the product mixture. Consistent second order rate constants have been obtained despite large variations in the individual reaction parameters, yielding the Arrhenius relationship log k1(l. mol–1 s–1)=(6.15 ± 0.68)–(16.3±1.5)/θ where θ equals 4.58 × 10–3T in kcal mol–1 or log k(l. mol–1 s–1=(6.15 ± 0.68)–(6.82 ± 0.63)/θ where θ equals 1.914 × 10–3T in kJ mol–1). The rate controlling step is the addition of ethylene to Alet3 to form n-butyl-diethyl-aluminium and the detailed reaction mechanism involves the establishment of a pre-equilibrium between Alet3 and ethylene to form a Alet3· C2H4π-complex prior to the formation of the four-centre cyclic transition state.

Far infrared spectra of homogeneous and heterogeneous dimers of some carboxylic acids

Far infrared spectra of homogeneous and heterogeneous dimers of some carboxylic acids

PRESENCE OF SEVERAL PHENOLIC COMPONENTS IN FRUIT PROANTHOCYANIDINS.

Forsyth and Roberts1 reported that chromatographically homogeneous cacao proanthocyanidin dimer yielded epicathechin and a new leucocyanidin when heated with 0.1 N hydrochloric acid, and cyanidin when heated with stronger acid. Similar dimeric proanthocyanidins were isolated from Crataegus oxyacantha and Gleditschia triacanthos by Freudenberg and Weinges2–5. The astringent proanthocyanidins isolated from various fruit tissues, unlike the above dimers, were found to be highly polymerized and not chromatographically mobile. This was true of the originally isolated persimmon proanthocyanidin6,7 and of the more recently isolated persimmon8 and apple9 preparations. These purified preparations, which were not mobile on paper in any of the solvent systems tested, were, however, found to yield mobile phenolics without any accompanying anthocyanidins when heated with dilute hydrochloric acid. Under these conditions several chromatographically identified phenolics and a non-mobile but apparently less highly polymerized fraction were obtained. The original preparation, and the residue after dilute acid hydrolysis, which was insoluble in ethyl acetate, were found to yield identifiable anthocyanidins on heating with more concentrated hydrochloric acid. The results of these observations, which continued investigations previously reported on the mechanism of acid conversion of proanthocyanidins into their corresponding anthocyanidins10, are reported here.