Stability constants and 1H relaxation effects of ternary complexes formed between Gd-DTPA, Gd-DTPA-BMA, Gd-DOTA, and Gd-EDTA and citrate, phosphate, and carbonate ions.

Formation of ternary complexes between Gd-DTPA, Gd-DTPA-BMA, and Gd-DOTA, used as contrast enhancement agents in MRI and the endogenously available carbonate and phosphate ions, has been demonstrated. The extent of ternary complex formation and its effect on the proton relaxation, measured at 9 MHz, rates is negligible at around pH < 8. The complex Gd-EDTA forms more stable ternary complexes with carbonate and phosphate and it also strongly coordinates the terdentate citrate ligand.

Evaluation of C-(beta-D-galactosyl) and C-(2-deoxy-D-lyxo-hex-1-enopyranosyl) (D-galactal type) derivatives as inhibitors of beta-D-galactosidase from Escherichia coli.

C-(2-Deoxy-D-lyxo-hex-1-enopyranosyl)formamide was prepared from acetylated C-(beta-D-galactopyranosyl)formamide by a radical-mediated bromination-zinc/N-methylimidazole-induced reductive elimination-Zemplén deacetylation reaction sequence. The preparation of acetylated 5-(2-deoxy-D-lyxo-hex-1-enopyranosyl)tetrazole was improved. Methyl C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formimidate was transformed by benzylamine into N-benzyl-C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formamidine and, after hydrolysis to methyl C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formate, into N-benzyl-C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formamide.

Determination of vitamin C in effervescent tablets containing other vitamins together with trace elements.

A simple, rapid method is reported for the determination of vitamin C in effervescent tablets containing other vitamins and several trace elements such as Mg(II), Zn(II), Fe(II), Mn(II), Cu(II) and Mo(VI). The procedure was developed on the basis of the bromate ion-iodide ion-ascorbic acid clock reaction (Landolt reaction). Interference effects of air oxygen and metal ions and the role of pH are discussed in detail.

A new combined electrothermal-hollow cathode atom and emission sourceInstrumentation and preliminary investigation.

A new radiation source based on the FANES-method has been developed in order to achieve an intensity enhancement of the radiation produced. Investigations carried out with this new source are controlled by a computer system connected with a multichannel spectrometer having a wavelength modulated background corrector. First results show that the combination of the two sources increases the emission intensity of spectral lines.

Potentiometric and spectroscopic studies on the copper(II) complexes of peptide hormones containing disulfide bridges.

Copper(II) complexes of oxytocin, 4-Glu-oxytocin, 5-Asp-oxytocin, and GlyGlyGly-Lys8-vasopressin were studied by potentiometric, EPR, and UV-visible spectroscopic methods. The formation of 4N-coordinated complexes was characteristic of all ligands. This type of coordination is especially favored for oxytocin due to the specific conformation of the ring coupled by the disulfide bridge.

Fast atom bombardment mass spectrometry of some lantibiotics.

Four lantibiotics namely epidermin, gallidermin, lanthiopeptin and mersacidin, have been studied by fast atom bombardment mass spectrometry. The molecular ion clusters of these compounds can be detected with reasonable abundance. The low-mass regions of the spectra show the presence of ions characteristic of the amino acids in the peptides.

Investigation of the active site of the cyanogenic beta-D-glucosidase (linamarase) from Manihot esculenta Crantz (cassava). I. Evidence for an essential carboxylate and a reactive histidine residue in a single catalytic center.

The broad-specificity cyanogenic beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.

Copper(II) complexes of low molecular weight derivatives of thymopoietin.

Copper(II) complexes of tri- and tetrapeptides containing either carboxylate or amide group in the side chain were studied by potentiometric and spectroscopic methods. The ligands are tri- and tetrapeptide segments of the hormones thymopoietin and splenin. It was found that internal aspartyl residues significantly enhance the metal binding ability of oligopeptides, resulting in the cooperative deprotonation of the amide nitrogens preceding the aspartyl residue, while the subsequent amide groups do not take part in metal ion coordination.

Preparation of C-(2-deoxyhex/pent-1-enopyranosyl)heterocycles.

Acetylated 1-cyanoglycals (2,6-anhydro-3-deoxyhept/hex-2-enononitriles) were prepared by direct elimination of acetic acid from the appropriate acetylated 2,6-anhydrohept/hexononitriles with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in aprotic solvents.

Chemical synthesis of the pyruvic acetal-containing trisaccharide unit of the species-specific glycopeptidolipid from Mycobacterium avium serovariant 8.

The functionalized, pyruvic acetal-containing haptenic trisaccharide, p-trifluoroacetamidophenyl 6-deoxy-2-O-(3-O-[4,6-O-(S)-(1-methoxycarbonylethylidene)-3-O-meth yl- beta-D-glucopyranosyl]-alpha-L-rhamnopyranosyl)-alpha-L-talopyranosid e (19), a component of the glycolipid from Mycobacterium avium serovar 8 was synthesized. For the preparation of the terminal pyruvic acetal-containing unit, benzyl 2-O-benzyl-3-O-methyl-beta-D-glucopyranoside (6) was condensed with methyl 2,2-di(ethylthio)propionate (1) in the presence of SO2Cl2-CF3SO3H catalyst to yield benzyl 2-O-benzyl-4,6-O-(S)-(1-methoxycarbonylethylidene)-3-O-methyl-beta -D- glucopyranoside (7S), which was then converted into the suitably substituted glycosyl donor 2-O-acetyl-4,6-O-(S)-(1-methoxycarbonylethylidene)-3-O-methyl-alph a-D- glucopyranosyl trichloroacetimidate (11). The disaccharide glycosyl acceptor p-nitrophenyl endo-3,4-O-benzylidene-6-deoxy-2-O-(2,4-di-O-benzyl-alpha-L-rhamnopyrano syl)- alpha-L-talopyranoside (15) was glycosylated with 11 in the presence of trimethyl trifluoromethanesulfonate to furnish the protected trisaccharide p-nitrophenyl 2-O-(3-O-[2-O-acetyl-4,6-O-(S)-(1-methoxycarbonylethylidene)-3-O-m ethyl-beta- D-glucopyranosyl]-2,4-di-O-benzyl-alpha-L-rhamnopyranosyl)-endo-3,4- O-benzylidene-6-deoxy-alpha-L-talopyranoside (16).

Copper(II) complexes of dipeptides containing aspartyl, glutamyl, and histidyl residues in the side chain.

Copper(II) complexes of various dipeptides containing carboxylate and imidazole-N3 donors (alpha- and gamma-GluVal, alpha- and beta-AspGly, beta-AspHis, gamma-GluHis, and homocarnosine) were studied by potentiometric and spectroscopic methods in solution. It was found that the presence of an alpha-carboxylate group in the N-terminal part of a peptide molecule significantly enhances the metal-binding ability of the ligands as a consequence of stable bis complex formation involving amino acid-like coordination. The interaction of copper(II) with beta-AspHis was characterized by the formation of an imidazole-bridged dimeric species, while the formation of bis complexes was detected in the case of gamma-GluHis.

Assay of N-acetyl-beta-D-glucosaminidase in urine from neonates: comparison of two new colorimetric methods using MNP-GlcNAc and VRA-GlcNAc as substrates.

The NAG activity present in urine from newborn babies was assayed using two colorimetric procedures with either MNP-GlcNAc or VRA-GlcNAc as substrate and compared with data obtained with the well established PNP-GlcNAc procedure. Both new assays were easy to perform and reproducible. The MNP-GlcNAc method has the advantage that it is now available as a kit; however, the VRA-GlcNAc procedure is more sensitive.

A quantitative assay to measure chromosome stability in Schizosaccharomyces pombe.

The fidelity of mitotic chromosome transmission in Schizosaccharomyces pombe was estimated quantitatively by using cycloheximide resistance as a means to select cells that had undergone chromosome loss or nondisjunction. We aimed to investigate the connection between recombination and mitotic chromosome stability. A number of mutants defective in mitotic recombination such as cdc17-L16, rec59-72, and rec50-25 were tested and in these an approximately ten fold elevation of mitotic haploidization rate was found compared with controls.

Studies on the N-acetyl-beta-D-hexosaminidase B from germinating Lupinus luteus L. seeds. II. Mechanism and inhibition with some 2-acetamido-2-deoxyaldono(1----4)lactones.

The N-acetyl-beta-D-hexosaminidase B of germinating yellow lupin seeds catalyzed the hydrolysis of both p-nitrophenyl-N-acetyl-beta-D-glucosaminide and -galactosaminide substrates. The investigation of the pH dependence of the kinetic parameters (Vmax and Vmax/Km) demonstrated that two common ionizable groups (probably two carboxyl groups) play an essential role in the catalysis. That is, the enzyme has a lysozyme-like splitting mechanism, and the possibility of an anchimeric assistance provided by the acetamido group seems to be negligible.

Studies on the N-acetyl-beta-D-hexosaminidase B from germinating Lupinus luteus L. seeds. I. Purification and characterization.

The N-acetyl-beta-D-hexosaminidase B of germinating Lupinus luteus L. seeds (McFarlane et al. (1984) Phytochemistry 23, 2431-2433) was partially purified with a six-step purification procedure following extraction.

Proof of the structure of ristotetraose: synthesis of propyl alpha-ristotetraoside.

A definitive synthesis of the propyl glycoside (1) of ristotetraose, the heterotetrasaccharide component of the antibiotic ristomycin A (ristocetin A) is described.

Kinetic investigation of the substrate specificity of the cyanogenic beta-D-glucosidase (linamarase) of white clover.

Partially purified linamarase from Trifolium repens (genotype Lili acac) plants was kinetically characterized. Kinetic evidence was found to support the assumption that this cyanogenic beta-D-glucosidase has a broad substrate spectrum. p-Nitrophenyl-beta-D-xylopyranoside and p-nitrophenyl-alpha-L-arabinopyranoside substrates bound almost as tightly to the active center of the enzyme as the glucono(1----5)lactone transition-state analog inhibitor.

Kinetic studies on the broad-specificity beta-D-glucosidase from pig kidney.

A broad-specificity beta-D-glucosidase from pig kidney cortex was isolated and purified to homogeneity by a rapid purification procedure. The pI (5.14 +/- 0.

Assignments of the 1H- and 13C-n.m.r. spectra of tobramycin at low and high pH.

The 1H-n.m.r.

Microscopic dissociation processes of some tyrosine derivatives.

The macroscopic and microscopic thermodynamic quantities relating to the dissociation of o-, m- and p-tyrosine, tyrosinol and tyramine have been determined at 25 degrees and I = 0.2 (KCl). The effects of the substituents are reflected unambiguously only in the DeltaG values and are due to changes in the solute-solvent interaction.

Analytical evaluation of the derivatives used in equilibrium calculations.

The derivatives of the total concentrations and other measured quantities with respect to the formation constants are calculated in general by a numerical method using finite increments. It is shown in this paper that these values can be calculated analytically, whereby the disadvantages of numerical differentiation may be avoided. The use of this method gives the possibility of writing faster programs for the calculation of the stability constants, based on the SCOGS and LETAGROP principle, without as large a memory requirement as in the LEAST and MINIQUAD programs.