Electrospray Mass Spectrometry of Thiophenolate-Capped Clusters of CdS, CdSe, and ZnS and of Cadmium and Zinc Thiophenolate Complexes: Observation of Fragmentation and Metal, Chalcogenide, and Ligand Exchange Processes.

Electrospray mass spectrometry provides a rapid, convenient technique for characterizing and studying the chemistry of anionic metal sulfide thiolate clusters. Negative-ion electrospray mass spectra have been recorded for the thiophenolate-capped clusters [Me(4)N](4)[E(4)Cd(10)(SPh)(16)] (E = S, Se), [Me(4)N](4)[S(4)Zn(10)(SPh)(16)], and [Me(4)N](2)[S(4)Cd(17)(SPh)(28)] and of the metal thiophenolate complexes [Me(4)N](2)[M(SPh)(4)], [Me(4)N](2)[M(4)(SPh)(10)] (M = Cd, Zn), and [Et(4)N](2)[Cd(4)X(4)(SPh)(6)] (X= Cl, Br, I). The exchanges of M, E, and X which occur in various mixtures of these clusters and complexes and the fragmentation processes have been investigated.

Indications of changed amino acid homeostasis in untreated and treated PKU.

Amino acid patterns were investigated in children with untreated and treated phenylketonuria (PKU) and compared with a hospitalized paediatric control group. Correlation ratios, i.e.

Plasma phenylalanine and tyrosine levels revisited in heterozygotes for hyperphenylalaninaemia.

We examined the value of the fasting plasma phenylalanine/tyrosine ratio obtained in an ordinary clinical setting for assessing the probability of being a heterozygote for hyperphenylalaninaemia. This biochemical test was found to be of little value in those with a high (66%) prior risk of heterozygosity, because it could not reduce the risk below 12%. However, in a population with a prior risk of only 2%, it discriminates the 3% with a 19% risk from the 97% with a risk of 1.

Study of the relationship between estimates of enzyme kinetic parameters.

Previous indications of an intrinsic relationship between estimates of Km and Vmax calculated from the Michaelis-Menten equation have been explored further. A mathematically linear relationship could be established for the estimates of the two parameters. The relationship--the trend line--holds whether or not the experimental error is linked to the rate of reaction, the substrate concentration or both, provided that the distribution of errors is symmetrical.