The reactions of dialkylgallium hydrides with tert-butylethynylbenzenes—a systematic investigation into the course of hydrogallation reactions

The reactions of bis- and tris(tert-butylethynyl)benzenes with dialkylgallium hydrides afforded two different types of products. 1,4-Di(tert-butylethynyl)benzene and dialkylgallium hydrides R(2)GaH bearing relatively small substituents (R = Et, nPr) gave the expected addition products with each C triple bond C triple bond inserted into a Ga-H bond. The intact GaR(2) groups are attached to those carbon atoms which are in alpha-position to the benzene rings, and intermolecular Ga-C interactions led to the formation of one-dimensional coordination polymers. In contrast secondary reactions with the release of the corresponding trialkylgallium derivatives GaR(3) (R = Et, nPr, iPr, CH(2)tBu, tBu) were observed for all hydrogallation reactions involving the trisalkyne 1,3,5-tris(tert-butylethynyl)benzene. A similar reaction was observed upon treatment of the 1,4-bisalkyne with a dialkylgallium hydride bearing a relatively bulky substituent (R = neopentyl). Cyclophane type molecules are formed in all these cases with two or three gallium atoms in the bridging positions between both benzene rings.

Crystal Structures of Recombinant Human Purple Acid Phosphatase With and Without an Inhibitory Conformation of the Repression Loop

The crystal structure of human purple acid phosphatase recombinantly expressed in Escherichia coli (rHPAP(Ec)) and Pichia pastoris (rHPAP(Pp)) has been determined in two different crystal forms, both at 2.2A resolution. In both cases, the enzyme crystallized in its oxidized (inactive) state, in which both Fe atoms in the dinuclear active site are Fe(III). The main difference between the two structures is the conformation of the enzyme "repression loop". Proteolytic cleavage of this loop in vivo or in vitro results in significant activation of the mammalian PAPs. In the crystals obtained from rHPAP(Ec), the carboxylate side-chain of Asp145 of this loop acts as a bidentate ligand that bridges the two metal atoms, in a manner analogous to a possible binding mode for a phosphate ester substrate in the enzyme-substrate complex. The carboxylate side-chain of Asp145 and the neighboring Phe146 side-chain thus block the active site, thereby inactivating the enzyme. In the crystal structure of rHPAP(Pp), the enzyme "repression loop" has an open conformation similar to that observed in other mammalian PAP structures. The present structures demonstrate that the repression loop exhibits significant conformational flexibility, and the observed alternate binding mode suggests a possible inhibitory role for this loop.

A comparison of dental caries experience in Native American and Caucasian children in Oklahoma

OBJECTIVES

In 1989 the Oklahoma Area Indian Health Service conducted an oral health survey of children attending public schools in Oklahoma to determine the extent of caries experience in the Native American population. Results were to be used to establish program priorities, gather baseline data, and compare the oral health status of Native American children with their non-Indian peers.

METHODS

A total of 934 elementary schoolchildren 5-6 years of age were examined along with 733 high school students 15-17 years of age. The study was designed so that approximately 50 percent of the students examined were Native American.

RESULTS

The mean dmfs for the 5-6-year-olds was 5.06 for the Caucasian children and 10.35 for the Native American children, a statistically significant difference (P < .001). For the 15-17-year-olds the mean DMFS for the Caucasian students (5.99) was significantly lower (P < .001) than the mean DMFS for the Native American students (10.12).

CONCLUSIONS

The prevalence and severity of caries in these Native American students appear to be substantially higher than in their non-Indian peers residing in the same communities. Further study is needed to identify factors contributing to these demonstrated differences in caries experience.