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Biomedical subjects

J F de Rooij

Publications and source records attributed to J F de Rooij.

10 recordsLinked to original sources
PubMed1984

The formation and remineralization of artificial white spot lesions: a constant composition approach.

Artificial white spot lesions have been prepared on bovine enamel surfaces by the controlled addition of lactate buffer containing methylhydroxydiphosphonate ions. The rates of remineralization have been measured using a constant composition method in solutions of calcium phosphate of low supersaturation. Deposition of new hydroxyapatite solid phase takes place exclusively within the white spot lesion at a rate appreciably slower than that of an acid-etched enamel surface, probably due to the presence of methylhydroxydiphosphonate located within the intact surface region of the lesion.

Animals↗
PubMed1980

Loopstructures in synthetic oligodeoxynucleotides.

A comparative nuclear magnetic resonance study of the hydrogen-bonded imino protons in a series of synthetic DNA fragments is presented. The fragments ATCCTA(Tn)TAGGAT are in principle capable of forming either a self-complementary hairpin loop structure (monomer form) or an interior loop structure (dimeric form). It has been shown, that for n = 1 only the dimer structure is present in aqueous solution, whereas the exclusive existence of the hairpin loop structure is indicated for n = 3, 4 & 5. Surprisingly, for n = 2 two different structures appear to be present in solution. Concentration studies show that both monomers and dimers exist side by side in this case. Hairpins as well as interior loops form extra "melting sites" in addition to the wellknown fraying phenomenon at the terminus of the double helix.

Base Composition↗
PubMed1979

Preparation of polydeoxynucleotides linked to a solid support by coupling CNBr-activated cellulose with 5'-NH2-terminated oligo and poly(pdT)'s.

Synthetically-prepared 5'-NH2-dT(pdT)n oligomers (66,n=4 or 7) were immobilized on cyanogen bromide activated cellulose. The influence of temperature, pH, and ionic strength on the rate of the coupling process was studied. The oligomer 5'-NH2-DT(pdT)8 could be elongated enzymatically to the polymers 5'-NH2-dT(pdT)n (n=20, 51 and 84), which could be immobilized on cellulose. The cellulose-NH-dT(pdT)84 polymer thus obtained could be assembled to a new solid-state polymer e.g. poly(dA)290 . poly(/3H/dT)200, poly(dT)85-cellulose which, in turn, was a very convenient substrate for assaying DNA-ligase.

Cellulose↗
PubMed1979

Neighbouring group participation in the unblocking of phosphotriesters of nucleic acids.

Two examples of neighbouring group participation during the removal of protecting groups from phosphotriesters of partially or fully protected intermediates of nucleic acids are presented. The first example shows that ammonolysis of aryl groups from phosphotriesters of partially protected - 5'- hydroxy free - nucleic acids (e.g., 4b approximately to; Ar=2C1C 6H4) gives rise to the formation of unnatural nucleic acids (e.g., 7 approximately to and 8 approximately to). The second one illustrates that fluoride ion promoted hydrolysis of 2,2,2-trichloroethyl groups from phosphotriesters of fully protected nucleic acids (e.g., 18a approximately to), having t-butyldimethylsilyl groups at the 2'-positions, leads to the formation of a considerable amount of side-products (e.g., 20 approximately to and 21 approximately to).

Alkylation↗