The effect of changing crosshead speed on the shear bond strength of orthodontic bonding adhesive.

Objective: To examine the influence of different crosshead speeds on the in vitro shear bond strength and adhesive remnant index scores for the same orthodontic adhesive.

Materials And Methods: One hundred human molars were randomly allocated to four groups. Brackets (.

The alkaline hydrolysis of phosphotriesters in alkylated mammalian DNA.

Isolated DNA was alkylated with N-[14C]methyl-N-nitrosourea or N-[14C]ethyl-N-nitrosourea. Sedimentation analysis of the alkylated DNA before and after alkaline hydrolysis was used to determine the number of single-strand breaks introduced by hydrolysis of the triesters. Vacuum distillation from alkylated DNA solutions before and after alkaline hydrolysis was used to determine the numbers of triesters hydrolysing to the alcohol.

Does high-mobility-group non-histone protein HMG 1 interact specifically with histone H1 subfractions?

The interaction of the non-histone chromosomal protein HMG (high-mobility group) 1 with histone H1 subfractions was investigated by equilibrium sedimentation and n.m.r.

The stability of methylated purines and of methylphosphotriesters in the DNA of V79 cells after treatment with N-methyl-N-nitrosourea.

V79-379A cells growing in suspension culture were treated with N-methyl-N-nitrosourea at concentrations of 0.6 and 1.2 mM.

The rate of hydrolysis of methyl phosphotriesters in DNA under conditions used in alkaline sucrose gradients.

Methyl phosphotriesters have been introduced into DNA, in vitro, by reaction with N-methyl-N-nitrosourea and the rate of degradation in alkali has been followed by measurements of the mean sedimentation coefficient using an analytical ultracentrifuge. In 0.3 M NaOH/0.

The formation and stability of methyl phosphotriesters in the DNA of rat tissues after treatment with the carcinogen N,N-dimethylnitrosamine.

Following the injection i.p. of N,N-dimethylnitrosamine (DMN) into Chester Beatty (CB) hooded, female rats (2 mg/kg) measurable concentrations of methyl phosphotriesters were found in the DNA of liver, lung and kidney but not in spleen, thymus or brain.

The stability of methyl and ethyl phosphotriesters in DNA in vivo.

C57BL male mice were injected with N-methyl-N-nitrosourea (MNUA) or N-ethyl-N-nitrosourea (ENUA) and the concentration of alkyl phosphotriesters in the DNA of lung, liver, brain, kidney, spleen and thymus determined from the extent of degradation induced in isolated DNA by alkali. The same total dose of reagent was given either as a single injection (i.p.

The interaction of acetoxy-dimethylnitrosamine, a proximate metabolite of the carcinogenic amine, and bacteriophages R17 and T7.

The biological and physicochemical effects of reacting bacteriophages R17 and T7 with acetoxy-dimethylnitrosamine (ADMN) have been studied. The rate-determining step in the reactions appeared to be the loss of the acetoxy group by hydrolysis, the hydroxymethyl-methylnitrosamine generated decomposing rapidly to give a methyldiazonium ion and formaldehyde. In experiments with bacteriophage suspended in phosphate buffer the biological inactivation observed was the sum of the effects of the formaldehyde and of alkylation by the methylcarbonium ion produced from the diazonium ion.

An assay for phosphotriester formation in the reaction of alkylating agents with deoxyribosenucleic acid in vitro and in vivo.

Preliminary studies in vitro using bacteriophage T7-DNA have shown that breaks formed in the DNA on the alkaline hydrolysis of apurinic sites and phosphotriesters can be distinguished from each other by measuring the extent of degradation of the DNA immediately after adding NaOH to 0.1 M and after incubating for 1 h in 0.5 M NaOH.

The kinetics of the alkaline hydrolysis of phosphotriesters in DNA.

The degradation in alkali of normal DNA and DNA alkylated with dimethyl sulphate (DMS), N-methyl-N-nitrosourea (MNUA) and N-ethyl-N-nitrosourea (ENUA) has been investigated using analytical ultracentrifugation techniques. For control T7-DNA (w.st.

Assays for phosphotriester formation in the reaction of bacteriophage R17 with a group of alkylating agents.

The interaction of bacteriophage R17 with 8 compounds has been studied, comparing the contribution of degradation of ribonucleic acid to the total toxicity. Breaks in the RNA chain result from the hydrolysis of phosphotriesters and thus are a measure of the extent of O-alkylation and of the SN1-type mechanism of the reaction. With many alkylating agents mutagenicity and carcinogenicity increase with increasing SN1 character of the reaction.

The inactivation of bacteriophage R17 by ethylating agents: the lethal lesions.

The biological inactivation of bacteriophage R17 by ethyl methanesulphonate (EMS) and N-ethyl-N-nitrosourea (ENUA) has been studied. At the mean lethal dose for the first compound 8 moles ethyl are bound/mole RNA and with the nitroso compound 3.5 moles ethyl are bound.

Interaction of a non-histone chromatin protein (high-mobility group protein 2) with DNA.

1. The interaction with DNA of the calf thymus chromatin non-histone protein termed the high-mobility group protein 2 has been studied by sedimentation analysis in the ultracentrifuge and by measuring the binding of the 125I-labelled protein to DNA. The results have been compared with those obtained previously by us [Eur.

The reaction of alkylating agents with bacteriophage R17. Biological effects of phosphotriester formation.

The extent of biological inactivation and of the degradation of the RNA after reaction of bacteriophage R17 with ethyl methanesulphonate, isopropyl methanesulphonate and N-ethyl-N-nitrosourea was studied. Formation of breaks in the RNA chain probably results from hydrolysis of phosphotriesters formed in the alkylation reactions. Near neutral pH the ethyl and isopropyl phosphotriesters are sufficiently stable for the kinetics of the hydrolysis reaction to be followed.

The molecular basis for biological inactivation of nucleic acids. The action of methylating agents on the ribonucleic acid-containing bacteriophage R17.

1. The inactivation of an RNA-containing bacteriophage after reaction with four methylating agents was studied. Measurements of the extent of methylation of the RNA and of the nature and amounts of the various reaction products were made.

The action of mono- and di-functional sulphur mustards on the ribonucleic acid-containing bacteriophage mu2.

Bacteriophage mu2 is inactivated by both mono- and di-functional sulphur mustards at relatively low extents of alkylation. No degradation of alkylated RNA was detected. Cross-linking of RNA to protein was observed with the difunctional agent, but this reaction was only a minor contribution to the inactivation.