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H C Box

Publications and source records attributed to H C Box.

At least 55 records · Page 3Linked to original sources
PubMed1987

Radiation chemistry of 2'-deoxycytidylyl-(3'-5')-2'-deoxyguanosine and its sequence isomer in N2O- and O2-saturated solutions.

The radiation chemistry of the dinucleoside monophosphate d(CpG) and its sequence isomer, d(GpC), has been examined in aqueous solutions saturated with either N2O or O2. The products were isolated using HPLC, and the major products were identified using proton NMR spectroscopy and mass spectrometry. The major products include 5,6-dihydroxy-5,6-dihydrouracil (glycol) derivatives, 5- and 6-hydroxycytosine substitution products, 1-carbamoyl-2-oxo-4,5-dihydroxyimidazolidine products, and the 8-hydroxyguanine substitution product. Both trans stereoisomers of the imidazolidine derivatives are obtained from d(CpG) as well as from its sequence isomer. These are prominent products when the irradiation is carried out in the presence of oxygen, but they are not observed in the absence of oxygen.

Deoxycytidine↗
PubMed1986

Radiation chemistry of a dinucleoside monophosphate and its sequence isomer.

A combination of high-performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy was used to analyze the products of X-irradiated aqueous solutions of the dinucleoside monophosphate thymidylyl(3'-5')-2'-deoxyadenosine, d(TpA), and its sequence isomer 2'-deoxyadenylyl(3'-5')thymidine, d(ApT). The products of d(TpA) include both bases and nucleotides and a variety of thymine modifications of d(TpA) including the two cis and two trans glycol stereoisomers, two cis monohydroxy derivatives, an N-formamide derivative, and the hydroxymethyl derivative. Attention is focused on using NMR spectral features to distinguish among the various stereoisomers. The radiation chemistry of d(ApT) is also explored and differences in product formation compared with d(TpA) are described, particularly the formation of two products involving modification of adenine base. The potential of the HPLC-NMR approach to the study of radiation chemistry in DNA model compounds is discussed.

Chemical Phenomena↗
PubMed1985

Synthesis, modification with N-acetoxy-2-acetylaminofluorene and physicochemical studies of DNA model compound d(TACGTA).

The deoxyhexanucleotide d(TACGTA) was synthesized by a modified phosphotriester method. The modified procedure made rapid synthesis of deoxyoligonucleotide possible in gram quantity. N-Acetoxy-2-acetylaminofluorene (AAAF) modified d(TACGTA). Thin layer chromatography and UV analysis of the acid treated AAF modified hexanucleotide showed that the covalent modification with AAF took place exclusively at C(8) of guanine in d(TACGTA). d(TACGTA) and AAF modified d(TACGTA) were purified by preparative high performance liquid chromatography (HPLC). The pure products were characterized by 1H and 31P-NMR. The circular dichroism (CD) spectrum of d(TACGTA) was consistent with DNA in the B form even in the presence of 4 M NaCl whereas the modified hexamer had nearly inverted spectrum in the absence of any added salt. Both NMR and CD analyses indicated profound alteration of conformation of d(TACGTA) upon covalent modification with AAF. The stabilization of the Z-like conformation in the modified hexamer under physiological conditions of salt and temperature suggests biological relevance.

2-Acetylaminofluorene↗
PubMed1984

13C-NMR studies of the effects of the carcinogen acetylaminofluorene on the conformation of dinucleoside monophosphate.

13C-NMR spectra are obtained in aqueous solution of dinucleoside monophosphates (ApG and GpA) and of their adducts formed by the addition of the carcinogen acetylaminofluorene (AAF) to the C8 position of the guanine. The base and sugar carbons of all dimers and adducts are assigned. The task of assigning base and carbohydrate resonances was accomplished using a series of reference compounds. Significant changes in many of the carbon resonances of the adducts are observed suggesting three general conformational changes, namely: (1) chemical shift changes are noted in base carbon atom resonances as a function of temperature and adduct formation which are indicative of stacking effects; (2) large upfield shifts of the furanose C2' resonance of the guanosine-adduct indicate a shift to higher populations of the syn conformation. Other shifts of carbohydrate resonances are indicative of a change in conformation of the carbohydrate itself. (3) Large temperature effects on linewidth of several fluorine and furanose resonances indicate interconversion of various conformers in the dimer adduct.

2-Acetylaminofluorene↗
PubMed1984

13C- and 31P-NMR studies of the conformation of carcinogen-modified nucleic acid dimers.

The effect of the carcinogen acetylaminofluorene (AAF) on nucleic acid structure was examined using 13C- and 31P-NMR spectroscopies. Conformational effects were compared in two AAF-modified dinucleoside monophosphates (ApG and GpA) and two AAF-modified deoxydinucleotides (dpApG and dpGpA). Changes in adenine 13C chemical shifts on formation of the AAF-adduct and as a function of temperature provided evidence of base stacking. Differences in fluorene 13C chemical shifts between the AAF-modified dimer and AAF-modified monomer provided evidence of fluorene stacking. The effect of forming the adduct on the phosphate backbone was examined using 31P-NMR. A correlation was demonstrated between the degree of adenine-fluorene stacking on one hand and the change in conformation of the backbone conformation on the other.

2-Acetylaminofluorene↗