The paper presents results of a comprehensive investigation on the pairing properties of homo-DNA oligonucleotides, the preparation of which has been described in Part IIof this series [2]. The investigation was carried out by using established methods described in the literature for the characterization of oligonucleotides in the natural series, such as determination of melting temperatures of oligonucleotide duplexes by temperature-dependent UV spectrosocpy, determination of thermodynamic data of duplex formation from the concentration dependence of melting temperatures, determination of pairing stoichiometry by ratio-dependent UV spectroscopy of binary mixtures of pairing partners, temperature-dependent CD spectroscopy, gel electrophoresis under non-denaturing conditions, and -in selected cases -'H-and "P-NMR spectroscopy.The systematic comparison of the paring properties of homo-DNA oligonucleotides with corresponding DNA nucleotides (up to dodecamers) indicates that homo-DNA is a highly efficient, autonomous, artificial pairing system with a pairing behavior that is in part similar to, but also, in part, strikingly different from, the pairing behavior of DNA. The pairing properties established so far are listed below in a manner that reflects the sequence of subtitles in Chapt.2 of the text; they were determined under the conditions: H20, 0 . 1 5~ NaCI, 0 . 0 1~ Tris-HC1 buffer, pH 7, oligonucleotide concentrations in the ~L M range, 1 : 1 ratio of single strands in the case of non-selfcomplementary sequences.

This paper describes the preparation of the 2',3'-dideoxy-P-~-glucopyranosyl-( = 2',3'-dideoxy-P-~-eryythro-hexopyranosy1)-derived nucleosides of the five bases adenine, cytosine, guanine, thymine, and uracil ( = 'homo-deoxyribonucleosides') as well as the synthesis of oligonucleotides derived from them. The methods used for both nucleoside and oligonucleotide synthesis closely follow the known methods of synthesis in the corresponding series of natural 2'-deoxyribonucleosides and oligonucleotides. The efficient methods of automated DNA synthesis proved to be fully applicable to the synthesis of homo-DNA oligonucleotides, the only change necessary for achieving satisfactory coupling yields being a slight lengthening of the coupling time. Homo-DNA oligonucleotides with chain lengths of up to twelve nucleoside units were assembled on solid support either manually or on a commercial DNA synthesizer in scales of 0.4 pmol to as much as 200 pmol and were purified by either reversedphase or ion-exchange HPLC to single-peak purity according to both chromatographic systems (estimated purity > 95 %). The choice of the specific base sequences to be synthesized was determined primarily by the constitutional problems of base pairing that emerged from experimental observations made in the course of systematic studies of the pairing properties of homo-DNA oligonucleotides. About 100 homo-DNA sequences were prepared for this purpose. Their pairing properties will he described in Part I11 of this series: the present paper is restricted to the characterization of the purity and constitutional integrity of a few selected (single-stranded) oligonucleotides by 'H-, "P-, and I3C-NMR spectroscopy as well as by FAB and time-of-flight mass spectroscopy.The English Footnotes to Schemes 1-9, Fig.

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