The infrared and Raman spectra of several dialkyl disulfides were measured and their conformations were discussed in relation with the characteristic S–S and C–S stretching vibrations. The infrared spectra in the solid state and the temperature dependence of Raman spectra were measured for ethyl methyl disulfide and diethyl disulfide. For ethyl methyl disulfide, the gauche-gauche isomer was more stable than the trans-gauche isomer by about 0.9 kcal/mol while for diethyl disulfide the gauche-gauche-gauche isomer was more stable than the trans-gauche-gauche isomer by about 0.6 kcal/mol in the liquid state. Only the gauche-gauche form for ethyl methyl disulfide and only the gauche-gauche-gauche form for diethyl disulfide were observed in the solid state.

The resonances of the imino protons and all of the non-exchangeable protons (except for H5'/H5'') of d(CGCAAAAAAGCG)d(CGCTTTTTTGCG) have been assigned by means of one- and two-dimensional NMR spectroscopies. Qualitative analyses showed that the overall structure is of the B-form, but local conformational deviations exist. The NOEs between the imino protons of thymines and H2 of adenines suggest that the A-T base pairs are propeller-twisted to almost the same degree as in crystals. A remarkable chemical shift of H1' was observed for the residue located just before the oligo(dA)oligo(dT) tract, suggesting the presence of conformational discontinuity at the junctions between the oligo(dA)oligo(dT) tract and the other portions. Analyses of cross peaks in NOESY spectra between H2 of adenines and H1' of the 3'-neighbouring residues on the complementary strand revealed that the minor groove of the oligo(dA)oligo(dT) tract is narrow and compressed gradually, from 5' to 3', along the tract.

The pK values of thermospermine, a novel asymmetric tetraamine (4,8-diazadodecane-l,12-diamine), have been determined for the first time by the conventional titration method with subsequent data analyses. It was found to be the most basic polyamine among naturally occurring tetraamines. The I5N N M R titration method was applied to determine its protonation site. Natural-abundance I5N magnetic resonance spectra of the polyamine have been recorded as a function of pH from its free to the protonated form. Its apparent pK values, as well as the intrinsic chemical shifts for each stage of protonation, have been calculated from the N M R titration curve by using a nonlinear least-squares method. The four protonation sites of thermospermine have been successfully determined to be Nt2, N', N-8, and N-4 in chat order from the free to the completely protonated form. In a similar manner the protonation sites of spermidine and two symmetric tetraamines, thermine and spermine, have been established. I3C N M R experiments for the four polyamines were almost consistent with those of I5N NMR. Owing to the much higher concentration of the polyamines furnished for N M R titration experiments, the pK values obtained by NMR were larger than those derived by the conventional titration methods.A considerable number of observations show a correlation of enhanced synthesis of polyamines with rapid growth or cell proliferation [1,2]. From the point of view of the physiological role of polyamines in cells, polyamines were implicated as regulators of cell proliferative activity [3-S]. Thus it is tempting to speculate that association as well as dissociation of polyamines with biological macromolecules may be controlled dynamically. In fact, it has been shown that polyamines can bind with nucleic acids [S -81 and that they exert a remarkable stabilization of a teritary structure of the nucleic acids [9 -121. This led us to determine the protonation sites in polyamines and the corresponding pK values, and to examine their effect on the interaction with biological macromolecules.The pK values of several naturally occurring and synthetic polyamines have been determined by means of potentiometric titration methods [I 3 -IS]. However, the pK values of thermospermine, i.e. 4,s-diazadodecane-l , 12-diamine have remained undetermined. This polyamine is a new asymmetric tetraamine which was found in an extremely thermophilic microorganism, Thermus tl~rrmnphilus, and its structure has been determined [16]. Thus we synthesized it and measured the p K values by potentiometric titration.Determination of the protonation sites in polyamines has been attempted by calorimetric measurements [I 7,181 and the calculation of protonation enthalpy by applying quantum chemical methods [I 91. These attempts were almost successfull, but they are indirect methods. NMR titration, on the other hand, provides pK values and information about the protonation pattern, since chemical shifts of the nuclei at the basic sites are often markedly influenced by the ionization o...

The conformations of double-stranded d(GGAAATTTCC) x 2, d(GGTTTAAACC) x 2, d(CGCAAAAAAGCG)d(CGCTTTTTTGCG) and d(GCATTTTGAAACG)d(CGTTTCAAAATGC) have been studied by NMR spectroscopy. Analyses of cross peaks in NOESY spectra between the H2 of an adenine and the H1' of a deoxyribose in the 3'-neighbouring residue on the complementary strand revealed that the minor groove of the oligo(dA) tract is compressed gradually from 5' to 3' in each duplex. In view of this gradual compression of the minor groove along the oligo(dA) tract, it can be understood clearly why d(GGAAATTTCC)n x 2 and d(GAAAATTTTC)n x 2 are bent, and d(GGTTTAAACC)n x 2 and d(GTTTTAAAAC)n x 2 are not bent. The relative extents of bending of a series of d(AjN10-j)nd(N10-jTj)n sequences can also be understood systematically. Additionally, it was found that the TA step disturbed the compression of the minor groove of the oligo(dA) tract to some extent.