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The effects of manganese (II), nickel (II), chromium (III), and platinum (II) (cisplatin) on the double helical structure of selected oligonucleotides and DNA as detected by vibrational circular dichroism spectroscopy (VCD) are reviewed. For (dG– dC)20, the VCD spectra displayed unambiguously the transition from the normal right-handed B-form to the left-handed Z-from at the highest concentration of Mn 2þ (8.5 [Mn]/[P]). For poly(rU)·poly(rA)·poly(rU), the double-triplesingle helix transition induced by nickel (II) was clearly observable at increasing temperatures. For calf thymus DNA, chromium (III) at 0.6 [Cr]/[P] produced a 4-fold increase of the main VCD couplets, which are characterized as c-type spectra. These unusual features are due to condensed particles with dimensions comparable to the wavelength of the probing light and with regular arrangements of DNA double-helices inside the aggregates. c-Type spectra were also observed for DNA with manganese (II) between 55 and 60 8C at 2.4 [Mn]/[P]. Between 2.4 and 10 [Mn]/[P], intense and indistinct VCD features appeared above the DNA melting point indicating aggregation induced by Mn 2þ ions at elevated temperature in a relatively wide range of experimental conditions, whereas DNA condensation with Mn 2þ ions occurs only in a very narrow range of concentration and temperature. The complexes formed by coordination of cisplatin with d(CCTGGTCC)·d(GGACCAGG) and d(CCTCTGGTCTCC)·d(GGAGACCAGAGG) yielded very detailed VCD spectra, which distinctly confirmed the G p 4pG p 5 and G p 6pG p 7 lesion sites, respectively. The octamer slowly isomerized to form other adducts, which was not the case

The VCD spectra in the region of 1750 to 850 cm −1 of six octadeoxynucleotides consisting of systematically varying sequences of d(CGNNNNGC) 2 , where N = A, T, C, G, are reported and tentatively interpreted based on previously reported VCD spectra of related natural and synthetic polymers and oligomers. The CO and skeletal stretching vibrations of the bases exhibit features that are characteristic for base sequences and reveal details that are not apparent in the absorption spectra. Other features, notably an unassigned band near 1500 cm −1 and the PO 2 − and furanose modes near 1080 cm −1 are independent of base sequences.

The vapour-phase infrared spectra in the range 50–500 cm −1 are reported for 2- and 3-methyl oxetan (2- and 3-MO), 2-methyl thietan (2-MT), 2,2-dimethyl oxetan (2,2-DMO) and 3,3-dimethyl thietan (3,3-DMT). The absorptions are interpreted as methyl deformation fundamentals and transitions within the ring-puckering manifold. Particular emphasis is placed on the latter, for which band sequences are analyzed with a general puckering potential function, V ( q ) = V ′ 2 q 2 + V ′ 3 q 3 + V ′ 4 q 4 , q being the dimensionless puckering normal coordinate. For the gem -dimethyl compounds for which V ′ 3 = 0, the barrier to ring inversion increases upon methyl substitution to 51.1 cm −1 for 2,2-DMO and 300.0 cm −1 for 3,3-DMT as compared to the parent molecules. The monomethyl compounds exist as stable equatorial and axial conformers at room temperature, the energy differences being 38.1, 43.8 and 117.6 cm −1 , and the inversion barriers 107.5, 98.7 and 341.1 cm −1 , respectively, for 2-MO, 3-MO and 2-MT. The trends in the potential function constants are discussed.

The infrared spectra in the region 50–600 cm −1 are reported for bicyclo[2.2.1]hept-2-ene (norbornene) and 7-oxabicyclo[2.2.1]heptane (7-oxanorbornane) in the vapour phase. All absorptions in this region show evidence of at least one low-energy anharmonic vibration. One sequence of Q branches in each of the two compounds is assigned to the first overtone transitions of skeletal deformations resembling a twisting of the six-membered rings. The transitions can be reproduced successfully by a one-dimensional Hamiltonian with positive quadratic and quartic terms. These observationsagrees with the structure derived from the microwave spectra and from electron diffraction for both compounds.

Doublet v(OH) bands in simple aliphatic alcohols due to rotational isomerism about the C-O bond are related to the number of α-CH bonds trans to an oxygen, lone pair orbital. v(OH) increases and v(α-OH) decreases when this condition is met. These frequency shifts can be rationalized by the participation of the oxygen lone pair in a σ* C-H orbital on the adjacent carbon, an interaction which appears to confer some stability on that conformer. This may be a significant factor governing rotational isomer populations in alcohols (and thiols). Specific studies of CH3CD2OH, (CH3)2CDOH and (CH3)2CDSH are reported. In aliphatic thiols the partial lone pair delocalization is found to be less significant, the overall order being N > O > S.