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Anthracycline antibiotics daunomycin and adriamycin are among the most widely used in cancer chemotherapy and DNA is believed to be the primary target of their biological action. The crystal structure of a morpholino derivative of adriamycin bound to the DNA hexamer d(CGTACG) has been determined at 1.5 A resolution. The complex crystallizes in space group P1 with unit cell dimensions a = 18.01 A, b = 18.83 A, c = 27.65 A, alpha = 92.6 degrees, beta = 100.5 degrees, gamma = 94.9 degrees and there are two drug molecules bound per duplex. Morpholino derivatives differ greatly from their parent compounds in their biological and pharmacological properties. Structural comparison of this complex with the series of previously reported anthracycline-DNA complexes offers an opportunity for studying relationships between structure and function. The anthracycline chromophore intercalates at the CpG step and DNA distortions from a B-type conformation are similar to those observed in the other DNA-anthracycline complexes. Interactions between drug and DNA show no differences at the intercalation site, while in the minor groove they are significantly affected by the presence of the bulky morpholinyl moiety on the anthracycline amino sugar. The binding site involves four base-pairs and the absence of a positive charge on the amino sugar appears to influence the hydration pattern on both grooves. The two halves of the duplex are symmetrically related by a non-crystallographic 2-fold axis but they are not equivalent. In one half, one magnesium cluster bridges both drug and DNA, further stabilizing the complex.

The hydroxybenzotriazole phosphotriester approach has been successfully applied to the PEG-supported synthesis ( HELP ) of oligodeoxynucleotides. Main advantages over the MSNT-based HELP procedure are the elimination of side-reactions at the guanosine level and the use of the 1ess expensive protected nucleosides as starting materials.

The radical adducts resulting from the reaction between group IVB organometallic radicals MR 3 (M = Si, Ge, Sn; R = alkyl or aryl) and a number of thioketones of the chromone and flavone series have been investigated by ESR spectroscopy. The spectral parameters obtained for these species have been compared with those of similar adducts of the corresponding ketones. Both classes of radicals adopt an orthogonal conformation, and the differences between the former and the latter paramagnetic species can be accounted for by the different electronegativity of oxygen and sulphur. the effects of substitution of the heterocyclic oxygen with a sulphur or selenium atom on the spin density distribution are likewise explained. INDO calculations have been carried out on the model systems CH 2 XSiH 3 (X = O, S).

The electron transmission spectra of the o,o ′-dimethyl substituted benzenes 2,6-(CH 3 ) 2 C 6 H 3 -XR (X = O,S, NR: R = H, CH 3 ) show that the substituents adopt a planar (R = H) or rotated (R = CH 3 ) conformation depending upon their size and they suggest that in the sulphur derivatives the 2 B 1 H anion states are stabilized by S3d orbital participation. MS Xα calculations performed on both the planar and orthogonal forms of the model systems p -(XH) 2 -C 6 H 4 (X = O, S) support this hypothesis and assign the extra resonance present in the ET spectra of the thio derivatives to electron capture into [ σ S-R * MOS. strongly mixed with sulphur 3d orbitals ( = 33% d character).

The shake-up satellites present in the O 1s and N 1s energy regions of the XPS spectra of the planar 4-N-piperidyl-nitrobenzene ( 1 ) and 2-N-piperidyl-5-nitrothiophen ( 3 ), and of the sterically hindered 2-N-piperidyl-nitrobenzene ( 2 ), 2-N-piperidyl-3-nitrothiophen ( 4 ) and 3-N-piperidyl-2-nitrothiophen ( 5 ) and, for comparison, of 2-bromo-3-nitrothiophen ( 6 ) have been analyzed with the help of CNDO/S CI calculations. The spectra of the planar derivatives closely resemble these of the related compounds previously analysed, the main satellites deriving from the transition between the highest occupied molecular orbital (HOMO, localized at the donor-ring moiety) towards the lowest unoccupied one (LUMO, localized at the nitro group). Calculations indicate that in the ortho derivatives new relaxation processes are allowed upon N 1s /NO 2 ionization. In 2 , where the angle of rotation θ is closer to 90° than 60°, the NR 2 lone-pair orbital relaxes through space towards the core-ionized N/NO 2 atom. In 4 and 5 , where 45° ⩽ θ ⩽ 60°, both through-ring and through-space relaxations are present. The assignment of the main N 1s /NO 2 line in 1 is discussed.

The ESR spectra of the paramagnetic species produced by photoreaction of benzo[2,1-b;3,4-b]dithiophen-4,5-dione with a number of organomercurials, RHgR, have been recorded. The spectral parameters and the temperature dependence of the 199Hg coupling constants are consistent with a structure of the adducts in which the Hg atom is bound to both carbonyl oxygens.

The photoelectron (He(I)) spectra of the tricyclic tetracarbonyl compounds pyromellitic dianhydride, dithioanhydride and diimide and of the tetracyclic hexacarbonyl compound trimellitic anhydride have been investigated. To aid the interpretation of the main features of the spectra, i.e. the ordering and splitting of the nCO ionisations and the behaviour of the ‘benzenic’ and heteroatom π ionisations, MO calculations based on a ZDO pragmatic model and semiempirical SCF-PP calculations have been carried out. The evolution of the nCO and πX ionisations upon progressive fusion of anhydride moieties with a benzene nucleus is analysed in detail. The proposed orbital sequences for the n orbitals are: ag(S+) $ b1u(AS+) $ b2u(S−) $ b3g(AS−) for the tetracarbonyls and a′1(S+) $ e′(AS+) $ a′2 (AS−) ≈ e′(S−) for the hexacarbonyl.

The photoelectron (He(I)) spectra of 1,2-indandione and heteroanalogues (coumarandione, thionaphthenequinone, and isatin), 1,3-indandione and heteroana

The photoelectron He(I) and He(II) spectra of 4H-pyran-4-one ( 1 ), 4H-thiopyran-4-one ( 2 ), 4H-pyran-4-thione ( 3 ) and 4H-thiopyran-4-thione ( 4 ) are reported. The assignments are based on experimental evidence, taking into account the results of theoretical calculations. The outermost orbital sequences proposed (X = O, S) are n X (σ), 3 b 1 (π), 1 a 2 (π) for 1 , 2 and 4 ; and 3 b 1 (π), n X (σ) and 1 a 2 (π) for 3 . The shifts of the core-ionization energy values for 1–4 are ascribed to a drift of π-charge from the intracyclic heteroatom towards the carbonyl or thiocarbonyl group. Low-energy shake-up satellites (up to 25% with respect to the main line) are observed in the various energy regions of the XPS spectra. They are qualitatively reproduced by CNDO/2 calculations. The most important satellites derive from the transition in the ion corresponding to the 3 b 1 (π) → 4 b 1 (π*) transition in the UV-visible spectra of the neutral molecules. Charge rearrangements accompanying this transition lead to charge depletion of the core-ionized atom.

The photoelectron (HeI) spectra of 1,3-thiazole and its 2F, 2Cl, 2Br, 4Br and 5Br-derivatives are reported. The assignment of the first few bands of the various spectra to the corresponding molecular orbital is based, for thiazole, on the results of an ab initio SCF—MO calculation, while for the various halogen derivatives, on reasonings based on perturbation theory. In particular, the first five outermost molecular orbitals of thiazole probably correspond to π3 (9.50 eV), π2 (10.24), σN (10.48; orbital mainly localized on the nitrogen atom), σS (12.78; orbital mainly localized on the sulphur atom) and π1 (13.5).

The intensity of the shake-up satellites present in the solid-phase XPS spectra of paranitroaniline ( 1 ), 2-amino-5-nitropyridine ( 2 ) and 2-amino-5-nitropyrimidine ( 3 ) decreases from ( 1 ) to ( 3 ) in agreement with CNDO/S CI calculations. The HOMO—LUMO energy gap appears to be responsible for the observed trend.

The ET spectra of monosubstituted benzenes containing the −OH, −OCH 3 , −OC(CH 3 ) 3 , −SH, −SCH 3 , −SC(CH 3 ) 3 and −NHCH 3 groups show that in the non-hindered nitrogen and oxygen derivatives the lone pair/π* interaction produces a significant destabilization of the ring 4b 1 π* MO, while the electron affinity (EA) of the LUMO π* 2a 2 is close to that of benzene. The stabilization of the empty π* MOs produced by the sulphur-containing substituents demonstrates the presence of interacting empty orbitals localized at the substituent. The stabilizing effect of these orbitals does not change significantly with the σ framework of the substituent nor with its torsional angle around the S-ring bond. This is consistent with the S 3d character of the stabilizing orbitals. The EA increase of the LUMO in the rotated −SC(CH 3 ) 3 derivative is mainly ascribed to the reduced interaction between the S lone-pair orbital and the 4b 1 π* MO, and, in part, to σ*/π* interaction.

The photoelectron (He(I)) spectra of 1,4-dithiin (1), 1,4-thiaselenin (2), 1,4-thiatellurin (3) and 4H-thiopyran (4) were assigned by comparison with published spectra of similar compounds and with the help of ab initio and semi-empirical calculations. The proposed orbital sequences for the outermost orbitals are π4, π3, π2, σ for 1, 2 and 3, and π4, π2, σ, π3 for 4. π4 and π3 correspond to the symmetric and antisymmetric combinations, respectively, of the heteroatom lone pairs, while π2 is the antisymmetric combination of the πeth orbitals.

The photoelectron spectra of the S[X(CH3)3]2 and CH3SX(CH3)3 series (X = C, Si, Ge, Sn and Pb) are reported, and assigned on the basis of the semilocalized orbitals approximation and a consideration of symmetry and substituent effects. The electronic interactions between the X(CH3)3 substituents and the sulfur nπ orbital are discussed in terms of the relative importance of hyperconjugation (nσ mixing), (pd)π bonding and electrostatic interactions.

The analysis of dipole moment data obtained for dibenzo-p-dioxin, phenoxathiin, phenoxaselenin and phenoxatellurin in benzene at 25°C in conjunction with EHT calculations of the ocnformational energies show that these molecules adopt a non-planar conformation in solution. Each of the phenoxachalcogenins is folded along the axis connecting the two heteroatoms. A butterfly flapping motion about the planar conformation canot be excluded. The uv and photoelectron spectroscopic data support the conclusions drawn from the dipole moment studies. The spectroscopic data were interpreted with the help of SCF-PPP-CI calculations.

A rapid equilibrium is present in enaminic systems derived from 3-substituted cyclohexanones. Their reactions with β-nitrostyrene have been studied and the stereochemical implications discussed.

Morpholine, piperidine and pyrrolidine enamines of 2-methylcyclohexanone react with ethyl azodicarboxylate to give, after hydrolysis, 2-methyl-6-(N,N′-dicarbethoxy)hydrazinocyclohexanone in 49%, 47% and 84%, yield, respectively. The same enamines by reaction with phenyl isocyanate and subsequent hydrolysis furnish 2-methyl-6-phenylcarbamylcyclohexanone in 51%, 42% and 88% yield, respectively. These results reflect the percentages of the less substituted isomeric enamines and are in good agreement with those determined by NMR spectroscopy, 1-N-Morpholino-, 1-N-piperidino- and 1-N-pyrrolidino-2-(N,N′-dicarbethoxy)hydrazinocyclohex-1-en by kinetically controlled acidic hydrolysis, lead to the 2,6-disubstituted cyclohexanone having trans configuration, as results from NMR analysis and equilibration into the more stable cis isomer. The stereochemistry of such a reaction is reported and discussed.

The spin adducts of triphenylsilyl, triphenylgermyl and triphenylstannyl radicals with γ-pyrone, γ-thiopyrone, thia-γ-pyrone and thia-γ-thiopyrone have been studied by ESR spectroscopy. The spectral parameters indicate that these radicals adopt the conformation where the O-M or S-M bonds are eclipsed with the 2 p z orbital of the γ-carbon, despite the absence of hindering substituent groups in proximity of the radical centre. The electronic effects of sulphur and oxygen on the spin density distribution are also discussed.

The UV photoelectron spectrum of [2,2] metacyclo-2,6-pyridinophane has been analyzed on the basis of a perturbational molecular orbital analysis and CNDO/2 calculations. Through space and through bond interactions are shown to be present between the two pyridine rings. In particular a strong interaction has been found between the nitrogen lone pairs and the π systems of the rings.

The analysis of the photoelectron HeI spectra of the compounds Hg(SR) 2 (R = Me, Et, Pr n , Pr i , Bu n , Bu i and Bu t ) and of the results of iterative extended Huckel calculations on selected members of the series suggests that in these compounds the HgS bonds have a partial double-bond character due to a weak π-interaction between the filled 3 p sulphur orbitals and the emply 6 p orbitals of mercury.

The electron transmission spectra of 4H-thiopyran-4-one. 4H-pyran-4-thione and 4H-thiopyran-4-thione have been recorded in the 0–6 eV energy range and the observed resonances assigned to the corresponding anion states. Unlike γ-pyrone, its sulphur derivatives possess low-energy Σ anion states.