Terpenoids—XXV Structure of saussurea lactone

Saussurea lactone is identical with the product of pyrolysis of dihydrocostunolide. On cyclisation in the presence of p-nitrobenzoic acid followed by hydrogenation it gives santanolide C. Hence structure (V) is assigned to saussurea lactone.     

Microwave specific Wolff rearrangement of alpha-diazoketones and its relevance to the nonthermal and thermal effect

alpha-Diazoketones possess high electric dipole moments, as a consequence of the dipolar nature of the diazocarbonyl functional group. The vectorial analysis, theoretical calculations (PM3 and ab initio), and literature reports based on experimental and theoretical calculations reveal a higher dipole moment for the Z-configuration of the diazo functional group. Microwave irradiation of alpha-diazoketone (1a-m) (Figure 1) promotes Wolff rearrangement specifically via the Z-configuration in excellent yields. The dielectric properties of the solvent govern the course of the microwave rearrangement. 3-Diazocamphor (1m) on microwave irradiation in benzylamine exhibits nonthermal effects to furnish exclusively the Wolff rearrangement product (4m), equivalent to its photochemical behavior. In the presence of an aqueous medium, through solvent heating predominates, leading to the formation of a tricyclic ketone (5) as the principal product, arising from an intramolecular C-H insertion. This behavior is similar to its known thermal and transition metal catalyzed reactivity pattern.     

Untersuchung von Fetten, ?len und ?lhaltigen Produkten

Ohne Zusammenfassung     

Dimeric Fe (II, III) complex of quinoneoxime as functional model of PAP enzyme: Mössbauer, magneto-structural and DNA cleavage studies

Purple acid phosphatase, (PAP), is known to contain dinuclear Fe₂ ^?+?2,?+?3 site with characteristic Fe^?+?3 ← Tyr ligand to metal charge transfer in coordination. Phthiocoloxime (3-methyl-2-hydroxy-1,4-naphthoquinone-1-oxime) ligand L, mimics (His/Tyr) ligation with controlled and unique charge transfers resulting in valence tautomeric coordination with mixed valent diiron site in model compound Fe-1: [μ-OH-Fe₂ ^?+?2,?+?3 (o-NQ_CH3ox) (o-NSQ_CH3ox)₂ (CAT) H₂O]. Fe-2: [Fe^?+?3(o-NQ_CH3ox) (p-NQ_CH3ox)₂]₂ a molecularly associated dimer of phthiocoloxime synthesized for comparison of charge transfer. ⁵⁷Fe Mössbauer studies was used to quantitize unusual valences due to ligand in dimeric Fe-1 and Fe-2 complexes which are supported by EPR and SQUID studies. ⁵⁷Fe Mössbauer spectra for Fe-1 at 300 K indicates the presence of two quadrupole split asymmetric doublets due to the differences in local coordination geometries of [Fe^?+?3]_A and [Fe^?+?2]_B sites. The hyperfine interaction parameters are δ _A = 0.152, (ΔE _Q)_A = 0.598 mm/s with overlapping doublet at δ _B = 0.410 and (ΔE _Q)_B = 0.468 mm/s. Due to molecular association tendency of ligand, dimer Fe-2 possesses 100% Fe^?+?3(h.s.) hexacoordinated configuration with isomer shift δ = 0.408 mm/s. Slightly distorted octahedral symmetry created by NQ_CH3ox ligand surrounding Fe^?+?3(h.s.) state generates small field gradient indicated by quadrupole split ΔE _Q = 0.213 mm/s. Decrease of isomer shifts together with variation of quadrupole splits with temperature in Fe-1 dimer compared to Fe-2 is result of charge transfers in [Fe₂ ^?+?2,?+?3 SQ] complexes. EPR spectrum of Fe-1 shows two strong signals at g ₁ = 4.17 and g ₂ = 2.01 indicative of S = 3/2 spin state with an intermediate spin of Fe^?+?3(h.s.) configuration. SQUID data of $\chi _m^{{\rm corr}} \mbox{.T}$ were best fitted by using HDVV spin pair model S = 2, 3/2 resulting in antiferromagnetic exchange (J = ?13.5 cm^???1 with an agreement factor of R = 1.89 × 10^???5). The lower J value of antiferromagnetic exchange leads to Fe⁺³μ-(OH) Fe^?+?2 bridging in Fe-1 dimer instead of μ-oxo bridge. The intermolecular association through H-bonds may lead to weakly coupled antiferromagnetic interaction between two Fe-2 molecules having Fe^?+?3(h.s.) centers. Using S = 5/2, 5/2 spin pair model we obtained best-fitted parameters such as J = ?12.4 cm^???1, g = 2.3 with R = 3.58 × 10^???5. Synthetic strategy results in non-equivalent iron sites in Fe-1 dimer analogues to PAP enzyme hence its reconstitution results in pUC-19 DNA cleavage activity, as physiological functionality of APase. It is compared with nuclease activity of Fe-2 RAPase.     

Electronic structure,electron density,electric field gradient-, magnetic susceptability- and G-tensor of K3Fe(CN)6

Molecular orbital calculations are presented for the electronic structure of K₃Fe(CN)₆ based on clusters of formula K₈Fe(CN)⁵⁺₆, using a semi-empirical molecular orbital method including mixing of low-lying electronic configurations and spin-orbit coupling. The energy splittings obtained are in qualitative agreement with ligand field studies from several workers, excluding those of Merrithew and Modestino. While other authors interpret either Mössbauer data, or ESR results, or susceptibility values only, we obtain from the electron structure calculations charge densities at the iron nucleus, and electric field gradient, magnetic susceptibility and gyromagnetic tensors, which consistently interpret experimental Mössbauer-, EST- and magnetic anisotropy results. From the electronic structure calculations as well as from the reanalysis of experimental quadrupole line intensities (obtained by Oosterhuis and Lang) we derive that orthorhombic polytypism of K₃Fe(CN)₆ has to be considered for a consistent interpretation of the experimental data. The successful correlation between calculation and experiment in an energy range of about 300 K above the electronic groundstate is a measure for the adequacy of our electronic structure calculations in this low-energy range.