The 77Se chemical shifts of nine selenium compounds, SeRR′ (R, R′ = H, Me, Et, Ph, SiH3, GeH3), are theoretically investigated by ab initio Hartree–Fock/finite perturbation method. The calculated values agree well with the experimental values. The Se chemical shift is dominated by the Se valence 4p AO contribution to the paramagnetic term, and shows a parallelism with the 4p-hole population and the net charge of the central Se atom. The Se chemical shift moves downfield as an increase of the hole in the 4p orbitals, and therefore, as an increase in the electron-withdrawing ability of the ligands attached to the selenium atom.
of these products is clearly demonstrated by their circular dichroism (CD) spectra, which show completely symmetric Cotton effects in the region of the Soret bands. The analogous reaction with 4-nitroisophthaloyl chloride gave, following chromatographic separation, meso-2 and 2/ent-2; the enantiomers could be separated again by HPLC.14] All compounds were characterized by 'H NMR spectroscopy and fast atom bombardment mass spectrometry (FAB-MS).In spite of the slight difference between the bridging positions of 1 (para) and 2 (mefa), the topological structures of these porphyrins were expected to be quite different; the angles between planes of the porphyrin and the bridging benzene units in 1 and 2 are predicted by calculations to be approximately 0" and 70-80", respectively (see Fig. 2
).I5ISynthetic chiral porphyrins have attracted much interest as model compounds for the chiral environments of heme proteins."' We report herein a new synthetic route to chiral porphyrins and their chiral recognition behavior. Since the required synthetic building blocks are achiral atropisomeric tetraarylporphyrins with ortho-substituted phenyl groups and simple bridging reagents, the route is suitable for the preparation of a series of chiral porphyrins for the systematic investigation of molecular recognition properties. Our synthetic scheme is based on the following strategy (Fig. 1). X = NH2 meso-1 l/ent-1 NO. 2 = CONH C I 0 0 Fig. 1. Schematic representation of the synthesis of chiral porphyrins When the a,a,P$ atropisomers of tetraarylporphyrins are doubly bridged with an unsymmetric, difunctionalized reagent, a mixture of a meso porphyrin and a pair of enantiomeric porphyrins with a C, symmetry axis parallel to the porphyrin plane may result,['] which may be separated by chromatography. For example, the reaction of a,a,P$tetrakis(orfho-aminophenyl) porphyrin with nitroterephthaloloyl chloride in T H F gave two doubly bridged porphyrins, meso-1 and llent-1, which could be purified by silica gel c h r~m a t o g r a p h y .~~~ The product with the larger R, value on a silica gel TLC plate was further resolved into the enantiomers 1 and ent-1 on a chiral HPLC column. The chirality Telefdx: Int. code +(75)753-4979 e c Fig. 2. Ball-and-stick molecular models of one each of the sets of enantiomers lien!-1 (left) and 2/ent-2 (right) (see ref. [5]).We attempted to evaluate the chiral recognition abilities of 1 and 2 by determining the association constants of the adducts formed by their Zn complexes and amino acid methyl esters.[61 Titration experiments indicate that various types of amino acid methyl esters form 1 : 1 complexes with 1-Zn and 2-Zn (Table 1). The following interesting aspects of the molecular recognition are clear: a) coordination of the amino acid to meso-1-Zn is hindered significantly compared with that to TPP-Zn, by the benzene bridge; b) in contrast, meso-2-Zn shows a high affinity for amino acids, while the affinity for corresponding simple amines is low; c) the chiral porphyrins 2 and ent-2 show significant c...
The X-ray photoelectron spectra of polyvinyl alcohol (PVA) were analyzed by an ab initio MO method using the 1,3,5-hexanetriol (HTO) molecule. The theoretical spectral patterns derived from the Gelius–Siegbahn model showed good agreement with the spectra observed between 0—30 eV. The present results suggest several new assignments for the XPS spectra. The core-level C1s peaks at 285.0 and 286.5 eV correspond to the C1s electron levels arising from the CH2 and CH(OH) groups, respectively.
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