Conformational characteristics of poly(ethylene imine) (PEI) have been investigated by a
rotational isomeric state (RIS) analysis of ab initio molecular orbital (MO) calculations and 1H and 13C
NMR experiments for a monomeric model compound, N,N
‘-dimethylethylenediamine (di-MEDA). From
the MO and NMR data, it was shown that the C−C and C−N bonds of di-MEDA have high gauche (71−93%) and trans (64−86%) preferences, respectively. Conformational energies of PEI were determined
from the MO calculations for di-MEDA at the MP2/6-311++G(3df, 3pd)//HF/6-31G(d) level. The high
gauche stability in the C−C bond was indicated to stem from a moderate and a weak intramolecular
N−H···N hydrogen bonds; the interaction energies were evaluated as −1.54 and −0.58 kcal mol-1,
respectively. The RIS scheme including rotational and inversional isomerizations was developed and
applied to PEI to evaluate the chain dimension and diad probabilities. With the conformational energies
determined as above, the characteristic ratio and meso-diad probability of PEI at 25 °C were calculated
to be 2.9 and 0.63, respectively. In polar and protic solvents, the intramolecular hydrogen bonds are
weakened, and consequently the PEI chain extends. Branching effects on the conformation were
investigated from MO and NMR analysis for monomeric model compounds of branched PEI, N,
N,N
‘-trimethylethylenediamine and N,
N,N
‘
,N
‘-tetramethylethylenediamine; the gauche preference in the C−C
bonds, due to the hydrogen bonds, is reduced with increasing number of methyl groups. Ab initio MO
calculations were carried out for the double-stranded helix found in anhydrous PEI crystal. The PEI
chain was indicated to adopt the isotactic form exclusively. The natural bond orbital analysis showed
that intermolecular N−H···N hydrogen bonds are formed between paired chains of the double helix. The
enthalpy of association per repeating unit was estimated to be −3.6 kcal mol-1 at the MP2/6-311+G(2d,p)//HF/6-31G(d) level.
were studied by the total electron yield method. Peaks were observed at 59.9, 60.3 and 61.4 eV in the XANES spectra of Li 3 PO 4 , Li 2 SO 4 ·H 2 O and LiNO 3 , respectively. The peak of the each sample was assigned as the core exciton. In the XANES spectra of Li 2 O, Li 2 S, Li metal, LiOH·H 2 O and Li 2 CO 3 , there were shoulder structures at the same energy. To clarify the origin of each peak, the XANES spectra were examined with the discrete variational (DV)-Xa molecular orbital method. Comparing the measured spectra with the calculated wavefunction, the shoulder structures at 61.8 eV (Li 2 O) and 60.4 eV (Li 2 S) in the XANES spectra were assigned as the core excitons, which appeared as remarkable exciton peaks in the lithium halide spectra. The spectrum of each lithium compound could be classified according to the shape of the core exciton peak, namely either a sharp or a shoulder structure. The strength of the ionic bond determined which of these shapes a core exciton peak assumed.
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