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.
Multichannel functional near-infrared spectroscopy (fNIRS) is a tool used to capture changes in cerebral blood flow. A consistent result for depression is a decrease in blood flow in the frontal cortex leading to hypofrontality, which indicates multidomain functional impairment. Repetitive transcranial magnetic stimulation (rTMS) and elective convulsive therapy (ECT) are alternatives to antidepressant drugs for the treatment of depression but the underlying mechanism is yet to be elucidated. The aim of the current study was to evaluate cerebral blood flow using fNIRS following rTMS treatment in patients with depression. The cerebral blood flow of 15 patients with moderate depression after rTMS treatment was measured using fNIRS. While there was clear hypofrontality during pre-treatment (5 ± 2.5), a notable increase in oxygenated hemoglobin was observed after 30 sessions with rTMS (50 ± 15). This increased blood flow was observed in a wide range of channels in the frontal cortex; however, the centroid values were similar between the treatments. Increased blood flow leads to the activation of neuronal synapses, as noted with other neuromodulation treatments such as electroconvulsive therapy. This study describes the rTMS-induced modulation of blood oxygenation response over the prefrontal cortex in patients with depression, as captured by fNIRS. Future longitudinal studies are needed to assess cerebral blood flow dynamics during rTMS treatment for depression.
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