A.I. Elshamy et al. / Journal of Molecular Structure 1200 (2020) 127061
5
methanolysis of 1 yielded methyl-2-hydroxyheptadecanoate (1a)
log (ε) ¼ 3.660 in methanol were observed. As shown in Table 2, in
all studied mediums, the higher basis set gave the higher wave-
length absorption and absorbance, but the lower transition energy
and oscillator strength. The studied environment greatly affected
the outcomes, the UVeVisible spectrum of 1 in gas was due to
excitation transitions H-1/ L (ca. 30%) and H-1 / Lþ1 (ca. 67%),
while excitation transition H-1 / Lþ1 (more than 97%) might be
claimed responsible for UVeVisible spectrum of 1 in either meth-
anol or water. In addition, it depended upon the influence of sol-
þ
that exhibited EIMS molecular ion peak at (m/z 301 [MþH] ) cor-
responding to molecular formula C18
H
36
O
3
. The D-erythro form
0
(
2S,3R) between C-2 and C-3, and R-configuration of C-2 were
13
established depending upon the C NMR chemical shifts of these
three carbons that confirmed by the positive optical rotation
1
7
½ ꢄ þ58.6 (c 1.0, MeOH) of 1 that similar to those of sarcoehre-
a
D
nosides A-B [26]. In addition, our DFTcalculated evidence, at B3LYP/
6
-311G(d,p) level of theory, has resulted in the same optical rota-
17
tion as (½
aꢄ
þ59.0 (c 1.0, MeOH) [28]. Based on these findings, 1
vent, all band absorptions lmax were red-shift and the natural
electronic excitations which might have as arriving state p/p* on
the two double bonds of 1.
D
was established as 9-methylated cerebroside derivative 1-O-(
b-
D-
0
0
glucopyranosyl)-(2S,3R,4E,8E)-2-[(2 R)-2 -hydrox-
yheptadecanoylamino]-9-methylheptadeca-4,8-diene-1,3-diol,
which trivially named ophiocordylongiiside A (1).
3.3. Geometric analysis
Nuclear magnetic resonance (NMR) spectroscopy has been
extensively employed for structural analysis of isolated and syn-
thetic organic compounds. A positive signal was that the combi-
nation of the quantum chemistry calculation DFT method and
experimental NMR data was recognized to be an exceptional tool to
determine the structure and elucidate molecular conformation.
Nowadays, available methods such as IGLO (Individual gauge
localized orbital), have been applied to calculated chemical shift,
but GIAO (Gauge independent or invariant or including atomic
orbital) that gave the high correction with different nuclei [29]. In
Numeric data reported that radicals scavenging powerful ca-
pacity, along with their three antioxidant pathways, are contingent
upon structural properties, especially in terms of the fluctuation of
hydroxyl groups [22]. As a consequence, the detailed analysis of
structural and electronic characteristic features seemed to be the
best way. In our present work, we provided the computational
outcomes on optimized structure 1 at DFT-B3LYP/6-31G (d,p) level.
As shown in Fig. 3 and Table 3, in the all mediums, the most striking
significance was observed from the polar solvents that the opti-
mized glucosylceramide (1) is able to form up to three intermo-
lecular hydrogen bonds between hydroxyl group of sugar and
1
13
the current paper, GIAO procedure will provide the H, C NMR
computational spectra of optimized structure 1 in MeOD, using
corresponding TMS shielding to predict chemical shifts as
0
0
0
carbonyl of amide [H(OeC2 )—O(C1 )/1.955e1.958 Å], and also
00 00
d
(ppm) ¼
30]. At B3LYP/6-31G (d,p) level. The NMR calculated results were
generally in a good agreement with the observed experimental
d
calc(TMS)
e
d
calc
(
s
is the absolute shielding constant)
between hydroxyl groups in sugars [H(OeC4 )—O (C2 )/1.983 Å;
0
0
00
[
H(OeC3 )—O(C6 )/1.930e1.933 Å], but this phenomenon is absent
in gas. Local minimum energies had no significant distinction
among studied environments, averagely reached ꢃ2339.440 au
(Table 4). Taking the selective bond lengths into consideration, in
1
3
ones (Table 1). For example, C NMR chemical shift of C-2 reached
to 54.9 ppm in comparison with the experimental value at
4.6 ppm. DFT calculated study on NMR data of the optimized
structure 1 also successfully identified non-equivalent proton
phenomenon with three pairs of methylene proton at 3.93 and
4.25 and 4.78 ppm which belonging to H-
d
C
0
00
5
contrast NeC1 and C1 -O, almost bond lengths tended to slightly
increasing by 0.01e0.07 Å when transferred from gas to solvents. In
00
d
H
the same manner, the tendency of bond angle values
q
(C1 -O-C1),
(NeC1 -C2 ) regards to change medium from
gas to liquids in 1 was opposite with that of (C1eC2eC3),
(C3eC4eC5), and (C4eC5eC6). Generally, our results described
bond lengths and bond angles are in accordance with X-ray data of
similar compound methylated -glalactosyl-N-octadecanoyl-
0
q (C2eNeC1 ) and q
0
0
4
1
.29;
d
H
1.55 and 1.99;
d
H
0
00
, H-3 , and H-6 , respectively. Two calculated aliphatic proton
q
q
0
groups H12eH14 and H5 -H15' were also determined by the
q
overlapped signals that range from 1.42 to 1.47 and 1.36e1.51 ppm,
respectively. However, due to shielding effect and particularly the
b
-D
D-
13
influence of electronegative oxygen atoms, the C NMR calculated
sphingosine (MCER) [15]. However, as the effects of the around
0
0
00
0
chemical shifts of C-1, C-3, C-1 , C-2 , and C-1 appeared as upfiel-
groups, especially 2 -OH in 1 and CH
3
N in MCER, bond angle
q
ꢀ
ded at 63.0, 62.7, 162.6, 63.1 and 95.9 ppm, respectively [31].
(C2eNeC1’) in 1 achieved approximately 133.8 and bigger than
ꢀ
those of MCER (118 ) [15]. In three mediums, the glycosyl plane
0
3.2. UV spectroscopy
formulated L-shape with the long alkyl chain axis (from C-2 to C-
7 ). The serial torsional angles
0
1
a
1
/a
2
/a
3
also showed well agree-
Although UVeVisible experimental spectra of cerebrosides were
ment with the status of ꢃsc/ꢃac/ap in MCER [15]. The optimized
available, the calculated procedure on this class of compound has
not yet been performed to date. Herein, the quantum chemical
analytical outcomes with the scope at the deepest comparison
between theoretical and experimental aspects were provided.
Based on using a reliable time dependent-density functional theory
structure 1 was greatly affected by two double bonds and two hy-
0
droxyl groups 3-OH and 2 -OH. Herein, our results showed that two
4 5 6
sides of each double bond are twisted with establishing a /a /a as
sc/ꢃap/ap. Meanwhile, because torsional angles
8 9 10 11
a /a /a /a
0
possess sc/sp/ap/ꢃap, it turned out that 2 -OH is more likely to be
(
TD-DFT) method with B3LYP/6-31G (d,p) and B3LYP/6-311G (d,p)
the main reason that the planarity of plane C2(H)eNHeCOeC2’ has
0
levels to predict the UV spectrum for natural products [32], the
experimental (in methanol) and the predicted (in mediums gas,
methanol and water) electronic excitations (energy, wavelength,
absorbance, oscillator and transition assignment) of cerebroside (1)
were presented in Table 2 and Fig. 2. The results exhibited that the
experimental UVeVisible spectrum of cerebroside (1) shows a peak
lost as well as the bond C1 -C2’ did not belong to zigzag plane of
0
0
alkyl chain (C-2 to C-17 ).
3.4. Frontier molecular orbital theory and spin density
With regards to electron delocalization, it involved in the sta-
bilization of neutral and radicals after proton abstractions. The
frontier orbital theoretical calculation seemed to be an effective
model for determining the relation between the neutral and radical
forms, especially the electron delocalization [22]. At the theoretical
level of DFT-B3LYP/6-31G(d,p), the results exhibited no differences
in HOMO and LUMO neutral illustrations when changed from gas to
at
l
max 224 nm with absorbance log (ε) ¼ 3.559. In agreement with
this, the calculated band absorption reached only one peak in each
medium at both two studied levels. Especially, in term of 6-311G
(
d,p) basis set, the gas values of
f ¼ 0.0887) and log (ε) ¼ 3.591 accurately coincided with experi-
ment, as compared to
max 220 nm (Evert ¼ 5.643 eV, f ¼ 0.0992) and
lmax 224 nm (Evert ¼ 5.536 eV,
l