Steroidal Molecular Rotors with 1,4-Diethynylphenylene Rotators: Experimental and Theoretical Investigations Toward Seeking Efficient Properties

Article abstract of DOI:10.1021/acs.jpcb.0c06464

Properly designed molecular rotors with sizable stators and a fast-moving rotator could provide efficient building blocks for amphidynamic crystals. Herein, we report the synthesis of steroidal compounds 1, 2, and 3 and their deuterated analogues 1D, 2D, and 3D envisioned to work as molecular rotors. The obtained compounds were characterized by attenuated total reflection-infrared, Raman, and circular dichroism (CD) spectroscopy measurements. The interpretation of spectra was supported by theoretical calculations using density functional theory methods. The analysis of the most characteristic bands confirmed different molecular dynamics of the rotors investigated. Angle-dependent polarized Raman spectra showed the crystallinity of some samples. Electronic CD (ECD) spectra of compounds 1-3 and their relevant deuterated analogues 1D-3D are identical. The increase of the band intensity with lowering the temperature shows that the equilibrium is shifted to the thermodynamically most stable conformer. ECD spectra simulated at the TDFFT level of theory for compound 3 were compared with experimental results. It was proved that conformer 3a, with a torsion angle of +50°, exhibits the best agreement with the experimental results. Simulated vibrational CD and IR spectra for conformer 3a and its deuterated analogue 3Da also display good agreement with experimental results. In light of our comprehensive investigations, we evidenced that steroidal compounds 1, 2, and 3 can work as molecular rotors.

Full text of DOI:10.1021/acs.jpcb.0c06464

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Steroidal Molecular Rotors with 1,4-Diethynylphenylene Rotators:
Experimental and Theoretical Investigations Toward Seeking
Efficient Properties
́
́
Karolina Olszewska, Izabella Jastrzebska,* Andrzej Łapinski, Marcin Gorecki,* Rosa Santillan,
́
Norberto Farfan, and Tomasz Runka*
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ABSTRACT: Properly designed molecular rotors with sizable stators
and a fast-moving rotator could provide efficient building blocks for
amphidynamic crystals. Herein, we report the synthesis of steroidal
compounds 1, 2, and 3 and their deuterated analogues 1D, 2D, and
3D envisioned to work as molecular rotors. The obtained compounds
were characterized by attenuated total reflection-infrared, Raman, and
circular dichroism (CD) spectroscopy measurements. The inter-
pretation of spectra was supported by theoretical calculations using
density functional theory methods. The analysis of the most
characteristic bands confirmed different molecular dynamics of the
rotors investigated. Angle-dependent polarized Raman spectra
showed the crystallinity of some samples. Electronic CD (ECD)
spectra of compounds 1−3 and their relevant deuterated analogues
1D−3D are identical. The increase of the band intensity with
lowering the temperature shows that the equilibrium is shifted to the thermodynamically most stable conformer. ECD spectra
simulated at the TDFFT level of theory for compound 3 were compared with experimental results. It was proved that conformer 3a,
with a torsion angle of +50°, exhibits the best agreement with the experimental results. Simulated vibrational CD and IR spectra for
conformer 3a and its deuterated analogue 3Da also display good agreement with experimental results. In light of our comprehensive
investigations, we evidenced that steroidal compounds 1, 2, and 3 can work as molecular rotors.
1. INTRODUCTION
In recent years, outlook on how a molecular machine is
perceived has changed drastically. In early research, a
molecular machine was primarily described as an isolated
molecular system, created in the image of molecular motors
one can find in a living cell.1,2 Nowadays, the definition of what
a molecular machine is has been extended to include linear,3
planar,4 and three-dimensional assemblies. Amid those, solid-
state molecular machines are considered as ideal candidates for
the development of new functional materials.5 Furthermore,
among crystalline molecular machines, a group of amphidy-
Figure 1. Schematic illustration of the molecular rotor and the
structure of the cyclic molecular rotor based on a 1,4-diethynylphe-
nylene rotator.7
namic crystals is an especially promising one. By that term, we
understand a broad group of molecular crystals that contain
highly mobile components inside rigid crystal frames.6 Those
crystals are assemblies of molecules called rotors. A rotor, as
shown in Figure 1, consists of three components: the stator,
whose role is to create a rigid frame; the rotator, responsible
for movement inside the assembly; and the axle of rotation.
As stated by Catalano and Naumov, in order to harness
useful functionality, those constructs must fulfill three main
design principles.8 Primarily, they must contain free space
around moving components in order to facilitate the
Received: July 15, 2020
Revised: September 9, 2020
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movement of the rotator. This can be achieved by numerous
means, for example, by introducing massive, steroid-based
stators and additional bridging chains connecting them.7,9
Second, they must contain a volume conserving rotator, which
translates into a requirement of high rotational symmetry.
Third, the motion of rotators must be correlated. Different
amphidynamic crystals that satisfy these conditions can find
application in numerous measurement techniques based on the
modulation of the rotator rotation because of the interaction
with the environment in which the rotor, or crystal, is being
placed. Thus, they can find application as molecular sensors,10
gas storage systems,11 or gas separation modules.12 If placed in
intracellular surroundings, they can act as viscosity sensors.13 It
has also been shown that they can provide tunable and
switchable dielectrics.14,15
In this paper, we present the synthesis and vibrational and
circular dichroism (CD) spectroscopy characterization of two
types of molecular rotors, with steroidal stators and 1,4-
diethynylphenylene and 1,4-diethynylphenylene-d4 groups as a
rotator. These compounds were selected based on the
similarities and differences between parts of the rotor
molecules in order to compare the molecular dynamics and
answer the question of which single C−C bond in the rotator
is responsible for the rotation (Figure 2). With the conferred
spectroscopic study, we will endeavor to solve the problem
connected with motion in steroidal molecular rotors.
Figure 3. Structures of rotors 2 and 2D.
homo-17β-ol-3-one]-benzene-d4) were obtained in the same
manner as rotors 1 and 1D (see Scheme 2). Compound 3 was
proved to be identical to that described by Santillan et al.17
The structure of compound 3D was established by H, 13C
1
NMR, ATR-IR, and HRMS.
2.2. Density Functional Theory Calculations. The
dynamics of selected molecular rotors were simulated with
the use of Gaussian0318 and Gaussian16.19 Density functional
theory (DFT) calculations using a B3LYP/6-31G(d) basis set
were carried out for an isolated molecule of rotor 3 (Figure 4)
on the basis of structural data from the CIF file arising from X-
ray analysis reported by Santillan et al.17 In order to select a
molecule for the optimization process, structural data analysis
was performed using Olex2 crystallography software.
This method is a hybrid DFT approach that combines the
Becke’s three-parameter nonlocal exchange potential with the
Lee−Yang−Parr nonlocal correlation functional.20,21 The
frequencies obtained as a result of the calculations were
multiplied by a uniform factor of 0.961 in order to eliminate
systematic errors related to anharmonicity.22,23 For the
calculation performed, Raman intensity was calculated from
scattering activities using the procedure described by Sun et
al.24 The data were calculated for an appropriate temperature
of 20 °C and excitation wavelength of 785 nm. The band
assignment was performed by the visual inspection of the
individual modes with the use of the GaussView 5 program.25
The input structures for CD study of 3 and 3D were found by
performing conformational searches and the optimizations of
the conformers obtained. Final optimizations were run at the
B3LYP/6-311+G(d,p) level, including the PCM solvation
model for CH3CN [in the case of electronic CD (ECD)] and
CHCl3 [vibrational CD (VCD)] resulted in one stable
conformation. Time-dependent-DFT calculations were run
with functional CAM-B3LYP and def2-TZVP basis sets,
including a PCM for CH3CN. This selection was inspired
based on our previous study on steroid-based com-
pounds.26−29 All spectra were generated using the program
SpecDis.30
Figure 2. Proposed bonds responsible for rotation in the rotator.
2. MATERIALS AND METHODS
2.1. Synthesis of the Materials. Treatment of steroid 1A
with ethynyl magnesium chloride in dry tetrahydrofuran at 0
°C provided alkyne 1B. Then, acetylation with Ac2O in
pyridine was performed. Dimers 1 (1,4-bis[17α-ethynyl-5α-
androstane-3β,17β-diacetate]-benzene) and 1D (1,4-bis[17α-
ethynyl-5α-androstane-3β,17β-diacetate]-benzene-d4) were
obtained by Sonogashira cross-coupling between alkene B
and 1,4-diiodobenzene or 2,3,5,6-tetradeuterium-1,4-diiodo-
benzene in the presence of Pd(Ph3)2Cl2, as outlined in Scheme
1. The structure of compound 1 and 1D was established by 1H,
13C NMR, attenuated total reflection-infrared (ATR-IR), and
high-resolution mass spectrometry (HRMS). Compound 2
and 2D were obtained according to the described protocol.16
Structures of compounds 2 and 2D are presented in Figure 3,
connected with the motion in steroidal molecular rotors.
Dimer 3 (1,4-bis[4-estren-17α-ethynyl-18a-homo-17β-ol-3-
one]-benzene) and 3D (1,4-bis[4-estren-17α-ethynyl-18a-
2.3. ATR-IR Spectroscopy. A Bruker Equinox 55 FTIR
spectrometer equipped with a Gateway 6 reflection horizontal
Scheme 1. Synthesis of Rotors 1 and 1D
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Scheme 2. Synthesis of Dimer 3 and 3D
electricallycooled charge-coupled device detector and near
IR laser working at 785 nm wavelengths. The Raman spectra
were recorded in the spectral range 100−3200 cm−1 with a
spectral resolution better than 2 cm−1. To avoid sample
overheating, the power of the laser beam was kept below 10
mW. The position of Raman peaks was calibrated before
collecting the data using a crystalline silicon sample as an
internal standard. The spectral parameters of the bands were
determined using the fitting package of Wire 3.4 software.
2.5. CD Spectroscopy. All experimental ECD spectra were
carried out using a J-815 spectrometer (Jasco, Tokyo, Japan) at
room temperature in spectroscopic grade CH3CN in a quartz
cell with path lengths of 1 and 0.1 cm for a solution with a
concentration of 0.28−0.30 mM. All spectra were measured
using a scanning speed of 100 nm min−1, a step size of 0.2 nm,
a band width of 2 nm, and accumulation of five scans. The
spectra were background-corrected using spectra of solvents.
Additionally, for compound 3, variable-temperature ECD
measurements were carried out by using an Optistat optical
spectroscopy cryostat (Oxford Instruments, Abingdon, UK)
fixed to the sample compartment of the ECD instrument, in
the temperature range from +25 to −160 °C, using the same
measurement parameters. Baseline correction was done by
subtracting the spectrum of a reference solvent obtained under
the same conditions; the normalization was done using a
concentration at 25 °C. The VCD and IR spectra of 3 and 3D
were measured simultaneously using a Chiral IR-2X from
BioTools (Jupiter, FL, USA) at a resolution of 4 cm−1 in the
range of 2000−950 cm−1 in CDCl3 as a solvent. A solution
with a concentration of ∼0.1 M was measured in a BaF2 cell
Figure 4. Model of the molecule of rotor 3.17
ATR system, a deuterated triglycine sulfate detector, and a KBr
beam splitter was used for spectral acquisition. The ATR
accessory consisted of an optical unit and a top plate assembly
with a 45° angle zinc selenide (ZnSe) crystal that allowed the
measurement of liquids and solids. All spectra were recorded in
the range of 4000−600 cm−1 using the ATR method with a
resolution of 2 cm−1 and 2500 scans.
2.4. Raman Spectroscopy. The Raman spectra of
nonoriented samples of molecular rotors 1, 2, and 3 and
deuterated 1D, 2D, and 3D compounds were recorded using a
Renishaw inVia Raman microscope equipped with a thermo-
Figure 5. Experimental and theoretical (scaling factor = 0.961) spectra of rotor 3: Raman (a,c) and IR (b,d).
C
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Figure 6. ATR-IR (a,b) and Raman (c,d) spectra of non-deuterated and deuterated compounds. Bands * and # are assigned to stretching vibrations
of C−D bonds.
Table 1. Positions (cm−1) of Bands in the Raman and ATR-IR Spectra of Rotors 1−3 and 1D−3D in the 2300−1400 cm−1
a
Range and Proposed Assignment
rotor 1
rotor 2
Raman IR-ATR
rotor 3
rotor 1D
rotor 2D
rotor 3D
Raman
IR-ATR
Raman
IR-ATR
Raman
IR-ATR
Raman
IR-ATR
Raman
IR-ATR interpretation
2291 w
2270 w
2226 s
2210 w
1744 w
1731 w
2289 w
2287 w
ν C−D (R)
2234 m
2219 s
2230 w
2220 s
2240 w
2216 s
2243 w
2215 s
ν CC
2223 s
1746 w
1727 w
1746 m
1729 s
1746 s
1732 s
ν CO (S)
1684 w
1683 w
1666 w
ν CO (S)
1677 s
1666 s
1653 s
1674 w
1654 m
1673 s
1659 v
1654 m
1623 w
1611 m
1672 s
1653 s
1671 s
1662 m
1665 s
1656 s
1639 m
1613 m
1653 s
1647 w
1623 w
1603 s
1593 s
1614 m
1603 s
1622 m
1613 m
1574 s
1567 s
1616 s
1574 s
1570 s
1617 s
ν CC (S)
ν CC (R)
1603 s
1575 s
1568 s
1559 w
1596 w
1597 m
1507 w
1497 w
1508 w
1500 w
1508 s
1498 w
1426 m
1424 m
1424 s
a
Abbreviations: sstrong, mmedium, wweak, Rrotator, Sstator.
with a path length of 100 μm over the course of ca. 8 h to
improve the signal-to-noise ratio. Baseline correction was
achieved by subtracting the spectrum of a solvent recorded
under the same conditions.
D
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3. RESULTS AND DISCUSSION
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rotator in 2D and 3D has a more substantial mass, and thus, a
higher moment of inertia, which causes a more significant
deformation of the rotating ring (it flattens in the direction of
the rotation axis). This leads to a slight elongation of the CC
bonds and then, due to the smaller value of bond force
constant, the wavenumber of the band assigned to the
stretching vibration of the CC bonds shifts to lower
wavenumber values. However, the wavenumber of the
stretching vibration of CC bonds for rotors 1 and 1D is
greater than for the rest of rotors because the steric hindrance
for ring rotation is larger because of the existence of acetate
groups in the proximity of the rotating ring. As a consequence,
the frequency of rotator rotation decreases and causes smaller,
compared to rotors 2, 2D, 3, 3D, ring deformation. As a result,
the length of CC bonds in rotors 1 and 1D is slightly
shorter, the force constant is greater, which leads to the higher
wavenumber of bands corresponding to stretching vibrations of
CC bonds being observed. However, there are no bands
present in the experimental ATR-IR spectra of all rotors (non-
deuterated and deuterated) assigned to the stretching
vibrations of CC bonds. This is in agreement with the
theoretical calculations that indicate practically negligible
intensity of this vibration in the IR spectrum (see Figure 5).
In the Raman spectra of rotors 1D, 2D, and 3D, bands
assigned to the stretching vibrations of C−D bonds are
revealed in the slope of the band assigned to the CC stretch,
on the higher energy side of the band. Two bands are present
for rotor 1D, and a singular band is observed for rotors 2D and
3D. All the bands assigned to the stretching vibrations of C−D
bonds are recorded with very low intensity.
3.1. Characterization of the Materials. ATR-IR and
Raman Spectroscopy. Three compounds named rotors 1, 2,
and 3 and their deuterated analogues 1D, 2D, and 3D were
chosen for vibrational spectroscopy characterization. Raman
and ATR-IR spectroscopy methods were used, and the
experimental results were verified by theoretical calculations
using the B3LYP/6-31G(d) method. The theoretical calcu-
lations were performed for molecules of rotor 3, for which the
crystallographic structure has been published.17 The calculated
and experimental Raman and IR spectra of rotor 3 are shown
in Figure 5. Moreover, all calculated wavenumbers, activity in
Raman and IR spectra, and proposed assignment are presented
in Table S1 in the Supporting Information.
The spectra consist of many bands, so for the analysis and
assignment of modes, and will be divided into subranges. In
the ATR-IR spectra of 2, 2D, 3, and 3D, broadbands observed
in the range 3500−3010 cm−1 are assigned to stretching
vibrations of O−H bonds (Figure S1 in Supporting
Information). In the range between 3050 and 2800 cm−1 in
both Raman and ATR-IR spectra, multicomponent bands
assigned to symmetric and antisymmetric stretching vibrations
of saturated C−H bonds are recorded for all compounds. The
above observation is confirmed by theoretical calculations.
The Raman and ATR-IR spectra of non-deuterated 1, 2, and
3 and deuterated 1D, 2D, and 3D rotors in the region of the
rotator vibrations are presented in Figure 6. In the range from
2400 to 1400 cm−1, bands of the highest intensity both in
Raman and ATR-IR spectra are observed. Most of these bands
are assigned to the different vibrations of a rotator, and the axle
of rotation and this range is of particular interest. In Table 1,
wavenumbers and the assignment of these bands are provided.
A medium intensity band located above 2200 cm−1 in Raman
spectra of both non-deuterated and deuterated rotors is
assigned to the stretching vibrations of CC bonds that form
the axle of rotation. The position and intensity of the band vary
for different rotors. In the Raman spectrum of rotor 1, a
singular band with a peak located at 2223 cm−1 is observed. In
the Raman spectra of a deuterated analogue 1D, the band
consists of two components; the main is located at 2226 cm−1
and a weaker band, in the form of asymmetry of main band, at
2210 cm−1. The opposite behavior can be perceived in the
spectra gathered for the pairs of rotors 2 and 2D and 3 and 3D.
For all of them, the band under discussion consists of two
components with the less intense one shifted to higher
wavenumbers. Comparing the positions, one can notice a red
shift of the main component and a blue shift of a secondary
component in the spectra of deuterated rotors 2D and 3D, in
relation to the spectra of rotors 2 and 3. The analysis of ATR-
IR spectra indicates a lack of the bands in the spectral region
discussed. Theoretical spectra confirm this observation (see
Figure 5). The interpretation of the experimental observations
discussed above leads to several essential remarks. Similar
values of wavenumbers of the main band attributed to CC
bonds for the pairs of rotors 2 and 3 and also for 2D and 3D
indicate a similar chemical environment of the rotators in pairs
of molecules (non-deuterated and deuterated). This indicates
that an additional ethyl group present in rotors 3 and 3D does
not influence the rotational dynamics of the rotator. The
decrease in the wavenumber of this band for pairs of rotors 2
(2219 cm−1) and 2D (2216 cm−1) and 3 (2220 cm−1) and 3D
(2215 cm−1) can be explained with mass effect. A deuterated
In the spectral range 1680−1620 cm−1, in the Raman and
ATR-IR spectra of rotors 2, 2D, 3, and 3D, multicomponent
bands are recorded that can be assigned to the in-phase and
out-of-phase stretching vibrations of CO bonds occurring in
rings A of the stators. For rotor 2D and 3D, bands present in
the Raman spectra are of higher intensity compared to the
analogous bands present in the Raman spectra of rotors 2 and
3. For rotors 1 and 1D, the ester carbonyl group stretching
vibrations are observed as two peaks in the range between
1750 and 1720 cm−1, strong in the ATR-IR spectra and very
weak in the Raman spectra. A substantial difference in the
position of bands attributed to the CO stretching vibration
between rotors 1 and 1D and 2, 2D, 3, and 3D is related to the
location of the group in the rotor molecule. As it is seen from
Schemes 1 and 2 and Figure 3 for rotors 1 and 1D, the acetate
groups are present at C17 in ring D, while in the case of rotors
2, 2D, 3, and 3D, there are α,β-unsaturated carbonyl CO
groups (A ring). It is worth to note that carbonyl bonds are
highly polar because of the large electronegativity between
carbon and oxygen. This generates a significant dipole moment
and, as a result, provides an intense band that corresponds to
the stretching vibration in the IR spectrum (usually very weak
in the Raman spectrum). Generally, the band assigned to
stretching vibrations of α,β-unsaturated carbonyl groups is
registered at much lower wavenumbers in vibrational spectra,
as compared to the CO bond stretch in acetate groups. This
is because the α,β-unsaturated carbonyl group is conjugated
with a carbon−carbon double bond. This causes the CO
bond to weaken, lowers the force constant, and, hence, shifts
the band position of stretching vibration toward lower
wavenumbers. The analysis of our results indicates a difference
of about 80 cm−1. Additionally, this promotes geometrical
changes and, in consequence, increases the activity of the
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stretching vibration of CO bonds in Raman spectra of rotors
2, 2D, 3, and 3D, as compared to 1 and 1D. Moreover, for
deuterated compounds 2D and 3D, the increase in the
intensity of the CO vibration, in Raman spectra with respect
to non-deuterated compounds, 2 and 3, can be caused by
changes in the rotational dynamics of the rotator and the
influence on α,β-unsaturated carbonyl groups in stators. For
the asymmetric stretching vibration of the CC bond in the
aromatic ring of the rotator, a two-component band near 1600
cm−1 and a two-component band near 1500 cm−1 are present,
respectively, in the Raman and the ATR-IR spectra of rotors 1,
2, and 3. The positions of the bands in the corresponding
spectra of rotors 1D, 2D, and 3D are shifted toward lower
wavenumbers. This is confirmed by theoretical calculations
conducted for rotor 3, according to which there are two
different stretching vibrations of double CC bonds present
in the rotator, one at 1597 cm−1, with high intensity in Raman
spectroscopy, and a second one at 1493 cm−1 of medium
intensity in an IR spectrum.
In the experimental spectra of rotors 2, 2D, 3, and 3D, there
is also an additional asymmetric band in the 1620−1610 cm−1
range, originating from the stretching vibration of CC bonds
present in the A ring of the stators mentioned above. In the
range between 1450 and 1400 cm−1, in both Raman and ATR-
IR spectroscopy, multicomponent bands are recorded. Bands
in this region can be assigned to scissoring vibrations of methyl
and methylene groups that are also present in the stators.
The observation of crystallite morphology of all samples
under an optical microscope allows us to select those for
further spectroscopic characterization. Samples of rotors 1, 3,
and 3D are the most interesting for further measurements
because of their well-shaped crystallites of size ranging from a
couple of microns, in the case of rotor 1, to several hundred
microns, in the case of rotor 3D. Rotors 2 and 2D present as
very fine powders, with particles of sizes distinctly below
micrometer. Here, we show the results of the spectroscopic
study concerning polarized Raman spectra measurements and
angular analysis for rotors 1, 3, and 3D. For each of the rotors,
one crystallite with a well-developed crystalline surface was
chosen for the measurements of polarized Raman spectra.
The polarized Raman spectra of the selected crystallites of
rotors 1, 3, and 3D are presented in Figure 7. In all cases,
spectra show significant changes in the intensity of the bands
for parallel (XX) and cross (XY) polarization, which indicates
the crystallinity of the sample. The comparison of the polarized
spectra for all other rotors are depicted in Figure S2
(Supporting Information). As it is seen from Figure 7a−c,
the intensity of modes assigned to the stretching vibration of
the CC bond in the axle and CC bonds in the ring of the
rotator for parallel (XX) and perpendicular (XY) polarization
is very different, that is, from about three to five times higher in
(XX) polarization, whereas the intensity of other modes
assigned to CO, CC (S) in stators, O−H or skeletal, and
C−D bonds (the last one only for deuterated compound) is
comparable for both polarizations. The relation between the
intensity of the bands mentioned above reverses after rotating
the samples by an angle of 90° (see Figure S3 in Supporting
Information). This is a consequence of the change in selection
rules for crystalline materials. In the discussed spectral range of
Raman spectra, it can be seen that the intensity of the bands
depends on the geometrical relationship between the polar-
ization of the incident laser light (direction of the electric field
vector) and the orientation of the rotor molecule. For a 0°
Figure 7. Selected parts of the Raman spectrum associated with
vibrations of double and triple CC bonds, carbonyl groups, C−D, and
O−H for rotors 1 (a), 3 (b), and 3D (c) are presented. Rrotator,
Sstator.
angle, the electric field vector of the incident laser light must be
parallel or almost parallel to the axle of the rotator in the rotor
molecule, that is, parallel to CC bonds, resulting in the
maximum intensity of the band assigned to CC bond
stretch. For an angle of a 90°, the electric field vector is
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perpendicular to the axle, and so the vibration observed cannot
be excited, resulting in the disappearance of the latter band.
For a rough analysis of the spectroscopic results of crystalline
samples, let us now assume that the stators are perpendicular
to the axle. Then, for an angle of 90°, the electric field vector of
incident light is parallel to the stators. Thus, the electric field
vector is close to parallel to CO and O−H bonds for rotors
3 and 3D. The intensity of the bands assigned to the vibrations
of these bonds would be then maximum. We should note that
there are no bands corresponding to such bonds (CO and
O−H) in the spectrum of rotor 1.
In the abovementioned approximation, we roughly assumed
the right-angle geometry of the rotor molecule and also that
the molecule lies in the plane of observation. Given that the
bands in the spectra appear as not quite polarized, this
assumption may not be entirely correct for a real crystal. The
geometry of rotor molecule 3 drawn on the basis of
crystallographic data (Figure 4) indicates that the angle
between stators and axle of rotator is slightly different than
90°. Additionally, the angular dependence of the intensity of
stretching vibrations of C−D bonds is similar to that of CO
and O−H bonds (3D), which confirms a similar geometrical
orientation of these three bonds in the molecule. To further
investigate the polarization differences, the measurements of
samples of rotors 1, 3, and 3D were carried out for different
angles while the crystallite was rotated by a predetermined
angle. Figures 8a and 9a show the dependence of the intensity
Figure 9. Dependencies of intensity vs angle of rotation of the sample
for the band assigned to stretching vibration of CC bonds in rotator
recorded in parallel (XX) polarization for rotor 3. The Raman spectra
recorded for corresponding angles are depicted on the right side.
approximation of the dependences measured. Experimental
dependences for all samples were fitted using the sine function
x − xC
i
y
j
z
z
z
j
y = y + A sin π
j
0
(1)
w
k
{
The maximum and minimum of the Raman signal are
separated by an angle of about 90°. The Raman spectra that
correspond to three different angular positions of the samples
are depicted in Figures 8b and 9b. Tracking the dotted lines
from the Raman spectra to the bottom part of the figures, one
can see the assignment of corresponding spectra to the angular
position of the crystal investigated (Figures 8c and 9c).
3.2. CD Analysis. CD spectroscopy has constantly
illustrated its high sensitivity in the study of conformational
diversity of chiral species, as well as their conformational
stability.26,31−37 Therefore, in the course of this work, we
decided to add this technique to our in-depth studies to
explore the ECD and VCD properties in order to gain more
insights into the conformational stability in solution of the
investigated steroidal rotors. First, ECD and UV spectra of 1−
3 and 1D−3D were recorded in acetonitrile at room
temperature (Figure 10). The ECD curves exhibit two types
of profiles, which are significantly different from each other in
the position of Cotton effects (CEs) and their intensity. In all
cases, ECD spectra of steroidal compounds 1−3 and their
relevant deuterated analogues 1D−3D are identical. The
replacement of hydrogen with deuterium is not expected to
have any effect on the ECD spectra, and this effect is also quite
minor on the presented VCD spectra because of the great
flexibility of the axle, as well as the rotator. The experimental
data of 1 and 1D display one negative CE at 275 nm and
shoulders at 250, 220, and 210 nm. These bands are mainly
attributed to π−π* transitions of the diethynylphenylene
chromophore. In the same region in the UV spectrum, there
are bands at ∼325, 290, 270, 220, and 213 nm. For rotors 2
and 3 and 2D and 3D, there is a broad long-wavelength
negative CE centered at ∼330 nm related to the n−π*
transition of the enone chromophore in the stator part of
molecule, then there are two intense bands centered at ∼240
Figure 8. Dependencies of intensity vs angle of rotation of the sample
for the band assigned to stretching vibration of CC bonds in the
rotator recorded in parallel (XX) polarization for rotor 1. The Raman
spectra recorded for corresponding angles are depicted on the right
side.
recorded in parallel (XX) polarization versus angle of rotation
of the samples 1 and 3 for the mode assigned to the stretching
vibration of the CC bond in the rotator. The dependence
for sample 3D is shown in Figure S4 in Supporting
Information. For all crystallites measured, the initial
orientation was not only different but also impossible to
determine in the midst of conducting measurement. Therefore,
the maximum intensity can be observed for different angles.
On that account, the scale of angles, as shown in Figures 8a, 9a,
and S4, was adjusted so that an angle of 0° would match the
maximum of the Raman signal calculated from the sine
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Figure 10. ECD and UV spectra of 1−3 and 1D−3D rotators measured in acetonitrile at room temperature.
Figure 11. Variable low-temperature ECD and UV measurements of 3 recorded in the mixture of MeOH/EtOH = 1:4.
Figure 12. Comparison of the experimental and simulated spectra of 3 by changing the torsion angle C16−C17−C20−C21 (band width = 0.43 eV,
UV shift = 0 nm).
nm derived from π−π* benzene transitions, and a band at
∼215 nm originating from admixture of the π−π* benzene and
enone transitions. However, because of the slight energy
difference between these excitations their precise determi-
nation is impeded. One may also notice that the CE centered
at 270 nm exhibits a well-developed vibrational structure.
Next, in the course of our work, the variable low-
temperature ECD measurements were carried out to check
the thermal stability of the investigated molecular rotors. As a
model for this part of the study, we selected rotor 3. In Figure
11, the ECD spectra recorded in the mixture MeOH/EtOH =
1:4 in the temperature range from +20 to −160 °C are shown.
As shown in Figure 11, lowering the measurement temperature
resulted in a substantial change in the intensity of all ECD/UV
bands, with the two isodichroic points at 260 and 291 nm. The
ECD spectra showed a systematic increase of band intensity
with lowering the temperature. This means that the
equilibrium is shifted to the thermodynamically most stable
conformer. The changes in the intensity of the main bands are
because of the flexibility of the bonds throughout the entire
rotator bridge, while the steroid part remains stable. This
hypothesis is supported by the fact that steroidal stators are
quite conformationally rigid and do not generate any
significant impact onto the variable-temperature ECD spectra.
In order to predict the most favorable conformation(s) in
solution, we simulated at the TDFFT level of theory ECD
spectra for representative conformers of rotor 3 by changing
systematically the torsion angle C16−C17−C20−C21 (acc.
numbering in Scheme 1 and Figure 12), starting directly from
the modification of the X-ray structure previously published for
a similar compound.16 We used this strategy because
computed conformers (obtained by simulations using molec-
ular mechanics level follow by DFT optimizations) exhibit
plenty of structures with quite similar energy differences
(Figure S5). This approach is based on the straight comparison
of experimental and simulated spectra: a good match supports
H
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Figure 13. Comparison of the experimental and calculated VCD and IR spectra of 3 and 3D (band width = 10 cm−1, scaling factor = 0.983).
the predicted conformational analysis.38 For all conformers,
ECD spectra were calculated at the CAM-B3LYP/def2-TZVP
level of theory using the PCM model for CH3CN. As a result
of our analysis, conformer 3a with the value of torsion angle
+50° shows the most intense CEs at ca. 230 nm. Thus, this
conformation exhibits the best agreement with the exper-
imental data (Figure 12), actually indicating the most stable
structure in solution among the set of investigated structures.
Some inconsistency in the range 300−380 nm are related to
the use of a constant band width for the whole investigated
spectral region (see also Figure S6). Another way of looking at
the question of conformational stability is VCD spectroscopy.
The experimental VCD and IR spectra of 3 and 3D are
recorded in chloroform and presented in Figure 13, together
with DFT simulations performed for previously selected
conformation 3a and 3Da at the B3LYP/6-311+G(d,p) level
of theory using the PCM model for CHCl3.
relevant deuterated analogues are identical because there is no
any influence of deuterium substitution onto the electronic
transitions of chromophore units. Furthermore, this influence
is also not visible in vibrational spectra perhaps because of the
great flexibility of the axle, as well as the rotator. The thermal
stability monitored by the low-temperature ECD measure-
ments shows that the equilibrium is shifted to the
thermodynamically most stable conformer. This finding was
fully confirmed by theoretical simulations of chiroptical data.
On the other hand, calculations of ECD and VCD data and
their good reproduction proved that the investigated rotors
exhibit properties which are not governed by supramolecular
interaction. In light of our experimental results supported by
theoretical calculations, we are able to probe the vibrational,
optical, and chiroptical properties of steroidal compounds and
confirm that they can work as molecular rotors.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jpcb.0c06464.
DFT simulations for 3a and its deuterated analogue 3Da
show good agreement with the experimental spectra; all
experimental spectral features are well reproduced. This
additionally confirms the validity of the computed conforma-
tional species and conclusions derived from ECD on the most
preferable conformation in solution.
■
sı
Synthesis details for 1, 1D, and 3D compounds (1H, 13
C
NMR, and HRMS), results of DFT calculation for the
model of rotor 3, ATR-IR spectra of rotors 2, 2D, 3, and
3D, polarized Raman spectra of rotors 1, 2, and 2D,
polarized Raman spectra of rotors 1D, 3, and 3D after
rotating the sample by 90°, simulated spectrum of 3a
and steroidal unit at the CAM-B3LYP/def2-TZVP/
PCM(CH3CN) level of theory, and overview of
conformational search for compounds 3 carried out at
the B3LYP/6-31G(d) level of theory (PDF)
4. CONCLUSIONS
The comprehensive spectroscopy analysis of molecular rotors
1−3 and their deuterated analogues 1D−3D was performed.
The interpretation of the experimental data was supported by
quantum chemical calculations. Vibrational spectroscopy
provided information which allows to distinguish structures
of rotors, mainly due to the differences between functional
groups in stators and deuterated rotator. The analysis of the
most characteristic bands confirmed different molecular
dynamics of the rotors investigated. However, there is no
spectroscopic evidence as to which single C−C bond is
responsible for the rotation of the rotator. Angle-dependent
polarized Raman spectra confirmed the crystallinity of three
samples. ECD and VCD spectra of compounds 1−3 and their
AUTHOR INFORMATION
Corresponding Authors
■
Izabella Jastrzebska − Faculty of Chemistry, University of
Białystok, 15-254 Białystok, Poland; Phone: +48 85 738 80
43; Email: i.jastrzebska@uwb.edu.pl
I
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J. Phys. Chem. B XXXX, XXX, XXX−XXX

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pubs.acs.org/JPCB
Article
́
(9) Runka, T.; Olszewska, K.; Fertsch, P.; Łapinski, A.; Jastrzebska,
́
Marcin Gorecki − Institute of Organic Chemistry, Polish
́
I.; Santillan, R.; Farfan, N. Vibrational spectroscopic characterization
Academy of Sciences, 01-224 Warsaw, Poland; orcid.org/
0000-0001-7472-3875; Phone: +48 22 343 20 00;
Email: marcin.gorecki@icho.edu.pl
of cyclic and acyclic molecular rotors with 1,4-diethynylphenylene-d4
rotators. Spectrochim. Acta, Part A 2018, 192, 393−400.
(10) Mu, X.; Liu, Y.; Liu, S.; Sun, Y.; Lu, N.; Lu, Y.; Li, W.; Zhou, X.;
Liu, B.; Li, Z. A cyanine-derived near-infrared molecular rotor for
ratiometric imaging of mitochondrial viscosity in cells. Sens. Actuators,
B 2019, 298, 126831−126839.
(11) Aguilar-Granda, A.; Perez-Estrada, S.; Sanchez-Gonzalez, E.;
Alvarez, J. R.; Rodríguez-Hernandez, J.; Rodríguez, M.; Roa, A. E.;
Hernandez-Ortega, S.; Ibarra, I. A.; Rodríguez-Molina, B. Transient
Tomasz Runka − Faculty of Materials Engineering and
Technical Physics, Poznan University of Technology, 60-965
Poznan, Poland; orcid.org/0000-0002-0965-2676;
Phone: +48 61 665 31 55; Email: tomasz.runka@
put.poznan
́
́
́
́
́
́
́
Authors
Porosity in Densely Packed Crystalline Carbazole-(p-Diethynylphe-
nylene)-Carbazole Rotors: CO2 and Acetone Sorption Properties. J.
Am. Chem. Soc. 2017, 139, 7549−7557.
Karolina Olszewska − Faculty of Materials Engineering and
Technical Physics, Poznan University of Technology, 60-965
Poznan, Poland
Andrzej Łapinski − Institute of Molecular Physics, Polish
Academy of Sciences, 60-179 Poznan, Poland
Rosa Santillan − Departamento de Quimica, Centro de
Investigacion y de Estudios Avanzados del IPN, Mexico D.F.
07000, Mexico
́
(12) Metrangolo, P.; Carcenac, Y.; Lahtinen, M.; Pilati, T.; Rissanen,
K.; Vij, A.; Resnati, G. Nonporous Organic Solids Capable of
Dynamically Resolving Mixtures of Diiodoperfluoroalkanes. Science
2009, 323, 1461−1464.
́
́
́
́
(13) Aguilar-Granda, A.; Perez-Estrada, S.; Roa, A. E.; Rodríguez-
́
́
́
́
Hernandez, J.; Hernandez-Ortega, S.; Rodriguez, M.; Rodríguez-
Molina, B. Synthesis of a Carbazole-[pi]-carbazole Molecular Rotor
with Fast Solid State Intramolecular Dynamics and Crystallization-
Induced Emission. Cryst. Growth Des. 2016, 16, 3435−3442.
(14) Zhang, W.; Ye, H.-Y.; Graf, R.; Spiess, H. W.; Yao, Y.-F.; Zhu,
R.-Q.; Xiong, R.-G. Tunable and Switchable Dielectric Constant in an
Amphidynamic Crystal. J. Am. Chem. Soc. 2013, 135, 5230−5233.
(15) Kobr, L.; Zhao, K.; Shen, Y.; Shoemaker, R. K.; Rogers, C. T.;
Michl, J. Tris-o-phenylenedioxycyclotriphosphazene (TPP) Inclusion
Compounds Containing a Dipolar Molecular Rotor. Cryst. Growth
Des. 2014, 14, 559−568.
(16) Rodríguez-Molina, B.; Pozos, A.; Cruz, R.; Romero, M.; Flores,
B.; Farfan, N.; Santillan, R.; Garcia-Garibay, M. A. Synthesis and solid
state characterization of molecular rotors with steroidal stators:
ethisterone and norethisterone. Org. Biomol. Chem. 2010, 8, 2993−
3000.
́
́
Norberto Farfan − Facultad de Quimica, Departamento de
Quimica Organica, Universidad Nacional Autonoma de
Mexico, 04510 Ciudad de Mexico D.F., Mexico
́
́
́
́
́
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jpcb.0c06464
Author Contributions
The manuscript was written through contributions of all the
authors. All the authors have given approval to the final version
of the manuscript.
́
Notes
The authors declare no competing financial interest.
(17) Ramirez-Montes, P. I.; Ochoa, M. E.; Santillan, R.; Ramírez, D.
ACKNOWLEDGMENTS
■
́
J.; Farfan, N. Steroidal Wheel-and-Axle Host Type Molecules:
This work was partially supported by the Ministry of Science
and Higher Education. M.G. thanks the Wroclaw Centre for
Networking and Supercomputing (WCSS) for the computa-
tional support. N.F. and R.S. acknowledge support from
PAPIIT (IN222819), DGAPA and CONACyT.
Insights from Awkward Shape, Conformation, Z′ > 1 and Packing.
Cryst. Growth Des. 2014, 14, 4681−4690.
(18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, J. T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Hona, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P.
Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S. A.; Daniels, D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe Gill, P. M. W.; Johnson, B.; Chen, W.;
Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision B.03;
Gaussian, Inc.: Pittsburgh PA, 2003.
REFERENCES
■
(1) Schliwa, M.; Woehlke, G. Molecular motors. Nature 2003, 422,
759−765.
(2) Bucci, E. M.; Bucci, O. M.; Sorrentino, R. Nanotechnology and
Life: An Engineer’s Perspective [Point of View]. Proc. IEEE 2014,
102, 930−935.
(3) Liu, Y.; Flood, A. H.; Bonvallet, P. A.; Vignon, S. A.; Northrop,
B. H.; Tseng, H.-R.; Jeppesen, J. O.; Huang, T. J.; Brough, B.; Baller,
M.; Magonov, S.; Solares, S. D.; Goddard, W. A.; Ho, C.-M.; Stoddart,
J. F. Linear Artificial Molecular Muscles. J. Am. Chem. Soc. 2005, 127,
9745−9759.
(4) Eelkema, R.; Pollard, M. M.; Vicario, J.; Katsonis, N.; Ramon, B.
S.; Bastiaansen, C. W. M.; Broer, D. J.; Feringa, B. L. Nanomotor
rotates microscale objects. Nature 2006, 440, 163.
(19) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson,
G. A.; Nakatsuji, H.; et al.Gaussian 16, Revision A.03; Gaussian, Inc.:
Wallingford, CT, USA, 2016.
(5) Garcia-Garibay, M. A. Crystalline molecular machines: Encoding
supramolecular dynamics into molecular structure. Proc. Natl. Acad.
Sci. U. S. A. 2005, 102, 10771−10776.
(6) Karlen, S. D.; Garcia-Garibay, M. A. Amphidynamic Crystals:
Structural Blueprints for Molecular Machines. In Molecular Machines.
Topics in Current Chemistry; Kelly, T. R., Ed.; Springer-Verlag Berlin
Heidelberg, 2005; Vol. 262, pp 179−227.
(7) Czajkowska-Szczykowska, D.; Jastrzebska, I.; Santillan, R.;
Morzycki, J. W. The synthesis of disteroidal macrocyclic molecular
rotors by an RCM approach. Tetrahedron 2014, 70, 9427−9435.
(8) Catalano, L.; Naumov, P. Exploiting rotational motion in
molecular crystals. CrystEngComm 2018, 20, 5872−5883.
(20) Becke, A. D. Density-functional thermochemistry. III. The role
of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652.
(21) Frisch, M. J.; Pople, J. A.; Binkley, J. S. Self-consistent
molecular orbital methods 25. Supplementary functions for Gaussian
basis sets. J. Chem. Phys. 1984, 80, 3265−3269.
(22) Merrick, J. P.; Moran, D.; Radom, L. An Evaluation of
Harmonic Vibrational Frequency Scale Factors. J. Phys. Chem. A 2007,
111, 11683−11700.
J
https://dx.doi.org/10.1021/acs.jpcb.0c06464
J. Phys. Chem. B XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry B
pubs.acs.org/JPCB
Article
(23) Scott, A. P.; Radom, L. Harmonic Vibrational Frequencies: An
Evaluation of Hartree−Fock, Møller−Plesset, Quadratic Configu-
ration Interaction, Density Functional Theory, and Semiempirical
Scale Factors. J. Phys. Chem. 1996, 100, 16502−16513.
(24) Sun, R.; Yao, J.; Li, S.; Gu, R. Raman spectroscopic and density
functional theory studies on a benzothiazole-2-thione derivative. Vib.
Spectrosc. 2008, 47, 38−43.
(25) Dennington, R.; Keith, T.; Millam, J. GaussView, version 5;
Semichem Inc.: Shawnee Mission, KS, 2009.
́
(26) Jastrzębska, I.; Gorecki, M.; Frelek, J.; Santillan, R.;
Siergiejczyk, L.; Morzycki, J. W. Photoinduced Isomerization of 23-
Oxosapogenins: Conformational Analysis and Spectroscopic Charac-
terization of 22-Isosapogenins. J. Org. Chem. 2012, 77, 11257−11269.
́
(27) Frelek, J.; Butkiewicz, A.; Gorecki, M.; Wojcieszczyk, R. K.;
Luboradzki, R.; Kwit, M.; Rode, M. F.; Szczepek, W. J. Structure −
chiroptical properties relationship of cisoidenones with an α-
methylenecyclopentanone unit. RSC Adv. 2014, 4, 43977−43993.
́
́
́
(28) Frelek, J.; Gorecki, M.; Dziedzic, A.; Jabıo̵ nska, E.; Kamienski,
B.; Wojcieszczyk, R. K.; Luboradzki, R.; Szczepek, W. J.
Comprehensive spectroscopic characterization of finasteride poly-
morphic forms. Does the form X exist? J. Pharm. Sci. 2015, 104,
1650−1657.
́
(29) Gorecki, M.; Dziedzic, A.; Luboradzki, R.; Ostaszewska, A.;
Frelek, J.; Szczepek, W. J. Synthesis and comprehensive structural and
physicochemical characterization of dutasteride hydrochloride hydrate
solvates. Steroids 2017, 124, 72−80.
̈
(30) Bruhn, T.; Schaumloffel, A.; Hemberger, Y.; Pescitelli, G.
SpecDis, version 1.71: Berlin, Germany, 2017. Available online:
https://specdis-software.jimdo.com.
(31) Woznica, M.; Kowalska, P.; Lysek, R.; Masnyk, M.; Gorecki,
́
M.; Kwit, M.; Furche, F.; Frelek, J. Stereochemical Assignment of β-
lactam Antibiotics and their Analogues by Electronic Circular
Dichroism Spectroscopy. Curr. Org. Chem. 2010, 14, 1022−1036.
́
(32) Grolik, J.; Dudek, Ł.; Eilmes, J.; Eilmes, A.; Gorecki, M.; Frelek,
J.; Heinrich, B.; Donnio, B. New chiral discotics with helical
organization of the mesophaseliquid crystalline derivatives of
dibenzotetraaza[14]annulene. Tetrahedron 2012, 68, 3875−3884.
́
́
(33) Kołodziejska, R.; Gorecki, M.; Frelek, J.; Draminski, M.
Enantioselective enzymatic desymmetrization of the prochiral
pyrimidine acyclonucleoside. Tetrahedron: Asymmetry 2012, 23,
683−689.
́
́
(34) Gorecki, M.; Karczmarska-Wodzka, A.; Kołodziejska, R.;
Draminski, M.; Frelek, J. Determination of the Stereostructure of
́
Pyrimidine Nucleoside Derivatives with a Combination of Various
Chiroptical Methods. Eur. J. Org. Chem. 2014, 43, 5204−5213.
(35) Jeziorna, A.; Stopczyk, K.; Skorupska, E.; Luberda-Durnas, K.;
́
Oszajca, M.; Lasocha, W.; Gorecki, M.; Frelek, J.; Potrzebowski, M. J.
Cyclic Dipeptides as Building Units of Nano- and Microdevices:
Synthesis, Properties, and Structural Studies. Cryst. Growth Des. 2015,
15, 5138−5148.
(36) Rehman, N. U.; Hussain, H.; Al-Shidhani, S.; Avula, S. K.;
́
Abbas, G.; Anwar, M. U.; Gorecki, M.; Pescitelli, G.; Al-Harrasi, A.
Incensfuran: isolation, X-ray crystal structure and absolute config-
uration by means of chiroptical studies in solution and solid state.
RSC Adv. 2017, 7, 42357−42362.
́
(37) Gorecki, M.; Carpita, L.; Arrico, L.; Zinna, F.; Di Bari, L.
Chiroptical methods in a wide wavelength range for obtaining Ln3+
complexes with circularly polarized luminescence of practical interest.
Dalton Trans. 2018, 47, 7166−7177.
(38) Pescitelli, G.; Bruhn, T. Good Computational Practice in the
Assignment of Absolute Configurations by TDDFT Calculations of
ECD Spectra. Chirality 2016, 28, 466−474.
K
https://dx.doi.org/10.1021/acs.jpcb.0c06464
J. Phys. Chem. B XXXX, XXX, XXX−XXX