Partially Acetylated or Benzoylated Arabinose Derivatives as Structurally Simple Organogelators: Effect of the Ester Protecting Group on Gel Properties

Article abstract of DOI:10.1002/chem.201701669

Sugar-based low-molecular-weight gelators (LMWGs) have been used for various applications for a long time. Herein, structurally simple, ester-protected arabinosides are reported as low-molecular-weight organogelators (LMOGs) that are able to gel aromatic solvents, as well as petrol and diesel. Studies on the mechanical strength of the gels, through detailed rheological experiments, indicate that gels from the 1,2-dibenzoylated arabinose gelator possess better mechanical properties than those from the 1,2-diacetylated gelator. These results are interpreted in terms of the tendency of the former to form fibers with comparatively lower diameter than those of the latter, based on detailed field-emission SEM and AFM studies. Investigations of the interactions responsible for the self-assembly of gelators through IR spectroscopy and wide-angle X-ray scattering reveal that the primary interactions responsible are hydrogen bonds between the hydroxyl groups and ester C=O, which is absent in the solid state of the gelators. In addition, π interactions present in the 1,2-dibenzoylated derivative result in a more regular arrangement, which, in turn, leads to better mechanical properties of the gels compared with those of the 1,2-diacetylated gelator.

Full text of DOI:10.1002/chem.201701669

A Journal of
Accepted Article
Title: Partially acetylated or benzoylated arabinose derivatives as
structurally simple organogelators: Effect of the ester protecting
group on gel properties
Authors: Rajkamal Rajkamal, Navendu P Pathak, Tanmoy Halder,
Shubhajit Dhara, and Somnath Yadav
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To be cited as: Chem. Eur. J. 10.1002/chem.201701669
Link to VoR: http://dx.doi.org/10.1002/chem.201701669
Supported by

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Partially acetylated or benzoylated arabinose derivatives as
structurally simple organogelators: Effect of the ester protecting
group on gel properties
[a]
[a]
[a]
[a]
[a]
Rajkamal, Navendu P. Pathak, Tanmoy Halder, Shubhajit Dhara, and Somnath Yadav*
Abstract: Sugar based low molecular weight gelators (LMWGs)
have been used for various applications since long time. In this work,
we report structurally simple, ester protected arabinosides as low
molecular weight organogelators (LMOGs) that are able to gel
aromatic solvents as well as petrol and diesel. Studies on the
mechanical strength of the gels through detailed rheological
experiments indicate that the gels from the 1,2-dibenzoylated
arabinose gelator possesses better mechanical properties than the
and carbohydrates.[19] During gelation, these small molecules
self-assemble into supramolecular structures through a variety
of non-covalent forces such as H-bonding, Van-der-Waal’s
forces, hydrophobic interactions, - stacking, CH- and dipole-
dipole interactions and halogen bonding.[
20-23]
Amongst carbohydrates, many monosaccharide derivatives
are known to be LMWGs, from the widely popular dibenzylidine
sorbitol (DBS) derivative known since a long time; to more
recent ones.[19b]. The design of supramolecular gelators based
on sugars revolve around one of the following basic strategies –
(i) protection of the 4,6-OH groups in the parent hexose sugar as
1,2-diacetylated gelator. These results are interpreted in terms of the
tendency of the former to form fibres with comparatively lower
diameter than the latter; based on detailed FESEM and AFM studies.
Investigation of the interactions responsible for the self-assembly of
gelators through IR and WXRD spectroscopy reveal that the primary
interactions responsible for it is H-bonding between the hydroxyl
groups and the ester C=O which is absent in the solid state of the
gelators. In addition, pi interactions present in the 1,2-dibenzoylated
derivative results in the more regular arrangement which in turn
leads to better mechanical properties of its gels compared to that of
the 1,2-diacetylated gelator.
the
benzylidine[24-26]
(ii)
synthesizing
amphiphilic
monosaccharide derivatives either as glycosides of moieties that
are well known to induce gelation such as steroids, long chains,
and polyaromatic hydrocarbons[
27-29]
or as protecting groups on
(
i) 4,6-O-benzylidine protected sugar based LMWGs
Ar/Ph
O
O
O
OMe/SAr
OH/OP/NHR
PO/HO
Introduction
(ii) Ampiphilic Sugar based LMWGs
Z = Aliphatic chains/
Polyaromatic
hydrocarbons
HO
HO
Low Molecular weight Gelator (LMWG) based gels are a class of
soft materials that have attracted a lot of attention in recent
years due to their wide applications.[1,2] The potential
applications of these gels include stimuli responsive materials[3,4]
O
HO
O
HO
OH
OR/NHR/NR2
OZ
/
aminoacids/ureas/
HO
OH
HO
thioureas
(
including stimuli such as changes in temperature, chemical
(
iii) Acyclic sugar based LMWGs
environment, pH, light, temperature and others), drug delivery
and tissue engineering,[
5,6]
waste water treatment and
OH OH
X
OH OH
[7]
[8]
environmental remediation, optical applications and as self-
healing materials.[3c,9] The LMWGs are based on a wide variety
Ar/R
OH
RN
OH
O
OH OH
OH OH
of compounds ranging from steroids,[10] amino acids and
peptides,[
11,12]
(uronic acid derivatives)
(imino derivatives)
molecules with conjugated -systems and/or
hydrocarbons,[
13,14]
[15]
X = O/N, R = Aliphatic chains/
Polyaromatic hydrocarbons/
aminoacids
polyaromatic
ureas and thioureas,
nucleosides and nucleobases,[16,17] dendrons and dendrimers
[18]
(
iv) "This Work" Simple partially ester protected gelators
[
a]
Dr. Rajkamal, Mr. N. P. Pathak, Mr. T. Halder, Mr. S. Dhara, Asstt.
Prof. Dr. S. Yadav
Department of Applied Chemistry
Indian Institute of Technology (ISM), Dhanbad
Dhanbad, 826004, Jharkhand, India
OCOR
OCOR
OH
HO
O
O
R = CH3, Ph
OH
HO
ROCO
E-mail: s_yadav1975@yahoo.co.in, yadav.s.ac@ismdhanbad.ac.in
OCOR
Figure 1. (i)
monosaccharide based LMWGs and (iv) “This work”
– (iii) Typical structural classes of previously reported
Supporting information for this article is given via a link at the end of
the document
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Chemistry - A European Journal
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one of the hydroxy (or amino) groups[30-31] and (iii) putting
additional hydrophobic/H-bond inducing substituents, that are
known to induce gelation properties, on the acyclic sugar as
imines or aldonic acid esters/amides (Figure 1).[32]
Similarly, the enantiomeric compounds 1a' and 1b' were also
synthesized from L-arabinose.
OH
O
OH
Each of these structural classes of monosaccharide based
gelators present some disadvantages such as the instability of
acetonide/benzylidine protected sugars under acidic conditions,
the requirement of multiple synthetic steps involving protection
and deprotection and the implementation of the stereoselective
glycosylation. The difficulties associated with the selective
protection/deprotection of monosaccharides can be lessened to
some extent by designing gelators based on pentose sugars
which have one less hydroxyl group that requires to be
manipulated. This has been demonstrated previously by us
when we reported an arabinose based supergelator that was
accessible in one single synthetic step.[33] Similarly, we have
also reported triazolyl arabinoside derivatives as phase selective
gelators of petrol, diesel and crude oil.[34] Additionally, amongst
sugars, arabinose based gelators provide the unique opportunity
towards the synthesis of economically feasible enantiomeric
gelators that may be required for chiral applications such as in
asymmetric catalysis and as chiral micro-reactors.[35]
O
(i)
(ii)
O
HO
OH
OH
O
OH
D-Arabinose
2
OR
OR
O
O
O
(iii)
OR
OR
O
O
O
3
a: R = COCH3
b: R = COPh
3
OR
OH
O
HO
O
OR
RO
OH
HO
OR
1
a': R = COCH3
1a:
R = COCH3
1b':
R = COPh
1b: R = COPh
L-Arabinose
In the present work we report simple partially ester
protected arabinose derivatives as LMOGs for aromatic solvents
(
Figure 1). The structurally simple gelators bear minimal and
Scheme 1. Synthesis of gelators 1a and 1b. Reagents and conditions: (i) 2,2-
Dimethoxypropane, p-TSA (catalytic), DMF, RT, 2 h; (ii) Ac O, pyridine, RT, 2
h or Bz O, pyridine, RT, 5 h; (iii).AcOH:H (7:3), 85 °C, 2 h. L-arabinose
simple protecting groups and are easily synthesized in three
simple steps. Two types of ester groups, viz. acetate and
benzoate have been explored for the gelation ability. Significant
differences in the mechanical properties have been found for the
two gels through rheological studies. Again, the structural
simplicity of the protecting groups have enabled detailed
mechanistic studies to probe the interactions responsible for
self-assembly mechanism leading to the variation of their
mechanical properties.
2
2
2
O
derivatives 1a’ and 1b’ were synthesized similarly.
Gelation properties
Initial gelation experiments using 1a and 1b revealed that they
were able to gel several aromatic solvents (Table 1) as well as
petrol and diesel. The gelation tests were performed by the
simple inversion test. For this the required amount of the gelator
in 1 mL of any solvent was taken in a capped vial and then
heated till the compound completely dissolved. Then the vial
was set aside to cool. In all the cases of the successful gelation,
it occurred almost instantly which was observed by inverting the
vial, wherein, the material was able to hold its own weight.
Other solvents were also tested but both 1a and 1b were unable
to congeal them.
Results and Discussion
Synthesis and structure of the gelators
We synthesized the gelators D- or L-1a and D- or L-1b from
commercially available D- or L- arabinose in three simple steps
(
Scheme 1). First, the D- or L- arabinose was converted to the
monoacetonide D- or L- 2 by reacting with 2,2-dimethoxy
propane using catalytic p-TSA, following a previously reported
procedure.[28,31] The exclusive -nature of the monoacetonide in
the 4C1 conformation, as reported by Kiso[36] and others, was
confirmed by its 1H-NMR spectra. Diacetylation of 2 using acetic
anhydride and pyridine in the presence of catalytic
The Minimum Gelation Concentrations (MGC) for all the
solvents was 0.3% (w/v) for both 1a and 1b as well as 1a' and
1b'. Experiments to explore the variation of the gel-sol transition
[37]
g
temperature T with the concentration of the gelator revealed
that the thermal stability of the gels could be increased by
increasing the gelator concentration (Figure 2). The thermal
reversibility of the gels was also evident from heating cooling
cycles which showed that the gels were thermally reversible up
to more than 10 heating-cooling cycles. Also, the gels were
stable up to many months under conditions to prevent loss of
solvents through evaporation.
Dimethylaminopyridine (DMAP) converted
2
to the 3,4-
isopropylidine-1,2-diacetate derivative 3a. The conversion of 3a
to the compound 1a was carried out by treatment of the former
with acetic acid and water. Similarly dibenzoylation of 2 using
benzoic anhydride and pyridine followed by removal of the
acetonide
gave
the
corresponding
1,2-dibenzoyl
A very interesting property of the gelators was also observed
when the gelation was studied with racemic mixtures of the 1a
and 1b. Unlike the pure enantiomers, the racemic mixtures
arabinopyranoside 1b as the -anomer in the 1C4 conformation.
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Table 1. Gelation abilities of compounds 1a and 1b.
Solvent
Benzene
Toluene
1a,[a] (MGC, T
g
)
1b, (MGC, T
g
)[b]
G, (0.3%, 53-54 °C)
G, (0.3%, 51-52 °C)
G, (0.3%, 51-52 °C)
G, (0.3%, 52-53 °C)
o-xylene
G, (0.3%, 48-49 °C)
G, (0.3%, 57-58 °C)
m-xylene
p-xylene
G, (0.3%, 49-50 °C)
G, (0.3%, 56-57 °C)
G, (0.3%, 51-52 °C)
G, (0.3%, 55-56 °C)
Chlorobenzene
Hexane
G, (0.3%, 47-48 °C)
G, (0.3%, 48-49 °C)
PG
PG
Dichloromethane
Chloroform
Ethyl acetate
Acetonitrile
Methanol
n-butyl alcohol
Amyl alcohol
DMF
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
DMSO
S
S
Figure 2. Variation of Gel-sol transition temperature (T
gelator (a) 1a; (b) 1b.
g
) with concentration of
Water
S
S
Petrol
G, (0.2%, 56-57 °C)
G, (0.2%, 55-56 °C)
G, (0.2%, 55-56 °C)
G, (0.2%, 58-59 °C)
summary of the results are presented in Table 2. From the DSS
experiments, values of  were obtained. The value  represents
the strain at which the storage modulus (G') becomes equal to
the loss modulus (G″) and represents the limiting strain beyond
which the material behaves more like a fluid than a viscoelastic
solid. For any particular solvent, comparison of the values of
shows that in general 1b was able to form gels that are more
resistant to strain than the gels from 1a as indicated by the
higher values of  for the former. From the DFS experiments,
plots of the linear viscoelastic range of the gels and the values of
the ratio of the loss modulus (G″) to the storage modulus (G'), in
the linear viscoelastic region, represented by tan , were
obtained. As can be seen in Table 2, the tan values any
particular solvent was lower for the gels from 1b than that of the
gel from 1a, indicating that 1b formed stronger gels than 1a for
the solvent.
Diesel
[
a] G = Gel, PG = Partial Gel and S = Solution; [b] MGC (Minimum Gelation
Concentration) are presented as % (w/v).
obtained by mixing equal amounts of the D- and L- isomers were
unable to gel any of the aromatic solvents. Such an unique
property of arabinose based gelators has also been observed
before.[33,34] Another interesting feature of the gels was their
stability under exposure to ultrasound and UV-light. Many
organogels from LMOGs have been reported to be responsive to
ultrasound, UV-light. The stability of the gels from 1a and 1b to
ultrasound therefore could be a useful property with potential for
applications in the presence of ultrasound and UV-radiations
such as micro-reactors for chemical reactions.
Mechanical properties of the gels.
Morphological studies through FESEM and AFM.
To study their response to mechanical stress, oscillatory
rheological studies of the organogels from both 1a and 1b were
performed at uniform concentration of 1% (w/v). Two types of
experiments were carried out for each of the gels viz. the
Dynamic Strain Sweep (DSS) experiments and the Dynamic
Frequency Sweep (DFS) experiments. The graphs obtained
from the rheological experiments are presented in the
accompanying Supporting Information (Figures S3-S17) and the
To rationalize the mechanical properties of the gels obtained
through rheological experiments, the detailed FESEM and AFM
experiments were carried out in order to reveal the
microstructure of the gels. From the micrographs obtained
(Figures S18 to S33, Supporting Information), it could be
generally concluded that the gelators self-assembled to form
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From the AFM image of 1b gel, fibres of approximate diameter
25 – 32 nm were measured (Figure 3c). It is well known that the
Table 2. Summary of the rheological properties of the organogels from 1a and 1b.
mechanical properties of fibre based materials are strongly
dependant on the fibre diameter – the smaller the diameter,
Organo- Solvent
gelator
 (%)
G' (Pa)[a]
G″ (Pa)[b]
tan  [c]
better are the mechanical properties.[38] It can be also concluded
x 10-
2
x 103
x 103
that the ribbon like structures observed in the FESEM images
were formed through aggregation of the smaller fibres that were
observed in AFM image.
Benzene
Toluene
o-xylene
m-xylene
5.99
38.62
36.62
61.40
26.40
12.22
13.40
6.29
14.93
12.90
25.10
7.09
0.38
0.35
0.41
0.27
0.31
0.39
0.45
0.46
0.24
0.18
0.18
0.14
0.10
0.20
0.24
0.16
2.96
16.93
6.54
(
a)
(b)
1a
p-xylene
PhCl
14.50
5.56
3.80
4.805
2.82
Petrol
52.43
50.31
35.8
Diesel
0.931
3.58
0.411
0.876
0.211
0.315
0.975
1.468
4.283
1.96
Benzene
Toluene
o-xylene
m-xylene
p-xylene
PhCl
(
d)
(
c)
50.10
25.30
25.91
20.82
11.73
70.83
62.34
1.35
1.73
7.30
1b
13.80
22.50
0.866
0.377
Petrol
Diesel
0.60
Figure 3. AFM images of the m-xylene organogels. (a) 2-D image of
organogel from 1a; (b) 3-D image of organogel from 1a; (c) 2-D image of
organogel from 1b; (d) 3-D image of organogel from 1b.
[
a] G' = Storage modulus; [b] G″ = Loss modulus; [c] tan  = G″/G'.
Mechanism of the self-assembly of the gelators
dense, fibrillar, entangled networks resulting in gelation of the
solvents. Also, from the micrographs of the gels from compound
The self-assembly of the gelators occurred through the strong H-
bonding between the free hydroxyl groups and the carbonyl of
the acetates or the benzoates to yield 1-dimensional fibres
which further underwent crosslinking to generate the 3-D
network. The involvement of H-bonding in the self-assembly
process was proven by FTIR studies (Figure 4). In the FTIR
spectra the peak for the OH groups at 3345 cm-1 (suggesting
strong H-bonding) in the crystalline powder state of 1a shifted to
1a it was observed that that the fibres in benzene, toluene, m-
xylene and chlorobenzene gels were much thicker than those of
o-xylene and p-xylene. Again the fibers from the xerogels of
petrol and diesel showed much more cross-linking which led
resulted in the formation of stronger gels. The micrographs for
the xerogels from compound 1b showed the formation of
collapsed ribbon like structures compared to those from 1a.
Once again, the stronger natures of the petrol and diesel gels
from 1b were justified by the observation of more extensively
cross-linked fibres.
3
354 cm-1 in the benzene gel (Figure 4a). The blue shift
indicates the weaker H-bonding in the gel state compared to the
crystalline state The involvement of the C=O in the H-bonding
during self-assembly was also proven by the red shift in the
carbonyl absorption from 1738 cm-1 (typical of a non-H-bonded
ester C=O) in the solid state to 1729 cm-1 in the gel state
These observations were further confirmed by Atomic Force
Microscopy (AFM) experiments of the m-xylene gels of 1a and
1b which offered better visual insight into the morphologies of
(
benzene). Taken together, the IR absorption data suggest that,
the gels (Figure 3). High resolution 3D images to study the
surface topography obtained by AFM showed a series of
mountain like 3D images for both the gels from both 1a and 1b
while in the solid crystalline powder state, the H-bonding
interactions are present purely between the OH groups, in the
gel state, the gelator 1a self-assembles through additional H-
bonding interactions between the OH and the C=O groups. In
(
Figures 3b and 3d). From the 2-D image of 1a gel, the diameter
of the individual fibres was measured to be 50 – 65 nm and
aggregation through intertwining was also observed (Figure 3a).
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Figure 4. IR spectra. (a) Crystalline solid state and benzene gel of 1a; (b) Crystalline solid state and benzene gel of 1b; (c) ) Crystalline solid state and hexane gel
of 1b.
case of 1b the initial OH stretching frequency at 3317 cm-1 in the
solid state was blue shifted to 3394 cm-1 in the benzene gel state
proving H-bonding. Again, the C=O stretching frequency at 1724
cm-1 present in the crystalline state (typical of a non-H-bonded
conjugated ester) was also present in the benzene gel. However,
an additional broad peak appeared as a shoulder at 1695 cm-1 in
the latter, clearly indicating the involvement of the C=O in the
self-assembly process. This also suggests that it is probably
only one of the two benzoyl groups that actually takes part in the
H-bonding. Further confirmation of the  interactions of the
phenyl group during self-assembly of 1b could be obtained from
its hexane gel. Whereas, in the pure solid, the aromatic C=C
under the same conditions. This in turn is due to the involvement
of H-bonding as well as  interactions in the former compared to
the latter where the self-assembly is only due to H-bonding.
These gels are stable under ultrasound and photochemical
irradiation, which could be useful for carrying out reactions in
these media, a work that is being pursued presently. Again,
applications of the gelators towards oil-spill remediation through
phase selective organogelation of crude-oil is also being
pursued at present.
Experimental Section
-
1
stretching appeared as a single peak at 1440 cm , in the
hexane gel two peaks corresponding to 1464 cm-1 and 1441 cm-
1. Gelation tests
1
appeared; indicating  interactions in the gel state (Figure 4c).
This additional -interaction during self-assembly of gelator 1b is
therefore, responsible for the stronger nature of its gels
compared to the 1a gels where only H-bonding interactions are
present.
The more organized structure of the self-assembled 1b
was also evident from the WXRD spectra of the corresponding
xerogels (Figures S34 and S35, Supporting Information). While
both the diffractograms showed periodic peaks, the number of
peaks for the 1b xerogel were fewer than that in the spectra of
the xerogel of 1a indicating better organization and self-
assembly.
Gelation test were carried out by adding exact weights of compounds 1a
or 1b individually to 1 ml of appropriate solvent in a vial. The vial was
sealed and the suspension was heated to dissolve the compound
providing a clear solution. It was then allowed to cool after which gelation
was tested by inverting the sample vial. If the inverted vial was able to
hold the system, it was considered as a gel.
2. Determination of the minimum gelation concentration (MGC)
1
ml of solvent was taken in 5 ml of sample vial, 1 mg of gelator 1a or 1b
was added to the solvent which was then heated till a clear solution was
obtained. Then the solution was cooled and the vial inverted to confirm
gelation. If partial or no gelation was observed, the cycle was repeated
adding 1 mg of 1a or 1b at the beginning of each heating cooling cycle till
complete gelation of the solvent was observed by inversion of the vial.
Conclusions
3
. Rheological experiments
In conclusion, this work reports two synthetically simple sugar
based super-organogelators that involve partially ester protected
arabinose moiety. The structural simplicity of the gelators implies
that they have very few kinds of interaction that results in the
self-assembly during gelation. Rheological characterizations of
the gels indicate that the gels from the dibenzoylated arabinose
gelator is mechanically more robust than the diacetylated
arabinose gelator. Spectroscopic studies revealed that the
increased mechanical strength of the latter is due to the
presence of thicker and more extensively cross-linked fibres
Rheological properties of gel sample were determined by using a Bohlin
Gemini-2 Malvern rheometer using parallel plates (25 mm, stainless
steel). The gap between the parallel plates was 500 micron. The
experiments were carried out for either of compounds 1a or 1b at 1%
(w/v) concentration. The gel samples were placed on parallel plates by
spatula in such a way that it covered the surface of the parallel plates.
The different tests Dynamic strain sweep (DSS) and Dynamic Frequency
sweep (DFS) were performed to determine the viscoelastic nature of the
gels. DSS experiment were carried out at a constant frequency of 1 Hz at
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Chemistry - A European Journal
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temperature 25 °C. The strain value was determined at a point where tan
[5]
For reviews see
-
a) X. Du, J. Zhou, J. Shi, B. Xu, Chem.

= 1 (G″ > G'). Variation of storage modulus (G') and loss modulus (G″)
Rev., 2015, 115, 13165–13307; b) K. J. Skilling, F. Citossi, T. D.
Bradshaw, M. Ashford, B. Kellama, M. Marlow, Soft Matter 2014, 10,
237-256; c) K. Rehman, M. H. Zulfakar, Drug Dev. Ind. Pharm. 2014,
was tested within frequency range of 1Hz to 100 Hz at strain of 0.001 %
by DFS experiments.
4
0, 433-440.
a) R. Parveen, B. Sravanthi, P. Dastidar, Chem. Eur. J., 2017, 23, 792-
03; b) M. -T. Popescu, G. Liontos, A. Avgeropoulos, E. Voulgari, K.
Avgoustakis, C. Tstsilianis, ACS, Appl. Mater. Interfaces, 2017, 8,
[6]
4. Field emission scanning electron microscopy (FESEM)
8
The experiments were performed by using a Zeiss supra-55 FESEM. The
xerogels of the samples were prepared by drop-casting a hot 1% (w/v)
solution of gelator 1a or 1b in gelling solvent on a glass slide (2mm x
1
7539-17548; c) R. Roy, P. Dastidar, Chem. Eur. J., 2016, 22, 14929-
4939; ; d) K. Nagy-Smith, Y. Yamada, J. P. Schneider, J. Mater. Chem.
1
B, 2016, 4, 1999-2007; e) R. Parveen, P. Dastidar, Chem. Eur. J., 2016,
2, 9257-9266; e) K. Basu, A. Baral, S. Basak, A. Dehsorki, J. Nanda,
2mm) and drying them overnight in air inside a vacuum dessicator. The
2
xerogel was then placed on a stub which was then coated with gold by a
Quorum -Q150RES sputter coater under vacuum of 5 x 10-5 millibar and
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Keywords Gels • Carbohydrates • Self-assembly •
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Partially acetylated or benzoylated
arabinose derivatives as structurally
simple organogelators: Effect of the
ester protecting group on gel
properties
Structurally simple partially acetylated or benzoylated arabinose derivatives are
reported as gelators. The reasons for the greater mechanical robustness of the
former compared to the latter is investigated and reported.
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