Boc-Protection on L-DOPA: an Easy Way to Promote Underwater Adhesion

Article abstract of DOI:10.1002/ejoc.202001264

The ability of mussels to adhere to underwater surfaces has attracted a lot of attention from the scientific community. As proteins containing L-DOPA (3,4-dihydroxyphenyl-l-alanine) are involved in their adhesion, a common strategy to synthesize adhesives

Full text of DOI:10.1002/ejoc.202001264

European Journal of Organic Chemistry
Accepted Article
Accepted Article
Title: Boc-protection on L-DOPA: an easy way to promote underwater
adhesion
Authors: Claudia Tomasini, Demetra Giuri, Kiran A. Jacob, and Paolo
Ravarino
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202001264
Link to VoR: https://doi.org/10.1002/ejoc.202001264
01/2020

10.1002/ejoc.202001264
European Journal of Organic Chemistry
FULL PAPER
Boc-protection on L-DOPA: an easy way to promote underwater
adhesion
Demetra Giuri,[a] Kiran A. Jacob,[a] Paolo Ravarino,[a] Claudia Tomasini *[a]
[a]
Ms. D. Giuri, Mr. K. A. Jacob, Mr. P. Ravarino, Prof. Dr. C. Tomasini
Dipartimento di Chimica “Giacomo Ciamician”
Alma Mater Studiorum Università di Bologna
Via Selmi 2, 40126 Bologna - Italy
E-mail: claudia.tomasini@unibo.it
https://site.unibo.it/peptide-foldamers-materials-lab/en
Supporting information for this article is given via a link at the end of the document.
Abstract: Mussels’ ability to adhere to underwater surfaces has
attracted a lot of attention from the scientific community. As proteins
containing L-DOPA (3,4-dihydroxyphenyl-L-alanine) are involved in
mussels’ adhesion, a common strategy to synthesize adhesives is
the incorporation of this amino acid into other compounds. Here we
report a study on four compounds of the family of Bocx-(L-DOPA)n-
OMe (x = 1-3; n = 1,2), that we prepared through simple synthetic
steps. Three of them showed the capability of underwater adhesion:
while they are not adhesive in the dry phase, the adhesiveness is
triggered when the dried sample is immersed in water or any
aqueous solutions. The introduction of protecting groups stabilizes L-
DOPA, preventing the oxidation of the catechol moiety and
enhances the hydrophobicity, helping the removal of water from the
surface to bind. These molecules show good adhesiveness, with
different properties, so they may be all used as adhesives for
different purposes. These outcomes pave the way for new set of
applications for these materials as green and biocompatible
adhesives.
binding to the surface.[2,6,8,9] Moreover, DOPA can efficiently
remove the layer of water and ions which generally covers
hydrophilic submerged surfaces, while tyrosine, lacking of
catechol group, cannot.[3,10]
Figure 1. (A) The mussel byssus. (B) To make a new thread, the foot emerges
from the living space within the mussel shell and touches a surface. (C) Three
gland clusters – phenol, collagen and accessory glands – synthesize and
stockpile specific byssal proteins. (D) Schematic representation of the
distribution of known proteins in the byssal plaque and distal thread. (E)
Sequence of Mfp-5 from Mytilus edulis, showing the prominence of DOPA (Y-
methyl catechol), Lys (K), Ser (S) and Gly (G). (F) Sequence of Mfp-6 from M.
californianus with abundant Cys (C), Arg (R) and Lys (K), Gly (G) and Tyr (Y).
Color key: Tyr/Dopa (blue), cationic side chains (red), anionic side chains
including phosphoSer (green) and thiols (purple). Reproduced from ref. [3] with
kind permission of The Company of Biologists Ltd.
Introduction
When it comes to underwater adhesion, shellfish are the true
experts.[1] Marine organisms’ mechanism of adhesion has been
largely studied and inspired the production of a huge number of
synthetic adhesives for underwater purposes. Over the last few
decades, the Mytilus edulis (blue mussels) attracted much
attention for its ability to secrete the byssus.[2,3] Mussels use the
byssus, a protein-based adhesive, for securing themselves to
various underwater surfaces, such as sea rocks and ship hulls,
and resist detachments even in marine’s harsh and wavy
conditions.[4,5] The byssus consists of a bundle of threads
composed by three parts: the adhesive plaque, the rigid distal
thread and the flexible proximal thread. The byssal thread is
composed by the mussel foot, which is the flexible part
responsible for the adhesion on the target surface. So far,
roughly 25-30 different mussel foot proteins (mfps) have been
identified in byssus, 5 of them (mfp-2 to mfp-6) being unique to
the plaque (Figure 1).[3,4,6] Mfp-3 and mfp-5 are considered the
main responsible for the adhesion of the plaque to the surface;
they contain a particularly high amount (up to 30 mol%) of the
post-translationally modified tyrosine to 3,4-dihydroxyphenyl-L-
alanine (L-DOPA).[7] For this reason, it is widely believed that
DOPA, and especially its catechol group, has a dominant role in
DOPA is related to a variety of different adhesion mechanism,
not fully understood yet, involving hydrogen bonding, metal-
oxide coordination, cation-π and hydrophobic interactions, all
depending also on the characteristics of the surrounding
environment (such as pH, ions concentrations, material of the
surfaces to attach).
In the preparation of synthetic adhesives inspired to mussels,
the incorporation of DOPA, catechol groups or other hydrophilic
moieties is a common strategy, to overcome the interactions of
water with the surface and to provide cohesive forces to the
adhesive.[8,11–14] The role of hydrophobic groups in the removal
of water has not been exploited likewise in designing underwater
adhesives. It is worth noticing that in water the adhesive forces
1
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10.1002/ejoc.202001264
European Journal of Organic Chemistry
FULL PAPER
required to separate two hydrophobic surfaces are very high,
even higher than the adhesive forces necessary to separate
mfps from model mica surfaces,[15] and it is also much easier to
remove water from two hydrophobic than hydrophilic
surfaces.[16,17] The design of adhesives which include
hydrophobic groups is likely to improve adhesion in wet
environments, as recently reported.[18–22] In sea water DOPA is
susceptible to oxidation to DOPA-quinone, which cannot form
hydrogen bonds with surfaces and has lower adhesive
properties. In mussels, DOPA oxidation tendency is limited not
only by tautomerization of DOPA-quinone to α,β-dehydro-DOPA
(restoring the possibility to form hydrogen bonds), but also by
the presence of nonpolar amino acids located close to DOPA.[8]
Because of their unique wet adhesive properties, mussels
inspired adhesives are interesting for several applications, but
have recently attracted lot of attention especially in the
biomedical and tissue engineering field, as surgical glue or drug
delivery systems.[6,23] For these purposes,
a systematic
understanding of the behaviour, stability and adhesion
mechanisms of these compounds is necessary.
In this work, a family of Bocx-L-(DOPA)n-OMe (Boc = t-
butyloxycarbonyl; Me = methyl; x = 1-3; n = 1,2) molecules was
synthesised. The number of Boc groups was progressively
increased, substituting one or both -OH in the catechol group
and compared with the dimer molecule, Boc-(L-DOPA)2-OMe,
having all the catechol groups free. These compounds were
used to form films that were tested through tack test, in order to
understand how the introduction of nonpolar groups and the
increase in the hydrophobicity of the molecules could affect their
adhesive properties. The production of these films is of great
interest for the production of highly biocompatible adhesives that
may find applications as wound closure materials or as carrier of
bioactive compounds.[24–26]
Figure 2. Chemical structure of the derivatives of L-DOPA described in this
work.
The preparation of Boc2-L-DOPA-OMe
2 implied several
problems, due to the presence of the two hydroxyl groups of the
catechol moiety (Scheme S2). The selective introduction of a
single Boc group on the ring was difficult, even though several
different procedures were tested. In any case, Boc2-L-DOPA-
OMe was always obtained as an inseparable mixture of meta
and para protected regioisomers m-2 and p-2 (Figure 2) in about
a 1:1 ratio, together with little amounts of Boc-L-DOPA-OMe 1
and/or Boc3-L-DOPA-OMe 3 (Figure S2). The best result was
achieved by reaction of Boc-L-DOPA-OMe
1
with
a
stoichiometric amount of Boc2O and NaHCO3 in water and THF,
with a final yield of about 60% after purification by flash
chromatography. Curiously, the direct preparation of Boc2-L-
DOPA-OMe 2 from L-DOPA-OMe∙HCl did not afford the same
results. The presence of two regioisomers m-2 and p-2 could be
checked only by 1H NMR (Figure S2) as they are inseparable by
LC-MS analysis.
In contrast, the preparation of the fully protected Boc3-L-DOPA-
OMe 3 was selectively obtained in excellent yield by reaction of
Boc-L-DOPA-OMe 1 with two equivalents of Boc2O, in presence
of DMAP (4-(dimethylamino)pyridine) in acetonitrile (Scheme
S3).[29]
With the increase of the number of Boc groups, the molecules
polarity and hydrophilicity are strongly modified, as Boc-L-
DOPA-OMe 1 is far more hydrophilic than the fully protected
Boc3-L-DOPA-OMe 3. The hydrophilicity variation may be
proved with the analysis of the contact angles between thin
layers of molecules 1, 2 or 3 and an aqueous medium.[30]
To carry out the test, a small amount of the sample is deposited
as ethyl acetate solution on a glass slide of an optical
tensiometer just enough to cover the entire surface. After the
solvent evaporation, we measured the contact angles obtained
with three media: MilliQ water, 1M CaCl2 aqueous solution and a
phosphate-buffered salin (PBS) solution at pH = 7.4, which is
commonly used to imitate the property of the body fluids.
Several examples of formation of three dimensional networks
among peptides and Ca2+ ions have been reported,[31–34] and the
Results and Discussion
We prepared Boc-L-DOPA-OMe
1
(methyl (S)-2-((t-
butoxycarbonyl)amino)-3-(3,4-dihydroxyphenyl)propanoate),
Boc2-L-DOPA-OMe 2, as a 1:1 inseparable mixture of the meta-
protected m-2 (methyl (S)-2-((t-butoxycarbonyl)amino)-3-(3-((t-
butoxycarbonyl)oxy)-4-hydroxyphenyl)propanoate) and the para-
protected p-2 (methyl (S)-2-((t-butoxycarbonyl)amino)-3-(4-((t-
butoxycarbonyl)oxy)-3-hydroxyphenyl)propanoate) isomer and
Boc3-L-DOPA-OMe
3
(methyl
(S)-3-(3,4-bis((t-
butoxycarbonyl)oxy)phenyl)-2-((t-butoxycarbonyl)amino)
propanoate) by modification of commercially available L-DOPA
(Figure 2). The first step was the preparation of the molecules
containing an increasing number of Boc protecting groups. The
protection of the primary amine is selective, yet the hydroxyl
groups on the catechol are reactive too towards this reaction
and a mixture of compounds 1, 2 and 3 is obtained in presence
of wide amount of Boc2O. For this reason, we found selective
preparations for the three compounds.
Boc-L-DOPA-OMe 1 is obtained by methylation of commercially
available L-DOPA, followed by the selective protection of the
nucleophilic primary amine group, according to a reported
procedure (Scheme S1).[27,28]
2
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10.1002/ejoc.202001264
European Journal of Organic Chemistry
FULL PAPER
presence of DOPA enhances this effect, as it has the ability to
chelate Ca2+ ions.[28,35–37]
former position (detachment phase) it registers a negative force.
In any case, the absolute value should be taken.
The values of the contact angles under the different conditions
are reported in
Both Boc2-L-DOPA-OMe 2 and Boc3-L-DOPA-OMe 3 behave
quite differently from Boc-L-DOPA-OMe 1. In fact, 2 and 3 reach
the maximum scale of the rheometer at 50 Newton, while 1
shows no adhesion at all. Moreover, the films of 3 completely
detach from the petri dish at the end of the experiment and
attach to the shaft (Figure 5). The film on the shaft is brittle in
nature and breaks into small pieces by touching. This behavior
prevents the film multiple use.
Table 1 and shown in Figures S3-S5.
Table 1. Contact angles of dried surface of 1, 2 (m-2 + p-2) and 3 with the
aqueous solutions listed below.
H2O
CaCl2 1M
PBS pH 7.4
54.7±3.9°
78.2±2.0°
94.0±0.5°
58.0±1.8°
63.7±1.0°
81.1±1.7°
49.9±1.0°
76.6±5.4°
84.0±1.1°
1
2
3
As we could foresee, there is a continuous increase of the
contact angle going from 1 to 3, although this effect is more
evident in MilliQ water. The adhesion efficiency can be linked to
the hydrophobicity of the molecule, thus to the contact
angle.[18,38]
Materials that are tacky or sticky are easily identified by touch,
however, quantify tack is not straightforward. The formation of
the adhesive bond is not directly measured but assessed by
breaking bonds by means of tack tests.[39] To evaluate the ability
of films of 1, 2 and 3 to adhere to a solid surface when brought
into contact by a very light pressure, we performed tack tests
using a rheometer.
Figure 4. Rheometer tack tests for molecules 1, 2 and 3 in water.
To prepare the films, 20 mg of each molecule were dissolved in
ethyl acetate (1 mL) and poured in a 25 mm glass petri dish
(deposition area = 490.6 mm2) previously fixed on a disposable
aluminium plate for rheometer. After solvent evaporation, 1 mL
of MilliQ water was added on the top of the dry layer, covering
the whole surface (Figure 3).
Figure 5. Adhesive film of 3 after the tack test.
The adhesive properties of films of 1, 2 and 3 were tested also in
1M CaCl2 aqueous solution and in PBS solution at pH = 7.4. To
test 1, we used the rheometer under the same conditions
previously reported for the analysis in MilliQ water: 1 behaves in
the same way in the three media, in agreement with the analysis
of the contact angles which range between 50° and 58° (Figure
S6).
As the rheometer tack tests for 2 and 3 reached the upper limit
of the instrument sensitivity, we analysed the adhesive
properties of films of 2 and 3 with traction tests, using an Instron
4465 testing system, as it has a wider measuring capacity, up to
5 kN load cell, although with a reduced sensitivity. The tests
were carried out with a 100 N load cell. In order to have a good
comparison, we tested the behavior of 2 and 3 in the three
aqueous media.
Figure 3. Procedure for the preparation of the films of 1, 2 and 3 to test their
adhesive properties.
Films of 1, 2 and 3 are not adhesive in the dry phase, the
adhesiveness is generally triggered when the dried sample is
immersed in water or any aqueous solution. Adhesion in humid
conditions is a fundamental challenge to both natural and
synthetic adhesives. Yet some glues from different biological
systems appear to enhance their performances with increasing
humidity.[40]
To perform the tack test, 25 N force is applied from the
rheometer shaft for 5 mins. The experiment was conducted at a
crosshead speed of 50 μm/s (3 mm/min). All measurements
were repeated at least three times (Figure 4). When the shaft
applies a compression force on the sample, the instrument
registers a positive force on the graph; while going back to its
The mechanical analysis of the films of 2 and 3 are summarised
in Figure 6.
3
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10.1002/ejoc.202001264
European Journal of Organic Chemistry
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To check the adhesive properties of the films produced by
deposition of 4, we measured the contact angles as we
previously reported with the three aqueous media (Table 2 and
Figure S7).
Boc2-L-DOPA-OMe, 2
Boc3-L-DOPA-OMe, 3
129.7 16.8
140
120
100
140
120
100
82.3 13.6
76.3 20.7
Table 2. Contact angles of dried surface of 4 with the aqueous solutions listed
79.4 5.5
80
71.6 5.4
80
60
40
20
0
below.
60
40
20
0
44.6 8.3
Solvent
Boc-(L-DOPA)2-OMe 4
Water
CaCl2 1M
PBS
CaCl2 1M
Water
PBS
H2O
69.3±2.5°
71.2±2.2°
67.7±3.9°
Figure 6. Results for traction tests performed on films of 2 (left) and 3 (right)
with an Instron 4465 testing system. Samples were prepared using the same
geometry (petri dish with 25 mm of diameter), deposition method and addition
of the triggers used for tack tests. All experiments were repeated at least three
times.
CaCl2 1M
PBS pH 7.4
The measured contact angles range between 67.7° and 71.2°.
This positive outcome encouraged us to record the tack tests of
the films in the three media, using the same technique that we
previously described (Figure 8 and Table 3).
From the tack test in the three media, it is very clear that the
application of CaCl2 solution has a strong impact on the
adhesive property of the molecule, compared with both the PBS
solution and MilliQ water.
Among them, the most intriguing material is the film of 2, that
shows good adhesiveness and good resistance to use. In fact,
its adhesiveness is remarkable if compared with the tack
strengths of already reported polymers containing DOPA.[41,42]
When the traction test for 2 was performed in a 1M CaCl2
solution, the instrument could not detach the cell from the
sample, meaning that the necessary force was higher than 100
N, the maximum force for that cell. For this reason, this
experiment was repeated using a 1 kN load cell and an average
value of 129.7 ± 16.8 N was measured. Unfortunately, this
material is obtained by deposition of an inseparable mixture of
m-2 and p-2, so the deposition on the glass surface cannot be
controlled. It is difficult to control the effective ratio and the
behavior of the two components and the exact 1:1 ratio in any
sample is not guaranteed.
Table 3. Rheometer average values and standard deviations for compound 4
in the different aqueous media.
Solvent
4, Normal Force (N)
In contrast, Boc3-L-DOPA-OMe 3 is a pure compound and has
high adhesiveness as it ranges between 76.3 and 82.3 N in all
the media, showing the best results in water. These adhesive
values are higher compared to what reported in literature for
more complex polymeric systems.[41,42]
With the aim of finding another molecule of the same family
having good properties and high reproducibility, we synthesized
another compound, Boc-(L-DOPA)2-OMe 4 (methyl (S)-2-((S)-2-
((t-butoxycarbonyl)amino)-3-(3,4-dihydroxyphenyl)
H2O
16.4 ± 4.9
46.7 ± 5.8
15.4 ± 0.8
CaCl2 1M
PBS pH 7.4
propanamido)-3-(3,4-dihydroxyphenyl)propanoate) (Figure 7).
The preparation of this molecule was suggested by the strong
adhesive properties of oligomers containing more than one
catechol group.[43–45]
Boc-(L-DOPA)2-OMe
20
10
0
-10
-20
-30
-40
-50
-60
CaCl2
PBS
H2O
0
5
10
15
20
Figure 7. Chemical structure of the derivative of Boc-(L-DOPA)2-OMe 4.
Time (s)
Boc-(L-DOPA)2-OMe 4 was prepared through some easy steps
in good yield starting from the already described Boc-L-
DOPA(OBn)2-OMe (Scheme S4).
Figure 8. Tack tests for Boc-(L-DOPA)2-OMe 4 in the three aqueous media.
4
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10.1002/ejoc.202001264
European Journal of Organic Chemistry
FULL PAPER
Boc-(L-DOPA)2-OMe in 1 M CaCl2
It is interesting to notice how for these molecules the increase in
adhesive forces and contact angle values can be nicely
correlated to the number of Boc groups substituting the catechol
in all the aqueous media tested (Figure S8). The increased
adhesion of compound 4 compared to the monomer 1 may be
yet ascribed to the additional catechol group.[8]
To verify and to quantify the multiple use properties of films of 4,
we repeated the tack test on the same sample for three times in
1M CaCl2 aqueous solution, that is the medium where the films
showed the most promising properties (Table 4). These
measures were not executed for films of 2 and 3, as we could
not use the rheometer, which has more reliability than the
Instron in terms of sensitivity and reproducibility.
a)
20
10
0
-10
-20
-30
-40
-50
-60
1
2
3
0,0
0,5
1,0
1,5
2,0
2,5
Time (s)
Table 4. Rheometer values of the multiple adhesion trials for compound 4 in 1
Boc-(L-DOPA)2-OMe in 0.1 M CaCl2
b)
20
M and 0.1 M CaCl2 solutions.
10
0
Trial
Normal Force (N)
1M CaCl2
Normal Force (N)
0.1M CaCl2
-10
-20
-30
-40
-50
-60
1
2
3
50.0
48.4
41.4
43.8
32.0
26.1
1
2
3
The repeated tests were done on the same sample with the
same parameters, except the enhanced crosshead speed at
which the shaft moves up for the test (1000 m/s or 60 mm/min),
to check the behavior of the material under these conditions
(Figure 9a).
0,0
0,5
1,0
1,5
2,0
2,5
Time (s)
Figure 9. Repeated tack tests for Boc-(L-DOPA)2-OMe 4: (a) in 1M CaCl2
aqueous solution; (b) in 0.1M CaCl2 aqueous solution
The results reported in Figure 9a clearly show that the film of 4
exhibits repeated adhesiveness even though the adhesive
strength is slightly decreased in each trial. This result
demonstrates the strong resistance against destructive effect of
water, which often adversely influences the strength of
adhesiveness.[10,46–48] Moreover, an increase in the crosshead
speed results in a faster detachment of the shaft from the
adhesive film (from 14 s to 2 s) but does not affect the maximum
force required. We repeated the tack test under the same
conditions using a 0.1M CaCl2 aqueous solution, to check the
effect of the variation of concentration of Ca2+ ions (Figure 9b).
Under these conditions, the adhesive strength decreases in
each trial more than in 1M CaCl2, and in general the values are
intermediate between the results obtained in water and 1M
CaCl2 (Figure 8). This outcome is in agreement with the
previously reported high affinity of the catechol moiety with Ca2+
ions:[31–37] when the Ca2+ ions concentration decreases, the film
efficiency for repeated measurements decreases accordingly.
Conclusion
In this work, a family of four L-DOPA based compounds were
synthesized and their adhesive properties were tested. Three of
them showed the capability of underwater adhesion: while they
are not adhesive in the dry phase, the adhesiveness is triggered
when the dried sample is immersed in water or any aqueous
solutions. The introduction of protecting groups on the catechol
moiety not only stabilizes the compounds inhibiting the oxidation,
but also increases the hydrophobicity of the compounds
analysed. Molecules 2, 3 and 4 have different properties, so they
all may be used as adhesives for different purposes:
- Boc2-L-DOPA-OMe 2 films show satisfactory performances for
all the media tested, mainly in CaCl2 aqueous solution,
suggesting that the presence of Ca2+ is crucial for the formation
of
a
complex
with
higher
adhesion
capability;
- Boc-(L-DOPA)2-OMe 4 has a similar behavior, showing the
highest adhesion value in CaCl2, yet appearing less efficient
than 2. Additionally, 4 shows the ability of repeated adhesion in
CaCl2
aqueous
solutions.
- Finally, Boc3-L-DOPA-OMe 3, where the catechol group is fully
protected, shows the best performance among these molecules
in PBS solution, so it may be used for biomedical purposes.
In this work we have investigated how these functionalizations
play a pivotal role in the adhesive behavior of L-DOPA, yet the
process controlling this phenomenon needs further studies, as
we cannot exclude that the changes in the cohesive strength
5
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10.1002/ejoc.202001264
European Journal of Organic Chemistry
FULL PAPER
across compounds may be also due to the introduction of
protecting groups and water absorption fenomena.
Acknowledgements
These outcomes pave the way for new set of applications for
these materials as green and biocompatible adhesives.
We gratefully acknowledge the University of Bologna and
Ministero dell’Università e della Ricerca (PRIN 2017 project
2017CR5WCH).
Experimental Section
Supporting Information. Synthesis and characterization of
compounds 1-4; 1H NMR and 13C NMR and IR spectra of
compounds 1-4; pictures of the contact angles of dried surface
of 1-4 with aqueous solutions.
Synthesis: General Remarks. Solvents were dried by
distillation before use. All reactions were carried out in dried
glassware. The melting points of the compounds were
determined in open capillaries and are uncorrected. High quality
infrared spectra (64 scans) were obtained at 2 cm-1 resolution
with an ATR-FT-IR Bruker Alpha System spectrometer. All
spectra were obtained in 3 mM solutions in CH2Cl2. All
compounds were dried in vacuo and all the sample preparations
were performed in a nitrogen atmosphere. NMR spectra were
recorded with a Varian Inova 400 spectrometer at 400 MHz (1H
NMR) and at 100 MHz (13C NMR). Chemical shifts are reported
in δ values relative to the solvent peak. HPLC-MS was used to
check the purity of compounds. For the details of the synthesis
and characterization of compounds 1-4, see the Supporting
Information.
Keywords: Contact angles • L-DOPA • tack tests • traction tests
• underwater adhesion
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Contact angle - Each sample is dissolved in ethyl acetate and
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10.1002/ejoc.202001264
European Journal of Organic Chemistry
FULL PAPER
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7
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10.1002/ejoc.202001264
European Journal of Organic Chemistry
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Entry for the Table of Contents
Among four compounds of the family Bocx-(L-DOPA)n-OMe (x = 1-3; n = 1,2), three of them show good adhesiveness. The
introduction of protecting groups stabilizes L-DOPA, preventing the oxidation of the catechol moiety and enhances the hydrophobicity.
These materials show good adhesiveness, with different properties, so they may find applications as green and biocompatible
adhesives.
Key topic
Molecular biocompatible adhesives
8
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