Enantioselective ester hydrolysis by an achiral catalyst co-embedded with chiral amphiphiles into a vesicle membrane

Article abstract of DOI:10.1039/c6ra06628c

Co-embedding of an amphiphilic non-chiral hydrolysis catalyst with amphiphilic chiral additives into the membrane of a phospholipid vesicle induces different rates of ester hydrolysis for enantiomeric amino acid esters.

Full text of DOI:10.1039/c6ra06628c

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: B. Koenig and M.
Poznik, RSC Adv., 2016, DOI: 10.1039/C6RA06628C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 4
View Article Online
DOI: 10.1039/C6RA06628C
Journal Name
COMMUNICATION
Enantioselective ester hydrolysis by an achiral catalyst co-
embedded with chiral amphiphiles into a vesicle membrane
M. Poznika and B. Königa*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Co-embedding of an amphiphilic non-chiral hydrolysis catalyst self-assembled capsules induce stereoselective reactions of
with amphiphilic chiral additives into the membrane of
achiral substrates by weak interactions.13-15
phospholipid vesicle induces different rates of ester hydrolysis for We report here the hydrolysis of enantiomeric amino acid
a
enantiomeric amino acid esters.
esters on the modified surface of phospholipid vesicles (Fig. 1).
chiral, catalytically inactive membrane additive is co-
A
The origin of chirality in nature,1 why natural molecules are
homochiral, and how such a rapid amplification of single
enantiomers occurred, are still unanswered questions.2,
embedded with a catalytically active achiral metal complex
16
Zn2Cy into the phospholipid membrane.12, The membrane
3
serves as two-dimensional platform with higher concentration
of the amphiphilic membrane additives compared to the bulk
solution.17 This proximity of the chiral additive to the achiral
metal complex affects its selectivity in ester hydrolysis and
induces thereby different reaction rates for both enantiomers.
Synthetic chemistry uses chiral catalyst or ligands to convert
achiral substrates enantioselective.4 The reactant and the
source of chirality require typical close contact. The simple
addition of chiral additives to the reaction mixture or using
enantiopure chiral solvents5, 6 provide none or minute enantio-
selectivity. The intermolecular chirality transfer improves in 3D
networks, such as chiral MOFs7, 8 or micellar solutions.9-12
Figure 1: Proposed concept of additive-induced enantioselectivity in a hydrolytic
reaction.
Figure 2: Molecular structures of the achiral catalyst for hydrolysis, racemic substrates
and chiral membrane additives.
The Raymond group reported an approach where chiral
The bis-zinc-cyclen complex Zn2Cy is anchored into the surface
of the vesicle by its lipophilic alkyl chain and promotes the
hydrolysis of activated carboxylic esters as previously reported
(Fig. 2).18 The Lewis acidic zinc ions coordinate one water
molecule and the ester functionality. Enantiopure amphiphilic
derivatives of L-proline L-Pro, (-)-sparteine (-)-Spa, L-glucose L-
Glu, L-tartaric acid L-Tar and L-histidine L-His-COOH and the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 4
View Article Online
DOI: 10.1039/C6RA06628C
COMMUNICATION
Journal Name
kL
kD
kL
kD
kL
kD
No cyclen
No lipid
corresponding alcohol L-His-OH were used as chiral membrane
additives. Enantiometrically pure 4-nitrophenol esters of
phenylalanine, PN-Phe, serve as substrates for the catalysed
hydrolysis. Upon cleavage of the ester bond, the coloured 4-
nitrophenolate anion is released, which enables a facile
determination of the reaction progress. However, derivatives
PN-Phe with free amine group show fast spontaneous
hydrolysis under the reaction conditions. Therefore com-
pounds PN-C12-Phe and PN-C2-Phe with a protected amino-
group were prepared, which are stable in the absence of the
hydrolysis catalyst.
kL
kD
31
15
30
15
65
63
50
61
201
166
277
229
46
198
159
236
242
46
ZnCy2
L-Pro
a
–
a
–
a
–
a
–
28
26
50
41
(-)-Spa
a
–
a
–
13
15
28
28
L-Glu
a
–
a
–
24
14
26
24
L-Tar
212
127
339
113
233
327
153
n.d.
357
129
n.d.
287
214
n.d.
513
286
n.d.
384
11
n.d.
6
2
n.d.
4
L-His-COOH
D-His-COOH
L-His-OH
Table 1: Pseudo first order kinetic rate constants for the hydrolysis of the L and D
enantiomer of P-C12-Phe using different systems. All kinetic values are given in 10-3s-1
a, no effect on hydrolysis observed.
.
Results and discussion
All measurements were done in buffered solutions (HEPES
buffer, 25 mM, 7.4 pH), at room temperature. Samples were
prepared by sonication according to a previously reported
procedure to form micellar solutions or 100 nm unilamelar
functionalised vesicles.18 The rate of substrate hydrolysis was
determined colorimetrically as an increase in absorbance
intensity at 400 nm (absorption maximum of 4-nitrophenol at
pH 7.4; no other species absorb at this wavelength). The
relative error of the measurement was estimated to be below
10 % (Fig. 3).
Kinetic effects
Hydrolysis of the ester PN-C12-Phe is favoured in micellar
solutions (Tab. 1). Confirming previous results,18 membrane
additives can affect the hydrolysis activity in vesicular and co-
micellar solutions significant.
In DOPC membranes the hydrolytic rates are affected by two
types of membrane additives: tartrate L-Tar decreases and
histidine derivatives L-His-COOH and L-His-OH increase the
initial rate of ester hydrolysis (Tab. 1). These observations are
in accordance to effects on the previously studied hydrolysis of
fluorescein diacetate by Zn2Cy 18
.
Enantiodiscrimination in ester hydrolysis
The rates of ester hydrolysis were determined for both
enantiomers as previously reported for micellar solutions.10
The largest relative difference in hydrolysis rates for the
enantiomeric esters is observed in DOPC vesicles with addition
of amphiphilic tartrate L-Tar or histidine acid L-His-COOH as
membrane additives (Fig. 4).
Figure 3: Examples of the kinetic data for hydrolysis of the PN-C12-Phe substrate by
vesicular solution (85 % DOPC), Zn2Cy (5%) and amphiphilic additive (10%).
1.0
DOPC
DSPC
Co-micelles
Pseudo first order rate constants were calculated using the
initial slope method. Every membrane additive was examined
as a sole micellar solution (without lipid or Zn2Cy), co-micellar
solution (without lipid in the presence of Zn2Cy), and in
0.8
0.6
0.4
0.2
0.0
vesicular
membranes
with
1,2-dioleoyl-sn-glycero-3-
phosphocholine (DOPC) and 1,2-distearoyl-sn-glycero-3-
phosphocholine (DSPC) lipids (5 mol. % Zn2Cy, 10 mol. %
membrane additive, 85 mol. % lipid). Lipids differ in their
transition temperatures providing fluid (DOPC) and rigid
(DSPC) membranes at room temperature. We measured the
hydrolytic rate constants separately for the two enantiomers
of the substrate PN-C12-Phe. This substrate is equipped with a
long alkyl chain, which increases its lipophilicity and the
adsorption to the surface of the membrane. The initial
hydrolysis rates for different functionalized vesicles and co-
micelles are summarised in Table 1.
Tar
His-COOH
His-OH
Figure 4: Effect of membrane additives on the relative ratio of ester hydrolysis rates of
enantiomeric amino acid esters represented by the fraction of pseudo first order
kinetic constants.
Both compounds contain free carboxy group. When the
carboxyl group of histidine is reduced the effect in vesicles is
lost. This indicates that the free acid might have a crucial role
in this cooperative action. In buffered solution the acid is
deprotonated and might interact with the Lewis acidic zinc
complex. This interaction is weak in bulk solution, but may
significantly increase due to the close proximity of the binding
partners at the vesicular surface. In fluid DOPC membranes,
DOPC
DSPC
Co-micelles
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 4
View Article Online
DOI: 10.1039/C6RA06628C
Journal Name
COMMUNICATION
embedded components diffuse and may thereby arrange two with co-embedded amphiphiles prepared from tartaric
optimal for the catalysis. In gel phase DSPC added amphiphiles acid or histidine. This resembles an ee of approx. up to 40%,
form patches with restricted lateral movement decreasing the which may be expected for reactions performed from race-
possibility for cooperative effects.19-21 This was also previously mate. The fluidity of the membrane is essential to achieve the
observed by us.18 Other membrane additives than tartrate or catalytic enantiodiscrimination and therefore only observed in
histidine do not show considerable effects on the relative DOPC vesicles. Although the measured rate differences may
hydrolysis rate of the enantiomeric esters. Substrates PN-C2- not be useful for practical applications, the results prove that
Phe and Pn-Phe exhibit similar enantioselective enhancement the intermolecular interaction between a Lewis acidic metal
(Table 2).
complex, chiral amphiphiles and activated amino acid esters
co-embedded into a fluid membrane without covalent con-
nection can affect reaction rates enantioselective.
kL [10-3s-1]
kD [10-3s-1]
PN-C2-Phe
PN- Phe
35
2059
17
1204
Table 2: Pseudo first order rate constants of hydrolysis for both enantiomers by a
Notes and references
vesicular solution of Zn2Cy (5 mol. %), L-Tar (10 mol. %) and DOPC (85 mol. %).
1. S. Mason, Trends Pharmacol. Sci.,
2. D. G. Blackmond, Cold Spring Harbor Perspectives in Biology,
2010, , a002147.
7, 20-23.
In order to confirm our observation, we prepared the
2
enantiomeric amphiphilic histidine D-His-COOH
.
This
3. W. Bonner, Origins Life Evol. Biosphere, 1991, 21, 59-111.
4. P. J. Walsh and M. C. Kozlowski, Fundamentals of
Asymmetric Catalysis, Macmillan Education, 2008.
compound was investigated under identical conditions as L-
His-COOH and induced a similar hydrolysis rate enhancement
of D-PN-C12-Phe (Fig. 5), but with opposite enantioselectivity.
5. S. K. Tulashie, H. Lorenz, L. Hilfert, F. T. Edelmann and A.
0.006
0.004
0.002
Seidel-Morgenstern, Cryst. Growth Des., 2008,
6. S. K. Tulashie, H. Lorenz and A. Seidel-Morgenstern, Cryst.
Growth Des., 2009, , 2387-2392.
8, 3408-3414.
9
7. L. Ma, C. Abney and W. Lin, Chem. Soc. Rev., 2009, 38, 1248-
1256.
L-His-COOH
0
0
0.2
0.4
0.6
0.8
1
8. C. García-Simón, R. Gramage-Doria, S. Raoufmoghaddam, T.
Parella, M. Costas, X. Ribas and J. N. H. Reek, J. Am. Chem.
Soc., 2015, 137, 2680-2687.
-0.002
-0.004
-0.006
D-His-COOH
9. J. You, X. Yu, X. Li, Q. Yan and R. Xie, Tetrahedron:
Time / minute
Asymmetry, 1998, 9, 1197-1203.
10. J.-S. You, X.-Q. Yu, X.-Y. Su, T. Wang, Q.-X. Xiang, M. Yang and
R.-G. Xie, J. Mol. Catal. A: Chem., 2003, 202, 17-22.
11. R. A. Moss and W. L. Sunshine, J. Org. Chem., 1974, 39, 1083-
1089.
Figure 5: Recorded difference in kinetics of L and D PN-C12-Phe substrate hydrolysis by
vesicular solution (85 % DOPC) with L or D His-COOH (10 %) and ZnCy2 (5%)
In addition, the effect of the membrane additive loading on
the enantioselectivity of the hydrolysis was investigated for D-
His-COOH (Fig. 6). Addition of 10 mol % provided the highest
relative difference between the hydrolysis rate constants.
12. F. Mancin, P. Scrimin, P. Tecilla and U. Tonellato, Coord.
Chem. Rev., 2009, 253, 2150-2165.
13. C. J. Brown, R. G. Bergman and K. N. Raymond, J. Am. Chem.
Soc., 2009, 131, 17530-17531.
400
L-PN-C12-Phe
D-PN-C12-Phe
14. C. J. Brown, F. D. Toste, R. G. Bergman and K. N. Raymond,
Chem. Rev., 2015, 115, 3012-3035.
300
15. C. Zhao, F. D. Toste, K. N. Raymond and R. G. Bergman, J. Am.
Chem. Soc., 2014, 136, 14409-14412.
200
100
0
16. F. Mancin, P. Scrimin and P. Tecilla, Chem. Commun., 2012,
48, 5545-5559.
17. B. Gruber and B. König, Chem. Eur. J., 2013, 19, 438-448.
18. M. Poznik and B. Konig, Org. Biomol. Chem., 2014, 12, 3175-
3180.
1%
5%
10%
15%
Figure 6: Pseudo first order rate constants of hydrolysis for both enantiomers by a
vesicular solution of Zn2Cy (5 mol. %) and DOPC with different loadings of D-His-COOH.
19. E. J. Shimshick and H. M. McConnell, Biochemistry, 1973, 12
,
2351-2360.
20. H.-J. Müller and H.-J. Galla, European Biophysics Journal, 14
,
Conclusions
485-491.
The relative catalytic hydrolysis rates of enantiomeric amino
acid esters with a non-chiral catalyst become significantly
different, if the catalyst is co-embedded into the surface of
DOPC vesicles with chiral amphiphiles. The rates for enantio-
meric phenylalanine nitrophenyl esters differ by a factor of
21. F. A. Heberle and G. W. Feigenson, Cold Spring Harbor
Perspectives in Biology, 2011, 3, a004630.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

RSC Advances
Page 4 of 4
View Article Online
DOI: 10.1039/C6RA06628C
30x12mm (300 x 300 DPI)