In this study, we propose a theoretical framework to explore the interactions between flexible polymer chains, specifically polyelectrolytes (PEs). Our analysis reaffirms that the thermodynamic drive for complex coacervation is influenced by key factors such as the number of ions bound to the polymer backbone and the entropy associated with free ions. By calculating the free energy of the system while considering position-dependent mutual interactions and chain conformations, we gain valuable insights into the local dielectricity as PEs overlap. Our findings indicate that global thermodynamic behavior is significantly shaped by local factors such as dielectric constant, providing an explanation for the discrepancies observed between experimental and computational studies. In addition, we found that entropy gain is inversely proportional to the local dielectric constant, provided that the electrostatic temperature remains constant. This relationship underscores the importance of polymer-specific parameters when examining the thermodynamic behavior of charged polymer complexation.
REFERENCES
1.
J. T. G.
Overbeek
and M. J.
Voorn
, “Phase separation in polyelectrolyte solutions. Theory of complex coacervation
,” J. Cell. Comp. Physiol.
49
(5
), 7
–26
(1957
).2.
V. Yu.
Borue
and I. Ya.
Erukhimovich
, “A statistical theory of weakly charged polyelectrolytes: Fluctuations, equation of state and microphase separation
,” Macromolecules
21
(11
), 3240
–3249
(1988
).3.
V. Yu.
Borue
and I. Ya.
Erukhimovich
, “A statistical theory of globular polyelectrolyte complexes
,” Macromolecules
23
(15
), 3625
–3632
(1990
).4.
K. A.
Mahdi
and M.
Olvera de la Cruz
, “Phase diagrams of salt-free polyelectrolyte semidilute solutions
,” Macromolecules
33
(20
), 7649
–7654
(2000
).5.
M.
Castelnovo
and J.-F.
Joanny
, “Complexation between oppositely charged polyelectrolytes: Beyond the random phase approximation
,” Eur. Phys. J. E
6
(1
), 377
–386
(2001
).6.
A. V.
Ermoshkin
and M.
Olvera de la Cruz
, “A modified random phase approximation of polyelectrolyte solutions
,” Macromolecules
36
(20
), 7824
–7832
(2003
).7.
A.
Kudlay
, A. V.
Ermoshkin
, and M.
Olvera de la Cruz
, “Complexation of oppositely charged polyelectrolytes: Effect of ion pair formation
,” Macromolecules
37
(24
), 9231
–9241
(2004
).8.
A.
Kudlay
and M.
Olvera de la Cruz
, “Precipitation of oppositely charged polyelectrolytes in salt solutions
,” J. Chem. Phys.
120
(1
), 404
–412
(2004
).9.
N. N.
Oskolkov
and I. I.
Potemkin
, “Complexation in asymmetric solutions of oppositely charged polyelectrolytes: Phase diagram
,” Macromolecules
40
(23
), 8423
–8429
(2007
).10.
S. L.
Perry
and C. E.
Sing
, “PRISM-based theory of complex coacervation: Excluded volume versus chain correlation
,” Macromolecules
48
(14
), 5040
–5053
(2015
).11.
A.
Salehi
and R. G.
Larson
, “A molecular thermodynamic model of complexation in mixtures of oppositely charged polyelectrolytes with explicit account of charge association/dissociation
,” Macromolecules
49
(24
), 9706
–9719
(2016
).12.
C. E.
Sing
, “Development of the modern theory of polymeric complex coacervation
,” Adv. Colloid Interface Sci.
239
, 2
–16
(2017
) Complex Coacervation: Principles and Applications.13.
K. L.
Tyler
and C. E.
Sing
, “Transfer matrix theory of polymer complex coacervation
,” Soft Matter
13
(39
), 7001
–7012
(2017
).14.
S.
Adhikari
, M. A.
Leaf
, and M.
Muthukumar
, “Polyelectrolyte complex coacervation by electrostatic dipolar interactions
,” J. Chem. Phys.
149
(16
), 163308
(2018
).15.
A. M.
Rumyantsev
and I. I.
Potemkin
, “Explicit description of complexation between oppositely charged polyelectrolytes as an advantage of the random phase approximation over the scaling approach
,” Phys. Chem. Chem. Phys.
19
(40
), 27580
–27592
(2017
).16.
M.
Rubinstein
, L.
Qi
, and S.
Panyukov
, “Structure of liquid coacervates formed by oppositely charged polyelectrolytes
,” Macromolecules
51
(23
), 9572
–9588
(2018
).17.
T. K.
Lytle
et al, “Designing electrostatic interactions via polyelectrolyte monomer sequence
,” ACS Cent. Sci.
5
(4
), 709
–718
(2019
).18.
P.
Zhang
et al, “Polyelectrolyte complex coacervation: Effects of concentration asymmetry
,” J. Chem. Phys.
149
(16
), 163303
(2018
).19.
A. S.
Ylitalo
et al, “Electrostatic correlations and temperature-dependent dielectric constant can model LCST in polyelectrolyte complex coacervation
,” Macromolecules
54
(24
), 11326
–11337
(2021
).20.
F.
Wang
, X.
Xu
, and S.
Zhao
, “Complex coacervation in asymmetric solutions of polycation and polyanion
,” Langmuir
35
(47
), 15267
–15274
(2019
).21.
A. M.
Rumyantsev
, E. Yu.
Kramarenko
, and O. V.
Borisov
, “Microphase separation in complex coacervate due to incompatibility between polyanion and polycation
,” Macromolecules
51
(17
), 6587
–6601
(2018
).22.
A. M.
Rumyantsev
et al, “Controlling complex coacervation via random polyelectrolyte sequences
,” ACS Macro Lett.
8
(10
), 1296
–1302
(2019
).23.
X.
Chen
et al, “Multiphase coacervates driven by electrostatic correlations
,” ACS Macro Lett.
10
(8
), 1041
–1047
(2021
).24.
A. R.
Knoerdel
, W. C.
Blocher McTigue
, and C. E.
Sing
, “Transfer matrix model of pH effects in polymeric complex coacervation
,” J. Phys. Chem. B
125
(31
), 8965
–8980
(2021
).25.
S.
Ryan
et al, “Charged polymers: From polyelectrolyte solutions to polyelectrolyte complexes
,” Macromolecules
54
(15
), 7183
–7192
(2021
).26.
S.
Mitra
and A.
Kundagrami
, “Polyelectrolyte complexation of two oppositely charged symmetric polymers: A minimal theory
,” J. Chem. Phys.
158
(1
), 014904
(2023
).27.
S.
Ghosh
, S.
Mitra
, and A.
Kundagrami
, “Polymer complexation: Partially ionizable asymmetric polyelectrolytes
,” J. Chem. Phys.
158
(20
), 204903
(2023
).28.
S.
Chen
and Z.-G.
Wang
. “Driving force and pathway in polyelectrolyte complex coacervation
.” Proc. Natl. Acad. Sci. U. S. A.
119
(36
) (2022
) e2209975119
.29.
M. T.
Record
, Jr, C. F.
Anderson
, and T. M.
Lohman
, “Thermodynamic analysis of ion effects on the binding and conformational equilibria of proteins and nucleic acids: The roles of ion association or release, screening, and ion effects on water activity
,” Q. Rev. Biophys.
11
(2
), 103
–178
(1978
).30.
V. A.
Kabanov
et al, “Cooperative interpolyelectrolyte reactions
,” Die Makromol. Chem.
13
(S19851
), 137
–155
(1985
).31.
H.
Dautzenberg
and W.
Jaeger
, “Effect of charge density on the formation and salt stability of polyelectrolyte complexes
,” Macromol. Chem. Phys.
203
(14
), 2095
–2102
(2002
).32.
F.
Cousin
et al, “Polyelectrolyte-protein complexes: Structure and conformation of each species revealed by SANS
,” Langmuir
21
(21
), 9675
–9688
(2005
).33.
J.
Gummel
, F.
Cousin
, and F.
Boué
, “Counterions release from electrostatic complexes of polyelectrolytes and proteins of opposite charge: A direct measurement
,” J. Am. Chem. Soc.
129
(18
), 5806
–5807
(2007
).34.
C. H.
Porcel
and J. B.
Schlenoff
, “Compact polyelectrolyte complexes: “Saloplastic” candidates for biomaterials
,” Biomacromolecules
10
(15
), 2968
–2975
(2009
).35.
E.
Spruijt
et al, “Binodal compositions of polyelectrolyte complexes
,” Macromolecules
43
(15
), 6476
–6484
(2010
).36.
R.
Chollakup
et al, “Phase behavior and coacervation of aqueous poly(acrylic acid)-poly(allylamine) solutions
,” Macromolecules
43
(5
), 2518
–2528
(2010
).37.
J.
van der Gucht
et al, “Polyelectrolyte complexes: Bulk phases and colloidal systems
,” J. Colloid Interface Sci.
361
(2
), 407
–422
(2011
).38.
D.
Priftis
and M.
Tirrell
, “Phase behaviour and complex coacervation of aqueous polypeptide solutions
,” Soft Matter
8
(36
), 9396
–9405
(2012
).39.
M.
Lemmers
et al, “The influence of charge ratio on transient networks of polyelectrolyte complex micelles
,” Soft Matter
8
(1
), 104
–117
(2012
).40.
J.
Wang
, M. A.
Cohen Stuart
, and J.
van der Gucht
, “Phase diagram of coacervate complexes containing reversible coordination structures
,” Macromolecules
45
(21
), 8903
–8909
(2012
).41.
R.
Chollakup
et al, “Polyelectrolyte molecular weight and salt effects on the phase behavior and coacervation of aqueous solutions of poly(acrylic acid) sodium salt and poly(allylamine) hydrochloride
,” Macromolecules
46
(6
), 2376
–2390
(2013
).42.
D.
Priftis
et al, “Ternary, tunable polyelectrolyte complex fluids driven by complex coacervation
,” Macromolecules
47
(9
), 3076
–3085
(2014
).43.
L.
Vitorazi
et al, “Evidence of a two-step process and pathway dependency in the thermodynamics of poly(diallyldimethylammonium chloride)/poly(sodium acrylate) complexation
,” Soft Matter
10
(47
), 9496
–9505
(2014
).44.
S.
Perry
et al, “The effect of salt on the complex coacervation of vinyl polyelectrolytes
,” Polymers
6
(6
), 1756
–1772
(2014
).45.
S.
Ali
et al, “Relationship between polyelectrolyte bulk complexation and kinetics of their layer-by-layer assembly
,” Macromolecules
48
(2
), 400
–409
(2015
).46.
Y.
Zhang
et al, “The influence of ionic strength and mixing ratio on the colloidal stability of PDAC/PSS polyelectrolyte complexes
,” Soft Matter
11
(37
), 7392
–7401
(2015
).47.
A. B.
Kayitmazer
, A. F.
Koksal
, and E.
Kilic Iyilik
, “Complex coacervation of hyaluronic acid and chitosan: Effects of pH, ionic strength, charge density, chain length and the charge ratio
,” Soft Matter
11
(44
), 8605
–8612
(2015
).48.
J.
Fu
and J. B.
Schlenoff
, “Driving forces for oppositely charged polyion association in aqueous solutions: Enthalpic, entropic, but not electrostatic
,” J. Am. Chem. Soc.
138
(3
), 980
–990
(2016
).49.
V. S.
Meka
et al, “A comprehensive review on polyelectrolyte complexes
,” Drug Discovery Today
22
(11
), 1697
–1706
(2017
).50.
J.
Fu
, H. M.
Fares
, and J. B.
Schlenoff
, “Ion-pairing strength in polyelectrolyte complexes
,” Macromolecules
50
(3
), 1066
–1074
(2017
).51.
S.
Ali
and V.
Prabhu
, “Relaxation behavior by time-salt and time-temperature superpositions of polyelectrolyte complexes from coacervate to precipitate
,” Gels
4
(1
), 11
(2018
).52.
L.
Li
et al, “Phase behavior and salt partitioning in polyelectrolyte complex coacervates
,” Macromolecules
51
(8
), 2988
–2995
(2018
).53.
A. B.
Marciel
, S.
Srivastava
, and M. V.
Tirrell
, “Structure and rheology of polyelectrolyte complex coacervates
,” Soft Matter
14
(13
), 2454
–2464
(2018
).54.
S.
Ali
, M.
Bleuel
, and V. M.
Prabhu
, “Lower critical solution temperature in polyelectrolyte complex coacervates
,” ACS Macro Lett.
8
(3
), 289
–293
(2019
).55.
J. B.
Schlenoff
et al, “Ion content of polyelectrolyte complex coacervates and the Donnan equilibrium
,” Macromolecules
52
(23
), 9149
–9159
(2019
).56.
J.
Huang
, F. J.
Morin
, and J. E.
Laaser
, “Charge-density-dominated phase behavior and viscoelasticity of polyelectrolyte complex coacervates
,” Macromolecules
52
(13
), 4957
–4967
(2019
).57.
B.
Saha
et al, “Unusual nanostructured morphologies enabled by interpolyelectrolyte complexation of polyions bearing incompatible nonionic segments
,” Macromolecules
53
(24
), 10754
–10764
(2020
).58.
S.
Meng
et al, “Effect of mixed solvents on polyelectrolyte complexes with salt
,” Colloid Polym. Sci.
298
(7
), 887
–894
(2020
).59.
S.
Meng
et al, “Solid-to-liquid phase transition in polyelectrolyte complexes
,” Macromolecules
53
(18
), 7944
–7953
(2020
).60.
L.
Li
et al, “Effect of solvent quality on the phase behavior of polyelectrolyte complexes
,” Macromolecules
54
(1
), 105
–114
(2020
).61.
Y.
Chen
et al, “Influence of nonstoichiometry on the viscoelastic properties of a polyelectrolyte complex
,” Macromolecules
54
(17
), 7890
–7899
(2021
).62.
A. E.
Neitzel
et al, “Polyelectrolyte complex coacervation across a broad range of charge densities
,” Macromolecules
54
(14
), 6878
–6890
(2021
).63.
D.
Priftis
and M.
Tirrell
, “Phase behaviour and complex coacervation of aqueous polypeptide solutions
,” Soft Matter
8
(36
), 9396
–9405
(2012
).64.
D.
Priftis
, N.
Laugel
, and M.
Tirrell
, “Thermodynamic characterization of polypeptide complex coacervation
,” Langmuir
28
(45), 15947–15957 (2012
).65.
A. V.
Subbotin
and A. N.
Semenov
, “The structure of polyelectrolyte complex coacervates and multilayers
,” Macromolecules
54
(3
), 1314
–1328
(2021
).66.
S.
Friedowitz
et al, “Looping-in complexation and ion partitioning in nonstoichiometric polyelectrolyte mixtures
,” Sci. Adv.
7
(31
), eabg8654
(2021
).67.
Y.
Ma
, S.
Ali
, and V. M.
Prabhu
, “Enhanced concentration fluctuations in model polyelectrolyte coacervate mixtures along a salt isopleth phase diagram
,” Macromolecules
54
(24
), 11338
–11350
(2021
).68.
S. M.
Lalwani
et al, “Relaxation times of solid-like polyelectrolyte complexes of varying pH and water content
,” Macromolecules
54
(17
), 7765
–7776
(2021
).69.
Z. A.
Digby
et al, “Salt resistance as a measure of the strength of polyelectrolyte complexation
,” Macromolecules
55
(3
), 978
–988
(2022
).70.
Y.
Hayashi
, M.
Ullner
, and P.
Linse
, “A Monte Carlo study of solutions of oppositely charged polyelectrolytes
,” J. Chem. Phys.
116
(15
), 6836
–6845
(2002
).71.
R. G.
Winkler
, M. O.
Steinhauser
, and P.
Reineker
, “Complex formation in systems of oppositely charged polyelectrolytes: A molecular dynamics simulation study
,” Phys. Rev. E
66
, 021802
(2002
).72.
Y.
Hayashi
, M.
Ullner
, and P.
Linse
, “Complex Formation in solutions of oppositely charged polyelectrolytes at different polyion compositions and salt content
,” J. Phys. Chem. B
107
(32
), 8198
–8207
(2003
).73.
Y.
Hayashi
, M.
Ullner
, and P.
Linse
, “Oppositely charged polyelectrolytes. Complex formation and effects of chain asymmetry
,” J. Phys. Chem. B
108
(39
), 15266
–15277
(2004
).74.
R.
Zhang
and B. I.
Shklovskii
, “Phase diagram of solution of oppositely charged polyelectrolytes
,” Physica A
. Physics Applied to Biological Systems, 352
(1
), 216
–238
(2005
).75.
Z.
Ou
and M.
Muthukumar
, “Entropy and enthalpy of polyelectrolyte complexation: Langevin dynamics simulations
,” J. Chem. Phys.
124
(15
), 154902
(2006
).76.
Y. O.
Popov
, J.
Lee
, and G. H.
Fredrickson
, “Field-theoretic simulations of polyelectrolyte complexation
,” J. Polym. Sci., Part B: Polym. Phys.
45
(24
), 3223
–3230
(2007
).77.
N.
Hoda
and R. G.
Larson
, “Explicit- and implicit-solvent molecular dynamics simulations of complex formation between polycations and polyanions
,” Macromolecules
42
(22
), 8851
–8863
(2009
).78.
A. A.
Lazutin
, A. N.
Semenov
, and V. V.
Vasilevskaya
, “Polyelectrolyte complexes consisting of macromolecules with varied stiffness: Computer simulation
,” Macromol. Theory Simul.
21
(5
), 328
–339
(2012
).79.
R. A.
Riggleman
, R.
Kumar
, and G. H.
Fredrickson
, “Investigation of the interfacial tension of complex coacervates using field-theoretic simulations
,” J. Chem. Phys.
136
(2
), 024903
(2012
).80.
E.
Meneses-Juárez
et al, “The structure and interaction mechanism of a polyelectrolyte complex: A dissipative particle dynamics study
,” Soft Matter
11
(29
), 5889
–5897
(2015
).81.
B.
Peng
and M.
Muthukumar
, “Modeling competitive substitution in a polyelectrolyte complex
,” J. Chem. Phys.
143
(24
), 243133
(2015
).82.
T. K.
Lytle
, M.
Radhakrishna
, and C. E.
Sing
, “High charge density coacervate assembly via hybrid Monte Carlo single chain in mean field theory
,” Macromolecules
49
(24
), 9693
–9705
(2016
).83.
X.
Xu
et al, “Potential of mean force and transient states in polyelectrolyte pair complexation
,” J. Chem. Phys.
145
(3
), 034901
(2016
).84.
T. D.
Kris
and G. H.
Fredrickson
, “Theory of polyelectrolyte complexation-complex coacervates are self-coacervates
,” J. Chem. Phys.
146
(22
), 224902
(2017
).85.
Li-W.
Chang
et al, “Sequence and entropy-based control of complex coacervates
,” Nat. Commun.
8
, 1273
(2017
).86.
M.
Radhakrishna
et al, “Molecular connectivity and correlation effects on polymer coacervation
,” Macromolecules
50
(7
), 3030
–3037
(2017
).87.
V. S.
Rathee
et al, “Weak polyelectrolyte complexation driven by associative charging
,” J. Chem. Phys.
148
(11
), 114901
(2018
).88.
V. S.
Rathee
et al, “Role of associative charging in the entropy–energy balance of polyelectrolyte complexes
,” J. Am. Chem. Soc.
140
(45
), 15319
–15328
(2018
).89.
A. M.
Rumyantsev
, A. A.
Gavrilov
, and E. Yu.
Kramarenko
, “Electrostatically stabilized microphase separation in blends of oppositely charged polyelectrolytes
,” Macromolecules
52
(19
), 7167
–7174
(2019
).90.
A.
Shakya
et al, “Role of chain flexibility in asymmetric polyelectrolyte complexation in salt solutions
,” Macromolecules
53
(4
), 1258
–1269
(2020
).91.
S. V.
Bobbili
and S. T.
Milner
, “Closed-loop phase behavior of nonstoichiometric coacervates in coarse-grained simulations
,” Macromolecules
55
(2
), 511
–516
(2022
).92.
S.
Chen
, P.
Zhang
, and Z.-G.
Wang
, “Complexation between oppositely charged polyelectrolytes in dilute solution: Effects of charge asymmetry
,” Macromolecules
55
(10
), 3898
–3909
(2022
).93.
A. S.
Michaels
, “Polyelectrolyte complexes
,” Ind. Eng. Chem.
57
(10
), 32
–40
(1965
).94.
K.-I.
Tainaka
, “Effect of counterions on complex coacervation
,” Biopolymers
19
(7
), 1289
–1298
(1980
).95.
C.
Márquez-Beltrán
et al, “Structure and mechanism formation of polyelectrolyte complex obtained from PSS/PAH system: Effect of molar mixing ratio, base–acid conditions, and ionic strength
,” Colloid Polym. Sci.
291
(3
), 683
–690
(2012
).96.
M.
Muthukumar
, “50th anniversary perspective: A perspective on polyelectrolyte solutions
,” Macromolecules
50
(24
), 9528
–9560
(2017
).97.
M.
Muthukumar
, Physics of Charged Macromolecules: Synthetic and Biological Systems
(Cambridge University Press
, 2023
).98.
S.
Liu
and M.
Muthukumar
, “Langevin dynamics simulation of counterion distribution around isolated flexible polyelectrolyte chains
,” J. Chem. Phys.
116
(22
), 9975
–9982
(2002
).99.
M.
Muthukumar
, “Theory of counter-ion condensation on flexible polyelectrolytes: Adsorption mechanism
,” J. Chem. Phys.
120
(19
), 9343
–9350
(2004
).100.
S.
Ghosh
and A.
Kundagrami
. “Effect of counterion size on polyelectrolyte conformations and thermodynamics
,” arxiv.2310.11250 (2023
)101.
S. F.
Edwards
and P.
Singh
, “Size of a polymer molecule in solution. Part 1.—Excluded volume problem
,” J. Chem. Soc., Faraday Trans.
75
, 1001
–1019
(1979
).102.
P. J.
Flory
and W. R.
Krigbaum
,“Statistical mechanics of dilute polymer solutions
,” J. Chem. Phys.
18
(8
), 1086
–1094
(1950
).103.
R.
Podgornik
, “A variational approach to charged polymer chains: Polymer mediated interactions
,” J. Chem. Phys.
99
(9
), 7221
–7231
(1993
).104.
M.
Muthukumar
, “Counterion adsorption theory of dilute polyelectrolyte solutions: Apparent molecular weight, second virial coefficient, and intermolecular structure factor
,” J. Chem. Phys.
137
(3
), 034902
(2012
).105.
N.
Laugel
et al, “Relationship between the growth regime of polyelectrolyte multilayers and the polyanion/polycation complexation enthalpy
,” J. Phys. Chem. B
110
(39
), 19443
–19449
(2006
).106.
E. L.
Mehler
and G.
Eichele
, “Electrostatic effects in water-accessible regions of proteins
,” Biochemistry
23
(17
), 3887
–3891
(1984
).107.
G.
Lamm
and G. R.
Pack
, “Calculation of dielectric constants near polyelectrolytes in solution
,” J. Phys. Chem. B
101
(6
), 959
–965
(1997
).108.
I.
Rouzina
and V. A.
Bloomfield
, “DNA bending by small, mobile multivalent cations
,” Biophys. J.
74
(6
), 3152
–3164
(1998
).109.
M.
Dinpajooh
and D. V.
Matyushov
, “Dielectric constant of water in the interface
,” J. Chem. Phys.
145
(1
), 014504
(2016
).110.
B.
Roux
, H. Ai.
Yu
, and M.
Karplus
, “Molecular basis for the Born model of ion solvation
,” J. Phys. Chem.
94
(11
), 4683
–4688
(1990
).111.
S. W.
Rick
and B. J.
Berne
, “The aqueous solvation of water: A comparison of continuum methods with molecular dynamics
,” J. Am. Chem. Soc.
116
(9
), 3949
–3954
(1994
).112.
R. M.
Lynden-Bell
and J. C.
Rasaiah
, “From hydrophobic to hydrophilic behaviour: A simulation study of solvation entropy and free energy of simple solutes
,” J. Chem. Phys.
107
(6
), 1981
–1991
(1997
).113.
S.
Rajamani
, T.
Ghosh
, and S.
Garde
, “Size dependent ion hydration, its asymmetry, and convergence to macroscopic behavior
,” J. Chem. Phys.
120
(9
), 4457
–4466
(2004
).114.
R.
Kumar
, B. G.
Sumpter
, and S. M.
Kilbey
II, “Charge regulation and local dielectric function in planar polyelectrolyte brushes
,” J. Chem. Phys.
136
(23
), 234901
(2012
).115.
J.
Andrew Grant
, B. T.
Pickup
, and N.
Anthony
, “A smooth permittivity function for Poisson–Boltzmann solvation methods
,” J. Comput. Chem.
22
(6
), 608
–640
(2001
).© 2025 Author(s). Published under an exclusive license by AIP Publishing.
2025
Author(s)
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