Post on 22-Jan-2019
BEIJING 北京
Biochemistry Professor, Universidade de São Paulo Advisor, Scien?fic Directorate, FAPESP Vice-‐President, Brazilian Academy of Sciences
1
Specific Ion Effects on Micelles: The case of trifluoromethane sulfonate, proper?es and applica?ons
HERNAN CHAIMOVICH
BEIJING 北京
OUTLINE
Ø Introduc+on Surfactants, aggregates and specific ion effects
Ø Trifluoromethane sulfonate (Triflate), a par+cular counterion
Ø Applica+ons
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Surfactants and micelles
• Surfactants: molecules with hydrophobic and hydrophilic groups; – ZwiEerionic, ionic, non-‐ionic;
• Micelle: aggregate formed by self-‐assembly of surfactants.
Dodecyltrimethylammonium (DTA) + X-‐
X-‐
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Ionic micelle forma+on
• Hydrophobic effect: – Hydrophobic moie+es aggregate spontaneously libera+ng water molecules;
• Aggrega+on leads to electrosta+c headgroup repulsion;
• Compensated by counterion condensa+on.
A delicate balance
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Specific ion effects in micelles • Ionic Micellar proper+es are exquisitely modulated by the nature of the counterion: – KraQ temperature; – Cri+cal micellar concentra+on
(cmc); – Degree of counteiron
dissocia+on (α); – Aggrega+on number (Nagg); – Shape.
DTAB
DTAC
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Micellar structure
• Micellar growth leads to different structures: – Growth depends on the nature
of the counterion; [surfactant], etc;
• Generally: – Inorganic counterions produce
spherical micelles with low Nagg; – Organic C.I.: rod-‐like micelles
with high Nagg;
• At the limit Nagg → ∞ : phase separa+on.
Lima, FS, et al, Langmuir, 2011, 27, 4319.
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Sphere-‐to-‐Rod Transi+on (StRT)
• StRT is observed with several aroma+c C.I.;
• C.I. inser+on into micellar core;
• StRT ion-‐pairing and dehydra+on are correlated.
Geng, Y, et al, Langmuir, 2005, 21, 562. ROMSTED, CHAIMOVICH, and coworkers Langmuir, v. 21, p. 562-‐569, 2005.
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Triflate: a special anion
• -‐SO3 group highly charged;
• -‐CF3 is dehydrated;
• Under some condi+ons, Tf-‐ forms ion-‐pairs with ca+ons.
Atom C F S O
Par+al Charge 0.31 -‐0.09 0.97 -‐0.67
CF
F
F
S O-
O
O
Lima, FS, et al, Langmuir, 2013, 29, 10037.
Gejji, SP, et al, JPCA, 1997, 101, 5678.
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Tf-‐ is surface ac+ve
• NaTf decreases the surface tension of water more than any other inorganic salt;
• Tf-‐ is oriented at the air/water interface in molecular dynamics (MD) simula+ons.
Lima, FS, et al, Langmuir, 2014, 30, 1239.
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Micelles of DTATf possess unusual proper+es
• High Nagg;
• Non-‐spherical;
• High TK and low cmc;
• Anions with similar structure to that of Tf-‐ induce different effects on DTA aggregates.
Property DTAC DTAMs DTAB DTATFA DTATf
TK / °C ~ 0 0 0 -‐ 37
cmc / 10-‐3 M 22,7 23,9 16,9 10 5
Nagg 42 43 45 71 263
α 0,49 0,3 0,29 0,15 0,1
Lima, FS, et al, Langmuir, 2013, 29, 4193.
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MD simula+ons substan+ates shape and high aggrega+on number of DTATf
• Ini+al shape: bilayers with exposed edges;
• 130 DTATf in 13 nm-‐edge cube;
• Rim forma+on.
Simulação MD DTATf 130
Lima, FS, et al, Langmuir, 2013, 29, 4193.
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DTAB aggregate with 130 monomers is unstable
• Tf-‐ were replace by Br-‐;
• At 0.6 ns: shape change;
• At 1.5 ns: first micellar division;
• At 3 ns: second micellar division.
MD de DTAB com 130 monomeros
Lima, FS, et al, Langmuir, 2013, 29, 4193.
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MD reproduced the high affinity of Tf-‐ to DTA interface
• High life+mes of Tf-‐ at the micellar interface;
• Micellar shape affects α.
Lima, FS, et al, Langmuir, 2014, 30, 1239.
DTAX Nagg αexp αMD tsimula+on
Tf 130 0,10 0,11 35 ns
Tf 50 0,10 0,13 100 ns
Br 50 0,32 0,39 100 ns
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DTATf micelles are discoidal
• Finite bicelle model provided the best fit to SAXS curves of DTATf aggregates;
• The thickness of the core suggests interdigita+on of chains.
Lima, FS, et al, Langmuir, 2013, 29, 4193.
model Rshell / Å Rcore / Å ρshell / e/Å3 ρcore / e/Å3 sized / Å bicelle 6.0 9.2 0.43 0.30 54 ± 20
infinite lamella 6.0 8.0 0.40 0.29 ∞ sphere 4.0 15.8 0.40 0.28 -‐
cyllinder 9.9 8.6 0.43 0.29 756
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DTATf aggregates are ordered, packed and dehydrated
• NMR showed: – Ion-‐exchange (Br-‐/Tf-‐) at the DTA interface; – High order along DTA’s chain;
• EPR probes showed: – Higher rota+onal correla+on +mes of
probes inside DTATf aggregates; – Smaller hyperfine coupling of probes in
DTATf (smaller hydra+on).
DTAX Order Parameter
HP HG H12
Ms 0,04 0,28 0,12
Br 0,05 0,32 0,12
Tf 0,24 0,47 0,18
Lima, FS, et al, Langmuir, 2013, 29, 4193.
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DTA’s chain is less mobile in DTATf aggregates
• Reorienta+onal correla+on func+on of DTA’s chain decays slower in DTATf than that in DTAB.
System A τ1 / ps τ2 / ps τr / ps DTAB 0.695 ± 0.002 144 ± 1 1066 ± 7 425 ± 10 DTATf 0.600 ± 0.002 199 ± 1 1203 ± 4 600 ± 10
● DTAB ■ DTATf - Fit
𝐶↓𝑡−𝑝 (𝑡)=𝐴𝑒↑−𝑡/ 𝜏↓1 +(1−𝐴) 𝑒↑−𝑡/ 𝜏↓2 𝜏↓𝑟 =∫0↑∞▒𝐶↓𝑡−𝑝 (𝑡) 𝑑𝑡
Lima, FS, et al, Langmuir, 2014, 30, 1239.
BEIJING 北京
DTATf aggregate is ordered and dehydrated in MD simula+ons
• RDF between the center of mass of the micelle and: – DTA’s headgroup: smaller
width in DTATf (smaller fluctua+ons);
– C.I.: Tf-‐ penetrates into the hydrophobic core of DTATf;
• DTA in DTATf micelle has fewer contacts with water.
Lima, FS, et al, Langmuir, 2014, 30, 1239.
BEIJING 北京
Hydra+on and C.I. dynamics at DTATf interface probed by dielectric relaxa+on spectroscopy
• DTATf DR spectra shows low Tf-‐ mobility at the micellar interface;
• Less water molecules were affected in DTATf than in DTAB solu+ons;
• MD simula+ons support these findings.
Surfactant Zib Zs Zt DTAC 9,8 29,3 39,1 DTAB 9,1 16,2 25,3 DTAMs 7,3 19,6 26,9 DTATf 11,3 -‐ 11,3
Lima, FS, et al, Langmuir, 2013, 29, 10037.
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MD simula+ons show high interac+on energies between Tf-‐ and DTA
• DTA/Tf-‐ interac+ons are more than 2.5 +mes that of DTA/Br-‐;
• High electrosta+c interac+on of DTA/Tf-‐ suggests ion-‐pairing;
• Considerable energe+c contribu+on from –CF3/surfactant’s tail.
Interac?on
%𝑬↓𝒕𝒐𝒕𝒂𝒍↑𝑫𝑻𝑨−𝑿
%𝑬↓𝑪𝒐𝒖𝒍↑𝑫𝑻𝑨−𝑿
%𝑬↓𝑳𝑱↑𝑫𝑻𝑨−𝑿
LJ (-‐CF3 – cauda) 5,95 -‐ 27,71 Elec (-‐CF3 – cauda) 0 0,00 -‐
LJ (-‐CF3 – CP) 2,72 -‐ 12,64 Elec (-‐CF3 – CP) 7,12 9,07 -‐ LJ (-‐SO3 – CP) 6,11 -‐ 28,45 Elec (-‐SO3 – CP) 71,40 90,93 -‐ LJ (-‐SO3 – cauda) 6,70 -‐ 31,19 Elec (-‐SO3 – cauda) 0 0,00 -‐
Lima, FS, et al, Langmuir, 2014, 30, 1239.
BEIJING 北京
DTA/Tf-‐ Interac+ons induces C.I. orienta+on at the micellar interface
• At the micellar interface, Tf-‐ exposes the –CF3 group to the core;
• No specific orienta+on of Tf-‐ is found at high distances from the micelle.
Lima, FS, et al, Langmuir, 2014, 30, 1239.
BEIJING 北京
A closer look at the DTATf interface
• Low Tf-‐ exit rate from the micellar interface;
• Low fluctua+ons of Tf-‐ and headgroups at the interface;
• Tf-‐ and headgroup are close.
MD da interface de DTATf
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Added NaTf increases the Nagg of DTATf aggregates and decreases α
• Nagg of DTATf increased with [NaTf] to finite values;
• Nagg increase is accompanied by dehydra+on;
• Micellar α is lowered.
[DTATf] / M [NaTf] / M
0 0.015 0.030 0.03 136 ± 2 224 ± 6 350 ± 13 0.045 162 ± 3 224 ± 6 365 ± 9 0.06 187 ± 5 250 ± 9 373 ± 14 0.08 212 ± 3 269 ± 8 404 ± 15 0.10 263 ± 10 263 ± 9 412 ± 5
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NaTf addi+on uppon DTATf solu+ons leads to Nagg increase and α decrease
• A maximum in viscosity of DTATf x [NaTf] is observed;
• Viscosity decay suggests surface charge lowering.
0.1 0.08
0.06
0.03 0.015 0.006
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Further NaTf addi+on upon DTATf leads to phase separa+on
• 0.05 M NaTf induces phase separa+on in DTATf solu+ons; – One is a surfactant-‐rich phase,
and the other is a surfactant-‐poor phase;
• The number of phases is a func+on of temperature.
Filme da separação de fase
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Summary
• DTATf forms dehydrated disk-‐like micelles; • The aggregates possess low α; • High packing and order of micellized monomers; • Micellar proper+es are reproduced in MD simula+ons;
• Specific Tf-‐/DTA interac+ons rules the micellar proper+es;
• Applica+ons?
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Proper+es of DNA-‐surfactant gel par+cles can be modulated by the surfactant’s C.I.
• Added drop of DNA solu+ons to surfactant solu+ons leads to gel par+cle forma+on;
• Par+cle’s hydrophobicity or hydrophilicity depends upon the surfactant’s C.I..
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Haemoly+c effects of the gel par+cles depends upon the nature of the C.I.
• Haemoly+c effect of gel par+cles depends upon the C.I.;
• The haemolysis kine+cs also depends on C.I..
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Flat gold nanopar+cles are obtained in DTATf
• AuCl4-‐ + ascorbic acid in DTATf generates nanodisks;
• The reac+on is fast and go without pre-‐formed nanopar+cles (seeds);
• Par+cle’s diameter/thickness can be controlled.
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Choice of surfactant’s C.I. enables kine+c and growth
control • These results suggests a new model of gold nanopar+cle growth in micellar media;
• Micellar proper+es are fundamental for guiding the growth and geometry of nanopar+cles.
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Procurar campo de força para as moléculas
Criar arquivo contendo os parâmetros de interação de cada átomo do sistema
Montar estrutura inicial com a quantidade de moléculas, criando interface “ar”/água (matriz com x0, y0, z0 de cada átomo) (Packmol)
Criar arquivo contendo os parâmetros de minimização de energia (energia alvo e número máximo de passos)
Arquivo com novas posições dos átomos (x1,y1,z1)
Criar arquivo contendo os parâmetros para equilíbrio NVT do sistema (∆t, T, integrador, etc)
Rodar minimização de energia (sem velocidades!) Daqui para baixo tudo no GROMACS
Arquivo com novas posições dos átomos e velocidades (x3,y3,z3, vx3, vy3, vz3) Rodar simulação NVT Arquivos com posições, velocidades e energias a cada 1000*∆t da simulação Extrair informações Valores de a, mobilidade de monômeros, hidratação, energias de interação, etc
1) Minimização
2) Equilíbrio NVT
Criar arquivo contendo os parâmetros para simulação do sistema (∆t, T, integrador, etc) 3) Simulação 4) Análise
MD de INTERFACE
Desenhar moléculas de DTA e íons (ChemDraw)
Rodar equilíbrio NVT Velocidades geradas por Maxwell-Boltzmann
BEIJING 北京
Procurar campo de força para as moléculas Criar arquivo contendo os parâmetros de interação de cada átomo do sistema
Criar arquivo contendo os parâmetros de minimização de energia (energia alvo e número máximo de passos)
Arquivo com novas posições dos átomos (x1,y1,z1) Criar arquivo contendo os parâmetros para equilíbrio NVT do sistema (∆t, T, integrador, etc)
Rodar minimização de energia (sem velocidades!) Daqui para baixo tudo no GROMACS
Rodar equilíbrio NVT Velocidades geradas por Maxwell-Boltzmann
Arquivo com novas posições dos átomos e velocidades (x2,y2,z2, vx2, vy2, vz2) Rodar equilíbrio NPT Arquivo com novas posições dos átomos e velocidades (x3,y3,z3, vx3, vy3, vz3) Rodar simulação Arquivos com posições, velocidades e energias a cada 1000*∆t da simulação Extrair informações Valores de a, mobilidade de monômeros, hidratação, energias de interação, etc
1) Minimização
2) Equilíbrio NVT
Criar arquivo contendo os parâmetros para equilíbrio NPT do sistema (∆t, T, pressão, integrador, etc) 3) Equilíbrio NPT
Criar arquivo contendo os parâmetros para simulação do sistema (∆t, T, pressão, integrador, etc) 4) Simulação 5) Análise
MD de MICELAS
Desenhar moléculas de DTA e íons (ChemDraw) Montar estrutura inicial com a quantidade de moléculas e na geometria desejada (matriz com x0, y0, z0 de cada átomo) (Packmol)