Speciﬁc’Ion’Eﬀects’on’Micelles:’The’case ... · • FTf"is"oriented" atthe"air/...

BEIJING 北京

Biochemistry Professor, Universidade de São Paulo Advisor, Scien?fic Directorate, FAPESP Vice-‐President, Brazilian Academy of Sciences

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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


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.


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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


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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


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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


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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.


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.


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


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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 


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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.


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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


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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 -‐


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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.


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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.

BEIJING 北京 Hernan Chaimovich CHBC-‐ Fapesp 30

The end

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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

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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)

Speciﬁc’Ion’Eﬀects’on’Micelles:’The’case ... · • FTf"is"oriented" atthe"air/...

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