Ion interaction at the interface of Langmuir monolayers

Ion interaction at the interface of Langmuir

monolayers having amine headgroups

Doseok Kim

Department of Physics, Sogang University, Seoul, Korea

[email protected]

http://smos.sogang.ac.kr

July 4, 2017

Soft Matter Summer School, KAIST

2

2

0 0

127.2 eV (2 Ry)

4

eE

a

e -e

a0 = 0.53 A

atomic stability

= 80

3

2

room

0 0

1 124 meV

4 13 B

eE k T

a

e -e

13a0 ~ 7 A ~ l B

biological versatility

2

0 0

1~2 eV

4 13

eE

a

1.Introduction

4

5

Amine and ammonium

Either in charge neutral

or cationic formAlways cationic

6

Amines and ammoniums in biological systems

Polypeptide chainPeptide bonding

Protein

7

Amines and ammoniums in biological systems

Cell

Lipid bilayer

Lipids : Main building block of cell

8

Cell membrane

Langmuir monolayer: model system mimicking biomembrane

Lipid bilayer Langmuir monolayer

9

Sum-frequency vibrational spectroscopy (SFVS)

2(2)

( ) : ( ) ( )SFG IR Vis eff IR VisI E E

reflects molecular

properties at interface

SFG

Vis

IRx y

z

10

SFVS: surface-selective, monolayer-sensitivy

(1) (2) (3)

0 0 0: :P E EE EEE

(2) (2) (2) (2)(2): ( 0)( ) : , P E E EE P

(2) 0

(2) 0

For medium possessing inversion symmetry,

3000 3200 3400 3600 3800 4000

IR absorption spectra

Liquid water

Vapor water

SF spectra

neat water surface

wavenumber (cm-1)

11

Experimental setup

pump

idler

signal

Sample

(Langmuir monolayer)

Nd-YAG laser (50 ps, 1.064 mm)

LiNbO3 LiNbO3

2.5 - 4 mm, 150 mJ

532 nm,1 mJ

Optical Parametric Generator/Amplifier (OPG/OPA)

KTP

ir

vis

SFG

OPG/OPA

Sample Stage

12

2800 3000 3200 3400 3600

-0.9

-0.6

-0.3

0.0

0.3

0.6

0.9

1.2

-0.9

-0.6

-0.3

0.0

0.3

0.6

0.9

1.2

Blue: OH of Interfacial water I

m

(2)

S

SP

SF

G In

ten

sity (

arb

. u

nit)

Wavenumber (cm-1)

(a)1-HD

Red: CH3 of alkyl chain

SF spectrum for charge-neutral monolayer/water

OH OH OH OH OH OHOH OH

1-Hexadecanol

(fatty alcohol)

13

SF spectrum for cationic monolayer/water

2800 3000 3200 3400 3600

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Wavenumber (cm-1)

Im

(2)

SS

P S

FG

In

tensity (

arb

. u

nit) (b) DPTAP(b) DPTAP

Sung, DK and others, Langmuir 26, 18266 (2010).

N(Me)3 N(Me)3N(Me)3 N(Me)3

1,2-dipalmitoyl-3-

trimethylammonium propane

(Cationic lipid)

Polar ordering of water molecules by surface charge

Area of one lipid

molecule ~ 40 Å 2

9~ ~ 10 /2

E V m

30 9(6.2 10 )(10 ~ 40 / ) B

U P E

C meV k Tm V m

Strong electric field aligns

interfacial water molecules

15

polar ordering increases SF signal

162800 3000 3200 3400 3600

-0.9

-0.6

-0.3

0.0

0.3

0.6

0.9

1.2

-0.9

-0.6

-0.3

0.0

0.3

0.6

0.9

1.2

Blue: OH of Interfacial water

Im

(2

)

S

SP

SF

G In

ten

sity (

arb

. u

nit)

Wavenumber (cm-1)

(a)1-HD

Red: CH3 of alkyl chain

2800 3000 3200 3400 3600

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Wavenumber (cm-1)

Im

(2)

SS

P S

FG

Inte

nsity (

arb

. unit) (b) DPTAP(b) DPTAP

2. Quaternary-amine

monolayer

17

Cationic surfactant: DPTAP

DPTAP

MeMe

Me

N+

Fully positively charged at any pH conditions.

1,2-dipalmitoyl-3-trimethylammonium propane

(Cationic lipid)

Cl-

I-

412 pm

354 pm

Cl-

Different anions

adsorbed to headgroup investigated

18

Halide anion

(I-, Br, Cl-)

354pm

364pm

412pm

[DPTAP]+

Anions (different sizes) under charged interface

no size dependence from classical theory!

++ ++ +

Gouy-Chapman model

2

0

0

2

: bul

( ) ~

k concentrati

,

on of salt

z

o

r o

z enc e

kT

c

Counterions screen the surface charge

Counterions are point charges (no ion dependence)20

20 30 400

10

20

30

40

50

60

70

S

urf

ace

Pre

ssure

(m

N/m

)

Surface Area (A2 / chain)

NaI (10 mM)/DPTAP

NaBr (10 mM)/DPTAP

NaCl (10 mM)/DPTAP

Water/DPTAP

- Pressure decreased in salt solutions

- Pressure decreased more for larger halide anion

Cl-Br -

I -

Pressure-area (-A) isotherm

adding ions in water

Sung, DK, and others, J. Phys. Chem. C 119, 7130 (2015).

Counterions decrease

SF intensity of the OH band.

Larger anions (I-) disturb

water dipole orientation more.

2800 2900 3000 3100 3200 3300 3400 3500 36000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Pure water

10 uM NaI

100 uM NaI

1 mM NaI

10 mM NaI

100 mM NaI

SS

P S

FG

Inte

nsity (

arb

. unit)

IR wavenumber (cm-1)

2800 2900 3000 3100 3200 3300 3400 3500 36000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Neat water (x5)

Pure water

10 uM NaCl

100 uM NaCl

1 mM NaCl

10 mM NaCl


SS

P S

FG

Inte

nsity (

arb

. unit)

100 mM NaCl

Detailed concentration dependence

DPTAP full monolayers

on NaCl solutionsDPTAP full monolayers

on NaI solutions

23

1E-4 1E-3 0.01 0.1 1 10 1000

5

50

100

150

200

250

300

350

Neat water

Salt concentration (mM)

DPTAP on pure water

Inte

gra

ted

SF

In

ten

sity (

arb

. u

nit)

ODA / NaCl solutions (3000 - 3550 cm-1)

ODA / NaI solutions (3000 - 3550 cm-1)

I- counterions adsorb at the surface

~1000 times more effectively than Cl-.

24


So there is a strong evidence (from the change of OH signal)

of counterion adsorption,

can we see the excess halide ions directly?

X-ray Florescence (XRF)

z

penetration depth

below c: 6 – 8 nm

Bu and Vaknin, J. Appl. Phys. 105, 084911 (2009).

Cu emission

(8.05keV)

Cl- emission (K-lines ~2.8 keV)

I- emission (L-lines ~3.5−5.0 keV)

c = 0.8o at Qz = 0.022A-1

1- ~= 1-10-4

W. Wang and D. Vaknin in Ames

26

Bulk XRFSurface XRF

c

XRF: Direct measurement of adsorbed counterions

Surface adsorption of I - observed

Wang, DK and others, JPCB (2013)

BulkSurface

c

Zion

oncentration

pressure

(mN/m)

Ion density

(×10−2 Å−2)

Depth

(D)

10 mM NaI 6 2.0 0.2 28 5

100 mM NaCl 26 2.9 0.9 37 20

2( ) | ( ) | exp[ | | / ( )]F z z s ion zI Q C t Q n z D Q

2( ) | ( ) | ( )F z z z bI Q C t Q D Q n

XRF from ions in bulk.

XRF from ions at surface.

28

X-ray Florescence (XRF)

1) Surface density similar between I- and Cl-

2) Cl- ions seem to be located deeper than I-

1E-4 1E-3 0.01 0.1 1 10 1000

5

50

100

150

200

250

300

350

Neat water


DPTAP on pure water

Inte

gra

ted

SF

In

ten

sity (

arb

. u

nit)



I- counterions adsorb at the surface

~1000 times more effectively than Cl-.29


Why does X-ray seem to contradict SFG?

- X-ray probes 6 ~ 8 nm (by evanescent wave)

- SFG can probe only where inversion symmetry is broken

X-ray

SFG

X-ray

SFG

Monolayer structure: X-ray reflectivity

High e- density:

Headgroups and ionsLow e- density:

Hydrocarbon tails

Surface structure of DPTAP monolayer

NaCl:

lateral ordering

disturbed by Cl- adsorption

no salt (counter ions):

well-ordered monolayerNaI:

disruption becomes more

severe due to adsorbed I-

- - -- -- - -

Alkyl chain conformation by SFG

2800 2900 3000 3100

Increasing

area/molecule

CH2,s CH2,as

CH3,s CH3,fr

Sung, DK and others, Langmuir (2010)

Neat monolayer: only terminal methyl (CH3) groups contribute to SFG

Disordered monolayer: methylene (CH2) groups contribute to SFG

34

Alkyl chain conformation for different counterions

- Green: CH3 stretch modes

- Red: CH2 stretch modes

DPTAP A1

(CH2,ss / ~2852cm-1)

A3

(CH3,ss / ~2875cm-1)

A1/A3

on pure water 0.5 0.9 5.4 0.8 0.09

on NaCl (100 mM) 0.7 0.6 5.8 0.5 0.12

on NaI (10 mM) 2.0 0.1 6.8 0.1 0.29

1. Surface excess of halide anions on charged interface:

- by surface SFG

- direct observation of the anions by X-ray

2. I-: direct adsorption to the headgroup

Cl-: broadly distributed over the double layer

3. X-ray and surface nonlinear optics are

complementary tools for surface science

Conclusion

Sung, DK and others, JPCC (2015)

X-ray

SFG

36

Growth of Au nanorods

37

Why does the rod only grow along the length direction?

38

Use of CTAB surfactant in the growth of Au nanorods

TEM images of Au nanocrystals

T. K. Sau, C. J. Murphy, Philos. Mag. 2007, 87, 2143

CTA-Cl [0.1M] CTA-Br [0.1 M]

Garg et al. Langmuir 2010, 26, 10271

3. Primary-amine

monolayer

40

DPTAP

Always positively charged

-N(CH3)3+

+e

choline and amine headgroups

n-octadecylamine (ODA)

Protonated/deprotonated at different pHs

+e

-NH3+ -NH2

High pHLow pH

pKa~10.5

n-octadecylamine (ODA) on water

Surface area~20Å 2/molecule

Langmuir trough 42

pH changed by

adding HCl or NaOH

ODA/water interface: pH dependence

2850 3000 3150 3300 3450

0

1

2

3

4

5

6

7

8

2850 2900 2950 3000

pH 2.0

pH 3.0

pH 3.5

pH 5.7

pH 9.0

pH 10.0

pH 11.0

Wavenumber (cm-1)

SS

P S

FG

Inte

nsity (

arb

. unit)

pH 11.0

pH 2.0

CH3 CH3

CH2CH2

Mostly trans

Gauche defects

OH water band intensity

increases at low pHs

Langmuir 31, 13753 (2015). 43

Isotherm compression curves

3D: PV ~ nRT

Langmuir trough

2D: A ~ nRT (gas phase)10 20 30 40 50

0

10

20

30

40

50

60

70

pH 2

pH 3

pH 3.5

Surf

ace P

ressu

re (

mN

/m)

Surface Area (A2/molecule)

pH 5.7

10 15 20 250

10

20

30

40

50

60

pH 4.0 pH 3.0 pH 2.75

pH 2.5 pH 2.25 pH 2.0

44

Isotherm compression curves

10 20 30 40 500

10

20

30

40

50

60

70

pH 2

pH 3

pH 3.5

S

urf

ace

Pre

ssu

re (

mN

/m)

Surface Area (A2/molecule)

pH 5.7

10 15 20 250

10

20

30

40

50

60

pH 4.0 pH 3.0 pH 2.75

pH 2.5 pH 2.25 pH 2.0

N

HH

Limitation area

~ 20 Å

Surface pressure increases again below pH 3

No surface pressure at pH ~ 3.5.

45

At pH 3.5 …

3000 3200 3400 3600 38000.0

0.1

0.2

0.3

0.4

0.5

0.6

S

SP

SF

G I

nte

nsity (

arb

. u

nit)

Wavenumber (cm-1)

ODA monolayer/water, pH 3.5

ODA monolayer/water, pH 5.7 (x5)

Air/neat water, pH 5.7 (x5)

N

HH𝐇+

enhancement of water OH band indicates the

existence of ODA molecules at air/water interface.

Free

OH

46

X-ray reflectivity measurement

-10 0 10 20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

/

wa

ter

d(Å )

0.1 0.2 0.3 0.4

0.1

1

10

R/R

f

qz(Å

-1)

ODA on pH 3.5

pure water

Interface

Modulation in electron

density profile.

Direct evidence of

diluted ODA monolayer

47

ODA on D2O/H2O mixture

2800 3000 3200 3400 36000.00

0.02

0.04

0.06

0.08

0.10S

SP

SF

G Inte

nsity (

arb

.unit)

Wavenumber (cm-1)

ODA on pH 3.5 (D2O/H

2O=90/10)

2800 2840 2880 2920 2960 30000.00

0.02

0.04

CH2,asCH2,ss

existence of disordered ODA molecules48

Reminder: pH dependence

2800 3000 3200 3400 36000.0

0.2

0.4

0.6

0.8

1.0

SS

P S

FG

Inte

nsity (

arb

.unit)

Wavenumber (cm-1)

ODA monolayers

on pure water (pH 5.7)

on pH 2.0 water

on pH 3.5 water

+ + ++ +++

pH 5.7 pH 3.5 pH 2.0

Why does the CH signal appear again at lower pH?49

Conjecture: Effect from Cl- ions

HCl

H3O+

Cl-

H3O+Cl-

H2O

H2O

H2O

H2O

H2O

50

Adding salt at pH 3.5

2800 3000 3200 3400 3600 38000.0

0.5

1.0

1.5

SS

P S

FG

Inte

nsity (

arb

. unit)

Wavenumber (cm-1)

ODA at pH 3.5 3mM NaCl

3mM NaBr

3mM NaI

without salt

pH 3.5 + 3 mM

NaCl gives

same Cl- anion

concentration as

water at pH 2.5

Adding 3 mM NaX salt recovers CHx bands. 51

10 20 30 40 500

10

20

30

40

50

60

Su

rfa

ce

Pre

ssu

re (

mN

/m)

Surface Area (إA2/molecule)

ODA on water

pH3.5+3mM NaBr

pH3.5+3mM NaI

pH3.5+3mM NaCl

pH3.5

pH2.5

Adding salt at pH 3.5 recovers isotherm curve at pH 2.5

Iodide anion makes the ODA monolayer collapses earlier 52


-10 0 10 20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

/

wa

ter

d(A)

At pH 3.5, W/O salt

Clear Kiessig fringe and electron density enhancement

Well organized ODA monolayer and adsorbed anions53


Conclusion

pH > 5 3 < pH < 5 pH < 3

1) Effective pKa of ODA in Langmuir monolayer (pKa ~ 5) is much lower

than its bulk value (pKa ~ 10.5).

2) When protonation of ODA amine happens (at low pH),

the monolayer becomes unstable.

3) Surface enrichment of counter Cl- ions stabilizes the ODA monolayer.

54

4. Primary-amine monolayer

with salt addition

55

2800 2900 3000 3100 3200 3300 3400 3500 36000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Pure water

10 uM NaCl

100 uM NaCl

1 mM NaCl

10 mM NaCl


SS

P S

FG

Inte

nsity (

arb

. unit)

100 mM NaCl

Y(z)

Reminder: salt adsorbed on cationic surface

z

2

0

0

2( ) ~ ,

: salt concentration

z

o

r o

c ez e

kT

c

0c

DPTAP/NaCl solution

56

2800 2900 3000 3100 3200 3300 3400 3500 36000.0

0.5

1.0

IR Wavenumber (cm-1)

SS

P S

FG

Inte

nsity (

arb

. unit)

Mostly charge neutral monolayer

57

ODA on pure water

2800 2900 3000 3100 3200 3300 3400 3500 36000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

DPTAP (x1)

100 mM

10 mM

10 uM

100 uM

No Salt

1 mM


SS

P S

FG

Inte

nsity (

arb

. unit)

2800 2900 3000 3100 3200 3300 3400 3500 36000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

No Salt

10 uM

100 uM

1 mM

10 mM

100 mM


SS

P S

FG

Inte

nsity (

arb

. unit)

Neat water (x5)

ODA / NaCl and NaI solutions

58

Why does SF signal increase by adding salt?

2

00

2( ) ~ , , : salt concentration

z

o

r o

c ez e c

kT

- Unexpected result

1E-6 1E-3 0.01 0.1 1 10 1000

50

100

150

200

250

300

350



Inte

gra

ted

SF

In

ten

sity (

arb

. u

nit)


No salt

DPTAP on pure water

59

+

ODA (amine headgroup)

The ODA surface become charged upon addition of salt?

- adsorbed cation (Na+)

- adsorbed anion (Cl-, I-)

- protonation of –NH2 into –NH3+

We need to know what charge is on the surface

DPTAP (choline headgroup)

++ ++ + +++

http://upload.wikimedia.org/wikipedia/commons/e/e1/Cetyl-alcohol-3D-vdW.png
































Wei bu et al. J. Phys. Chem. Lett. 1, 1936 (2010).

Previous XRF study – only anions

I-Cs+

Only anions at the surface !

Bu et al. J. Phys. Chem. Lett. 1, 1936 (2010).61

square measurement is not enough to determine the phase

I() = |E()|2 = |- E()|2

I() = |ELO() + E()|2 = ILO() + I() + 2Re(ELO()E*())

≠ |ELO() - E()|2 = ILO() + I() - 2Re(ELO()E*())

Interference by introducing

the local oscillator field, ELO()

Phase sensitive (PS)-SFVS

2

2 2

* *

( ) i t

SF sample LO

sample L

i t i t

LO sample LO sample

O

E E e

I E E e

E E

E E e

2

SF sampleI E

Direct measurement of sum-frequency E-field, not |E|2

63

Nihonyanagi et al. J. Chem. Phys. 130, 204704 (2009).

2

2 2 * *

2wher ( ) 1e,

i

sample LO

i i

sample LO LO

F

sample LO sam le

S

p

E E e

E E E E e

n d

E E e

monochromator

CCD

Camera

(Constructive)

(Destructive)

Schematics of PS-SFVS

2( 1)FSn d

Interference fringe from the reference (z-cut quartz)

-3000 -2000 -1000 0 1000 2000 3000-2.00E+008

-1.00E+008

0.00E+000

1.00E+008

2.00E+008

SF

G Inte

nsity (

arb

. un

it)

Time (fs)

FT real part

FT imaginary part

1200 1400 1600 1800 2000 2200 2400

ImFTSFGref

ReFTSFGref

+1.7 psCutoff time:

+1.2 ps

(x1)

(x0)

Fourier

Transform2 2

( )

* ( )

* ( )

( ) ( )

( ) ( ) ( ) ( )

( ) ( )

i t

ref LO

i t i T t

LO ref

i T t

LO ref

E E e d

I t I e d E E e d

E E e d

( 1)2

~ (1.7 )

FSn dc

c

T ps

Principles of PS-SFVS

*( ) ( ) i T

LO refE E e

640 645-2.00E+009

-1.00E+009

0.00E+000

1.00E+009

2.00E+009

SF

G In

ten

sity (

arb

. u

nit)

SF wavelength (nm)

IFT real part

IFT imaginary part

620 625 630 635 640 645 650 655 660-2.00E+009

-1.00E+009

0.00E+000

1.00E+009

2.00E+009

SF

G Inte

nsity (

arb

. un

it)

SF wavelength (nm)

IFT real part

IFT imaginary part

Interference fringe (by inverse Fourier transform)

620 625 630 635 640 645 650 655 660-1.00E+009

-5.00E+008

0.00E+000

5.00E+008

1.00E+009

SF

G In

ten

sity (

arb

. u

nit)

SFG wavelength (nm)

DPTAP monolayer/water interface

IFT real part

IFT imaginary part

*( ) ( ) i T

LO sampleE E e

620 625 630 635 640 645 650 655 660-3.00E+009

-2.00E+009

-1.00E+009

0.00E+000

1.00E+009

2.00E+009

3.00E+009

SF wavelength (nm)

Air/z-cut quartz interface

IFT real part

IFT imaginary part

*( ) ( ) i T

LO refE E e

*

(2) (2)

, , *

(2) * *

(2) * *

( ) ( )Re Im

( ) ( )

( ) ( )

( ) ( )

i T

LO sample

norm sample norm sample i T

LO ref

sample IR IR Vis Vis

ref IR IR Vis Vis

E E ei

E E e

E ER

E E

interference fringe (sample & reference)

(2

2 22 2

)(( )

()

(~

))

q

q IR

q

SFG NR

q I

q IR q

q IRq qq qR qq

A

i

AAE

i

When molecules at interface are excited resonantly by IR,

Non-resonant

contribution

(very weak)

Im (2)R

(determines sign of Aq

directly)

Resonant contribution,

(2)R

(damped oscillation)

Re (2)R

^ ^ ^^ ^ ^(2) (2)

, ,

( )( )( )( )

iNR

i IR i i

sNA

i j ki

Molecular moiety

orientation

ensemble average over molecules

Sum-frequency field

2800 2900 3000 3100 3200 3300 3400 3500-5.0

-2.5

0.0

2.5

5.0

SF

fie

ld a

mplit

ude (

arb

.unit)

DPTAP / pH 5.7 water

Im(2)

Re(2)

Wavenumber (cm-1)

HD-SFVS: OH band sign change

2800 2900 3000 3100 3200 3300 3400 3500-5.0

-2.5

0.0

2.5

5.0

SF

fie

ld a

mplit

ude (

arb

.unit) Arachidic acid / pH 12.0 water

Im(2)

Re(2)

Negatively charged surface

- dipole upward

- positive OH band

CH3CH3

+ +

- - Positively charged surface

- dipole downward

- Negative OH band+

-

CH3

70

2800 2900 3000 3100 3200 3300 3400 3500-5

-4

-3

-2

-1

0

1

2

3

4

5

SF

fie

ld a

mplit

ude (

arb

.unit) DPTAP / water - Im

(2)

DPTAP / NaCl(10 mM) - Im(2)

Comparison between DPTAP and ODA

2800 2900 3000 3100 3200 3300 3400 3500-5

-4

-3

-2

-1

0

1

2

3

4

5

SF

fie

ld a

mplit

ude (

arb

.unit)


ODA / water- Im (2)

ODA / NaCl(10 mM)- Im (2)

salt addition

salt addition

screening by positive

surface charges

becomes more positively

charged!

CH3CH3

CH3

N+

71

protonation of amine groups by added salt

1E-6 1E-3 0.01 0.1 1 10 1000

50

100

150

200

250

300

350



Inte

gra

ted

SF

In

ten

sity (

arb

. u

nit)


No salt

DPTAP on pure water

72

Why?? (from Poisson-Boltzmann theory)

0 1 2 3 4 51E-4

1E-3

0.01

0.1

1

Bulk conc.

Coion

Counterion

10 mM monovalent salt

Conc (

M)

Distance (nm)

0 1 2 3 4 51E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

Bulk conc.

Coion

Counterion10 mM monovalent salt

Co

nc (

M)

Distance (nm)

Petersen et al. J. Phys. Chem. B 108, 14804 (2004).

Depth Profile of proton follows coion

distribution.

For high salt concentration, difference

between bulk and surface coion

concentration becomes less.

More chance to protons diffuse

into surface region.

Diff ~ 10-4

Diff ~ 10-1

73

74

++ ++ + +++

0

+ +

3 2 2 3 0

++2 3 0

a 3 0+

3

[NH ]+[H O] [NH ]+[H O ] ,

[NH ][H O ]K = , [H O ]

[NH ]

B

z

e

k Tzz HC e

[H3O+]z=0 : interfacial proton concentration

CH+ : bulk proton concentration

x : ionization fraction, [NH3+]/([NH3

+]+[NH2]

0b a 10

(1 )pH pK log

2.3

B

ex

x k T

+++++++

(z)

0

+

- - - -

- -

-

-

+

++

Surface pH is different from bulk pH

















75

Adding salt also changes surface proton concentration

,

,

(z) ~ (z)

H bulk

H coion

coion bulk

CC C

C

76

For more quantitative prediction….

00 0

e8 sinh( ) , (Graham equation)

2

r B

B

eC k T x

k T A

0b a 10

(1 )pH pK log , (surface pH)

2.3

B

ex

x k T

10 b a

13410

(1 )sinh((log pH p ) / 0.87)

bpH

tot salt H salt

xC C C C

xA K

x

77

10 b a

13410

(1 )sinh((log pH p ) / 0.87)

bpH

tot salt H salt

xC C C C

xA K

x

78

(1) Different ions (Cl-, I-) worked differently

(2) Adding salt increased (did not decrease) the E field

2

0

1 1

4

eE

r

Science 340, 1265 (2013)

80

Central Dogma (of molecular biology)

81

82

Epigenetic modification of the histone

Science, Mar. 2017

Dr.Woongmo SungZaure Avazbaeva

Jonggwan Lee

David Vaknin

(Ames Natl Lab)

Kwanwoo Shin

(Sogang Univ)

Documents

Ion interaction at the interface of Langmuir monolayers