Electrochemistry of Methylene Blue Bound to a DNA-Modified Electrode

Bioconjugate Chem., 1997, 8(1), 31-37, DOI:10.1021/bc960070o

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Supporting

Material

Electrochemistry

of

Methylene

Blue

bound

to

a

DNA-Modified

Electrode

Shana

0.

Kelley

and

Jacqueline

K.

Barton*

Beckman

Institute,

Division

of

Chemistry

and

Chemical

Engineering,

California

Institute

of

Technology,

Pasadena,

CA

91125

Nicole

M.

Jackson

and

Michael

G.

Hill*

Department

of

Chemistry,

Occidental

College,

Los

Angeles,

CA

90041

*

to

whom

correspondence

should

be

addressed.

R

ECEIV

ED

Figure

Captions

If

1!9

(Sl)

Plot

of

E-Epc

vs.

log(v/ko);

comparison

of

theoretical

curve

(line,

ref.

29)

to

data

for

0.1

tM

methylene

blue

at

a

gold

electrode

derivatized

with

5'SH-(CH

2

)

6

-P-

AGTACAGTCATCGCG

3'

hybridized

to

its

complement

(filled

triangles)

in

25

mM

phosphate,

75

mM

NaCI,

pH=7.

The

fit

yields

a

value

of

ko

equal

to

60(5)

s-

1.

We

note

that

the

formalism

described

in

reference

29

is

based

on

Marcus

theory

and

was

derived

for

redox-active

species

immobilized

on

electrode

surfaces.

In

our

case,

the

strong

adsorption

of

MB

to

DNA

in

both

its

oxidized

and

reduced

states,

and

the

adherence

to

a

Langmuir

isotherm

ensure

that

electron-transfer

is

not

diffusion

controlled

(see

ref.

30).

Additionally,

this

treatment

assumes

symmetric

cathodic

and

anodic

shifts

about

the

reduction

potential

(a

transfer

coefficient,

o,

of

0.5,

within

the

Butler-Volmer

formalism);

this

condition

appears

to

hold

for

MB

reduction

at

our

DNA-modified

electrodes.

Additionally,

in

aqueous

solution

at

pH

7,

MB

undergoes

a

2e-,

1H+

transfer

via

an

ECE

mechanism

(25).

has

shown

that

the

follow-up

reactions

are

fast,

and

we

have

assumed

this

to

hold

for

our

system.

Spectroelectrochemical

experiments

show

isobestic

conversion

between

the

oxidized

and

doubly

reduced

states.

Therefore,

we

have

treated

this

system

assuming

a

2e-

transfer.

(S2)

Cyclic

voltammograms

of

0.1

mM

MB

at a

octadecanethiol-modified

electrode.

(B)

Plots

of

ipc

and

ipa

versus

scan

rate

1

/2.

3 00

250

A

experimental

200

theoretical

150

M

100

50

-50

-5

-4

-3

-2

-1

0

1

2

log(v/k

0)

Figure

Si

C

+150.0-

C

0.000-

L

_

L

-150.0-

-300.0-

-450.0-

-600.0-

-750.0-

0.00

-0.10

-0.20

-0.30

-0.40

-0.50

Potential/V

1.6

1.4

1.2

pa

0.8

U

06

0.6

00

P.

0.4

PC

0.2

0

2

5

1

v

2

a

I

a

U

1

2

N

5

1

a

1

0

1

Wi

-

a

*

0.1

0.2

0.3

0.4

0.5

0.6

0.7

(Volts/s)

1

/2

Figure

S2B