Molecular Biomimetics: Synthesizing Gold Nanostructures with Amino Acids Alexander Chen Chemical and Environmental Engineering Department, UC Riverside

Molecular Biomimetics:Synthesizing Gold

Nanostructures with Amino Acids

Alexander ChenChemical and Environmental Engineering Department, UC Riverside

Reasons For Using Biomimetics

• Simple and efficient method that creates consistent nanostructures and patterns in easily controllable environments.

• Environmentally Safe- no harmful waste are produced in comparison to chemical methods of synthesis.

• Has potential for greater compatibility and efficiency for integration within biological environments during medical use.

Process of Synthesizing Gold Nanostructures with Amino Acids

• The nanostructures are synthesized through mixing AuCl4 and specific amino acids within an aqueous solution and incubated (Mimicking physiological environments in which typical synthesis reactions occur).

• The gold structures that are formed are based on the specific binding properties of each particular amino acid and the control of concentration, contents of solution, pH, and temperature.

• Synthesis Conditions and Procedure:

– 1mL samples consisting of 940ųL water, 40ųL 0.5mM or 20mM AuCl4, and 10ųL amino acid (Alanine,

Arginine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Histidine, Isoleucine,

Leucine, Lysine, Methionine, Phenylalanine, Proline, Serine,Threonine, Tryptophan, Tyrosine, and Valine) and

1 control sample with no amino acid

– Excess chloride concentration were set at 0N, 0.1N, and 0.5N for various sets.

– 25M NaOH used to adjust pH to 3 and 5 for 0.5mM AuCl4 and to 3.2, 4.5, 5.2, 7.5, and 11.6 for 20mM AuCl4

- Initial pH of each individual sample is recorded to ensure uniformity between samples (±0.1)

- Solutions are incubated for 3 days at 37°C

- Centrifuged and washed for three cycles at 10 rpm and 10min/cycle.

- Final pH after the reaction are measured to examine correlation with synthesizing and binding efficiency.

- 10ppm of amino acid solution mixed with HCl(10%) to create 5mL solutionand measured gold ion concentration in

solution with AAS (Atomic Absorbtion Spectrophotometer).

- Photographs of gold nanostructures and speciation taken with microscope.

Amino Acids and Gold Chloride Used to Make Standard Solution

Alanine Ala A 89.1g/mol C3H7NO2 1.8 .0009mol(.08019g)

Arginie Arg R 174.2g/mol C6H14N4O2 -4.5 .0009mol(.15678g)

Asparagine Asn N 132.188g/mol C4H8N2O3 -3.5 .0009mol(.1189692g)

Aspartic Acid Asp D 133.10g/mol C4H7NO4 -3.5 .0009mol(.11979g)

Cysteine Cys C 121.16g/mol C3H7NO2S 2.5 .0009mol(.109004g)

Glutamic Acid Glu E 147.13g/mol C5H9NO4 -3.5 .0009mol(.132417g)

Glutamine Gln Q 146.15g/mol C5H10N2O3 -3.5 .0009mol(.131535g)

Glycine Gly G 75.07g/mol C2H5NO2 -0.4 .0009mol(.067563g)

Histidine His H 155.16g/mol C6H9N3O2 -3.2 .0009mol(.139644g)

Isoleucine Ile I 131.17g/mol C6H13NO2 4.5 .0009mol(.118053g)

Leucine Leu L 131.18g/mol C6H13NO2 3.8 .0009mol(.118062g)

Lysine Lys K 146.188g/mol C6H14N2O2 12 -3.9 .0009mol(.1315692g)

Methionine Met M 149.21g/mol C5H11NO2S 1.9 .0009mol(.134289g)

Phenylalanine Phe F 165.19g/mol C9H11NO2 2.8 .0009mol(.148671g)

Proline Pro P 115.13g/mol C5H9NO2 12 -1.6 .0009mol(.103617g)

Serine Ser S 105.09g/mol C3H7NO3 -0.8 .0009mol(.094581g)

Threonine Thr T 119.12g/mol C4H9NO3 -0.7 .0009mol(.107208g)

Tryptophan Trp W 204.225g/mol C11H12N2O2 -0.9 .0009mol(.1838025g)

Tyrosine Tyr Y 181.19g/mol C9H11NO3 -1.3 .00045mol(.0815355g)

Valine Val V 117.15g/mol C5H11NO2 4.2 .0009mol(.105435g)

HAuCL4 3H2O 393.845g/mol 0.0005mol(.196923g)

CExtremely small, granular gold structures

DMedium, thin, overlapping, truncated triangle

gold structuresP

Medium, solid, polygonal gold structures

WExtremely small, granular gold

structures

Speciation of Gold Nanostructures (0.5mM AuCl4 pH 3 0.0M NaCl)

Reduction Rate of Amino Acids (0.5mM AuCl4 pH 3 0.0M NaCl)

W Y C M H K N D F L I T S G P R E V Q A CT0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14S

ynth

esiz

ed G

old

(m

g/m

L)

Amino Acids

Averages and Standard Deviation for Gold Synthesized by Amino Acids (Set 1,2,3)

L-PH5-0.0N NaClSmall, head and tail w/

granular, gold structures

N-PH5-0.0N NaClSmall, granular, gold

structures

L-PH5-0.1N NaClLarge, head and tail w/

morphing into polygonal plates

N-PH5-0.1N NaClSmall, head and tail w/ clusters, gold structures

L-PH5-0.5N NaClLarge, solid polygonal plate, gold structures

N-PH5-0.5N NaClVery small, solid polygonal

plate, gold structures

0.5mM AuCl4 (0.0M, 0.1M, 0.5M NaCl) pH 5 Comparison

(Lysine and Asparagine)

200 400 600 800 1000 1200

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24A

bso

rbance

Wavelength(nm)

F G I L P V

Absorbance vs Wavelength (Set 1)

200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Abso

rbance

Wavelength(nm)

C M N Q S T W Y


200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

Abs

orba

nce

Wavelength(nm)

H K R

Absorbsance vs Wavelength (Set 1)

200 400 600 800 1000 12000.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Abso

rbance

Wavelength(nm)

D E


Wavelength Scans by Functional Group (pH 5)

Lysine

Asparagine

0.5mM AuCl4 (0.0M, 0.1M, 0.5M NaCl) pH 5 Color Comparison

V-PH3Medium, solid, hexagonal gold

structures

V-PH5Small, head and tail, gold structures with extremely small, granular gold

structures

N-PH3Large, solid & thin, gold structures

N-PH5Extremely small, granular gold

structures

0.5mM AuCl4 0.0M NaCl pH 3 and 5 Comparison of Geometry

0.0N NaCl 0.1N NaCl 0.5N NaCl

pH

3.2

4.5

5.2

7.5

11.6

Geometry Change (20mM AuCl4)

A F C M H K D E CTRL0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.0NNaCl 0.1NNaCl 0.5NNaCl

Gol

d S

ynth

esiz

ed (m

g/m

L)

Amino Acids

Gold Synthesized by Amino Acids (0.02M AuCl pH 3.2)


0.005

0.010

0.015

0.020

0.025

0.030

Amino Acids

Gol

d S

ynth

esiz

ed (m

g/m

L)

Gold Synthesized by Amino Acids (pH 3.2)



0.005

0.010

0.015

0.020

0.025

0.030 Gold Synthesized by Amino Acids (pH 4.5)

Amino Acids

Gol

d S

ynth

esiz

ed (m

g/m

L)



0.005

0.010

0.015

0.020

0.025


Gol

d S

ynth

esiz

ed (m

g/m

L)

Amino Acids


Reduction Rate (20mM AuCl4)


0.005

0.010

0.015

0.020


Amino Acids

Gol

d S

ynth

esiz

ed (m

g/m

L)



0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.022

0.024Gold Synthesized by Amino Acids (pH 4.5)

Gol

d S

ynth

esiz

ed (m

g/m

L)

Amino Acids



0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040


Amino Acids

Gol

d S

ynth

esiz

ed (m

g/m

L)



0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040


Amino Acids

Gol

d S

ynth

esiz

ed (m

g/m

L)



0.01

0.02

0.03

0.04

0.05

0.06Gold Synthesized by Amino Acids (pH 5.2)

Amino Acids

Gold

Syn

thesi

zed (

mg/m

L)



0.01

0.02

0.03

0.04

0.05


Amino Acids

Gold

Syn

thesi

zed (

mg/m

L)


pH 3.2 pH 4.5 pH 5.2

pH 7.5 pH 11.6

pH Species Geometry

3.2 AuCl4- (Yellow) Plates

4.5 AuCl3(OH)- (Yellow) Plates

5.2 AuCl2(OH)2- (Yellow) Head and Tail

7.5 AuCl2(OH)2- + AuCl(OH)3-(Orange) Dark Orange Film

11.6 AuC(OH)3- + Au(OH)4- (Clear) Granular Partcles

Conclusion• Decrease in pH allows for greater synthesizing and bonding efficiency.

• Size of nanostructure and thickness is inversely related to synthesizing efficiency.

• Lowering the pH shifts the species towards [AuCl4] – and plate structures.

• Increasing excess chloride concentration using NaCl has same effect as lowering pH down.

• Initial structure for 0.0N NaCl has a strong correlation with the specific wavelength in UV/vis spectrophotometer, color of sample, and pH:

– Granular particles: 480 nm, Violet/Brown/Green/Grey, pH<3.8

– Head and tail w/ granular particles: 500nm, Black or Dark Green/Grey Precipitates with Clear-Light Grey Solutions, pH>3.8

• Morphology of the nano structures from [AuCl(OH)3]- to [AuCl4] -, : granular->dark film->head and

tail->cluster->solid plates

• Morphology has a trend based on functional group of amino acids.

-Hydrocarbons: small head and tail w/ granular->medium/large head and tail morphing into plates->very small/small

solid plates.

-Neutral: granular->small head and tail or granular w/ gold clusters->very small-very large solid plates.

-Base: small head and tail/granular->plate/morphing into plate->small-medium plate

-Acid: small head and tail/granular->head and tail w/ clusters->plate

• When morphology shifts, the amount of gold synthesized increases dramatically (Figure 4).

• Increasing gold concentration has a similar, but reduced, effect as increasing chloride concentration or

lowering pH and increases the size of the structures formed, as well. Also increases consistency of

species and variation of pH between different amino acids (Figure 2 and 6).

Reduction rate increases whenever there is a shift in morphology or shape and size of geometry

Future Experiments• Determine quantity of dominant species formed for each amino acid at various other pHs and concentrations.

• Further correlate trends between speciation, pH, solution color, wavelength, and concentration.

• Controlling the shape of synthesized gold structures through changes in pH levels and chloride concentration.

• Use specific peptides to synthesize uniform nanowires and nanoplates for use in electronic and medical sensors.

Acknowledgments

Thanks goes to the BRITE program and Jun Wang for organizing this wonderful opportunity in research, and to Professor Nosang Myung and Ms. Jungok Kim of the Chemical and Environmental Engineering Department for their guidance and mentoring.

Documents

Molecular Biomimetics: Synthesizing Gold Nanostructures with Amino Acids Alexander Chen Chemical and Environmental Engineering Department, UC Riverside