hydrophobized plant polyphenol: self-assembly and ... · hydrophobized plant polyphenol:...

S1

Supporting information Hydrophobized Plant Polyphenol: Self-Assembly and Promising Antibac-

terial, Adhesive, and Anticorrosion Coatings Debabrata Payra,a Masanobu Naito, * a Yoshihisa Fujii,b and Yuki Nagaoc a Research Center for Strategic Materials, Structural Materials Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan b Advanced Key Technologies Division, Polymer Materials Unit, National Institute for Materials Sci-ence (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan c School of Materials Science, Japan Advanced Institute of Science, and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan For all correspondence: [email protected] Contents

1. General information……………………………………………………….S2-S3 2. Synthesis………………………………………………………………….. S4 3. Characterization and physical properties……………………………… S5-S10 4. Thin-film properties………………………………………………………. S11-S16 5. Anti-corrosion tests………………………………………………………. S17-S19 6. Anti-bacterial test…………………………………………………………. S20 7. References………………………………………………………………... S21

Electronic Supplementary Material (ESI) for Chemical Communications.This journal is © The Royal Society of Chemistry 2015

S2

1. General Information

Materials: All manipulations were carried out under argon atmosphere employing standard

Schlenk techniques. Ultrapure water (resistivity=18.2 MΩ, pH = 6.82) used in all experiments was

obtained from a Millipore. Tannic acid (TA) was purchased from Wako chemicals, alkyl (hexyl,

decyl, and hexadecyl) iodides from Tokyo Chemical Industry Co. Ltd. (TCI), and other chemi-

cals/solvents were from commercial sources and used without further purification.

Instrumentation:

a. NMR & FT-IR: 1H NMR spectra were measured for C2D6SO (containing 1% TMS) solutions

at 25 °C on JEOL JNM-ECX 300 spectrometer and the chemical shifts are reported in ppm

with respect to the reference SiMe4. FT-IR was measured for KBr pellet in a JASCO FT-IR

6100 instrument.

b. TGA & DSC: Thermogravimetric analysis (TGA) and differential scanning calorimetry

(DSC) were studied using SII Seiko instruments TG/DTA 6200 and X-DSC 7000, respective-

ly. Aluminum pan was used as a sample holder and alumina (Al2O3) powder was used a ref-

erence for all cases. Heating rate was 10 °C/min for both analysis. The second heat-

ing/cooling cycle is reported in all cases of DSC to avoid impurity/solvent peak.

c. Surface profiler & Contact angle: Thin-film thickness was measured by a DEKTAK 6M

Stylus surface profiler. Reported thicknesses are average of 5-6 measurements for each sam-

ple. Static water contact angle of coated glass surface was measured using Dropmaster 300

instrument at 298 K. Reported contact angles are average of 5-6 measurements.

d. AFM & SEM: Atomic force microscopy (AFM) was studied using NanoNavi SII instru-

ment. Scanning electron microscope (SEM) was studied by Hitachi SU4800/ 8000 instru-

ment. Samples were Pt coated for 30 s in all cases.

e. Thin-film XRD & WAXD: Thin-film X-ray diffraction (XRD) was measured using

SmartLab apparatus and the film was made on a cover slip by simple drop-casting method

followed by solvent evaporation under ambient condition or annealing at 80°C for 1 h. Wide-

angle X-ray diffraction (WAXD) experiments in out-of-plane geometry were carried out with

a Rigaku Smartlab using CuKα radiation. These data were collected with the angular interval

between steps 0.08 º and a scan speed of 0.5 º per min.

f. Electro-polarization and salt-water immersion test: Anti-corrosion study by electrochemical

method was done using ALS-CHI 660A electrochemical set up having four electrodes com-

S3

binations. Metal/alloy rods were cut into small plates of 2 mm thickness, polished with SiC

paper, and cleaned according to a previous report.a Coated/uncoated Mg substrates were used

as working electrode, standard calomel electrode as reference electrode, platinum foil con-

nected with a wire as counter electrode and sense. Before final measurement, all samples

were immersed in 3.5 wt.% NaCl solution for 1 h. Open circuit potential was monitored for

10 min for each case to reach an electrochemical steady state. Finally, cathodic/anodic cur-

rent were measured independently at a scan rate of 1 mV/s. Salt-water immersion test was

studied for all samples in 3.5 wt.% NaCl aq. solution at room temperature. Al (99%, Nilaco

Corp.), Cu (99.9%, Nilaco Corp.), Fe (3N5 purity, ESPI), Zn (6N purity, ESPI), and Mg

(AZ31) were used in this study. Schematic diagrams of these tests have been shown in Figure

S14.

S4

2. Synthesis

Scheme S1: Chemical modification of tannic acid (TA). Incorporation of different alkyl chains

(hexyl, decyl or hexadecyl) to the TA backbone was done in the presence of potassium carbonate.

TA (1 gm., 0.587 mmol) and K2CO3 (m eq.) was mixed in a two-necked round bottom flask fitted with a water condenser. Flask was back-filled with argon twice and dimethylformamide (DMF, 15 mL) was added to the solid mixture. After shaking/stirring the reaction mixture for 10-15 minutes, alkyl iodide (m eq.) was added to the reaction mixture by a syringe at room temperature and reaction mixture was stirred vigorously at 85°C for 20 h. Finally, dark brown reaction mixture was cooled down to room temperature, solid residue was filtered out by simple filtration and washed few times with DMF. Collected filtrate was mixed together and most of the solvent was removed by high vacu-um at 50°C. Excess amount of distilled water was added to the concentrated reaction mixture and vigorously stirred using a vortex mixing equipment. After 1 h, solid precipitate/sticky material was isolated by simple filtration/centrifugation. Solid materials were further dissolved in excess chloro-form (~150 mL) by gentle heating/sonication and dried over sodium sulfate. After filtration and washing several times with chloroform, organic solvent was removed by a rotary evaporator. Dark brown product was further dried under high vacuum at 45°C for 10 h.

Table S1: Various composition and combination of alkyl iodide and TA with different weight ratios.

OO

OOH

OH

OO

OH

OHHO

OO

OHOHO

O

OHHO

HO

OO

OHHO

O

O

OH

OH

OHO

O

HO

HO

OO

HO OH

OH

O

O

HO

HO

OOHO

HOOH

OO

OOH

OH

OO

O

OHO

OO

OHOHO

O

OHO

O

OO

OHHO

O

O

O

O

OHO

O

HO

HO

OO

O OH

O

O

O

HO

HO

OOO

HOO

H2n+1Cn

H2n+1Cn

H2n+1CnH2n+1Cn

H2n+1Cn

CnH2n+1

CnH2n+1

CnH2n+1

H2n+1Cn

CnH2n+1

Compound Alkyl iodide (wt.%) TA (wt.%) Aromatic

-OH converted (mol %)

TA(C6)5

TA(C6)10

Yield (%)

TA(C10)5

TA(C10)10

TA(C16)5

TA(C10)20

TA(C10)15

TA(C16)10

C6H13I (38)

C6H13I (55)

C10H21I (44)C10H21I (61)C10H21I (70)C10H21I (76)

C16H33I (51)C16H33I (67)

62

45

39

2430

56

4933

20

40

40

8060

20

2040

73

87

74

9476

88

7261

Alkyl iodide (m eq.), K2CO3 (m eq.), DMF, 85 °C, 20 h m= 5, 10, 15, or 20

n: 2 (Hexyl) 6 (Decyl) 12 (Hexadecyl)

Tannic acid (TA) Partially alkyl substituted TA (PATA)

S5

3. Characterization and physical properties

Figure S1: 1H NMR comparison among TA and PATAs in DMSO at 298K. Appearance of multiple

broad peaks around 0.8~1.5 ppm indicate incorporation of alkyl chains to the TA backbone. In

addition, appearance of peak around 4 ppm indicates formation of ether (–OCH2-) linkages.

OH

OH

OH

Tannic Acid

a

a

a

b

b

O

OH

O

cd

CpH2p+1

CpH2p+1

b

b

e

PATA

0"2"4"6"8"

TA"

TA(C10)5"

TA(C10)10"

TA(C10)15"

PPM

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PPM


PPM


PPM


PPM


PPM


DMSO

TA(C16)10"

TA(C6)10"

TA(C10)20"

b

a

d

e

c

ppm

S6

Figure S2: FT-IR comparison among TA and PATAs in KBr pellet. Gradual decrease of aromatic

hydroxyls broad peak (3100~3600 cm-1) and appearance of typical alkyl –CH2 & -CH3 signals

(~2800-2950 cm-1) indicate conversion of aromatic hydroxls to ether linkages.

4000 3600 3200 2800 2400

6

5

4

3

2

1

0

2000 1600 1200 800

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Wavelength (cm-1)

Abso

rban

ce (a

.u.)

Aromatic -OH

TA

2923 cm-1

(Alkyl str.anti)2852 cm-1

(Alkyl str.sym)

TA(C10)5

TA(C10)10

TA(C10)15

TA(C10)20

TA(C16)10

S7

S: Soluble, MS: Partially soluble/dispersible, IN: Insoluble

Figure S3: (a) Comparison of physical appearance before and after alkyl substitutions. TA appears

as a yellow powder while, turns to dark brown shiny materials after alkylation. Image scale bar is 1

cm. (b) Comparison of solubility in water and different organic media. Obviously, partial

alkylization significantly improves organosolubility of TA.

Tannic acid (TA) TA(C10)5

TA(C6-16)10 TA(C10)15-20

Water Compound n-Hexane

Ethyl acetate

Chloroform THF

Diethyl ether

TA(C6)10

TA

TA(C6)5

TA(C10)5

TA(C10)10

TA(C16)10

TA(C16)5

S

MS

IN

MS

IN

MS

IN

S

MS

S

S

S

S

S

IN IN

IN

IN

IN

MS

S

MS

S

S

S

S

MS

MS

IN

S S

S MS

S

S

S

MS MS

S S

S

S

(a)

(b)

S8

Figure S4: Thermo gravimetric analysis (TGA) plots of pristine TA and PATAs. Comercially

available TA powder was used for this study without further purification. There was a rapid volume

expansion for TA after 255 °C, which caused falling the sample pan from holder (red line).

Therefore, correct measurement of weight loss above this temperature was difficult. Further, we

observed about 8% weight loss in between 50-100 °C for comercially available TA sample, possibly

due to low molecular weight or other foreign species. In contrast, these phenomena were not detected

after introducing long alkyl units to the TA backbone and PATAs were thermally stable atleast upto

180 °C (black, green, and blue line). However, gradual weight loss was observed for PATA samples

above ca. 200 °C, and ~80% decomposition was recorded above 350 °C.

100

80

60

40

20

0500400300200100

TA (control) TA(C6)10 TA(C10)10 TA(C16)10

Wei

ght (

%)

Temperature (° C)

Rapid volume expansion~ 255 ° C

~ 8% weight loss

S9

Figure S5: Differential scanning calorimetry (DSC) thermograms of TA and PATAs. Pristine TA

does not have significant phase transition in the observed temperature range (red plot). However,

PATAs have distinct transition depending on the type of alkyl side chains. For example, hexyl and

decyl substituted samples show a glass transition (Tg) close to 43 °C and 34 °C, respectively (black

& green plot). More longer alkyl unit (C16) substituted sample shows a distinct melting point (Tm)

close to 7 °C (blue plot). These phenomena clearly indicate the change and dependence of intra-

/intermolecular physical interaction in solid phase with the incorporation of soft alkyl chain brushes.

S10

Molecular simulation : Density functional theory (DFT) calculations were performed using the DMol3 package in Materials

Studio v7.0 (Accelrys Software). The Perdew−Burke−Ernzerhof (PBE) function was chosen. The

convergence threshold for the maximum force and maximum displacement for normal geometry op-

timization were set, respectively, to 0.02 Ha Å−1 and 0.05 Å.

Figure S6: Most stable molecular structure of PATA as estimated by DFT. For clarity, aromatic

hydroxyls of the most outer ring were substituted by ten n-hexyl alkyl chains. The glucose core was

preferably in chair conformation and alkyl units were surrounded like a disc-like molecular structure.

side view

top view bottom view

� ) ) -)(

core

S11

4. Thin-film properties

Figure S7: (a) Relation between amount drop-casted and film thickness. (b) Comparison of static

water contact angle among different (un)coated glass surfaces. TA coated surface is hydrophilic

while, PATAs were relatively hydrophobic which is reasonable for the incorporation of long alkyl

chains to TA backbone.

Figure S8: Photographs of (a) TA coated, and (b) PATA coated glass plate. Distinctly, film of

pristine TA was unstable under ambient condition but PATA film was smooth, stable, and uniform

on glass surface. Image scale bar is 1 cm.

100

80

60

40

20

0 uncoated

100

80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

Con

tact

ang

le (°

)302520151050

2.52.01.51.00.50.0Amount drop-casted (mg/cm2)

Film

thic

knes

s (µ

m)

TA coated PATA coated

(a) (b)

(a) (b)

S12

Figure S9: Atomic force microscope (AFM) phase images of (a) TA film, and (b) TA(C16)10 film on

glass surface. Average particle size of TA aggregates was 100-130 nm. On the contrary, TA(C16)10

film produced a uniform fibre-like network assembly. These figures clarify that TA aggregates to a

particle morphology possibly due to random intra-/intermolecular hydrogen bonding among aromatic

ester/hydroxyls groups. However, alkyl substitutions give network assembly via intramolecular

hydrophobic interactions.

TAthin-film

PATA thin-film

1 µm

1 µm

500 nm

500 nm

(a)

(b)

S13

Figure S10: Top surface scanning electron microscope (SEM) images of TA (control) and TA(C16)10

film. We verified thin-film morphology on both untreated glass (hydrophobic) and plasma treated

glass (hydrophilic). Obviously, TA film has many cracks formed possibly during solvent evaporation

process and indicate poor film stability on both (hydro)phobic/philic surfaces. On the other hand,

TA(C16)10 coated film was smooth, crack-free, and well-adhered to the surface indicating good film

stability. Therefore, we believe defect in TA film is not due to weak TA/glass interaction but due to

poor intramolecular interactions. Hydrophobization of TA helps to overcome this drawback by

stronger alkyl-alkyl hydrophobic interactions. Scale bar of the images are 10 µm.

Plasma cleaning (2 min)

Untreated glass

CA: ~ 58 °

Plasma treated glass

CA: ~ 0 °

TA coated

PATA coated

(b)

S14

Figure S11: Cross-sectional SEM images of (a) TA (control) and (b) TA(C16)10 film. TA film was

cracked and peeled-off from the glass surface but TA(C16)10 coated film was well-adhered to the

surface indicating good anchoring and mechanical stability.

TA film (control)

glass substrate

coating

glass substrate

coating

PATA film

TA film (control)

glass substrate

coating

glass substrate

coating

PATA film

(a)

(b)

(b)

S15

Figure S12: Thin-film XRD comparison of (a) as coated and (b) annealed film of PATA.

Comparison of WAXD plots between (c) as coated and (d) annealed film of PATA. In both cases,

there was no significant change in diffraction pattern indicating similar pattern of molecular stacking

without/with thermal treatment.

25

20

15

10

5

0

x103

5040302010

2θ (°)

Inte

nsity

(a. u

.)

25

20

15

10

5

0

x103

5040302010

2θ (°)

Inte

nsity

(a. u

.)As coated Annealed

30

25

20

15

10

5

0

x103

1086422θ (°)

30

25

20

15

10

5

0

x103

108642

Inte

nsity

(a. u

.)

As coated Annealed

2θ (°)In

tens

ity (a

. u.)

(a) (b)

(c) (d)

S16

Figure S13: Although, AFM and SEM studies indicate good film-stability but we further verified

mechanical stability of PATA coating by scotch-tape test and also effect of thermal treatment.

Briefly to describe, few drops solution of TA(C16)10 was drop-casted on polished and well-cleaned

magnesium alloy (AZ31) plate followed by drying under ambient condition or at 80 °C for 1 h.

Small amount of Rhodamine B dye was added to visibly understand the difference. Afterthat,

commercially available scotch-tape was repeatedly attached and peeled out using new one each time.

We found major damage in the film without thermal treatment but annealed film was very stable

upto many (>20) (de)attachment cycles. This result indicated thermal treatment enhances film

stability and thus annealing was employed for all cases of anti-corrosion/bacterial study.

Scotch-tape test

Scotch-tape test

10 times

> 20 times

TA(C16)10 + Dye

Annealed

As coated

S17

5. Anti-corrosion tests

Figure S14: A simple schematic diagram of (a) electro-polarization test and (b) salt-water

immersion test. All studies were performed at 298 K under air.

a: WE: (Un)coated metal/alloy platesb: RE: Std. Calomel electrodec: CE: Platinum foild: Electrolyte: 3.5 wt.% NaCl (aq.) at 298 K

200 rpm

Working Electrode (WE)

Reference Electrode (RE)

CounterElectrode (CE)

a bd

I

V

⧘"

c d

(a) (b)

S18

Figure S15: Photographs of different Mg alloy (AZ31) plates before and after electropolarization

test. Plates were 15 mm in diameter. Obviously, TA coated (control) sample badly damaged after

this test. Interestingly, there is a distinct variation among degree of substitution as revealed by this

study. Penta-substitution, TA(C10)5 coated sample got severe damage (pinholes) during the test. Also,

substitution more than ten (15, or 20) is not physically stable and become soft during the test.

Therefore, the best choice of substitution was ten as TA(C10)10 coated sample was completely

undamaged after the test. Considering, both electrochemical plots (Fig. 3) and visual inspections we

conclude that deca-substitution gives perfect balance between anchoring aromatic hydroxyls and

hydrophobic alkyl units to produce a well-adhered film and efficiently protect penetration of

corrosive ions/ water molecules.

TA(C10)5"coated"

TA"coated"(control)"

As#coated#

A*er#test#

Condi8ons" TA(C10)10"coated"

TA(C10)15"coated"

TA(C10)20"coated"

S19

Figure S16: Effect of thermal treatment and time of immersion on elctro-polarization test. (a)

Cathodic, and (b) anodic current comparison among blank, as coated, and annealed samples. We

discussed in earlier section that annealing has certain benefits to obtain a stable and firm flim.

However, to further demonstrate the relation between annealing and corrosion protection ability

we compared corrosion current density (icorr) between as coated and annealed film. Considering

much less and smooth change of icorr with potetial sweep for annealed sample, it is obvious that

thermal treatment has an important role for better corrosion protection. Fig. (c) demonstrates that

long immersion time (upto 40 h) does not affect icorr significantly, indicating long-lasting stability

of our coating.

10-11

10-9

10-7

10-5

10-3

10-1

-1.9 -1.8 -1.7 -1.6 -1.5 -1.4

10-1110-1010-910-810-710-610-510-410-310-2

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6

Potential (V vs SCE) Potential (V vs SCE)

Cur

rent

den

sity

(A. c

m-2

)

Cur

rent

den

sity

(A. c

m-2

)

Blank

TA(C16)10 [as coated]

TA(C16)10 [annealed]

TA(C16)10 [annealed]

TA(C16)10 [as coated]

Blank

10-1010-910-810-710-610-5

Cor

rosi

on c

urre

nt d

ensi

ty (A

/ cm

2 )

403020100Time of immersion (h)

pittingpitting

(a) (b)

(c)

S20

6. Anti-bacterial test: As a test method, Japanese Industrial Standard (JIS Z 2801) was followed in this study.b Three kinds

of bacterial strains, [i] Escherichia coli (E. coli), [ii] Staphylococcus aureus (S. aureus), and (iii)

Methicillin-resistant S. aureus (MRSA) were used in our study. Glass plate (5 x 5 cm2) was used as a

substrate for coating. Minimum three tests were performed for each type of study.

Figure S17: Photographs of different bacterial solutions after immersion of control (uncoated), and

PATA coated glass substrates. While bacterial colony remained unchanged or increased in control

samples, PATA samples completely killed the bacterial cells.

Control (MRSA) PATAs (MRSA)

Control (S. Aureus) PATAs (S. Aureus)

1 cm 1 cm

1 cm1 cm

S21

7. References

a. Z. She, Q. Li, Z. Wang, L. Li, F. Chen and J. Zhou, ACS Appl. Mater. Interfaces, 2012, 4, 4348.

b. Japanese Industrial Standard/Antimicrobial products-Test for antimicrobial activity and effi-

cacy JIS Z 2801:2010 (Japanese standard association 4-1-24, Akasaka, Minato-ku, Tokyo, 107-8440 Japan.)

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