Nanomechanics of Polyphenylacetylene Derivatives by AFM-based SMFS†

doi:10.7503/cjcu20180261

Abstract

Abstract:

We quantitatively investigated the effect of iodine and pH on the stability of the helical structure formed by polyphenylacetylene derivatives using atomic force microscopy(AFM) based single-molecule force spectroscopy(SMFS) and circular dichroism(CD). The AFM measurement results showed that the addition of iodine into the system caused the decrease of the plateau heights in the stretching curves recorded during the SMFS experiments. In addition, the pH value increase can weaken the intra-polymer hydrogen bond and interrupt the integrity of the helical structure. However, the CD result did not show any detectable changes upon the addition of iodine and the change of pH value, which indicate that SMFS is a very sensitive and powerful method for subtle structure study.

Key words: Polyphenylacetylene, Single-molecule force spectroscopy(SMFS), Iodine doping, pH response

CLC Number:

O631

TrendMD:

LI Xun, WANG Xiao, YAO Ruixiang, SUN Jingzhi, ZHANG Wenke. Nanomechanics of Polyphenylacetylene Derivatives by AFM-based SMFS^†[J]. Chem. J. Chinese Universities, 2018, 39(11): 2565.

Figures/Tables 10

Scheme 1 Cleaning and modification processes of Si3N4 AFM tip and Si substrate in SMFS experiments

Scheme 2 Molecular structure of polymers P1—P3

Fig.1 Comparison on normalized representative curves of P1 obtained at different doping ratios of iodine(A) and histograms of the plateau heights with different concentrations of iodine(B—F)

Fig.2 CD spectra of P1 with different doping ratios of iodine

Fig.3 Representative force curves of P2 in the presence of different doping ratios of iodine(A) and histograms of the plateau heights with iodine(B—F)

Fig.4 Comparison of the heights and length of plateaus of P1 along with the addition of KOH in DMF(A) Representative stretching curves of P1; (B) enlarged view of the plateau part in (A); (C) histograms of the plateau heights(forces) with KOH 0, KOH 15 and KOH 150; (D) histograms of plateau length with KOH 0, KOH 15 and KOH 150.

Table 1 Comparison of the plateau heights(force) and length of P1 and P3 along with the addition of KOH in DMF

Solvent	P1		P3
Solvent	Force/pN	Normalized length^b	Force/pN	Normalized length
DMF	58±14	0.28	50±5	0.16
DMF/MeOH/KOH 15^a	50±7	0.26	50±4	0.23
DMF/MeOH/KOH 150	50±8	0.15	49±4	0.07

Fig.5 CD spectra of P1 with different concentrations of KOH

Fig.6 Comparison of the heights and length of plateaus of P3 along with the addition of KOH in DMF(A) Representative stretching curves of P3; (B) enlarged view of the plateau part in (A); (C) histograms of the plateau heights(forces) with KOH 0, KOH 15 and KOH 150; (D) histograms of plateau length with KOH 0, KOH 15 and KOH 150.

Scheme 3 Schematic of the partial breakage of the helical structure of polymers by the increase of pH value

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