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N7-(carboxymethyl)guanine-Lithium Crystalline Complex: A Bioinspired Solid Electrolyte.

Dutta D, Nagapradeep N, Zhu H, Forsyth M, Verma S, Bhattacharyya AJ - Sci Rep (2016)

Bottom Line: G7Li, with it's in-built supply of Li(+)-ions, exhibited remarkably high lithium-ion transference number (= 0.75) and tunable room temperature ionic conductivity spanning three decades (≈10(-7) to 10(-3) Ω(-1) cm(-1)) as a function of moisture content.The ionic conductivity show a distinct reversible transition around 80-100 °C, from a dual Li(+) and H(+) (<100 °C) to a pure Li(+) conductor (>100 °C).Systematic studies reveal a transition from water-assisted Li-ion transport to Li hopping-like mechanism involving guanine-Li coordination.

View Article: PubMed Central - PubMed

Affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012 (Karnataka), India.

ABSTRACT
Electrochemical device with components having direct significance to biological life processes is a potent futuristic strategy for the realization of all-round green and sustainable development. We present here synthesis design, structural analysis and ion transport of a novel solid organic electrolyte (G7Li), a compound reminiscent of ion channels, derived from regioisomeric N7-guanine-carboxylate conjugate and Li-ions. G7Li, with it's in-built supply of Li(+)-ions, exhibited remarkably high lithium-ion transference number (= 0.75) and tunable room temperature ionic conductivity spanning three decades (≈10(-7) to 10(-3) Ω(-1) cm(-1)) as a function of moisture content. The ionic conductivity show a distinct reversible transition around 80-100 °C, from a dual Li(+) and H(+) (<100 °C) to a pure Li(+) conductor (>100 °C). Systematic studies reveal a transition from water-assisted Li-ion transport to Li hopping-like mechanism involving guanine-Li coordination. While as-synthesized G7Li has potential in humidity sensors, the anhydrous G7Li is attractive for rechargeable batteries.

No MeSH data available.


Related in: MedlinePlus

(a) Static 7Li-NMR spectra and (b)7Li line-width (FWHM: full width at half maximum) as afunction of temperature for G7Li solid powder.
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f5: (a) Static 7Li-NMR spectra and (b)7Li line-width (FWHM: full width at half maximum) as afunction of temperature for G7Li solid powder.

Mentions: The pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy, analternative tool to measure transference numbers of various ionic entities in asample, also could not successfully deconvolute the individual diffusioncoefficients for Li+ and H+ present in the sample dueto their short T2 relaxation times as well as the slow diffusion.However, the Li+ ion mobility in G7Li is clearly recognized bymonitoring the change in line-width (full width at half maximum, FWHM) as a functionof temperature of the solid-state NMR spectra of 7Li in G7Li obtainedfrom the stationary powder sample (c/f Fig. 5a). The7Li being a quadrupolar nucleus(I = 3/2), the magnetic dipolar and electric quadrupolarinteractions usually influence the 7Li NMR spectra (chemical shiftinteractions are normally small for 7Li). When a nucleus is fixed,the quadrupolar or internuclear dipole-dipole interactions are accentuated resultingin a broad line-width (usually known as rigid lattice line-width). The line-widthsfor G7Li (Fig. 5b) are obtained by fitting the spectra using atwo components model consisting of the broad Gaussian peak (rigid latticeline-width) and the sharper Lorenzian peak corresponding to the central transition.The Li+ ion when it resides in a tetrahedral symmetry site, thequadrupolar contributions are expected to be negligible and so the7Li line-width is in fact dominated by the dipolar interactions. Inthe range of temperature under investigation (−20 to75 °C) no distinct quadrupolar satellite transitions(+3/2 ↔ +1/2 and−1/2 ↔ −3/2) areobserved in the 7Li spectra of G7Li indicating that theLi+ ions are located at sites with tetrahedral symmetry(Td) and that there are no impurity ions51. This observation exactly supports the single crystal X-ray data.This concurrence also encouraged us to investigate the Li+ ionmobility by measuring the 7Li line-widths only of the centraltransition (+1/2 ↔ −1/2) as afunction of temperature. At lower temperature (263 K) the spectrum isdominated by broad lattice line-width indicating that vast majority of theLi+ ions are relatively rigid, but still noticeable amount ofmobile ones can be identified from the little narrow peak on top. The not so broadline-width of 4.3 kHz (Fig. 5b) of the centraltransition suggests that the Li+ ions may be mobile even at such alow temperature. As temperature increases, the line-widths gradually becomenarrower, (Figs 5 and S11). The line-widths steadily decrease to 2.4 kHzat 293 K (≈ambient temperature) after which it shows aslight increase to 2.7 kHz at 323 K. The steady decrease inline-width is due to higher mobility of Li+ ion at high temperature.Since broadening of line-width usually originates from the increased quadrupolar orinternuclear dipole-dipole interactions52 the increase in7Li line-width from 293 K to 323 K may beaccounted on the basis of weak 1H-7Li dipolarinteractions. This is also supported by the fact that the onset of motionalnarrowing of proton is also around 318 K (c/f Figure S11). This explainsthat the Li+ ion mobility below 373 K is water assistedas mentioned earlier and the decrease in ionic conductivity is also partially due todecrease in Li+ ion mobility in this temperature regime. Theadditional evidence of the water assisted movement of Li+ ion arisesfrom the fact that Li+ ion hopping between theTd sites, which are 6.991 Å and4.261 Å (=d) apart (c/f Figures S2 and S4), isdifficult. The jump period (τ) (ESI) at a particular temperatureis related to the local diffusion coefficient (D) by the equationD = d2/4τ,and the obtained values are1.22 × 10−13 and0.74 × 10−13 m2/sfor d = 4.261 and 6.991 Årespectively. Once water starts exiting from the system(T = 333 K) the1H-7Li dipolar interactions weakens and thiseffect together with the increase in Li+ ion mobility reinitiate the7Li motional line-width narrowing. The line-width data shows asudden and sharp decrease between 333 K (2.6 kHz) to343 K (1.4 kHz). The sudden increase in motional narrowingmay be due to the loss of large number of water molecules during this stage. Afurther decrease of line-width is expected at and above 373 K, i.e. inthe new dehydrated phase when water molecules have fully exited from the system. Inthe dehydrated phase within the temperature regime(373–573) K (c/f Fig. 4), there willalso be an expected motional narrowing and it will purely be due to the fastLi+ hopping between the carboxylate and carbonyl oxygens of theguanine moieties in the G7Li. The activation energy calculated for the G7Li phase(≈21–40 °C) from the line-widthmeasurements (c/f ESI) is 0.15 eV. Such low activation energies stronglysupport the water assisted diffusion of Li+ ions in G7Li at room andin proximity to the room temperature. Estimation of a lower activation energybarrier (compared to the ionic conductivity in the similar temperature range, FigureS9) can be anticipated primarily due to the differences in the probing methods andtime scale of measurement between the ac-impedance and NMR techniques. The NMRdetects specific ion motions on a much more local scale whereas the ionicconductivity data represents net number of mobile charges on a larger lengthscale5354.


N7-(carboxymethyl)guanine-Lithium Crystalline Complex: A Bioinspired Solid Electrolyte.

Dutta D, Nagapradeep N, Zhu H, Forsyth M, Verma S, Bhattacharyya AJ - Sci Rep (2016)

(a) Static 7Li-NMR spectra and (b)7Li line-width (FWHM: full width at half maximum) as afunction of temperature for G7Li solid powder.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4835778&req=5

f5: (a) Static 7Li-NMR spectra and (b)7Li line-width (FWHM: full width at half maximum) as afunction of temperature for G7Li solid powder.
Mentions: The pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy, analternative tool to measure transference numbers of various ionic entities in asample, also could not successfully deconvolute the individual diffusioncoefficients for Li+ and H+ present in the sample dueto their short T2 relaxation times as well as the slow diffusion.However, the Li+ ion mobility in G7Li is clearly recognized bymonitoring the change in line-width (full width at half maximum, FWHM) as a functionof temperature of the solid-state NMR spectra of 7Li in G7Li obtainedfrom the stationary powder sample (c/f Fig. 5a). The7Li being a quadrupolar nucleus(I = 3/2), the magnetic dipolar and electric quadrupolarinteractions usually influence the 7Li NMR spectra (chemical shiftinteractions are normally small for 7Li). When a nucleus is fixed,the quadrupolar or internuclear dipole-dipole interactions are accentuated resultingin a broad line-width (usually known as rigid lattice line-width). The line-widthsfor G7Li (Fig. 5b) are obtained by fitting the spectra using atwo components model consisting of the broad Gaussian peak (rigid latticeline-width) and the sharper Lorenzian peak corresponding to the central transition.The Li+ ion when it resides in a tetrahedral symmetry site, thequadrupolar contributions are expected to be negligible and so the7Li line-width is in fact dominated by the dipolar interactions. Inthe range of temperature under investigation (−20 to75 °C) no distinct quadrupolar satellite transitions(+3/2 ↔ +1/2 and−1/2 ↔ −3/2) areobserved in the 7Li spectra of G7Li indicating that theLi+ ions are located at sites with tetrahedral symmetry(Td) and that there are no impurity ions51. This observation exactly supports the single crystal X-ray data.This concurrence also encouraged us to investigate the Li+ ionmobility by measuring the 7Li line-widths only of the centraltransition (+1/2 ↔ −1/2) as afunction of temperature. At lower temperature (263 K) the spectrum isdominated by broad lattice line-width indicating that vast majority of theLi+ ions are relatively rigid, but still noticeable amount ofmobile ones can be identified from the little narrow peak on top. The not so broadline-width of 4.3 kHz (Fig. 5b) of the centraltransition suggests that the Li+ ions may be mobile even at such alow temperature. As temperature increases, the line-widths gradually becomenarrower, (Figs 5 and S11). The line-widths steadily decrease to 2.4 kHzat 293 K (≈ambient temperature) after which it shows aslight increase to 2.7 kHz at 323 K. The steady decrease inline-width is due to higher mobility of Li+ ion at high temperature.Since broadening of line-width usually originates from the increased quadrupolar orinternuclear dipole-dipole interactions52 the increase in7Li line-width from 293 K to 323 K may beaccounted on the basis of weak 1H-7Li dipolarinteractions. This is also supported by the fact that the onset of motionalnarrowing of proton is also around 318 K (c/f Figure S11). This explainsthat the Li+ ion mobility below 373 K is water assistedas mentioned earlier and the decrease in ionic conductivity is also partially due todecrease in Li+ ion mobility in this temperature regime. Theadditional evidence of the water assisted movement of Li+ ion arisesfrom the fact that Li+ ion hopping between theTd sites, which are 6.991 Å and4.261 Å (=d) apart (c/f Figures S2 and S4), isdifficult. The jump period (τ) (ESI) at a particular temperatureis related to the local diffusion coefficient (D) by the equationD = d2/4τ,and the obtained values are1.22 × 10−13 and0.74 × 10−13 m2/sfor d = 4.261 and 6.991 Årespectively. Once water starts exiting from the system(T = 333 K) the1H-7Li dipolar interactions weakens and thiseffect together with the increase in Li+ ion mobility reinitiate the7Li motional line-width narrowing. The line-width data shows asudden and sharp decrease between 333 K (2.6 kHz) to343 K (1.4 kHz). The sudden increase in motional narrowingmay be due to the loss of large number of water molecules during this stage. Afurther decrease of line-width is expected at and above 373 K, i.e. inthe new dehydrated phase when water molecules have fully exited from the system. Inthe dehydrated phase within the temperature regime(373–573) K (c/f Fig. 4), there willalso be an expected motional narrowing and it will purely be due to the fastLi+ hopping between the carboxylate and carbonyl oxygens of theguanine moieties in the G7Li. The activation energy calculated for the G7Li phase(≈21–40 °C) from the line-widthmeasurements (c/f ESI) is 0.15 eV. Such low activation energies stronglysupport the water assisted diffusion of Li+ ions in G7Li at room andin proximity to the room temperature. Estimation of a lower activation energybarrier (compared to the ionic conductivity in the similar temperature range, FigureS9) can be anticipated primarily due to the differences in the probing methods andtime scale of measurement between the ac-impedance and NMR techniques. The NMRdetects specific ion motions on a much more local scale whereas the ionicconductivity data represents net number of mobile charges on a larger lengthscale5354.

Bottom Line: G7Li, with it's in-built supply of Li(+)-ions, exhibited remarkably high lithium-ion transference number (= 0.75) and tunable room temperature ionic conductivity spanning three decades (≈10(-7) to 10(-3) Ω(-1) cm(-1)) as a function of moisture content.The ionic conductivity show a distinct reversible transition around 80-100 °C, from a dual Li(+) and H(+) (<100 °C) to a pure Li(+) conductor (>100 °C).Systematic studies reveal a transition from water-assisted Li-ion transport to Li hopping-like mechanism involving guanine-Li coordination.

View Article: PubMed Central - PubMed

Affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012 (Karnataka), India.

ABSTRACT
Electrochemical device with components having direct significance to biological life processes is a potent futuristic strategy for the realization of all-round green and sustainable development. We present here synthesis design, structural analysis and ion transport of a novel solid organic electrolyte (G7Li), a compound reminiscent of ion channels, derived from regioisomeric N7-guanine-carboxylate conjugate and Li-ions. G7Li, with it's in-built supply of Li(+)-ions, exhibited remarkably high lithium-ion transference number (= 0.75) and tunable room temperature ionic conductivity spanning three decades (≈10(-7) to 10(-3) Ω(-1) cm(-1)) as a function of moisture content. The ionic conductivity show a distinct reversible transition around 80-100 °C, from a dual Li(+) and H(+) (<100 °C) to a pure Li(+) conductor (>100 °C). Systematic studies reveal a transition from water-assisted Li-ion transport to Li hopping-like mechanism involving guanine-Li coordination. While as-synthesized G7Li has potential in humidity sensors, the anhydrous G7Li is attractive for rechargeable batteries.

No MeSH data available.


Related in: MedlinePlus