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Dive into the research topics where C. Vinod Chandran is active.

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Featured researches published by C. Vinod Chandran.


Science | 2009

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Seung-Mo Lee; Eckhard Pippel; Ulrich Gösele; Christian Dresbach; Yong Qin; C. Vinod Chandran; Thomas Bräuniger; Gerd Hause; Mato Knez

Infiltration of spider silk with impurities enhances the mechanical performance. Improving on Spider Silk? In a conventional atomic layer deposition, alternating pulses of a reactive metal-based precursor and a reactant, such as water, are deposited onto a solid surface to create a coating that conforms closely to the original surface. Lee et al. (p. 488) apply this process to fibers of spider silk, which are soft and porous. In addition to forming a coating on the fibers, some of the metal ions penetrate the fibers and react with the protein structure. These doped fibers show significant increase in toughness as measured by the work required to deform them. In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.


Science | 2009

Greatly increased toughness of infiltrated spider silk.

Seung-Mo Lee; Eckhard Pippel; Ulrich Gösele; Christian Dresbach; Yong Qin; C. Vinod Chandran; Thomas Bräuniger; Gerd Hause; Mato Knez

Infiltration of spider silk with impurities enhances the mechanical performance. Improving on Spider Silk? In a conventional atomic layer deposition, alternating pulses of a reactive metal-based precursor and a reactant, such as water, are deposited onto a solid surface to create a coating that conforms closely to the original surface. Lee et al. (p. 488) apply this process to fibers of spider silk, which are soft and porous. In addition to forming a coating on the fibers, some of the metal ions penetrate the fibers and react with the protein structure. These doped fibers show significant increase in toughness as measured by the work required to deform them. In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.


Magnetic Resonance in Chemistry | 2008

Swept-frequency two-pulse phase modulation (SWf-TPPM) sequences with linear sweep profile for heteronuclear decoupling in solid-state NMR

C. Vinod Chandran; P.K. Madhu; Narayanan D. Kurur; Thomas Bräuniger

Recently, a pulse scheme for heteronuclear spin decoupling in solid‐state NMR, called swept‐frequency two‐pulse phase modulation (SWf‐TPPM), was introduced which outperforms the standard TPPM and small phase incremental alteration (SPINAL) schemes. It has also been shown that the frequency‐sweep profile can be varied to achieve optimal efficiency for crystalline and liquid‐crystalline samples, respectively. Here we present a detailed comparison of the proton decoupling performance for SWf‐TPPM sequences with tangential sweep profiles (SWftan‐TPPM) and linear sweep profiles (SWflin‐TPPM). Using the 13CH2 resonance of crystalline tyrosine as a model system, it is shown that linear profiles have a decoupling performance which is at least as good and in some instances slightly better than that obtained from tangential sweep profiles. While tangential sweep profiles require a tangent cut‐off angle as an additional parameter, the lack of that parameter makes linear sweep profiles easier to implement and optimise. Copyright


Journal of Magnetic Resonance | 2010

Frequency-swept pulse sequences for 19F heteronuclear spin decoupling in solid-state NMR.

C. Vinod Chandran; P.K. Madhu; Philip Wormald; Thomas Bräuniger

Heteronuclear spin decoupling pulse sequences in solid-state NMR have mostly been designed and applied for irradiating 1H as the abundant nucleus. Here, a systematic comparison of different methods for decoupling 19F in rigid organic solids is presented, with a special emphasis on the recently introduced frequency-swept sequences. An extensive series of NMR experiments at different MAS frequencies was conducted on fluorinated model compounds, in combination with large sets of numerical simulations. From both experiments and simulations it can be concluded that the frequency-swept sequences SWf-TPPM and SWf-SPINAL deliver better and more robust spin decoupling than the original sequences SPINAL and TPPM. Whereas the existence of a large chemical shift anisotropy and isotropic shift dispersion for 19F does compromise the decoupling efficiency, the relative performance hierarchy of the sequences remains unaffected. Therefore, in the context of rigid organic solids under moderate MAS frequencies, the performance trends observed for 19F decoupling are very similar to those observed for 1H decoupling.


Journal of Magnetic Resonance | 2010

Improving sensitivity and resolution of MQMAS spectra: a 45Sc-NMR case study of scandium sulphate pentahydrate.

C. Vinod Chandran; Jérôme Cuny; Régis Gautier; Laurent Le Pollès; Chris J. Pickard; Thomas Bräuniger

To efficiently obtain multiple-quantum magic-angle spinning (MQMAS) spectra of the nuclide 45Sc (I=7/2), we have combined several previously suggested techniques to enhance the signal-to-noise ratio and to improve spectral resolution for the test sample, scandium sulphate pentahydrate (ScSPH). Whereas the 45Sc-3QMAS spectrum of ScSPH does not offer sufficient resolution to clearly distinguish between the 3 scandium sites present in the crystal structure, these sites are well-resolved in the 5QMAS spectrum. The loss of sensitivity incurred by using MQMAS with 5Q coherence order is partly compensated for by using fast-amplitude modulated (FAM) sequences to improve the efficiency of both 5Q coherence excitation and conversion. Also, heteronuclear decoupling is employed to minimise dephasing of the 45Sc signal during the 5Q evolution period due to dipolar couplings with the water protons in the ScSPH sample. Application of multi-pulse decoupling schemes such as TPPM and SPINAL results in improved sensitivity and resolution in the F(1) (isotropic) dimension of the 5QMAS spectrum, the best results being achieved with the recently suggested SW(f)-TPPM sequence. By numerical fitting of the 45Sc-NMR spectra of ScSPH from 3QMAS, 5QMAS and single-quantum MAS at magnetic fields B(0)=9.4 T and 17.6 T, the isotropic chemical shift delta(iso), the quadrupolar coupling constant chi, and the asymmetry parameter eta were obtained. Averaging over all experiments, the NMR parameters determined for the 3 scandium sites, designated (a), (b) and (c) are: delta(iso)(a)=-15.5+/-0.5 ppm, chi(a)=5.60+/-0.10 MHz, eta(a)=0.06+/-0.05; delta(iso)(b)=-12.9+/-0.5 ppm, chi(b)=4.50+/-0.10 MHz, eta(b)=1.00+/-0.00; and delta(iso)(c)=-4.7+/-0.2 ppm, chi(c)=4.55+/-0.05 MHz, eta(c)=0.50+/-0.02. The NMR scandium species were assigned to the independent crystallographic sites by evaluating their experimental response to proton decoupling, and by density functional theory (DFT) calculations using the PAW and GIPAW approaches, in the following way: Sc(1) to (c), Sc(2) to (a), and Sc(3) to (b). The need to compute NMR parameters using an energy-optimised crystal structure is once again demonstrated.


Solid State Nuclear Magnetic Resonance | 2011

19F-decoupling of half-integer spin quadrupolar nuclei in solid-state NMR: application of frequency-swept decoupling methods.

C. Vinod Chandran; Günter Hempel; Thomas Bräuniger

In solid-state NMR studies of minerals and ion conductors, quadrupolar nuclei like (7)Li, (23)Na or (133)Cs are frequently situated in close proximity to fluorine, so that application of (19)F decoupling is beneficial for spectral resolution. Here, we compare the decoupling efficiency of various multi-pulse decoupling sequences by acquiring (19)F-decoupled (23)Na-NMR spectra of cryolite (Na(3)AlF(6)). Whereas the MAS spectrum is only marginally affected by application of (19)F decoupling, the 3Q-filtered (23)Na signal is very sensitive to it, as the de-phasing caused by the dipolar interaction between sodium and fluorine is three-fold magnified. Experimentally, we find that at moderate MAS speeds, the decoupling efficiencies of the frequency-swept decoupling schemes SW(f)-TPPM and SW(f)-SPINAL are significantly better than the conventional TPPM and SPINAL sequences. The frequency-swept sequences are therefore the methods of choice for efficient decoupling of quadrupolar nuclei with half-integer spin from fluorine.


Journal of Magnetic Resonance | 2011

Sweep direction and efficiency of the swept-frequency two pulse phase modulated scheme for heteronuclear dipolar-decoupling in solid-state NMR.

Subhradip Paul; C. Vinod Chandran; Thomas Bräuniger; P.K. Madhu

We present here a bimodal Floquet theoretical and experimental investigation of the direction of sweep in the swept-frequency two pulse phase modulated (SW(f)-TPPM) scheme used for heteronuclear dipolar decoupling in solid-state NMR. The efficiency of the decoupling turns out to be independent of the sweep direction.


Science | 2009

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Seung-Mo Lee; Eckhard Pippel; Ulrich Gösele; Christian Dresbach; Yong Qin; C. Vinod Chandran; Thomas Bräuniger; Gerd Hause; Mato Knez

Infiltration of spider silk with impurities enhances the mechanical performance. Improving on Spider Silk? In a conventional atomic layer deposition, alternating pulses of a reactive metal-based precursor and a reactant, such as water, are deposited onto a solid surface to create a coating that conforms closely to the original surface. Lee et al. (p. 488) apply this process to fibers of spider silk, which are soft and porous. In addition to forming a coating on the fibers, some of the metal ions penetrate the fibers and react with the protein structure. These doped fibers show significant increase in toughness as measured by the work required to deform them. In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.


Science | 2009

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Seung-Mo Lee; Eckhard Pippel; Ulrich Gösele; Christian Dresbach; Yong Qin; C. Vinod Chandran; Thomas Bräuniger; Gerd Hause; Mato Knez

Infiltration of spider silk with impurities enhances the mechanical performance. Improving on Spider Silk? In a conventional atomic layer deposition, alternating pulses of a reactive metal-based precursor and a reactant, such as water, are deposited onto a solid surface to create a coating that conforms closely to the original surface. Lee et al. (p. 488) apply this process to fibers of spider silk, which are soft and porous. In addition to forming a coating on the fibers, some of the metal ions penetrate the fibers and react with the protein structure. These doped fibers show significant increase in toughness as measured by the work required to deform them. In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.


Science | 2009

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Seung-Mo Lee; Eckhard Pippel; Ulrich Gösele; Christian Dresbach; Yong Qin; C. Vinod Chandran; Thomas Bräuniger; Gerd Hause; Mato Knez

Infiltration of spider silk with impurities enhances the mechanical performance. Improving on Spider Silk? In a conventional atomic layer deposition, alternating pulses of a reactive metal-based precursor and a reactant, such as water, are deposited onto a solid surface to create a coating that conforms closely to the original surface. Lee et al. (p. 488) apply this process to fibers of spider silk, which are soft and porous. In addition to forming a coating on the fibers, some of the metal ions penetrate the fibers and react with the protein structure. These doped fibers show significant increase in toughness as measured by the work required to deform them. In nature, tiny amounts of inorganic impurities, such as metals, are incorporated in the protein structures of some biomaterials and lead to unusual mechanical properties of those materials. A desire to produce these biomimicking new materials has stimulated materials scientists, and diverse approaches have been attempted. In contrast, research to improve the mechanical properties of biomaterials themselves by direct metal incorporation into inner protein structures has rarely been tried because of the difficulty of developing a method that can infiltrate metals into biomaterials, resulting in a metal-incorporated protein matrix. We demonstrated that metals can be intentionally infiltrated into inner protein structures of biomaterials through multiple pulsed vapor-phase infiltration performed with equipment conventionally used for atomic layer deposition (ALD). We infiltrated zinc (Zn), titanium (Ti), or aluminum (Al), combined with water from corresponding ALD precursors, into spider dragline silks and observed greatly improved toughness of the resulting silks. The presence of the infiltrated metals such as Al or Ti was verified by energy-dispersive x-ray (EDX) and nuclear magnetic resonance spectra measured inside the treated silks. This result of enhanced toughness of spider silk could potentially serve as a model for a more general approach to enhance the strength and toughness of other biomaterials.

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P.K. Madhu

Tata Institute of Fundamental Research

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