Engineered protein polymers that display responsiveness to multiple stimuli are emerging as a pro... more Engineered protein polymers that display responsiveness to multiple stimuli are emerging as a promising class of soft material with unprecedented functionality. The remarkable advancement in genetic engineering and biosynthesis has created the opportunity for precise control over the amino acid sequence, size, structure and resulting functions of such biomimetic proteins. Herein, we describe the multi-stimuli-responsive characteristics of a resilin-mimetic protein, An16-resilin (An16), derived from the consensus sequence of resilin gene in the mosquito Anopheles gambiae. We demonstrate that An16 is an intrinsically disordered protein that displays unusual dual-phase thermal transition behavior along with responsiveness to pH, ion, light and humidity. Identifying the molecular mechanisms that allow An16 to sense and switch in response to varying environments furthers the ability to design intelligent biomacromolecules.
This paper reports the use of X-ray photoelectron spectroscopy (XPS) to investigate bisphosphonat... more This paper reports the use of X-ray photoelectron spectroscopy (XPS) to investigate bisphosphonate (BP) adsorption onto plasma sprayed hydroxyapatite (HA) coatings commonly used for orthopaedic implants. BPs exhibit high binding affinity for the calcium present in HA and hence can be adsorbed onto HA-coated implants to exploit their beneficial properties for improved bone growth at the implant interface. A rigorous XPS analysis of pamidronate, a commonly used nitrogenous BP, adsorbed onto plasma sprayed HA-coated cobalt-chromium substrates has been carried out, aimed at: (a) confirming the adsorption of this BP onto HA; (b) studying the BP diffusion profile in the HA coating by employing the technique of XPS depth profiling; (c) confirming the bioactivity of the adsorbed BP. XPS spectra of plasma sprayed HA-coated discs exposed to a 10 mM aqueous BP solution (pamidronate) for periods of 1, 2 and 24 h showed nitrogen and phosphorous photoelectron signals corresponding to the BP, confirming its adsorption onto the HA substrate. XPS depth profiling of the 2 h BP-exposed HA discs showed penetration of the BP into the HA matrix to depths of at least 260 nm. The bioactivity of the adsorbed BP was confirmed by the observed inhibition of osteoclast (bone resorbing) cell activity. In comparison to the HA sample, the HA sample with adsorbed BP exhibited a 25-fold decrease in primary osteoclast cells.
The effect of carbon black concentration on the dynamic mechanical properties of bromobutyl rubbe... more The effect of carbon black concentration on the dynamic mechanical properties of bromobutyl rubber vulcanizates has been studied over a wide range of temperature (− 150 to + 250 °C), frequency (3.5 to 110 Hz) and dynamic strain amplitude (0.07 to 5%). The influence of carbon black concentration on the glass-rubber transition has also been investigated with respect to the isochronal variation in dynamic properties. The influence of carbon black concentration consists mainly of the change in the levels of the moduli values in the glassy and rubbery state. In the glassy region; the increase in stiffness with carbon black loading may be fully explained by the hydrodynamic effect of the carbon black particles embedded in the polymer continuum. With increased carbon black concentration the glass-rubber transition temperature (tan δ peak temperature) does not show a shift in its location but peak shoulder broadening and decrease in peak height are observed. At a particular temperature, the effect of carbon black concentration on dynamic properties of bromobutyl rubber is dependent on the combined effects of applied strain amplitude and frequency. With increase in filler concentration the thermal stability of the vulcanizate increases.
The dynamic mechanical, and physical properties of bromobutyl rubber were investigated to determi... more The dynamic mechanical, and physical properties of bromobutyl rubber were investigated to determine the effect of particle size and of the structure of carbon black and silica. Filler loading was so adjusted that all the experimental compositions had the same hardness level. The results indicate that the type and loading of filler have no significant effect on the molecular relaxation transition. However, elastomer having a desirable storage modulus with low sensitivity to temperature change can be developed using filler with smaller particle size. Higher elongation at break, and better tensile strength, energy density at break, and fatigue life could be obtained by using finer particle or high structure black than with the low structure and higher particle size black. Finer particle size filler loaded systems exhibit pronounced strain dependence, higher thixotropic change, and delayed recovery in dynamic mechanical properties compared to that exhibited by large particle size filler.
Transparent organic-inorganic hybrid material was synthesized via the sol-gel method using polyet... more Transparent organic-inorganic hybrid material was synthesized via the sol-gel method using polyethylene-co-Zn-acrylic acid (Zn-PEAA) ionomer and a metal alkoxide, tetraethyl orthosilicate (TEOS). The resulting material was characterized using various spectroscopic, microscopic, and thermal techniques. Photoacoustic Fourier transform infrared spectroscopy (PA-FTIR) and 29 Si solid-state nuclear magnetic resonance spectroscopy ( 29 Si solid-state NMR) results prove that silica is formed via the sol-gel reaction. Scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDAX), transmission electron microscopy (TEM), and atomic force microscopy (AFM) studies indicate that silica particle size is in nanoscopic level (50 nm average size), and silica nanoparticles are uniformly dispersed in the polymer matrix after the sol-gel process. Thermogravimetric analysis (TGA) results show that the silica content of the hybrid is about 19%. The thermal stability of the ionomer increases after hybridization. The crystallinity of the hybrid material is found to decrease from modulated differential scanning calorimetry (MDSC) and wide-angle X-ray scattering (WAXS) results. Dynamic mechanical analysis (DMA) of the hybrid shows that the storage modulus of ionomer increases after the sol-gel reaction, and the order-disorder transition temperature of the ionic cluster also increases, indicating the existence of silica mostly in the microphase separated cluster template.
Recently, the nanosized noble metal particles and clusters have attracted significant attention d... more Recently, the nanosized noble metal particles and clusters have attracted significant attention due to their unique properties and potential applications in the fields of photochemistry, electrochemistry, optics, magnetics, electronics and catalysis. The profound enhancement in catalytic activity with the reduction in particle size (<10 nm) along with high selectivity and stability, such nanoparticles offer the promise of developing sustainable chemistry with significant material and energy saving. However, the design and role of the carrier/ support of the particle for such applications is crucial, as it determines the activity and life time of the nanoparticles in various applications ranging from fuel cell to drug delivery Last two decades saw the emergence of novel supports (polymers, block copolymers, carbon, and functionalized silica matrices) for stabilizing noble metallic colloids. Recently, highly attractive bottom-up fabrication schemes for synthesizing nanoparticles by template method that uses natural (such as DNA, bacterial surface layer proteins, ferritin, chaperonin, viruses, etc.) or artificial nanoarchitectures have been reported. Miyamura et al. observed higher catalytic performances for gold nanoparticles supported on polymers than that on metal oxides. The meso-phase separated block copolymers [BCP] offer distinctive advantages as support for nanoparticles over other materials. The potential of phase separated BCP to create controlled growth of desired nanoparticle derives from the diversity of their architectural possibilities, ease of handling, low cost, and unique tunability of the organization, size, shape, periodicity and binding of nanoparticles to the self assembled nano-domains. The advantage of this approach is that control over the size and spacing of the catalyst particles can be achieved by growing the desired colloids within the block domains of suitable size, shape and functionality.
The effect of ethylene/propylene content on the thermal degradation behaviour of ethylene±propyle... more The effect of ethylene/propylene content on the thermal degradation behaviour of ethylene±propylene-diene (EPDM) elastomers was investigated using conventional non-isothermal and isothermal thermogravimetric analysis (TGA) as well as modulated thermogravimetric analysis (MTGA 1 ). Kinetic parameters of degradation were evaluated using single heating rate data under a pseudo-®rst order assumption; the Flynn±Wall±Ozawa isoconversional method; isothermal methods; and MTGA 1 . Although the ethylene/propylene ratio in¯uences the onset and peak temperatures of degradation, it appears that not only the ethylene content but microstructure is also a controlling factor in determining the activation energy of degradation. Pseudo-®rst order analyses show that at least two different ®rst-order degradation reaction mechanisms dominate the degradation process. MTGA 1 analyses show that the activation energy of degradation increases throughout the reaction. Isothermal TGA con®rms that the degradation processes for PE, PP and EPDM are complicated and do not follow an nth order reaction path, rather they follow a random degradation process. #
In this investigation, for the first time we report the effects of pH on the molecular orientatio... more In this investigation, for the first time we report the effects of pH on the molecular orientation, packing density, structural properties, adsorption characteristics and viscoelastic behaviour of resilin-mimetic protein rec1-resilin at the solideliquid interface using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) spectroscopy. QCM-D and SPR data confirm that the binding ability of rec1-resilin on a substrate is strongly pH-dependent the protein packing density on a gold surface is calculated to be 4.45 Â 10 13 per cm 2 at the isoelectric point (IEP w 4.9), 8.79 Â 10 11 per cm 2 at pH 2 and 9.90 Â 10 11 per cm 2 at pH 12, respectively. Our findings based on the thickness, dissipation and viscoelasticity of the rec1-resilin adlayer also indicate that it is adsorbed onto the gold substrate with different orientation depending on pH, such as back-on adsorption at acidic pH of 2, compact end-on bilayer adsorption at the IEP and side-on at high alkaline pH of 12. When rec1-resilin is 'pinned' to the substrate at IEP and subsequently exposed to an electrolyte solution adjusted to different pH, it switches from a compact globular conformation of the bio-macromolecule at the IEP to a coil conformation at pH between IEP to IED (IED ¼ pKa value of tyrosine amino acid residue) and an extended coil conformation at pH > IED. This transformation from globule to coil to extended coil conformation is kinetically fast, robust and completely reversible. Such responsive surfaces created using 'smart' biomimetic rec1-resilin have the potential to find applications in many areas including biotechnology, medicine, sensors, controlled drug delivery systems and engineering.
In this study, three mass spectrometry techniques matrix-assisted laser desorption ionization mas... more In this study, three mass spectrometry techniques matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF MS) combined with thin-layer chromatography (TLC), laser desorption/ionization on silicon-mass spectrometry (DIOS-MS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used to investigate the thermooxidative degradation and resultant discoloration of poly(ethylene terephthalate) PET that frequently occurs during melt processing. The MALDI-TOF MS spectra of the degraded polymer showed the formation of oligomers containing carboxyl end groups via chain scission at the ether link present in PET. In addition, a variety of cyclic oligomers are found to form via two different mechanisms from the linear oligomers of the virgin PET. Thus, our results not only confirm the oligomers containing carboxyl end groups and cyclic oligomers as the low molecular weight degradation products but also deepen the understanding about their structures, molecular weights, and molecular weight distributions. Furthermore, a MALDI-TOF MS study directly on the TLC plate and DIOS-MS enable us to identify low molecular weight compounds (not detected previously due to matrix interference) that are contributors to color formation.
Novel supported liquid membranes (SLMs) have been developed by impregnating Nafion and Hyflon mem... more Novel supported liquid membranes (SLMs) have been developed by impregnating Nafion and Hyflon membranes with ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-BTSI). These supported liquid membranes were characterized in terms of their ionic liquid uptake behavior, leaching of ionic liquid by water, thermal stability, mechanical properties, glass transition temperature, ion exchange capacity, and proton conductivity. In general, modified membranes are more flexible than unmodified samples due to the plasticization effects of the ionic liquid. However, these supported liquid membranes exhibit a significant increase in their operational stability and proton conductivity over unmodified membranes. We also demonstrate that proton conductivity of these supported liquid membranes allows conduction of protons in anhydrous conditions with conductivity increasing with temperature. Conductivity of up to 3.58 mS cm -1 has been achieved at 160°C in dry conditions, making these materials promising for various electrochemical applications.
In this research, we examine the effect of non-selective solvent on the large-scale mesoscopic or... more In this research, we examine the effect of non-selective solvent on the large-scale mesoscopic ordering in asymmetric block copolymers, poly(styrene-block-ethylene/butylene-block-styrene) (SEBS) using small angle neutron scattering technique (SANS). SANS measurements were carried out over a wide range of concentrations and temperatures. Evolution of the self-assembled phase morphology in such polymer with the thermodynamic selectivity of solvent, temperature and concentration has
The discolouration, that occurs in virgin poly(ethylene terephthalate) – PET during melt processi... more The discolouration, that occurs in virgin poly(ethylene terephthalate) – PET during melt processing, was studied using various bulk and surface analytical techniques. Proton nuclear magnetic resonance (1H NMR) was used to study the bulk chemical changes occurring in the polymer during thermo-oxidative degradation. Chemical derivatisation with trifluoroacetic anhydride (TFAA) was used to label the hydroxyl groups introduced on the polymer surface by thermal oxidation.From the surface analysis studies using photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) it was evident that colour formation starts initially with the hydroxylation of the terephthalic ring. Further, the formation of additional carbonyl functionalities and conjugated chromophoric systems complete the colour formation process.
In this investigation we report the synthesis of optically coupled hybrid architectures based on ... more In this investigation we report the synthesis of optically coupled hybrid architectures based on a new biomimetic fluorescent protein rec1-resilin and nanometer-scale gold nanoparticles (AuNPs) in a one-step method using a non-covalent mode of binding protocol. The presence of uniformly distributed fluorophore sequences, eSer(Thr)-Tyr-Glyalong the molecular structure of rec1-resilin provides signnificant opportunity to synthesize fluorophore-modified AuNPs bioconjugates with unique photophysical properties. The detailed analyses of the AuNP-bioconjugates, synthesized under different experimental conditions using spectroscopic, microscopic and scattering techniques demonstrate the organizational pathways and the electronic and photophysical properties of the developed AuNP-rec1-resilin bioconjugates. The calculation of the bimolecular quenching constant using the SterneVolmer equation confirms that the dominant mechanism involved in quenching of fluorescence of rec1-resilin in the presence of AuNP is static. Photoacoustic infrared spectroscopy was employed to understand the nature of the interfacial interaction between the AuNP and rec1-resilin and its evolution with pH. In such bioconjugates the quenched emission of fluorescence by AuNP on the fluorophore moiety of rec1-resilin in the immediate vicinity of the AuNP has significant potential for fluorescence-based detection schemes, sensors and also can be incorporated into nanoparticle-based devices.
In this paper we report successful simple synthesis of unique elastic polyesters by carrying out ... more In this paper we report successful simple synthesis of unique elastic polyesters by carrying out catalystfree polyesterification of multifunctional non-toxic monomers: 1,8-octanediol (OD), citric acid (CA) and sebacic acid (SA). The chemical, physical, and surface chemical properties of the resulting copolyester polyoctanediol citrate/sebacate [p(OCS)] have been investigated. This new material was characterized by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF-MS), nuclear magnetic resonance spectroscopy (NMR), thermal analysis (TA), mechanical tests, photo-acoustic Fourier-transform infrared spectroscopy (PA-FTIR), X-ray photoelectron spectroscopy (XPS) and swelling experiments. We demonstrate that the chemical structure, morphology, physical integrity and surface chemistry of the synthesized co-polymer can be controlled by simply varying the initial acid concentration (CA/SA) in the pre-polymer. This novel p(OCS) polymer exhibits versatility in mechanical properties, hydration and hydrolytic degradation as determined by the chemical structure of the polyester elastomer.
Protein adsorption on surfaces is a fundamental step in many applications. While various methods ... more Protein adsorption on surfaces is a fundamental step in many applications. While various methods such as lithography, self assembly using nanoparticles, layer-by-layer attachment, etc. have been employed, here we report fabrication of controlled nanostructure of a new resilin-mimetic elastic protein rec1resilin using physical approaches. We investigate the assembly, morphology and tunability of the nanostructure of adsorbed rec1-resilin architectures by atomic force microscopy (AFM) and scanning thermal microscopy (SThm) demonstrating that the protein conformation and structure during assembly can be controlled by tuning the physical conditions at the surface. Our findings show distinct morphology and height of monomolecular rec1-resilin film, dependent on substrate surface energy. We also show that these heights, a function of molecular orientation, can be maintained on swelling and drying.
Engineered protein polymers that display responsiveness to multiple stimuli are emerging as a pro... more Engineered protein polymers that display responsiveness to multiple stimuli are emerging as a promising class of soft material with unprecedented functionality. The remarkable advancement in genetic engineering and biosynthesis has created the opportunity for precise control over the amino acid sequence, size, structure and resulting functions of such biomimetic proteins. Herein, we describe the multi-stimuli-responsive characteristics of a resilin-mimetic protein, An16-resilin (An16), derived from the consensus sequence of resilin gene in the mosquito Anopheles gambiae. We demonstrate that An16 is an intrinsically disordered protein that displays unusual dual-phase thermal transition behavior along with responsiveness to pH, ion, light and humidity. Identifying the molecular mechanisms that allow An16 to sense and switch in response to varying environments furthers the ability to design intelligent biomacromolecules.
This paper reports the use of X-ray photoelectron spectroscopy (XPS) to investigate bisphosphonat... more This paper reports the use of X-ray photoelectron spectroscopy (XPS) to investigate bisphosphonate (BP) adsorption onto plasma sprayed hydroxyapatite (HA) coatings commonly used for orthopaedic implants. BPs exhibit high binding affinity for the calcium present in HA and hence can be adsorbed onto HA-coated implants to exploit their beneficial properties for improved bone growth at the implant interface. A rigorous XPS analysis of pamidronate, a commonly used nitrogenous BP, adsorbed onto plasma sprayed HA-coated cobalt-chromium substrates has been carried out, aimed at: (a) confirming the adsorption of this BP onto HA; (b) studying the BP diffusion profile in the HA coating by employing the technique of XPS depth profiling; (c) confirming the bioactivity of the adsorbed BP. XPS spectra of plasma sprayed HA-coated discs exposed to a 10 mM aqueous BP solution (pamidronate) for periods of 1, 2 and 24 h showed nitrogen and phosphorous photoelectron signals corresponding to the BP, confirming its adsorption onto the HA substrate. XPS depth profiling of the 2 h BP-exposed HA discs showed penetration of the BP into the HA matrix to depths of at least 260 nm. The bioactivity of the adsorbed BP was confirmed by the observed inhibition of osteoclast (bone resorbing) cell activity. In comparison to the HA sample, the HA sample with adsorbed BP exhibited a 25-fold decrease in primary osteoclast cells.
The effect of carbon black concentration on the dynamic mechanical properties of bromobutyl rubbe... more The effect of carbon black concentration on the dynamic mechanical properties of bromobutyl rubber vulcanizates has been studied over a wide range of temperature (− 150 to + 250 °C), frequency (3.5 to 110 Hz) and dynamic strain amplitude (0.07 to 5%). The influence of carbon black concentration on the glass-rubber transition has also been investigated with respect to the isochronal variation in dynamic properties. The influence of carbon black concentration consists mainly of the change in the levels of the moduli values in the glassy and rubbery state. In the glassy region; the increase in stiffness with carbon black loading may be fully explained by the hydrodynamic effect of the carbon black particles embedded in the polymer continuum. With increased carbon black concentration the glass-rubber transition temperature (tan δ peak temperature) does not show a shift in its location but peak shoulder broadening and decrease in peak height are observed. At a particular temperature, the effect of carbon black concentration on dynamic properties of bromobutyl rubber is dependent on the combined effects of applied strain amplitude and frequency. With increase in filler concentration the thermal stability of the vulcanizate increases.
The dynamic mechanical, and physical properties of bromobutyl rubber were investigated to determi... more The dynamic mechanical, and physical properties of bromobutyl rubber were investigated to determine the effect of particle size and of the structure of carbon black and silica. Filler loading was so adjusted that all the experimental compositions had the same hardness level. The results indicate that the type and loading of filler have no significant effect on the molecular relaxation transition. However, elastomer having a desirable storage modulus with low sensitivity to temperature change can be developed using filler with smaller particle size. Higher elongation at break, and better tensile strength, energy density at break, and fatigue life could be obtained by using finer particle or high structure black than with the low structure and higher particle size black. Finer particle size filler loaded systems exhibit pronounced strain dependence, higher thixotropic change, and delayed recovery in dynamic mechanical properties compared to that exhibited by large particle size filler.
Transparent organic-inorganic hybrid material was synthesized via the sol-gel method using polyet... more Transparent organic-inorganic hybrid material was synthesized via the sol-gel method using polyethylene-co-Zn-acrylic acid (Zn-PEAA) ionomer and a metal alkoxide, tetraethyl orthosilicate (TEOS). The resulting material was characterized using various spectroscopic, microscopic, and thermal techniques. Photoacoustic Fourier transform infrared spectroscopy (PA-FTIR) and 29 Si solid-state nuclear magnetic resonance spectroscopy ( 29 Si solid-state NMR) results prove that silica is formed via the sol-gel reaction. Scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDAX), transmission electron microscopy (TEM), and atomic force microscopy (AFM) studies indicate that silica particle size is in nanoscopic level (50 nm average size), and silica nanoparticles are uniformly dispersed in the polymer matrix after the sol-gel process. Thermogravimetric analysis (TGA) results show that the silica content of the hybrid is about 19%. The thermal stability of the ionomer increases after hybridization. The crystallinity of the hybrid material is found to decrease from modulated differential scanning calorimetry (MDSC) and wide-angle X-ray scattering (WAXS) results. Dynamic mechanical analysis (DMA) of the hybrid shows that the storage modulus of ionomer increases after the sol-gel reaction, and the order-disorder transition temperature of the ionic cluster also increases, indicating the existence of silica mostly in the microphase separated cluster template.
Recently, the nanosized noble metal particles and clusters have attracted significant attention d... more Recently, the nanosized noble metal particles and clusters have attracted significant attention due to their unique properties and potential applications in the fields of photochemistry, electrochemistry, optics, magnetics, electronics and catalysis. The profound enhancement in catalytic activity with the reduction in particle size (<10 nm) along with high selectivity and stability, such nanoparticles offer the promise of developing sustainable chemistry with significant material and energy saving. However, the design and role of the carrier/ support of the particle for such applications is crucial, as it determines the activity and life time of the nanoparticles in various applications ranging from fuel cell to drug delivery Last two decades saw the emergence of novel supports (polymers, block copolymers, carbon, and functionalized silica matrices) for stabilizing noble metallic colloids. Recently, highly attractive bottom-up fabrication schemes for synthesizing nanoparticles by template method that uses natural (such as DNA, bacterial surface layer proteins, ferritin, chaperonin, viruses, etc.) or artificial nanoarchitectures have been reported. Miyamura et al. observed higher catalytic performances for gold nanoparticles supported on polymers than that on metal oxides. The meso-phase separated block copolymers [BCP] offer distinctive advantages as support for nanoparticles over other materials. The potential of phase separated BCP to create controlled growth of desired nanoparticle derives from the diversity of their architectural possibilities, ease of handling, low cost, and unique tunability of the organization, size, shape, periodicity and binding of nanoparticles to the self assembled nano-domains. The advantage of this approach is that control over the size and spacing of the catalyst particles can be achieved by growing the desired colloids within the block domains of suitable size, shape and functionality.
The effect of ethylene/propylene content on the thermal degradation behaviour of ethylene±propyle... more The effect of ethylene/propylene content on the thermal degradation behaviour of ethylene±propylene-diene (EPDM) elastomers was investigated using conventional non-isothermal and isothermal thermogravimetric analysis (TGA) as well as modulated thermogravimetric analysis (MTGA 1 ). Kinetic parameters of degradation were evaluated using single heating rate data under a pseudo-®rst order assumption; the Flynn±Wall±Ozawa isoconversional method; isothermal methods; and MTGA 1 . Although the ethylene/propylene ratio in¯uences the onset and peak temperatures of degradation, it appears that not only the ethylene content but microstructure is also a controlling factor in determining the activation energy of degradation. Pseudo-®rst order analyses show that at least two different ®rst-order degradation reaction mechanisms dominate the degradation process. MTGA 1 analyses show that the activation energy of degradation increases throughout the reaction. Isothermal TGA con®rms that the degradation processes for PE, PP and EPDM are complicated and do not follow an nth order reaction path, rather they follow a random degradation process. #
In this investigation, for the first time we report the effects of pH on the molecular orientatio... more In this investigation, for the first time we report the effects of pH on the molecular orientation, packing density, structural properties, adsorption characteristics and viscoelastic behaviour of resilin-mimetic protein rec1-resilin at the solideliquid interface using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) spectroscopy. QCM-D and SPR data confirm that the binding ability of rec1-resilin on a substrate is strongly pH-dependent the protein packing density on a gold surface is calculated to be 4.45 Â 10 13 per cm 2 at the isoelectric point (IEP w 4.9), 8.79 Â 10 11 per cm 2 at pH 2 and 9.90 Â 10 11 per cm 2 at pH 12, respectively. Our findings based on the thickness, dissipation and viscoelasticity of the rec1-resilin adlayer also indicate that it is adsorbed onto the gold substrate with different orientation depending on pH, such as back-on adsorption at acidic pH of 2, compact end-on bilayer adsorption at the IEP and side-on at high alkaline pH of 12. When rec1-resilin is 'pinned' to the substrate at IEP and subsequently exposed to an electrolyte solution adjusted to different pH, it switches from a compact globular conformation of the bio-macromolecule at the IEP to a coil conformation at pH between IEP to IED (IED ¼ pKa value of tyrosine amino acid residue) and an extended coil conformation at pH > IED. This transformation from globule to coil to extended coil conformation is kinetically fast, robust and completely reversible. Such responsive surfaces created using 'smart' biomimetic rec1-resilin have the potential to find applications in many areas including biotechnology, medicine, sensors, controlled drug delivery systems and engineering.
In this study, three mass spectrometry techniques matrix-assisted laser desorption ionization mas... more In this study, three mass spectrometry techniques matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF MS) combined with thin-layer chromatography (TLC), laser desorption/ionization on silicon-mass spectrometry (DIOS-MS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used to investigate the thermooxidative degradation and resultant discoloration of poly(ethylene terephthalate) PET that frequently occurs during melt processing. The MALDI-TOF MS spectra of the degraded polymer showed the formation of oligomers containing carboxyl end groups via chain scission at the ether link present in PET. In addition, a variety of cyclic oligomers are found to form via two different mechanisms from the linear oligomers of the virgin PET. Thus, our results not only confirm the oligomers containing carboxyl end groups and cyclic oligomers as the low molecular weight degradation products but also deepen the understanding about their structures, molecular weights, and molecular weight distributions. Furthermore, a MALDI-TOF MS study directly on the TLC plate and DIOS-MS enable us to identify low molecular weight compounds (not detected previously due to matrix interference) that are contributors to color formation.
Novel supported liquid membranes (SLMs) have been developed by impregnating Nafion and Hyflon mem... more Novel supported liquid membranes (SLMs) have been developed by impregnating Nafion and Hyflon membranes with ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-BTSI). These supported liquid membranes were characterized in terms of their ionic liquid uptake behavior, leaching of ionic liquid by water, thermal stability, mechanical properties, glass transition temperature, ion exchange capacity, and proton conductivity. In general, modified membranes are more flexible than unmodified samples due to the plasticization effects of the ionic liquid. However, these supported liquid membranes exhibit a significant increase in their operational stability and proton conductivity over unmodified membranes. We also demonstrate that proton conductivity of these supported liquid membranes allows conduction of protons in anhydrous conditions with conductivity increasing with temperature. Conductivity of up to 3.58 mS cm -1 has been achieved at 160°C in dry conditions, making these materials promising for various electrochemical applications.
In this research, we examine the effect of non-selective solvent on the large-scale mesoscopic or... more In this research, we examine the effect of non-selective solvent on the large-scale mesoscopic ordering in asymmetric block copolymers, poly(styrene-block-ethylene/butylene-block-styrene) (SEBS) using small angle neutron scattering technique (SANS). SANS measurements were carried out over a wide range of concentrations and temperatures. Evolution of the self-assembled phase morphology in such polymer with the thermodynamic selectivity of solvent, temperature and concentration has
The discolouration, that occurs in virgin poly(ethylene terephthalate) – PET during melt processi... more The discolouration, that occurs in virgin poly(ethylene terephthalate) – PET during melt processing, was studied using various bulk and surface analytical techniques. Proton nuclear magnetic resonance (1H NMR) was used to study the bulk chemical changes occurring in the polymer during thermo-oxidative degradation. Chemical derivatisation with trifluoroacetic anhydride (TFAA) was used to label the hydroxyl groups introduced on the polymer surface by thermal oxidation.From the surface analysis studies using photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) it was evident that colour formation starts initially with the hydroxylation of the terephthalic ring. Further, the formation of additional carbonyl functionalities and conjugated chromophoric systems complete the colour formation process.
In this investigation we report the synthesis of optically coupled hybrid architectures based on ... more In this investigation we report the synthesis of optically coupled hybrid architectures based on a new biomimetic fluorescent protein rec1-resilin and nanometer-scale gold nanoparticles (AuNPs) in a one-step method using a non-covalent mode of binding protocol. The presence of uniformly distributed fluorophore sequences, eSer(Thr)-Tyr-Glyalong the molecular structure of rec1-resilin provides signnificant opportunity to synthesize fluorophore-modified AuNPs bioconjugates with unique photophysical properties. The detailed analyses of the AuNP-bioconjugates, synthesized under different experimental conditions using spectroscopic, microscopic and scattering techniques demonstrate the organizational pathways and the electronic and photophysical properties of the developed AuNP-rec1-resilin bioconjugates. The calculation of the bimolecular quenching constant using the SterneVolmer equation confirms that the dominant mechanism involved in quenching of fluorescence of rec1-resilin in the presence of AuNP is static. Photoacoustic infrared spectroscopy was employed to understand the nature of the interfacial interaction between the AuNP and rec1-resilin and its evolution with pH. In such bioconjugates the quenched emission of fluorescence by AuNP on the fluorophore moiety of rec1-resilin in the immediate vicinity of the AuNP has significant potential for fluorescence-based detection schemes, sensors and also can be incorporated into nanoparticle-based devices.
In this paper we report successful simple synthesis of unique elastic polyesters by carrying out ... more In this paper we report successful simple synthesis of unique elastic polyesters by carrying out catalystfree polyesterification of multifunctional non-toxic monomers: 1,8-octanediol (OD), citric acid (CA) and sebacic acid (SA). The chemical, physical, and surface chemical properties of the resulting copolyester polyoctanediol citrate/sebacate [p(OCS)] have been investigated. This new material was characterized by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF-MS), nuclear magnetic resonance spectroscopy (NMR), thermal analysis (TA), mechanical tests, photo-acoustic Fourier-transform infrared spectroscopy (PA-FTIR), X-ray photoelectron spectroscopy (XPS) and swelling experiments. We demonstrate that the chemical structure, morphology, physical integrity and surface chemistry of the synthesized co-polymer can be controlled by simply varying the initial acid concentration (CA/SA) in the pre-polymer. This novel p(OCS) polymer exhibits versatility in mechanical properties, hydration and hydrolytic degradation as determined by the chemical structure of the polyester elastomer.
Protein adsorption on surfaces is a fundamental step in many applications. While various methods ... more Protein adsorption on surfaces is a fundamental step in many applications. While various methods such as lithography, self assembly using nanoparticles, layer-by-layer attachment, etc. have been employed, here we report fabrication of controlled nanostructure of a new resilin-mimetic elastic protein rec1resilin using physical approaches. We investigate the assembly, morphology and tunability of the nanostructure of adsorbed rec1-resilin architectures by atomic force microscopy (AFM) and scanning thermal microscopy (SThm) demonstrating that the protein conformation and structure during assembly can be controlled by tuning the physical conditions at the surface. Our findings show distinct morphology and height of monomolecular rec1-resilin film, dependent on substrate surface energy. We also show that these heights, a function of molecular orientation, can be maintained on swelling and drying.
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Papers by Naba Dutta