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  • 1
    Language: English
    In: The journal of physical chemistry. B, 20 March 2014, Vol.118(11), pp.3207-17
    Description: Supramolecular assembly allows for enhanced control of bulk material properties through the fine modulation of intermolecular interactions. We present a comprehensive study of a cross-linkable amphiphilic wedge molecule based on a sulfonated trialkoxybenzene with a sodium counterion that forms liquid crystalline (LC) phases with ionic nanochannel structures. This compound exhibits drastic structural changes as a function of relative humidity (RH). Our combined structural, dynamical, and transport studies reveal deep and novel information on the coupling of water and wedge molecule transport to structural motifs, including the significant influence of domain boundaries within the material. Over a range of RH values, we employ (23)Na solid-state NMR on the counterions to complement detailed structural studies by grazing-incidence small-angle X-ray scattering. RH-dependent pulsed-field-gradient (PFG) NMR diffusion studies on both water and the wedge amphiphiles show multiple components, corresponding to species diffusing within LC domains as well as in the domain boundaries that compose 10% of the material. The rich transport and dynamical behaviors described here represent an important window into the world of supramolecular soft materials, carrying implications for optimization of these materials in many venues. Cubic phases present at high RH show fast transport of water (2 × 10(-10) m(2)/s), competitive with that observed in benchmark polymeric ion conductors. Understanding the self-assembly of these supramolecular building blocks shows promise for generating cross-linked membranes with fast ion conduction for applications such as next-generation batteries.
    Keywords: Strukturumwandlung ; Röntgenstrahl ; Diffusion ; Natrium ; Ionenkanal ; Relative Feuchtigkeit ; Dynamisches Verhalten ; Ionenleitung ; Baugruppe ; Selbstassemblierung ; Membran ; Chemistry;
    ISSN: 15206106
    E-ISSN: 1520-5207
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  • 2
    Language: English
    In: Polymer, 02 June 2017, Vol.118, pp.150-162
    Description: In order to understand the influence of composition on oxygen permeability, the morphology of model silicone hydrogels in both the dry and hydrated states was characterized using a variety of techniques (AFM, HAADF-STEM, solid-state NMR, and X-ray scattering). The model system studied is heterogeneous on length scales below 20 nm and consists of globular silicone-rich domains that rearrange in response to changes in hydration. In contrast to the well-defined morphologies of block copolymer systems, these radically cured amphiphilic networks are less ordered, showing gradual composition fluctuations. Comprehensive morphology characterization rationalizes the transport behavior of these heterogeneous hydrogels: the non-linear permeability increase with increasing silicone monomer content is not only related to changes in the spatial arrangement of silicone-rich domains but also to their mobility. This understanding is needed for further optimizing soft contact lens materials where oxygen transport and optical clarity are critical features.
    Keywords: Silicone Hydrogel ; Contact Lens ; Morphology ; Engineering ; Chemistry
    ISSN: 0032-3861
    E-ISSN: 1873-2291
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  • 3
    Language: English
    In: Macromolecules, 07/25/2017, Vol.50(14), pp.5392-5401
    Description: We report a simple photo-cross-linking process to chemically arrest the different liquid-crystalline structures formed by self-assembly of wedge-shaped amphiphilic mesogens. Using this route, we obtained free-standing polymer membranes with columnar or bicontinuous cubic structures, depending primarily on the relative humidity conditions during UV-induced cross-linking. These cross-linked mesostructures show much higher thermal stability in comparison with that of the liquid-crystalline structures of the initial monomers. The ionic conductivity of the membranes strongly depends on the water uptake preceding the polymerization reaction. According to NMR diffusometry, which can quantify water transport in one or two environments in these materials, the water diffusion rate in the membrane with bicontinuous cubic structures can approach values of commercial ion conducting membranes. These studies show promise for use of this fabrication route in practical applications for selective ion and water transport.
    Keywords: Crystal-Structure ; Cubic-Structure ; Polymerisation-Reaction ; Ion-Transport ; Conducting-Polymers ; Diffusion-Rate ; Relative-Humidity ; Self-Assembly ; Ion-Conductivity ; Polymer-Membranes ; Monomers ; Absorption-Water ; Waterway-Transportation ; Kristalline Struktur ; Kubische Struktur ; Polymerisationsreaktion ; Ionentransport ; Leitendes Polymer ; Diffusionsgeschwindigkeit ; Relative Feuchtigkeit ; Selbstassemblierung ; Ionenleitfähigkeit ; Polymermembran ; Monomer ; Wasseraufnahme ; Wassertransport ; Chemistry;
    ISSN: 0024-9297
    E-ISSN: 1520-5835
    Source: American Chemical Society (via CrossRef)
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  • 4
    Language: English
    In: Journal of Magnetic Resonance, 2008, Vol.192(2), pp.230-234
    Description: Sensitivity enhancement of solid-state NMR spectrum of half-integer spin quadrupolar nuclei under both magic-angle spinning (MAS) and static cases has been demonstrated by transferring polarisation associated with satellite transitions to the central = −1/2 → 1/2 transition with suitably modulated radio-frequency pulse schemes. It has been shown that after the application of such enhancement schemes, there still remains polarisation in the satellite transitions that can be transferred to the central transition. This polarisation is available without having to wait for the spin system to return to thermal equilibrium. We demonstrate here the additional sensitivity enhancement obtained by making use of this remaining polarisation with fast amplitude-modulated (FAM) pulse schemes under both MAS and static conditions on a spin-3/2 and a spin-5/2 system. Considerable signal enhancement is obtained with the application of the multiple FAM sequence, denoted as -FAM. We also report here some of the salient features of these multiple FAM sequences with respect to the nutation frequency of the pulses and the spinning frequency.
    Keywords: Solid-State NMR ; Quadrupolar Nuclei ; Sensitivity Enhancement ; FAM ; Sw(1/ Τ)-FAM ; M-FAM ; M-Sw(1/ Τ)-FAM ; Chemistry ; Physics
    ISSN: 1090-7807
    E-ISSN: 1096-0856
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  • 5
    Language: English
    In: Chemical Physics Letters, 2007, Vol.445(4), pp.217-220
    Description: Quantum dots acquire a protective protein corona in physiological solutions, which helps it retain its fluorescence quantum efficiency. We report that proteins in physiological buffers spontaneously attach to polyethylene glycol coated fluorescent quantum dots (QDs) and strongly inhibit the gradual loss of QD fluorescence. This interaction does not strongly depend on the nature or solubility of the proteins tested (amyloid beta, barstar, cytochrome , bovine serum albumin and lysozyme). Fluorescence correlation spectroscopy shows that each QD acquires a ‘corona’ of ∼100 protein molecules, which confers protection against ionic attacks in aqueous solutions. This effect would be important for any biological application, and also offers a potential assay for soluble proteins.
    Keywords: Chemistry
    ISSN: 0009-2614
    E-ISSN: 1873-4448
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  • 6
    Language: English
    In: Chemistry Central Journal, Nov 9, 2009, Vol.3, p.15
    Description: Background Organic light emitting devices (OLED) are becoming important and characterisation of them, in terms of structure, charge distribution, and intermolecular interactions, is important. Tris(8-hydroxyquinolinato)-aluminium(III), known as Alq.sub.3 , an organomettalic complex has become a reference material of great importance in OLED. It is important to elucidate the structural details of Alq.sub.3 in its various isomeric and solvated forms. Solid-state nuclear magnetic resonance (NMR) is a useful tool for this which can also complement the information obtained with X-ray diffraction studies. Results We report here .sup.27.sup.Al one-dimensional (1D) and two-dimensional (2D) multiple-quantum magic-angle spinning (MQMAS) NMR studies of the meridional ([alpha]-phase) and the facial ([delta]-phase) isomeric forms of Alq.sub.3 . Quadrupolar parameters are estimated from the 1D spectra under MAS and anisotropic slices of the 2D spectra and also calculated using DFT (density functional theory) quantum-chemical calculations. We have also studied solvated phase of Alq.sub.3 containing ethanol in its lattice. We show that both the XRD patterns and the quadrupolar parameters of the solvated phase are different from both the [alpha]-phase and the [delta]-phase, although the fluorescence emission shows no substantial difference between the [alpha]-phase and the solvated phase. Moreover, we have shown that after the removal of ethanol from the matrix the solvated Alq.sub.3 has similar XRD patterns and quadrupolar parameters to that of the [alpha]-phase. Conclusion The 2D MQMAS experiments have shown that all the different modifications of Alq.sub.3 have .sup.27.sup.Al in single unique crystallographic site. The quadrupolar parameters predicted using the DFT calculation under the isodensity polarisable continuum model resemble closely the experimentally obtained values. The solvated phase of Alq.sub.3 containing ethanol has structural difference from the [alpha]-phase of Alq.sub.3 (containing meridional isomer) from the solid-state NMR studies. Solid-state NMR can hence be used as an effective complementary tool to XRD for characterisation and structural elucidation.
    Keywords: Anisotropy -- Analysis ; Aluminum (Metal) -- Analysis ; Leds -- Analysis ; X-ray Diffraction -- Analysis
    ISSN: 1752-153X
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: Chemistry Central Journal, Nov 9, 2009, Vol.3, p.15
    Description: Background Organic light emitting devices (OLED) are becoming important and characterisation of them, in terms of structure, charge distribution, and intermolecular interactions, is important. Tris(8-hydroxyquinolinato)-aluminium(III), known as Alq.sub.3 , an organomettalic complex has become a reference material of great importance in OLED. It is important to elucidate the structural details of Alq.sub.3 in its various isomeric and solvated forms. Solid-state nuclear magnetic resonance (NMR) is a useful tool for this which can also complement the information obtained with X-ray diffraction studies. Results We report here .sup.27.sup.Al one-dimensional (1D) and two-dimensional (2D) multiple-quantum magic-angle spinning (MQMAS) NMR studies of the meridional ([alpha]-phase) and the facial ([delta]-phase) isomeric forms of Alq.sub.3 . Quadrupolar parameters are estimated from the 1D spectra under MAS and anisotropic slices of the 2D spectra and also calculated using DFT (density functional theory) quantum-chemical calculations. We have also studied solvated phase of Alq.sub.3 containing ethanol in its lattice. We show that both the XRD patterns and the quadrupolar parameters of the solvated phase are different from both the [alpha]-phase and the [delta]-phase, although the fluorescence emission shows no substantial difference between the [alpha]-phase and the solvated phase. Moreover, we have shown that after the removal of ethanol from the matrix the solvated Alq.sub.3 has similar XRD patterns and quadrupolar parameters to that of the [alpha]-phase. Conclusion The 2D MQMAS experiments have shown that all the different modifications of Alq.sub.3 have .sup.27.sup.Al in single unique crystallographic site. The quadrupolar parameters predicted using the DFT calculation under the isodensity polarisable continuum model resemble closely the experimentally obtained values. The solvated phase of Alq.sub.3 containing ethanol has structural difference from the [alpha]-phase of Alq.sub.3 (containing meridional isomer) from the solid-state NMR studies. Solid-state NMR can hence be used as an effective complementary tool to XRD for characterisation and structural elucidation.
    Keywords: X-ray Diffraction -- Analysis ; Aluminum (Metal) -- Spectra ; Aluminum (Metal) -- Structure ; Nuclear Magnetic Resonance -- Usage ; Density Functional Theory -- Usage
    ISSN: 1752-153X
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: Chemistry Central Journal, 2009, Vol.3(1), pp.1-11
    Description: BACKGROUND: Organic light emitting devices (OLED) are becoming important and characterisation of them, in terms of structure, charge distribution, and intermolecular interactions, is important. Tris(8-hydroxyquinolinato)-aluminium(III), known as Alq3, an organomettalic complex has become a reference material of great importance in OLED. It is important to elucidate the structural details of Alq3 in its various isomeric and solvated forms. Solid-state nuclear magnetic resonance (NMR) is a useful tool for this which can also complement the information obtained with X-ray diffraction studies.RESULTS: We report here 27Al one-dimensional (1D) and two-dimensional (2D) multiple-quantum magic-angle spinning (MQMAS) NMR studies of the meridional (alpha-phase) and the facial (delta-phase) isomeric forms of Alq3. Quadrupolar parameters are estimated from the 1D spectra under MAS and anisotropic slices of the 2D spectra and also calculated using DFT (density functional theory) quantum-chemical calculations. We have also studied solvated phase of Alq3 containing ethanol in its lattice. We show that both the XRD patterns and the quadrupolar parameters of the solvated phase are different from both the alpha-phase and the delta-phase, although the fluorescence emission shows no substantial difference between the alpha-phase and the solvated phase. Moreover, we have shown that after the removal of ethanol from the matrix the solvated Alq3 has similar XRD patterns and quadrupolar parameters to that of the alpha-phase.CONCLUSION: The 2D MQMAS experiments have shown that all the different modifications of Alq3 have 27Al in single unique crystallographic site. The quadrupolar parameters predicted using the DFT calculation under the isodensity polarisable continuum model resemble closely the experimentally obtained values. The solvated phase of Alq3 containing ethanol has structural difference from the alpha-phase of Alq3 (containing meridional isomer) from the solid-state NMR studies. Solid-state NMR can hence be used as an effective complementary tool to XRD for characterisation and structural elucidation.
    Keywords: Chemistry;
    E-ISSN: 1752-153X
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  • 9
    In: Journal of Cardiovascular Disease Research, 2010, Vol.1(2), p.81-85
    Description: Background: No study has been undertaken on people of Asian Indian origin to investigate the age and sex variation in the prevalence of cardiovascular disease (CVD) risk factors. Objectives: To investigate the age and sex variation in the prevalence of CVD risk factors among the people of Asian Indian origin. Materials and Methods: A total of 682 (302 males and 380 females) participants aged 25–85 years took part in the study. The subjects were categorized into 4 groups, namely, Group I (25–34 years), Group II (35–44 years), Group III (45–54 years), and Group IV (55 years and above). Height, weight, and the circumferences of minimum waist (MWC) and maximum hip were collected using standard techniques. Waist–hip ratio (WHR) was then calculated. Percentage of body fat (%BF) and body mass index (BMI) were measured using an Omron body fat analyzer. Left arm systolic (SBP) and diastolic (DBP) blood pressure were taken from each participant with the help of an Omron MI digital electronic blood/pulse monitor. Metabolic profiles, namely, total cholesterol (TC), triglyceride (TG), high (HDL), low (LDL), very low-density lipoprotein (VLDL), and fasting blood glucose (FBG) were also measured using an autoanalyzer. Results: One-way analysis of variance revealed significant differences for age, BMI, MWC, WHR, SBP, DBP, TC, TG, LDL, VLDL, and TC:HDL and TG:HDL ratios across the groups. It was observed that there were significant sex-specific group differences (male [χ 2 (12)] =29.22, P 〈 0.01 and female [χ 2 (12)] =56.69, P 〈 0.001) for obesity, high BP, high TC, high TG, and high FBG. But no significant group-specific sex difference was evident for either of the risk factors, except for Group IV. Conclusion: Age irrespective of sex modulates CVD risk factors and warranted prevention as early as middle age.
    Keywords: Aging; Asian Indians; cardiovascular disease; metabolic syndrome; obesity
    ISSN: 0975-3583
    E-ISSN: 09762833
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  • 10
    Language: English
    In: Journal of Magnetic Resonance, 2009, Vol.197(1), pp.14-19
    Description: We compare the performance of the windowed phase-modulated Lee–Goldburg ( PMLG) and the windowed decoupling using mind boggling optimisation ( DUMBO) sequences at various magic-angle spinning rates and nutation frequencies of the pulses. Additionally, we introduce a supercycled version of DUMBO and compare its efficiency with that of the non-supercycled implementation of DUMBO. The efficiency of the supercycled version of PMLG, denoted PMLG-S2, is compared with a new supercycled version of PMLG that we notate as PMLG-S3. The interaction between the supercycled homonuclear dipolar decoupling sequences and the sample rotation is analysed using symmetry-based selection rules.
    Keywords: Solid-State NMR ; Homonuclear Dipolar Decoupling ; Pmlg ; Dumbo ; Mas ; 1h Spectra ; Chemistry ; Physics
    ISSN: 1090-7807
    E-ISSN: 1096-0856
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