Showing papers by "Indian Association for the Cultivation of Science published in 2008"
TL;DR: This tutorial review aims at highlighting some of the developments covering both molecular and crystal engineering approaches in designing LMOGs, especially low molecular mass organic gelators, not only for academic interests but also for their potential applications in materials science.
Abstract: The last two decades have witnessed an upsurge of research activities in the area of supramolecular gelators, especially low molecular mass organic gelators (LMOGs), not only for academic interests but also for their potential applications in materials science. However, most of the gelators are serendipitously obtained; their rational design and synthesis is still a major challenge. Wide structural diversities of the molecules known to act as LMOGs and a dearth of molecular level understanding of gelation mechanisms make it difficult to pin-point a particular strategy to achieve rational design of gelators. Nevertheless, some efforts are being made to achieve this goal. Once a gelling agent is serendipitously obtained, new gelling agents with novel properties may be prepared by modifying the parent gelator molecule following a molecular engineering rationale; however, such approach is limited to the same class of gelling agent generated from the parent gelating scaffold. A crystal engineering approach wherein the single-crystal structure of a molecule is correlated with its gelling/nongelling behaviour (structure–property correlation) allows molecular level understandings of the self-assembly of the gelator and nongelator molecules and therefore, provides new insights into the design aspects of supramolecular gelling agents. This tutorial review aims at highlighting some of the developments covering both molecular and crystal engineering approaches in designing LMOGs.
693 citations
TL;DR: These results prove a consequence of local strains due to a size mismatch between the dopant and the host that can be avoided by optimizing the composition of the alloyed host.
Abstract: It has been an outstanding problem that a semiconducting host in the bulk form can be doped to a large extent, while the same host in the nanocrystal form is found to resist any appreciable level of doping rather stubbornly, this problem being more acute in the wurtzite form compared to the zinc blende one. In contrast, our results based on the lattice parameter tuning in a ZnxCd1−xS alloy nanocrystal system achieves ∼7.5% Mn2+ doping in a wurtzite nanocrystal, such a concentration being substantially higher compared to earlier reports even for nanocrystal hosts with the “favorable” zinc-blende structure. These results prove a consequence of local strains due to a size mismatch between the dopant and the host that can be avoided by optimizing the composition of the alloyed host. Additionally, the present approach opens up a new route to dope such nanocrystals to a macroscopic extent as required for many applications. Photophysical studies show that the quantum efficiency per Mn2+ ion decreases exponential...
226 citations
TL;DR: It is shown that the ultrafast (approximately 1 ps) component arises from an extended hydrogen bond network while the ultraslow component originates from binding of a water molecule to a biological macromolecule.
194 citations
TL;DR: A highly chemoselective reduction of aromatic nitro compounds to the corresponding amino derivatives has been achieved by a combination of copper nanoparticles and ammonium formate in ethylene glycol at 120 degrees C.
Abstract: A highly chemoselective reduction of aromatic nitro compounds to the corresponding amino derivatives has been achieved by a combination of copper nanoparticles and ammonium formate in ethylene glycol at 120 °C. The reductions are successfully carried out in presence of a wide variety of other reducible functional groups in the molecule, such as Cl, I, OCH2Ph, NHCH2Ph, COR, COOR, CN, etc. The reactions are very clean and high yielding.
187 citations
TL;DR: In this article, the authors summarize the recent updates on miRNA-induced gene-silencing mechanism, modulating host-virus interactions with a glimpse of the miRNAbased antiviral therapy for near future.
Abstract: MicroRNAs (miRNAs) mark a new paradigm of RNA-directed gene expression regulation in a wide spectrum of biological systems. These small non-coding RNAs can contribute to the repertoire of host-pathogen interactions during viral infection. This interplay has important consequences, both for the virus and the host. There have been reported evidences of host-cellular miRNAs modulating the expression of various viral genes, thereby playing a pivotal role in the host-pathogen interaction network. In the hide-and-seek game between the pathogens and the infected host, viruses have evolved highly sophisticated gene-silencing mechanisms to evade host-immune response. Recent reports indicate that virus too encode miRNAs that protect them against cellular antiviral response. Furthermore, they may exploit the cellular miRNA pathway to their own advantage. Nevertheless, our increasing knowledge of the host-virus interaction at the molecular level should lead us toward possible explanations to viral tropism, latency and oncogenesis along with the development of an effective, durable and nontoxic antiviral therapy. Here, we summarize the recent updates on miRNA-induced gene-silencing mechanism, modulating host-virus interactions with a glimpse of the miRNA-based antiviral therapy for near future.
184 citations
TL;DR: In this paper, the effect of sol concentration on the crystallinity and surface morphology of ZnO thin films was investigated, and the results showed that with an increase in sol concentration, the value of full width at half maximum (FWHM) of (0,0,2) peak decreases while the strain first increases and then decreases.
174 citations
TL;DR: This study reveals the existence of very soft infrared active phonons that couple strongly with spins at the Ni and Mn sites through modification of the superexchange interaction, and suggests that these modes are the origin for the observed dielectric anomaly in La2NiMnO6.
Abstract: Using first-principles density functional calculations, we study the electronic and magnetic properties of the ferromagnetic insulating double perovskite compound La2NiMnO6, which has been reported to exhibit an interesting magnetic field sensitive dielectric anomaly as a function of temperature. Our study reveals the existence of very soft infrared active phonons that couple strongly with spins at the Ni and Mn sites through modification of the superexchange interaction. We suggest that these modes are the origin for the observed dielectric anomaly in La2NiMnO6.
160 citations
TL;DR: It is demonstrated that ZnS nanostructures could be easily doped with useful impurities via this synthesis approach to tailor their luminescent properties.
Abstract: ZnS nanoparticles and nanorods with control over their crystal structure are fabricated through a solvothermal approach by changing the solvent used for the synthesis. The synthetic approach is suitable to fabricate ZnS nanoparticles with various sizes by varying the synthesis temperatures. Quantum confinement phenomena are studied by tailoring the particle sizes for both wurtzite and sphalerite polymorphs of ZnS. Photoluminescence studies reveal that the surface states greatly influence the emissions from the nanostructures. Wurtzite nanoparticles exhibit band-edge related UV emission owing to the effective surface passivation by the ethylene glycol molecules used as the solvent for the synthesis. On the other hand, the photoluminescence spectra of the cubic nanoparticles are mainly dominated by their surface states. Some of the nanorod samples exhibited Zn-vacancy related green emissions along with the surface defect related blue emission band. It is also demonstrated that ZnS nanostructures could be easily doped with useful impurities via this synthesis approach to tailor their luminescent properties.
157 citations
TL;DR: In this article, a solution-based technique was used to synthesize LaPO4:Er:Yb-doped nanoparticles/nanorods and LaPO 4:Er@Yb core−shell nanoparticles or nanorods by a solution based technique.
Abstract: We demonstrated the synthesis of LaPO4:Er:Yb-doped nanoparticles/nanorods and LaPO4:Er@Yb core−shell nanoparticles/nanorods by a solution-based technique The mechanism related to morphology control of LaPO4:Er:Yb nanorods/nanoparticles is proposed and discussed Bright-green (550 nm) and red (670 nm) emission were observed due to the transitions 2H11/2 + 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, respectively The experimental data for 550- and 670-nm emission bands of doped nanoparticle/nanorod and core−shell nanoparticles/nanorods have been fit with a straight line with a slope of ∼2, which confirms the two-photon absorption process The enhancement of upconversion emission of LaPO4:Er:Yb-doped nanoparticles and LaPO4:Er@Yb core−shell nanoparticles/nanorods are mainly due to modifications of surface-related effects It is found that the tensile strain increases from +10% to +19% with changing the shape from nanoparticle to nanorod and reversal of the lattice strain (compressive) is obtained for coated nanopa
154 citations
TL;DR: In this paper, the exchange bias was observed in mixed valent polycrystalline manganites (MPGM) with cluster-glass-like and spin-glasslike spin configurations, where the spin configurations are strongly affected by the cooling field strength.
Abstract: Exchange-bias (EB) phenomena have been observed in the ${L}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ ($L=\mathrm{Y}$, ${\mathrm{Y}}_{0.5}{\mathrm{Sm}}_{0.5}$, and ${\mathrm{Y}}_{0.5}{\mathrm{La}}_{0.5}$)-type manganites showing cluster-glass-like and spin-glass-like behavior. The field cooled magnetic hysteresis loops exhibit shifts both in the field and magnetization axes. The values of exchange field $({H}_{E})$, coercivity $({H}_{C})$, remanence asymmetry $({M}_{E})$, and magnetic coercivity $({M}_{C})$ of ${L}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ are found to depend strongly on temperature, measuring field, as well as strength of cooling field ${H}_{\mathrm{cool}}$. ${H}_{E}$ increases sharply with the magnitude of ${H}_{\mathrm{cool}}$ $(\ensuremath{\leqslant}3\phantom{\rule{0.3em}{0ex}}\mathrm{T})$, but for larger ${H}_{\mathrm{cool}}$ $(g3\phantom{\rule{0.3em}{0ex}}\mathrm{T})$, it decreases due to the growth of the ferromagnetic cluster size. This observed behavior has been explained in terms of interfacial exchange coupling between coexisting ferromagnetic cluster glass and the disordered spin-glass-like phases, where the spin configurations are strongly affected by the cooling field strength. Below the spin and/or cluster glass freezing temperature $({T}_{f})$, both ${H}_{E}$ and ${M}_{E}$ decrease exponentially with temperature. The value of ${H}_{C}$ increases almost exponentially with increasing magnetic-field step size $(\ensuremath{\Delta}H)$. In addition, the observed training effect of the EB behavior has been explained well in terms of the existing relaxation model developed for other classical EB systems. In view of the use of manganites in spintronics, the present observation of EB-like shift even in the mixed valent polycrystalline manganites such as ${L}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ is of paramount importance.
152 citations
TL;DR: Interestingly, these simple dipeptide-based organogelators with a minimum gelation concentration of 6-0.15 % could selectively gelate aromatic solvents from their mixtures with water and showed a striking property of adsorbing dyes such as crystal violet, rhodamine 6G from water.
Abstract: The development of new low-molecular-weight gelators for organic solvents is motivated by several potential applications of gels as advanced functional materials. In the present study, we developed simple dipeptide-based organogelators with a minimum gelation concentration (MGC) of 6-0.15 %, w/v in aromatic solvents. The organogelators were synthesized using different L-amino acids with nonpolar aliphatic/aromatic residues and by varying alkyl-chain length (C-12 to C-16). The self-aggregation behavior of these thermoreversible organogels was investigated through several spectroscopic and microscopic techniques. A balanced participation of the hydrogen bonding and van der Waals interactions is crucial for efficient organogelation, which can be largely modulated by the structural modification at the hydrogen-bonding unit as well as by varying the alkyl-chain length in both sides of the hydrophilic residue. Interestingly, these organogelators could selectively gelate aromatic solvents from their mixtures with water. Furthermore, the xerogels prepared from the organogels showed a striking property of adsorbing dyes such as crystal violet, rhodamine 6G from water. This dye-adsorption ability of gelators can be utilized in water purification by removing toxic dyes from wastewater.
TL;DR: In this article, the synthesis of polygonal gold nanoparticles (GNPs) by an in situ reduction technique using ferric ammonium citrate as reducing agent in absence of any surfactant or polymeric template was reported.
Abstract: We report the synthesis of polygonal gold nanoparticles (GNPs) by an in situ reduction technique using ferric ammonium citrate as reducing agent in absence of any surfactant or polymeric template. Transmission electron microscopic analysis and selected area electron diffraction patterns confirmed the formation of well-crystalline polygonal GNPs grown preferentially along the (111) direction, which is consistent with the results of X-ray diffractometry analysis. The results of control experiments of HAuCl4 with tri-ammonium citrate in presence of different externally added metal ions like Fe3+, Ni2+, Cu2+, Zn2+, and Al3+ suggested the ion-induced growth mechanism in the formation of polygonal GNPs. The purified polygonal GNPs were then successfully used as catalyst in the borohydride reduction of three isomeric nitrophenols and also in the aerobic oxidation of different D-hexoses (e.g., D-glucose, D-mannose, D-fructose). The catalytic activity of these polygonal GNPs is higher by a factor of 300–1000, depending on the GNP's sample type, in nitrophenol reduction compared to that of spherical GNPs. Similar activity enhancement was also observed in the aerobic oxidation of different D-hexoses. These polygonal GNPs catalyst are very stable and could be reused several times in the borohydride reduction of nitrophenols without much losing in their virgin catalytic activity.
TL;DR: Results indicate that Au nanoparticle quenches BSA fluorescence mainly through a static quenching mechanism, and analysis suggests that binding constant and bound/unbound ratio varies with changing the conformation of protein.
Abstract: In the present study, Au nanoparticle based surface energy transfer (SET) has been used to measure conformational changes in proteins. A significant photoluminescence (PL) quenching (91−97%) of tryptophan intensities of bovine serum albumin (BSA) protein is observed in the presence of Au nanoparticles, and the measured distances (r) between the donor (tryptophan) and the acceptor (Au nanoparticle) are 27.0, 22.9, and 25.7 A for E, N, and B forms of BSA protein, respectively. Results indicate that Au nanoparticle quenches BSA fluorescence mainly through a static quenching mechanism. Analysis suggests that binding constant and bound/unbound ratio varies with changing the conformation of protein. The PL quenching of dye varies from 47.2 to 86.6% with changing the conformation of protein without changing the radiative rate of dye. The measured distances (d) between the donor (dye) and the acceptor (Au nanoparticle) are 116.5, 76.1, and 86.4 A for E, N, and B forms of BSA protein, respectively, using the effic...
TL;DR: In this article, the authors reported the observation of room temperature ferromagnetism in high quality, single crystalline dilute Fe-doped δ-nodes.
Abstract: We report the observation of room temperature ferromagnetism in high quality, single crystalline dilute Fe-doped $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_{3}$. The large equilibrium solubility of Fe ions in the matrix refutes uncertainties about secondary phase magnetism, which has often eclipsed this interesting field of research. While room temperature ferromagnetism is observed at and above 5% Fe concentrations, one finds a highly concave temperature dependence of the susceptibility. Using detailed ab initio calculation, this has been related to intrinsic magnetic inhomogeneities arising from positional disorder. Apart from providing a mechanism for the observed high temperature ferromagnetism, our results point out that intrinsic disorder is a generic and essential component of dilute magnetism.
TL;DR: In this paper, the authors highlight the efficient fluorescence resonance energy transfer from Rhodamine 6G dye to Au@ZnO core−shell nanoparticle by steady state and time-resolved spectroscopy.
Abstract: The present study highlights the efficient fluorescence resonance energy transfer from Rhodamine 6G dye to Au@ZnO core−shell nanoparticle by steady state and time-resolved spectroscopy. The calculated energy transfer efficiencies from dye to nanoparticles are 41.3, 52.6, and 72.6% for Au, mixture of Au and ZnO, and core−shell Au@ZnO nanoparticles, respectively. There is a pronounced effect on the PL quenching and a shortening of the lifetime of the dye in the presence of Au@ZnO core−shell nanoparticle which is associated with high charge storage capacity. The nonradiative decay rates are 2.80 × 108, 3.90 × 108 and 7.67 × 108 s−1 for pure Au, mixture of Au and ZnO and core- shell Au@ZnO nanoparticles, respectively, indicating the resonance energy transfer process. The calculated Forster distances (R0) are 135.0 and 144.4 A for Au, and core- shell Au@ZnO nanoparticles, respectively and corresponding the calculated distances (d) between the donor and acceptor are 143.05, and 123.5 A. Considering the interact...
TL;DR: The rational design and synthesis of amino acid-based amphiphilic hydrogelators, which were systemically fine-tuned at the head group to develop pH-responsive hydrogels, have established the prospect of the hydrogEL as an efficient drug delivery vehicle.
Abstract: The present study describes the rational design and synthesis of amino acid-based amphiphilic hydrogelators, which were systemically fine-tuned at the head group to develop pH-responsive hydrogels. To understand the basic structural requirements of a low molecular weight amphiphilic hydrogelator, 10 analogous amphiphiles based on l-phenylalanine and l-tyrosine with structurally related head group were synthesized. Among them, three with quaternary ammonium substitution at the head group formed transparent hydrogels at room temperature while others were unable to gelate water. To establish correlations between the head group architecture of the gelators and their supramolecular arrangements, a variety of spectroscopic and microscopic techniques were investigated that showed that a balance between hydrophilicity and hydrophobicity is required to achieve hydrogelation. Interestingly, the gelator with tyrosinate in its head group showed remarkable response toward external pH. All hydrogels including the pH-re...
TL;DR: In this article, a mixture of NaBr and NaBrO3 in two different ratios have been used for highly stereoselective bromination of alkenes and alkynes, and regioselectively bromine substitution at the α-carbon of ketones and at the benzylic position of toluene derivatives.
TL;DR: In this article, an emulsion based wet chemical method for preparing Eu3+ doped cubic NaYF4 and hexagonal Na(Y1.5Na0.5)F6 nanocrystals was demonstrated.
Abstract: We demonstrated an emulsion based wet chemical method for preparing Eu3+ doped cubic NaYF4 and hexagonal Na(Y1.5Na0.5)F6 nanocrystals. Here, we report the control of the crystal phase as a function of the Y3+/F- ratio and pH of the solution. It was found that cubic NaYF4 and hexagonal Na(Y1.5Na0.5)F6 nanocrystals were prepared at 1:4 and 1:8 Y3+/F- ratios, respectively. The hexagonal Na(Y1.5Na0.5)F6 and cubic NaYF4 phases appeared in the pH range of 6−7 and 2−3, respectively, indicating that the pH of the solution also plays an important role in tuning the crystal structure. The mechanism related to crystal phase control is proposed and discussed. It was also found that the emission intensity of the peak at 614 nm (5D0 − 7F2) for Eu3+ ions and decay time are sensitive to the crystal structure, which is again controlled by the Y3+/F- ratio and pH of the solution. Again, it is seen that the interlayered water molecules strongly influence the photoluminescence of Eu3+ ions up to 300 °C, which was confirmed b...
TL;DR: This bactericidal effect of cationic hydrogelators is quite comparable or in some cases markedly better than that of clinically available antibiotics and most excitingly, they selectively attack the bacterial pathogens while remain biocompatible to the mammalian cells.
Abstract: Development of biomaterials, which are inherently antibacterial having broad-spectrum activity against both Gram-positive and Gram-negative bacteria with considerable biocompatibility, is of tremendous importance in biomedicinal chemistry. Microbial infections are still of great concern, often originated from indwelling medical devices typically in hospitalized patients. To this end, hydrogelating soft materials particularly from low-molecular-weight (LMW) gelators have generated significant interest in preparing and modifying biomedicinal implants. Herein, we have developed L-tryptophan based cationic amphiphilic hydrogelators with varying degree of hydrophobicity that exhibited remarkable bactericidal activity against wide range of Gram-positive (MIC = 0.1–75 µg/mL) and Gram-negative bacteria (MIC = 0.5–5 µg/mL). Antimicrobial efficacy of the amphiphiles was greatly influenced by their alkyl chain length. This bactericidal effect of cationic hydrogelators is quite comparable or in some cases markedly better than that of clinically available antibiotics. Most excitingly, they selectively attack the bacterial pathogens while remain biocompatible to the mammalian cells. Thus, we have developed LMW biocompatible, inherently antibacterial hydrogels having potential applications in biomedicines. Biotechnol. Bioeng. 2008;100: 756–764. © 2008 Wiley Periodicals, Inc.
TL;DR: Results revealed transformation of smooth discoid red cells into evaginated echinocytic form in the exposed individuals and the involvement of both erythrophagocytosis and hemolysis in the destruction of human erythrocytes during chronic arsenic exposure.
TL;DR: In this paper, the authors synthesize gold nanoparticles of different shapes by in situ reduction within the structure-directing low molecular weight gel template of tryptophan-containing peptide amphiphiles in water without using any external reducing or capping agents.
Abstract: We have synthesized the gold nanoparticles (GNPs) of different shaped by in situ reduction within the structure-directing low molecular weight gel template of tryptophan-containing peptide amphiphiles in water without using any external reducing or capping agents. Gold nanocrystals with sheet, wire, octahedral, and decahedral shapes were modulated with the help of the different morphology of the supramolecular gel network. The gel morphology at minimum gelation concentration is the prime requirement to prepare such different nanocrystals of gold. We also elucidated that the seeding growth approach did not have any stimulating affect to control the shape of GNPs. The supramolecular template itself has the structure-directing capability. The formation of gold species in the aqueous solution was monitored by UV−vis spectroscopy, transmission electron microscopy, and X-ray diffraction studies. The tryptophan-based peptide hydrogelators are elegant hosts as structure-directing templates for in situ shape-contr...
TL;DR: In this paper, the authors found a pronounced effect on the PL and shortening of the overall lifetime of rhodamine 6G when interacting with the spherical, shaped, and capped Au NPs, but there are no measured effects on radiative rate of the dye.
Abstract: In the present study, we found a pronounced effect on the PL and shortening of the overall lifetime of rhodamine 6G (R6G) when interacting with the spherical, shaped, and capped Au NPs, but there are no measured effects on radiative rate of the dye. The observed Forster distances (R0) are 105.75, 170, and 124 A for spherical, shaped, and capped Au nanoparticles, respectively and the distances between the donor and acceptor are 103.56, 194.77, and 134.43 A. However, the distances between the donor and acceptor are 78.26, 99.04, and 88.43 A for spherical, shaped, and capped Au nanoparticles, respectively, using the efficiency of surface energy transfer which follows a 1/d4 distance dependence between donor and acceptor. On the basis of these findings, we may suggest that surface energy transfer process has a more reasonable agreement with experimental finding. The anisotropy decay of R6G with spherical Au nanoparticles is single exponential with correlation time constant of 240 ps. However, the anisotropy d...
TL;DR: In this article, a simple one-pot three component condensation of an amine, carbon disulfide, and an aryl iodide or a styrenyl bromide catalyzed by copper nanoparticles in water is presented.
TL;DR: The interactions between DNA and a number of different cationic surfactants, differing in headgroup polarity, were investigated by electric conductivity measurements and fluorescence microscopy and it was observed that the critical association concentration (cac), characterizing the onset of surfactant binding to DNA, does not vary significantly with the architecture of the headgroup.
Abstract: The interactions between DNA and a number of different cationic surfactants, differing in headgroup polarity, were investigated by electric conductivity measurements and fluorescence microscopy. It was observed that, the critical association concentration (cac), characterizing the onset of surfactant binding to DNA, does not vary significantly with the architecture of the headgroup. However, comparing with the critical micelle concentration (cmc) in the absence of DNA, it can be inferred that the micelles of a surfactant with a simple quaternary ammonium headgroup are much more stabilized by the presence of DNA than those of surfactants with hydroxylated head-groups. In line with previous studies of polymer-surfactant association, the cac does not vary significantly with either the DNA concentration or its chain length. On the other hand, a novel observation is that the cac is much lower when DNA is denaturated and in the single-stranded conformation, than for the double-helix DNA. This is contrary to expectation for a simple electrostatically driven association. Thus previous studies of polyelectrolyte-surfactant systems have shown that the cac decreases strongly with increasing linear charge density of the polyion. Since double-stranded DNA (dsDNA) has twice as large linear charge density as single-stranded DNA (ssDNA), the stronger binding in the latter case indicates an important role of nonelectrostatic effects. Both a higher flexibility of ssDNA and a higher hydrophobicity due to the exposed bases are found to play a role, with the hydrophobic interaction argued to be more important. The significance of hydrophobic DNA-surfactant interaction is in line with other observations. The significance of nonelectrostatic effects is also indicated in significant differences in cac between different surfactants for ssDNA but not for dsDNA. For lower concentrations of DNA, the conductivity measurements presented an "anomalous" feature, i.e., a second inflection point for surfactant concentrations below the cac; this feature was not displayed at higher concentrations of DNA. The effect is attributed to the presence of a mixture of ss- and dsDNA molecules. Thus the stability of dsDNA is dependent on a certain ion atmosphere; at lower ion concentrations the electrostatic repulsions between the DNA strands become too strong compared to the attractive interactions, and there is a dissociation into the individual strands. Fluorescence microscopy studies, performed at much lower DNA concentrations, demonstrated a transformation of dsDNA from an extended "coil" state to a compact "globule" condition, with a broad concentration region of coexistence of coils and globules. The onset of DNA compaction coincides roughly with the cac values obtained from conductivity measurements. This is in line with the observed independence of cac on the DNA concentration, together with the assumption that the onset of binding corresponds to an initiation of DNA compaction. No major changes in either the onset of compaction or complete compaction were observed as the surfactant headgroup was made more polar.
TL;DR: The husk of Lathyrus sativus (HLS) has been functionalized by introducing thio groups with the help of carbon disulphide treatment in alkaline environment as mentioned in this paper.
TL;DR: The role of different functional groups and cell wall components of Rhizopus oryzae on adsorption of rhodamine B is described and carboxyl and amino groups were identified as most important moieties involved in the binding process.
TL;DR: In this article, the Eu3+-doped cubic NaYF4 and hexagonal Na(Y1.5Na0.5)F6 nanocrystals and the crystal phase is modified by temperature of heating and varying the Y3+/F− ratio.
Abstract: Here we report the preparation of Eu3+-doped cubic NaYF4 and hexagonal Na(Y1.5Na0.5)F6 nanocrystals and the crystal phase is modified by temperature of heating and varying the Y3+/F− ratio. The volume fraction of the cubic phase decreases from 100 to 55% with increasing the temperature from 80 to 400 °C, and the lattice strain can be modified by changing the crystal phase. The PL intensity, decay time, and quantum efficiency are found to be sensitive to the crystal phase and excitation wavelength. The PL intensity of hexagonal phase sample is stronger than the cubic phase sample under direct excitation and reversal result is obtained under charge transfer (CT) excitation. Under 394 nm excitation, the decay time increases from 5.92 to 7.58 ms with changing the crystal phase from cubic to hexagonal. It is interesting to note that the decay time also varies with changing the excitation wavelength. The quantum efficiency value increases from 4.3 to 67.4% with changing from charge transfer excitation to direct...
15 Jun 2008
TL;DR: The present study reveals that the modified Rubingh-Holland method along with the Rosen's model can be applied to analyze the interfacial characteristics of ternary surfactant mixtures with a fair degree of success thereby widening the domain of applicability of this model.
Abstract: Mixed micelle formation and interfacial properties of aqueous binary and ternary combinations of hexadecyltrimethylammonium bromide (C(16)Br), hexadecylbenzyldimethylammonium chloride (C(16)BzCl) and polyoxyethylene (20) cetyl ether (Brij58) at 25 degrees C in 30 mM aqueous NaCl have been studied in detail employing tensiometric and fluorimetric techniques. The micellar and adsorption characteristics like composition, activity coefficients, mutual interaction parameters and free energy of micellization have been estimated using the theoretical approaches of Clint, Rosen, Rubingh, Blankschtein et al., Rubingh-Holland and Maeda. A comprehensive account of the comparative performance of these models on the selected cationic-cationic-nonionic surfactant mixtures at constant ionic strength has been presented. The Blankschtein model predicted lower synergism than from Rubingh's method because it neglects the contribution due to steric interaction between surfactant head groups of different sizes and charges. Free energy of micellization calculated using Maeda's approach, which employs interaction parameter and micellar mole fraction from Rubingh's model as inputs, shows good correlation with that calculated from commonly used phase separation model. The present study also reveals that the modified Rubingh-Holland method along with the Rosen's model can be applied to analyze the interfacial characteristics of ternary surfactant mixtures with a fair degree of success thereby widening the domain of applicability of this model.
TL;DR: In this paper, the suitability of the 7s (2)S(1/2) 6d(2)D(3/2)-transition in singly ionized radium to measure parity nonconservation was analyzed.
Abstract: We report on a theoretical analysis of the suitability of the 7s (2)S(1/2) 6d (2)D(3/2) transition in singly ionized radium to measure parity nonconservation, in the light of an experiment planned at the KVI of the University of Groningen. Relativistic coupled-cluster theory has been employed to perform an ab initio calculation of the parity-nonconserving electric dipole amplitude of this transition, including single, double, and leading triple excitations. We discuss the prospects for a sub-1% precision test of the electroweak theory of particle physics.
TL;DR: High-resolution transmission electron microscopy (HRTEM) showed that the as-grown nanowires were of single crystal hexagonal wurtzite structure, growing along the [101] direction.
Abstract: ZnO nanowire arrays were synthesized on zinc foil by a simple thermal evaporation process at relatively low temperature. Morphology and size controlled synthesis of the ZnO nanostructures was achieved by variation of the synthesis temperature, reaction time and the surface roughness of the substrate. A gas–solid and self-catalytic liquid–solid mechanism is proposed for the growth of nanowires at different temperatures. High-resolution transmission electron microscopy (HRTEM) showed that the as-grown nanowires were of single crystal hexagonal wurtzite structure, growing along the [101] direction. Photoluminescence exhibited strong UV emission at ~382 nm and a broad green emission at ~513 nm with 325 nm excitation. Raman spectroscopy revealed a phonon confinement effect when compared with results from bulk ZnO. The nanowire arrays also exhibited a field emission property.