Showing papers by "Thalappil Pradeep published in 2017"
TL;DR: Luminescence in the visible region, especially by clusters protected with proteins, with a large Stokes shift, has been used for various sensing applications, down to a few tens of molecules/ions, in air and water.
Abstract: Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...
1,443 citations
TL;DR: In this study, an eco-friendly and facile methodology to develop a multifunctional waterproof paper via the fabrication of fluoroalkyl functionalized CNFs in the aqueous medium is presented, thereby minimizing cost as well as reducing safety and environmental concerns.
Abstract: In view of a great demand for paper-based technologies, nonwettable fibrous substrates with excellent durability have drawn much attention in recent years. In this context, the use of cellulose nanofibers (CNFs), the smallest unit of cellulosic substrates (5–20 nm wide and 500 nm to several microns in length), to design waterproof paper can be an economical and smart approach. In this study, an eco-friendly and facile methodology to develop a multifunctional waterproof paper via the fabrication of fluoroalkyl functionalized CNFs in the aqueous medium is presented. This strategy avoids the need for organic solvents, thereby minimizing cost as well as reducing safety and environmental concerns. Besides, it widens the applicability of such materials as nanocellulose-based aqueous coatings on hard and soft substrates including paper, in large areas. Water droplets showed a contact angle of 160° (±2°) over these surfaces and rolled off easily. While native CNFs are extremely hydrophilic and can be dispersed in...
144 citations
TL;DR: The emergence of a new branch of chemistry involving the reactions of atomically precise cluster systems, which are prototypical nanoparticles, is presented, and it is demonstrated that such interparticle chemistry is not limited to metal clusters; it occurs across zero-, one- and two-dimensional nanosystems leading to specific transformations.
Abstract: ConspectusNanoparticles exhibit a rich variety in terms of structure, composition, and properties. However, reactions between them remain largely unexplored. In this Account, we discuss an emerging aspect of nanomaterials chemistry, namely, interparticle reactions in solution phase, similar to reactions between molecules, involving atomically precise noble metal clusters. A brief historical account of the developments, starting from the bare, gas phase clusters, which led to the synthesis of atomically precise monolayer protected clusters in solution, is presented first. Then a reaction between two thiolate-protected, atomically precise noble metal clusters, [Au25(PET)18]− and [Ag44(FTP)30]4– (PET = 2-phenylethanethiol, FTP = 4-fluorothiophenol), is presented wherein these clusters spontaneously exchange metal atoms, ligands, and metal–ligand fragments between them under ambient conditions. The number of exchanged species could be controlled by varying the initial compositions of the reactant clusters. Ne...
85 citations
TL;DR: In this article, the reduction of water dispersed graphene oxide (GO) by sunlight as an environmentally friendly alternative to conventional methods of reduction of GO was explored and the possible mechanism of the reduction process was delineated.
Abstract: This paper explores the reduction of water dispersed graphene oxide (GO) by sunlight as an environmentally friendly alternative to conventional methods of reduction of GO. The possible mechanism of the reduction process is delineated. The electrical and thermal conductivity, the degree of reduction and structural defects of sunlight reduced GO (sRGO) are studied thoroughly and compared with RGO samples produced through hydrazine (hRGO) and hydrothermal (hyRGO) reduction routes. The study reveals that the production of sRGO is feasible and its electronic properties are on a par with those of hRGO. Interestingly, sRGO showed the least structural defects, good dispersibility and higher conductivity vis-a-vis its counterparts. This cost effective and environmentally friendly method of reducing GO to RGO with enhanced electronic properties may find applications in bio-sensing and electrochemical energy storage devices.
84 citations
TL;DR: The first example of Ir metal incorporation in a monolayer-protected noble metal cluster is demonstrated where the ligand PET is 2-phenylethanethiol and the cluster composition was confirmed by detailed high-resolution electrospray ionization mass spectrometry and other spectroscopic techniques.
Abstract: An intercluster reaction between Au25(PET)18 and Ir9(PET)6 producing the alloy cluster, Au22Ir3(PET)18 exclusively, is demonstrated where the ligand PET is 2-phenylethanethiol. Typical reactions of this kind between Au25(PET)18 and Ag25(SR)18, and other clusters reported previously, produce mixed cluster products. The cluster composition was confirmed by detailed high-resolution electrospray ionization mass spectrometry (ESI MS) and other spectroscopic techniques. This is the first example of Ir metal incorporation in a monolayer-protected noble metal cluster. The formation of a single product was confirmed by thin layer chromatography (TLC). Density functional theory (DFT) calculations suggest that the most favorable geometry of the Au22Ir3(PET)18 cluster is one wherein the three Ir atoms are arranged triangularly with one Ir atom at the icosahedral core and the other two on the icosahedral shell. Significant contraction of the metal core was observed due to strong Ir–Ir interactions.
59 citations
TL;DR: In this article, an attempt to probe into the energy demand of the fragmentation of atomically precise silver clusters using collision induced dissociation mass spectrometry was made, which revealed that fragmentation occurs in a stepwise fashion, conserving the closed shell electronic stability of the parent ion at each step.
Abstract: We report an attempt to probe into the energy demand of the fragmentation of atomically precise silver clusters using collision induced dissociation mass spectrometry. Energy resolved collisions of several gas phase ions of clusters, Ag29(S2R)12, Ag25(SR)18, and Ag44(SR)30, reveal distinct fragmentation kinetics involving charge separation. The fragmentation pattern of [Ag25(SR)18]− is found to be different from its structural analog, [Au25(SR)18]−. Survival yield analysis has been used to establish a direct comparison between the stability of the ions of these clusters, which reveals that [Ag29(S2R)12]3– is the most stable cluster ion, followed by [Ag25(SR)18]− and [Ag44(SR)30]4–. Gas phase stabilities reflect their solution phase stabilities, indicating that the molecular nature of the clusters is retained in the gas phase, too. We further report that fragmentation occurs in a stepwise fashion, conserving the closed shell electronic stability of the parent ion at each step. Such studies are important in...
46 citations
TL;DR: Confined metastable 2-line ferrihydrite, stable at ambient temperature, shows continuous arsenic uptake in the presence of other complex species in natural drinking water and an affordable water-purification device is made using the same.
Abstract: Arsenic-free drinking water, independent of electrical power and piped water supply, is possible only through advanced and affordable materials with large uptake capacities. Confined metastable 2-line ferrihydrite, stable at ambient temperature, shows continuous arsenic uptake in the presence of other complex species in natural drinking water and an affordable water-purification device is made using the same.
46 citations
TL;DR: The results present a unique example of a structure-reactivity relationship in the metal atom substitution chemistry of monolayer protected clusters, wherein a systematic trend, reflecting the geometric and the electronic shell structures of the reactant as well as the product clusters, was observed.
Abstract: Monolayer protected clusters exhibit rich diversity in geometric and electronic structures. However, structure–reactivity relationships in these clusters are rarely explored. In this context, [Ag44(SR)30]4–, where −SR is an alkyl/aryl thiolate, is an interesting system due to its geometrically and electronically closed-shell structures and distinct charge states. We demonstrate that these structural features of [Ag44(SR)30]4– are distinctly manifested in its solution-state reaction with another cluster, [Au25(SR)18]−. Through this reaction, an alloy cluster anion, [Au12Ag32(SR)30]4–, evolves spontaneously as revealed by high-resolution electrospray ionization mass spectrometry. Ultraviolet–visible absorption spectroscopy and density functional theory calculations indicate that [Au12Ag32(SR)30]4– is formed by the substitution of all of the Ag atoms in the innermost icosahedral shell of [Ag44(SR)30]4– and the abundance is attributed to its higher stability due to closed geometric as well as electronic shell...
44 citations
TL;DR: In this article, a modified TiO2 with band gap excitations in visible light was used for the degradation of carbamazepine and diclofenac under visible light.
Abstract: The present paper deals with photocatalytic degradation of carbamazepine and diclofenac by using a modified catalyst with band gap excitations in visible light. The C-doped TiO2 was synthesized using a microwave digestion method from titanium oxyacetylacetate with glucose as the carbon source. The synthesized catalyst was then characterized using Scanning Electron microscopy (SEM), X-ray Diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and UV-VIS-NIR spectrophotometer. The TiO2 present was in anatase phase and showed significant absorption in visible region. The catalyst was tested for the degradation of carbamazepine and diclofenac under visible light, where complete removal was achieved and the reaction followed first order kinetics. System parameters like catalyst and pollutant concentration, light intensity and time of reaction, were optimized using response surface methodology. In optimum conditions (catalyst concentration of 244 mg/L and light intensity of 7715 lx) 99% removal was achieved.
43 citations
TL;DR: Experimental evidence for the existence of gas phase isomers in monolayer protected noble metal clusters is presented, taking Ag44(SR)30 (SR = 4fluorothiophenol, p-mercaptobenzoic acid) and Ag29(BDT)12 (BDT: benzene dithiol) clusters as examples which do not show any isomeric structures in their crystals Electrospray ionization coupled with ion mobility separation allowed for the identification of multiple isomers of Ag44SR30 cluster in its 3 and 4-charge states,
Abstract: Experimental evidence for the existence of gas phase isomers in monolayer protected noble metal clusters is presented, taking Ag44(SR)30 (SR = 4-fluorothiophenol, p-mercaptobenzoic acid) and Ag29(BDT)12 (BDT: benzene dithiol) clusters as examples which do not show any isomeric structures in their crystals Electrospray ionization coupled with ion mobility separation allowed for the identification of multiple isomers of Ag44SR30 cluster in its 3– and 4– charge states, their most abundant gas phase ions Ag29(BDT)12 showed isomerism in its common 3– charge state Isomerism is likely to be due to different types of ligand orientations in the staples leading to changes in the overall size and shape of the cluster ions, which was further confirmed by density functional theory calculations on Ag44(FTP)304– No isomers were seen in the ions of the well-known cluster, Au25SR18 (SR = phenylethanethiol, dodecanethiol, and butanethiol)
39 citations
TL;DR: The synthesis and unique reactivity of a new green dithiol protected cluster (DTPC) is reported, exposing a new avenue of research for monolayer protected clusters, which will give additional impetus to explore the chemistry of DTPCs.
Abstract: We report the synthesis and unique reactivity of a new green dithiol protected cluster (DTPC), Ag51(BDT)19(TPP)3 (BDT and TPP are 1,3-benzenedithiol and triphenylphosphine, respectively). The cluster composition was confirmed by electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric studies as well as by other supporting data. Surprisingly, the chemical reactivity between this DTPC and Au25(SR)18 involves only metal ion exchange in Au25(SR)18 without any ligand exchange, while reactions between monothiol protected clusters (MTPCs) show both metal and ligand exchange, an example being the reaction between Ag25DMBT18 and Au25PET18 (where DMBT and PET are 2,4-dimethylbenzenethiol and phenylethanethiol, respectively). The conclusions have been confirmed by the reaction of another DTPC, Ag29(BDT)12(TPP)4 with Au25BT18 (where BT corresponds to butanethiol) in which only metal exchange happens in Au25BT18. We also show the conversion of Ag51(BDT)19(TPP)3 to Ag29(BDT)12(TPP)4 in the presence of a second monothiol, DMBT which does not get integrated into the product cluster. This is completely different from the previous understanding wherein the reaction between MTPCs and a second thiol leads to either mixed thiol protected clusters with the same core composition or a completely new cluster core protected with the second thiol. The present study exposes a new avenue of research for monolayer protected clusters, which in turn will give additional impetus to explore the chemistry of DTPCs.
TL;DR: This approach developed bridges the usually distinct fields of gas-phase metal cluster chemistry and solution-phaseMetal cluster chemistry, and it is hoped that the findings will enrich nanoscience and nanotechnology beyond the field of clusters.
Abstract: We report the formation of naked cluster ions of silver of specific nuclearities, uncontaminated by other cluster ions, derived from monolayer-protected clusters. The hydride and phosphine co-protected cluster, [Ag18(TPP)10H16]2+ (TPP, triphenylphosphine), upon activation produces the naked cluster ion, Ag17+, exclusively. The number of metal atoms present in the naked cluster is almost the same as that in the parent material. Two more naked cluster ions, Ag21+ and Ag19+, were also formed starting from two other protected clusters, [Ag25(DPPE)8H22]3+ and [Ag22(DPPE)8H19]3+, respectively (DPPE, 1,2-bis(diphenylphosphino)ethane). By systematic fragmentation, naked clusters of varying nuclei are produced from Ag17+ to Ag1+ selectively, with systematic absence of Ag10+, Ag6+, and Ag4+. A seemingly odd number of cluster ions are preferred due to the stability of the closed electronic shells. Sequential desorption of dihydrogen occurs from the cluster ion, Ag17H14+, during the formation of Agn+. A comparison of...
TL;DR: A new graphene-TeNW binary hybrid that exhibits a maximum photoresponsivity of ∼106 A W-1 at 175 K in the NIR regime (920 nm-1720 nm), which exceeds the photoreSponsivity of the most common NIR photodetectors.
Abstract: The optoelectronic performance of hybrid devices from graphene and optically sensitive semiconductors exceeds conventional photodetectors due to a large in-built optical gain. Tellurium nanowire (TeNW), being a narrow direct band gap semiconductor (∼0.65 eV), is as an excellent potential candidate for near infra-red (NIR) detection. Here we demonstrate a new graphene-TeNW binary hybrid that exhibits a maximum photoresponsivity of ∼106 A W-1 at 175 K in the NIR regime (920 nm-1720 nm), which exceeds the photoresponsivity of the most common NIR photodetectors. The resulting noise-equivalent power (NEP) is as low as 2 × 10-18 W Hz-1/2, and the specific detectivity (D*) exceeds 5 × 1013 cm Hz1/2 W-1 (Jones). The temperature range of optimal operation, which extends up to ≈220 K and ≈260 K for 1720 nm and 920 nm excitation, respectively, is primarily limited by the electrical conductivity of the TeNW layer, and can further be improved by lowering of the defect density as well as inter-wire electronic coupling.
TL;DR: In this paper, a bovine apo α-Lactalbumin (apo-α-LA) has a specific binding site for Ca2+, and La3+ occupies this position when apo-α -LA is treated with lanthanum trichloride, which results in the formation of a protein-coated Au10 nanocluster where the protein reduces Au3+ to Au0 and protects the nanoclusters which are luminescent.
Abstract: In this paper, we report the studies relevant to controlling the size of protein-protected gold nanoclusters (AuNCs) In order to demonstrate this, we have chosen bovine apo α-Lactalbumin (apo-α-LA), which has a specific binding site for Ca2+, and La3+ occupies this position when apo-α-LA is treated with lanthanum trichloride When the Apo-α-LA is treated with Au3+, it results in the formation of a protein-coated Au10 nanocluster where the protein reduces Au3+ to Au0 and protects the nanoclusters (apo-α-LA-AuNCs) which are luminescent In these protein-protected luminescent gold nanoclusters, the protein is involved both in reduction as well as protection, thereby supporting green synthesis As La3+ occupies the Ca2+ site in apo-α-LA, the size of AuNCs formed is reduced to smaller than the Au10, where the size is dependent on the extent to which La3+ is bound to the protein with a concomitant increase in luminescence The apo-α-LA-AuNCs and the same formed in the presence of different concentrations of La
TL;DR: The use of Pt nanoparticle-decorated nanotubes as highly active catalysts for the reduction of 2,4,6-trinitrotoluene to 2, 4, 6-triaminotoluenes and subsequent easy detection of the product by in situ ambient ionization mass spectrometry is shown.
Abstract: Materials are making inroads into mass spectrometry, and an example is the use of advanced materials for enhanced ionization by transformation of a less-ionizable molecule to an easily ionizable one. Here we show the use of Pt nanoparticle-decorated nanotubes as highly active catalysts for the reduction of 2,4,6-trinitrotoluene to 2,4,6-triaminotoluene and subsequent easy detection of the product by in situ ambient ionization mass spectrometry.
01 Feb 2017
TL;DR: In this paper, gold and silver clusters are used as sensitizers for the photoanodes fabricated using TiO2 nanotubes (NTs) and the commercial P25TiO2 nanoparticles.
Abstract: Atomically precise gold and silver clusters are a new class of sensitizers which can be used as substitutes for dyes in the classical dye-sensitized solar cells (DSCs). Here noble metal clusters protected by proteins and thiols (Au30@BSA, Au25SBB18, and Ag44MBA30) have been used for photovoltaic studies. These metal clusters were used as sensitizers for the photoanodes fabricated using TiO2 nanotubes (NTs) and the commercial P25 TiO2 nanoparticles. The TiO2, clusters and the solar cells were characterized by spectroscopy, microscopy, current-voltage (I-V) and incident photon-to-current conversion efficiency (IPCE) measurements. A systematic I-V study revealed a conversion efficiency of 0.35 % for the Au30@BSA sensitized solar cell made from TiO2 NTs which showed an IPCE maximum of 3 % at ∼ 400 nm.
TL;DR: The conversion of one cluster to several other clusters under ambient conditions and the effect of ligand structure in silver cluster synthesis give new insights into the cluster chemistry.
Abstract: We report the synthesis of a new silver cluster, [Ag59(2,5-DCBT)32]3− (I) (2,5-DCBT: 2,5-dichlorobenzenethiol), which acts as a precursor for the synthesis of three well-known silver clusters, [Ag44(2,4-DCBT/4-FTP)30]4− (II) (4-FTP: 4-fluorothiophenol and 2,4-DCBT: 2,4-dichlorobenzenethiol), [Ag25(2,4-DMBT)18]− (III) (2,4-DMBT: 2,4-dimethylbenzenethiol) and [Ag29(1,3-BDT)12(PPh3)4]3− (IV) (1,3-BDT: 1,3-benzenedithiol and PPh3: triphenylphosphine) This newly synthesized silver cluster, I, is characterized using UV-vis absorption studies, high resolution electrospray ionization mass spectrometry (ESI MS) and other analytical tools The optical absorption spectrum shows distinct features which are completely different from the previously reported silver clusters We perform the rapid transformations of I to other well-known clusters II, III and IV by reaction with different thiols The time-dependent UV-vis and ESI MS measurements reveal that I dissociates into distinct thiolate entities in the presence of thiols and the thiolates recombine to produce different clusters The conversion mechanism is found to be quite different from the previous reports where it occurs through the initial formation of ligand exchanged products Here, we also show the synthesis of a different cluster core, [Ag44(2,4-DCBT)30]4− (IIa) using 2,4-DCBT, a structural isomer of 2,5-DCBT under the same synthetic conditions used for I This observation demonstrates the effect of isomeric thiols on controlling the size of silver clusters The conversion of one cluster to several other clusters under ambient conditions and the effect of ligand structure in silver cluster synthesis give new insights into the cluster chemistry
TL;DR: The deposited sample was able to switch between amorphous and crystalline phases repeatedly under temperature cycles between 10K and 130K with subsequent loss of molecules in every phase change.
TL;DR: In this article, the structure-reactivity correlations in metal atom substitution reactions of three model monolayer-protected alloy clusters, Ag25-xAux(SR)18 (I), Au25−xAgx(SR)-18 (II), and AuxAg44-x-30 (III) where (−SR = alkyl/arylthiolate), are demonstrated.
Abstract: Structure–reactivity correlations in metal atom substitution reactions of three model monolayer-protected alloy clusters, Ag25–xAux(SR)18 (I), Au25–xAgx(SR)18 (II), and AuxAg44–x(SR)30 (III) where (−SR = alkyl/arylthiolate), are demonstrated. We show that the Au atoms of I and III and Ag atoms of II can be substituted by their reactions with the parent clusters Ag25(SR)18, Ag44(SR)30, and Au25(SR)18, respectively. Though these alloy clusters possess certain common structural features, they exhibit distinctly different reactivities in these substitution reactions. The Au of I and III and Ag of II at the outermost sites, i.e., M2(SR)3 staples of I and II and M2(SR)5 mounts of III, were substituted more easily compared to those at the inner, icosahedral sites. Au atoms at the icosahedral shell of I were completely substituted while Ag atoms of II at similar positions were not labile for substitution. This shows that the icosahedral shell of II is more rigid compared to that in I. We show that the Au atom in ...
TL;DR: In this paper, a paste-based method of synthesizing silver nanoparticles using a paste format instead of a metal salt solution was proposed, using a stoichiometric silver-thiolate polymer as a precursor to intimately mix the metal atoms and ligands.
Abstract: Nanoparticles rival pharmaceuticals in synthetic inefficiency, in particular as measured by process mass intensity, with by far the largest contribution to waste being from solvents. We have therefore developed a greener method of synthesizing silver nanoparticles using a paste format instead of a metal salt solution. The paste-based synthesis requires 87% less solvent yet still produces exclusively Na4Ag44(p-MBA)30 nanoparticles, without size sorting, with 89% yield. By using a stoichiometric silver-thiolate polymer as a precursor to intimately mix the metal atoms and ligands, and by using a small amount of liquid to form a paste to promote mass transport, the heterogeneity and kinetics problems that are associated with entirely solid-state syntheses were avoided. Because the nanoparticle product was also a paste, solvent use for postprocessing was minimized. Use of the silver-thiolate polymer can also reduce health risks associated with hazardous free thiols in conventional solution-phase syntheses. Usi...
TL;DR: Structural insights were used to understand similar unfolding in the solution state as seen via circular dichroism and Fourier transform infrared (FTIR) spectroscopy and this open structure is indeed necessary to accommodate a cluster core inside a protein cavity during luminescent cluster synthesis.
Abstract: Ion mobility mass spectrometry studies on Aun-Lyz adducts showed gradual unfolding of the protein structure during binding of Au+ to the protein. The change of the charge state envelope in Aun-Lyz from that of Lyz in ESI MS data confirmed the relaxation of the protein structure. This Au+ binding occurs at cysteine sites through the breakage of disulfide bonds and this ruptures the H-bonded folded network structure of the protein leading to ∼30% change in helicity. Nearly 15% loss in the total H-bonding occurred during the attachment of 8 Au to the protein as calculated by a molecular dynamics simulation. Different Aun-Lyz structures were simulated, which confirmed significant unfolding of the protein. The structural insights were used to understand similar unfolding in the solution state as seen via circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy. This open structure is indeed necessary to accommodate a cluster core inside a protein cavity during luminescent cluster synthesis. T...
TL;DR: Fragile transition metal complex ions such as [Cr(H2O)4Cl2]+, difficult to be observed by gas-phase spectroscopy, are detected easily with carbon nanotube (CNT)-assisted low-voltage ambient ionization mass spectrometry.
Abstract: Fragile transition metal complex ions such as [Cr(H2O)4Cl2]+, difficult to be observed by gas-phase spectroscopy, are detected easily with carbon nanotube (CNT)-assisted low-voltage ambient ionization mass spectrometry. Observation of various substituted ions with D2O and ROH (R = CH3, C2H5, ...) established the versatility of the technique in detecting diverse species. Ligand substitution occurring in solution was captured by the low-voltage technique. The extreme softness of the technique coupled with nanoscale ion sources enabled the creation of such species. Analysis was extended to other halides as well. The intensity of these fragile ions gradually disappeared at voltages beyond 500 V and are completely absent in standard high-voltage ionization. Detection of inorganic complexes further enhances the scope of low-voltage ionization.
03 Nov 2017
TL;DR: A dual probe sensor capable of sensing changes in luminescence and conductivity is introduced, utilizing bovine serum albumin-protected atomically precise gold clusters hosted on nanofibers, and a hybrid nanofiber with a conducting core with a porous dielectric shell is developed.
Abstract: This article adds a new direction to the functional capability of protein-protected atomically precise gold clusters as sensors. Counting on the extensively researched intense luminescence of these clusters and considering the electron donating nature of select amino acids, we introduce a dual probe sensor capable of sensing changes in luminescence and conductivity, utilizing bovine serum albumin-protected atomically precise gold clusters hosted on nanofibers. To this end, we have also developed a hybrid nanofiber with a conducting core with a porous dielectric shell. We show that clusters in combination with nanofibers offer a highly selective and sensitive platform for the detection of trace quantities of trinitrotoluene, both in solution and in the vapor phase. In the solution phase, trinitrotoluene (TNT) can be detected down to 1 ppt at room temperature, whereas in vapor phase, 4.8 × 109 molecules of TNT can be sensed using a 1 mm fiber. Although the development in electrospinning techniques for fabri...
TL;DR: In this article, temperature-dependent interaction of acetonitrile with methanol and ethanol, as codeposited and sequentially deposited films, was studied in the 10-130 K window, in ultra high vacuum.
Abstract: Temperature-dependent interaction of acetonitrile with methanol and ethanol, as codeposited and sequentially deposited films, was studied in the 10–130 K window, in ultra high vacuum. Films in the range of 50–100 monolayers were investigated using temperature-dependent reflection–absorption infrared spectroscopy (RAIRS), Cs+ ion scattering mass spectrometry, and temperature-programmed desorption (TPD). Acetonitrile interacts with methanol and ethanol through intermolecular hydrogen bonding. When a codeposited system was annealed, acetonitrile underwent a phase segregation at 110 K, and large changes in the infrared spectrum were observed. The OH stretching of methanol gave two peaks characteristic of the change to the α-phase of methanol, while ethanol gave three peaks at the same temperature. The surface composition of the systems probed by 40 eV Cs+ scattering showed that both the alcohols and the acetonitrile were of equal intensity below 110 K, while above 110 K the intensity of the latter went down s...
TL;DR: In this article, a study of 505 native rice landraces showed that nine of them accumulate silver at a high concentration when grown in the same soil, and that the metal accumulates mostly in the grain.
Abstract: Uptake of noble metals by cereal plants is not reported in literature. Our study of 505 native rice landraces showed that nine of them accumulate silver at a high concentration when grown in the same soil. Among these, a medicinal rice landrace from West Bengal, Garib-sal was found to accumulate silver at an especially high concentration in the grains. Cultivation of Garib-sal rice in three successive years in Basudha farm in the rice growing period of June–October confirmed that for the same concentration of silver in the soil (∼0.15 mg/kg), Garib-sal accumulates it in the grains to the extent of ∼15 mg/kg. Laboratory experiments also demonstrated that silver uptake by Garib-sal is significantly greater than for other varieties grown on the same soil, and that the metal accumulates mostly in the grain. To detect the location of deposition of silver in the grains, secondary ion mass spectrometry was performed. The images reveal that the silver is concentrated in the aleuronic layer of the rice bran. Its c...
TL;DR: In this paper, a calorimetric study of the reaction of glutathione (GSH) protected silver clusters in the presence of excess ligand, GSH, using IWC was performed.
Abstract: Reactivity of monolayer protected atomically precise clusters of noble metals is of significant research interest. To date very few experimental data are available on the reaction thermodynamics of such clusters. Here we report a calorimetric study of the reaction of glutathione (GSH) protected silver clusters in the presence of excess ligand, GSH, using isothermal titration calorimetry (ITC). We have studied Ag11(SG)7 and Ag32(SG)19 clusters and compared their reactivity with GSH protected silver nanoparticles (AgNPs) and silver ions. Clusters show intermediate reactivity toward excess ligand compared to nanoparticles and silver ions. Several control experiments were performed to understand the degradation mechanism of these silver clusters and nanoparticles. The effect of dissolved oxygen in the degradation process was studied in detail, and it was found that it did not have a significant role, although alternate pathways of degradation with the involvement of oxygen cannot be ruled out. Direct confirma...
TL;DR: In this paper, the use of electrospray deposition of metal ions from solutions in air is reported, to bring about chemical transformations across mm2-sized areas of nanostructures.
Abstract: The performance of semiconductor devices can be fine-tuned through chemical transformation of their nanostructured components. Such transformations are often carried out in controlled conditions. Herein, the use of electrospray deposition of metal ions from solutions in air is reported, to bring about chemical transformations across mm2-sized areas of nanostructures. This is illustrated with monolayer assemblies of ultrathin tellurium nanowires (NWs). The process does not require any reducing agent and can transform the NWs chemically, in the solid state itself, under ambient conditions. By using suitable masks, the beam of ions can be patterned to localize such transformations with nanometer precision to obtain aligned multiphasic NWs, containing atomically precise phase boundaries. By controlling the time of exposure of the spray, the scope of the process is further expanded to produce tellurium-metal telluride core–shell NWs. The method described here represents a crucial step for ambient processing of nanostructured components, useful for applications such as semiconductor device fabrication.
TL;DR: In this paper, it was shown that there are large synergistic effects in the extraction process, which results in ca. 45 times larger leaching with specific molecules, when used along with glucose.
Abstract: Extraction of silver into water occurs from its apparently inert metal surface by the simple carbohydrate glucose. Here we show that there are large synergistic effects in the extraction process, which results in ca. 45 times larger leaching with specific molecules, when used along with glucose. While glucose (1 g) alone can extract ca. 650 ppb of silver from the metal, 60 mg of it extracts ca. 30000 ppb in a combination with 200 mg of glutathione (GSH) under similar experimental conditions of 70 °C and an extraction time of 7 d, in deionized (DI) water (200 mL). This enhancement is similar when glucose is replaced with cyclodextrin (CD). This enhanced concentration of silver in solution enables the formation of the silver clusters protected with glutathione and cyclodextrin, Ag20(SG)15CD3–, in the presence of a reducing agent. A similar extraction for copper leads to excessive leaching, and typical concentrations are even higher than the solubility limit of the copper–glutathione complex. As a result, these complexes are precipitated. This synergistic extraction is observed for zinc and stainless steel as well. Enhanced extraction is a result of the formation of complexes of metals with glutathione and the consequent leaching of the complex into solution as well as the stabilization of the complex by inclusion complexation with cyclodextrin. Enhanced leaching in the presence of glucose is mostly due to simultaneous complexation with glucose as well as glutathione. The science presented may be used for the green extraction of different metals and could be a new potential top-down approach for metal cluster synthesis. This may also be useful for green and sustained leaching of minerals into water to regulate its quality.
TL;DR: Spatially, cotyledonary tissues of the seed had the highest amount of CPT followed by seed coat and fruit coat, which is best explained by selection to deter fruit predators during fruit development, but attracting the fruit dispersers when fruits are mature and ripe.
Abstract: Camptothecin (CPT), a quinoline indole alkaloid, is one of the important inhibitors of eukaryotic DNA topoisomerase I. The highest concentration of this alkaloid has been reported from the fruits of Pyrenacantha volubilis Hook. Here we report the spatial and temporal distribution pattern of CPT in seeds and fruits of P. volubilis. Temporally, CPT content
was highest in mature but unripe fruits compared to ripened fruits. Spatially, cotyledonary tissues of the seed had the highest amount of CPT followed by seed coat and fruit coat. This pattern is best explained by selection to deter fruit predators during fruit development, but attracting the fruit dispersers when fruits are mature and ripe.