Total Synthesis and Structure Confirmation of Fusaroside.

Recently, we synthesized the proposed structure of the fungal glycolipid fusaroside and suggested corrections in its structure with respect to the positions of the double bonds in the lipid portion. Herein, we report the first total synthesis of the proposed revised structure of fusaroside and thereby confirm its structure. The synthesis involved Julia-Kocienski olefination for the construction of fatty acid and its coupling with trehalose at the O4 position followed by late-stage gem-dimethylation as key steps.

Stacking-Dependent Electrical Transport in a Colloidal CdSe Nanoplatelet Thin-Film Transistor.

Here, we report an exceptional feature of the one-dimensional threadlike assemblies of a four-monolayer colloidal CdSe nanoplatelet (NPL)-based thin-film transistor. A series of different lengths of threads (200-1200 nm) was used as an active n channel in thin-film transistors (TFTs) to understand the change in mobility with the length of the threads. The film with the longest threads shows the highest conductivity of ∼12 S/cm and electron mobility of ∼14.3 cm2 V-1 s-1 for an applied gate voltage of 2 V. The mobility trends with the length seem to be driven mostly by the lower defects in threads, where the loss of electron hopping is less. Furthermore, our results show the mobility trends in stacking-dependent CdSe NPL threads and provide a new insight into fabricating high-mobility TFTs with the use of colloidal CdSe NPLs.

Bandlike Transport in FaPbBr3 Quantum Dot Phototransistor with High Hole Mobility and Ultrahigh Photodetectivity.

Halide perovskites have been widely explored for numerous optoelectronic applications among which phototransistors have appeared as one of the most promising light signal detectors. However, it is still a great challenge to endow halide perovskites with both mobility and high photosensitivity because of their high sensitivity to moisture in ambient atmosphere. Here, we explore an FAPbBr3 perovskite quantum dot (QD) phototransistor with bandlike charge transport and measure a dark hole mobility of 14.2 cm2 V-1 s-1 at ambient atmosphere. Attaining both high mobility and good optical figures of merit, a detectivity of ∼1016 Jones is achieved, which is a record for halide perovskite nanocrystals. Simple A-site salt (FABr) treatments offer a mechanism for connecting between perovskite QDs for better charge transfer in high-quality devices. All of these important properties are superior to most advanced inorganic semiconductor phototransistors, indicating a promising future in optoelectronic applications.

Synthesis of trehalose glycolipids.

Trehalose containing glycolipids have been isolated from various species of mycobacteria, fungi and worms. Owing to their versatile biological roles, and heterogenicity of the natural isolates, there is great interest in the synthesis of trehalose glycolipids. In this review we discuss recent developments in the total synthesis of biologically important and structurally complex trehalose glycoconjugates and oligosaccharides.

First total synthesis of trehalose containing tetrasaccharides from Mycobacterium smegmatis.

Total synthesis of three important trehalose containing tetrasaccharides isolated from Mycobacterium smegmatis is reported for the first time, using regioselective opening of benzylidene acetals and stereoselective glycosylations as key steps. The 1,2-cis stereoselectivity in the glycosylation reactions was achieved using anchimeric assistance from a remote participating group, steric effects and solvent participation. The synthetic strategy can also be utilized for the assembly of structurally related oligosaccharides from M. tuberculosis.

The preparation of γ-crystalline non-electrically poled photoluminescant ZnO-PVDF nanocomposite film for wearable nanogenerators.

Polyvinylidene fluoride (PVDF) films are filled with various mass fractions (wt%) of zinc oxide nanoparticles (ZnO-NPs) to fabricate the high performance of a wearable polymer composite nanogenerator (PCNG). The ZnO-NPs can induced a fully γ-crystalline phase in PVDF, where traditional electrical poling is not necessary for the generation of piezoelectric properties. The PCNG delivers up to 28 V of open circuit voltage and 450 nA of short circuit current by simple repeated human finger imparting (under a pressure amplitude of 8.43 kPa) that generates sufficient power to turn on at least 48 commercial blue light emitting diodes (LEDs) instantly. Furthermore, it also successfully charged the capacitors, signifying practical applicability as a piezoelectric based nanogenerator for self-powering devices. The applicability of PCNG by wearable means is clarified when it gives rise to a sensible response, say up to 400 mV of output voltage synchronized with the PCNG embedded human finger in a bending and releasing gesture. UV-visible absorption spectral analysis revealed the possibility of estimating a change in the optical band gap value (E g), refractive index (n) and optical activation energy (E a) in different concentrations of ZnO-NP incorporated PVDF nanocomposite films, and it possesses a useful methodology where ZnO-NPs can be used as an optical probe. Near blue light emission is observed from photoluminescence spectra, which are clearly shown from a Commission Internationale de L'Eclairage (CIE) diagram. The piezoelectric charge coefficient of the nanocomposite film is estimated to be -6.4 pC/N, where even electrical poling treatment is not employed. In addition, dielectric properties have been studied to understand the role of molecular kinetic and interfacial polarization occurring in nanocomposite films at different applied frequencies.

CdSe Nanoplatelets: Living Polymers.

Colloidal CdSe nanoplatelets are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self-assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face-to-face self-assembly of CdSe nanoplatelets into micron-long polymer-like threads made of up to ∼1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re-dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1-dimensional structures are flexible and feature a "living polymer" character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends.

Stacking and Colloidal Stability of CdSe Nanoplatelets.

Colloidal CdSe nanoplatelets with monolayer control over their thickness can now be synthesized in solution and display interesting optical properties. From a fundamental point of view, the self-assembly of CdSe nanoplatelets can impact their optical properties through short-range interactions, and achieving control over their dispersion state in solution is of major relevance. The related issue of colloidal stability is important from an applicative standpoint in the perspective of the processing of these materials. Using UV-vis spectroscopy, we assess the colloidal stability of dispersions of CdSe nanoplatelets at different nanoparticle and ligand (oleic acid) concentrations. We unravel an optimum in oleic acid concentration for colloidal stability and show that even moderately concentrated dispersions flocculate on a time scale ranging from minutes to hours. Small-angle X-ray scattering shows that the precipitation proceeds through a face-to-face stacking of the nanoplatelets due to long-ranged van der Waals attraction. To address this issue, we coated the platelets with a carboxylic acid-terminated polystyrene, thus achieving colloidal stability while retaining the optical properties of the platelets.

The influence of hydrogen bonding on the dielectric constant and the piezoelectric energy harvesting performance of hydrated metal salt mediated PVDF films.

Polyvinylidene fluoride (PVDF) films are filled with various mass fractions (wt%) of hydrated metal salt (MgCl2·6H2O) (Mg-salt) to fabricate high performance piezoelectric energy harvesters (PEHs). They deliver up to 4 V of open circuit voltage by simply repeated human finger imparting (under a pressure of ∼4.45 kPa) and also generate sufficient power to turn on at least ten commercial blue light emitting diodes (LEDs) instantly. The enhanced piezo-response is attributed to the combined effect of the change in the inherent dipole moment of the electroactive phase containing PVDF itself and H-bonding arising between the Mg-salt filler and PVDF via electrostatic interactions. Furthermore, it also successfully charged the capacitors, signifying practical applicability as a piezoelectric based energy harvester power source. UV-visible optical absorption spectral analysis revealed the possibility to estimate a change in the optical band gap value at different concentrations of Mg-salt filler added PVDF films that possess a useful methodology where the Mg-salt can be used as an optical probe. In addition dielectric properties have been studied to understand the role of molecular kinetic and interfacial polarization occurs in H-bond PVDF films at different applied frequencies at room temperature.

Mutagenicity and clastogenicity evaluation of metaphenoxy benzyl chloride by ames and micronucleus assays.

Metaphenoxy Benzyl Chloride (3-PBC; CAS # 53874-66-1) is a commonly used intermediate in organic synthesis and is a widely used chemical building block. There is likelihood of human contact with 3-PBC in the process of organic or pesticide synthesis and even through as impurity in the product. Further, this chemical has been reported to be found in water reservoirs causing a threat to aqueous flaura and fauna. Genotoxic alert has been suspected for the chemical 3-PBC based on its structure hence, the impetus of present work was to assess the mutagenic potential of 3-PBC using Ames bacterial reverse-mutation assay and in vitro micronucleus assay. 3-PBC was tested for mutagenic potential at six different concentrations, with 0.05 (without metabolic activation) and 0.50 (with metabolic activation) µL/plate as the highest concentrations, followed by five lower concentrations with 2-fold spacing. In clastogenic evaluation, 3-PBC was tested at concentrations ranged from 0.31 to 4.88 µL/mL to assess micronucleus induction in mammalian cells viz. Chinese Hamster Ovarian-K1 cells (CHO-K1 cells). In the Ames assay, 3-PBC did not show mutagenicity in all five tester strains of Salmonella typhimurium viz. TA98, TA100, TA102, TA1535 and TA1537 both in the presence and absence of a metabolic activation system and found to be nonclastogenic when evaluated in "CHO-K1 cells".

MXene-Enhanced Nanoscale Photoconduction in Perovskite Solar Cells Revealed by Conductive Atomic Force Microscopy.

The use of MXene materials in perovskite solar cells (PSCs) has received significant interest due to their distinct features that result from the termination of functional groups and the oxidation of MXene. Herein, we have used photoconductive atomic force microscopy (pcAFM) to map the local (nanoscale) photovoltaic performances of the Ti3C2Tx MXene nanosheet-integrated TiO2 (MXene@TiO2) electron transport layer-based PSCs to determine the influence of the treatment on the microscopic charge flow inside the devices. At different applied voltages, the morphology and current have been simultaneously measured with nanoscale resolution from the top surfaces of the solar cells without back contacts. The PSCs based on MXene@TiO2 exhibit more enhanced current flow across the grains than the only TiO2-based PSCs. At zero applied bias, the average local photocurrent for MXene-integrated PSCs is several times higher than the reference PSCs and decreases gradually when the positive bias is increased until the open circuit voltage. Considerable differences were also observed in the short circuit current among different locations that appear identical in AFM topography. Our findings reveal the potential of MXene-integrated ETLs to enhance the nanoscale photoconduction and inherent characteristics of the active layers, thereby improving the performance of the polycrystalline photovoltaic devices.

Surface modification of halide perovskite using EDTA-complexed SnO2 as electron transport layer in high performance solar cells.

The long-term performance of metal halide perovskite solar cells (PSCs) can be significantly improved by tuning the surface characteristics of the perovskite layers. Herein, low-temperature-processed ethylenediaminetetraacetic acid (EDTA)-complexed SnO2 (E-SnO2) is successfully employed as an electron transport layer (ETL) in PSCs, enhancing the efficiency and stability of the devices. The effects of EDTA treatment on SnO2 are investigated for different concentrations: comparing the solar cells' response with 15%-2.5% SnO2 and E-SnO2 based ETLs, and it was found that 7.5% E-SnO2 provided the best results. The improved surface properties of the perovskite layer on E-SnO2 are attributed to the presence of small amount of PbI2 which contributes to passivate the defects at the grain boundaries and films' surface. However, for the excess PbI2 based devices, photocurrent dropped, which could be attributed to the generation of shallow traps due to excess PbI2. The better alignment between the Fermi level of E-SnO2 and the conduction band of perovskite is another favorable aspect that enables increased open-circuit potential (VOC), from 0.82 V to 1.015 V, yielding a stabilized power conversion efficiency of 15.51%. This complex ETL strategy presented here demonstrates the enormous potential of E-SnO2 as selective contact to enhance the perovskite layer properties and thereby allow stable and high-efficiency PSCs.

Tuning the emission colors of semiconductor nanocrystals beyond their bandgap tunability: all in the dope.

Adopting the concept of one dopant for one color, all the prominent emitting colors in the visible windows are obtained by doping selective dopants (Ag, Cu, Ni, and Cu) in an appropriate host (alloy of Cdx Zn1-x S) with fixed size/composition and bandgap. Analyzing the origin of these emissions the relative position of respective dopant states are correlated.

Total Synthesis of a Trehalose-Containing Lipooligosaccharide Analogue from Mycobacterium linda.

A short and efficient methodology has been developed to synthesize an analogue of a lipooligosaccharide from Mycobacterium linda isolated from Crohn's disease. The total synthesis of the tetrasaccharide was achieved via a convergent [2 + 2] glycosylation approach. The key features of the synthesis involve the selective functionalization of a trehalose core via highly regioselective acylations and regioselective glycosylations. The synthesis was completed via a longest linear sequence of 14 steps in a 14.2% overall yield.

Synthesis of Gentamicins C1, C2, and C2a and Antiribosomal and Antibacterial Activity of Gentamicins B1, C1, C1a, C2, C2a, C2b, and X2.

Complementing our earlier syntheses of the gentamicins B1, C1a, C2b, and X2, we describe the synthesis of gentamicins C1, C2, and C2a characterized by methyl substitution at the 6'-position, and so present an alternative access to previous chromatographic methods for accessing these sought-after compounds. We describe the antiribosomal activity of our full set of synthetic gentamicin congeners against bacterial ribosomes and hybrid ribosomes carrying the decoding A site of the human mitochondrial, A1555G mutant mitochondrial, and cytoplasmic ribosomes and establish structure-activity relationships with the substitution pattern around ring I to antiribosomal activity, antibacterial resistance due to the presence of aminoglycoside acetyl transferases acting on the 6'-position in ring I, and literature cochlear toxicity data.

Mutagenicity and clastogenicity evaluation of tacrine by Ames and micronucleus assays.

Tacrine was evaluated for its mutagenic and clastogenic activities using the Ames bacterial reverse-mutation assay and the rodent bone marrow micronucleus assay. Tacrine was tested for mutagenic potential at six different concentrations, with 1,250 µg/plate as the highest concentration, followed by five lower concentrations with 2-fold spacing. In clastogenic evaluation, tacrine was administered orally to Wistar rats for 2 days at 5, 10, and 20 mg/kg body weights to assess micronucleus induction in bone marrow erythrocytes. In the Ames assay, tacrine showed nonmutagenicity in four tester strains of Salmonella typhimurium viz. TA98, TA100, TA102, and TA1535, but it was found to be mutagenic in the TA1537 tester strain, both in the presence and absence of a metabolic activation system. Tacrine was found to be nonclastogenic on bone marrow cells of rats at all doses tested and was found to be mutagenic in only the TA1537 strain of Salmonella.

Synthesis of Gentamicin Minor Components: Gentamicin C1a and Gentamicin C2b.

Gentamicin C1a and the minor isomer C2b have been reported to have favorable properties in terms of antibacterial activity and toxicity compared to the commercial mixture from which they have previously been isolated by preparative high-performance liquid chromatography. We report straightforward syntheses of both compounds from readily available sisomicin by selective oxidation of the side chain in ring I, hydrogenation of the double bond in ring I to give the 5'-epi series, inversion of configuration at position 5' under thermodynamic conditions, and installation of the 6'-amino group by reductive amination.

Unusual C-C bond cleavage of an α-trifloxy Sialic acid hemiacetal under Lattrell-Dax conditions.

We describe the novel oxidative fragmentation of methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-5-deoxy-3-O-trifluoromethanesulfonyl-ß-D-erythro-L-gluco-2-nonulopyranos)onate 2 on stirring with sodium nitrite in DMF to give the novel 3-acetamido-2,5,6,7-tetra-O-acetyl-d-glycero-d-galacto-heptono-1,4-lactone 3 in excellent yield. Stirring of the same triflate with sodium carbonate on the other hand affords the novel methyl (5-acetamido-7,8,9-tri-O-acetyl-3,6-anhydro-5-deoxy-d-manno-3-ene-2-nonulos)onate 19 also in excellent yield. Reduction of the heptono lactone with sodium borohydride followed by acetylation gives a peracetylated aminodeoxyheptitol 6 that adopts the zig zag conformation of its carbon backbone.

Doping Cu in semiconductor nanocrystals: some old and some new physical insights.

Cu-doped inorganic semiconductors with concomitant optical properties have garnered enormous research interest in the last two decades. However, uncertainties over the origin of Cu emission, its oxidation state, resemblance with trap state emission, position of Cu d-state, emission spectral width, and moreover understanding of the doping mechanism restricted the wide development of the synthetic methodology for high-quality Cu-doped nanocrystals. It has been shown recently that the emission from Cu-doped semiconductor nanocrystals can span over a wide spectral window and could be a potential color tunable dispersed nanocrystal emitter. Herein, we report the size and composition of variable Cu-doped ZnS/Zn(1−x)Cd(x)S zinc-blende (ZB) surface alloyed nanocrystals with intense, stable, and tunable emission covering the blue to red end of the visible spectrum. Further, the Cu dopant emission is distinguished from trap state emission, and the composition variable spectral broadening has been justified on the account of a different environment around the Cu ions in the host lattice. Whereas some findings are in agreement with past reports, several new physical insights presented here would help the community for an in-depth mechanistic study on Cu doping. Moreover, these doped nanocrystal emitters can be a promising candidate for application ranging from optoelectronics to bio-labeling.

Total Synthesis and Structure Revision of a Fungal Glycolipid Fusaroside.

Herein, we report a strategy for the total synthesis of a structurally unique fungal glycolipid fusaroside. The first total synthesis of the proposed structure involved construction of the complex, branched lipid chain having a variety of alkenes with E stereochemistry and attachment of the masked α,ß-unsaturated ß-keto acid at the O-4 position of trehalose as key steps. We propose a revision in the structure of fusaroside, particularly the position of olefins in the lipid chain.