Judicious Choice Of Solvents Research Articles

High Quantum Yield Sensitization of Single Crystal TiO2 Electrodes with CsPbBr3 Nanocrystals

Abstract Lead halide perovskites are promising materials for solar cells and photodetectors. Nanocrystals of this family of perovskites also have distinct properties. In this study we report the attainment of high quantum yield sensitized photocurrents from stabilized CsPbBr3 perovskite nanocrystals thermally evaporated onto doped single crystal rutile (110) TiO2 electrodes. Sensitized photocurrent stabilization was achieved by capping the nanocrystals with a thin NiOx layer and Au carrier transport and protection layers respectively as well as the judicious choice of solvent and electrolyte.

Thickness control of organic semiconductor-incorporated perovskites.

Two-dimensional organic semiconductor-incorporated perovskites are a promising family of hybrid materials for optoelectronic applications, owing in part to their inherent quantum well architecture. Tuning their structures and properties for specific properties, however, has remained challenging. Here we report a general method to tune the dimensionality of phase-pure organic semiconductor-incorporated perovskite single crystals during their synthesis, by judicious choice of solvent. The length of the conjugated semiconducting organic cations and the dimensionality (n value) of the inorganic layers can be manipulated at the same time. The energy band offsets and exciton dynamics at the organic-inorganic interfaces can therefore be precisely controlled. Furthermore, we show that longer and more planar π-conjugated organic cations induce a more rigid inorganic crystal lattice, which leads to suppressed exciton-phonon interactions and better optoelectronic properties as compared to conventional two-dimensional perovskites. As a demonstration, optically driven lasing behaviour with substantially lower lasing thresholds was realized.

Copper-Catalyzed Regiodivergent and Enantioselective Hydrosilylation of Allenes.

A copper-catalyzed regiodivergent hydrosilylation of a wide range of simple allenes is reported. Linear and branched allylsilanes were formed by judicious choice of solvents. Furthermore, branched allylsilanes were obtained with high enantioselectivity (up to 97% enantiomeric excess) with the aid of a C2-symmetric bisphosphine ligand in the unprecedented asymmetric allene hydrosilylation.

C-H Bond Arylation of Pyrazoles at the β-Position: General Conditions and Computational Elucidation for a High Regioselectivity.

Direct arylation of most five-membered ring heterocycles are generally easily accessible and strongly favored at the α-position using classical palladium-catalysis. Conversely, regioselective functionalization of such heterocycles at the concurrent β-position remains currently very challenging. Herein, we report general conditions for regioselective direct arylation at the β-position of pyrazoles, while C-H α-position is free. By using aryl bromides as the aryl source and a judicious choice of solvent, the arylation reaction of variously N-substituted pyrazoles simply proceeds via β-C-H bond functionalization. The β-regioselectivity is promoted by a ligand-free palladium catalyst and a simple base without oxidant or further additive, and tolerates a variety of substituents on the bromoarene. DFT calculations revealed that a protic solvent such as 2-ethoxyethan-1-ol significantly enhances the acidity of the proton at β-position of the pyrazoles and thus favors this direct β-C-H bond arylation. This selective pyrazoles β-C-H bond arylation was successfully applied for the straightforward building of π-extended poly(hetero)aromatic structures via further Pd-catalyzed combined α-C-H intermolecular and intramolecular C-H bond arylation in an overall highly atom-economical process.

Drug Leads from Endophytic Fungi: Lessons Learned via Scaled Production.

Recently, the isolation and elucidation of a series of polyhydroxyanthraquinones were reported from an organic extract of a solid phase culture of an endophytic fungus, Penicillium restrictum (strain G85). One of these compounds, ω-hydroxyemodin (1: ), showed promising quorum-sensing inhibition against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) in both in vitro and in vivo models. The initial supply of 1: was 19 mg, and this amount needed to be scaled by a factor of 30 to 50 times, in order to generate material for further in vivo studies. To do so, improvements were implemented to enhance both the fermentation of the fungal culture and the isolation of this compound, with the target of generating > 800 mg of study materials in a period of 13 wk. Valuable insights, both regarding chemistry and mycology, were gained during the targeted production of 1: on the laboratory-scale. In addition, methods were modified to make the process more environmentally friendly by judicious choice of solvents, implementing procedures for solvent recycling, and minimizing the use of halogenated solvents.

Tuning the gelation behavior of short laminin derived peptides via solvent mediated self-assembly.

Controlling the self-assembly pathways through solvent mediated approach can be an effective means to create complex, multifunctional structures. However, predicting the effect of solvent environment on both solubility of the monomer and their self-assembling behaviour remains a challenge. Our work mainly aims to understand the role of solvents in driving the supramolecular self-assembly of structurally related bioinspired pentapeptides (IKVAV and YIGSR), derived from native laminin protein. The exploration of the short sequences from this useful functional protein is still in its infancy. An N-terminal hydrophobic modification of IKVAV and YIGSR has been used to illustrate the gelator-gelator and gelator-solvent intermolecular interactions. Microscopic investigation of hydrophobic derivatives showed the transformation of fibrous morphology to sheet like structures, on varying solvent polarity from aqueous-organic mixture to aqueous solvent. Interestingly, these gels possess mechano-responsive and thermo-reversible properties, which also showed the remarkable solvent susceptibility. Our study clearly indicates that judicious choice of solvents may help in designing new soft materials with controlled properties, lesser defects and higher reproducibility.

Modulating the selectivity of a colorimetric sensor based on a Schiff base-functionalized diarylethene towards anions by judicious choice of solvent

A novel diarylethene derivative with a 9-fluorenone hydrazone unit has been synthesized, which showed multi-responsive for light, acid-base and anions. Its sensing properties were well studied by colorimetric and spectroscopic method, and the selectivity could be modulated through judicious choice of solvent. It can simultaneously colorimetric sensing of carbonate ion in methanol with the detection limit of 1.25 × 10−6 mol L-1 and cyanide ion in tetrahydrofuran with the detection of 2.85 × 10−7 mol L−1, respectively. The different sensing mechanism for carbonate ion and cyanide ion was confirmed by UV–vis and 1H-NMR characterization techniques. Moreover, the compound can be used detect carbonate ion and cyanide ion in natural water sample with a high accuracy.

Spontaneous Aryldiazonium Grafting for the Preparation of Functional Cyclodextrin-Modified Materials.

A mild and efficient surface modification protocol for the preparation of β-cyclodextrin (βCD) modified surfaces through aryldiazonium-mediated grafting is reported. Monosubstituted 6-O-aminophenol-β-cyclodextrin (amβCD) was synthesized through a three-step protocol. This compound was found to form supramolecular aggregates in aqueous solutions at relatively low concentrations via cavity-directed self-assembly. Disruption of these supramolecular structures through judicious choice of solvent was found to be essential for the formation of the reactive aryldiazonium species from the amino-phenolic precursor and for spontaneous surface grafting from aqueous solutions. Cyclodextrin thin films were prepared on carbon macroscopic substrates and electrodes and were characterized via infrared reflectance absorption spectroscopy (IRRAS), cyclic voltammetry, and water contact angle measurements. Protein adsorption studies demonstrated that βCD adlayers reduced nonspecific protein adsorption. βCD moieties in adlayers can be used nonetheless for specific host-guest complexation and are grafted at the surface with monolayer coverage (1.2 × 10-10 mol cm-2) as demonstrated via experiments using ferrocene, a redox probe. Finally, cyclodextrin covalent immobilization was demonstrated also on stainless steel and polyamide samples, two substrates with wide ranging technological applications.

Peptide Sequence and Solvent as Levers to Control Disulfide Connectivity in Multiple Cysteine Containing Venom Toxins.

Judicious choice of solvent, temperature, and strategic mutations along a peptide backbone can minimize formation of non-native disulfide bond isoforms in chemical synthesis of multiple cysteine containing venom toxins. By exploiting these controls, one can drive the population distribution in favor of a particular isoform. Some chosen ionic liquids (ILs), like 1-ethyl-3-methyl-imidazolium acetate, [Im21][OAc], have proven efficient in favoring the native globular isoform in some conotoxins. To comprehend such a preference, we report an explicit solvent replica exchange molecular dynamics (REMD) study of two conotoxins, AuIB and GI, solvated in either neat water or ∼50% (v/v) mixture of water-[Im21][OAc]. Our simulations indicate that compared to neat water, the probability of obtaining native globular isoform of AuIB significantly increases in a water-IL mixture at 305 K. Strikingly, and aligned with experimental observations, peptide GI does not favor the native connectivity in the water-IL mixture. In presence of IL, strong solvent mediated fluctuations of the GI backbone are observed in our simulations. Uneven ion accumulation along the backbone owing to strong H-bonding interactions of some GI residues with IL ions, especially the anion OAc-, restricts conformational freedom of the peptide. Estimation of backbone entropy and Helmholtz free energy corroborates the lack of conformational freedom in GI as compared to AuIB, especially in the presence of IL. In line with prior experiments, simulations of GI mutants indicate that one could possibly force a given pair of Cys residues to come closer by strategically mutating GI residues with glycine and/or alanine, resulting in the breakage/formation of helix-like motifs.

Pd-catalyzed enantiodivergent and regiospecific phospha-Michael addition of diphenylphosphine to 4-oxo-enamides: efficient access to chiral phosphinocarboxamides and their analogues.

The palladacycle-catalyzed asymmetric P-H addition of 4-oxo-enamides has been developed, which provides efficient access to phosphinocarboxamides and their analogues. Solvent-mediated reversal of stereoselectivity (ee from +96% to -92%) was observed, and the underlying mechanism that allows facile access to both enantiomers of the product by judicious choice of solvents is revealed.

Solar cells based on inks of n-type colloidal quantum dots.

New inorganic ligands including halide anions have significantly accelerated progress in colloidal quantum dot (CQD) photovoltaics in recent years. All such device reports to date have relied on halide treatment during solid-state ligand exchanges or on co-treatment of long-aliphatic-ligand-capped nanoparticles in the solution phase. Here we report solar cells based on a colloidal quantum dot ink that is capped using halide-based ligands alone. By judicious choice of solvents and ligands, we developed a CQD ink from which a homogeneous and thick colloidal quantum dot solid is applied in a single step. The resultant films display an n-type character, making it suitable as a key component in a solar-converting device. We demonstrate two types of quantum junction devices that exploit these iodide-ligand-based inks. We achieve solar power conversion efficiencies of 6% using this class of colloids.

Synthesis of [(11)C]Bexarotene by Cu-Mediated [(11)C]Carbon Dioxide Fixation and Preliminary PET Imaging.

Bexarotene (Targretin) is a retinoid X receptor (RXR) agonist that has applications for treatment of T cell lymphoma and proposed mechanisms of action in Alzheimer's disease that have been the subject of recent controversy. Carbon-11 labeled bexarotene ([(11)C-carbonyl]4-[1-(3,5,5,8,8-pentamethyltetralin-2-yl)ethenyl]benzoic acid) was synthesized using a Cu-mediated cross-coupling reaction employing an arylboronate precursor 1 and [(11)C]carbon dioxide under atmospheric pressure in 15 ± 2% uncorrected radiochemical yield (n = 3), based on [(11)C]CO2. Judicious choice of solvents, catalysts, and additives, as well as precursor concentration and purity of [(11)C]CO2, enabled the preparation of this (11)C-labeled carboxylic acid. Formulated [(11)C]bexarotene was isolated (>37 mCi) with >99% radiochemical purity in 32 min. Preliminary positron emission tomography-magnetic resonance imaging revealed rapid brain uptake in nonhuman primate in the first 75 s following intravenous administration of the radiotracer (specific activity >0.3 Ci/μmol at time of injection), followed by slow clearance (Δ = -43%) over 60 min. Modest uptake (SUVmax = 0.8) was observed in whole brain and regions with high RXR expression.

New symmetrical conjugated thiophene-azomethines containing triphenylamine or carbazole units: Synthesis, thermal and optoelectrochemical properties

New oligo- and poly(azomethine)s containing 3,4-dicyanothiophene and triphenylamine or carbazole units were synthesized under condensation reaction conditions. Although the different amino group reactivity, a one-pot synthesis of symmetric conjugated oligoazomethines was possible by judicious choice of solvent and careful control of reagent stoichiometry. Different polycondensation strategies (in solution and bulk polymerization reactions) were applied in order to obtain soluble oligoazomethines and poly(azomethine)s. Their expected chemical structures were confirmed by 1H-NMR and Fourier transform infrared (FT-IR) characterization techniques. Electronic properties of the synthesized oligoazomethines were investigated in different solvents, using UV-Vis and photoluminescence spectroscopy (PL) and these revealed that there is a slight dependency between the solvent polarity and absorption wavelength, while the emissions peaks are shifted at higher wavelength with increasing the solvent polarity. The thermogravimetric and differential scanning calorimetry analysis showed a high thermal stability up to 350 °C and no glass transition temperature. Having in their structure electroactive sites, i.e., carbazole and triphenylamine units, cyclic voltammetry technique was used to investigate the oxido-reduction behavior and to determine the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels.

Intermolecular Hydroacylation: High Activity Rhodium Catalysts Containing Small-Bite-Angle Diphosphine Ligands

Readily prepared and bench-stable rhodium complexes containing methylene bridged diphosphine ligands, viz. [Rh(C(6)H(5)F)(R(2)PCH(2)PR'(2))][BAr(F)(4)] (R, R' = (t)Bu or Cy; Ar(F) = C(6)H(3)-3,5-(CF(3))(2)), are shown to be practical and very efficient precatalysts for the intermolecular hydroacylation of a wide variety of unactivated alkenes and alkynes with β-S-substituted aldehydes. Intermediate acyl hydride complexes [Rh((t)Bu(2)PCH(2)P(t)Bu(2))H{κ(2)(S,C)-SMe(C(6)H(4)CO)}(L)](+) (L = acetone, MeCN, [NCCH(2)BF(3)](-)) and the decarbonylation product [Rh((t)Bu(2)PCH(2)P(t)Bu(2))(CO)(SMePh)](+) have been characterized in solution and by X-ray crystallography from stoichiometric reactions employing 2-(methylthio)benzaldehdye. Analogous complexes with the phosphine 2-(diphenylphosphino)benzaldehyde are also reported. Studies indicate that through judicious choice of solvent and catalyst/substrate concentration, both decarbonylation and productive hydroacylation can be tuned to such an extent that very low catalyst loadings (0.1 mol %) and turnover frequencies of greater than 300 h(-1) can be achieved. The mechanism of catalysis has been further probed by KIE and deuterium labeling experiments. Combined with the stoichiometric studies, a mechanism is proposed in which both oxidative addition of the aldehyde to give an acyl hydride and insertion of the hydride into the alkene are reversible, with the latter occurring to give both linear and branched alkyl intermediates, although reductive elimination for the linear isomer is suggested to have a considerably lower barrier.

N-Demethylation of N-methyl alkaloids with ferrocene

Under Polonovski-type conditions, ferrocene has been found to be a convenient and efficient catalyst for the N-demethylation of a number of N-methyl alkaloids such as opiates and tropanes. By judicious choice of solvent, good yields have been obtained for dextromethorphan, codeine methyl ether, and thebaine. The current methodology is also successful for the N-demethylation of morphine, oripavine, and tropane alkaloids, producing the corresponding N-nor compounds in reasonable yields. Key pharmaceutical intermediates such oxycodone and oxymorphone are also readily N-demethylated using this approach.

Layer-by-Layer Deposited Chitosan/Silk Fibroin Thin Films with Anisotropic Nanofiber Alignment

Chitosan/silk fibroin multilayer thin films were assembled using layer-by-layer deposition. The resultant multilayer films contained nanofibers aligned parallel to the dipping direction. Fiber deposition and orientation was enabled uniquely by a judicious choice of solvent and drying conditions and layer-by-layer assembly with chitosan. The deposition of oriented nanofibers was found to be the result of a unique combination of layer-by-layer and Langmuir-Blodgett type processing. Fiber orientation was confirmed by fast Fourier transform (FFT) analysis of optical micrographs and atomic force microscopy (AFM). Bidirectional fiber alignment was realized by rotating the substrate between multilayer deposition steps. Infrared spectroscopy revealed that the silk fibroin adopted the silk II secondary structure in the deposited films. We anticipate that these anisotropic films are able to combine the biocompatibility of a natural polymer system with the mechanical strength of SF, two properties useful in many biological applications including scaffolds suitable for guiding cell attachment and spreading.

Ring-Opening of Aziridine-2-Carboxamides with Carbohydrate C1-O-Nucleophiles. Stereoselective Preparation of α- and β-O-Glycosyl Serine Conjugates

The stereoselective formation of the alpha-GalNAc-Ser linkage via the ring opening of aziridine-2-carboxamides with pyranose C1-O-nucleophiles is described. The process is tolerant to the native C2-NHAc group, can be modulated to provide either the alpha- or beta-glycoside through judicious choice of solvent and metal counterion, and is amenable to other classes of O-glycosyl-Ser constructs such as the beta-GlcNAc-Ser and alpha-Man-Ser linkages. This coupling reaction also led to the development of the o-allylbenzyl (ABn) moiety as a new C-terminus carboxyl protective group, which allows for the use of novel methods for N- and C-terminus extension of amino acids following carbohydrate conjugation.

Photophysical, Crystallographic, and Electrochemical Characterization of Symmetric and Unsymmetric Self-Assembled Conjugated Thiopheno Azomethines

Novel conjugated azomethines consisting uniquely of thiophene units are presented. The highly conjugated compounds were synthesized by simple condensation of a stable diamino thiophene (2) with its complementary thiophene aldehydes. These interesting nitrogen-containing thiophene units exhibit variable reactivity leading to controlled aldehyde addition. Because of the different amino reactivity, a one-pot synthesis of unsymmetric and symmetric conjugated azomethines with varying number of thiophene units was possible by judicious choice of solvent and careful control of reagent stoichiometry. The resulting covalent conjugated connections are both reductively and hydrolytically resistant. The thermodynamically E isomer is formed uniquely for all of the azomethines synthesized, which is confirmed by crystallographic studies. These also demonstrated that the azomethine bonds and the thiophene units are highly planar and linear. The fluorescence and phosphorescence of the thiopheno azomethines measured are similar to those of thiophene analogues currently used in functional devices, but with the advantage of low triplet formation and band-gaps as low as 1.9 eV. The time-resolved and steady-state temperature-dependent photophysics revealed the thiopheno azomethines do not populate extensively their triplet manifold by intersystem crossing. Rather, their excited-state energy is dissipated predominantly by nonradiative means of internal conversion. Quasi-reversible electrochemical radical cation formation of the thiophene units was found. These compounds further undergo electrochemically induced oxidative cross-coupling, resulting in conjugated products that also exhibit reversible radical cation formation.

Tuning the pore size and surface area of monodisperse Poly(Methyl Acrylate) beads via parallel seeded polymerisation

A library of 36 monodisperse Poly(Methyl Acrylate)(PMA) beads prepared by seeded polymerisation, for potential application in bio-separations and coatings, were synthesized in a high-throughput (HT) manner and analysed with respect to pore size, surface area and morphology. Beads with high porosity were obtained even with a minimum swelling time of 1 h. Both poly(vinyl alcohol) (PVA) and sodium n-dodecyl sulfate (SDS) were used as the surfactants to obtain particles with a high roundness index. The surface areas were essentially controlled by the ratio of the seed particles introduced in the system relative to the monomer, but did little to affect the average pore size. Increasing the swelling time from 1 to 48 h did not make any significant change in the particle morphology. High surface areas (84 m 2/g) and pore sizes up to 110 Å could be induced by judicious choice of solvent, while increasing concentrations of so called ‘good solvents’ increased the surface areas.

Mild Colorimetric Detection of Sialic Acid

As part of a broader program focusing on the detection of colorless biomolecules in the visible region, a simple and mild procedure for the visual detection of the most abundant sialic acid at room temperature and neutral pH is reported. The role of the interaction of the sialic acid amide with boron in a readily synthesized boronic acid-based receptor is an important feature of the signaling mechanism. Selectivity of reaction can be tuned by the judicious choice of solvents. This study embodies a departure from many of the author's earlier efforts in sugar solutions that are not heated, affording relatively more selective and milder detection.