SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Lithium aluminium hydride

168

We report an enhancement in the efficiency of organic solar cells via the incorporation of gold (Au) or silver (Ag) nanoparticles (NPs) in the hole-transporting buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which was formed on an indium tin oxide (ITO) surface by the spin-coating of PEDOT:PSS-Au or Ag NPs composite solution. The composite solution was synthesized by a simple in situ preparation method which involved the reduction of chloroauric acid (HAuCl4) or silver nitrate (AgNO3) with sodium borohydride (NaBH4) solution in the presence of aqueous PEDOT:PSS media. The NPs were well dispersed in the PEDOT:PSS media and showed a characteristic absorption peak due to the surface plasmon resonance effect. Organic solar cells with the structure of ITO/PEDOT:PSS-Au, Ag NPs/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM)/LiF/Al exhibited an 8% improvement in their power conversion efficiency mainly due to the enlarged surface roughness of the PEDOT:PSS, which lead to an improvement in the charge collection and ultimately improvements in the short-circuit current density and fill factor.

Concepts: Gold, Lithium aluminium hydride, Solar cell, Indium tin oxide, Energy conversion, Silver, Surface plasmon resonance, PEDOT:PSS

28

Within the general area of early main group metal chemistry, the controlled synthesis of well-defined metal hydride complexes is a rapidly developing research field. As group 1 and 2 metal complexes are generally highly dynamic and lattice energies for their [MH](∞) and [MH(2)](∞) salts are high, the synthesis of well-defined soluble hydride complexes is an obvious challenge. Access to molecular early main group metal hydrides, however, is rewarding: these hydrocarbon-soluble metal hydrides are highly reactive, have found use in early main group metal catalysis and are potentially also valuable molecular model systems for polar metal hydrides as a hydrogen storage material. The article focusses specifically on alkali and alkaline-earth metal hydride complexes and discusses the synthetic challenge, molecular structures, reactivity and applications.

Concepts: Hydrogen, Hydrogenation, Ion, Lithium aluminium hydride, Hydrogen economy, Hydride, Alkali metal, Hydrogen storage

27

Transfer your hydrogen: Fast and general transfer hydrogenation of nitriles to form primary amines is possible with a homogeneous Ru/1,4-bis(diphenylphosphino)butane (DPPB) catalyst. The use of 2-butanol as the hydrogen transfer reagent is essential for the selective reduction of aromatic, heteroaromatic, and aliphatic nitriles with this system.

Concepts: Amine, Functional group, Hydrogen, Hydrogenation, Nitrogen, Lithium aluminium hydride, Imine, Nitrile

25

Over the past few years, CuH-catalyzed hydroamination has been discovered and developed as a robust and conceptually novel approach for the synthesis of enantioenriched secondary and tertiary amines. The success in this area of research was made possible through the large body of precedent in copper(I) hydride catalysis and the well-explored use of hydroxylamine esters as electrophilic amine sources in related copper-catalyzed processes. This Minireview details the background, advances, and mechanistic investigations in CuH-catalyzed hydroamination.

Concepts: Amino acid, Amine, Functional group, Nitrogen, Alkene, Amide, Lithium aluminium hydride, Amines

24

A new chitosan microparticles loading paclitaxel(PTX) for application as an oral delivery system was developed using a novel double emulsion cross-linking method. To improve the targeted effect, folic acid (FA) was introduced onto the surface of microparticles using chemical method. The method was based on Schiff reaction between amino group of chitosan and carboxyl group of FA, and folate-chitosan(FA-CS) conjuate was characterized using infrared spectrum analysis(FT-IR), and the microparticles were named as FA-CS-PTX/MPs. FA-CS-PTX/MPs had larger size of average diameter 223.6nm, while PTX-loaded chitosan microparticles (CS-PTX/MPs) had 179.1nm average diameter. The zeta potential of CS-PTX/MPs and FA-CS-PTX/MPs was 22.3mV and 33.1mV respectively. SEM and TEM showed both the two microparticles had well-defined spherical structure. The in vitro drug release was studied under different pH conditions, and a two phase kinetics model was found to be the most adequate kinetic model. Furthermore, the cytotoxicity activities of drug-carriers against L929 cells and the cellular uptake of PTX-loaded microparticles against HepG2 cells were investigated. Results demonstrated that FA-CS-PTX/MPs might be a promising drug carrier for promoting PTX cellular uptake and could be used as a potential tumor-targeted drug vector.

Concepts: Alcohol, Amino acid, Acid, Amine, Functional group, Carboxylic acid, Amide, Lithium aluminium hydride

23

Although my research has no common theme or defining area, a coherence connects the diverse topics insofar as one project leads logically to another. Thus, studies on mechanisms of hydrogen exchange in amides and amidines led to the influence of hydrogen bonding and to NMR methods for chemical kinetics, including 2D-EXSY spectroscopy. Another connection was the OH(-)-catalyzed NH exchange in amines that had supported the hypothesis of stereoelectronic control. We therefore analyzed that hypothesis critically, tested it, found counterexamples, and proposed an alternative hypothesis. We next addressed one-bond NMR coupling constants in ethers and the reverse anomeric effect. The latter studies required a highly accurate NMR titration method that we developed to measure the additional steric bulk resulting from protonation of a substituent. This method is also applicable to measuring secondary isotope effects on acidity, and we could demonstrate that they arise from n-σ* delocalization, not from an inductive effect. Other studies included kinetic isotope effects for both dissociation and H exchange of aqueous NH4(+), for C-N rotation in amides, and for a hydride transfer. The role of hydrogen bonding led us to the rotation of NH4(+) within its solvent cage and then to the symmetry of hydrogen bonds.

Concepts: Oxygen, Acid, Hydrogen, Atom, Lithium aluminium hydride, Covalent bond, Hydronium, Physical organic chemistry

8

Driven by the ever-increasing pace of drug discovery and the need to push the boundaries of unexplored chemical space, medicinal chemists are routinely turning to unusual strained bioisosteres such as bicyclo[1.1.1]pentane, azetidine, and cyclobutane to modify their lead compounds. Too often, however, the difficulty of installing these fragments surpasses the challenges posed even by the construction of the parent drug scaffold. This full account describes the development and application of a general strategy where spring-loaded, strained C-C and C-N bonds react with amines to allow for the “any-stage” installation of small, strained ring systems. In addition to the functionalization of small building blocks and late-stage intermediates, the methodology has been applied to bioconjugation and peptide labeling. For the first time, the stereospecific strain-release “cyclopentylation” of amines, alcohols, thiols, carboxylic acids, and other heteroatoms is introduced. This report describes the development, synthesis, scope of reaction, bioconjugation, and synthetic comparisons of four new chiral “cyclopentylation” reagents.

Concepts: Alcohol, Amino acid, Acid, Amine, Functional group, Carboxylic acid, Lithium aluminium hydride, Drug discovery

6

The widespread use of alkyl boronic acids and esters is frequently hampered by the challenges associated with their preparation. Herein we describe a simple and practical method to rapidly access densely functionalized alkyl boronate esters from abundant carboxylic substituents. This broad-scope Ni-catalyzed reaction uses the same activating principle as amide bond formation to replace a carboxylic acid with a boronate ester. Application to peptides allowed expedient preparations of α-amino boronic acids, often with high stereoselectivity, facilitating the synthesis of both FDA approved alkyl boronic acid drugs (Velcade and Ninlaro) as well as a boronic acid version of the iconic antibiotic vancomycin. The reaction also enabled the discovery and extensive biological characterization of potent elastase inhibitors which may have a strategic advantage due to their covalent-reversible binding properties.

Concepts: Alcohol, Amino acid, Acetic acid, Functional groups, Carboxylic acid, Ester, Amide, Lithium aluminium hydride

6

A rational approach is needed to design hydrogenation catalysts that make use of Earth-abundant elements to replace the rare elements such as ruthenium, rhodium, and palladium that are traditionally used. Here, we validate a prior mechanistic hypothesis that partially saturated amine(imine)diphosphine ligands (P-NH-N-P) activate iron to catalyze the asymmetric reduction of the polar bonds of ketones and imines to valuable enantiopure alcohols and amines, with isopropanol as the hydrogen donor, at turnover frequencies as high as 200 per second at 28°C. We present a direct synthetic approach to enantiopure ligands of this type that takes advantage of the iron(lI) ion as a template. The catalytic mechanism is elucidated by the spectroscopic detection of iron hydride and amide intermediates.

Concepts: Amine, Functional group, Hydrogen, Catalysis, Hydrogenation, Catalytic converter, Nitrogen, Lithium aluminium hydride

5

Cross couplings of alkyl halides and organometallic species based on single electron transfer (SET) using Ni- and Fe-catalyst systems have been studied extensively, and separately, for decades. Here we demonstrate the first couplings of redox-active esters (both isolated and derived in situ from carboxylic acids) with organozinc and organomagnesium species using a Fe-based catalyst system originally developed for alkyl halides. This work is placed in the proper context by showing a direct comparison with a Ni catalyst for >40 examples spanning a range of primary, secondary, and tertiary substrates. This new C-C coupling is scalable, sustainable, and exhibits a number of clear advantages in several cases over its Ni-based counterpart.

Concepts: Alcohol, Amino acid, Acetic acid, Functional groups, Carboxylic acid, Ester, Amide, Lithium aluminium hydride