Highly modular synthesis of C1-symmetric aminosulfoximines and their use as ligands in copper-catalyzed asymmetric Mukaiyama-aldol reactions

The development of C1-symmetric aminosulfoximines, their highly modular synthesis, and their application in enantioselective copper-catalyzed Mukaiyama-type aldol reactions between pyruvates and enolsilanes is described. In this context, the influence of the ligand architecture as well as the optimization of the reaction conditions are discussed. In detail, the dependence of the catalyst efficiency on the solvent, the metal source and the temperature are reported, and an interesting additive effect is highlighted. Furthermore, the substrate scope will be presented. With the optimized catalyst system, a number of aldol products with quaternary stereogenic centers have been obtained in high yields and with enantiomeric excesses up to 99 %.     

Synthesis of thiol-derivatized ferrocene-porphyrins for studies of multibit information storage

One approach toward storage of multiple bits of information at the molecular level requires the construction of molecular architectures comprised of multiple redox-active units. Four new ferrocene-porphyrins have been synthesized to investigate questions concerning (1) the scope of redox-active molecules that can be employed in molecular information-storage schemes and (2) writing/reading rates as well as retention of charge in redox-active units located at different sites in a molecular architecture. Three of the ferrocene-porphyrins have linkers of different lengths between the ferrocene and porphyrin. The fourth ferrocene-porphyrin has two ferrocenes positioned at the lateral sites on the porphyrin. The latter architecture is designed to provide a shorter distance between the electroactive surface and the ferrocene while maintaining an upright orientation of the porphyrin. Each ferrocene-porphyrin affords three cationic oxidation states (ferrocene monocation, porphyrin monocation, porphyrin dication) in addition to the neutral state, thereby affording the capability of storing two bits of information. Each ferrocene-porphyrin bears an S-acetyl or S-(N-ethyl)carbamoyl-protected thiol moiety, thereby avoiding handling of free thiols. Each ferrocene-porphyrin forms a self-assembled monolayer (SAM) on gold via in situ cleavage of the thiol protecting group. The SAM of each array is electrochemically robust and exhibits three well-resolved, reversible oxidation waves.     

Dearomative Photocatalytic Construction of Bridged 1,3-Diazepanes

The construction of diverse sp³-rich skeletal ring systems is of importance to drug discovery programmes and natural product synthesis. Herein, we report the photocatalytic construction of 2,7-diazabicyclo[3.2.1]octanes (bridged 1,3-diazepanes) via a reductive diversion of the Minisci reaction. The fused tricyclic product is proposed to form via radical addition to the C4 position of 4-substituted quinoline substrates, with subsequent Hantzsch ester-promoted reduction to a dihydropyridine intermediate which undergoes in situ two-electron ring closure to form the bridged diazepane architecture. A wide scope of N-arylimine and quinoline derivatives was demonstrated and good efficiency was observed in the construction of sterically congested all-carbon quaternary centers. Computational and experimental mechanistic studies provided insights into the reaction mechanism and observed regioselectivity/diastereoselectivity.     

Achieving Ultrahigh Molecular Weights with Diverse Architectures for Unconjugated Monomers through Oxygen-Tolerant Photoenzymatic RAFT Polymerization

Achieving well-defined polymers with ultrahigh molecular weight (UHMW) is an enduring pursuit in the field of reversible deactivation radical polymerization. Synthetic protocols have been successfully developed to achieve UHMWs with low dispersities exclusively from conjugated monomers while no polymerization of unconjugated monomers has provided the same level of control. Herein, an oxygen-tolerant photoenzymatic RAFT (reversible addition-fragmentation chain transfer) polymerization was exploited to tackle this challenge for unconjugated monomers at 10 °C, enabling facile synthesis of well-defined, linear and star polymers with near-quantitative conversions, unprecedented UHMWs and low dispersities. The exquisite level of control over composition, MW and architecture, coupled with operational ease, mild conditions and environmental friendliness, broadens the monomer scope to include unconjugated monomers, and to achieve previously inaccessible low-dispersity UHMWs.     

Utilizing photocurrent transients for dithiolene-based photodetection: stepwise improvements at communications relevant wavelengths

Photodetection based on bis-(4-dimethylaminodithiobenzil)-Ni(II) (BDN), a representative and well-studied metal dithiolene that shows strong absorption in the near-infrared region of the electromagnetic spectrum, has been investigated. By adopting a metal/insulator/semiconductor/metal (MISM) structure, the peak photocurrent response to an oscillating light chain is increased by up to 50 times, compared to devices without an insulating layer. The transient form of the MISM photoresponse, while unsuitable for steady-state photodetection, can be used to detect periodic light signals of frequencies up to 1 MHz, and is thus applicable for optical communication. Further improvements have been realized by nanostructuring carbon black into the dithiolene layer, improving charge collection, and yielding detectivity of up to 1.6 × 10(11) Jones at wavelengths beyond the scope of silicon photodiodes. Such an architecture may allow the favorable absorption properties of other such metal dithiolenes to be harnessed, where their low charge carrier mobilities and short excitation lifetimes have previously limited their applicability to this field.     

Dearomative Photocatalytic Construction of Bridged 1,3‐Diazepanes

The construction of diverse sp³‐rich skeletal ring systems is of importance to drug discovery programmes and natural product synthesis. Herein, we report the photocatalytic construction of 2,7‐diazabicyclo[3.2.1]octanes (bridged 1,3‐diazepanes) via a reductive diversion of the Minisci reaction. The fused tricyclic product is proposed to form via radical addition to the C4 position of 4‐substituted quinoline substrates, with subsequent Hantzsch ester‐promoted reduction to a dihydropyridine intermediate which undergoes in situ two‐electron ring closure to form the bridged diazepane architecture. A wide scope of N‐arylimine and quinoline derivatives was demonstrated and good efficiency was observed in the construction of sterically congested all‐carbon quaternary centers. Computational and experimental mechanistic studies provided insights into the reaction mechanism and observed regioselectivity/diastereoselectivity.     

Self‐Healing Materials from V‐ and H‐Shaped Supramolecular Architectures

Integrating self‐healing capability into supramolecular architectures is an interesting strategy, and can considerably enhance the performance and broaden the scope of applications for this important class of polymers. Herein we report the rational design of novel V‐shaped barbiturate (Ba) functionalized soft–hard–soft triblock copolymers with a reversible supramolecular healing motif (Ba) in the central part of the hard block, which undergoes autonomic repair at 30 °C. The designed synthesis also offers a suitable macromolecular building block to further self‐assemble with heterocomplementary α,ω‐Hamilton wedge (HW) functionalized polyisoprene (PI; HW‐PI‐HW), resulting in an H‐shaped supramolecular architecture with efficient self‐healing capabilities that can recover up to around 95 % of the original mechanical performance at 30 °C within 24 h.     

High-resolution protein hydration NMR experiments: probing how protein surfaces interact with water and other non-covalent ligands

High-resolution solution NMR experiments are extremely useful to characterize the location and the dynamics of hydrating water molecules at atomic resolution. However, these methods are severely limited by undesired incoherent transfer pathways such as those arising from exchange-relayed intra-molecular cross-relaxation. Here, we review several complementary exchange network editing methods that can be used in conjunction with other types of NMR hydration experiments such as magnetic relaxation dispersion and ¹J_NC′ measurements to circumvent these limitations. We also review several recent contributions illustrating how the original solution hydration NMR pulse sequence architecture has inspired new approaches to map other types of non-covalent interactions going well beyond the initial scope of hydration. Specifically, we will show how hydration NMR methods have evolved and have been adapted to binding site mapping, ligand screening, protein-peptide and peptide-lipid interaction profiling.     

Protein secondary structure prediction using neural networks and deep learning: A review

Literature contains over fifty years of accumulated methods proposed by researchers for predicting the secondary structures of proteins in silico. A large part of this collection is comprised of artificial neural network-based approaches, a field of artificial intelligence and machine learning that is gaining increasing popularity in various application areas. The primary objective of this paper is to put together the summary of works that are important but sparse in time, to help new researchers have a clear view of the domain in a single place. An informative introduction to protein secondary structure and artificial neural networks is also included for context. This review will be valuable in designing future methods to improve protein secondary structure prediction accuracy. The various neural network methods found in this problem domain employ varying architectures and feature spaces, and a handful stand out due to significant improvements in prediction. Neural networks with larger feature scope and higher architecture complexity have been found to produce better protein secondary structure prediction. The current prediction accuracy lies around the 84% marks, leaving much room for further improvement in the prediction of secondary structures in silico. It was found that the estimated limit of 88% prediction accuracy has not been reached yet, hence further research is a timely demand.     

Synthesis of Thieno[3,4-b]pyrazine-based Alternating Conjugated Polymers via Direct Arylation for Near-infrared OLED Applications

Three alternating conjugated polymers,namely PFTP,PCz TP,and PSi TP,which combine a thieno[3,4-b]pyrazine(TP)unit with different benzene-based donor units such as 9,9-dioctylfluorene,9-heptadecyl-9H-carbazole and 5,5-dioctyl-5H-dibenzo[b,d]silole,were synthesized in good yield(>85%)and high molecular weight up to Mn=5.82×10⁴ via direct arylation polymerization(DAr P).All the resultant polymers exhibit moderate bandgap of about 1.80 e V and strong deep red/near-infrared emitting in the solid state.Among them,the PSi TP-based electroluminescence(EL)devices with an architecture of ITO/PEDOT:PSS/PTAA/emitting layer/TPBi/Li F/Al give the best performance with a maximum luminance of 2543 cd/m² at 478 m A/cm².This work expands the application scope of high-performance conjugated polymers which can be synthesized by DAr P.     

Liquid crystal dimers and higher oligomers: between monomers and polymers

The underlying theme of this Critical Review is the relationship between molecular structure and liquid crystalline behaviour in a class of materials referred to as liquid crystal oligomers. For the purposes of this review, a liquid crystal oligomer will be defined as consisting of molecules composed of semi-rigid mesogenic units connected via flexible spacers. Much of the review will be devoted to structure-property relationships in the simplest oligomers, namely dimers, in which just two mesogenic units are connected by a single spacer. Along the way we will see how this molecular architecture has been exploited to address issues in a range of quite different areas and has given rise to potential applications for these materials. On the whole, only compounds in which the mesogenic units are linked essentially in a linear fashion will be considered while structures such as liquid crystal dendrimers and tetrapodes fall outside the scope of this review. The review will be of interest not only to scientists working directly in this area but in particular to those interested in understanding the relationships between structure and properties in polymers, and those designing materials for new applications.     

X‐ray Crystallography in Open‐Framework Materials

Open‐framework materials, such as metal–organic frameworks (MOFs) and coordination polymers have been widely investigated for their gas adsorption and separation properties. However, recent studies have demonstrated that their highly crystalline structures can be used to periodically organize guest molecules and non‐structural metal compounds either within their pore voids or by anchoring to their framework architecture. Accordingly, the open framework can act as a matrix for isolating and elucidating the structures of these moieties by X‐ray diffraction. This concept has broad scope for development as an analytical tool where obtaining single crystals of a target molecule presents a significant challenge and it additionally offers potential for obtaining insights into chemically reactive species that can be stabilized within the pore network. However, the technique does have limitations and as yet a general experimental method has not been realized. Herein we focus on recent examples in which framework materials have been utilized as a scaffold for ordering molecules for analysis by diffraction methods and canvass areas for future exploration.     

Substrate discrimination by cholapod anion receptors: geometric effects and the "affinity-selectivity principle"

Cholapod anion receptors can achieve high affinities while maintaining compatibility with nonpolar media. Previously they have been shown to transport anions across cell and vesicle membranes. In the present work, the scope of the architecture is expanded and structure-selectivity relationships are investigated. Eight new receptors have been synthesized, with up to six H-bond donor centers. Using Cram's extraction method, these compounds plus five known examples have been tested for binding to seven monovalent anions (tetraethylammonium salts, wet chloroform as solvent). Association constants in excess of 10(10) M(-1) have been measured for several pairings. Selectivities vary with receptor geometry, as expected. More remarkably, they also depend on receptor strength: more powerful receptors show a wider range of binding free energies, and therefore a greater spread of Ka(X-)/Ka(Y-). This "affinity-selectivity" effect can be derived from empirical relationships for H-bond strengths, and could prove widely operative in supramolecular chemistry.     

Microwave Synthetic Routes for Shape-Controlled Catalyst Nanoparticles and Nanocomposites

The use of microwave irradiation for the synthesis of inorganic nanomaterials has recently become a widespread area of research that continues to expand in scope and specialization. The growing demand for nanoscale materials with composition and morphology tailored to specific applications requires the development of facile, repeatable, and scalable synthetic routes that offer a high degree of control over the reaction environment. Microwave irradiation provides unique advantages for developing such routes through its direct interaction with active reaction species, which promotes homogeneous heat distribution, increased reaction rates, greater product quality and yield, and use of mild reaction conditions. Many catalytic nanomaterials such as noble metal nanoparticles and intricate nanocomposites have very limited synthetic routes due to their extreme temperature sensitivity and difficulty achieving homogeneous growth. This work presents recent advances in the use of MW irradiation methods to produce high-quality nanoscale composites with controlled size, morphology, and architecture.     

The flexible scope of accreditation

The scope of accreditation for testing laboratories can inhibit, in certain cases, their quick response to customers needs, if the scope is too rigid with regard to the modification of test methods and the introduction of new ones using the same measurement principles. Document EA-2-05 published by the European Cooperation for Accreditation describes possibilities to allow flexibility in accredited laboratories. Several examples of a flexible scope are given.     

Synthesis of trans-A2B2-porphyrins bearing phenylethynyl substituents

Efficient and convenient conditions for the preparation of trans-A(2)B(2)-porphyrins bearing two phenylethynyl moieties directly from phenylpropargyl aldehydes and dipyrromethanes of diversified lipophilicity and reactivity have been developed. This new procedure allows the preparation of a library of porphyrins of this architecture with a wide range of substituents. Thanks to the identification of the reagent solubility as one of the key factors influencing the yield of the porphyrinogens, we were able to improve yields to ca. 30%. The scope and limitations of two sets of conditions have been explored. The methodological advantage of this approach is its straightforward access to building blocks and the formation of the porphyrin core in the last step without the need for deprotection of the triple bond or bromination and consecutive coupling reaction, which often demands copper salts to proceed smoothly, especially with electron-deficient alkyne partners. Therefore, it prevents undesired copper porphyrin formation, as well as the need for utilizing expensive alkynes. A two-step method for the preparation of phenylpropargyl aldehydes has also been refined.     

二次阳极氧化方法制备有序多孔氧化铝膜

通过二次阳极氧化方法制备多孔氧化铝膜与一次阳极氧化方法制备多孔氧化铝膜孔排布规律性的对比,结果发现,二次阳极氧化方法制取的多孔氧化铝膜孔排布规律性明显好于一次阳极氧化法制取的多孔膜.在几个微米范围内,孔呈理想的六角排布.去除一次阳极氧化膜后,二次阳极氧化得以在更良好的表面进行,制取的氧化铝膜孔规律性和有序度更高.有序区域的尺寸与晶粒内的亚晶大小有一定关系.     

Mesoscopic superstructures of flexible porous coordination polymers synthesized via coordination replication

The coordination replication technique is employed for the direct conversion of a macro- and mesoporous Cu(OH)₂–polyacrylamide composite to three-dimensional superstructures consisting of the flexible porous coordination polymers, Cu₂(bdc)₂(MeOH)₂ and Cu₂(bdc)₂(bpy) (bdc^2– = 1,4-benzenedicarboxylate, bpy = 4,4′-bipyridine). Detailed characterization of the replicated systems reveals that the structuralization plays an important role in determining the adsorptive properties of the replicated systems, and that the immobilization of the crystals within a higher-order architecture also affects its structural and dynamic properties. The polyacrylamide polymer is also found to be crucial for maintaining the structuralization of the monolithic systems, and in providing the mechanical robustness required for manual handling. In all, the results discussed here demonstrate a significant expansion in the scope of the coordination replication strategy, and further confirms its utility as a highly versatile platform for the preparation of functional three-dimensional superstructures of porous coordination polymers.     

Nano-kinetics of probe-particles in solution visualized by a pin-fiber video scope.

The nano-kinetics of colloidal particles and living cells with the colloidal particles were visualized by a newly developed video scope. The system of the new video scope has a feature of fine controlling the illumination conditions by using a single optical fiber. This characteristic enables one to obtain clear images of living cells and the motions of colloidal particles by light-scattering effects. In the experiments, RBL-2H3 cells and gold colloidal particles were observed. Scattering images with high contrast and a dark background like in dark-field observations could be attained. In the experiments, a pulsed laser was also applied. The results obtained in this study could validate the effectiveness and possibility of a new video scope for applications to biological and biomedical fields.