Efficient access to new chemical space through flow--construction of druglike macrocycles through copper-surface-catalyzed azide-alkyne cycloaddition reactions

A series of 12‐ to 22‐membered macrocycles, with druglike functionality and properties, have been generated by using a simple and efficient copper‐catalyzed azide–acetylene cycloaddition reaction, conducted in flow in high‐temperature copper tubing, under environmentally friendly conditions. The triazole‐containing macrocycles have been generated in up to 90 % yield in a 5 min reaction, without resorting to the high‐dilution conditions typical of macrocyclization reactions. This approach represents a very efficient method for constructing this important class of molecules, in terms of yield, concentration, and environmental considerations.     

Time domain dielectric spectroscopy. A new effective tool for physical chemistry investigation

The general principles of time domain dielectric spectroscopy (TDS) are summarized. The methods of data treatment and presentation, and different TDS methods which enable one to obtain the permanent spectrum of ^* () in the frequency range of 10⁵–10¹⁰ are given. The examples of TDS application for the investigation of dielectric properties in samples of different nature and structure are considered in this review.     

The Kalman filter in analytical chemistry

During the past ten years, the means by which more information can be extracted from experimental data have become an important area of research in analytical chemistry. Digital filters have been demonstrated to have a number of applications to analytical problems. These techniques typically involve a least-squares fit of experimental data to some model of the process being filtered. One method for filtering experimental data is based on the Kalman filter, a recursive, linear digital filter first developed for use in navigation, but now used in many fields. This paper discusses the implementation of Kalman filters in analytical chemistry. The principles of state-space digital filtering are reviewed, and the development of state/space models is discussed. Discussion is focused on the discrete Kalman algorithms. Two examples are provided to demonstrate the operation of the discrete Kalman filtering algorithm. Similarities between Kalman filtering and weighted least-squares methods are considered, and the specific advantages and disadvantages of linear and nonlinear Kalman filtering approaches are evaluated. To illustrate the range of problems which benefit from use of the filter, a comprehensive literature survey of the application of Kalman filtering to chemical problems is provided.     

Boron chemistry in a new light

Photocatalysis has recently opened up new avenues for the generation of radical species under visible light irradiation conditions. A particularly fascinating class of photocatalyzed transformations relies on the activation of stable boron species with visible-light since it allows the creation of boryl and/or carbon radicals through single electron transfer or energy transfer without the need for specific and costly equipment. This new paradigm has found numerous applications in synthetic organic chemistry, catalysis, and macromolecular chemistry. In this minireview, the concepts underlying photoactivation of boron-species as well as applications to the creation of C–H, C–C, C–O, B–C and B–S bond are discussed.     

Topological polymer chemistry by programmed self-assembly and effective linking chemistry

Ongoing challenges in topological polymer chemistry are reviewed. In particular, we focus on recent developments in an “electrostatic self-assembly and covalent fixation (ESA–CF)” process in conjunction with effective linking/cleaving chemistry including a metathesis process and an alkyne–azide click reaction. A variety of novel cyclic polymers having specific functional groups and unprecedented multicyclic macromolecular topologies have been realized by combining intriguing synthetic protocols.     

A database of new zeolite-like materials

We here describe a database of computationally predicted zeolite-like materials. These crystals were discovered by a Monte Carlo search for zeolite-like materials. Positions of Si atoms as well as unit cell, space group, density, and number of crystallographically unique atoms were explored in the construction of this database. The database contains over 2.6 M unique structures. Roughly 15% of these are within +30 kJ mol(-1) Si of α-quartz, the band in which most of the known zeolites lie. These structures have topological, geometrical, and diffraction characteristics that are similar to those of known zeolites. The database is the result of refinement by two interatomic potentials that both satisfy the Pauli exclusion principle. The database has been deposited in the publicly available PCOD database and in www.hypotheticalzeolites.net/database/deem/.     

Ultrasonics in organoborane chemistry. A novel and powerful method for rapid hydroboration

Ultrasound enhances remarkably the rates of certain hydroborations which are slow under normal conditions.     

A peptide motif recognizing a polymer stereoregularity

A combinatorial phage display method was applied to films composed of a stereoregular polymer of methacrylates. The phage clones with selective affinity for isotactic (it) poly(methyl methacrylate) (PMMA) were isolated. Greater amounts of the phage clones bound to it-PMMA, compared to other stereoregular PMMAs. The phage expressing ELWRPTR most strongly bound to the polymer, and the selectivity was also the best. The peptide motif essential for the specific interaction with the stereoregular polymer was revealed.     

A sense of new beginnings in positron and positronium chemistry

Conclusion This has been the most future-oriented workshop in my memory. Many participants are thinking about the next experiments to perform, new phenomena to study, and new parameters to measure. We look forward to new optical correlations, both with exciting radiation and intrinsic fluorescence. We very badly need positron and positronium binding energies to atoms, molecules, and radicals. We very badly need work functions, band gaps and edges, and trap depths for positron and positronium in molecular liquids and solids. The binding energies of positronium itself in various molecular materials is an important and poorly understood quantity. New data presented at this workshop on the energy of positronium at its formation, and its thermalization time, are most significant,³ and we look forward to refinements in those measurements and in their interpretation. We need to understand the thermalization times of positrons much better than we do. The role of voids and/or surfaces in positronium formation needs to be illuminated, including numerical estimates and measurements for the cross section of this most important process.Finally, a note of thanks and appreciation to the hard-working organizers of this workshop, without whose selfless labors we would not have enjoyed the many benefits of talking face to face with our colleagues from far away.     

A quantum chemistry study: a new kind of boron nitrides

At the B3LYP/6-311+G** and the BP86/6-311+G** levels of theory, BNN, H(3)BNN, NNBH(2)-BH(2)NN, (BNN)(2)H(2), NNBBNN, (BNN)(3) (+), (BNN)(4), (BNN)(4) (2+), (BNN)(4) (2-), B(4)(NN)(2), (BNN)(5) (-), (BNN)(6), (BNN)(7) (+), and (BNN)(8) (2+) are investigated. Neutral (BNN)(4) is aromatic with its triplet state but antiaromatic with its singlet state. (BNN)(4) dication favors D(2d) structure, while (BNN)(4) dianion favors a planar D(4h) structure. (BNN)(3) (+), (BNN)(4) (2-), (BNN)(5) (-), (BNN)(6), (BNN)(7) (+), (BNN)(7) (3-), (BNN)(8) (2+), and (BNN)(8) (2-) are all aromatic with planar monocyclic conformation, following the 4n + 2 rule. Moreover, according to the CASSCF and MRCI calculations, the planar B(4)(NN)(2) of D(2h) symmetry prefers to be a sigma-pi diradical in spite of open-shell singlet or triplet and is also aromatic. Akin to the sigma-pi back interaction in compounds containing transition metal, there exists the sigma-pi back interaction between boron and N(2) ligand among some species reported herein, which strengthens B(-)N bond but activates N-N bond, especially in (4)Sigma(-) BNN. The T-shaped structure lies lowest in energy among seven isomers of the (BNN)(2)H(2) dimer, and the parallel-displaced structure is favored between two isomers of the (BNN)(6) dimer.     

一系列新型硼氮化合物的理论研究

借助密度泛函理论,在B3LYP/6-311 G**和BP86/6-311 G**水平上,对一系列包含BNN单元的硼氮化合物BNN,H3BNN,NNBH2-BH2NN,(BNN)2H2,NN-BBNN,(BNN)3 ,(BNN)42 ,(BNN)5-,(BNN)6,(BNN)7 和(BNN)82 进行了理论计算研究.结果表明:在这些硼氮化合物中,尤其是BNN,B原子和N2配体之间存在着σ-π反馈作用.这种作用增强了B-N键,而活化了N-N键.结果还显示,(BNN)3 ,(BNN)42 ,(BNN)5-,(BNN)6,(BNN)7 和(BNN)82 都是具有平面单环结构并且满足4n 2规则的芳香性体系.     

A triazene-based new photolabile linker in solid phase chemistry

An extension of the T2 linker methodology by showing its applicability as a photocleavable linker is reported. Photocleavage was carried out with 355 nm UV laser irradiation (3ω Nd-YAG) in methanol/diethyl ether and is suitable for protected amino acid derivatives, as well as simple small organic molecules including resin-bound biotin. The linker is stable under a wide range of conditions with the exception of strongly acidic media.     

A rapid and effective synthesis of propylene carbonate using a supercritical CO2-ionic liquid system

The synthesis of propylene carbonate from propylene oxide and carbon dioxide under supercritical conditions in the presence of 1-octyl-3-methylimidazolium tetrafluoroborate was achieved in nearly 100% yield and 100% selectivity within 5 minutes, whose TOF value is 77 times larger than those so far reported.     

Infrared intensities: A new tool in chemistry.

The interpretation of the infrared intensities in terms of atomic polar tensors and of electrooptical parameters allows to derive rich information on the charge distribution in the molecules. Using the results of several studies of this kind, it is now possible to derive information on intramolecular and intermolecular interactions even from “poor” data such as absolute intensities of whole regions in the spectrum or even from relative intensities.