Direct Metalation of 1,3,5,7-Tetranitrocubane with Amides of Tin and Lead. Preparation and Chemistry of o-Nitrostannanes and o-Nitroplumbanes in the Cubyl Series(1)

Trialkyltin and trialkyllead amides react directly and remarkably easily with 1,3,5,7-tetranitrocubane to form mono- to tetrakis(trialkyltin)- and -(trialkyllead) tetranitrocubanes. These are all stable compounds. The X-ray crystallographic properties of some are given. The (trialkylstannyl)cubanes react with electrophiles such as bromine with unexpected cleavage of alkyltin bonds rather than cubyl-tin bonds. On the other hand, the (trialkylplumbyl)cubanes do ultimately undergo cubyl-lead bond cleavage. This provides a useful way to achieve substitution on the cubane nucleus and provides access to compounds such as 1,3,5,7-tetrabromo-2,4,6,8-tetranitrocubane. The lead derivatives of tetranitrocubane are also useful for making 1,2,3,5,7-pentanitrocubane and 1,2,3,4,5,7-hexanitrocubane.     

Computer-aided determination of relative stereochemistry and 3D models of complex organic molecules from 2D NMR spectra

A method for elucidation of the relative stereoconfiguration of natural product molecular structures and their 3D models based on NOE data and the application of a genetic algorithm is described. The method is applicable mainly for rigid polycyclic structures commonly encountered in natural products. It is demonstrated that the technique of simulated annealing cannot be easily used when dealing with low-weight fused ring molecules but the application of a genetic algorithm is proven successful. Examples of a typical genetic algorithm workflow and the optimization of the algorithmic parameters are discussed. The efficiency of the approach developed here is demonstrated on the complex natural products of both Taxol^® (C₄₇H₅₁NO₁₄) and brevetoxin B (C₅₀H₇₀O₁₄).     

Structure elucidation from 2D NMR spectra using the StrucEluc expert system: detection and removal of contradictions in the data

The elucidation of chemical structures from 2D NMR data commonly utilizes a combination of COSY, HMQC/HSQC, and HMBC data. Generally COSY connectivities are assumed to mostly describe the separation of protons that are separated by 1 skeletal bond (3JHH), while HMBC connectivities represent protons separated from carbon atoms by 1 to 2 skeletal bonds (2JCH and 3JCH). Obviously COSY and HMBC connectivities of lengths greater than those described have been detected. Though experimental techniques have recently been described to aid in the identification of the nature of the couplings the detection of whether a coupling is 2-bond or greater still remains a challenge in most laboratories. In the StrucEluc software system the common lengths of the connectivities, 1-bond for COSY and 1- or 2-bond for HMBC, derived from 2D NMR data are set as the default. Therefore, in the presence of any extended connectivities contradictions can appear in the 2D NMR data. In this article, algorithmic methods for the detection and removal of contradictions in 2D NMR data that have been developed in support of StrucEluc are described. The methods are based on the analysis of molecular connectivity diagrams, MCDs. These methods have been implemented in the StrucEluc system and tested by solving 50 structural problems with 2D NMR spectral data containing contradictions. The presence of contradictions was detected by the algorithm in 90% of the cases, and the contradictions were automatically removed in approximately 50% of the problems. A method of "fuzzy" structure generation in the presence of contradictions has been suggested and successfully tested in this work. This work will demonstrate examples of the application of developed methods to a number of structural problems.     

Automated structure elucidation — the benefits of a symbiotic relationship between the spectroscopist and the expert system

Characteristic features of a new expert system StrucEluc are described. The system is intended for the structure elucidation of complex organic molecules using a variety of spectroscopic data including 2D NMR. We review here the results of challenging this system with over 100 structure elucidation problems where the 2D NMR peak tables presented in original journal publications provided the input data. This contribution is focused on methods to overcome difficult situations that can arise when contradictions are present in the input data and/or when the structure is underdetermined as a result of insufficient 2D NMR correlations. Methods by which to address these situations are examined. It has been shown that synergy between the spectroscopist and the expert system allows the solution of problems that seemed to be hopeless at the outset of the structure elucidation process.     

New approach to chemical modification of PIM-1 for gas separation membranes

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Excitonic Emission in van der Waals Nanotubes of Transition Metal Dichalcogenides

Nanotubes (NTs) of transition metal dichalcogenides (TMDs), were first synthesized more than a quarter of a century ago; nevertheless, many of their optical properties have so far remained basically unknown. Herein, the state of the art in the knowledge of the optical properties of TMD NTs is presented. First, general properties of multilayered crystals are evaluated, and available data on related NTs are analyzed. Then, the technology for the formation and the structural characteristics of NTs are represented, focusing on the structures synthesized by chemical transport reaction. The core of this work is the presentation of the ability of synthesized TMD NTs to emit bright photoluminescence (PL), which has been discovered recently. By means of micro‐PL spectroscopy of individual tubes, we show that excitonic transitions relevant to both direct and indirect band gaps contribute to the emission spectra of the NTs despite having the dozens of monolayers in their walls. The performance of the tubes as efficient optical resonators is highlighted, where confined optical modes strongly affect the emission. Finally, a brief conclusion is presented, along with an outlook of the future studies of this novel radiative member of the NTs family, which have unique potential for different nanophotonics applications.     

Association of Spherical Porous Nanocluster Keplerate-Type Polyoxometalate Mo<Subscript>72</Subscript>Fe<Subscript>30</Subscript> with Biologically Active Substances

The peculiarities of formation of ionic associates of the spherical porous nanocluster polyoxometalate [Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₁₂{Mo₂O₇(H₂O)}₂{H₂Mo₂O₈(H₂O)}(H₂O)₉₁] ~ 150H₂O with biologically active substances, in particular, thiamine chloride using the methods of UV/Vis spectroscopy, pH-metry, laser light scattering (the measurement of Zeta potential and particle size distribution), Raman spectroscopy, infrared spectroscopy and inductively coupled plasma atomic emission spectroscopy has been studied. The location of thiamine molecules on POM’s surface is given. The solubility product of associate was estimated. The formation of molecular associates of polyoxometalate with insulin, albumin has been shown. Using the meglumine acridonacetate the influence of complexing agents on the possibility of obtaining associates on the basis of [Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₁₂{Mo₂O₇(H₂O)}₂{H₂Mo₂O₈(H₂O)}(H₂O)₉₁] ~ 150H₂O has been studied.     

A new promising Pt(Mo2C) catalyst for hydrogen evolution reaction prepared by galvanic displacement reaction

Journal of Solid State Electrochemistry - A new method for the synthesis of Pt(Mo2C) catalysts using the redox reaction between Mo2C and solution containing potassium tetracholoplatinate (II) is...