Multidimensional molecular materials

Metal organic co-ordination frameworks have attracted much interest recently [1-5] owing to their potential as materials for solvent-inclusion [6-11] or gas adsorption [12-15] or with electronic [16, 17] or non-linear optical properties [18,19]. The rational design and targeted synthesis of multidimensional molecular architectures is also of significance in the quest not only to understand how crystalline and ordered materials may be engineered [20-22], but also to elucidate the underlying processes of self-assembly [23-27]. 

These structures are unique for several reasons. First, they represent three new multidimensional 12-MR systems, which are rare even among zeolites. Second, the amount of framework substitution by metals such as Mn2+ and Mg2+ was unknown prior to this series. Also, the ease of forming both gallium and aluminum phosphates appear to be comparable. Finally, it would appear the charge-matching approach has proven to be a successful strategy for the synthesis of new molecular sieves. It is not clear whether these materials are thermally or hydrothermally stable but they do represent novel pore structures that should impart some unusual properties. 

New techniques for data analysis and improvements in instrumentation have now made it possible to carry out stmctural and conformational studies of biopolymers including proteins, polysaccharides, and nucleic acids. NMR, which may be done on noncrystalline materials in solution, provides a technique complementary to X-ray diffraction, which requires crystals for analysis. One-dimensional NMR, as described to this point, can offer structural data for smaller molecules. But proteins and other biopolymers with large numbers of protons will yield a very crowded spectrum with many overlapping lines. In multidimensional NMR (2-D, 3-D, 4-D), peaks are spread out through two or more axes to improve resolution. The techniques of correlation spectroscopy (COSY), nuclear Overhausser effect spectroscopy (NOESY), and transverse relaxation-optimized spectroscopy (TROSY) depend on the observation that nonequivalent protons interact with each other. By using multiple-pulse techniques, it is possible to perturb one nucleus and observe the effect on the spin states of other nuclei. The availability of powerful computers and Fourier transform (FT) calculations makes it possible to elucidate structures of proteins up to 40,000 daltons in molecular mass and there is future promise for studies on proteins over 100,000... 

The reviewed results showed that online coupling of separation techniques to multiple analytical detectors can provide the most powerful tools for exploring multidimensional chemical space of NOM and HS. The huge potential of applying this approach to unfolding molecular complexity of natural materials is best of all demonstrated by the results of offline characterization of the fractionated humic materials which are discussed below. 

Multidimensional NMR spectroscopy proves to be a powerful method to reveal structural and dynamical information at the molecular level in elastomers. Residual dipolar couplings can be measured site-selectively and correlated with the crosslink density and mechanical stress. The local segmental order and information on local molecular motions can be also obtained with newly developed 2D NMR methods. The information at the molecular level can be correlated with macroscopic properties of elastomers and provides the basis for a better design of material properties for specific applications. 

Polymers are typically complex mixtures in which the composition depends on polymerization kinetics and mechanism and process conditions. To obtain polymeric materials of desired characteristics, polymer processing must be carefully controlled and monitored. Furthermore, one needs to understand the influence of molecular parameters on polymer properties and end-use performance. Molar mass distribution and average chemical composition may no longer provide sufficient information for process and quality control nor define structure-property relationships. Modern characterization methods now require multidimensional analytical approaches rather then average properties of the whole sample [1]. 

From numerous results achieved using combinatorial and high-throughput methods, the most successful have been in the areas of molecular imprinting, polymeric compositions, catalytic metals for field-effect devices, and metal oxides for conductometric sensors. In those materials, the desired selectivity and sensitivity have been achieved by the exploration of multidimensional chemical composition and process parameters space at a previously unavailable level of detail at a fraction of time required for conventional one-at-a-time experiments. These new tools provided the opportunity for the more challenging, yet more rewarding explorations that previously were too time consuming to pursue. 

The effort must be multidimensional, taking into account all of the properties and characteristics of the material. Extreme caution is advised when average structures are used. For example, models that could better explain the asphaltene behavior should be selected from the various parts of the molecular weight-polarity diagram. The easiest would be to select the two extremes of this diagram and design highly polar and neutral species. This would be the amphoteric and substantially less polar (or near neutral) constituents of asphaltenes (IS, 19, 93). 

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