Elements structural studies

Most structural studies have relied exclusively on the use of X-ray techniques but these elements have nuclei, " Sc, and La with abundances in excess of 99.9% and I respectively. 

The only crystalline phase which has been isolated has the formula Pu2(OH)2(SO )3(HaO). The appearance of this phase is quite remarkable because under similar conditions the other actinides which have been examined form phases of different composition (M(OH)2SOit, M=Th,U,Np). Thus, plutonium apparently lies at that point in the actinide series where the actinide contraction influences the chemistry such that elements in identical oxidation states will behave differently. The chemistry of plutonium in this system resembles that of zirconium and hafnium more than that of the lighter tetravalent actinides. Structural studies do reveal a common feature among the various hydroxysulfate compounds, however, i.e., the existence of double hydroxide bridges between metal atoms. This structural feature persists from zirconium through plutonium for compounds of stoichiometry M(OH)2SOit to M2 (OH) 2 (S0O 3 (H20) i,. Spectroscopic studies show similarities between Pu2 (OH) 2 (SOO 3 (H20) i, and the Pu(IV) polymer and suggest that common structural features may be present. 

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

Thus tin chemical shifts are of considerable use in structural studies. In addition, tin-element coupling constants are easily visible, and particularly in proton and carbon-13 spectra the relevant coupling constant values are of diagnostic use for example both tin-proton and tin-carbon coupling constants show a Karplus-type behaviour. 

Crystal Chemical Studies of the 5/-Series of Elements. VIII. Crystal Structure Studies of Uranium Silicides and of CeSia, NpSi3 and PuSia. Acta crystallogr. (London) 2, 94 (1949). 

Since the cell agglutinating form of ConA is a tetramer, a simple model for the potent activity of the polymers would be that the saccharide recognition elements presented by these agents can simultaneously bind two or more sites on the protein. A structural study of ConA reveals that adjacent saccharide binding... 

These figures are based on published and submitted papers. Among others, carboranes, donor-acceptor complexes of boron, ring molecules with silicon, phosphoranes, sul-fones have received much attention. The lack of gas-phase structural studied of other classes of compounds, e. g., sulfuranes, is also noteworthy. The above elements were selected as most typical. Much interest is concentrated however on other elements as well, which may have been somewhat neglected in the past. The increase of the amount of structural data is also facilitating demand for further extension of the circle of compounds studied. 

The results from structural studies on pectins isolated from a number of different plant sources have been reported in several papers and review articles (10,22-28). Chemical investigations of tobacco pectin (15,29-31) have demonstrated that its structure is consistent with the basic structural elements found in pectins from other sources. 

Once the normal modes are computed, the nature or properties of the excited vibrational states can also be of use for structural studies. The most obvious of these is the dipole strength, directly proportional to the IR absorption intensity, which will depend on the environment and stereochemistry of the amide group. A key element in utilizing these calculational results is the use of intensities, through spectral simulation, to compare pre-... 

Multifaceted aspects of research on biomedical polymers are shown in Table 1. End-use devices are manufactured starting from their original concept. To approach the target, materials design is carried out so that the materials can exhibit the desirable property when they are brought into contact with any particular biological element. Fundamental studies are carried out in order to elucidate structure-property relationships in the interaction of materials with biological elements. 

In the case of DNA, Troisi and Orlandi [26] have completed an integrated molecular dynamics/electronic structure study that examines precisely the issue of the dependence of the matrix element on geometry. These investigators studied a ten-base-pair double helical strand, whose interior contained two GC base pairs separated by four AT base pairs. They placed... 

In 2006, Lobinski et al.1 reported on the imaging and speciation analysis of trace elements to study the element distribution, oxidation state, metal site and metal structure in biological environments using mass spectrometric techniques (LA-ICP-MS, SIMS, MALDI-MS) and non-mass-spectrometric techniques such as micro-PIXE (proton induced X-ray emission), XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) -the latter two techniques are very sensitive due the use of a more intense synchrotron beam.1... 

X-ray and neutron diffraction methods and EXAFS spectroscopy are very useful in getting structural information of solvated ions. These methods, combined with molecular dynamics and Monte Carlo simulations, have been used extensively to study the structures of hydrated ions in water. Detailed results can be found in the review by Ohtaki and Radnai [17]. The structural study of solvated ions in lion-aqueous solvents has not been as extensive, partly because the low solubility of electrolytes in 11011-aqueous solvents limits the use of X-ray and neutron diffraction methods that need electrolyte of -1 M. However, this situation has been improved by EXAFS (applicable at -0.1 M), at least for ions of the elements with large atomic numbers, and the amount of data on ion-coordinating atom distances and solvation numbers for ions in non-aqueous solvents are growing [15 a, 18]. For example, according to the X-ray diffraction method, the lithium ion in for-mamide (FA) has, on average, 5.4 FA molecules as nearest neighbors with an... 

Mn is an essential element and occurs in a number of enzymes and is also known to stimulate enzymic activity by reversible association. ESR and NMR line broadening are particularly useful techniques for studying Mn" environments in proteins.148 These measurements and crystal structure studies (concanavalin, Table 11) suggest near regular octahedral coordination by O and N donors. 

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