Structural Evidence

Structure determinations by X-ray and electron diffraction methods have demonstrated the presence of unbranched chains of up to six divalent sulfur atoms in inorganic polysulfides, four divalent ones in salts of polythionic acids, and three in disulfonyl, dialkyl, and cyanogen derivatives. The synthetic and Raman-spectroscopic work of Feh6r has established the presence of unbranched structures with up to five sulfur atoms in organic polysulfides, and eight in the cyanogen polysulfide, polysulfur dichloride, and hydrogen polysulfide series. The results are supported by extensive physicochemical evidence of less conclusive nature. 

There exist in the literature claims concerning the occurrence of branching in particular compounds the more definite of these have been refuted in recent years. Backer and co-workers (10, 11) formulated some cyclic di- and trisulfides with branched sulfur groupings from a comparison of their ultraviolet and infrared spectra with those of other di- and polysulfides, Schotte (202) concluded that branching does not occur. Baroni (15), on the basis of parachor measurements, assigned isomeric branched 

In fact, no substantiated example of branching is known. Feh r (p. 313 in ref. 56) states that We have tried for many years to prepare branched-chain polysulfides, but without success.  

The only instances in which sulfur forms only one bond to sulfur and none to another atom, are apparently in the polysulfide ions as terminal atoms, and in the thiosulfate and thiosulfonate ions, S—S03 and 

S—S02R, in which the S—S bond appears to be partly double. Thus, crystal structure determinations of sodium thiosulfate pentahydrate (213) and sodium methanethiosulfonate monohydrate (100) have shown the S—S bond to be 1.97-1.98 A, as compared with 2.04 A in orthorhombic sulfur. The reason (87) why coordinated structures are unstable relative to unbranched ones may be that a sulfur atom as an electroneutral, nonpolar acceptor can add only to donors which are less electronegative, or to donors which can expand the valency shell for jr-bonding. 

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Usually, the cychc isomers 272 are preferred in the sohd state. X-Ray structural evidence was obtained for compound 272 [R = COPh, R = Me, R = R" = H, R = CF3 X = O (92KK1184)]. In solution, the cyclic and ring-opened isomers are found in equihbria in ratios depending on polarity of the solvent and structural factors (see 88KGS3 95ZOB705 96AHC(66)1 for reviews). 

P. Griinberg, R. Schreiber, Y. Pang, M.B. Brodsky, and H. Sowers, Layered magnetic structures Evidence for antiferromagnetic coupling of Fe layers across Cr interlayers, Phys. Rev. Lett. 57, 2442 (1986). 

Figure 3.55 Structural evidence for the reduction in strain attending the formation of a...

Structural evidence Only one dichlorobenzene in which the two chlorine atoms are attached to adjacent carbon atoms exists. 

Thus the x-ray data do not decide between this structure and a truly plane structure. Evidence from another source is at hand, however. A plane C03= or N03 ion should show three characteristic fundamental vibrational frequencies. These have been observed as reflection maxima in the infra-red region. But two of the maxima, at 7 m and 14m, are double,27 and this doubling, which is not explicable with a plane configuration, is just that required by a pyramidal structure, the separation of the components giving the frequency of inversion of the pyramid.28... 

Reinen D, Friebel C (1979) Local and Cooperative Jahn-Teller Interactions in Model Structures. Spectroscopic and Structural Evidence. 37 1-60 Reinen D (1970) Kationenverteilung zweiwertiger 3dn-Ionen in oxidischen SpineU-, Granat und anderen Strukturen. 7 114-154... 

The molyhdopterin cofactor, as found in different enzymes, may be present either as the nucleoside monophosphate or in the dinucleotide form. In some cases the molybdenum atom binds one single cofactor molecule, while in others, two pterin cofactors coordinate the metal. Molyhdopterin cytosine dinucleotide (MCD) is found in AORs from sulfate reducers, and molyhdopterin adenine dinucleotide and molyb-dopterin hypoxanthine dinucleotide were reported for other enzymes (205). The first structural evidence for binding of the dithiolene group of the pterin tricyclic system to molybdenum was shown for the AOR from Pyrococcus furiosus and D. gigas (199). In the latter, one molyb-dopterin cytosine dinucleotide (MCD) is used for molybdenum ligation. Two molecules of MGD are present in the formate dehydrogenase and nitrate reductase. 

Successive 1,4 units in the synthetic polyisoprene chain evidently are preponderantly arranged in head-to-tail sequence, although an appreciable proportion of head-to-head and tail-to-tail junctions appears to be present as well. Apparently the growing radical adds preferentially to one of the two ends of the monomer. Which of the reactions (6) or (7) is the preferred process cannot be decided from these results alone, however. Positive identification of both 1,2 and 3,4 units in the infrared spectrum shows that both addition reactions take place during the polymerization of isoprene. The relative contributions of the alternative addition processes cannot be ascertained from the proportions of these two units, however, inasmuch as the product radicals formed in reactions (6) and (7), may differ markedly in their preference for addition in one or the other of the two resonance forms available to each. We may conclude merely that structural evidence indicates a preference for oriented (i.e., head-to-tail) additions but that the 1,4 units of synthetic polyisoprene are by no means as consistently arranged in head-to-tail sequence as in the naturally occurring poly-isoprenes. 

Characterization of various types of damage to DNA by oxygen-derived species can be achieved by the technique of gas chromatography-mass spectrometry (GC-MS), which may be applied to DNA itself or to DNA-protein complexes such as chromatin (Dizdaroglu, 1991). For GC-MS, the DNA or chromatin is hydrolysed (usually by heating with formic acid) and the products are converted to volatile derivatives, which are separated by gas chromatography and conclusively identified by the structural evidence provided by a mass spectrometer. Stable isotope-labelled bases may be used as internal standards... 

Lewis, C.D. and Laemmli, U.K. (1982). Higher order metaphase chromosome structure evidence for metal-loprotein interactions. Cell 29, 171-181. 

While structural evidence indicates that radical 44 is delocalized through the five carbon centers, it has been suggested that annelation of the cyclopentadienyl framework with rigid bicyclic systems leads to localized structures, as in compound 45 (Fig. 7.20). The X-ray structure of 45 indicates that the rather long distances between C1-C2 (1.445 A), C1-C5 (1.442 A), and C3-C4 (1.482 A) correspond to... 

The authors have now reviewed in detail four cases of unexpected death following the use of neck holds in PCP-intoxicated individuals. In all of the cases, multiple carotid compression holds had been attempted, according to the history. Skin abrasions, hemorrhage into the soft tissues of the neck, and fractures of the hyoid bone and thyroid cartilage provide structural evidence of the application of substantial force to the neck. On autopsy, there has been no evidence of lethal injuries to the bronchial tree, bra in, or heart. 

Radiologic evidence may be misleading because structural evidence of OA correlates poorly with symptoms. 

Galliot, B., Dolle, P., Vigeron, M., Featherstone, M., Baron, A., and Duboule, D. (1989). The mouse Hox-1.4 gene primary structure, evidence for promoter activity and expression during development. Development 107 343-359. 

A compound for which there is spectroscopic and structural evidence for more conventional p-p 7r-bonding involving main group 3 and 4 elements was not reported until recently.538 Treatment of the stable phosphi-nocarbene (R2N)2PC(SiMe3) with MMe3 (M = Al, Ga, or In) results in the product depicted by... 

The first copper(I) complex of tris(hydroxymethyl)phosphine ((760) tetrahedral) has been reported by Samuelson and co-workers. This group addressed the question of anion-controlled nuclearity and metal-metal distances in copper(I)-bis(diphenylphosphino)methane complexes, and in this endeavor they reported the structures of complexes (761) (Cu-Cu separation 3.005-3.128 A), (762) (Cu-Cu separation 3.165 A) and (763) (tetrahedral Cu-Cu 3.293 A). 6 They synthesized and provided structural evidence of oxy anion- encapsulated copper(I) complexes of this ligand. The complexes (764) (distorted tetrahedral Cu-Cu 3.143 A), (765) (distorted tetrahedral Cu-Cu 3.424A), (766) (distorted trigonal Cu-Cu 3.170A), and (767) (Cu-Cu 3.032-3.077A) were reported. They studied solid-state emission spectra of these complexes.567 During this pursuit they... 

Barondeau DP, Tainer JA, Getzoff ED (2006) Structural evidence for an enolate intermediate in GFP fluorophore biosynthesis. J Am Chem Soc 128 3166-3168... 

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