Centering types

The enantiophore query used in the search is derived from the CSP and directly built from a 3D structure model of the target CSP molecule, as it can be used today for the determination of new lead compounds [20, 21]. This procedure does not need an important modeling expertise. One can easily recognize the different center types in the receptor in question. These can be hydrogen-bond donors and acceptors, charged... 

Hasegawa, M., Suzuki, Y., Suzuki, F. and Nakanishi, H. (1972). Four-Center Type Photopolymerization in the Crystalline State, vol. 5, pp. 143-203. Kodansha, Tokyo... 

Type I copper centers, Type II copper centers Type III copper centers... 

Enzyme/ of Cu centers, Type, Ligands (M-L Bond Length, A)... 

Hasegawa et al. established the four-center-type photopolymerization of diolefin crystals, in which diolefin molecules are superimposed in the direction of the long molecular axes displaced by about half a molecule, as shown in... 

In addition to their varied biological roles, non-heme iron proteins contain a magnificent assortment of iron sites having a multitude of chemical and structural properties. Indeed, the catalog of iron centers is a bit like the taxonomy of insects—a seemingly limitless variation of a few structural themes, yet each new form sufficiently different to define a new species. It is beyond the scope of any review of non-heme iron proteins to be inclusive, and there are excellent recent reviews which detail selected topics. Rather, it is our intention to provide in one chapter an overview of the major classes with an emphasis on proteins for which a crystal structure is available. This review begins with a survey of the types of protein iron structures and a discussion of some methods and problems associated with establishing the iron center type. This should provide an introduction to readers less familiar with the area. Sections II to IV include the current status and recent developments for a limited number of proteins from the major iron classes. These have been chosen in the subjective vein of a limited review the omission of a topic does not indicate its relative importance or interest, only the limitation of space. The purpose of this section is to emphasize the diversity of iron center structures and functions. 

Fig. 1. Iron center types found in non-heme iron proteins.

The analysis presented on the next page, which requires consultation of reference 4 with respect to finer details of Sequence Rule 4, shows that the spiro-carbon is a stereogenic center type 1 of the rare type X(FFGG) (see Section 1.1.3.5.). 

At present, it is common knowledge that not only the photoreactivity, but also the stereochemistry, of the photoproduct is predictable from crystallographic information of starting olefin substrates. This ability of olefinic crystals to dimerize has been widely applied to the topochemical photocycloaddition polymerization of conjugated diolefinic compounds, so called "four-center type photopolymerizations" (7,8). All the photopolymerizable diolefin crystals are related to the center of symmetry mode (centrosymmetric -type crystal) and thus give polymers having cyclobutanes with a 1,3-trans configuration in the main chain on irradiation. 

The Fe-S Reaction Center (Type I Reaction Center) Photosynthesis in green sulfur bacteria involves the same three modules as in purple bacteria, but the process differs in several respects and involves additional enzymatic reactions (Fig. 19-47b). Excitation causes an electron to move from the reaction center to the cytochrome bei complex via a quinone carrier. Electron transfer through this complex powers proton transport and creates the proton-motive force used for ATP synthesis, just as in purple bacteria and in mitochondria. 

Reineke TM, Davis ME (2003) Structural effects of carbohydrate-containing polycations on gene delivery. 2. Charge center type. Bioconjug Chem 14(1) 255—261... 

The Body-Centered Type Crystal Structure of AlCr2... 

H12. Harris, N. L., Nadler, L. M., and Bhan, A. K., Immunohistologic characterization of two malignant lymphomas of germinal center type (centroblastic/centrocytic and centrocytic) with monoclonal antibodies. Follicular and diffuse lymphomas of small-cleaved-cell type are related but distinct entities. Am. J. Pathol. 117, 262-272 (1984). 

Q Submission name Site Center Type Status Dote... 

Transmission of directional properties from the monomer lattice reveals that many photopolymerizations of the four-center type are topotactic, but this information is insufficient to determine whether the reactions occur via homogeneous or heterogeneous phase-separation mechanisms. Powder x-ray studies done in... 

Reactions in which Carbonyl Croups in Glycosuloses are Converted into New Asymmetric Centers [Type 3]... 

Table 9.5 b. The intramolecular hydrogen bonds in y5-cyclodextrin undecahydrate at 120 K are all of the three-center type, one is a flip-flop. Data taken from a neutron diffraction study [455]. (For atom numbering see Part IIB, Chap. 18)... 

A significant number of intramolecular hydrogen bonds are observed. Those between the purine or pyrimidine bases and the sugar moieties have received particular attention because they can impart additional rigidity to the conformation of the nucleosides and nucleotides (Part IB, Chap. 9). Moreover, in the ribo series, there are frequently hydrogen bonds as the minor component of the three-center type between the vicinal hydroxyl groups. 

The intramolecular flip-flop hydrogen bonds are of the three-center type. All... 

This procedure is comparable to that used to analyze the N-H 0=C interactions in small molecule crystal structures described in Part I A, Chapter 2.3 [75]. For those groups with rotational freedom such as the -OH in serine, threonine, and tyrosine, the S-H in cysteine, and the - +NH3 in lysine and at the amino terminus, it is more difficult to guess the likely position of the hydrogen atoms. In these instances, the assumptions are made that the hydrogen bonds are of the two-center type when the R-X - A angle is close to 110°. The bonds are assumed to be linear with X-ft A angles of 180° (a better approximation would be to take the most commonly observed angle of —160°). 

In region II, y /4 < A, and therefore < 0, but k 0. This region relates to stable focuses where the system evolution toward the initial point is described by a spiral curve. Unstable focuses and nodes are arranged in regions III and IV > 0)> respectively, and also are separated by curve y /4 = A. On axis y = 0, there are center type points for which k = 0, 7 0, and ki 2 = i ir Region V relates to unstable exceptional points of the saddle type. Here, = 0 and k have different signs > 0, 2 0)-... 

Most realistic Hamiltonians with simple saddles do not appear in this form. In what follows, we show how to transform such a Hamiltonian into this form using Normal-Form theory [13]. The phase-space structures that form the subject of this review will then be expressed in terms of the normal-form coordinates (qi,..., q ,pi,..., p ). Therefore, before analyzing Eq. (2) we show that any Hamiltonian vector field in the neighborhood of an equilibrium point of saddle (g) center (8> center type can be transformed to the form of Eq. (2). 

Figure 6.8-19 Reaction scheme for the four-center-type polymerization of 2,5-distyryl pyrazine as well as part of the Raman spectra of the -DSP monomer and its polymer at 100 K.

The same publication also describes the investigation of the photopolymerization of 2,5-distyryl pyrazine (DSP) as an example of the four-center type polymerization of diolehnes. This reaction produces a highly crystalline polymer. 

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