Characterization example

Class " Colour Surface (T/K) Spectral characterization Examples... 

Salt-like carbides containing individual C anions are sometimes called methanides since they yield predominantly CH4 on hydrolysis. Be2C and AI4C3 are the best-characterized examples, indicating the importance of small... 

The simplest solid—solid reactions are those involving two solid reactants and a single barrier product phase. The principles used in interpreting the results of kinetic studies on such systems, and which have been described above, can be modified for application to more complex systems. Many of these complex systems have been resolved into a series of interconnected binary reactions and some of the more fully characterized examples have already been mentioned. While certain of these rate processes are of considerable technological importance, e.g. to the cement industry [1], the difficulties of investigation are such that few quantitative kinetic studies have been attempted. Attention has more frequently been restricted to the qualitative identifications of intermediate and product phases, or, at best, empirical rate measurements for technological purposes. 

Although not yet published in a journal, according to thesis work, the vanadium compounds VSCl (11), VSBr, and VSI (208) seem to exist. Numerous niobium chalcogenide halides have been reported, and among these are the best characterized examples of Group VB (see Table X). Only two tantalum compounds, TaSjCU (361) and TaSCls (13) have thus far been described in the literature. 

Barton and coworkers have shown that proteins can in fact modulate the DNA electron transfer [168]. Methyltransferases are enzymes that recognize distinct DNA sequences, e.g., 5 -G CGC-3, and effect methylation by extrading the target base cytosine ( C) completely out of the DNA duplex while the remainder of the double helix is left intact. The methyltransferase Hha 1-DNA complex is a well-characterized example, revealing that the structure of the DNA is significantly but locally distorted [169,170]. In a recent study, Raj ski et al. used DNA duplex 20 containing the M.Hha I binding site between two oxidizable 5 -GG-3 sites [168] (Fig. 20). The duplex contains a complementary strand, selectively 5 -modified with a Rh intercalator that can function as a photooxidant. Upon... 

Type IV collagen, the best-characterized example of a coUagen with discontinuous triple helices, is an important component of basement membranes, where it forms a mesh-hke network. 

Of all the known sites for metal-ion binding to the heteroatoms of DNA bases, G-N3 is the most elusive. The adjacent 2-amino group is often considered to offer steric hindrance to binding at this site. However, while this undoubtedly influences the chemistry it does not preclude binding. The tri-metalated [ [Pt(N]3(9-Et G N1,N3,N7)]5 compound has for many years been the only structurally characterized example of an N3-coordinated guanine (66). A second example has now been reported, the tetranuclear octacation 16 (56). In this complex both the N7 and N3 atoms are bound to Pd2+ (Fig. 22). The molecule presents an interesting new architecture for a guanine-tetramer. Such structures are well known in DNA chemistry and are almost inevitably metal-ion stabilized (67,68). 

Notes Well-characterized examples for mutant loci and their respective gene products (when known) in the mouse are given (see text for references). 

Some antagonists combine the ability to block open ion channels with a competitive action at or near the agonist binding site. A well-characterized example is the nicotinic blocker tubocurarine (see Chapter 6). Agonists may also be open channel blockers, thus limiting the maximal response that they can elicit. Such agents (e g., decamethonium) may therefore behave as partial agonists when tested on an intact tissue ... 

The monovalent Co chemistry of amines is sparse. No structurally characterized example of low-valent Co complexed exclusively to amines is known. At low potentials and in non-aqueous solutions, Co1 amines have been identified electrochemically, but usually in the presence of co-ligands that stabilize the reduced complex. At low potential, the putative monovalent [Co(cyclam)]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) in NaOH solution catalyzes the reduction of both nitrate and nitrite to give mixtures of hydroxylamine and ammonia.100 Mixed N-donor systems bearing 7r-acceptor imine ligands in addition to amines are well known, but these examples are discussed separately in Section 6.1.2.1.3. 

Novel cationic methyl and neutral methyl, chloro Pd11 complexes have been synthesized with various functionalized imidazole ligands. For the first time, structurally characterized examples of this type of Pd complex could be obtained. The chelate ligand is shown to adopt a boat conformation. Inversion of the chelate ring was established by NMR spectroscopy. Depending on electronic and steric features of the ligand, the complexes can act as catalysts in the CO/ethylene as well as the Fleck reaction.186... 

In a study of the hydrolysis of platinum(II)-nitrile complexes to afford the corresponding amides, the first well-characterized examples of platinum(II) complexes that dimerize spontaneously to form weakly bonded Pt-Pt dimers with an unsupported intermetallic bond have been described.166 For example, treatment of cw-[PtCl2(NCBut)2] with excess KOH affords the amide species cw-[PtCl2 HN=C(OH)But 2], which exists as a dimer (49) both in solution and in the solid state, with a Pt-Pt bond length of 3.165(1) A, as determined by X-ray crystallography. Four... 

The first structurally characterized example of a platinum(II) derivative containing a saturated tetraamine macrocycle, 6,13-dimethyl-l,4,8,ll-tetraazacyclotetradecane-6,13-diamine has been reported (80).251 The species crystallizes as the colorless tetra-cationic complex from dilute HC104 solution by slow evaporation, where the two pendant primary amines are protonated. Other macrocyclic tetraamine complexes including [Pt([14]aneN4)]Cl2 have also been described.252... 

Again, weak coordination is expected for ether ligands to zinc, however, the larger number of structurally characterized examples is at least partially attributable to the frequent use of solvents such as diethyl ether or tetrahydrofuran which may provide additional ligands to the metal center. 

Dimeric zinc carboxylates do not have a large number of structurally characterized examples.362,363 Quite a number of monomeric carboxylate and particularly salicylate complexes have been structurally characterized.364"367... 

A structurally characterized example of a dinuclear zinc complex with a bridging phosphate monoester was provided by Kitajima and co-workers using the tris(pyrazolyl)borate ligand system. The P—O bond in a tris- or bis-phosphate ester is cleaved by a hydroxo zinc complex resulting in the monoester compound.443... 

Thioether ligand complexes are not very common, however, studies since the mid 1990s have dramatically increased the number of structurally characterized examples. Almost all of these compounds are with chelate or macrocyclic ligands that will stabilize thioether coordination. Mixed donor multidentate ligands containing thioether donors will be discussed in Section 6.8.11. 

The amino acid complexes [TcNCl(L)(PPh3)] (HL=L-cysteine, L-cysteine ethyl ester, cysteamine) have been prepared from [TcNC PPlfj ] or ASPI14 [TcNCU]/PPh3 [88]. The crystal structure of the L-cysteine ethyl ester complex 21 shows a Tc=N bond length of 1.605(3) A and the Tc atom displaced by 0.594(1) A above the square basal plane [88]. Other structurally characterized examples are the square pyramidal 22 with ONSP coordination and Tc=N 1.611(3) A [81], and 23 with NSPC1 coordination and Tc=N 1.615(7) A [89],... 

Table 2 Characterized examples of binary sulfur, selenium, and tellurium halogen cations...

In contrast, (BDTA)[Ni(dmit)2]2 has been fully characterized [89] (X-ray structure, magnetic susceptibility data, band structure and conductivity). It exhibits an SC behavior with a room-temperature conductivity of 0.1 S cm-1. Its magnetic behavior is dominated by AFM interactions, probably due to the coupling between the Ni(dmit)2 moieties. Although its properties are not spectacular, this complex is the first well-characterized example of a salt containing partially-oxidized Ni(dmit)2 moieties with a radical cation. 

Extracellular ligands (hormones, neurotrophins, carrier protein, adhesion molecules, small molecules, etc.) will bind to specific transmembrane receptors. This binding of specific ligand induces the concentration of the receptor in coated pits and internalization via clathrin-coated vesicles. One of the best studied and characterized examples of RME is the internalization of cholesterol by mammalian cells [69]. In the nervous system, there are a plethora of different membrane receptors that bind extracellular molecules, including neurotrophins, hormones and other cell modulators, being the best studied examples. This type of clathrin-mediated endocytosis is an amazingly efficient process, capable of concentrating... 

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