ligand


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ligand

(lĭg`ənd), charged or uncharged molecule with one or more unshared pairs of electrons that can attach to a central metallic atomatom
[Gr.,=uncuttable (indivisible)], basic unit of matter; more properly, the smallest unit of a chemical element having the properties of that element. Structure of the Atom
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 or ionion,
atom or group of atoms having a net electric charge. Positive and Negative Electric Charges

A neutral atom or group of atoms becomes an ion by gaining or losing one or more electrons or protons.
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 to form an aggregate known as a complex ion (see chemical bondchemical bond,
mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as an
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). Some ligands that share electrons with metals form very stable complexes. Some common bases that act as ligands are water and ammonia molecules and halide, hydroxide, acetate, cyanide, thiocyanate, and nitrite anionsanion
, atom or group of atoms carrying a negative charge. The charge results because there are more electrons than protons in the anion. Anions can be formed from nonmetals by reduction (see oxidation and reduction) or from neutral acids (see acids and bases) or polar compounds
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. These ligands are monofunctional, i.e., they are attached by one unshared pair of electrons during complexing. Polyfunctional ligands, which bind to the metal ion with two or more pairs of electrons, are called chelates (see chelating agentschelating agents
. Certain organic compounds are capable of forming coordinate bonds (see chemical bond) with metals through two or more atoms of the organic compound; such organic compounds are called chelating agents.
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). Ethylenediamine-tetraacetate, a commonly used chelating compound, has six pairs of electrons to bind to metal ions. Electron-donating functional groups containing nitrogen, oxygen, sulfur, phosphorous, or carbon may act as ligands in complex biological systems. For example, in enzymes that need complexed metal ions to function, mercapto (sulfur-containing) groups and amino (nitrogen-containing) groups act as chelating agents; these groups fix the metal ion in a specific position. Other biologically important molecules, such as chlorophyll, vitamin B12, and heme, also have nitrogen-containing groups that donate electrons and have a chelating function.

ligand

[′lī·gənd]
(chemistry)
The molecule, ion, or group bound to the central atom in a chelate or a coordination compound; an example is the ammonia molecules in [Co(NH3)6]3+.
References in periodicals archive ?
As of today, Ligand's shares continue to plummet,1 contributing to a drop in the share price of as much as 65 percent since late September 2018, and destroying billions of dollars in shareholder value, even as markets recently achieved record highs.
Lemelson isn't the only short seller than has been highly critical of Ligand. Back in January, Citron Research's Andrew Left called Ligand's business model a "pipe dream" and accused Ligand of deceiving its shareholders.
The electronic absorption spectra of pyrazoloisoindol derivative ligand and its [Ag.sup.+], [Co.sup.2+], [Hg.sup.2+], [Zn.sup.2+], [Ni.sup.2+], [Cu.sup.2+], [Cd.sup.2+], [Mn.sup.2+], [Cr.sup.3+], [Fe.sup.3+] and [Pb.sup.2+] complexes in acetonitrile are shown in Figure 2.
Then, P(DEAMSt-co-St)L" used as ligand was dried at 40[degrees]C under vacuum for 24 h (Figure 1).
From a graph of a ligand, we obtain two important features: a hub and a cycle.
Research into optimisation of electronic and emissive characteristics in ruthenium complexes, in which the auxiliary ligand is systematically changed, has shown a well-defined relationship between the absorption and emission wavelengths and the electronic effect of the auxiliary ligand as measured by the electronic redox potential [14].
Keywords: ligand binding kinetics, ligand--receptor complex isomerization, drug residence time, mathematical modeling.
In the past decade, a great research effort around four-stranded guanine-rich DNA sequences known as G4-quadruplexes (G4) [1] and small molecule ligand interactions was motivated as both innovative basis for the design of novel inhibitors of telomerase activity [2] and selective fluorescent probes [3].
In contrast to this, bacterial lipopeptides such as the TLR2/6 ligand [Pam.sub.2][CysK.sub.4] have been shown to be stable and potent adjuvants that induce tolerogenic DC and regulatory T cell responses [8, 9].

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