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47-419: DCPG ( (S)-3,4-DCPG ) is a drug used in scientific research, which acts as a potent and subtype-selective agonist for the metabotropic glutamate receptor mGluR 8 . It has anticonvulsant effects in animal studies, and has also been investigated as a possible treatment for hyperalgesia . This anticonvulsant -related article is a stub . You can help Misplaced Pages by expanding it . Agonist From

94-417: A magnesium ion unless the cell is also experiencing depolarization . These differences show that agonists have unique mechanisms of action depending on the receptor activated and the response needed. The goal and process remains generally consistent however, with the primary mechanism of action requiring the binding of the agonist and the subsequent changes in conformation to cause the desired response at

141-444: A magnetic field . Electrons, due to their smaller mass and thus larger space-filling properties as matter waves , determine the size of atoms and molecules that possess any electrons at all. Thus, anions (negatively charged ions) are larger than the parent molecule or atom, as the excess electron(s) repel each other and add to the physical size of the ion, because its size is determined by its electron cloud . Cations are smaller than

188-421: A + or - is present, it indicates a +1 or -1 charge. To indicate a more severe charge, the number of additional or missing atoms is supplied, as seen in O 2 (negative charge, peroxide ) and He (positive charge, alpha particle ). Ions consisting of only a single atom are termed atomic or monatomic ions , while two or more atoms form molecular ions or polyatomic ions . In the case of physical ionization in

235-487: A combination of energy and entropy changes as the ions move away from each other to interact with the liquid. These stabilized species are more commonly found in the environment at low temperatures. A common example is the ions present in seawater, which are derived from dissolved salts. As charged objects, ions are attracted to opposite electric charges (positive to negative, and vice versa) and repelled by like charges. When they move, their trajectories can be deflected by

282-451: A drug is used therapeutically, it is important to understand the margin of safety that exists between the dose needed for the desired effect and the dose that produces unwanted and possibly dangerous side-effects (measured by the TD 50 , the dose that produces toxicity in 50% of individuals). This relationship, termed the therapeutic index , is defined as the ratio TD 50 : ED 50 . In general,

329-398: A fluid (gas or liquid), "ion pairs" are created by spontaneous molecule collisions, where each generated pair consists of a free electron and a positive ion. Ions are also created by chemical interactions, such as the dissolution of a salt in liquids, or by other means, such as passing a direct current through a conducting solution, dissolving an anode via ionization . The word ion

376-415: A gas is extensively used for the detection of radiation such as alpha , beta , gamma , and X-rays . The original ionization event in these instruments results in the formation of an "ion pair"; a positive ion and a free electron, by ion impact by the radiation on the gas molecules. The ionization chamber is the simplest of these detectors, and collects all the charges created by direct ionization within

423-400: A gas with less net electric charge is called the ionization potential , or ionization energy . The n th ionization energy of an atom is the energy required to detach its n th electron after the first n − 1 electrons have already been detached. Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of atomic orbitals

470-483: A minus indication "Anion (−)" indicates the negative charge. With a cation it is just the opposite: it has fewer electrons than protons, giving it a net positive charge, hence the indication "Cation (+)". Since the electric charge on a proton is equal in magnitude to the charge on an electron, the net electric charge on an ion is equal to the number of protons in the ion minus the number of electrons. An anion (−) ( / ˈ æ n ˌ aɪ . ən / ANN -eye-ən , from

517-440: A molecule/atom with multiple charges is by drawing out the signs multiple times, this is often seen with transition metals. Chemists sometimes circle the sign; this is merely ornamental and does not alter the chemical meaning. All three representations of Fe , Fe , and Fe shown in the figure, are thus equivalent. Monatomic ions are sometimes also denoted with Roman numerals , particularly in spectroscopy ; for example,

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564-402: A neutral atom or molecule is called ionization . Atoms can be ionized by bombardment with radiation , but the more usual process of ionization encountered in chemistry is the transfer of electrons between atoms or molecules. This transfer is usually driven by the attaining of stable ("closed shell") electronic configurations . Atoms will gain or lose electrons depending on which action takes

611-592: A positive charge, forming the ion NH + 3 . However, this ion is unstable, because it has an incomplete valence shell around the nitrogen atom, making it a very reactive radical ion. Due to the instability of radical ions, polyatomic and molecular ions are usually formed by gaining or losing elemental ions such as H , rather than gaining or losing electrons. This allows the molecule to preserve its stable electronic configuration while acquiring an electrical charge. The energy required to detach an electron in its lowest energy state from an atom or molecule of

658-411: A precise ionic gradient across membranes , the disruption of this gradient contributes to cell death. This is a common mechanism exploited by natural and artificial biocides , including the ion channels gramicidin and amphotericin (a fungicide ). Inorganic dissolved ions are a component of total dissolved solids , a widely known indicator of water quality . The ionizing effect of radiation on

705-414: A stable configuration. This property is known as electropositivity . Non-metals, on the other hand, are characterized by having an electron configuration just a few electrons short of a stable configuration. As such, they have the tendency to gain more electrons in order to achieve a stable configuration. This tendency is known as electronegativity . When a highly electropositive metal is combined with

752-401: A −2 charge is known as a dianion and an ion with a +2 charge is known as a dication . A zwitterion is a neutral molecule with positive and negative charges at different locations within that molecule. Cations and anions are measured by their ionic radius and they differ in relative size: "Cations are small, most of them less than 10 m (10 cm) in radius. But most anions are large, as is

799-627: Is equal and opposite to the charge of a proton , which is considered to be positive by convention. The net charge of an ion is not zero because its total number of electrons is unequal to its total number of protons. A cation is a positively charged ion with fewer electrons than protons (e.g. K (potassium ion)) while an anion is a negatively charged ion with more electrons than protons. (e.g. Cl (chloride ion) and OH (hydroxide ion)). Opposite electric charges are pulled towards one another by electrostatic force , so cations and anions attract each other and readily form ionic compounds . If only

846-429: Is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, sodium has one valence electron in its outermost shell, so in ionized form it is commonly found with one lost electron, as Na . On the other side of the periodic table, chlorine has seven valence electrons, so in ionized form it is commonly found with one gained electron, as Cl . Caesium has

893-615: Is in the breakdown of adenosine triphosphate ( ATP ), which provides the energy for many reactions in biological systems. Ions can be non-chemically prepared using various ion sources , usually involving high voltage or temperature. These are used in a multitude of devices such as mass spectrometers , optical emission spectrometers , particle accelerators , ion implanters , and ion engines . As reactive charged particles, they are also used in air purification by disrupting microbes, and in household items such as smoke detectors . As signalling and metabolism in organisms are controlled by

940-607: Is one short of the stable, filled shell with 8 electrons. Thus, a chlorine atom tends to gain an extra electron and attain a stable 8- electron configuration , becoming a chloride anion in the process: This driving force is what causes sodium and chlorine to undergo a chemical reaction, wherein the "extra" electron is transferred from sodium to chlorine, forming sodium cations and chloride anions. Being oppositely charged, these cations and anions form ionic bonds and combine to form sodium chloride , NaCl, more commonly known as table salt. Polyatomic and molecular ions are often formed by

987-451: Is possible to mix the notations for the individual metal centre with a polyatomic complex, as shown by the uranyl ion example. If an ion contains unpaired electrons , it is called a radical ion. Just like uncharged radicals, radical ions are very reactive. Polyatomic ions containing oxygen, such as carbonate and sulfate, are called oxyanions . Molecular ions that contain at least one carbon to hydrogen bond are called organic ions . If

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1034-432: Is written in superscript immediately after the chemical structure for the molecule/atom. The net charge is written with the magnitude before the sign; that is, a doubly charged cation is indicated as 2+ instead of +2 . However, the magnitude of the charge is omitted for singly charged molecules/atoms; for example, the sodium cation is indicated as Na and not Na . An alternative (and acceptable) way of showing

1081-549: The Fe (positively doubly charged) example seen above is referred to as Fe(III) , Fe or Fe III (Fe I for a neutral Fe atom, Fe II for a singly ionized Fe ion). The Roman numeral designates the formal oxidation state of an element, whereas the superscripted Indo-Arabic numerals denote the net charge. The two notations are, therefore, exchangeable for monatomic ions, but the Roman numerals cannot be applied to polyatomic ions. However, it

1128-463: The Greek αγωνιστής (agōnistēs), contestant; champion; rival < αγων (agōn), contest, combat; exertion, struggle < αγω (agō), I lead, lead towards, conduct; drive Receptors can be activated by either endogenous agonists (such as hormones and neurotransmitters ) or exogenous agonists (such as drugs ), resulting in a biological response. A physiological agonist is a substance that creates

1175-428: The muscarinic acetylcholine receptor and NMDA receptor and their respective agonists. For the muscarinic acetylcholine receptor , which is a G protein-coupled receptor (GPCR), the endogenous agonist is acetylcholine . The binding of this neurotransmitter causes the conformational changes that propagate a signal into the cell. The conformational changes are the primary effect of the agonist, and are related to

1222-537: The Greek word ἄνω ( ánō ), meaning "up" ) is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged). A cation (+) ( / ˈ k æ t ˌ aɪ . ən / KAT -eye-ən , from the Greek word κάτω ( kátō ), meaning "down" ) is an ion with fewer electrons than protons, giving it a positive charge. There are additional names used for ions with multiple charges. For example, an ion with

1269-514: The NMDA receptor requires both the endogenous agonists , N-methyl-D-aspartate (NMDA) and glycine . These co-agonists are both required to induce the conformational change needed for the NMDA receptor to allow flow through the ion channel , in this case calcium. An aspect demonstrated by the NMDA receptor is that the mechanism or response of agonists can be blocked by a variety of chemical and biological factors. NMDA receptors specifically are blocked by

1316-415: The agonist's binding affinity and agonist efficacy . Other agonists that bind to this receptor will fall under one of the different categories of agonist mentioned above based on their specific binding affinity and efficacy. The NMDA receptor is an example of an alternate mechanism of action, as the NMDA receptor requires co-agonists for activation. Rather than simply requiring a single specific agonist,

1363-519: The charge in an organic ion is formally centred on a carbon, it is termed a carbocation (if positively charged) or carbanion (if negatively charged). Monatomic ions are formed by the gain or loss of electrons to the valence shell (the outer-most electron shell) in an atom. The inner shells of an atom are filled with electrons that are tightly bound to the positively charged atomic nucleus , and so do not participate in this kind of chemical interaction. The process of gaining or losing electrons from

1410-455: The concentration of agonist needed to elicit half of the maximum biological response of the agonist. The EC 50 value is useful for comparing the potency of drugs with similar efficacies producing physiologically similar effects. The smaller the EC 50 value, the greater the potency of the agonist, the lower the concentration of drug that is required to elicit the maximum biological response. When

1457-409: The corresponding parent atom or molecule due to the smaller size of the electron cloud. One particular cation (that of hydrogen) contains no electrons, and thus consists of a single proton – much smaller than the parent hydrogen atom. Anion (−) and cation (+) indicate the net electric charge on an ion. An ion that has more electrons than protons, giving it a net negative charge, is named an anion, and

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1504-454: The gaining or losing of elemental ions such as a proton, H , in neutral molecules. For example, when ammonia , NH 3 , accepts a proton, H —a process called protonation —it forms the ammonium ion, NH + 4 . Ammonia and ammonium have the same number of electrons in essentially the same electronic configuration , but ammonium has an extra proton that gives it a net positive charge. Ammonia can also lose an electron to gain

1551-435: The gas through the application of an electric field. The Geiger–Müller tube and the proportional counter both use a phenomenon known as a Townsend avalanche to multiply the effect of the original ionizing event by means of a cascade effect whereby the free electrons are given sufficient energy by the electric field to release further electrons by ion impact. When writing the chemical formula for an ion, its net charge

1598-417: The least energy. For example, a sodium atom, Na, has a single electron in its valence shell, surrounding 2 stable, filled inner shells of 2 and 8 electrons. Since these filled shells are very stable, a sodium atom tends to lose its extra electron and attain this stable configuration, becoming a sodium cation in the process On the other hand, a chlorine atom, Cl, has 7 electrons in its valence shell, which

1645-409: The lowest measured ionization energy of all the elements and helium has the greatest. In general, the ionization energy of metals is much lower than the ionization energy of nonmetals , which is why, in general, metals will lose electrons to form positively charged ions and nonmetals will gain electrons to form negatively charged ions. Ionic bonding is a kind of chemical bonding that arises from

1692-503: The luminescence of the Sun to the existence of the Earth's ionosphere . Atoms in their ionic state may have a different color from neutral atoms, and thus light absorption by metal ions gives the color of gemstones . In both inorganic and organic chemistry (including biochemistry), the interaction of water and ions is often relevant for understanding properties of systems; an example of their importance

1739-479: The most common Earth anion, oxygen . From this fact it is apparent that most of the space of a crystal is occupied by the anion and that the cations fit into the spaces between them." The terms anion and cation (for ions that respectively travel to the anode and cathode during electrolysis) were introduced by Michael Faraday in 1834 following his consultation with William Whewell . Ions are ubiquitous in nature and are responsible for diverse phenomena from

1786-454: The mutual attraction of oppositely charged ions. Ions of like charge repel each other, and ions of opposite charge attract each other. Therefore, ions do not usually exist on their own, but will bind with ions of opposite charge to form a crystal lattice . The resulting compound is called an ionic compound , and is said to be held together by ionic bonding . In ionic compounds there arise characteristic distances between ion neighbours from which

1833-445: The narrower this margin, the more likely it is that the drug will produce unwanted effects. The therapeutic index emphasizes the importance of the margin of safety, as distinct from the potency, in determining the usefulness of a drug. Ion An ion ( / ˈ aɪ . ɒ n , - ən / ) is an atom or molecule with a net electrical charge . The charge of an electron is considered to be negative by convention and this charge

1880-497: The other. In correspondence with Faraday, Whewell also coined the words anode and cathode , as well as anion and cation as ions that are attracted to the respective electrodes. Svante Arrhenius put forth, in his 1884 dissertation, the explanation of the fact that solid crystalline salts dissociate into paired charged particles when dissolved, for which he would win the 1903 Nobel Prize in Chemistry. Arrhenius' explanation

1927-455: The potential to bind in different locations and in different ways depending on the type of agonist and the type of receptor. The process of binding is unique to the receptor-agonist relationship, but binding induces a conformational change and activates the receptor. This conformational change is often the result of small changes in charge or changes in protein folding when the agonist is bound. Two examples that demonstrate this process are

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1974-403: The receptor. This response as discussed above can vary from allowing flow of ions to activating a GPCR and transmitting a signal into the cell . Potency is the amount of agonist needed to elicit a desired response. The potency of an agonist is inversely related to its half maximal effective concentration (EC 50 ) value. The EC 50 can be measured for a given agonist by determining

2021-449: The same bodily responses but does not bind to the same receptor. New findings that broaden the conventional definition of pharmacology demonstrate that ligands can concurrently behave as agonist and antagonists at the same receptor, depending on effector pathways or tissue type. Terms that describe this phenomenon are " functional selectivity ", "protean agonism", or selective receptor modulators . As mentioned above, agonists have

2068-434: The spatial extension and the ionic radius of individual ions may be derived. The most common type of ionic bonding is seen in compounds of metals and nonmetals (except noble gases , which rarely form chemical compounds). Metals are characterized by having a small number of electrons in excess of a stable, closed-shell electronic configuration . As such, they have the tendency to lose these extra electrons in order to attain

2115-410: The then-unknown species that goes from one electrode to the other through an aqueous medium. Faraday did not know the nature of these species, but he knew that since metals dissolved into and entered a solution at one electrode and new metal came forth from a solution at the other electrode; that some kind of substance has moved through the solution in a current. This conveys matter from one place to

2162-525: Was coined from neuter present participle of Greek ἰέναι ( ienai ), meaning "to go". A cation is something that moves down ( Greek : κάτω , kato , meaning "down") and an anion is something that moves up ( Greek : ἄνω , ano , meaning "up"). They are so called because ions move toward the electrode of opposite charge. This term was introduced (after a suggestion by the English polymath William Whewell ) by English physicist and chemist Michael Faraday in 1834 for

2209-477: Was that in forming a solution, the salt dissociates into Faraday's ions, he proposed that ions formed even in the absence of an electric current. Ions in their gas-like state are highly reactive and will rapidly interact with ions of opposite charge to give neutral molecules or ionic salts. Ions are also produced in the liquid or solid state when salts interact with solvents (for example, water) to produce solvated ions , which are more stable, for reasons involving

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