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58-524: Each amino acid has an amine group and a carboxylic group . Amino acids link to one another by peptide bonds which form through a dehydration reaction that joins the carboxyl group of one amino acid to the amine group of the next in a head-to-tail manner to form a polypeptide chain. The chain has two ends – an amine group, the N-terminus, and an unbound carboxyl group, the C-terminus . When

116-615: A basic nitrogen atom with a lone pair . Formally, amines are derivatives of ammonia ( NH 3 ), wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group (these may respectively be called alkylamines and arylamines; amines in which both types of substituent are attached to one nitrogen atom may be called alkylarylamines). Important amines include amino acids , biogenic amines , trimethylamine , and aniline . Inorganic derivatives of ammonia are also called amines, such as monochloramine ( NClH 2 ). The substituent −NH 2

174-424: A chemical compound ; the concept is most readily understood when considering pure chemical substances . It follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction , into compounds or substances each having fewer atoms. A chemical formula is a way of expressing information about the proportions of atoms that constitute

232-419: A solid-state reaction , or the electron transfer reaction of reactive metals with reactive non-metals, such as halogen gases. Ionic compounds typically have high melting and boiling points , and are hard and brittle . As solids they are almost always electrically insulating , but when melted or dissolved they become highly conductive , because the ions are mobilized. An intermetallic compound

290-472: A ... white Powder ... with Sulphur it will compose a blood-red and volatile Cinaber. And yet out of all these exotick Compounds, we may recover the very same running Mercury. Boyle used the concept of "corpuscles"—or "atomes", as he also called them—to explain how a limited number of elements could combine into a vast number of compounds: If we assigne to the Corpuscles, whereof each Element consists,

348-541: A compound molecule, using the standard chemical symbols with numerical subscripts . Many chemical compounds have a unique CAS number identifier assigned by the Chemical Abstracts Service . Globally, more than 350,000 chemical compounds (including mixtures of chemicals) have been registered for production and use. The term "compound"—with a meaning similar to the modern—has been used at least since 1661 when Robert Boyle's The Sceptical Chymist

406-412: A continuous three-dimensional network, usually in a crystalline structure . Ionic compounds containing basic ions hydroxide (OH ) or oxide (O ) are classified as bases. Ionic compounds without these ions are also known as salts and can be formed by acid–base reactions . Ionic compounds can also be produced from their constituent ions by evaporation of their solvent , precipitation , freezing ,

464-566: A particular chemical compound, using chemical symbols for the chemical elements, and subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H 2 O. In the case of non-stoichiometric compounds , the proportions may be reproducible with regard to their preparation, and give fixed proportions of their component elements, but proportions that are not integral [e.g., for palladium hydride , PdH x (0.02 < x < 0.58)]. Chemical compounds have

522-801: A peculiar size and shape ... such ... Corpuscles may be mingled in such various Proportions, and ... connected so many ... wayes, that an almost incredible number of ... Concretes may be compos’d of them. In his Logick , published in 1724, the English minister and logician Isaac Watts gave an early definition of chemical element, and contrasted element with chemical compound in clear, modern terms. Among Substances, some are called Simple, some are Compound ... Simple Substances ... are usually called Elements, of which all other Bodies are compounded: Elements are such Substances as cannot be resolved, or reduced, into two or more Substances of different Kinds. ... Followers of Aristotle made Fire, Air, Earth and Water to be

580-496: A positively charged cation . The nonmetal will gain the electrons from the metal, making the nonmetal a negatively charged anion . As outlined, ionic bonds occur between an electron donor, usually a metal, and an electron acceptor, which tends to be a nonmetal. Hydrogen bonding occurs when a hydrogen atom bonded to an electronegative atom forms an electrostatic connection with another electronegative atom through interacting dipoles or charges. A compound can be converted to

638-601: A protein from following a secretory pathway . The N-terminus can be modified by the addition of a myristoyl anchor. Proteins that are modified this way contain a consensus motif at their N-terminus as a modification signal. The N-terminus can also be modified by the addition of a fatty acid anchor to form N-acetylated proteins. The most common form of such modification is the addition of a palmitoyl group. Amine In chemistry , amines ( / ə ˈ m iː n , ˈ æ m iː n / , UK also / ˈ eɪ m iː n / ) are compounds and functional groups that contain

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696-427: A protein is translated from messenger RNA , it is created from N-terminus to C-terminus. The amino end of an amino acid (on a charged tRNA ) during the elongation stage of translation, attaches to the carboxyl end of the growing chain. Since the start codon of the genetic code codes for the amino acid methionine , most protein sequences start with a methionine (or, in bacteria, mitochondria and chloroplasts ,

754-447: A solid state dependent on how low the temperature of the environment is. A covalent bond , also known as a molecular bond, involves the sharing of electrons between two atoms. Primarily, this type of bond occurs between elements that fall close to each other on the periodic table of elements , yet it is observed between some metals and nonmetals. This is due to the mechanism of this type of bond. Elements that fall close to each other on

812-469: A unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds . Chemical compounds can be molecular compounds held together by covalent bonds , salts held together by ionic bonds , intermetallic compounds held together by metallic bonds , or the subset of chemical complexes that are held together by coordinate covalent bonds . Pure chemical elements are generally not considered chemical compounds, failing

870-541: Is a chemical substance composed of many identical molecules (or molecular entities ) containing atoms from more than one chemical element held together by chemical bonds . A molecule consisting of atoms of only one element is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction , which may involve interactions with other substances. In this process, bonds between atoms may be broken and/or new bonds formed. There are four major types of compounds, distinguished by how

928-403: Is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties. They can be classified as stoichiometric or nonstoichiometric intermetallic compounds. A coordination complex consists of a central atom or ion, which is usually metallic and is called

986-449: Is called an amino group. The chemical notation for amines contains the letter "R", where "R" is not an element, but an "R-group", which in amines could be a single hydrogen or carbon atom, or could be a hydrocarbon chain. Compounds with a nitrogen atom attached to a carbonyl group , thus having the structure R−C(=O)−NR′R″ , are called amides and have different chemical properties from amines. Amines can be classified according to

1044-408: Is determined by the connectivity of the substituents attached to the nitrogen: It is also possible to have four organic substituents on the nitrogen. These species are not amines but are quaternary ammonium cations and have a charged nitrogen center. Quaternary ammonium salts exist with many kinds of anions . Amines are named in several ways. Typically, the compound is given the prefix "amino-" or

1102-493: Is neutral overall, but consists of positively charged ions called cations and negatively charged ions called anions . These can be simple ions such as the sodium (Na ) and chloride (Cl ) in sodium chloride , or polyatomic species such as the ammonium ( NH 4 ) and carbonate ( CO 3 ) ions in ammonium carbonate . Individual ions within an ionic compound usually have multiple nearest neighbours, so are not considered to be part of molecules, but instead part of

1160-601: Is represented in this article by two dots above or next to the N. The water solubility of simple amines is enhanced by hydrogen bonding involving these lone electron pairs. Typically salts of ammonium compounds exhibit the following order of solubility in water: primary ammonium ( RNH 3 ) > secondary ammonium ( R 2 NH 2 ) > tertiary ammonium (R 3 NH ). Small aliphatic amines display significant solubility in many solvents , whereas those with large substituents are lipophilic. Aromatic amines, such as aniline , have their lone pair electrons conjugated into

1218-593: The Delépine reaction , although this is rarely employed on an industrial scale. Selectivity is also assured in the Gabriel synthesis , which involves organohalide reacting with potassium phthalimide . Aryl halides are much less reactive toward amines and for that reason are more controllable. A popular way to prepare aryl amines is the Buchwald-Hartwig reaction . Disubstituted alkenes react with HCN in

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1276-816: The Hinsberg reaction , is a chemical test for the presence of amines. Because amines are basic, they neutralize acids to form the corresponding ammonium salts R 3 NH . When formed from carboxylic acids and primary and secondary amines, these salts thermally dehydrate to form the corresponding amides . Amines undergo sulfamation upon treatment with sulfur trioxide or sources thereof: Amines reacts with nitrous acid to give diazonium salts. The alkyl diazonium salts are of little importance because they are too unstable. The most important members are derivatives of aromatic amines such as aniline ("phenylamine") (A = aryl or naphthyl): Anilines and naphthylamines form more stable diazonium salts, which can be isolated in

1334-452: The coordination centre , and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Many metal-containing compounds, especially those of transition metals , are coordination complexes. A coordination complex whose centre is a metal atom is called a metal complex of d block element. Compounds are held together through a variety of different types of bonding and forces. The differences in

1392-473: The nitrogen inversion of the stereocenter is about 7  kcal/mol for a trialkylamine. The interconversion has been compared to the inversion of an open umbrella into a strong wind. Amines of the type NHRR' and NRR′R″ are chiral : the nitrogen center bears four substituents counting the lone pair. Because of the low barrier to inversion, amines of the type NHRR' cannot be obtained in optical purity. For chiral tertiary amines, NRR′R″ can only be resolved when

1450-449: The oxygen molecule (O 2 ); or it may be heteronuclear , a chemical compound composed of more than one element, as with water (two hydrogen atoms and one oxygen atom; H 2 O). A molecule is the smallest unit of a substance that still carries all the physical and chemical properties of that substance. An ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding . The compound

1508-449: The secretory pathway . In eukaryotic cells , these proteins are synthesized at the rough endoplasmic reticulum . In prokaryotic cells , the proteins are exported across the cell membrane . In chloroplasts , signal peptides target proteins to the thylakoids . The N-terminal mitochondrial targeting peptide (mtTP) allows the protein to be imported into the mitochondrion . The N-terminal chloroplast targeting peptide (cpTP) allows for

1566-463: The Earth. Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. A molecule may be homonuclear , that is, it consists of atoms of one chemical element, as with two atoms in

1624-645: The R, R', and R″ groups are constrained in cyclic structures such as N -substituted aziridines ( quaternary ammonium salts are resolvable). In aromatic amines ("anilines"), nitrogen is often nearly planar owing to conjugation of the lone pair with the aryl substituent. The C-N distance is correspondingly shorter. In aniline, the C-N distance is the same as the C-C distances. Like ammonia, amines are bases . Compared to alkali metal hydroxides, amines are weaker. The basicity of amines depends on: Owing to inductive effects,

1682-534: The Truth ;; tho' they are not all agreed ... Compound Substances are made up of two or more simple Substances ... So a Needle is simple Body, being made only of Steel; but a Sword or a Knife is a compound because its ... Handle is made of Materials different from the Blade. Any substance consisting of two or more different types of atoms ( chemical elements ) in a fixed stoichiometric proportion can be termed

1740-445: The amino acid lysine . The anionic polymer DNA is typically bound to various amine-rich proteins. Additionally, the terminal charged primary ammonium on lysine forms salt bridges with carboxylate groups of other amino acids in polypeptides , which is one of the primary influences on the three-dimensional structures of proteins. Hormones derived from the modification of amino acids are referred to as amine hormones. Typically,

1798-417: The aromatic ring, and their positions relative to the amino group, also affect basicity as seen in the table. Solvation significantly affects the basicity of amines. N-H groups strongly interact with water, especially in ammonium ions. Consequently, the basicity of ammonia is enhanced by 10 by solvation. The intrinsic basicity of amines, i.e. the situation where solvation is unimportant, has been evaluated in

N-terminus - Misplaced Pages Continue

1856-504: The bands appearing below 1600 cm , which are weaker and overlap with C-C and C-H modes. For the case of propyl amine , the H-N-H scissor mode appears near 1600 cm , the C-N stretch near 1000 cm , and the R 2 N-H bend near 810 cm . Alkyl amines characteristically feature tetrahedral nitrogen centers. C-N-C and C-N-H angles approach the idealized angle of 109°. C-N distances are slightly shorter than C-C distances. The energy barrier for

1914-423: The basicity of an amine might be expected to increase with the number of alkyl groups on the amine. Correlations are complicated owing to the effects of solvation which are opposite the trends for inductive effects. Solvation effects also dominate the basicity of aromatic amines (anilines). For anilines, the lone pair of electrons on nitrogen delocalizes into the ring, resulting in decreased basicity. Substituents on

1972-643: The benzene ring, thus their tendency to engage in hydrogen bonding is diminished. Their boiling points are high and their solubility in water is low. Typically the presence of an amine functional group is deduced by a combination of techniques, including mass spectrometry as well as NMR and IR spectroscopies. H NMR signals for amines disappear upon treatment of the sample with D 2 O. In their infrared spectrum primary amines exhibit two N-H bands, whereas secondary amines exhibit only one. In their IR spectra, primary and secondary amines exhibit distinctive N-H stretching bands near 3300 cm . Somewhat less distinctive are

2030-1699: The case of formaldehyde (R' = H), these products typically exist as cyclic trimers : RNH 2 + R 2 ′ C = O ⟶ R 2 ′ C = NR + H 2 O {\displaystyle {\ce {RNH2 + R'_2C=O -> R'_2C=NR + H2O}}} Reduction of these imines gives secondary amines: R 2 ′ C = NR + H 2 ⟶ R 2 ′ CH − NHR {\displaystyle {\ce {R'_2C=NR + H2 -> R'_2CH-NHR}}} Similarly, secondary amines react with ketones and aldehydes to form enamines : R 2 NH + R ′ ( R ″ CH 2 ) C = O ⟶ R ″ CH = C ( NR 2 ) R ′ + H 2 O {\displaystyle {\ce {R2NH + R'(R''CH2)C=O -> R''CH=C(NR2)R' + H2O}}} Mercuric ions reversibly oxidize tertiary amines with an α hydrogen to iminium ions: Hg 2 + + R 2 NCH 2 R ′ ↽ − − ⇀ Hg + [ R 2 N = CHR ′ ] + + H + {\displaystyle {\ce {Hg^2+ + R2NCH2R' <=> Hg + [R2N=CHR']+ + H+}}} An overview of

2088-431: The constituent atoms are bonded together. Molecular compounds are held together by covalent bonds ; ionic compounds are held together by ionic bonds ; intermetallic compounds are held together by metallic bonds ; coordination complexes are held together by coordinate covalent bonds . Non-stoichiometric compounds form a disputed marginal case. A chemical formula specifies the number of atoms of each element in

2146-493: The crystalline form. Diazonium salts undergo a variety of useful transformations involving replacement of the N 2 group with anions. For example, cuprous cyanide gives the corresponding nitriles: Aryldiazoniums couple with electron-rich aromatic compounds such as a phenol to form azo compounds . Such reactions are widely applied to the production of dyes. Imine formation is an important reaction. Primary amines react with ketones and aldehydes to form imines . In

2204-400: The fixed ratios. Many solid chemical substances—for example many silicate minerals —are chemical substances, but do not have simple formulae reflecting chemically bonding of elements to one another in fixed ratios; even so, these crystalline substances are often called " non-stoichiometric compounds ". It may be argued that they are related to, rather than being chemical compounds, insofar as

2262-513: The four Elements, of which all earthly Things were compounded; and they suppos'd the Heavens to be a Quintessence, or fifth sort of Body, distinct from all these : But, since experimental Philosophy ... have been better understood, this Doctrine has been abundantly refuted. The Chymists make Spirit, Salt, Sulphur, Water and Earth to be their five Elements, because they can reduce all terrestrial Things to these five : This seems to come nearer

2320-456: The gas phase, but ten thousand times less so in aqueous solution. In aprotic polar solvents such as DMSO , DMF , and acetonitrile the energy of solvation is not as high as in protic polar solvents like water and methanol. For this reason, the basicity of amines in these aprotic solvents is almost solely governed by the electronic effects. Industrially significant alkyl amines are prepared from ammonia by alkylation with alcohols: Unlike

2378-399: The gas phase. In the gas phase, amines exhibit the basicities predicted from the electron-releasing effects of the organic substituents. Thus tertiary amines are more basic than secondary amines, which are more basic than primary amines, and finally ammonia is least basic. The order of pK b 's (basicities in water) does not follow this order. Similarly aniline is more basic than ammonia in

N-terminus - Misplaced Pages Continue

2436-437: The modified version N -formylmethionine , fMet). However, some proteins are modified posttranslationally , for example, by cleavage from a protein precursor , and therefore may have different amino acids at their N-terminus. The N-terminus is the first part of the protein that exits the ribosome during protein biosynthesis . It often contains signal peptide sequences, "intracellular postal codes " that direct delivery of

2494-454: The nature and number of substituents on nitrogen . Aliphatic amines contain only H and alkyl substituents. Aromatic amines have the nitrogen atom connected to an aromatic ring. Amines, alkyl and aryl alike, are organized into three subcategories (see table) based on the number of carbon atoms adjacent to the nitrogen (how many hydrogen atoms of the ammonia molecule are replaced by hydrocarbon groups): A fourth subcategory

2552-678: The nitroaromatics. In industry, hydrogen is the preferred reductant, whereas, in the laboratory, tin and iron are often employed. Many methods exist for the preparation of amines, many of these methods being rather specialized. Aside from their basicity, the dominant reactivity of amines is their nucleophilicity . Most primary amines are good ligands for metal ions to give coordination complexes . Amines are alkylated by alkyl halides. Acyl chlorides and acid anhydrides react with primary and secondary amines to form amides (the " Schotten–Baumann reaction "). Similarly, with sulfonyl chlorides, one obtains sulfonamides . This transformation, known as

2610-1131: The original structure of the amino acid is modified such that a –COOH, or carboxyl, group is removed, whereas the –NH 3 , or amine, group remains. Amine hormones are synthesized from the amino acids tryptophan or tyrosine . Primary aromatic amines are used as a starting material for the manufacture of azo dyes . It reacts with nitrous acid to form diazonium salt, which can undergo coupling reaction to form an azo compound. As azo-compounds are highly coloured, they are widely used in dyeing industries, such as: Most drugs and drug candidates contain amine functional groups: Aqueous monoethanolamine (MEA), diglycolamine (DGA), diethanolamine (DEA), diisopropanolamine (DIPA) and methyldiethanolamine (MDEA) are widely used industrially for removing carbon dioxide (CO 2 ) and hydrogen sulfide (H 2 S) from natural gas and refinery process streams. They may also be used to remove CO 2 from combustion gases and flue gases and may have potential for abatement of greenhouse gases . Related processes are known as sweetening . Chemical compound A chemical compound

2668-536: The periodic table tend to have similar electronegativities , which means they have a similar affinity for electrons. Since neither element has a stronger affinity to donate or gain electrons, it causes the elements to share electrons so both elements have a more stable octet . Ionic bonding occurs when valence electrons are completely transferred between elements. Opposite to covalent bonding, this chemical bond creates two oppositely charged ions. The metals in ionic bonding usually lose their valence electrons, becoming

2726-599: The presence of a nickel catalyst. Suitable groups include nitriles , azides , imines including oximes , amides, and nitro . In the case of nitriles, reactions are sensitive to acidic or alkaline conditions, which can cause hydrolysis of the −CN group. LiAlH 4 is more commonly employed for the reduction of these same groups on the laboratory scale. Many amines are produced from aldehydes and ketones via reductive amination , which can either proceed catalytically or stoichiometrically. Aniline ( C 6 H 5 NH 2 ) and its derivatives are prepared by reduction of

2784-479: The presence of strong acids to give formamides, which can be decarbonylated. This method, the Ritter reaction , is used industrially to produce tertiary amines such as tert -octylamine . Hydroamination of alkenes is also widely practiced. The reaction is catalyzed by zeolite-based solid acids . Via the process of hydrogenation , unsaturated N-containing functional groups are reduced to amines using hydrogen in

2842-427: The properties of primary and secondary amines. For example, methyl and ethyl amines are gases under standard conditions, whereas the corresponding methyl and ethyl alcohols are liquids. Amines possess a characteristic ammonia smell, liquid amines have a distinctive "fishy" and foul smell. The nitrogen atom features a lone electron pair that can bind H to form an ammonium ion R 3 NH . The lone electron pair

2900-599: The protein to be imported into the chloroplast . Protein N-termini can be modified co - or post-translationally. Modifications include the removal of initiator methionine (iMet) by aminopeptidases , attachment of small chemical groups such as acetyl , propionyl and methyl , and the addition of membrane anchors, such as palmitoyl and myristoyl groups N-terminal acetylation is a form of protein modification that can occur in both prokaryotes and eukaryotes . It has been suggested that N-terminal acetylation can prevent

2958-458: The protein to the proper organelle . The signal peptide is typically removed at the destination by a signal peptidase . The N-terminal amino acid of a protein is an important determinant of its half-life (likelihood of being degraded). This is called the N-end rule . The N-terminal signal peptide is recognized by the signal recognition particle (SRP) and results in the targeting of the protein to

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3016-403: The reaction of amines with alcohols the reaction of amines and ammonia with alkyl halides is used for synthesis in the laboratory: In such reactions, which are more useful for alkyl iodides and bromides, the degree of alkylation is difficult to control such that one obtains mixtures of primary, secondary, and tertiary amines, as well as quaternary ammonium salts. Selectivity can be improved via

3074-440: The reactions of amines is given below: Amines are ubiquitous in biology. The breakdown of amino acids releases amines, famously in the case of decaying fish which smell of trimethylamine . Many neurotransmitters are amines, including epinephrine , norepinephrine , dopamine , serotonin , and histamine . Protonated amino groups ( –NH 3 ) are the most common positively charged moieties in proteins , specifically in

3132-452: The suffix "-amine". The prefix " N -" shows substitution on the nitrogen atom. An organic compound with multiple amino groups is called a diamine , triamine , tetraamine and so forth. Lower amines are named with the suffix -amine . Higher amines have the prefix amino as a functional group. IUPAC however does not recommend this convention, but prefers the alkanamine form, e.g. butan-2-amine. Hydrogen bonding significantly influences

3190-494: The two or more atom requirement, though they often consist of molecules composed of multiple atoms (such as in the diatomic molecule H 2 , or the polyatomic molecule S 8 , etc.). Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service (CAS): its CAS number . There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, which require

3248-455: The types of bonds in compounds differ based on the types of elements present in the compound. London dispersion forces are the weakest force of all intermolecular forces . They are temporary attractive forces that form when the electrons in two adjacent atoms are positioned so that they create a temporary dipole . Additionally, London dispersion forces are responsible for condensing non polar substances to liquids, and to further freeze to

3306-421: The variability in their compositions is often due to either the presence of foreign elements trapped within the crystal structure of an otherwise known true chemical compound , or due to perturbations in structure relative to the known compound that arise because of an excess of deficit of the constituent elements at places in its structure; such non-stoichiometric substances form most of the crust and mantle of

3364-409: Was published. In this book, Boyle variously used the terms "compound", "compounded body", "perfectly mixt body", and "concrete". "Perfectly mixt bodies" included for example gold, lead, mercury, and wine. While the distinction between compound and mixture is not so clear, the distinction between element and compound is a central theme. Quicksilver ... with Aqua fortis will be brought into

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