Porphyrins are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−). In vertebrates, an essential member of the porphyrin group is heme, which is a component of hemoproteins, whose functions include carrying oxygen in the bloodstream. In plants, an essential porphyrin derivative is chlorophyll, which is involved in light harvesting and electron transfer in photosynthesis.
An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Enamines are versatile intermediates.
An aldol condensation is a condensation reaction in organic chemistry in which two carbonyl moieties react to form a β-hydroxyaldehyde or β-hydroxyketone, and this is then followed by dehydration to give a conjugated enone.
Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces, electrostatic charge, or hydrogen bonding to strong covalent bonding, provided that the electronic coupling strength remains small relative to the energy parameters of the component. While traditional chemistry concentrates on the covalent bond, supramolecular chemistry examines the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi–pi interactions and electrostatic effects.
Resorcinol (or resorcin) is a phenolic compound. It is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1,3-isomer (or meta-isomer). Resorcinol crystallizes from benzene as colorless needles that are readily soluble in water, alcohol, and ether, but insoluble in chloroform and carbon disulfide.
In supramolecular chemistry, host–guest chemistry describes complexes that are composed of two or more molecules or ions that are held together in unique structural relationships by forces other than those of full covalent bonds. Host–guest chemistry encompasses the idea of molecular recognition and interactions through non-covalent bonding. Non-covalent bonding is critical in maintaining the 3D structure of large molecules, such as proteins and is involved in many biological processes in which large molecules bind specifically but transiently to one another.
The Pictet–Spengler reaction is a chemical reaction in which a β-arylethylamine undergoes condensation with an aldehyde or ketone followed by ring closure. The reaction was first discovered in 1911 by Amé Pictet and Theodor Spengler. Traditionally an acidic catalyst in protic solvent was employed with heating, however the reaction has been shown to work in aprotic media in superior yields and sometimes without acid catalysis. The Pictet–Spengler reaction can be considered a special case of the Mannich reaction, which follows a similar reaction pathway. The driving force for this reaction is the electrophilicity of the iminium ion generated from the condensation of the aldehyde and amine under acid conditions. This explains the need for an acid catalyst in most cases, as the imine is not electrophilic enough for ring closure but the iminium ion is capable of undergoing the reaction.
A calixarene is a macrocycle or cyclic oligomer based on a methylene-linked phenols. With hydrophobic cavities that can hold smaller molecules or ions, calixarenes belong to the class of cavitands known in host–guest chemistry.
In chemistry, a cavitand is a container-shaped molecule. The cavity of the cavitand allows it to engage in host–guest chemistry with guest molecules of a complementary shape and size. The original definition proposed by Cram includes many classes of molecules: cyclodextrins, calixarenes, pillararenes and cucurbiturils. However, modern usage in the field of supramolecular chemistry specifically refers to cavitands formed on a resorcinarene scaffold by bridging adjacent phenolic units. The simplest bridging unit is methylene, although dimethylene, trimethylene, benzal, xylyl, pyridyl, 2,3-disubstituted-quinoxaline, o-dinitrobenzyl, dialkylsilylene, and phosphonates are known. Cavitands that have an extended aromatic bridging unit, or an extended cavity containing 3 rows of aromatic rings are referred to as deep-cavity cavitands and have broad applications in host-guest chemistry. These types of cavitands were extensively investigated by Rebek, and Gibb, among others.
Dynamic covalent chemistry (DCvC) is a synthetic strategy employed by chemists to make complex molecular and supramolecular assemblies from discrete molecular building blocks. DCvC has allowed access to complex assemblies such as covalent organic frameworks, molecular knots, polymers, and novel macrocycles. Not to be confused with dynamic combinatorial chemistry, DCvC concerns only covalent bonding interactions. As such, it only encompasses a subset of supramolecular chemistries.
In chemistry, a salt bridge is a combination of two non-covalent interactions: hydrogen bonding and ionic bonding. Ion pairing is one of the most important noncovalent forces in chemistry, in biological systems, in different materials and in many applications such as ion pair chromatography. It is a most commonly observed contribution to the stability to the entropically unfavorable folded conformation of proteins. Although non-covalent interactions are known to be relatively weak interactions, small stabilizing interactions can add up to make an important contribution to the overall stability of a conformer. Not only are salt bridges found in proteins, but they can also be found in supramolecular chemistry. The thermodynamics of each are explored through experimental procedures to access the free energy contribution of the salt bridge to the overall free energy of the state.
The Strecker amino acid synthesis, also known simply as the Strecker synthesis, is a method for the synthesis of amino acids by the reaction of an aldehyde with ammonia in the presence of potassium cyanide. The condensation reaction yields an α-aminonitrile, which is subsequently hydrolyzed to give the desired amino acid. The method is used commercially for the production of racemic methionine from methional.
Julius Rebek Jr. is a Hungarian-American chemist and expert on molecular self-assembly.
In polymer chemistry and materials science, the term "polymer" refers to large molecules whose structure is composed of multiple repeating units. Supramolecular polymers are a new category of polymers that can potentially be used for material applications beyond the limits of conventional polymers. By definition, supramolecular polymers are polymeric arrays of monomeric units that are connected by reversible and highly directional secondary interactions–that is, non-covalent bonds. These non-covalent interactions include van der Waals interactions, hydrogen bonding, Coulomb or ionic interactions, π-π stacking, metal coordination, halogen bonding, chalcogen bonding, and host–guest interaction. The direction and strength of the interactions are precisely tuned so that the array of molecules behaves as a polymer in dilute and concentrated solution, as well as in the bulk.
In chemistry, a water cluster is a discrete hydrogen bonded assembly or cluster of molecules of water. Many such clusters have been predicted by theoretical models (in silico), and some have been detected experimentally in various contexts such as ice, bulk liquid water, in the gas phase, in dilute mixtures with non-polar solvents, and as water of hydration in crystal lattices. The simplest example is the water dimer (H2O)2.
In organic chemistry, the Claisen–Schmidt condensation is the reaction between an aldehyde or ketone having an α-hydrogen with an aromatic carbonyl compound lacking an α-hydrogen. It can be considered as a specific variation of the aldol condensation. This reaction is named after two of its pioneering investigators Rainer Ludwig Claisen and J. Gustav Schmidt, who independently published on this topic in 1880 and 1881. An example is the synthesis of dibenzylideneacetone ( -1,5-diphenylpenta-1,4-dien-3-one).
Pillararenes are macrocycles composed of hydroquinone or dialkoxybenzene units linked in the para position by methylene bridges. They are structurally similar to the cucurbiturils and calixarenes that play an important part in host–guest chemistry. The first pillararene was the five membered dimethoxypillar[5]arene.
Supramolecular catalysis is not a well-defined field but it generally refers to an application of supramolecular chemistry, especially molecular recognition and guest binding, toward catalysis. This field was originally inspired by enzymatic system which, unlike classical organic chemistry reactions, utilizes non-covalent interactions such as hydrogen bonding, cation-pi interaction, and hydrophobic forces to dramatically accelerate rate of reaction and/or allow highly selective reactions to occur. Because enzymes are structurally complex and difficult to modify, supramolecular catalysts offer a simpler model for studying factors involved in catalytic efficiency of the enzyme. Another goal that motivates this field is the development of efficient and practical catalysts that may or may not have an enzyme equivalent in nature.
Colin Llewellyn Raston is a Professor of Chemistry of Flinders University in Adelaide, South Australia and the Premier's Professorial Fellow in Clean Technology. In 2015, he was awarded an Ig Nobel Prize in "for inventing a chemical recipe to partially un-boil an egg". In 2016, Raston was made an Officer of the Order of Australia for his services to science.
A pyrogallolarene is a macrocycle, or a cyclic oligomer, based on the condensation of pyrogallol (1,2,3-trihydroxybenzene) and an aldehyde. Pyrogallolarenes are a type of calixarene, and a subset of resorcinarenes that are substituted with a hydroxyl at the 2-position.
![Preparation of resorcin[4]arenes from resorcinol and an aldehyde. Resorcinarene synth.svg](http://upload.wikimedia.org/wikipedia/commons/thumb/e/ec/Resorcinarene_synth.svg/351px-Resorcinarene_synth.svg.png)