Figure 1. Dendrimer and dendron

Crystal structure of a first-generation polyphenylene dendrimer reported by Müllen and coworkers in Chem. -Eur. J. , 2002, 3858-3864.

Dendrimers are repeatedly branched molecules. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by The huge number of papers on dendritic architectures such as dendrimers, dendronized, hyperbranched and brush-polymers has generated a vast variety of inconsistent terms and definitions making a clear and concise unfolding of this topic highly difficult. The purpose of this section is to provide the vocabulary required for the description of chemical and physical phenomena as well as application aspects associated with the research in the area of dendritic molecules.

Dendritic molecules are repeatedly branched species that are characterized by their structure perfection. The latter is based on the evaluation of both symmetry and polydispersity. The area of dendritic molecules can roughly be divided into the low-molecular weight and the high-molecular weight species. The first category includes dendrimers and dendrons whereas the second encompasses dendronized polymers, hyperbranched polymers, and brush-polymers (also called bottle-brushes).

The name comes from the Greek "δενδρον"/dendron, meaning "tree". Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Synonymous terms are arborols and cascade-molecules. Dendrimer is an internationally accepted term. Dendrimers and dendrons are repeatedly branched, monodisperse, and usually highly symmetric compounds. There is no apparent difference in defining dendrimer and dendron. A dendron usually contains a single chemically addressable group that is called the focal point. Because of the lack of the molar mass distribution high-molar-mass dendrimers and dendrons are macromolecules but not polymers.

The first dendrimers were synthesized divergently by Vögtle in 1978^[1], by Denkewalter and coworkers at Allied Corporation as polylysine dendrimers in 1981^[2], by Tomalia at Dow Chemical in 1983^[3] and in 1985^[4], and by Newkome in 1985^[5]. Allied Corporation was a major American company with operations in the aerospace automotive oil and gas industries Lysine (abbreviated as Lys or K) is an α- Amino acid with the Chemical formula HO2CCH(NH2(CH24NH2 The Dow Chemical Company () is an American Multinational corporation headquartered in Midland Michigan. In 1990 a convergent synthesis was introduced by Fréchet^[6]. Professor Jean MJ Fréchet is the Henry Rapoport Chair of Organic Chemistry at the Department of Dendrimers then experienced an explosion of scientific interest because of their unique molecular architecture (Fig 1). This resulted in over 5,000 scientific papers and patents published by the end of 2005.

Properties and applications

The properties of dendrimers are dominated by the functional groups on the molecular surface. In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. Dendritic encapsulation of functional molecules allows for the isolation of the active site, a structure that mimics the structure of active sites in biomaterials because dendritic scaffolds separate internal and external functions. ^[7][8][9]. For example, a dendrimer can be water-soluble when its end-group is a hydrophilic group, like a carboxyl group. An end-group in Polymer chemistry is a constitutional unit that is an extremity of a Macromolecule or Oligomer molecule Hydrophile, from the Greek (hydros "water" and φιλια (philia "friendship" refers to a physical property of a Molecule Carboxyl group or CO2H is a Functional group present in Amino acids and Carboxylic acids Its structure is composed of one carbon atom attached It is theoretically possible to design a water-soluble dendrimer with internal hydrophobicity, which would allow it to carry a hydrophobic drug in its interior. In Chemistry, hydrophobicity (from the combining form of water in Attic Greek hydro- and for fear phobos) refers to the physical property of A drug, broadly speaking is any chemical substance that when absorbed into the body Recently it has been shown that redox-active nanoparticles can be synthesized, placing the redox molecules between the nanoparticle core and the dendritic wedges; despite their isolation, some of the redox molecules (COOH in this case) remained uncoupled, and thus still reactive. ^[10]

Another property is that the volume of a dendrimer increases when it has a positive charge. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. If this property can be applied, dendrimers can be used for drug delivery systems (DDS) that can give medication to the affected part inside a patient's body directly^[11].

Photonic excited molecules

The inside of a dendrimer has a unique chemical environment because of its high density. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different From this property, it has been discovered that azobenzene is photoisomerized by very weak infrared rays when covered by a dendrimer ^[12]. Azobenzene is a Chemical compound composed of two Phenyl rings linked by a N=N Double bond. In Chemistry, photoisomerization is molecular behavior in which structural change between Isomers is caused by photoexcitation Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Through the discovery of a function that catches light and conveys this energy using excitation of the molecule, attempts have recently been made to synthesize dendrimers that insert porphyrin, absorb light, and photosynthesize artificially. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Excitation or excitement can refer to The Excited state of an atom The Excitation (magnetic provided with an electrical A porphyrin is a heterocyclic Macrocycle derived from four Pyrroline subunits interconnected via their α carbon atoms via Methine bridges (=CH- Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. In addition, the development of organic electroluminescent devices and their applications has been undertaken by researchers all over the world. An Organic Light Emitting Diode ( OLED) also Light Emitting Polymer ( LEP) and Organic Electro Luminescence ( OEL) is any

Synthesis

In the synthesis of dendrimers, monomers lead to a monodisperse polymer, tree-like, or generational structure. A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other A collection of objects are called monodisperse or monosized if they have the same size shape and mass There are two defined methods of dendrimer synthesis, divergent synthesis and convergent synthesis. In Chemistry a divergent synthesis is a strategy with the aim to improve the efficiency of Chemical synthesis. In Chemistry a convergent synthesis is a strategy that aims to improve the efficiency of multi-step Chemical synthesis. Divergent syntheses assemble the molecule from the core, extending radially to the periphery and in contrast convergent methods start at the surface and proceed inwards, before the attachment of pre-synthesised dendrons to the core.

However, because a repeated reaction which consists of many steps is needed to protect the active site, it is difficult to synthesize dendrimers even if both methods are used. The active site of an Enzyme contains the catalytic and Binding sites. This is why there are obstacles to the synthesis of large quantities of dendrimers. Presently, the only kilogram-scale producers of dendrimers is Dendritech ^[13]

The original Newkome dendrimer or arborol (1985) started by nucleophilic substitution of 1-bromopentane by triethyl sodiomethanetricarboxylate in dimethylformamide and benzene. In organic and Inorganic chemistry, nucleophilic substitution is a fundamental class of Substitution reaction in which an "electron rich" Dimethylformamide is the Organic compound with the formula ( CH3)2NC(OH Benzene, or benzol, is an organic Chemical compound and a known Carcinogen with the molecular formula C 6 H 6 The ester groups were then reduced by lithium aluminium hydride to a triol in a deprotection step. Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least Organic reductions or organic oxidations or organic redox reactions are Redox reactions that take place with Organic compounds In Organic Lithium aluminium hydride ( Li[[Aluminium Al]] H4) commonly abbreviated to LAH, is a Reducing agent used in Organic synthesis In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon A protecting group or protective group is introduced into a molecule by chemical modification of a Functional group in order to obtain Chemoselectivity Activation of the chain ends was achieved by converting the alcohol groups to tosylate groups with tosyl chloride and pyridine. A tosyl group (abbreviated Ts or Tos) combines the Toluene and Sulfonyl Functional groups. A tosyl group (abbreviated Ts or Tos) combines the Toluene and Sulfonyl Functional groups. Pyridine is a Chemical compound with the formula C5[[Hydrogen H5]] N. The tosyl group then served as leaving groups in another reaction with the tricarboxylate, forming generation two. A leaving group is an Atom or group of atoms that detaches from a chemical substance

This sequence can be repeated many times.

References