Dendrimers – Everything you need to know!

Dendrimers – Everything you need to know! Everything about the molecule – Definition, Types, Structure, Applications & Properties. Learn from scratch!

The scientists in every field of modern research have always been intrigued by natural and synthetic polymers. Synthetic polymers have improved further the drug distribution applications of newer medication delivery systems, especially biodegradable polymers.

The spectrum of pharmaceutical and biomedical applications is further expanded by nano biopolymers. In this context, dendrimers have emerged as one of the best revolutionary polymer nanocarriers for various bioactive therapeutic categories.

The expression dendrimer is derived from a Greek term dendron that means “tree”, which is logical in view of their typical structure with a number of branching units

Dendrimers are novel, nano polymeric architectures hyper-branched, three-dimensional. Attractive characteristics like nanoscopic sizes, small poly-diffusion indexes, excellent molecular structure control, numerous peripheral functional groups, and internal cavities distinguish them from current polymers.

Dendrimers – Everything you need to know!

What is a dendrimer?

Dendrimers are highly branched, star-shaped macromolecules with nanometer-scale dimensions. They are nano-sized, radially symmetric, well-defined, homogeneous, and monodisperse molecules with a normally symmetrical core, an inner shell, and an outer shell.

The three typical macromolecular architectural groups are widely recognized for producing products of different molecular weights that are rather polydisperse. There are a number of dendrimers, each having biological characteristics such as polyvalence, self-assembly, electrostatic interactions, chemical stability, low cytotoxicity, and solubility.

Dendrimers are defined by three components: a central core, an interior dendritic structure (the branches), and an exterior surface with functional surface groups.

The various combinations of these components produce products in various shapes and sizes with shielded internal cores, which can be used in the biological and material science fields.

While the attached surface groups affect the solubility and chelation ability, the varied cores impart unique properties to the cavity size, absorption capacity, and capture-release characteristics.

Dendrimers – Everything you need to know!

Types of Dendrimers?

S.No. Types of dendrimer Synthesis Examples Identification
1.PAMAM (Poly Amido Amine) DendrimerDivergentDendritech TM (USA)These are spheroidal or ellipsoidal in shape. It has high solubility and reactivity due to the incidence of a number of functional end groups and empty internal cavities.
2.PPI (Poly Propylene Imine ) DendrimerDivergentAsramol by DSM (Netherlands)Its core structure is based on Di amino butane with primary amines as end groups and tertiary propylene amines as the center. These are commercially available up to G-5 and are extensively used in material science and biology.
3.Chiral DendrimerConvergentchiral dendrimers derived from pentaerythritol The chirality of the dendrimers was based upon the building of constitutionally different but chemically alike branches to the chiral core.
4.Multilingual DendrimersConvergentVivaGelThese are the dendrimers that hold multiple copies of a particular functional group on their surface.
5.Tecto DendrimersDivergent Stratus® CS Acute Care TM, Starburst®, MercaptoThese were made up of core dendrimers, which can be surrounded by other dendrimers, which execute a specific function leading to a smart therapeutic system used for diagnosing the diseased state and deliver API to the accepted diseased cell.
6.Hybrid Dendrimers Divergent Hybrid dendritic linear polymer, PolysilsesquioxanesThese dendrimers have the characteristic of both dendritic and linear polymer.
7.Amphiphilic DendrimersDivergentSuperFect, Hydraamphiphiles, and bola-amphiphiles.These have one half that is electron-donating and another half is electron retreating.
8.Peptide DendrimersConvergentBeta Casomorphin (human)Peptide dendrimers are those which hold amino acid as branching or interior unit. These are used for diagnostic purposes and vaccine delivery.
9.Frechet-Type DendrimersConvergentFrechet type dendron azides, TM PriostarThese were based on polybenzyl ether hyperbranched skeleton. The carboxylic acid group attached to the surface of dendrimers that provides a site for further functionalization and also improves the solubility of dendrimers.
10.PAMAMOS (Poly Amidoamine Organosilicon) DendrimersConvergent and DivergentSARSOXThese are silicon-containing commercial dendrimers which are inverted unimolecular micelles and contain exterior hydrophobic organosilicon (OS) and interiorly hydrophilic, nucleophilic polyamidoamine.
11.Multiple Antigen Peptide DendrimersMultiple Antigen Peptide DendrimersMultiple Antigen Peptide DendrimersThese are dendron-like molecular assembly based upon a polylysine frame. Lysine with its alkyl amino side-chain performed as an excellent monomer for the overture of frequent branching points.

Structure of Dendrimer?

Dendrimer molecules are organized in accordance with a core central atom or atomic group. This central structure creates a variety of chemical reactions in the branches of other atoms known as’ dendrons.’

The exact structure of dendrimers is still debated, especially if they are totally extended to the surface with maximum density or if the final groups dot back towards a densely packed interior.

Dendrimers can be made to regulate the structure of certain dendrimer repeating units, such as the 1,3 diphenyl acetylene unit produced by Moore, with the majority of linear polymers that are not attainable and lead to almost single scattered, globular macromolecules with a high number of Peripheral Groups.

Dendrimers – Everything you need to know!

Application of Dendrimers

One of the first suggested dendrimer applications was as a container compound in which small substrates are bound into the internal dendrimer voids. For hyper branch polymers[30] and dendrimers, experimental evidence was developed for unimolecular micelle properties several years ago.

Applications highlighted in recent literature include drug delivery, gene transfection, catalysis, energy harvesting, photo activity, molecular weight and size determination, rheology modification, and nanoscale science and technology.

Dendrimers have been applied in a broad range of supramolecular chemical applications, particularly in host-guest reactions and self-assembly processes.

Dendrimers have special characteristics that make them promising candidates for many applications. Dendrimers are strongly defined macromolecules that are characterized by a strong combination of functional and compact groups.

Dendritic macromolecules play a remarkable function in anticancerous treatment and diagnostic imaging. These well established materials give the benefit of being the newest class of nano-scale macromolecular feeders.

The dendritic macromolecules continue to linearly increase in diameter with an increasing dendrimer generation and become more globular in shape. Dendrimers, therefore, became a perfect supplier of material to directly investigate the effects of polymer size, charge, and composition on biologically relevant features such as interactions in the lipid bilayer, cytotoxicity, internalization, time of plasma retention, biodiversity, and filtration.

Dendrimers – Everything you need to know!

Properties of Dendrimers?

In comparison to linear polymers, dendrimers are monodisperse macromolecules. The classical method of polymerization resulting in linear polymers produces molecules of various sizes and is typically randomly distributed in nature. Dendriors of the size and molecular mass can be controlled during synthesis.

Dendrimers have considerably better physical and chemical properties than conventional linear polymers due to their molecular architecture.

Linear chain solutions consist of flexible bows; dendrimers, on the other hand, form a tight sphere. This impacts their rheological properties greatly. Solutions with dendrimer have a considerably lower viscosity than linear polymers.

When the molecular mass of dendrimers increases, at the fourth generation their intrinsic viscosity reaches a maximum and then starts to decline. Unlike linear polymers, this behavior is special. The intrinsic viscosity increases continually with molecular weight for classical polymers.

Pharmacokinetic properties

One of the most significant aspects to be considered for the successful biomedical application of dendrimers, such as drug delivery, imaging, photodynamic therapy, and neutron capture therapy, are pharmacokinetic properties.

The diversity of potential dendrimer applications in medicine is leading to increased interest in this area. There are several modifications of the peripheral groups of dendrimers, for example, that allow obtaining antibody-dendrimer, peptide-dendrimer conjugates or dendritic boxes that encapsulate guest molecules.

Covalent conjugation strategies

For over three decades, the technique of binding small molecules to polymer scaffolds by covalent linkages to boost their pharmacological properties has been under experimental testing[43–46]. Nevertheless, in most situations, the conjugated dendritic assembly acts as a’ pro-drug’ where the conjugate must be released to activate the drug after internalization into the target cell.

Polyvalency

Polyvalence is useful as it allows for robust functionalization; multiple interactions with biological receptor sites are also extremely important in the design of antiviral therapeutic agents, for example.

Self-assembling dendrimers

Another fascinating area of chemistry that is developing rapidly is that of self-assembly. Self-assembly is the spontaneous, precise combination of the chemical species by specific intermolecular complementary forces. Increasing interest has recently been in the self-assembly of dendritic structures.

Because dendrimers contain three distinct structural parts (the core, end-groups, and branched units that connect the core and periphery), there are three strategies to self-assemble dendrimers.

The first is to create dendrons with a core unit that can recognize itself or a ditopic or polytopic core structure, thus leading to spontaneous dendrimer formation[48–51]. Gibson and coworkers reported a self-assembling dendrimer using pseudorotaxane formation as the organizing force.

Electrostatic interactions

A large number of often similar end-groups provided by the dendritic host distinguish the molecular recognition events at dendrimer surfaces. The surface may have as a polyelectrolyte when these groups are charged and is likely to attract oppositely charged molecules electrostatically.

The accumulation of methylene blue on the dendrimer surface and the binding of EPR samples such as copper complexes and nitroxide cation radicals are one example of electrostatic interactions between polyelectrolyte dendrimers and charged cells.

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