Nanocrystals Properties of a nanocrystals are largely determined by size and shape Size specifies the surface area and the ratio of surface to bulk atoms while the shape controls the facets and determines the surface structure and the fractions of atoms at corners and edges Shape offers greater versatility to nanocrystals as compared to size or other parameters determining the catalytic properties of the nanocrystals Pd nanocrystals has been synthesized successfully in the past decade in a variety of shapes Nanocrystals are divided on the basis of types of facets that are exposed to the surface They are divided into 5 groups Pd nanocrystals are synthesized in a number of shapes rhombic dodecahedrons cubes octahedrons by reduction of H2PdCl4 with ascorbic acid in an aqueous solution which contains cetyl trimethyl ammonium bromide CTAB potassium iodide and Pd cubic seeds Icosahedrons nanocrystals are usually stable at smaller sizes while dodecahedrons shaped nanocrystals are more stable at medium sizes 3 2 Quantum dots Quantum dots are Fluorescent semiconductor based nanoparticles which represent a huge platform for design and development of nano drug delivery vehicles which

 Consist of hundreds to a few thousand atoms Quantum Dots have an extremely small core size only 2 10 nm in diameter which ranks across the dimensions of large proteins In fact only gold and magnetic material based nanocrystals possess such dimensions whereas majority of nanocarriers for example polymeric viral and liposomal often show 10 100 nm in size QDots are compact in nature so they show threefold benefits

As they are smaller in size than other nanocarriers so they can be easily swapped with them in order to study their nanocarrier behavior and optimizing their properties Quantum Dots being smaller in size can be easily incorporated within larger drug delivery vehicles and act as tracers in order to monitor intracellular trafficking and biodistribution Quantum Dots released from larger carriers can also be used to mimic redistribution and elimination of drug or its components 3 3 Nanopores Metal organic frameworks MOFs are recently developed regular nanoporous materials They are composed of a network of transition metal ions which are linked by bridging ligands except oxygen The synthesis of the first coordination polymers before the mid 1990s was actually driven mostly by the topological interest Several prominent examples of nanopores has been identified Porosity and chemical stability are two major factors that pose limitations to the preparation

A larger number of new MOFs having cationic anionic and neutral properties have been synthesized Recent innovations in the newly synthesized coordination polymer pose higher degrees of microporosity and chemical stability Coordination polymers possess finely controlled pore structure that's why they provide greater advantages as compared to other microporous materials for example zeolites and microporous carbons 3 4 Dendrimers Dendrimers are synthetic macromolecules with specialized architecture and are synthesized by frequentative controlled reaction steps Their synthesis starts from a trifunctional monomer generation 0 is termed as initial core subsequent monomers are connected to this trifunctional monomer resulting in a treelike architecture Hence the molecular mass of the dendrimers increases exponentially with the subsequent increase in the number of generations The basic structure gets saturated at a specified generation number In this regard dendrimers appear as captivating intermediates between the linear polymers and colloidal particles Dendrimers having low number of generation in their structure will be closely related to the star polymers which represents great number of conformations Dendrimers having high generation Number in their structure possess a densely packed radial structure and have less degrees of freedom 3 5 

Nanotubes Nanotechnology emphasizes the bottom up approach which refers to the precursor molecules being assembled spontaneously self assembly into Nanostructures of desired characters when water or other solvents are introduced to them This innate ability in the biomolecules such as proteins lipids and synthetic amphiphiles including surfactants and detergents to self assemble upon interaction with solvents Self assembly mechanism has been used since years and we have various kinds of self assembled nanoparticles that might be lesser understood as compared to others Nanotubes is a class of structures composed of one dimensional 1 D usually bilayer aggregates which enclose fibers ribbons and tubes These structures are prepared only by specific chiral amphipathic molecules and are stable under a specified conditions Nanotubes are formed by lipids steroids and their mixtures or collagen materials by their self assembly into triple helical fibers C12 β 12 3 6 Liposomes

Liposomes are spherical self assembled structures which comprise of curved lipid bilayers phospholipids in which surrounding solvents are encircled into their interior Liposomes consist of a variety of sizes ranging from some 20 nm up to 1 micrometer Liposomes they may be composed of one or more concentric membranes each membrane having a thickness of about 4 nm Liposomes show unique properties depending upon the amphipathic properties of the phospholipids and cholestrol which provides them stability and suitability to act as drug carriers 3 7 Nanoshells Nanoshells are considered as one of the fundamental elements of living systems Capsids carboxysomes exosomes vacuoles are major examples of nanoshells They are easily self assembled from organic molecules for example lipids or proteins but not from inorganic nanomaterials because of difficult replication of inorganic materials

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