Current Organic
Chemistry, Volume 9, No. 11, 2005
Contents
Nano- and
Microparticles with Tailored Properties
Guest Editor:
Stanislaw Slomkowski
Editorial Pp. 1023-1023
Stanislaw Slomkowski
Dendrimers – Nanoparticles with Precisely Engineered
Surfaces Pp. 1023-1051
I. Gitsov and C. Lin
Nanoscopic Confinement of Semi-Crystalline Polymers Pp. 1053-1066
Qi Zhang, Min Wang and
Karen L. Wooley
Functionalized Polymer Colloids: Synthesis and
Colloidal Stability Pp. 1067-1084
Jacqueline Forcada and
Roque Hidalgo-Alvarez
Poloxamer-Mediated Functionalization of Bioanalytical
Surfaces – The Role of Nanoparticles as Model Surfaces Pp. 1085-1098
Parke M. Byron, Karin
Fromell and Karin D. Caldwell
Functionalized Magnetic Emulsion for Genomic
Applications Pp. 1099-1106
R. Veyret, Th. Delair
C. Pichot and A. Elaissari
Abstracts
[Back to top] Editorial
Stanislaw Slomkowski
I have been invited to provide the present issue of
Current Organic Chemistry by Professor Stanislaw Penczek, the Executive Guest
Editor of COC. The papers focus on chemical reactions leading to nano- and
microparticles with tailored properties allowing for using these objects as
useful tools for various applications, in particular in the area of medicine.
Each particle consists of at least two zones – an interior and periphery.
Selective control of chemical structure of these zones leads to particles with
required internal integrity and properly adjusted interactions with molecules
in particle’ environment.
Authors of the first paper (I. Gitsov, C. Lin)
report on synthesis of dendrimers - the most precisely defined synthetic
unimolecular nanoparticles. Since their discovery dendrimers attracted
attention of many researchers and many reviews were published in this area.
Authors are specialist in post-synthesis modification of dendrimers, in
particular at their periphery, and in the review they discuss this subject in
details. The following paper (Q. Zhang, M. Wang, and K.L. Wooley) discusses
preparation and properties of nanoconfined crystalline organic polymers.
Crosslinking of core-crystallized polymer micelles in solution is presented as
a method for preparation of nanocrystalline objects. Authors of the next paper
(J. Forcada and R. Hidalgo-Álvarez) present a comprehensive review on synthesis
of polymer colloids with functional groups in the interfacial layer and on
relation between chemical structure of synthesized particles and their colloidal
stability. Importance of tailored chemical structure of interfacial layer of
colloidal particles for their suitability for immunodiagnostics has been
highlighted. Authors of the following review (M.P. Byron, K. Fromell and K.D.
Caldwell) report on controlled modification of surfaces, in particular surfaces
of colloidal particles, by attachment of surfactants with different types of
reactive groups. The discussed approach allows preparation of surfaces with
pre-determined levels of functionalization. Finally, Authors of the last review
on hybrid nanoparticles (R. Veyret, Th. Delair C. Pichot and A. Elaissari)
report on preparation of this new class of polymeric organic-inorganic
materials with core containing magnetic nanocrystals and tight shell formed by
layer-by-layer adsorption of purposely synthesized polyelectrolytes and on
using the core-shell magnetic colloids for binding, extraction, concentration,
and enzymatic amplification nucleic acids with desired oligonucleotide
sequences.
[Back to top] Dendrimers – Nanoparticles with Precisely Engineered
Surfaces
I.
Gitsov and C. Lin
Dendritic macromolecules or "dendrimers"
are artificial nanoparticles with precisely defined covalent macromolecular
architecture and broad application potential. Their discovery, construction
strategies, postsynthetic peripheral modifications, surface-related properties
and selected potential applications are the subject of this review. The
standard dendrimer is characterized by three distinct zones, the periphery, the
interior, and the core. All formation approaches ultimately yield structures
with these spatial arrangements. The specific interactions of the dendritic
molecules with their local nanoenvironment is determined by factors that include
the nature of starting building blocks, the synthetic pathway, and more
importantly – the postformation modifications on the periphery of the dendritic
globules or to a minor extent – on their interior. The review examines the
different chemistries used to tailor dendrimers and their properties for
specific applications.
[Back to top] Nanoscopic Confinement of Semi-Crystalline Polymers
Qi
Zhang, Min Wang and Karen L. Wooley
Nanocrystallinity is an important phenomenon in
natural and synthetic systems. Whether an inorganic or organic material, the
mechanism for confinement of crystal growth within nanoscopic dimensions
usually employs an organic mediator, which adsorbs to and stabilizes the
growing crystal. Following an introduction to nanocrystalline biomaterials and
inorganic materials, this review focuses upon the preparation and study of
nanoconfined crystalline organic polymers. Confinement is limited to nanoscopic
domains, by the phase segregation of crystalline-amorphous block copolymers in
the bulk or in solution. The effects of nanoconfinement upon the
crystallization behaviors are discussed, including reports of small-angle X-ray
scattering (SAXS), wide-angle X-ray scattering (WAXS), transmission electron
microscopy (TEM), and differential scanning calorimetry (DSC) studies. Examples
of nanoconfinement vs. break-out crystal growth are presented. Finally,
irreversible trapping of nanocrystalline domains via covalent crosslinking of
core-crystallized polymer micelles in solution is highlighted as a method for
the preparation of permanent, discrete nanocrystalline objects. Confinement
within the nanoscopic core domain of the shell crosslinked knedel-like (SCK)
polymer micelle and covalent attachment to the crosslinked SCK shell impart
interesting perturbations in local chain packing and disrupt the extent of
crystallinity. In addition, SCKs with a toroidal morphology are prepared by
micellization of diblock copolymers at high concentrations. A variety of
physicochemical techniques are employed to characterize the thermal properties
for SCKs of differing size and morphology. DSC is used to monitor the melting
and crystallization transitions and to assess the percentage of the
crystallinity of poly(e-caprolactone) (PCL) within the SCK cores, quenched at
different temperatures from the melt. The core-shell morphology of the SCK
imposes a fractionated crystallization onto the PCL and induces homogenous and
heterogeneous nucleation. In addition, the low percentage of crystallinity
found for PCL in SCKs, relative to that for PCL homopolymer and PCL-b-PAA
copolymer is interpreted as the product of spatial confinement and covalent
attachment to a crosslinked surface (the shell) provided by the containment of
the PCL chains within the SCK core domain.
[Back to top] Functionalized Polymer Colloids: Synthesis and Colloidal
Stability
Jacqueline Forcada and
Roque Hidalgo-Alvarez
Functionalized polymer colloids were synthesized by
emulsion polymerization having specific ionic groups on surface. In this
review, a comprehensive study on the synthesis of functionalized polymer
colloids is carried out. Monodisperse polymer colloids with acetal, aldehyde,
chloromethyl, and amino functionalities were synthesized by a multi-step
emulsion polymerization process. In the first step, the seeds were synthesized
by batch emulsion polymerization of styrene; and in the following steps, onto
the previously formed polystyrene latex particles, the functional monomers were
co- and/or ter-polymerized. Some of the synthesized latexes were chosen as the
polymeric support to carry out the covalent coupling with a protein and to test
the utility of the latex-protein complexes formed in immunoassays. In addition,
the colloidal stability of polymer colloids is theoretically and experimentally
analyzed. This study shows that classical DLVO (Derjaguin, Landau, Verwey,
Overbeek) theory can explain the stability of weakly charged polymer colloids.
This is not sufficient in the case of highly charged polymer colloids using
hydrophilic monomers. In such a system, the steric repulsion is not negligible
and an electrosteric repulsion mechanism must be considered. Our interest has
centered on studying this effect from a quantitative point of view. Although
the method used contains five variables, it is possible to considerably reduce
this number if some of them are calculated by alternative methods (yd, d) or
taken from literature (A, c).
[Back to top] Poloxamer-Mediated Functionalization of Bioanalytical
Surfaces – The Role of Nanoparticles as Model Surfaces
Parke
M. Byron, Karin Fromell and Karin D. Caldwell
Because of their availability in discrete sizes and
the relative ease with which they can be derivatized and characterized,
polymeric nanoparticles have become important model surfaces in bioanalytical
work. One finds that increased reaction rates and reduced steric hindrance are
the results when proteins or other reactive macromolecules are attached to ever
smaller particulate carriers in the sub-micron size range. The introduction of
new chemical features to a surface can be followed and optimized through work
with polymeric surfactants that adsorb in a stable manner to hydrophobic surfaces,
such as those associated with the latex particles. By introducing reactive
structures into the end-groups of such polymeric surfactants, and then mixing
derivatized with underivatized product prior to adsorption, one can let the
process yield surfaces with pre-determined levels of functionalization. By
mixing surfactants with different types of reactive structures it is possible
to engineer surfaces with distinctly optimal performance in specific
situations. One such situation is the attachment of the particle to some other
substrate, e.g. a flat surface for optical read-out. Such attachments have been
performed and the bound particles have proven to resist shear-induced removal
even at high rates of laminar flow.
Through this strategy, particles attached in large
arrays may be relied upon to facilitate the complex analyses mandated by the
rapidly growing field of proteomics.
[Back to top] Functionalized Magnetic Emulsion for Genomic Applications
R.
Veyret, Th. Delair C. Pichot and A. Elaissari
Narrowly size-distributed functionalized magnetic
emulsions with diameters between 200 and 300 nm bearing reactive amine or
carboxylic groups were prepared respectively via single adsorption or
layer-by-layer adsorption process. The colloidal stability of the
functionalized magnetic emulsion was related to the polymer adsorbed amount and
to the adsorption methodology. The single adsorption of poly(ethyleneimine)
onto negatively charged magnetic emulsion led to amino-containing magnetic
nanodroplets for nucleic acid extraction, concentration and amplification. The
enzymatic amplification of adsorbed nucleic acid molecules (i.e. RNA) was found
to be related to both initial nucleic acid concentration and the used magnetic
particles in the amplification step. The undesirable inhibition phenomena
observed in the enzymatic amplification (i.e. RT-PCR) process was eliminated by
the addition of appropriate negatively charged polyelectrolyte before the
amplification step. The encapsulation of magnetic emulsion via layer-by-layer
polyelectrolytes adsorption process was used to elaborate functionalized
core-shell magnetic colloids. The characterized final magnetic dispersions were
evaluated in specific nucleic acids capture and detection, and in proteins
immobilization process.