Charge-transfer interactions for the fabrication of multifunctional viral nanoparticles

Article abstract of DOI:10.1039/c4cc05195e

A facile strategy to fabricate multifunctional viral nanoparticles was described by introducing charge-transfer interactions between a pyrenyl motif with dinitrophenyl and pyridinium-contained guest molecules. This journal is

Full text of DOI:10.1039/c4cc05195e

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Charge-transfer interactions for the fabrication of
multifunctional viral nanoparticles†
Cite this: Chem. Commun., 2014,
50, 14125
Jun Hu,‡ab Peiyi Wang,‡c Xia Zhao,a Lin Lv,b Song Yang,c Baoan Song*c and
Qian Wang*b
Received 7th July 2014,
Accepted 16th September 2014
DOI: 10.1039/c4cc05195e
www.rsc.org/chemcomm
A facile strategy to fabricate multifunctional viral nanoparticles was electron-rich and electron-deficient species has been extensively
described by introducing charge-transfer interactions between a applied to smart materials, self-assembly, drug and gene delivery
pyrenyl motif with dinitrophenyl and pyridinium-contained guest due to its modularity, reversibility and stimuli-responsiveness.6 For
molecules.
example, Huang and co-workers found that 2,4,6-trinitrotoluene
(TNT) can be encapsulated by microtubes assembled from the
Significant progress has been made in the development of pillar[5]arene amphiphile using CT interactions.7a Guchhait and
multifunctional nanoparticles for their wide biomedical appli- co-workers successfully utilized the interactions of human serum
cations in the past decades.1 Specifically, viral nanoparticles albumin with a CT-probe (ethyl ester of N,N-dimethylamino
(VNPs) derived from bacteria or plants have attracted consider- naphthyl acrylic acid) to study the protein micro-environment.7b
able interest because of their multivalent programmable and To date, reports on the application of CT-interactions modified
monodispersed structures, as well as their low toxicity and good VNPs are still rare,8 though several works on protein modification
biocompatibility.2 For better use of the inherent features of using supramolecular interactions have been reported.9
VNPs, a series of multifunctional VNPs has been fabricated
Herein, we used the pyrene (PYR) moiety bearing a PEG
by bio-orthogonal conjugation approaches, in which various chain to link the tobacco mosaic virus, TMV(wt), consequently
targeting catalytic units, ligands, diagnostic probes and therapeutic fabricating an electron-donor based on VNPs (Fig. 1a). PYR and
cargoes have been modified on the surface or inside of the internal its derivatives have been widely used as fluorescence probes in
cavity of VNPs.3
a large number of complex systems because of their high
However, these covalent-constructed methods are irreversible fluorescence quantum yields, long excited state lifetimes, and
and normally require long reaction times and lengthy purification the ability to form excimers.10 TMV(wt) is a model VNP having a
steps to introduce functional groups in the synthesis.4 Consequently, rod-shape, 300 nm in length and 18 nm in diameter, consisting
supramolecular interactions are becoming more attractive because it of 2130 identical subunit proteins arranged helically around a
is easy to realize the predictable change through attaching different genomic single RNA strand.11 On the other hand, dinitrophenyl
stimuli-responsive groups on the basis of noncovalent synthesis, and pyridinium-contained guest molecules (Fig. 1b) are chosen
including hydrogen bonds, p-stacking, charge-transfer (CT) inter- to be the electron-acceptors to form the CT complex.12 The
actions, electrostatic interactions, and host–guest complexation.5 modified fluorescent TMV(wt)-PYR can form supra-amphiphiles
In the supramolecular interactions family, CT interactions between with different electron-deficient molecules through CT interactions
(Fig. 1c), in which a marked ‘‘switch off’’ of fluorescence from the
a State Key Lab of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, China
b Department of Chemistry and Biochemistry, University of South Carolina,
Columbia, SC 29208, USA. E-mail: wang263@mailbox.sc.edu
c State Key Lab Breeding Base of Green Pesticide & Agricultural Bioengineering
Centre for R&D of Fine Chemicals, Guizhou University, Guiyang, 550025, China.
E-mail: songbaoan22@yahoo.com
PYR motif could be observed.
As shown in Fig. 1a, PYR was attached to the exterior surface of
TMV(wt) by the sequential diazonium-coupling and CuI-catalyzed
azide–alkyne cycloaddition (CuAAC) reaction (see ESI† for experi-
mental details).13 The formation of TMV(wt)-PYR was confirmed
by UV-Vis and fluorescence spectra, as well as MALDI-TOF MS and
SDS-PAGE analyses. As shown in Fig. 2a, two new peaks at 345 and
511 nm are observed. The peak at 345 nm is typical for the PYR
group, while the peak at 511 nm could be attributed to the
conjugative effect between the azobenzenyl and 1,2,3-triazole
moieties, implying the successful attachment of the PYR moieties
† Electronic supplementary information (ESI) available: The details of instruments,
reagents, and sample preparations; synthetic details, MS, and NMR spectra of
PYR-Azide, TMV(wt)-Alkyne, TMV(wt)-PYR, DNB, DDNB, DNB-Polyhema, MV, TV,
and 2-AP; data of SDS-PAGE, SEC, DLS, TEM, and Job’s plot. See DOI: 10.1039/
c4cc05195e
‡ These two authors contribute equally to this work.
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Fig. 1 (a) Preparation of TMV(wt)-PYR using diazonium-coupling and ‘CuAAC’ reactions. (b) Structures of electron-deficient guest molecules and CB[8].
(c) Schematic demonstration of the formation of multifunctional TMV(wt) via CT interactions between PYR and electron-deficient molecules.
To test the CT interactions between PYR and electron-
deficient molecules, six guest molecules, DNB, DDNB, DNB-
Polyhema, MV, TV, and 2-AP (Fig. 1b), were synthesized (see
ESI† for experimental details). As a general protocol, TMV(wt)-
PYR was incubated with electron-deficient molecules at different
concentrations for 10 min at r.t. prior to fluorescence measure-
ment. As shown in Fig. 3a, the fluorescence intensity of TMV(wt)-
PYR is quenched dramatically upon the addition of DNB, revealing
the CT interactions between TMV(wt)-PYR and DNB. The Job’s plot
shows a 1 : 1 complex formation for TMV(wt)-PYR/DNB (Fig. S4,
ESI†),15 which indicates that each TMV(wt)-PYR subunit associates
with one DNB molecule. Other DNB-contained small molecules
(DDNB) and polymers (DNB-Polyhema) were also tested using the
aforementioned method. As shown in Fig. 3b and c, DDNB and
DNB-Polyhema can quench the fluorescence of PYR with the
binding modes as 1 : 2 and 1 : 1, respectively (Fig. S5 and S6, ESI†).
Furthermore, there is no change in the integrity of TMV(wt)-PYR
TMV(wt)-PYR, and PYR-Azide. Excitation wavelength is 345 nm. (c) MALDI-
Fig. 2 (a) UV-Vis and (b) fluorescence spectra of TMV(wt), TMV(wt)-Alkyne,
upon complexation, as observed with TEM (Fig. S7, ESI†). It is
apparent that the DNB-contained electron-deficient molecules can
form CT-complexes with the TMV(wt)-PYR nanoparticles. However,
all the attempts to measure binding constants using isothermal
titration calorimetry (ITC) failed, likely due to the existence of
DMSO (as the co-solvent to dissolve the small molecules).
In contrast, when MV was used to form the CT-complex
TOF MS of the subunit proteins of TMV(wt), TMV(wt), and TMV(wt)-PYR the
calculated MS for TMV(wt), TMV(wt)-Alkyne, and TMV(wt)-PYR are 17534,
17 662, and 18 109, respectively; the 452 m/z difference between TMV(wt)-PYR
and TMV(wt)-Alkyne is consistent with the theoretical molar mass (447 m/z)
of newly added PYR-Azide within the permitted error. (d) TEM image of
uranyl acetate-stained TMV(wt)-PYR. Scale bar is 300 nm.
to the exterior surface of TMV(wt) by the ‘CuAAC’ reaction. This under the same condition as the DNB-derivatives, no obvious
can be further verified by fluorescence spectra, in which TMV(wt)- reduction in the emission could be observed (Fig. 3d). It was
PYR shows a strong fluorescence signal at 417 nm as compared to probably due to the electronic attractions between the positive
TMV(wt) and TMV(wt)-Alkyne (Fig. 2b). It should be noted that charge of MV and the negative charge on TMV(wt),11 consequently
the slight wavelength shift between TMV(wt)-PYR and the small leading to the absence of electron-deficient components for the
molecular PYR-Azide could be attributed to the intermolecular formation of the CT-complex. To prohibit such binding, cucurbit-
interactions of the PYR groups on the virus.14 The MALDI-TOF MS [8]uril (CB[8]) was used as a ‘‘molecular handcuff’’ to bring the MV
result afforded the direct evidence for this complete conjugation and PYR moieties together.16 It is known that CB[8] is a macrocyclic
reaction. As shown in Fig. 2c, the peak of the alkyne-modified molecule that can form inclusive complexes with a high selectivity
TMV(wt) at m/z 17 659 disappears completely, while a new peak at and binding affinity in aqueous media.17 In addition, it was found
m/z 18 111 is observed, indicating the full conversion of TMV(wt)- that the size of PYR allowed the 1 : 1 complexation with CB[8], and
Alkyne to TMV(wt)-PYR upon conjugation. It is consistent with the CB[8] is large enough to encapsulate two molecules at the same
results from the SDS-PAGE analysis (Fig. S1, ESI†). In addition, time. Therefore, we utilized PYR and MV as the guest for CB[8] to
the integrity of the TMV(wt) nanoparticles upon conjugation was study their CT interactions in CB[8]. The emission spectra (Fig. 3e)
confirmed by size exclusion chromatography (SEC, Fig. S2, ESI†), indicate the formation of a supramolecular amphiphile because a
transmission electron microscopy (TEM, Fig. 2d) and dynamic significant fluorescence quenching effect could be observed from
light scattering (DLS, Fig. S3, ESI†).
the CT interactions between PYR and MV inside the CB[8] cavity.
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pH 7.8, Fig. S8, ESI†).22 Whereas under the same conditions, only
a partial fragile hydrogel formed for TMV(wt). It indicates that the
CT interactions between the PYR moieties and the pyridiniums
promote gelation. The detailed mechanism is being studied.
We demonstrated a facile strategy to fabricate multifunctional
viral nanoparticles using CT interactions between pyrene-contained
TMV(wt) nanoparticles with dinitrophenyl and pyridinium-based
guest molecules. It is expected that the reversibility and the stimuli-
responsive features of such supramolecular interactions can lead to
the development of novel functional biomaterials.
This work is financially supported by US NSF-CHEM 1307319
and China Scholarship Council (200001). BS and SY thank
the financial support of International Science & Technology
Cooperation Program of China (2010DFB60840), National Key
Program for Basic Research (2010CB126105), and National
Nature Science Foundation of China (21132003). QW and JH
are thankful for the support of State Key Laboratory of Polymer
Physics and Chemistry, CIAC, China.
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