Targeted Drug Delivery in Covalent Organic Nanosheets (CONs) via

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Targeted Drug Delivery in Covalent Organic Nanosheets (CONs) via Sequential Postsynthesis Shouvik Mitra, Himadri Sekhar Sasmal, Tanay Kundu, Sharath Kandambeth, Kavya S. Illath, David Díaz Díaz, and Rahul Banerjee J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b00925 • Publication Date (Web): 03 Mar 2017 Downloaded from http://pubs.acs.org on March 3, 2017

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Journal of the American Chemical Society

Targeted Drug Delivery in Covalent Organic Nanosheets (CONs) via Sequential Postsynthesis Shouvik Mitra,a‡ Himadri Sekhar Sasmal,a,b‡ Tanay Kundu,a,b Sharath Kandambeth,a,b Kavya I.,a,b David Díaz Díaz,c and Rahul Banerjee*a,b a

Physical/Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune-411008, India.

b

Academy of Scientific and Innovative Research (AcSIR), New Delhi, India.

c

Institut für Organische Chemie, Universität Regensburg,Universitätsstr.31, 93040 Regensburg, (Germany); and IQAC-CSIC, Jordi Girona 18-26, Barcelona 08034, (Spain). ABSTRACT: Covalent organic nanosheets (CONs) have emerged as a new class of functional two-dimensional (2D) porous organic polymeric materials with a high accessible surface, diverse functionality and chemical stability. They could become a versatile candidate for targeted drug delivery. Despite their many advantages, there are limitations to use them for target specific drug delivery. We anticipated that these drawbacks could be overturned by judicious postsynthetic modification steps to use CONs for targeted drug delivery. The postsynthetic modification would not only produce the desired functionality, it would also help in exfoliation to CONs as well. In order to meet this requirement, we have developed a facile, salt-mediated synthesis of covalent organic frameworks (COFs) in presence of p-toluenesulphonic acid (PTSA). The COFs were subjected to sequential postsynthetic modifications to yield functionalized targeted CONs for targeted delivery of 5-fluorouracil to the breast cancer cells. This postsynthetic modification resulted in simultaneous chemical delamination and functionalization to targeted CONs. Targeted CONs showed sustained release of the drug to the cancer cells through receptor-mediated endocytosis, which led to cancer cell death via apoptosis. Considering easy and facile COF synthesis, functionality based postsynthetic modifications and chemical delamination to CONs for potential advantageous targeted drug delivery, this process can have a significant impact in biomedical applications.

INTRODUCTION Functional two-dimensional (2D) materials have picked up attention of the researchers worldwide due to their promising applications in catalysis, sensing, electronics, drug delivery, and separation.1,2 Among these, two-dimensional covalent organic frameworks (2D COFs), an emerging class of porous crystalline polymers, have attracted significant attention due to their crystalline, ordered and relatively large accessible porous structures.3 As a result, these COFs have undergone rapid development in terms of synthesis, chemical stability, and applications.3d-3i Further research on these materials has led to the discovery of the covalent organic nanosheets (CONs), via exfoliation of the COFs.4 Thin layered CONs with high aspect ratio are expected to showcase dimension related excellent properties that are different from their bulk counterparts.1c, 4a, 4c, 4f Although, the hydrolytic instability of the CONs appeared to be the setback for their further potential applications; recently, the introduction of combined reversible-irreversible enol-keto tautomerism within the thin CONs has imparted exceptional chemical stability.4d, 4g, 4k, 4l Therefore, one would anticipate, because of their high accessible surface, diverse functionality, and chemical stability, these CONs could become a potential candidate for biomedical applications, especially for targeted drug delivery. In general, a targeted drug delivery system requires (i) good loading capacity and sustained release of the payload, (ii) local control of the site-specific payload

release, (iii) non-toxic nature of the carrier, and (iv) the possibility of surface engineering of the nanocarriers.5 Although nanoparticles, biocompatible polymeric materials, liposomes and metal organic frameworks have been extensively used as a vector for drug delivery, the lack of functionality, chemical stability, tedious synthetic hurdles and unwanted toxic metal ions leached from the carriers might lead to unsatisfactory drug delivery performance.5 Hence, metal ion free, chemically stable, functionalized CONs could possibly become a solution for the targeted drug delivery. Indeed, COFs has been tested for the encapsulation and release of drugs like ibuprofen and quercetin.6-8 However, the usage of the bulk COF materials could present a few serious drawbacks owing to their low dispersibility and, subsequently, low bioavailability within the cells.9 Therefore, functionalized CONs with good aqueous dispersibility could act as a possible replacement of COFs for the targeted drug delivery. The synthetic hurdles, possible restacking and difficult processability further limit their usage for the targeted drug delivery.4 We anticipated that these drawbacks could be overturned by judicious postsynthetic modifications so that these CONs could become appropriate for targeted drug delivery.4,10 A typical postsynthetic modification technique would offer incorporation of ‘on demand’ desired functionality on the surface, which could be further fabricated.10 Additionally, the postsynthetic modifications could weaken the π-π stacking to exfoliate the COFs to thin layered functionalized postsynthetically modified CONs. It is noteworthy to mention that direct incorporation of such functionality within the CONs framework is

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Figure 1. (a) Synthetic scheme of two COFs: TpAPH and TpASH, (b) PXRD pattern of TpAPH, inset shows space-filling model of TpAPH, (c) PXRD pattern of TpASH, inset shows space-filling model of TpASH, (d) Synthetic scheme of monomer (SaASH) [(4E,10E)-N'-(2hydroxybenzylidene)-4-(2-hydroxybenzylideneamino)-2-hydroxybenzohydrazide], (e) ORTEP diagram of the monomer (SaASH) at 50% probability level.

very limited and still remains a daunting task.10 Hence, we have made an attempt to present a facile salt-mediated synthesis of two COFs namely, TpASH and TpAPH via a newly developed solid state mixing procedure.11 Three sequential postsynthetic modifications were used on the TpASH to yield folate conjugated CONs (TpASH-FA) for targeted drug delivery of the anticancer drug 5-fluorouracil (5-FU) within the breast cancer cells MDAMB-231. Postsynthetically modified targeted CONs preferentially delivers the drug to the breast cancer cells through receptormediated endocytosis that leads to cancer cell death. To the best of our knowledge, this is the first report of a targeted drug delivery

using CONs via functionality based sequential postsynthetic modifications.

EXPERIMENTAL SECTION Synthesis of COFs. TpAPH and TpASH were synthesized via salt-mediated Schiff base condensation between 0.3 mmol 1,3,5triformylphloroglucinol (Tp) (63 mg) and 0.45 mmol of diamines (APH: 68 mg, ASH: 75 mg) in the presence of PTSA (500 mg) via a newly developed solid state mixing procedure.11 Diamines and PTSA were mixed in a mortar to obtain a sticky salt. Tp and deionized water were added to it. The mixture was then transferred to a glass vial and kept in 90 ˚C for 12 h. The resultant product was


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Journal of the American Chemical Society For cellular migration studies, MDA-MB-231 cells were grown in a 6 well plate, striped with a pipette tip, and allowed to recover. Control and treated cells were assessed for the cellular migration. Cellular migration was determined by measuring the wound width under an inverted microscope using the image J software. For cellular uptake study, the functionalized CONs were conjugated with fluorescent dye rhodamine-B-isothiocyanate (RITC) and tested against MDA-MB-231 cells after incubation and fixing. For postsynthetically modified targeted CONs, we used TpASH-FARITC, and for non-targeted CONs, we used TpASH-APTESRITC. A detailed description of all the biological experiments has been provided in Section S10, ESI.

RESULTS AND DISCUSSIONS

Figure 2. (a) 13C CP MAS solid state NMR, (b) Nitrogen adsorption isotherm (c) Water vapor uptake of TpAPH and TpASH respectively.

washed extensively with hot water (to remove PTSA), DMAc and acetone respectively. The product was dried at 90 ˚C overnight to obtain brown colored COFs. COF to targeted CONs via postsynthetic modifications. Three sequential postsynthetic modifications were carried out on TpASH, to yield postsynthetically modified functionalized targeted CONs (TpASH-FA) for the delivery of 5-FU. The first step involved the conjugation of glycidol (Glc) to convert the phenolic hydroxyl groups to surface alkyl hydroxyl groups. The surface hydroxyl (–OH) groups were then used for conjugation of 3aminopropyltriethoxysilane (APTES) to give amine (–NH2) functionalized CONs (TpASH-APTES). Finally, folic acid was conjugated to TpASH-APTES to yield the targeted CONs (TpASHFA) using the EDC/NHS coupling reaction (detailed in Section S9, ESI). Drug loading, drug release experiments, and amine quantification studies are also detailed in Section S9-S10, ESI. Biological experiments. Breast cancer cell lines (MDA-MB231) were assessed for the in vitro toxicity study via MTT assay. Cancer cells were implanted in a 96 well plate and kept for 24 h. The cells were then incubated for 48 h with TpASH, TpASHAPTES-5FU (non-targeted drug loaded CONs) and TpASH-FA5FU (targeted drug loaded CONs) of different concentrations, followed by the incubation with the MTT reagent for 3–4 h at 37 ºC. Formazan was dissolved in solubilization buffer and cellular viability was checked by measuring the absorbance at λ = 570 nm.

Hydroxyl (–OH) functionalities are ideal for the postsynthetic modifications due to their easy derivatizable nature under mild reaction conditions.12 Therefore, we have selected 4aminosalicylhydrazide (ASH) as one of the linker units for COF construction. In addition, 4-aminobenzohydrazide (APH) was also selected for the synthesis of a non-hydroxyl COF analogue for comparison (Figure 1a, Section S2, ESI). It is noteworthy to mention that ASH attains a planar structure as the o-hydroxyl group remains H-bonded with amide carbonyl oxygen [O-H•••O=C, D= 2.544(4) Å, d =1.83 Å, θ = 146˚] (Figure S7).13 This gave us the idea that planar diamine structure could be useful for COF synthesis, and these hydroxyl (–OH) groups could be used for further postsynthetic modifications to produce functionalized CONs for targeted drug delivery. Two COFs were synthesized via the saltmediated Schiff base condensation reaction in the presence of ptoluenesulphonic acid (PTSA) in ~80% yield (Figure 1a).11 PXRD patterns of TpAPH and TpASH show the first peak at 2θ = ~4.6° and ~4.3° respectively, which corresponds to the reflection from the (100) planes. The broad peak at 2θ = ~27.7° and ~27.6° could be indexed to the π-π stacked planes (001) of TpAPH and TpASH respectively (Figure 1b, 1c). In order to get further structural insights, the TpASH monomer (SaASH) [(4E,10E)-N'-(2hydroxybenzylidene)-4-(2-hydroxybenzylideneamino)-2hydroxybenzohydrazide] was synthesized and crystallized in DMF (Figure 1d, 1e). Based on the monomer structure (Figure 1e, S8 ESI), TpAPH and TpASH were modeled in possible eclipsed and staggered structures (Section S4, S5, ESI), where AA eclipsed stacking mode corroborated well with the experimentally observed PXRD patterns (Figure S9-S12, ESI). Both TpAPH and TpASH crystallized in the P1 space group, with the cell parameters a = 25.93, b = 26.01, c = 3.40 Ǻ for TpAPH [Rwp: 3.7%, Rp: 2.3%]. While the cell parameters for TpASH were a = 24.40, b = 24.41, c = 3.41 Ǻ [Rwp: 2.2%, Rp: 1.3%]. Planar structure of the monomeric unit indicates the reason for the crystallinity in COFs. FTIR spectra of both the COFs showed characteristic C=C and C–N stretching frequencies at 1569 cm-1 and 1250-1257 cm-1 respectively (Figure S13, S14). 13C CP MAS solid state NMR showed characteristic exocyclic C=C signals at 103-106 ppm and the signature C=O signals were observed at 184 ppm arising from irreversible enol to keto tautomerism (Figure 2a).10 Thermogravimetric analysis (TGA) of both the COFs showed their stability up to 300



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Figure 3. (a) Chem Draw and space fill representation of assembled COF sheets, (b) Sequential postsynthetic modification scheme of TpASH to functionalized targeted CONs (TpASH-FA) (c) 13C CP MAS solid state NMR spectra of functionalization steps after postsynthetic modifications, (d) SEM and (e) TEM images of TpASH after sequential postsynthetic modifications.

°C (Figure S16). Brunauer-Emmett-Teller surface area (SBET) of activated TpAPH and TpASH were calculated to be 525 and 500 m2g-1 respectively. Both COFs followed a regular type-II adsorption isotherm (Figure 2b). The pore diameter of TpAPH and TpASH were found to be 1.4 and 1.3 nm respectively, which was also consistent with the BET analysis (Figure S17).14 Comparable surface areas of both the COFs indicate the similarity of the linkers used for their synthesis. Water uptake properties of TpAPH and TpASH signified greater hydrophilicity of TpASH. TpAPH showed water uptake of 198 ccg-1 at 298K, 0.9 bar pressure (Figure 2c). While TpASH showed an elevated water uptake of 254 ccg-1 at 298K, 0.9 bar pressure, owing to the presence of the hydroxyl groups (Figure 2c). Scanning electron microscopy (SEM) analysis of both COFs demonstrated aggregation of sheet-like assemblies (Figure S18). Notably, transmission electron microscopy (TEM) images of TpAPH and TpASH showed rippled sheet-like structures with a lateral dimension of 800 nm to 1.5 µm (Figure S19).

Fabrication of the targeted drug delivery system often requires surface amine (–NH2) groups which could be used for anchoring targeting ligands for the site-specific drug delivery.10, 12 Herein, we judiciously selected TpASH with free hydroxyl (–OH) groups, which could be utilized for anchoring surface amine (–NH2) groups for further sequential postsynthetic modifications. We anticipated that these postsynthetic modifications would introduce the desired functionality as well as chemical delamination to convert TpASH to TpASH-FA CONs.4 This functionalized CONs, in result, would offer greater bioavailability, and cellular internalization for a targeted drug delivery.15 Keeping this idea in perspective, we have deployed three sequential postsynthetic modification steps to produce the targeted CONs-based nanocarriers (Figure 3a). The first step consisted of the conversion of the phenolic hydroxyl groups to alkyl hydroxyl groups in presence of glycidol (Glc) via epoxy ring opening to yield TpASH-Glc CONs.16a The second step involved the conversion of these surface alkyl hydroxyl groups to amines in presence of APTES to afford the desired amine function


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Figure 4. (a) Schematic representation of targeted drug delivery by CONs (sheet-like material denotes CONs here), (b) Drug loading study of 5-FU by UV-Vis, (c) MTT assay on MDA-MB-231 cell lines showing cellular viability, (d) Comparison of cellular migration study between control and TpASH-FA-5-FU treated sets.

alized CONs (TpASH-APTES).16b The third step involved the conjugation of the cellular targeting ligand folic acid (FA), resulting in folate conjugated targeted CONs (TpASH-FA) (Figure 3a).16b In order to confirm the successful postsynthetic modifications in CONs, we have used FTIR and 13C CP MAS solid state NMR analysis. FTIR of TpASH indicated characteristic C=C and C–N stretching frequencies at 1569 cm-1 and 1250-1257 cm-1 respectively. However, in TpASH-Glc CONs, additional peaks corresponding to C–H asymmetric and symmetric stretching frequencies were observed at 2920 cm-1 and 2853 cm-1 respectively. This was attributed to the methylene fragments of glycidol. The second modification on TpASH-Glc resulted in surface accessible amines. The C–H asymmetric and symmetric stretching were slightly shifted to 2882 cm-1 and 2830 cm-1 respectively; and Si–O stretching frequency arising from APTES fragments was merged with the C–N signal of TpASH. In TpASH-FA, additional amide signals at 1655 cm-1 and 1546 cm-1 were merged with strong C=C signal of the pristine COF, whereas the rest of the signals remained unaltered (Figure S22). Change in the surface functionality was further supported by zeta potential measurements. At an acidic pH 3, TpASH showed a negative zeta potential of -3 mV, while TpASHAPTES CONs showed a positive zeta potential of +2.98 mV. As expected, the zeta potential value of TpASH was negative, as it contained surface hydroxyl (–OH) groups. As the pH value increased, its zeta potential value was increased due to the ionization of the –OH groups. On the other hand, the positive zeta potential

of TpASH-APTES CONs, at an acidic pH, was attributed to the protonated –NH3+ groups; while the zeta potential value of TpASH-FA lies in between (Figure S23).16b This surface charge reversal in the CONs further confirms its surface amination. Fabrication of a targeted drug delivery system after sequential postsynthetic modifications was further verified by 13C CP MAS solid state NMR analysis. Two additional sharp signals in the deshielded aliphatic region (70.2 and 64.2 ppm) signified the binding of Glc to TpASH. In TpASH-APTES CONs, three shielded aliphatic methylene signals (9.8, ~24.1 and ~22.2 ppm) derived from the APTES fragment were attributed to the successful addition of APTES to TpASH-Glc. Additional peaks in aliphatic region (39.9 to 58.2 ppm) in TpASH-FA were ascribed to the FA conjugation. However, the amide carbon signal in TpASH-FA CONs was overlapped with that of the pristine COF at 163 ppm (Figure 3c). Nevertheless, a small shoulder at 363 nm, and a characteristic peak at 280 nm in the UV-Vis spectra is an evidence of the folate conjugation to TpASH (Figure S24).16b 29Si CP MAS solid state NMR and EDX analysis was further used to support the conjugation of APTES fragment on the TpASH. TpASH was 29Si CP MAS solid state NMR silent, while TpASH-APTES CONs showed two characteristic peaks at -58 and -66 ppm (Figure S25).17 These peaks confirmed the successful conjugation of APTES and were consistent with the literature.17 A detailed morphological comparison was carried out after postsynthetic modifications using SEM and TEM. SEM images demonstrated sheet-like morphology, which was maintained after functionalization (Figure 3d, S29). TEM analysis



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also corroborated with the SEM results, where transparent, rippled sheet-like CONs were observed with an average lateral dimension of 1 µm to 1.5 µm. TEM images of the sequential functionalization steps are shown in Figure 3e and Figure S30. Functionalized targeted CONs produced a uniform dispersion in water and executed the ‘Tyndall Effect’ (Figure S32).4 This dispersion stability in the postsynthetically modified CONs could be attributed to their surface functionalization. This postsynthetic modification resulted in further weakening of the π-π stacking between the layers, which leads to the exfoliation.4l A sharp reduction in the BrunauerEmmett-Teller surface area (SBET) in functionalized targeted CONs confirmed this exfoliation phenomenon (Figure S28).4l Although the surface area was reduced in CONs, PXRD patterns suggested the preservation of the structural integrity (Figure S26). Chemical delamination of the TpASH to targeted functionalized CONs was also verified by atomic force microscopy (AFM) carried out in tapping mode. A reduction in average height profile to 15 nm in CONs signified the same (Figure S33). EDX analysis associated with TEM showed the presence of Si in TpASH-APTES CONs, which also corroborated with 13C and 29Si CP MAS solid state NMR (Figure S31). Once more, detailed characterizations confirmed the functionality based modifications to yield the postsynthetically modified CONs, but not their existence as a physical mixture. In order to showcase the importance of the –OH functionality for postsynthetic modifications, we used the non-hydroxyl TpAPH COF for comparison. Under identical reaction conditions, APTES functionalization was fruitless due to the lack of hydroxyl (–OH) functionality in TpAPH (Figure S27). Reversible p-nitro benzaldehyde assay of imine formation16b, 18 (Section S9, ESI) indicated that 0.058 mMmg-1 and 0.054 mMmg-1 surface accessible amine groups were present on CONs TpASH-APTES and TpASH-FA respectively. The remaining surface amines on TpASH-FA were used for dye conjugation, required for cellular uptake studies.

anticancer activity, only 14% of the cells were viable at a dosage of 50 μgmL-1 (Figure 4c). It is noteworthy to mention that the drug loaded targeted CONs (TpASH-FA-5-FU) showed the preferential killing of cancer cells over the non-targeted one (TpASH-APTES-5-FU). This was attributed to the MDA-MB231 cell specific targeting of TpASH-FA, where the folate receptor is over expressed.16b MTT assay was further validated by cellular migration studies carried out on MDA-MB-231 cells for 24 h. After 24 h the control cell showed cellular migration, but in the treated cells the cellular migration was reduced in a concentration dependent manner (Figure 4d).19 This addresses the potential of TpASH-FA-5-FU for targeted drug delivery. Successful targeting of CONs was also validated by cellular uptake studies carried out under fluorescent microscopy. TpASH-FA (targeted CONs) and TpASH-APTES (non-targeted CONs) both were conjugated with fluorescent dye rhodamine-B-isothiocyanate (RITC) (Section S10, ESI, Figure S39). When DAPI stained MDA-MB-231 cells were incubated with TpASH-FA-RITC and TpASH-APTES-RITC, and observed under a fluorescent microscope at 540 nm excitation wavelength, the targeted CONs (TpASH-FA-RITC) showed preferential distribution within the cytoplasm (Figure S40). Hence, the targeted ones are readily internalized within MDA-MB-231 cells in comparison to the non-targeted CONs. In order to draw conclusions, we carried out apoptosis analysis. Interestingly the morphologies of the control cells were unperturbed, without abnormality, whereas the treated ones showed blebbing/fragmentation inducing apoptosis (Figure S41).16b Therefore, drug loaded targeted CONs (TpASH-FA-5-FU) preferentially delivers the drug (5-FU) to the folate overexpressed breast cancer cells through receptor-mediated endocytosis that leads to the cell death via apoptosis (Figure 4a).

5-Fluorouracil (5-FU) is an antimetabolite based anticancer chemotherapy drug.19 We selected 5-FU as a model drug due to its small kinetic diameter and a possible easy loading on to the surface of the CONs. Drug loading was monitored via UV-Vis spectroscopy by comparing the absorbance of the drug standard and supernatant solution respectively (Section S10, ESI). UV-Vis analysis demonstrated 12% loading (0.06 mg of 5- FU/mg of TpASH-FA) of 5-FU on to the targeted functionalized CONs TpASH-FA (Figure 4b; Figure S36-S37). Although the loading efficiency of the drug on to the CONs was less compared to 3D COF or PI-n-COFs,6-8 the successful targeting endowed its potential application in targeted drug delivery, which has not yet been performed. Notably, the loading of drug in CONs was higher in comparison to the biocompatible polymers like polyethylene glycol-4000 (PEG-4000), polyvinylpyrrolidone (PVP), polylactic acid (PLLA) (Figure S34). The cumulative drug release profile was monitored at two different pH values (7.4 and 5) (Section S10, ESI). At pH 5 (lysosomal pH of cancer cells), 74 % sustained release of 5-FU was noted for about 72 h (Figure S35).16b Hence, targeted drug loaded CONs could establish cancer specific drug release and is expected to minimize the unwanted side effects of non-specific targeting. Prior to the evaluation of anticancer efficacy, the toxicity of TpASH was evaluated against MDA-MB-231 cell lines. MTT assay demonstrated its biocompatible nature against the cell lines.16b In contrast, drug loaded samples showed good

In conclusion, we have demonstrated a new approach for a targeted drug delivery system based on salt-mediated synthesis of new COFs and subsequent functionality based sequential postsynthetic modifications to yield functionalized targeted CONs. Specifically, postsynthetic modification on TpASH via ring-opening of glycidol provided the necessary anchoring sites for conjugation of cellular targeting agents to the CONs for preferential delivery of a drug (5FU) to the cancer cells. Sustained release of the drug from targeted CONs led to the death of cancer cells by apoptosis. To the best of our knowledge, we could, for the first time, showcase a facile synthesis of new functional COFs and sequential postsynthetic modifications to yield exfoliated functionalized targeted CONs for targeted drug delivery. However, one must admit that, CONsbased drug delivery systems are still in a nascent stage compared to the biocompatible polymer-based systems. Biocompatible polymeric materials have been well researched as a drug delivery system; the lack of finite and tunable porosity, predesignable functionality could be the possible drawbacks. In contrast, easy and scalable synthetic routes, predesignable control on functionality, tunable porosity to load guest/drug molecules and chemical stability could be the specific advantages of CONs-based drug delivery system. Still, bio-degradation kinetics, in vivo toxicities, detailed bio-safety studies with proper clinical trials of the CONs are the key issues which needs to be addressed in the future research. Despite

CONCLUSION


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challenging aspects, this process could be used as a roadmap for further development of a CONs-based targeted drug delivery system.

ASSOCIATED CONTENT Synthesis and crystallographic details of ligand, characterization of COFs, postsynthetic modifications to CONs, and biological experiments details are provided in Supporting Information file. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *[email protected].

Author Contributions ‡

SM and HSS have contributed equally.

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT SM acknowledges CSIR Nehru Science PDF for fellowship. HSS, TK, SK acknowledges CSIR for fellowships. RB acknowledges CSIR [CSC0122 and CSC0102], DST (SR/S1/IC-22/2009), DST IndoSingapore Project (INT/SIN/P-05) and DST Nano-mission Project (SB/S1/IC-32/2013) for funding. DDD thanks DFG for the Heisenberg Professorship Award. We acknowledge Dr. Prasun Patra, Saurav Bhattacharya, Manisha Ahir and Dr. Arghya Adhikary (CRNN, University of Calcutta) for their assistance in biological studies. We sincerely acknowledge Dr. T. G. Ajithkumar for providing solid state NMR facility and Dr. Guruswamy K. for PXRD facility.

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SYNOPSIS TOC



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Figure 1 25x23mm (600 x 600 DPI)


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TOC Graphic 12x6mm (600 x 600 DPI)


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Targeted Drug Delivery in Covalent Organic Nanosheets (CONs) via

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