Novel permethylated beta-cyclodextrin derivatives appended with chromophores as efficient fluorescent sensors for the molecular recognition of bile salts

Calixarenes and cyclodextrins as off- and on-fluorescence probes for carbazole

Absorption and fluorescence spectra of the nitrogen polycyclic aromatic hydrocarbon carbazole (CZL) were analyzed with native cyclodextrins (CD;α,β,γ); derivatizedCD(hydroxypropyl-β-cyclodextrin,HPCD; methyl-β-cyclodextrin,MeCD) and p-sulfonated calixarenes (SCAn, with n = 6 and 8) macrocycles. The results showed a slight increase in the absorbance ofCZLwithCD, but the mixture ofCZLwithSCAshowed lower absorption than the sum of the individual spectra. Also, changes in fluorescence were observed by adding the macrocycles, quenching withSCA, and significant increases withCD. The higher fluorescence enhancement was withHPCDrationalized as a complex formation with 1:1 stoichiometry, with an average value for the association constant (KA) of (12 ± 1) x 102M-1, and a quantum yield ratio between the complexedCZLand freeCZL(ΦCZL-HPCD/ΦCZL) of (1.56 ± 0.02) at neutral pH and 25.0 °C. These increases in fluorescence were used as an on-fluorescence switch to develop a supramolecular analytical method forCZLin aqueous samples. The best analytical parameters were inHPCD(LOD = 1.41 ± 0.01 ng mL-1). The method was validated in aqueous samples of river and tap water with recoveries between 96%-104%. The proposed supramolecular method is quick, direct, selective and represents an alternative and low-cost analysis method.

Water-soluble pillar[6]arene bearing pyrene on alternating methylene bridges for direct spermine sensing

This paper describes the design and synthesis of a conjugate, which is composed of a percarboxylated water-soluble pillar[6]arene and three fluorescent pyrene chromophores on alternating methylene bridges. The optical characteristics are investigated. This conjugate is capable of encapsulating polycationic guest spermine, which results in an enhancement in the fluorescence intensity of pyrene. This host-pyrene conjugate is used for direct sensing of spermine, which shows selectivity towards a variety of biological analytes. The detection of spermine is demonstrated in live cells.

Inclusion Complexes of 3,4-Ethylenedioxythiophene with Per-Modified β- and γ-Cyclodextrins

Herein, we report the synthesis of inclusion complexes (ICs) based on 3,4-ethylenedioxythiophene (EDOT) with permethylated β-cyclodextrins (TMe-βCD) and permethylated γ-cyclodextrins (TMe-γCD) host molecules. To prove the synthesis of such ICs, molecular docking simulation, UV-vis titrations in water, ¹H-NMR, and H-H ROESY, as well as matrix-assisted laser desorption ionization mass spectroscopy (MALDI TOF MS) and thermogravimetric analysis (TGA) were carried out on each of the EDOT∙TMe-βCD and EDOT∙TMe-γCD samples. The results of computational investigations reveal the occurrence of hydrophobic interactions, which contribute to the insertion of the EDOT guest inside the macrocyclic cavities and a better binding of the neutral EDOT to TMe-βCD. The H-H ROESY spectra show correlation peaks between H-3 and H-5 of hosts and the protons of the guest EDOT, suggesting that the EDOT molecule is included inside the cavities. The MALDI TOF MS analysis of the EDOT∙TMe-βCD solutions clearly reveals the presence of MS peaks corresponding to sodium adducts of the species associated with the complex formation. The IC preparation shows remarkable improvements in the physical properties of EDOT, rendering it a plausible alternative to increasing its aqueous solubility and thermal stability.

Photophysical and NMR studies of encapsulation of 2-cyano-6-hydroxy benzothiazole in p-sulfonatocalix[6]arene and its biological applications

This work deals with the study of the interaction between 2-cyano-6-hydroxy benzothiazole (CHBT) and p-sulfonatocalix[6]arene (SCX6) at different pH values in aqueous medium by UV-visible absorption spectroscopy and steady-state fluorescence spectroscopy. The results demonstrate the strong influence of SCX6 on the fluorescence properties of CHBT. The steady-state emission of CHBT shows strong sensitivity to its environment. The mode of inclusion complexation of CHBT and SCX6 has also been investigated using HR-MS, FT-IR, NMR, 2D NMR, and FESEM analysis. With the increase in SCX6 concentration, absorbance decreased with an isosbestic point at 305 nm. The binding constant is calculated by a spectrofluorimetric method and stoichiometry by Job's method. The formation of an inclusion complex has been confirmed by 2D NMR NOESY, COSY, ROESY, HMBC, and HSQC spectroscopic methods. The complex is seen to be stabilized by electrostatic interactions between CHBT and the nanocavity of SCX6. Studies with cellular systems support that the CHBT-SCX6 complex is more effective in killing cancerous cells and hence, SCX6 may prove to be an effective carrier for drug molecules like CHBT.

Selective modifications at the different positions of cyclodextrins: a review of strategies

Cyclodextrins (CDs) are natural, nontoxic, and biodegradable macrocyclic oligosaccharides. As supramolecular hosts, CDs have numerous applications in many aspects. However, nonsubstituted CDs have the disadvantages of solubility, unspecific recognition sites, and weak interactions with guest molecules. Therefore, new CD-based derivatives are successfully designed, synthesized, and widely used in various fields. This contribution outlines the research progress in CD derivatives. In particular, this review emphasizes the synthesis and application of CDs modified through functionalization in definite positions, random substitution, and reconstruction of the skeleton. At the end of this review, a summary and future directions are presented.

A Quinoline-Appended Cyclodextrin Derivative as a Highly Selective Receptor and Colorimetric Probe for Nucleotides

The design and development of specific recognition and sensing systems for biologically important anionic species has received growing attention in recent years, as they play significant roles in biology, pharmacy, and environmental sciences. Herein, a new supramolecular sensing probe L1 was developed for highly selective differentiation of nucleotides. L1 displayed extremely marked absorption and emission differentiation upon binding with nucleotide homologs of AMP, ADP, and ATP, due to the divergent spatial orientations of guests upon binding, which allowed for a naked-eye colorimetric differentiation for nucleotides. A differentiating mechanism was unambiguously rationalized by using various spectroscopic studies and theoretical calculations. Furthermore, we successfully demonstrated that L1 can be applied to the real-time monitoring of the enzyme-catalyzed phosphorylation/dephosphorylation processes and thus demonstrated an unprecedented visualizable strategy for selectively differentiating the structurally similar nucleotides and real-time monitoring of biological processes via fluorescent and colorimetric changes.

Rapid Ion Mobility Separations of Bile Acid Isomers Using Cyclodextrin Adducts and Structures for Lossless Ion Manipulations

Bile acids (BAs) constitute an important class of steroid metabolites often displaying changes associated with disease states and other health conditions. Current analyses for these structurally similar compounds are limited by a lack of sensitivity and long separation times with often poor isomeric resolution. To overcome these challenges and provide rapid analyses for the BA isomers, we utilized cyclodextrin adducts in conjunction with novel ion mobility (IM) separation capabilities provided by structures for lossless ion manipulations (SLIM). Cyclodextrin was found to interact with both the tauro- and glyco-conjugated BA isomers studied, forming rigid noncovalent host-guest inclusion complexes. Without the use of cyclodextrin adducts, the BA isomers were found to be nearly identical in their respective mobilities and thus unable to be baseline resolved. Each separation of the cyclodextrin-bile acid host-guest inclusion complex was performed in less than 1 s, providing a much more rapid alternative to current liquid chromatography-based separations. SLIM provided capabilities for the accumulation of larger ion populations and IM peak compression that resulted in much higher resolution separations and increased signal intensities for the BA isomers studied.

Development of Dipicolylamine-Modified Cyclodextrins for the Design of Selective Guest-Responsive Receptors for ATP

The construction of supramolecular recognition systems based on specific host–guest interactions has been studied in order to design selective chemical sensors. In this study, guest-responsive receptors for ATP have been designed with cyclodextrins (CyDs) as a basic prototype of the turn-on type fluorescent indicator. We synthesized dipicolylamine (DPA)-modified CyD–Cu²⁺ complexes (Cu·1α, Cu·1β, and Cu·1γ), and evaluated their recognition capabilities toward phosphoric acid derivatives in water. The UV-Vis absorption and fluorescence spectra revealed that Cu·1β selectively recognized ATP over other organic and inorganic phosphates, and that β-CyD had the most suitable cavity size for complexation with ATP. The 1D and 2D NMR analyses suggested that the ATP recognition was based on the host–guest interaction between the adenine moiety of ATP and the CyD cavity, as well as the recognition of phosphoric moieties by the Cu²⁺–DPA complex site. The specific interactions between the CyD cavity and the nucleobases enabled us to distinguish ATP from other nucleoside triphosphates, such as guanosine triphosphate (GTP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). This study clarified the basic mechanisms of molecular recognition by modified CyDs, and suggested the potential for further application of CyDs in the design of highly selective supramolecular recognition systems for certain molecular targets in water.

Highly Functionalized β-Cyclodextrins by Solid-Supported Synthesis

Using covalent capture, a high yielding selective mono-functionalization of heptakis-[6-deoxy-6-(2-aminoethylsulfanyl)]-β-CD with a 5-mercaptopentyl functional group has been achieved. Here, we demonstrate the immobilization of the mono-thiol functionalized β-CD on PEGA resin via a disulfide bond, enabling solid-phase elaboration of the remaining six primary amines. To showcase the potential of this method, the amines were elaborated to tripeptides through standard Fmoc-peptide chemistry. A small library of CD-tripeptide conjugates was generated which, when reduced from the solid support, could be tagged at the released thiol with an environmentally sensitive fluorophore. The resulting library of sensors showed potential for the differential sensing of various bile salts. The described methodology provides a rapid and versatile route to synthesize highly functionalized libraries of CD derivatives that may be tailored towards applications in sensing, catalysis, and multivalent displays.

Peptide-Appended Permethylated β-Cyclodextrins with Hydrophilic and Hydrophobic Spacers

A novel synthetic methodology, employing a combination of the strain-promoted azide–alkyne cycloaddition and maleimide–thiol reactions, for the preparation of permethylated β-cyclodextrin-linker-peptidyl conjugates is reported. Two different bifunctional maleimide cross-linking probes, the polyethylene glycol containing hydrophilic linker bicyclo[6.1.0] nonyne-maleimide and the hydrophobic 5′-dibenzoazacyclooctyne-maleimide, were attached to azide-appended permethylated β-cyclodextrin. The successfully introduced maleimide function was exploited to covalently graft a cysteine-containing peptide (Ac-Tyr-Arg-Cys-Amide) to produce the target conjugates. The final target compounds were isolated in high purity after purification by isocratic preparative reverse-phase high-performance liquid chromatography. This novel synthetic approach is expected to give access to many different cyclodextrin–linker peptides.

Design and Function of Supramolecular Recognition Systems Based on Guest-Targeting Probe-Modified Cyclodextrin Receptors for ATP

In this study, we have developed a rational design strategy to obtain highly selective supramolecular recognition systems of cyclodextrins (CyDs) on the basis of the lock and key principle. We designed and synthesized dipicolylamine (dpa)-modified γ-CyD-Cu²⁺ complexes possessing an azobenzene unit (Cu·1-γ-CyD) and examined how they recognized phosphoric acid derivatives in water. The results revealed that Cu·1-γ-CyD recognized ATP with high selectivity over other phosphoric acid derivatives. The significant blue shift in the UV-vis spectra and ¹H NMR analysis suggested that the selective ATP recognition was based on the multipoint interactions between the adenine moiety of ATP and both the CyD cavity and the azobenzene unit in addition to the recognition of phosphoric moieties by the Cu-dpa complex site. Our unique receptor made it capable of distinguishing ATP from AMP and ADP, revealing the discrimination of even a length of one phosphoric group. This study demonstrates that, compared to conventional recognition systems of CyDs, this multipoint recognition system confers a higher degree of selectivity for certain organic molecules, such as ATP, over their similar derivatives.

Enantioselective Hydrolysis of Amino Acid Esters Promoted by Bis(β-cyclodextrin) Copper Complexes

It is challenging to create artificial catalysts that approach enzymes with regard to catalytic efficiency and selectivity. The enantioselective catalysis ranks the privileged characteristic of enzymatic transformations. Here, we report two pyridine-linked bis(β-cyclodextrin) (bisCD) copper(II) complexes that enantioselectively hydrolyse chiral esters. Hydrolytic kinetic resolution of three pairs of amino acid ester enantiomers (S₁–S₃) at neutral pH indicated that the “back-to-back” bisCD complex CuL¹ favoured higher catalytic efficiency and more pronounced enantioselectivity than the “face-to-face” complex CuL². The best enantioselectivity was observed for N-Boc-phenylalanine 4-nitrophenyl ester (S₂) enantiomers promoted by CuL¹, which exhibited an enantiomer selectivity of 15.7. We observed preferential hydrolysis of L-S₂ by CuL¹, even in racemic S₂, through chiral high-performance liquid chromatography (HPLC). We demonstrated that the enantioselective hydrolysis was related to the cooperative roles of the intramolecular flanking chiral CD cavities with the coordinated copper ion, according to the results of electrospray ionization mass spectrometry (ESI-MS), inhibition experiments, rotating-frame nuclear Overhauser effect spectroscopy (ROESY), and theoretical calculations. Although the catalytic parameters lag behind the level of enzymatic transformation, this study confirms the cooperative effect of the first and second coordination spheres of artificial catalysts in enantioselectivity and provides hints that may guide future explorations of enzyme mimics.

Design of β-CD-surfactant complex-coated liquid crystal droplets for the detection of cholic acid via competitive host-guest recognition

β-CD-C14TAB complex-coated 5CB droplets are designed by the adsorption of β-CD-C14TAB complexes at the 5CB/aqueous interface. We show that the 5CB droplets can be used as an optical probe for the selective detection of cholic acid in aqueous solution containing uric acid and urea via competitive host-guest recognition.

Predicting self-assembly and structure in diluted aqueous solutions of modified mono- and bis-β-cyclodextrins that contain naphthoxy chromophore groups

Mono-cyclodextrins, whose appended groups contain a naphthoxy moiety, form tail-to-tail non-covalent dimers in water solution. Bis-CDs do not exhibit self-association.

Molecularly imprinted fluorescent chemosensor synthesized using quinoline-modified-β-cyclodextrin as monomer for spermidine recognition

Preparation of imprinted fluorescent chemosensor using quinoline-modified-β-cyclodextrin as monomer for spermidine recognition.

Influence of the macroring size on the self-association thermodynamics of cyclodextrins with a double-linked naphthalene at the secondary face

The conformational properties and aggregation behavior of two selectively modified cyclomaltooligosaccharides (cyclodextrins, CDs) containing a double-linked 1,8-dimethylnaphthalene cap-like moiety at the secondary face, namely, 2(I),3(I)-O-(1,8-dimetylnaphthalene-α,α'-diyl)-per-O-Me-α- and -γ-cyclodextrins (NmαCD and NmγCD, respectively), in water and in organic solvents were investigated. Both CD derivatives self-associated in water to form dimer species, but the characteristics of the dimerization process and of the resulting dimer strongly depended on the size of the macrocycle. Dimerization constants, thermodynamic parameters upon association, and information about the preferred conformations of the monomer and dimer CD structures were obtained by using NMR, UV-vis, steady-state and time-resolved fluorescence, and circular dichroism experimental techniques, as well as molecular mechanics (MM) and molecular dynamics (MD) simulations. The complexation of 1,8-di(methoxymethyl)naphathalene (oNy) and the heteroassociation of both NmCDs with their permethylated CD partners (mCDs), lacking the aromatic cap, were examined. In addition, the influence of the size of the chromophore moiety on the thermodynamics of self-association was also assessed by comparison of the results obtained for the new naphthalene derivatives with those of the 2(I),3(I)-O-(1,2-xylylene)-modified CD analogues (XmCDs).

Optical detection of lithocholic acid with liquid crystal emulsions

The concentration level of bile acids is a clinical biomarker for the diagnosis of intestinal diseases because individuals suffering from intestinal diseases have a sharply increased concentration of bile acids at micromolar levels. Here, we report the detection of lithocholic acid (LCA) in aqueous solution by using surfactant-stabilized 4-n-pentyl-4'-cyanobiphenyl (5CB) liquid crystal droplets as an optical probe. We find that the surfactant adsorbed at the 5CB/water interface can be replaced by LCA, triggering a radial-to-bipolar configuration transition of the 5CB in the droplets. By simply observing the LCA-triggered transition with a polarizing optical microscope, micromolar levels of LCA in aqueous solution can be detected. The detection limit and selectivity of surfactant-stabilized 5CB droplets for LCA depend on the chain length and headgroup of the surfactants used for stabilizing 5CB droplets.

Methylated β-cyclodextrins: influence of degree and pattern of substitution on the thermodynamics of complexation with tauro- and glyco-conjugated bile salts

The complexation of 6 bile salts with various methylated β-cyclodextrins was studied to elucidate how the degree and pattern of substitution affects the binding. The structures of the CDs were determined by mass spectrometry and NMR techniques, and the structures of the inclusion complexes were characterized from the complexation-induced shifts of (13)C nuclei as well as by 2D ROESY NMR. Thermodynamic data were generated using isothermal titration calorimetry. The structure-properties analysis showed that methylation at O3 hinders complexation by partially blocking the cavity entrance, while methyl groups at O2 promote complexation by extending the hydrophobic cavity. Like in the case of 2-hydroxypropylated cyclodextrins, the methyl substituents cause an increased release of ordered water from the hydration shell of the bile salts, resulting in a strong increase in both the enthalpy and the entropy of complexation with increased number of methyl substituents. Due to enthalpy-entropy compensation the effect on the stability constant is relatively limited. However, when all hydroxyl groups are methylated, the rigid structure of the free cyclodextrin is lost and the complexes are severely destabilized due to very unfavorable entropies.

Fluorescent sensing of chlorophenols in water using an azo dye modified β-cyclodextrin polymer

A water soluble azo dye modified β-cyclodextrin polymer 4 was synthesized and used as a chemosensor for the detection of chlorinated phenols, model chlorinated by-products (CBPs) of water treatment for drinking purposes. The characterization of the intermediates and the azo dye modified β-CD polymer was done by UV/Vis Spectrophotometry, FT-IR and ¹H-NMR spectroscopies. The chlorophenols were capable of quenching the fluorescence of the polymer. The polymer showed greater sensitivity towards 2,4-dichlorophenol, with a sensitivity factor of 0.35 compared to 0.05 and 0.12 for phenol and 4-chlorophenol, respectively. The stability constants (K_s) of the pollutants were also determined by the Benesi-Hildebrand method to be 2.104 × 10³ M⁻¹ for 2,4-dichlorophenol and 1.120 × 10² M⁻¹ for 4-chlorophenol.

The design, synthesis and photochemical study of a biomimetic cyclodextrin model of photoactive yellow protein (PYP)

The design, synthesis and study of the photophysical and photochemical properties of the first biomimetic cyclodextrin (CD) model of photoactive yellow protein (PYP) are described. This model bears a deprotonated trans-p-coumaric acid chromophore, covalently linked via a cysteine moiety to a permethylated 6-monoamino β-CD. NMR and UV/Visible spectroscopy studies showed the formation of strong self-inclusion complexes in water at basic pH. Steady-state photolysis demonstrated that, unlike the free chromophore in solution, excitation of the model molecule leads to the formation of a photoproduct identified as the cis isomer by NMR spectroscopy. These observations provide evidence that the restricted CD cavity offers a promising framework for the design of biomimetic models of the PYP hydrophobic pocket.

Thermodynamic origin of selective binding of β-cyclodextrin derivatives with chiral chromophoric substituents toward steroids

Two β-cyclodextrin derivatives with chiral chromophoric substituents, that is, L- (1) and D-tyrosine-modified β-cyclodextrin (2), were synthesized and fully characterized. Their inclusion modes, binding abilities, and molecular selectivities with four steroid guests, that is, cholic acid sodium salt (CA), deoxycholic acid sodium salt (DCA), glycochoic acid sodium salt (GCA), and taurocholic acid sodium salt (TCA), were investigated by the circular dichroism, 2D NMR, and isothermal titration microcalorimetry (ITC). The results obtained from the circular dichroism and 2D NMR showed that two hosts adopted the different binding geometry, and these differences subsequently resulted in the significant differences of molecular binding abilities and selectivities. As compared with native β-cyclodextrin and tryptophan-modified β-cyclodextrin, host 2 showed the enhanced binding abilities for CA and DCA but the decreased binding abilities for GCA and TCA; however, host 1 showed the decreased binding abilities for all four bile salts. The best guest selectivity and the best host selectivity were K(S)(2-DCA)/K(S)(2-TCA) = 12.6 and K(S)(2-CA)/K(S)(1-CA) = 10, respectively, both exhibiting great enhancement as compared with the corresponding values of the previously reported L- and D-tryptophan-modified β-cyclodextrins. Thermodynamically, it was the favorable enthalpic gain that led to the high guest selectivity and host selectivity.

Validating a strategy for molecular dynamics simulations of cyclodextrin inclusion complexes through single-crystal X-ray and NMR experimental data: a case study

A theoretical and experimental study about the formation and structure of the inclusion complex (-)-menthyl-O-beta-D-glucopyranoside 1 with beta-cyclodextrin (beta-CD) 2 is presented as paradigmatic case study to test the results of molecular dynamics (MD) simulations. The customary methodological approach-the use of experimental geometrical parameters as restraints for MD runs-is logically reversed and the calculated structures are a posteriori compared with those obtained from NMR spectroscopy in D(2)O solution and single crystal X-ray diffraction so as to validate the simulation procedure. The guest molecule 1 allows for a broad repertoire of intermolecular interactions (dipolar, hydrophobic, hydrogen bonds) concurring to stabilize the host-guest complex, thus providing the general applicability of the simulation procedure to cyclodextrin physical chemistry. Many starting geometries of the host-guest association were chosen, not assuming any a priori inclusion. The simulation protocol, involving energy minimization and MD runs in explicit water, yielded four possible inclusion geometries, ruling out higher-energy outer adducts. By analysis of the average energy at room temperature, the most stable geometry in solution was eventually obtained, while the kinetics of formation showed that it is also kinetically favored. The reliability of such geometry was thoroughly checked against the NOE distances via the pair distribution functions, that is, the statistical distribution of intermolecular distances among selected diagnostic atoms calculated from the MD trajectories at room temperature. An analogous procedure was adopted both with implicit solvent and in vacuo. The most stable geometry matched that found with explicit solvent but major differences were observed in the relative stability of the metastable complexes as a consequence of the lack of hydration on the polar moiety of the guest. Finally, a control set of geometrical parameters of the thermodynamically favored complex matched the corresponding one obtained from the X-ray structure, while local conformational differences were indicative of packing effects.

A survey of the year 2007 literature on applications of isothermal titration calorimetry

Elucidation of the energetic principles of binding affinity and specificity is a central task in many branches of current sciences: biology, medicine, pharmacology, chemistry, material sciences, etc. In biomedical research, integral approaches combining structural information with in-solution biophysical data have proved to be a powerful way toward understanding the physical basis of vital cellular phenomena. Isothermal titration calorimetry (ITC) is a valuable experimental tool facilitating quantification of the thermodynamic parameters that characterize recognition processes involving biomacromolecules. The method provides access to all relevant thermodynamic information by performing a few experiments. In particular, ITC experiments allow to by-pass tedious and (rarely precise) procedures aimed at determining the changes in enthalpy and entropy upon binding by van't Hoff analysis. Notwithstanding limitations, ITC has now the reputation of being the "gold standard" and ITC data are widely used to validate theoretical predictions of thermodynamic parameters, as well as to benchmark the results of novel binding assays. In this paper, we discuss several publications from 2007 reporting ITC results. The focus is on applications in biologically oriented fields. We do not intend a comprehensive coverage of all newly accumulated information. Rather, we emphasize work which has captured our attention with originality and far-reaching analysis, or else has provided ideas for expanding the potential of the method.

Chemical Sensors Based on Cyclodextrin Derivatives

This review focuses on chemical sensors based on cyclodextrin (CD) derivatives. This has been a field of classical interest, and is now of current interest for numerous scientists. First, typical chemical sensors using chromophore appended CDs are mentioned. Various "turn-off" and "turn-on" fluorescent chemical sensors, in which fluorescence intensity was decreased or increased by complexation with guest molecules, respectively, were synthesized. Dye modified CDs and photoactive metal ion-ligand complex appended CDs, metallocyclodextrins, were also applied for chemical sensors. Furthermore, recent novel approaches to chemical sensing systems using supramolecular structures such as CD dimers, trimers and cooperative binding systems of CDs with the other macrocycle [2]rotaxane and supramolecular polymers consisting of CD units are mentioned. New chemical sensors using hybrids of CDs with p-conjugated polymers, peptides, DNA, nanocarbons and nanoparticles are also described in this review.