Nonpolymeric thermosensitive supramolecules

Quantifying and Modulating Protein Encapsulation in Guanosine-Based Supramolecular Particles

The encapsulation of proteins is an effective way to preserve their structure and enhance their function. One exciting possibility is adjusting the protective agent to match the specific protein's characteristics to influence its properties. In a recent study, we developed a flow cytometry-based method to quantify the encapsulation of small-molecule dyes in colloidal particles made from guanosine derivatives (supramolecular hacky sacks (SHS) particles). We aimed to determine whether this method could quantify protein encapsulation and track changes and if the particles could be tuned to bind to specific proteins. Our results showed that fluorescein isothiocyanate (FITC)-labeled proteins had apparent association constants in the micromolar range with hydrophobicity as the dominant factor enhancing the affinities. Confocal laser scanning microscopy (CLSM) imaging supported these results and provided additional information about the protein distribution within the particles. We also tested the feasibility of tuning the avidin affinity (AVI) for SHS particles with a biotin ligand. We found that increasing the amount of biotin initially enhanced AVI binding, but then reached saturation, which we hypothesize results from noncovalent cross-linking caused by strong biotin/AVI interactions. CLSM images showed that the linker also impacted the AVI distribution within the particles. Our strategy provides an advantage over other methods for quantifying protein encapsulation by being suitable for high-throughput analysis with high reproducibility. We anticipate that future efforts to use lower-affinity ligands would result in better strategies for modulating protein affinity for drug delivery applications.

Hydrochromic Perovskite System with Reversible Blue-Green Color for Advanced Anti-Counterfeiting

The intrinsic instability of halide perovskites toward to external stimulus, has created a competitive advantage for designing stimuli-responsive materials. However, the external environment tuning reversibly fluorescence emission of perovskite system is still limited. In this work, humidity is verified to act as a new option to modulate the emission properties of mixed-halide perovskite. The perovskite nanocrystals (PNCs) photoirradiated in dichloromethane are easily and stably redispersed in water, and emit bright fluorescence which is quite different from the original. Moreover, the perovskites confined on glass slide can reversibly switch their fluorescence between blue and green colors under moisture. It is demonstrated that the factors of different solubilities of CsCl and CsBr in water, the structural transformation of perovskites and the confine of glass matrix play key roles in the reversible transformation. Finally, the combination of hydrochromic CsPb(Brx Cly )3 and water-resistant CsPb(Brx Cly )3 -polymethyl methacrylate have been applied in advanced anti-counterfeiting, which greatly improves the information security. This work not only give an insight into the effects of humidity on fluorescence and structures of PNCs, but also offer a new class of hydrochromic PNCs materials based on reversible emission transformation for potential application in sensors, anti-counterfeiting and information encryption.

Transferring Micellar Changes to Bulk Properties via Tunable Self-Assembly and Hierarchical Ordering

Hierarchical self-assembly is an effective means of preparing useful materials. However, control over assembly across length scales is a difficult challenge, often confounded by the perceived need to redesign the molecular building blocks when new material properties are needed. Here, we show that we can treat a simple dipeptide building block as a polyelectrolyte and use polymer physics approaches to explain the self-assembly over a wide concentration range. This allows us to determine how entangled the system is and therefore how it might be best processed, enabling us to prepare interesting analogues to threads and webs, as well as films that lose order on heating and "noodles" which change dimensions on heating, showing that we can transfer micellar-level changes to bulk properties all from a single building block.

Screening and Quantification of the Encapsulation of Dyes in Supramolecular Particles

The encapsulation of therapeutic agents, such as drugs and vaccines, into colloidal particles offers an attractive strategy to enhance their efficacy. Previously, we reported the development of guanosine-based supramolecular colloidal particles suitable for encapsulating a broad array of guests ranging from small molecule drugs, like doxorubicin, to proteins, like GFP. Many biomedical applications of such particles require a precise determination of the amount of encapsulated therapeutic agents. Despite many studies describing the development of particle-based delivery systems, a general method for the precise and quick quantification of the encapsulated payload is still lacking. Here, we report a method based on flow cytometry measurements for complexes made from guanosine-based particles and a variety of commercially available fluorescent dyes. This method allows us to determine the apparent affinities of such dyes for two variants of these particles, which in turn provides insightful structure-affinity relationships. In contrast to the current methods, such as those that rely on fluorescence microscopy based on measurements of absorption/fluorescence of dissolved particles or on the supernatant of the solution, the reported method is suitable for high-throughput screening and more reproducible results. The protocol described here should be applicable to a wide variety of colloidal particles being developed around the world. Our group is currently expanding the scope to quantify the encapsulation of other molecules of biomedical interest, such as proteins and nucleic acids.

Construction of Supramolecular Organogel with Circularly Polarized Luminescence by Self-Assembled Guanosine Octamer

Gel formation using guanosine self-assembly is an important process in supramolecular chemistry. Here, we report the stepwise construction of circularly polarized luminescent supramolecular organogels from self-assembled guanosine quadruplexes. A lipophilic guanosine derivative (aldG) is designed and synthesized for the formation of a well-defined G8-octamer. The diamine linkers are used to connect G8-octamer units by imine formation to facilitate the construction of the supramolecular gel networks. 1H NMR experiments show that the pre-assembled aldG8-octamer remains intact and is crucial for transparent and stiff organogel formation. With extended conjugation, the aldG organogels exhibit strong green fluorescence emission and circularly polarized properties without the assistance of any external fluorescent dyes, suggesting an alternative approach to construct molecular probes for biological and material applications.

Construction of a cross-layer linked G-octamer via conformational control: a stable G-quadruplex in H-bond competitive solvents

Methanol soluble and stable guanosine octamers were successfully achieved via H-bond self-assembly. Through structural conformational design, we developed a new class of guanosine derivatives with modification on guanine (8-aryl) and ribose (2',3'-isopropylidene). This unique design led to the formation of the first discrete G8-octamer with its structure characterized by single crystal X-ray diffraction, MS and NMR spectroscopy. The G8-octamer showed unique cation recognition properties, including the formation of a stable Rb+ templated G-quadruplex. Based on this observation, further modification on the 8-aryl moiety was performed to incorporate a cross-layer H-bond or covalent linkage. Similar G-octamers were obtained in both cases with structures confirmed by single crystal X-ray diffraction. Furthermore, the covalently linked G-quadruplex exhibited excellent stability even in MeOH and DMSO, suggesting a promising future for this new H-bond self-assembly system in biological and material applications.

LCST phase behavior of benzo-21-crown-7 with different alkyl chains

The introduction of hydrophobic units into crown ethers can dramatically decrease the critical transition temperature of LCST and realize macroscopic phase separation at low to moderate temperature and concentration. Minor modifications in the chemical structure of crown ethers (benzo-21-crown-7, B21C7s) can effectively control the thermo-responsive properties.

Tracking the formation of supramolecular G-quadruplexes via self-assembly enhanced emission

We report the synthesis and self-assembly of two lipophilic 2'-deoxyguanosine (G) derivatives whose fluorescence intensity is modulated by self-assembly into supramolecular G-quadruplexes (SGQs). Whereas both derivatives self-assemble isostructurally, one shows up to 100% emission enhancement while the other shows an initial enhancement, followed by 10% quenching. Thus, the rotational restrictions resulting from self-assembly are enough to induce significant changes in emission, but it is critical to consider the specific interactions between fluorophores since they will determine the ultimate emission signature. These findings could open the door to the development of luminescent supramolecular sensors and probes.

G4-quartet hydrogels from 5'-hydrazino-guanosine for the non-covalent and covalent remediation of contaminants from water

The creation of supramolecular hydrogels from relatively simple building blocks demonstrates the power of molecular self-assembly to make functional materials. G4-quartet hydrogels are appealing for a number of applications, including the environmental remediation of pollutants in water. We find that the guanosine analog, 5'-deoxy-5'-hydrazinoguanosine (HG 2) self-assembles into a self-standing hydrogel in the presence of stoichiometric amounts (0.25 equiv.) of KCl. The higher water solubility of HG 2 (14.5 mM), compared to that of the parent compound G 1 (2.1 mM), likely contributes to its enhanced gelation. The structural basis for this HG 2·KCl hydrogel, confirmed by PXRD, IR and CD, is the G4·K+ quartet, which forms extended 1D ion-channel assemblies that entangle to give a stable and long-lived hydrogel. We also find that adding KCl to a saturated solution of HG 2 triggers the generation of colloidal G4·K+ assemblies in situ that selectively and efficiently binds the anionic dye naphthol blue black (NBB) over a cationic dye. In addition to this non-covalent electrostatic binding of anions, the nucleophilic 5'-hydrazino group in the HG 2·KCl hydrogel HG 2 enables the efficient absorption of propionaldehyde from both the gas phase and from water solution via the formation of covalent hydrazone linkages with the gel matrix.

Polymeric crown ethers: LCST behavior in water and stimuli-responsiveness

A crown ether-functionalized poly(vinyl alcohol) (PVA) system shows lower critical solution temperature (LCST) phase separation behavior in water.

An ultra-small thermosensitive nanocomposite with a Mo154-core as a comprehensive platform for NIR-triggered photothermal-chemotherapy

A uniform ultra-small (<10 nm) nanosized dendritic composite was reported for combined photothermal-chemotherapy, wherein a giant ring-like polymolybdate cluster was introduced for the first time as a photothermal therapeutic agent. The giant polyoxometalate cluster possesses strong absorption characteristics in the near infrared region, whereas it has never been applied for biomaterials due to its sensitivity towards environment and structural instability under physiological conditions. Herein, a cationic dendron bearing triethylene glycol monomethyl ether terminal groups was used to cover a giant polyanionic cluster Mo₁₅₄ surface through a simple electrostatic interaction. Arising from their assembly, the formed core-shell supramolecular composite that has uniform size, precise chemical composition and definite molecular weight not only exhibited mono-dispersion and low cytotoxicity, but also imparted anticancer drug loading and thermoresponsive properties, thus leading to NIR-controlled drug release. When irradiated with an 808 nm NIR laser, the formed complex had significant in vivo photothermal-chemotherapeutic effects on tumor tissue, which makes it a promising material for applications in nanomedicine.

Multi-modulation for self-assemblies of amphiphilic rigid-soft compounds through alteration of solution polarity and temperature

A new class of small molecule-based amphiphilic carbazole-containing compounds has been designed and synthesized. Detailed analysis of the temperature- and solvent-dependent UV-vis absorption spectra has provided insights into the cooperative self-assembly mechanism of the carbazole-containing compounds. Interestingly, the prepared amphiphilic rigid-soft compounds were also found to display a lower critical solution temperature (LCST) behavior in aqueous solution, which is relatively less explored in small molecule-based materials, leading to promising candidates for the design of a new class of thermo-responsive materials.

Probing the Limits of Supramolecular G-Quadruplexes Using Atomistic Molecular Dynamics Simulations

Guanosine and related derivatives self-assemble in the presence of cations like potassium into supramolecular G-quadruplexes (SGQs), where four guanine moieties form planar tetrads (T) that coaxially stack into columnar aggregates with broad size distributions. However, SGQs made from 8-aryl-2'-deoxyguanosine derivatives (8ArGs), form mostly octamers, or two-tetrad (2T)-SGQs, while some form dodecamers (3T-SGQs), or hexadecamers (4T-SGQs), and none reported to date form higher assemblies. A theoretical model that addresses the configurational space available for the multiple pathways available for 8ArGs to self-assemble into SGQs is used to frame a series of molecular dynamics simulations (MDS) with selected SGQs. Some key insights from this work include: (a) The predicted entropic costs are not significantly higher for SGQs with more subunits due to their hierarchical assembly pathways; (b) The multiple isomeric SGQs vary in the interfacial contacts between consecutive tetrads, due to their two distinct sides (head, h; tail, t), with the MDS supporting the predicted order of stability of hh > ht > tt for octamers. (c) Such order also applies to dodecamers and hexadecamers, but with context-dependent exceptions due to strong allosteric effects. (d) The main factor disfavoring the tt interface is the repulsive dipolar interactions between the O4' from ribose moieties on adjacent tetrads. (e) SGQs with 5 or more tetrads are disfavored because the attractive interactions are not large or strong enough to overcome the many repulsive forces resulting from the addition of further tetrads. We expect these findings provide some guidelines to enable the further development of SGQs into functional materials.

Structural Studies of Supramolecular G-Quadruplexes Formed from 8-Aryl-2'-deoxyguanosine Derivatives

Self-assembly is a powerful tool for the construction of complex nanostructures. Despite advances in the field, the development of precise self-assembled structures remains a challenge. We have shown that, in the presence of suitably sized cations like K(+), 8-aryl-2'-deoxyguanosine (8ArG) derivatives self-assemble into sets of coaxially stacked planar tetramers, which we term supramolecular G-quadruplexes (SGQs). Previously, we reported that, when the 8-aryl group is a phenyl ring with a meta-carbonyl group, the resulting supramolecule is a hexadecamer, which is remarkably robust as illustrated by its isostructural assembly in both organic and aqueous environments. We report here a detailed three-dimensional structure of the SGQs formed by lipophilic, and hydrophilic, 8ArG derivatives with either 8-(meta-acetylphenyl), 8-(para-acetylphenyl), or 8-(meta-ethoxycarbonylphenyl) groups. The chirality and close contacts between the subunits impose different levels of steric and electrostatic constraints on opposite sides of the tetrads, which determine their preferred relative orientation. The balance between attractive noncovalent interactions juxtaposed with repulsive steric and electrostatic interactions explains the high cooperativity, fidelity, and stability of these SGQs. These structural studies, together with titration experiments and molecular dynamics simulations, provide insight into the mechanism of formation of these SGQs.

Organic Nanoflowers from a Wide Variety of Molecules Templated by a Hierarchical Supramolecular Scaffold

Nanoflowers (NFs) are flowered-shaped particles with overall sizes or features in the nanoscale. Beyond their pleasing aesthetics, NFs have found a number of applications ranging from catalysis, to sensing, to drug delivery. Compared to inorganic based NFs, their organic and hybrid counterparts are relatively underdeveloped mostly because of the lack of a reliable and versatile method for their construction. We report here a method for constructing NFs from a wide variety of biologically relevant molecules (guests), ranging from small molecules, like doxorubicin, to biomacromolecules, like various proteins and plasmid DNA. The method relies on the encapsulation of the guests within a hierarchically structured particle made from supramolecular G-quadruplexes. The size and overall flexibility of the guests dictate the broad morphological features of the resulting NFs, specifically, small and rigid guests favor the formation of NFs with spiky petals, while large and/or flexible guests promote NFs with wide petals. The results from experiments using confocal fluorescence microscopy, and scanning electron microscopy provides the basis for the proposed mechanism for the NF formation.

"Inverse" thermoresponse: heat-induced double-helix formation of an ethynylhelicene oligomer with tri(ethylene glycol) termini

Ethynylhelicene oligomers with TEG terminal groups showed a unique thermoresponse in aqueous solvents: double-helix formation upon heating and disaggregation upon cooling.

An ethynylhelicene oligomer [(M)-d-4]-C₁₂-TEG with six tri(ethylene glycol) (TEG) groups at the termini was synthesized, and double-helix formation was studied using CD, UV-Vis, vapor pressure osmometry, dynamic light scattering, and ¹H NMR. [(M)-d-4]-C₁₂-TEG reversibly changed its structure between a double helix and a random coil in response to heating and cooling in aromatic solvents, non-aromatic polar organic solvents, and aqueous solvent mixtures of acetone/water/triethylamine. Notably, [(M)-d-4]-C₁₂-TEG in acetone/water/triethylamine (1/2/1) formed a double helix upon heating and disaggregated into random coils upon cooling. The double helix/random coil ratio sharply changed in response to temperature changes. This is an unprecedented “inverse” thermoresponse, which is opposite to the “ordinary” thermoresponse in molecular dimeric aggregate formation. This phenomenon was explained by the dehydration of the terminal TEG groups and the formation of condensed triethylamine domains upon heating.

Lower critical solution temperature (LCST) phase behaviour of an ionic liquid and its control by supramolecular host–guest interactions

Unique LCST phase behaviour of imidazolium-based ionic liquids is reported, which can be controlled by concentration, the choice of cation, anion and solvent, and by supramolecular complex formation. MD simulations provide insight into the molecular basis of this LCST phenomenon.

Controlling molecularity and stability of hydrogen bonded G-quadruplexes by modulating the structure's periphery

Identity of 5′-ester controls G-quadruplex structure and stability.

Tuning thermoresponsive supramolecular G-quadruplexes

Thermoresponsive systems are attractive due to their suitability for fundamental studies as well as their practical uses in a wide variety of applications. While much progress has been achieved using polymers, alternative strategies such as the use of well-defined nonpolymeric supramolecules are still underdeveloped. Here we report three 8-aryl-2'-deoxyguanosine derivatives (8ArGs) that self-assemble in aqueous media into precise thermoresponsive supramolecular G-quadruplexes (SGQs). We report the synthesis of such derivatives, studies of their isothermal self-assembly, and the thermally induced assembly to form higher-order meso-globular assemblies we term supramolecular hacky sacks (SHS). The lower critical solution temperature (LCST) that indicates the formation of the SHS was modulated by changing (a) intrinsic parameters (i.e., structure of the 8ArGs); (b) extrinsic parameters such as the salt used to promote the formation of the SGQ; and (c) supramolecular parameters such as the coassembly different 8ArGs to form heteromeric SGQs. Changes in the intrinsic parameters lead to LCST variations in the range of 28-59 °C. Modulating extrinsic parameters such as replacing KI with KSCN abolishes the thermoresponsive phenomenon whereas changing the cation from K(+) to Na(+) or adjusting the pH (in the range of 6-8) has negligible effects on the LCST. Modulating supramolecular parameters results in transition temperatures that are intermediate between those obtained by the respective homomeric SGQs, although the specific proportions of the subunits are critical in determining the reversibility of the process. Given the extensive applications of thermoresponsive polymers, the nonpolymeric supramolecular counterparts presented here may represent an attractive alternative for fundamental studies and biorelevant applications.

Reversible and contrasting changes of the cloud point temperature of pillar[5]arenes with one quinone unit and tri(ethylene oxide) chains induced by redox chemistry and host–guest complexation

A new water-soluble redox-active pillar[5]arene was synthesized by incorporation of one benzoquinone unit.

A discrete amphiphilic organoplatinum(II) metallacycle with tunable lower critical solution temperature behavior

Oligo(ethylene glycol) (OEG)-decorated supramolecular assemblies are distinguished by their neutral character and macroscopic temperature-sensitive phase transition behavior. OEG functionalization is an emerging strategy to obtain thermoresponsive macrocyclic amphiphiles, although known methods organize the hydrophilic and hydrophobic segments by covalent bonding. Coordination-driven self-assembly offers an alternative route for organizing OEG-functionalized precursors into nanoscopic architectures, resulting in well-defined metallacycle cores surrounded by hydrophilic scaffolds to impart overall amphiphilic character. Here a tri(ethylene glycol)-functionalized thermosensitive amphiphilic metallacycle was prepared with high efficiency by means of the directional-bonding approach. The ensembles thus formed showed good lower critical solution temperature behavior with a highly sensitive phase separation and excellent reversibility. Moreover, the clouding point decreased with increasing metallacycle concentration and addition of K(+).

Guanosine and isoguanosine derivatives for supramolecular devices

Guanosine (G) and isoguanosine (isoG) derivatives can self-assemble, yielding supramolecules that have found broad applications in diverse fields.

Triple helix formation in amphiphilic discotics: demystifying solvent effects in supramolecular self-assembly

A set of chiral, amphiphilic, self-assembling discotic molecules based on the 3,3'-bis(acylamino)-2,2'-bipyridine-substituted benzene-1,3,5-tricarboxamide motif (BiPy-BTA) was prepared. Amphiphilicity was induced into the discotic molecules by an asymmetrical distribution of alkyl and oligo(ethylene oxide) groups in the periphery of the molecules. Small-angle X-ray scattering, cryogenic transmission electron microscopy, and circular dichroism spectroscopy measurements were performed on the discotic amphiphiles in mixtures of water and alcohol at temperatures between 0 °C an 90 °C. The combined results show that these amphiphilic discotic molecules self-assemble into supramolecular fibers consisting of either one or three discotic molecules in the fiber cross-section and that the presence of water induces the bundling of the supramolecular fibers. The rich phase behavior observed for these molecules proves to be intimately connected to the mixing thermodynamics of the water-alcohol mixtures.

LCST-type phase behavior induced by pillar[5]arene/ionic liquid host-guest complexation

The host-guest complex of dipropoxypillar[5]arene and an ionic liquid 1,3-dimethylimidazolium iodide is found to exhibit a lower critical solution temperature (LCST)-type phase transition in chloroform. This LCST-type phase behavior can be conveniently modulated by experimental parameters and can be easily combined with the ionic liquid for potential application in product and educt separation.

A photoresponsive supramolecular G-quadruplex

Photoirradiation of a hexadecameric supramolecular G-quadruplex leads to a diastereoselective [2 + 2] cyclodimerization of half of its constituent subunits, which in turn shifts the equilibrium toward the formation of a precise heteromeric octamer.

An aquatic host-guest complex between a supramolecular G-quadruplex and the anticancer drug doxorubicin

We describe the synthesis of a fluorescent deoxyguanosine derivative that co-assembles (in water) with an unlabeled analogue into a heteromeric supramolecular G-quadruplex, which forms a host-guest complex with doxorubicin as evidenced by FRET experiments.

Patchy supramolecules as versatile tools to probe hydrophobicity in nanoglobular systems

We describe precise supramolecules that enable the evaluation of the effective hydrophobicity of amphiphilic or "patchy" nanoglobular systems. These supramolecules exhibit the lower critical solution temperature phenomenon, which provides a quantitative measure of their effective hydrophobicity. Specifically, two isomeric 8-aryl-2'-deoxyguanosine derivatives with a transposed pair of methylene groups self-assemble into hexadecameric nanoglobular supramolecular G-quadruplexes (SGQs) that show large differences in their transition temperatures as determined by turbidity and differential scanning calorimetry studies. Molecular modeling studies suggested that differential clustering of the hydrophobic patches on the surface is responsible for the striking differences between the two isomeric supramolecules.

Light-triggered self-assembly of triarylamine-based nanospheres

Tailored triarylamine units modified with terpyridine ligands were coordinated to Zn(2+) ions and characterized as discrete dimeric entities. Interestingly, when these complexes were subsequently irradiated with simple visible light in chloroform, they readily self-assembled into monodisperse spheres with a mean diameter of 160 nm.

Supramolecular dendrimers: convenient synthesis by programmed self-assembly and tunable thermoresponsivity

We report here the noncovalent synthesis of thermosensitive dendrimers. Short oligoguanosine strands were linked to the focal point of a dendron by using "click chemistry", and quadruplex formation was used to drive the self-assembly process in the presence of metal ions. The dynamic nature of these noncovalent assemblies can be exploited to create combinatorial libraries of dendrimers as demonstrated by the co-assembly of two components. These supramolecular dendrimers showed thermoresponsive behavior that can be tuned by varying the templating cations or the number of guanines in the oligonucleotide strand.

Metallo-responsive switching between hexadecameric and octameric supramolecular G-quadruplexes

We report the metallo-responsive high fidelity switching between hexadecameric and octameric supramolecular G-quadruplexes triggered by a change in the metal cation promoter from potassium to strontium, respectively.

Assemblies of functional small-sized molecules having 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl responsive to heat and pH in water and their water proton relaxivities

1,3,5-Triureabenzene derivatives carrying alkyl (C(n)) and poly(ethylene glycol) (Eg(m)) chains C(n)Eg(3) (1, 2, and 3, n = 6, 7, and 8, respectively) and C(n)N(X)Eg(m) (4 and 5, X = M (methyl), n = 6 and 8, respectively, m = 3; 6 and 7, X = T (2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPO), n = 6, m = 3 and 6, respectively) were prepared. All compounds in aqueous solutions exhibited the lower critical solution temperature (LCST) phenomena unique for small-sized molecules and formed self-assemblies above the transition temperature, T(t), of the LCST. Only compound 3 formed a hydrogel with a minimum gelation concentration of 0.5 mM (0.05 wt %). In 1.0 mM aqueous solution, the T(t) values were determined to be in the range of 12-40 °C. In addition, the T(t) values for 4-7 containing tertiary amine also responded to the solution pH with high sensitivity. The LCST behaviors for all compounds were reversible in the cycles of warming and cooling. The water proton relaxivities, r(1), for 6 and 7 carrying TEMPO were altered below and above T(t) and were largely reduced by the formation of self-assemblies above T(t). Compound 6 showed r(1) values at 25 °C of 0.92 and 0.23 mM(-1) s(-1) at pH 7.0 and 6.0, respectively. In transmission electron microscopy (TEM) images, globular particles with polydispersity were observed, and their average hydrodynamic diameters (D(H)) were determined to be in the range of 2400-730 nm by dynamic light scattering. In the TEM and scanning electron microscopy images of a xerogel sample of 3, bundles of fibers with a diameter of ca. 10 nm and a network structure, respectively, were observed.