Self-assembled dendrimers with uniform structure

Calix[4]arenes substituted at their wide rim by four aryl urea residues (1) form hydrogen-bonded dimers in apolar solvents. Replacement of one urea residue by an acetamido moiety leads to calix[4]arene derivatives (5) which form hydrogen-bonded tetramers under the same conditions. Both self-assembly processes occur independently. Therefore, molecules have been prepared in which a tetra-urea calix[4]arene and a tri-urea mono acetamide derivative are covalently connected between their narrow rims by a long, mainly aliphatic chain [-O-(CH(2))(n)-C(O)-NH-(CH(2))(m)-O-] (7). In the presence of an equimolar amount of tetra-tosyl urea calix[4]arene () they form dendritic assemblies since the well known heterodimerization of tetra-tosyl and tetra-aryl urea calix[4]arenes prevents the formation of a cross-linked structure. Covalent connection of adjacent urea residues leads to tetra-loop derivatives (3) that cannot form homodimers, but instead form heterodimers with tetra-aryl or tetra-tosylureas. Therefore, similar dendrimers should be available using the selective dimerization observed for 3. The formation of a single, structurally uniform dendrimer from eight building blocks is confirmed by (1)H NMR spectra, showing only peaks that are also found for respective model assemblies. Translational diffusion coefficients of the assemblies have been determined using (1)H DOSY NMR.     

A Facile Solution-Phase Approach to Transparent and Conducting ITO Nanocrystal Assemblies

Monodisperse 11 nm indium tin oxide (ITO) nanocrystals (NCs) were synthesized by thermal decomposition of indium acetylacetonate, In(acac)(3), and tin bis(acetylacetonate)dichloride, Sn(acac)(2)Cl(2), at 270 °C in 1-octadecene with oleylamine and oleic acid as surfactants. Dispersed in hexane, these ITO NCs were spin-cast on centimeter-wide glass substrates, forming uniform ITO NC assemblies with root-mean-square roughness of 2.9 nm. The assembly thickness was controlled by ITO NC concentrations in hexane and rotation speeds of the spin coater. Via controlled thermal annealing at 300 °C for 6 h under Ar and 5% H(2), the ITO NC assemblies became conductive and transparent with the 146 nm-thick assembly showing 5.2 × 10(-3) Ω·cm (R(s) = 356 Ω/sq) resistivity and 93% transparency in the visible spectral range-the best values ever reported for ITO NC assemblies prepared from solution phase processes. The stable hexane dispersion of ITO NCs was also readily spin-cast on polyimide (T(g) ～360 °C), and the resultant ITO assembly exhibited a comparable conductivity and transparency to the assembly on a glass substrate. The reported synthesis and assembly provide a promising solution to the fabrication of transparent and conducting ITO NCs on flexible substrates for optoelectronic applications.     

Disulfide exchange in hydrogen-bonded cyclic assemblies: stereochemical self-selection by double dynamic chemistry

Stereoselective cyclization of cystine-based bifunctional 2-ureido-4[1H]-pyrimidinone derivatives in CDCl(3) solutions was demonstrated by (1)H NMR spectroscopy. Thiolate-catalyzed disulfide exchange in solution led to the equilibration of different diastereomers of 1. At low concentrations, where formation of cyclic assemblies is the dominant mode of association, the molecules act as their own template. At these concentrations the meso diastereomer is formed preferentially, indicating a higher stability of its cyclic assemblies under the applied conditions, in comparison to the other diastereomers.     

Bacteriophage Tail‐Tube Assembly Studied by Proton‐Detected 4D Solid‐State NMR

Obtaining unambiguous resonance assignments remains a major bottleneck in solid‐state NMR studies of protein structure and dynamics. Particularly for supramolecular assemblies with large subunits (>150 residues), the analysis of crowded spectral data presents a challenge, even if three‐dimensional (3D) spectra are used. Here, we present a proton‐detected 4D solid‐state NMR assignment procedure that is tailored for large assemblies. The key to recording 4D spectra with three indirect carbon or nitrogen dimensions with their inherently large chemical shift dispersion lies in the use of sparse non‐uniform sampling (as low as 2 %). As a proof of principle, we acquired 4D (H)COCANH, (H)CACONH, and (H)CBCANH spectra of the 20 kDa bacteriophage tail‐tube protein gp17.1 in a total time of two and a half weeks. These spectra were sufficient to obtain complete resonance assignments in a straightforward manner without use of previous solution NMR data.     

Self-organization of crown-containing hetarylphenylethenes,phthalic acid,and potassium cations into supramolecular assemblies

Multicomponent molecular assemblies of 15-crown-5-containing 4-styrylpyridine with phthalic acid in the presence of potassium perchlorate were studied. The structure of the obtained complicated assemblies was determined by ¹H and ¹³C NMR spectroscopy, UV spectroscopy, and X-ray analysis. The composition of the supramolecular complexes was established by spectrophotometric titration, and the stability constants were calculated. The quantum yields of fluorescence for the ligand and its complexes of various nature were determined.     

Self-assembly and gelation behavior of tris(phenylisoxazolyl)benzenes

Low-molecular-mass organic gelators (LMOG), tris(phenylisoxazolyl)benzenes, were synthesized, and their self-assembling behavior was examined using (1)H NMR and UV-vis absorption spectroscopies. They turned into a gel in both nonpolar and highly polar solvents such as methylcyclohexane, ether, acetone, dimethylsulfoxide, etc. Field emission scanning electron microscopy (FESEM) observation of the xerogels of 1 and 3 possessing the saturated alkyl chains revealed that well-developed straight fibers were formed, whereas the unsaturated termini of the alkyl chains of 2 promoted the formation of both the right- and left-handed helical fibers. The self-association behavior of 1, 2, and 5 in solution were investigated using (1)H NMR and UV-vis spectroscopies. The flat aromatic compound 1 stacked in a columnar fashion along its C(3) axis via π-π stacking interactions. The assemblies were regulated by the peripheral alkyl substituents; the saturated alkyl groups facilitated the assemblies while terminal double bonds impeded the intermolecular association, and the branched substituents obviously interfered in the formation of the stacks, probably due to steric requirements. Theoretical calculations suggest that the three dipoles of the isoxazole groups adopt the circular array. The conformational search of the hexameric stacks of 4 using MacroModel V9.1 gave rise to two major conformers: one is nonhelical and the other is helical. Further detailed structural analysis of the assemblies of chiral 5 using circular dichroism (CD) measurements indicated that their assemblies adopt helical structures in solution. CD spectra and DFT calculations revealed that R-5 forms a left-handed supramolecular helicate. The coassembly of R- and S-5 displayed chiral amplification, since the chiral information from 5 was transferred to the supramolecular chirality of the helical assemblies of 1. A small amount of optically active 5 provided enough chiral stimulus to produce a remarkable chiral response and supramolecular helical structures of 1.     

Resorcinarene assemblies as synthetic receptors

The host-guest complexes of resorcinarenes are re-examined in solution through modern spectroscopic methods; the assemblies are characterized by 1H NMR and the guest exchange rates are measured by EXSY NMR spectroscopy.     

A novel type of hydrogen-bonded assemblies based on the melamine.cyanuric acid motif

This paper reports the formation of novel hydrogen-bonded assemblies 1(3).CA obtained upon mixing cyanuric acid (CA) with melamine derivatives 1, in which two of the three possible H-bonding arrays have been blocked. The four components are held together by 9 hydrogen bonds and form a rigid planar structure in which a central CA (three ADA motifs: A = acceptor, D = donor) is hydrogen bonded to three peripheral melamine derivatives (DAD motif). Furthermore, the synthesis and assembly studies are described of hydrogen-bonded assemblies 2-4.CA, comprised of three melamine derivatives that are covalently connected, and CA. The overall thermodynamic stability of assemblies 2-4.CA is superior to 1(3).CA (I(Tm) = 9 vs 3.6). The presence of the 2.CA complex in chloroform was confirmed by (1)H NMR spectroscopy and MALDI-TOF mass spectrometry. Substitution of the trimelamines with chiral or fluorescent groups (R(3)) enabled the study of the assemblies by CD and fluorescence spectroscopy. Titration experiments revealed strongly enhanced stabilities even in the presence of polar solvents, such as THF and CH(3)OH. Depending on the polarity of the solvent, stacking between the planar assembly units was observed.     

Artificial Multienzyme Supramolecular Device: Highly Ordered Self‐Assembly of Oligomeric Enzymes In Vitro and In Vivo

A strategy for scaffold‐free self‐assembly of multiple oligomeric enzymes was developed by exploiting enzyme oligomerization and protein–protein interaction properties, and was tested both in vitro and in vivo. Octameric leucine dehydrogenase and dimeric formate dehydrogenase were fused to a PDZ (PSD95/Dlg1/zo‐1) domain and its ligand, respectively. The fusion proteins self‐assembled into extended supramolecular interaction networks. Scanning‐electron and atomic‐force microscopy showed that the assemblies assumed two‐dimensional layer‐like structures. A fluorescence complementation assay indicated that the assemblies were localized to the poles of cells. Moreover, both in vitro and in vivo assemblies showed higher NAD(H) recycling efficiency and structural stability than did unassembled structures when applied to a coenzyme recycling system. This work provides a novel method for developing artificial multienzyme supramolecular devices and for compartmentalizing metabolic enzyme cascades in living cells.     

Interaction of methemoglobin with GDA/n-C5H11OH/water assemblies

In the present paper, we studied the interaction between n-dodecylammonium alpha-glutamate (GDA)/n-C5H11OH/H2O assemblies and methemoglobin by UV-vis spectroscopy, X-ray diffraction, electron spin resonance (ESR), rheology, and freeze-fractured transmission electron microscopy (FF-TEM). It is found that W/O microemulsion forms at a lower n-pentanol content and O/W microemulsion forms at a lower water content with the addition of methemoglobin. The existence of methemoglobin reduces the hexagonal liquid crystal region, while the lamellar liquid crystal region is little changed in the presence of methemoglobin. Moreover, methemoglobin and GDA/n-C5H11OH/H2O assemblies can affect their structures and properties and the change in behavior is dependent on the content of methemoglobin and the composition and structure of the GDA/n-C5H11OH/H2O system. The relationship among the changes in the structure and properties of GDA/n-C5H11OH/H2O assemblies, the content of methemoglobin, and the composition and structure of GDA/n-C5H11OH/H2O assemblies may provide some important theoretical information for elucidation of the interaction between methemoglobin and blood cell membrane and may also be helpful for the cure of some blood diseases.     

Applicability of the H NMR chemical shifts computed by the ab initio/GIAO-HF methodology to the study of geometrical features of Zn-porphyrin dimers

Several porphyrin dimers have been newly designed and synthesized to construct assemblies with 1,4-diazabicyclo[2.2.2]octane (DABCO) as a bidentate binding ligand. Semi empirical (AM1) and ab initio calculations have been used to study the assemblies generated by the organization of dimers and DABCO, including the computation of ¹H NMR complexation-induced chemical shifts using the ab initio/GIAO methodology. The diagnostic capacity of the theoretical method has been applied to explain experimental results and geometrical features of the complexes.     

A general method for constructing optically active supramolecular assemblies from intrinsically achiral water-insoluble free-base porphyrins

We have developed a general method to construct optically active porphyrin supramolecular assemblies by using a simple air-water interfacial assembly process. The method involved the in situ diprotonation of the free-base porphyrins at the air-water interface and subsequent assembly under compression. We showed that two intrinsically achiral water-insoluble free-base porphyrin derivatives, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (H(2)OEP) and 5,10,15,20-tetra-p-tolyl-21H,23H-porphine (H(2)TPPMe), could be diprotonated when spread onto a 2.4 M hydrochloric acid solution surface, and the Langmuir-Schaefer (LS) films fabricated from the subphase exhibited strong circular dichroism (CD) absorption, whereas those fabricated from pure Milli-Q water subphase did not. The experimental data suggested that the helical stacking of the achiral porphyrin building blocks was responsible for the supramolecular chirality of the assemblies. Interestingly, such a method was successfully applied to a series of other intrinsically achiral free-base porphyrins such as 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine (H(2)TPPOMe), 5,10,15,20-tetraphenyl-21H,23H-porphine (H(2)TPP), 5,10,15,20-tetrakis(4-(allyloxy)phenyl)-21H,23H-porphine (H(2)TPPOA), and 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)-21H,23H-porphine (H(2)TPPDOMe). A possible mechanism has been proposed. The method provides a facile way to obtain optically active porphyrin supramolecular assemblies by using intrinsically achiral water-insoluble free-base porphyrin derivatives.     

Self-assembly dynamics of modular homoditopic bis-calix[5]arenes and long-chain alpha,omega-alkanediyldiammonium components

Homoditopic building blocks 1, featuring two pi-rich cone-like calix[5]arene moieties connected at their narrow rims by a rigid o-, m-, or p-xylyl spacer in a centrosymmetric divergent arrangement, show a remarkable tendency to spontaneously and reversibly self-assemble with the complementary homoditopic alpha,omega-alkanediyldiammonium dipicrate guest salts C8-C12 x 2Pic through iterative intermolecular inclusion events, forming supramolecular assemblies whose composition and dynamics strongly depend upon the length of the connector, the geometry of the spacer, as well as the concentration and/or molar ratios between the two components. (1)H NMR spectroscopy and ESI-MS studies of 1/C(n) x 2Pic modular homoditopic pairs support the formation of discrete (bis)-endo-cavity assemblies with the shorter C8 and C9 connectors, and/or (poly)capsular assemblies with the longer C10-C12 components under appropriate concentrations and molar ratios (50 mM equimolar solutions). (1)H NMR titration experiments and diffusion NMR studies provide clear evidence for the self-assembly dynamics of the complementary pairs here investigated.     

Equilibria between metallosupramolecular squares and triangles with the new rigid linker 1,4-bis(4-pyridyl)tetrafluorobenzene. Experimental and theoretical study of the structural dependence of NMR data

The new fluorinated rigid ligand L, 1,4-bis(4-pyridyl)tetrafluorobenzene, was used in combination with different diphosphine Pd(II) and Pt(II) triflates to build metallosupramolecular assemblies. Complex equilibria between triangular and square entities were detected for all the cases. Characterization of the equilibria was accomplished by 1H, 31P(1H), 19F, and 195Pt(1H) NMR in combination with mass spectrometry. The square/triangle ratio was seen to depend on several factors, such as the nature of the metal corners, the concentration, and the solvent. The relative stability of the square and triangular complexes was explored by using force field methods. A GIAO-DFT study was carried out to analyze the changes of the 31P and 1H NMR data with the geometry of the complexes.     

Self-assembly of coumarin-conjugated acidic proteinoids

Photo- and pH-responsive self assembly was prepared by dispersing coumarin-conjugated acidic proteinoid in an aqueous phase. Proteinoid composed of Asp, Ser and Leu (PASL) was prepared as an acidic one by a melt-condensation method. Epoxypropoxy coumarin (EPC) was conjugated to PASL through its reaction with Ser. Assuming all Ser residues reacted with EPC, the calculated molar ratio of Asp/Ser-EPC/Leu in EPC-PASL conjugate was about 202/18/1 on ¹H NMR spectrum. EPC-PASL conjugates exhibited the dimerization and the de-dimerization of their EPC residues under cyclic irradiation of 365 nm and 254 nm. They were self-assembled into microparticle (about 500 nm), possibly due to the hydrophobic interaction among Leu residues and EPC residues. The EPC-PASL assemblies were linked each other by the photo-dimerization under the UV irradiation of 365 nm. EPCs are the hydrophobic pendants of the PASL conjugates and they could be easy to be hydrophobically assemblied. This may account for why EPC-PASL assemblies were much greater than PASL assemblies. On the contrary, EPC of PASL conjugates was cleavaged by the photo-dedimerization under the UV irradiation of 254 nm. The size of the assemblies increased and decreased in a cyclic manner under the cyclic irradiation, and the size of the photo cross-linked assembly was larger at a higher pH, possibly due to stronger intermolecular repulsion.     

Ionic core-shell dendrimers with an octacationic core as noncovalent supports for homogeneous catalysts

Ionic core-shell dendrimers with an octacationic core have been applied as noncovalent supports for homogeneous catalysts. Catalytically active arylpalladium complexes, which bear a tethered sulfato group, were noncovalently attached to the ionic core-shell dendritic supports via a straightforward ion-exchange reaction under mild conditions. Diagnostic shifts in (1)H NMR and Overhauser contacts show that the sulfato groups of the catalysts are located close to the octacationic core of the dendritic support in the resulting assemblies. The location of the catalytic Pd(II) sites has been varied via two strategies: by increasing the dendrimer generation and/or by shortening of the sulfato tether. In addition, a metallodendritic assembly was prepared, which bears an alternative shell of apolar dodecyl groups. Both the dendrimer size and the nature of the dendritic shell have no influence on the binding properties of the dendritic supports, i.e., the octacationic dendrimers of generations 1-3 form discrete 1:8 assemblies with the arylpalladium complexes. The structural aspects and the nature of the metallodendritic assemblies have been studied by means of pulse gradient spin-echo NMR diffusion methods, Overhauser spectroscopy, and electron microscopy (TEM). These techniques showed that the dendritic supports and arylpalladium complexes are strongly associated in solution to give unimolecular assemblies of nanoscopic dimensions. Membrane dialysis can recover these metallodendritic assemblies due to their nanoscopic size. The catalytic performances of the metallodendritic assemblies are comparable, but slightly lower than the performance of the unsupported catalyst.     

Incorporation of 2,6-di(4,4'-dipyridyl)-9-thiabicyclo[3.3.1]nonane into discrete 2D supramolecules via coordination-driven self-assembly

The synthesis and characterization of three new supramolecular complexes 6-8 (a rhomboid and two hexagons) via coordination-driven self-assembly are reported in excellent yields (>90%). These assemblies have 2,6-di(4,4'-dipyridyl)-9-thiabicyclo[3.3.1]nonane 2 as the bridging tecton. All assemblies were characterized by multinuclear NMR (1H and 31P), mass spectrometry (ESI-MS and ESI-FT-ICR), and elemental analysis. The X-ray structure of the 120 degrees tecton 2 is also discussed.     

Self-assembly of a donor-acceptor nanotube. A strategy to create bicontinuous arrays

The self-assembly of bolaamphiphile 1 into nanotubes containing a nanostructured electron donor/acceptor heterojunction is reported. In 10% MeOH/H(2)O, the tetraphenylporphyrin (TPP) and 1,4,5,8-naphthalenetetracarboxylic acid diimide chromophores engage in strong J-type π-π interactions within monolayer rings that further stack into the nanotube assemblies. In 10% MeOH/H(2)O at pH 1 or 11 or in pure MeOH, assembly is driven exclusively by the TPP ring, leading to the formation of nonspecific, unstructured aggregates. Steady-state, time-resolved fluorescence and femtosecond transient absorption spectroscopy revealed a strong dependence of the fluorescence decay and electron-transfer/charge-recombination time constants on the nature of the assemblies. These studies highlight the importance of local nanostructure in determining the photophysical properties of optoelectronic materials.     

Sorting the assemblies of unsymmetrically covalently functionalized mn-anderson polyoxometalate clusters with mass spectrometry

The unsymmetrical Mn-Anderson polyoxometalate cluster, [N(C4H9)4]3[MnMo6O18(C4H6O3NO2)(C4H6O3NH2)] (1; N(C4H9)4(+) = TBA(+)), has been prepared and characterized by X-ray crystallography and electrospray ionization mass spectrometry (ESI-MS). Covalent functionalization of compound 1 leads to the controlled assemblies of unsymmetrical alkoxopolyoxometalate clusters of compounds 2-5, which can be directly observed in solution as revealed by ESI-MS studies.     

Robust core-shell supramolecular assemblies based on cationic vesicles and ring-shaped [Mo154] polyoxomolybdate nanoclusters: template-directed synthesis and characterizations

Substantial progress has been made recently in extending the supramolecular assembly of biomimetic structures to vesicle-based sophisticated nanocomposites and mesostructures. We report herein the successful preparation of unilamellar surfactant vesicles coated with a monolayer of ring-shaped [Mo(154)] polyoxometalate (POM) nanoclusters, (NH(4))(28)[Mo(154)(NO)(14)O(448)H(14)(H(2)O)(70)]. approximately 350 H(2)O, by coulomb attractions using preformed didodecyldimethylammonium bromide (DDAB) surfactant vesicles as templates. The resultant vesicle-templated supramolecular assemblies are robust (they do not disintegrate upon dehydration) both at room-temperature ambient and vacuum conditions, as characterized by conventional transmission electron microscopy (TEM) and atomic force microscopy (AFM). The flexibility of the complex soft assemblies was also revealed by AFM measurements. The effect of POM-vesicle coulomb attractions on the dimensions of the templating vesicles was also investigated by using dynamic light scattering (DLS). Although origins of the structure stability of the as-prepared supramolecular assemblies are not clear yet, the nanometer scale cavities and the related properties of macroions of the POM clusters may play an important role in it.