Zeroth Generation Research Articles

Protein discrimination by fluorescent sensor array constituted of variously charged dendritic phenylene–ethynylene fluorophores

A protein fluorescent sensor array based on variously charged dendritic fluorophores is developed. The variation of charge is achieved by different combinations of cationic trimethylammonium, anionic carboxylate and non-ionic methyl ester or N,N-dimethylamino on the peripheries of the fluorophores. Nine phenylene–ethynylene dendritic fluorophores, seven zeroth generation bearing charges varied from −3 to +3 and two first generation bearing −6 and +6 charges, are synthesized from triiodotriphenylamine through series of Sonogashira coupling. In phosphate buffer saline pH 7.4, five out of these nine compounds fluorogenically response to eight protein analytes distinctively. The data set of fluorescent intensities obtained from 5 fluorophores × 8 proteins × 9 replicated measurements can be statistically sorted into eight clusters corresponding to each protein by principal component analysis (PCA). Factorial discriminant analysis (FDA) cross-validation is applied to locate the optimum detection wavelength and reduce the number of sensing elements from nine to two with 100% discriminating accuracy. The method described should be generally practical for the development of electronic tongue for protein related food analysis and medical diagnosis.

Synthesis of Calixarene-Capped Carbosilane Dendrimers

A new class of polycalix[4]arene hosts has been constructed based on a carbosilane dendrimer architecture, in which each dendritic branch terminates with a calix[4]arene entity. This study reports the synthesis and characterization of the zeroth generation example with four calix[4]arenes and of the first generation example with 12 calix[4]arenes.

Role of main chain rigidity and side-chain substitution on the supramolecular organization of rigid–flexible polymers

The synthesis, characterization and supramolecular organization of rigid–flexible aromatic–aliphatic polyethers are reported. The polymers contain substituted quinquephenyl moieties along their main chains separated by flexible aliphatic units of various lengths. The oligophenylene segments bear different types of dodecyloxy tailed side groups, either attached on the periphery of side dendritic wedges (G 1) or as direct side-chains (G 0). Their structural characterization was performed by means of differential scanning calorimetry, polarizing optical microscopy and X-ray scattering from oriented fibers. These techniques revealed the presence of supramolecular organization in different levels and in the absence of solvent, reflecting a delicate balance of interactions produced by the rigid–flexible backbone segments and the size of dendritic side-chains. It was concluded that the polymers with only two dodecyloxy side-chains (zeroth generation, G 0) possess smectic order. On the other hand, substitution of the quinquephenyl backbone with the dodecyloxy decorated dendrons (first generation, G 1) disrupts the lateral order giving rise to a nematic state. These results are compared with the corresponding rigid–flexible polyethers having terphenyl rigid segments.

Orientational order and dynamics of the dendritic liquid crystal organo-siloxane tetrapodes determined using dielectric spectroscopy

The dielectric measurements have been carried out on the two zeroth generation dendrimers with four branched arms (called tetrapodes) based on the siloxane cores. The results are analyzed in the framework of the molecular theory of dielectric permittivity by Maier and Meier for nematogens. At least four molecular processes are resolved in the dielectric relaxation spectra in the nematic phase for each of the two tetrapodes. Three of them are assigned to the reorientation of the monomeric unit whereas the fourth is assigned to the rotation of the molecular segments in the individual arms of the monomeric unit around the long molecular axis. The dielectric relaxation strength of the low frequency process has been used to calculate the orientational order parameter. The dynamics of the resolved processes has been quantitatively analyzed using the results of the microscopic model of the rotational diffusion, given by Coffey and Kalmykov [W. T. Coffey and Yu. P. Kalmykov, Adv. Chem. Phys. 113, 487 (2000)] using the calculated order parameter. All molecular processes: the rotation around the short molecular axis (end-over-end rotation), precession around the director and the rotation around the long molecular axis (also called the spinning motion) are shown to have successfully been reproduced by the model. The anisotropy of the rotational diffusion coefficients gradually increases with a reduction in temperature, to a factor of 3 in the nematic phase relative to its isotropic phase.

Poly(amidoamine) Dendrimers Bearing Electron-Donating Chromophores: Fluorescence and Electrochemical Properties

Poly(amidoamine) dendrimers from the zeroth generation (G 0) to the fifth generation (G 5) bearing electron-donating chromophores, i.e. N, N-dimethylphenylamine (PA), carbazole (Cz) and pyrene (Py) chromophores have been synthesized. The macromolecular reactions of chromophoric modifications of PAMAM dendrimers were monitored by fluorescence spectroscopy. The reliability of fluorescence monitoring was confirmed by NMR spectroscopy. Compared with widely applied environment-sensitive fluorescence probe techniques, a distinct feature of the fluorescence monitoring was that it directly reflected the conversion of chemical bonds. A comparative study revealed that the fluorescence quenching of small molecular Py by the high generation dendrimers of PAMAM-PA was a static quenching process. The high generation dendrimers of PAMAM-Py possessed relatively compact Py shells as compared with the same generation PAMAM-PA. Electrochemical studies revealed an architectural transition occurring from an open and flexible structure to a closely packed globular structure between G 2 and G 3. The electron-donating ability of PAMAM-PA was affected by dendritic architectures.

Bis(2-pyridylimino)isoindole (BPI) Ligands with Novel Linker Units: Synthesis and Characterization of Their Palladium and Platinum Complexes

With the aim of immobilizing bis(2-pyridylimino)isoindolate (BPI) ligands their backbone structure has been functionalized with several linker units. Their fixation was carried out at the stage of the phthalodinitrile precursor by nucleophilic ipso-substitution of 4-nitrophthalodinitrile. Subsequent synthesis of the functionalized phthalodinitriles with two molar equivalents of the 2-aminopyridine derivatives gave the corresponding BPI ligands. Reaction of the ethyleneglycol functionalized BPI derivative with the zeroth generation carbosilane dendrimer [G-0]4-exo-Cl yielded the functionalized dendrimer [G-0]4-exo-[O(CH2)2O]-10-MeBPI (7). The synthesis of the palladium complexes was carried out by reaction of the protioligands with [(PhCN)2PdCl2] in benzene using triethylamine as auxiliary base whereas the first examples of BPI-platinum complexes were prepared using [(COD)PtCl2] as starting material.

L-Lysine Dendronized Polystyrene

This paper reports the synthesis and characterization of a novel class of dendronized polymers which are based on styrene functionalized dendritic l-lysine macromonomers. Free radical polymerization of zeroth and first generation macromonomers afforded dendronized polymers with number-average degrees of polymerization (DP) between 50 and 240, corresponding to number-average molecular weights between 50 × 103 and 240 × 103 g/mol. In contrast, only short oligomers (DP = 5−15) were obtained on polymerization of the second generation dendritic l-lysine macromonomers. Molecularly resolved AFM images allowed first insight into the structure of these peptide dendronized polymers. Depending on the degree of polymerization, either rods, short rods, or globular structures were found.

Influence of nanoparticles and polymer branching on the dewetting of polymer films

Previous studies have shown that spun-cast films of unentangled synthetic polymers commonly dewet inorganic or organic substrates, leading to technologically detrimental results for many applications. We illustrate two strategies for influencing polymer film dewetting on inorganic and organic substrates. First, the addition of small amounts of C 60 fullerene nanoparticles to the spin-casting polymer solutions of model synthetic polymers [polystyrene (PS) and polybutadiene (PB)] leads to a significant inhibition of film dewetting on Si. This effect is associated with the formation of a diffuse fullerene layer near the solid substrate that frustrates the dewetting hole growth process. Next, we consider polymer branching effects on the dewetting of various generations of hypergraft polymer poly(2-ethyl-2-oxazoline) (PEOX) films cast on high molecular weight polystyrene substrates. The early stage of dewetting is found to be similar in a zeroth generation G0 hypergraft (a comb polymer) and a G2 hyper-graft (resembling a spherical ‘micro-gel’ particle). The late stage of dewetting in the G2 films, however, differs significantly from the low generation films because of an inhibition of hole coalescence in the intermediate stage of film dewetting. This behavior resembles previous observations of dewetting in ‘entangled’ polystyrene films. Thus, the viscoelasticity of the polymer film can have an inhibitory effect on film dewetting, leading to changes in the dewetted film morphology rather than a suppression of film dewetting.

Influence of generation number on the dewetting of hypergraft poly(2-ethyl-2-oxazoline) films

We investigate the influence of polymer branching (generation number G) on the dewetting of hypergraft poly(2-ethyl-2-oxazoline) (PEOX) polymer films from model non-polar synthetic polymer and inorganic substrates. The present study contrasts the cases of a zeroth generation G0 hypergraft, which is a comb polymer, and a G2 hypergraft, which resembles a nearly spherical 'microgel' particle. The early stage of dewetting is found to be similar in the G0 and G2 films and is largely independent of substrate (entangled polystyrene film or acid-cleaned silica wafer). However, the late stage of dewetting in the G2 films differs significantly from the GO films because of an inhibition of hole coalescence in the intermediate stage of film dewetting. The holes in the G2 hyperbranched films continue to grow in size until they impinge on each other to form a foam-like structure with a uniform 'cell' size. The boundaries of these cells break up and the vertices of the former cellular network retract to form a relatively uniform droplet configuration. In contrast, hole coalescence in the GO films occurs readily, leading to a polydisperse hole size distribution, and the fluid borders of the holes break up to form the non-uniform 'Voronoi' droplet configuration normally associated with film dewetting. Similar trends have been observed in the dewetting of linear polymer films where entangled polymers behave similarly to the branched (G2) polymers of the present study. This effect is attributed to the viscoelasticity of the G2 hyperbranched polymer fluid.

Synthesis and structure–optical rotation relationships of homochiral, monodisperse, tartaric acid-based dendrimers

Optically active, homochiral dendrimers of both the zeroth generation 1 and first generation 2 have been synthesized from (2R, 3R)-tartaric acid and phloroglucinol by an iterative, convergent method. These chiral dendrimers comprise 4-tert-butylphenoxy as the surface groups and phloroglucinol as the branching junctures. The chiral element, which is a derivative of L-tartaric acid, serves as the connecting unit between the surface group and the branching juncture, or between two branching junctures. Homochiral (2S,3S)-(–)-2, 3-O-isopropylidene-1, 4-di-O-tosyl-L-threitol 3 was first connected to the surface moiety via mono-O-arylation with 4-tert-butylphenol to generate the optically active mono-O-tosyl ester 4. Excessive O-alkylation of the branching juncture, 5-benzyloxyresorcinol 5, with 2 molar equivalents of the mono-O-tosyl derivative 4, followed by activation of the benzyl-protected phenol moiety at the focal point, led to dendritic ‘wedge’7. Treatment of the phenol 7 with a further molar equivalent of intermediate 4 gave the zeroth generation dendrimer 1 in 36% overall yield from the di-O-tosyl ester 3. By application of the same reaction sequence, the phenol 7 could similarly be transformed into the first generation dendrimer 2 in 13% overall yield from homochiral diester 3. Investigation on the optical rotation properties of these dendritic compounds showed that their specific rotations remained essentially constant and that the molar rotations were roughly proportional to the number of chiral tartrate units in the molecule.

Longitudinal dispersion in model of central airways during high-frequency ventilation

We have measured the longitudinal dispersion of boluses of helium, acetylene and sulphur hexafluoride in a plastic model of the human airways - generations zero through six - during high frequency ventilation (HFV). HFV was maintained by a piston pump. Frequency f and tidal volume Vt ranged from 2.5 to 25 Hz and from 5 to 20 ml, respectively. Boluses were injected near the entrance of the zeroth generation (trachea), and the dispersion curves were measured by mass spectrometry at the end of the sixth airway generation. The shapes of the bolus dispersion curves could be well described with Gaussian distribution functions. With the exception of the HFV-conditions with Vt = 5 ml , the effective dispersion coefficient D DISP appeared to be independent of the molecular diffusion coefficient. This independency was also found by other investigators in studies with dogs and human subjects. The measured results for D DISP for different f and Vt could be satisfactorily described with the empirical equation D DISP = 0.0617 f 0.8 V T 1.38 [ cm 2 s −1] . Application of this equation to f and Vt values normally applied in man resulted in D DISP values which should be considered to be too small for maintaining eucapnic ventilation in vivo. On the basis of this result we believe that during HFV in intubated subjects gas transport by longitudinal dispersion will be limited to the instrumental dead space - the endotracheal tube inclusive - and a few generations of large bronchi.

The joint distribution for the sizes of the generations in a cascade process

Consider a cascade or random branching process, with discrete time, with a positive integral number s , of female sexes, and where the reproductive behaviour of the individuals depends on time. Starting with any number of individuals of the various types in the zeroth generation, the joint p.g.f. (probability generating function) will be obtained for the numbers of individuals in each of the first n generations. The power of the result will be shown by the ease with which several deductions can be made.