Study on the obtaining of cobalt oxides by thermal decomposition of some complex combinations,undispersed and dispersed in SiO<Subscript>2</Subscript> matrix

In order to obtain cobalt oxides nanoparticles we have used the thermal decomposition of some carboxylate type precursors. These precursors were obtained by the redox reaction between cobalt nitrate and ethylene glycol, either bulk or dispersed in silica matrix. The redox reaction takes place by heating the Co(NO₃)₂·6H₂O-C₂H₆O₂ solution or the Si(OC₂H₅)₄-Co(NO₃)₂·6H₂O-C₂H₆O₂ gels. Thermal analysis of the Co(NO₃)₂·6H₂O-C₂H₆O₂ solution and Si(OC₂H₅)-Co(NO₃)₂·6H₂O-C₂H₆O₂ gels allowed us to establish the optimal value for the synthesis temperature of the carboxylate precursors. By fast heating of the solution Co(NO₃)₂·6H₂O-C₂H₆O₂, the redox reaction is immediately followed by the decomposition of the precursor, which represents an autocombustion process. The product of this combustion contains CoO as unique phase. We have obtained a mixture of CoO and Co₃O₄ by annealing the synthesized carboxylate compounds for 2 h at 400°C. With longer annealing time (6 h), we have obtained Co₃O₄ as unique phase. The XRD study of the crystalline phases resulted by thermal decomposition of the precursors embedded in silica matrix, showed that the formation of Co₂SiO₄ and Co₃O₄, as unique phases, depends on the thermal treatment.     

Potential curves of two-molecule interactions in some smectic and ferroelectric liquid crystals

The atom-atomic potential method is used to study the potential curve of pairwise intermolecular interactions in smectic crystals C [C₅H₁₁O-(OH)C₆H₃-CH=N-C₆H₄-C₅H₁₁ (A), C₁₀H₂₁O-C₆H₄-CH=CH-C₆H₄-OC₁₀H₂₁ (B)], ferroelectric smectic liquid crystals C* [C₇H₁₅O-C₆H₄-C₆H₄-COOCH₂C*H(CH₃)C₂H₅ (C), C₈H₁₇O-C₆H₄-C₆H₄-C₂H₄C*H(CH₃)C₂H₅ (D)], and binary systems A+C and A+D. Both inter- and intramolecular parameters as well as their mutual effects are taken into consideration. The intermolecular interactions are shown to significantly affect the conformations of isolated molecules. For the CC, DD, and AD interactions, the antiparallel ⇅ packing of molecules is found to be most favorable. In the case of the AA and AC interactions, the ⇈ and ⇅ packings are equally favorable in terms of energy (energy difference U_pair does not exceed 0.8 kcal/mole). Despite the structural similarity between the chiral molecules C and D, the presence of the highly polar groups -O- , OH, CH=N, and COO leads to pronounced changes in the position and orientation of molecules in their packing in the AC and AD pairs. The pair interaction energy U_pair near the minimum point was studied as a function of the shift of molecules relative to each other along the long axis X and of the angle 9 between the long molecular axes. The curve of U(pair) vs the shift along X has a few deep local extrema. The possibility of formation of energetically favorable molecular associates (dimers) in the compounds is demonstrated. The associates are stabilized by dipole-dipole intermolecular interactions. Translated from Zhumal Strukturnoi Khimii, Vol. 41, No. 4, pp. 709-717, July-August, 2000     

Electrochemical determination of standard thermal diffusion characteristics for chlorides of hydrogen and potassium in water-ethanol solutions

Initial and steady-state temperature coefficients of the voltage generated by thermogalvanic cells comprising silver chloride and quinhydrone electrodes in the systems HCl-H₂O-C₂H₅OH and KCl-H₂O-C₂H₅OH are determined. Standard thermal diffusion Soret coefficients, the entropy of thermal diffusion transport of electrolytes, and the entropy of mobile ions H⁺, K⁺, and Cl^? are calculated for 298 K. The effect the nature of ions and the solvent composition exert on the obtained thermal diffusion transport characteristics is considered in terms of the De Bethune theory.     

Potential curves of two-molecule interactions in some smectic and ferroelectric liquid crystals

The atom-atomic potential method is used to study the potential curve of pairwise intermolecular interactions in smectic crystals C [C₅H₁₁O-(OH)C₆H₃-CH=N-C₆H₄-C₅H₁₁ (A), C₁₀H₂₁O-C₆H₄-CH=CH-C₆H₄-OC₁₀H₂₁ (B)], ferroelectric smectic liquid crystals C* [C₇H₁₅O-C₆H₄-C₆H₄-COOCH₂C*H(CH₃)C₂H₅ (C), C₈H₁₇O-C₆H₄-C₆H₄-C₂H₄C*H(CH₃)C₂H₅ (D)], and binary systems A+C and A+D. Both inter- and intramolecular parameters as well as their mutual effects are taken into consideration. The intermolecular interactions are shown to significantly affect the conformations of isolated molecules. For the CC, DD, and AD interactions, the antiparallel ⇅ packing of molecules is found to be most favorable. In the case of the AA and AC interactions, the ⇈ and ⇅ packings are equally favorable in terms of energy (energy difference U_pair does not exceed 0.8 kcal/mole). Despite the structural similarity between the chiral molecules C and D, the presence of the highly polar groups -O- , OH, CH=N, and COO leads to pronounced changes in the position and orientation of molecules in their packing in the AC and AD pairs. The pair interaction energy U_pair near the minimum point was studied as a function of the shift of molecules relative to each other along the long axis X and of the angle 9 between the long molecular axes. The curve of U(pair) vs the shift along X has a few deep local extrema. The possibility of formation of energetically favorable molecular associates (dimers) in the compounds is demonstrated. The associates are stabilized by dipole-dipole intermolecular interactions. Translated from Zhumal Strukturnoi Khimii, Vol. 41, No. 4, pp. 709-717, July-August, 2000     

Synthesis and properties of carbosilane dendrimers with perfluorohexyl groups in the outer layer of the molecular structure

Branched perfluorohydrosiloxane with CF₃CF₂CF₂C(CF₃)₂(CH₂)₃ groups at the silicon atom was synthesized by a sequence of chemical reactions. The resulting compound was used as a modifying agent for carbosilane dendrimers of the 3rd and 6th generations. Dendrimers with perfluorohexyl terminal groups in surface layer are characterized by a complex of physicochemical methods. It is demonstrated that due to the branching of perfluoroalkyl terminal groups, obtained carbosilane dendrimers are soluble in organic and inorganic media. Differences in the solubility of small and large dendrimers are caused by the formation of the outer fluoride shell of different densities.     

Solubility diagrams of the potassium iodide-water-ethanol and iodine-water-ethanol ternary systems

The solubility of potassium iodide and iodine in water-methanol mixed solvents was studied by the method of sections at 25°C and atmospheric pressure. The solubility of potassium iodide was found to decrease as the content of ethanol in aqueous-alcoholic solutions increased. The solubility of crystalline iodine had a complex dependence on mixed solvent composition; it was maximum in mixtures containing 90 wt % alcohol. The compositions of the solid phases that crystallized in the KI-H₂O-C₂H₅OH and I₂-H₂O-C₂H₅OH systems were substantiated by X-ray measurements.     

Interactions and Encapsulation of Vitamins C,B3, and B6 with Dendrimers in Water

Titrations of commercial diaminobutane (DAB) and polyamidoamine (PAMAM) dendrimers by vitamins C (ascorbic acid, AA), B₃ (nicotinic acid), and B₆ (pyridoxine) were monitored by ¹H NMR spectroscopy using the chemical shifts of both dendrimer and vitamin protons and analyzed by comparison with the titration of propylamine. Quaternarizations of the terminal primary amino groups and intradendritic tertiary amino groups, which are nearly quantitative with vitamin C, were characterized by more or less sharp variations (Δδ) of the ¹H chemical shift (δ) at the equivalence points. The peripheral primary amino groups of the DAB dendrimers were quaternarized first, but not selectively, whereas a sharp chemical‐shift variation was recorded for the inner methylene protons near the tertiary amines, thereby indicating encapsulation, when all the dendritic amines were quaternarized. With DAB‐G5‐64‐NH₂, some excess acid is required to protonate the inner amino groups, presumably because of basicity decrease due to excess charge repulsion. On the other hand, this selectivity was not observed with PAMAM dendrimers. The special case of the titration of the dendrimers by vitamin B₆ indicates only dominant supramolecular hydrogen‐bonding interactions and no quaternarization, with core amino groups being privileged, which indicates the strong tendency to encapsulate vitamins. With vitamin B₃, a carboxylic acid, titration of DAB‐G3‐16‐NH₂ shows that only six peripheral amino groups are protonated on average, even with excess vitamin B₃, because protonation is all the more difficult due to increased charge repulsion, as positive charges accumulate around the dendrimer. Inner amino groups interact with this vitamin, however, thus indicating encapsulation presumably with supramolecular hydrogen bonding without much charge transfer.     

Carbosilane liquid crystalline dendrimers with terminal chiral mesogenic groups: structure and properties

This paper presents a systematic study of two series of carbosilane liquid crystalline (LC) dendrimers from first to fifth generations bearing 8, 16, 32, 64 and 128 terminal chiral mesogenic groups, respectively. All the LC dendrimers synthesized are characterized by the same glass transition temperature around -5°C. It has been shown that the LC dendrimers of the lower generations (G-1-G-3) form a ferroelectric SmC* phase over a very broad temperature range up to about 180°C, while the LC dendrimers of the higher generations (G-4 and G-5) display a rectangular columnar mesophase (Col_r). Schemes of packing in the SmC* and Col_r mesophases formed by the LC dendrimers are suggested and discussed. Electrical measurements on the ferroelectric LC dendrimers have shown that an increase in generation number leads to a decrease in the value of the spontaneous polarization and an increase in switching time.     

含氨基酸和多肽的树枝状化合物的合成与分子动力学模拟研究

合成了一系列以氨基酸和多肽为外周功能基团的醚-酰胺型树枝状化合物, 化合物结构经NMR, ESI-MS确证. 并对该系列化合物在水溶液中的状态进行了分子动力学模拟. 结果显示: 化合物的构象与原子数相关, 随原子数的增加有逐渐接近球形的趋势; 氨基酸α碳原子径向分布显示, 随着外周功能基团的增大, 分子可能存在部分卷曲构象.     

Synthesis and Characterization of New Conjugated Fluorenyl‐Porphyrin Dendrimers for Optics

A new family of conjugated meso‐tetraphenylporphyrin‐based dendrimers with four ( TPP1 , TPP2 ), eight ( TPP3 , TPP4 , TPP5 ) and up to sixteen ( TPP6 ) fluorenyl groups has been synthesized and fully characterized. These tetraphenylporphyrin‐cored dendrimers present peripheral alkynyl π‐conjugated dendrons with fluorenyl termini. The meso‐aryl rings of these porphyrins are functionalized either in para‐ ( TPP1 , TPP2 , and TPP3 ) or meta‐positions ( TPP4 , TPP5 , and TPP6 ). Their detailed luminescence properties are discussed in reference to two porphyrins lacking fluorenyl dendrons ( TPP ‐ H_1,2,3 and TPP ‐ H_4,5,6 ). A strong dependence of their luminescence quantum yield and lifetime on their structures is stated, their nonlinear optical properties were also discussed.     

Dendritic polyols based on carbosilanes - lipophilic dendrimers with hydrophilic skin

Carbosilane dendrimers with up to 108 end groups were prepared by a divergent synthetic route via repeated alternating Grignard-reaction with allylmagnesium bromide and hydrosilylation. Quantitative hydroboration of the dendrimers was achieved with 9-BBN/H₂O₂,OH⁻. Employing this synthetic route, rather monodisperse dendritic polyols with lipophilic carbosilane core and hydrophilic shell were prepared. All dendrimers were characterized with MALDI-TOF, showing low polydispersities. The novel dendritic polyols constitute interesting molecular scaffolds for the preparation of unusual supermolecules. As an example, reaction with cholesteryl chloro-formiate was used to prepare a series of dendrimers with 12, 36 and 108 mesogenic cholesteryl end groups.     

Efficient halogen-lithium exchange reactions to functionalize poly(alkyl aryl ether) dendrimers

Poly(alkyl aryl ether) dendrimers were functionalized with bromophenyl groups at their peripheries, so as to have 3, 6, 12, and 24 groups in the zero, first, second, and third generation dendrimers, respectively. The new bromophenyl functionalized dendrimers were assessed for their reactivities in C-heteroatom and C-C bond forming reactions. For this purpose, the bromophenyl functionalized dendrimers were converted quantitatively to their polylithiated derivatives, using n-BuLi in benzene. The polylithiated dendrimers were reacted either with D₂O or with CO₂, so as to afford the corresponding deuterated and carboxylic acid functionalized dendrimers, respectively. The carboxylic acid functionalized dendrimers were modified further to the methyl esters during their characterization.     

Synthesis of carbosilane dendrons and dendrimers derived from 1,3,5-trihydroxybenzene

Several carbosilane wedges of generations 1-3 have been synthesized, following the divergent method, containing at the focal point a C-Br bond and as peripheral functional groups SiMeCl₂, SiMe(C₃H₅)₂, SiMe₂Cl, SiMe₂H, and ester units SiMe₂{(C₃H₆)N(C₂H₄CO₂Me)₂}. The dendrons functionalized with SiMe(C₃H₅)₂ and SiMe₂{(C₃H₆)N(C₂H₄CO₂Me)₂} groups were used to synthesize spherical dendrimers derived from 1,3,5-(HO)₃C₆H₃, leaving the outer groups unchanged. The allyl dendrimers thus obtained were used as precursors to prepare new dendrimers functionalized with SiMeCl₂, SiMe₂Cl, SiMe₂H, amine units SiMe₂{(C₃H₆)NH₂} and also ester units SiMe₂{(C₃H₆)N(C₂H₄CO₂Me)₂}.     

Synthesis of Chiral Starburst Dendrimers from PHB-Derived Triols as Central Cores

Chiral triols 1 – 3 (‘tris(hydroxymethyl)methane’ derivatives), prepared from (R)-3-hydroxybutanoic acid and aldehydes, are used as center pieces of dendrimers. The triols may be employed as such or after attachment of spacers containing alkyl or aryl moieties (see 5 and 7 ). The branches combined with the original or elongated triols are those first reported by Fréchet ( 9 – 12 , benzyl ethers of 3,5-dihydroxybenzyl alcohol and bromide). In this way, 1st-, 2nd-, and 3rd-generation chiral dendrimers without ( 13 – 15 ), or with aliphatic ( 16 – 18 ) or aromatic ( 19 – 21 ) spacers are prepared. The molecular weights range from 447 to 2716 Dalton. Two of the chiral triols, i.e., 2 and 3 , are used as center pieces for chiral dendrimers containing 6 NH₂, or 6 and 12 NO₂ groups on the periphery ( 22 – 27 ), with 3,5-dinitrobenzoyl chloride as the branching unit. All compounds thus synthesized are of course monodisperse and are fully characterized. In some cases, the optical activity of the dendrimers indicates that conformationally chiral substructures might be present. The NH₂- and NO₂-substituted compounds avidly clathrate smaller molecules; they are sorbents exchanging host molecules through the gas phase.     

Preparation, characterization, and antimicrobial property of cotton cellulose fabric grafted with poly (propylene imine) dendrimer

Two generations of poly (propylene imine) dendrimer with amino terminated groups (G2- and G5-PPI-NH₂) were grafted on cotton cellulose fabric using cross linking agents (citric or glutaric acids). Fourier transform infrared (FTIR) spectroscopy identified ester groups which were formed between hydroxyl groups of the cotton fabric and carboxylic groups of the cross linking agents. Also, attenuated total reflectance-FTIR (ATR-FTIR) analysis confirmed formation of amide groups between the carboxylic groups of the cross linking agents and the amino end groups of the dendrimers. Nitrogen content (N-content) analysis revealed the presence of the dendrimers on the cotton fabric even after 5 washing cycles. In order to study the dispersion of the PPI dendrimers on the surface of the cotton fabric, field emission scanning electron microscopy (FE-SEM) was performed. The particle size distribution of the G2- and G5-PPI-NH₂ aqueous solutions was also determined by dynamic light scattering (DLS) analysis. Antimicrobial activity of the PPI dendrimer aqueous solutions and the cotton cellulose fabric grafted with the dendrimers was evaluated both quantitatively and qualitatively against Gram-positive bacterium (Staphylococcus aureus), Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli) and fungus (Candida albicans). The dendrimer grafted cotton cellulose fabric exhibited a 99 % reduction in bacterial counts against S. aureus, E. coli and C. albicans. The antimicrobial activities of the grafted cotton cellulose fabric with the PPI dendrimers were maintained even after 5 washing cycles.     

Syntheses and nickel coordination properties of cyclen substituted with mixed stilbene/poly(ethylene glycol) dendritic arms

We synthesized a series of cyclens substituted with mixed stilbene and poly(ethylene glycol) dendritic arms. All dendrimers terminated with different peripheral groups had good solubility in common organic solvents, and dendrimers terminated with ? CO₂H groups (CO₂H‐dendrimers) were also soluble in alkaline solutions. The nickel coordination properties of these dendrimers were investigated in organic solvents. Dendrimers terminated with ? CN groups (CN‐dendrimers) and the second‐generation CO₂H‐dendrimer [(CO₂H)₈L2] could produce pentacoordinated nickel complexes; the third‐generation CO₂H‐dendrimer [(CO₂H)₁₆L3] could form tetra‐ and pentacoordinated nickel complexes, and the nickel complex of the fourth‐generation CO₂H‐dendrimer [(CO₂H)₃₂L4] could not be obtained. This result was due to the fact that the globular surface of (CO₂H)₁₆L3 formed a hydrogen‐bond network that selectively penetrated cations and inhibited the access of anions to the core. The formation of the hydrogen‐bond network was confirmed by Fourier transform infrared, ¹H NMR, and fluorescence data. The CN‐dendrimers could not form hydrogen bonds on the surface, and the first‐ and second‐generation CO₂H‐dendrimers could not form intramolecular hydrogen‐bond networks. Therefore, they had no selectivity for positive nickel ions and negative chloride ions. (CO₂H)₃₂L4 could not produce a nickel complex because it had a crammed backbone structure that could not penetrate nickel and chloride ions. Therefore, it was possible to control the ion access of cations and anions with the hydrogen‐bond network of (CO₂H)₁₆L3. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5414–5428, 2005     

Benzoxazine/Triphenylamine‐Based Dendrimers Prepared through Facile One‐Pot Mannich Condensations

A series of thermally polymerizable dendrimers of various generations, equipped with triphenylamine (TPA) and benzoxazine (BZ) groups, is synthesized through facile one‐pot Mannich condensations of N ¹,N¹‐bis(4‐aminophenyl)benzene‐1,4‐diamine (TPA–3NH₂, as the core group), 4‐(bis(4‐aminophenyl)amino)phenol (TPA–2NH₂–OH, as the AB₂ branching group), and CH₂O in 1,4‐dioxane. The ratios of the integrated areas in the ¹H nuclear magnetic resonance spectra of these dendrimers are consistent with the theoretical numbers of protons, suggesting their successful syntheses. Bathochromic shifts of signals are evident in the UV–vis and photoluminescence spectra upon increasing the generation of the TPA–BZ dendrimers, consistent with an increase in the effective conjugation length. The TPA–BZ dendrimers are able to undergo thermal polymerization and display unique optical physical properties, resulting in thermoset TPA networks after thermal ring‐opening polymerization.     

Synthesis,Redox Activity of Rigid Ferrocenyl Dendrimers,and Isolation of Robust Ferricinium and Class‐II Mixed‐Valence Dendrimers

The coupling reactions of ethynylferrocene with trihalogenoarenes do not lead to ethynylferrocenyl arenes that are soluble enough to form the basis of a suitable construction of stiff ferrocenylethynyl arene‐cored dendrimers, which explains the previous lack of reports on stiff ferrocenyl dendrimers. However, rigid ferrocenyl‐terminated dendrimers have been synthesized from 1,3,5‐tribromo‐ and triiodobenzene through Sonogashira and Negishi reactions with 1,2,3,4,5‐pentamethyl‐1′‐ethylnylferrocene ( 1 a ), according to 1→2 connectivity. With compound 1 a , the construction of a soluble dendrimer ( 10 a ) that contained 12 ethynylpentamethylferrocenyl termini was achieved. Stiff dendrimer 10 a shows a single, reversible cyclic voltammetry (CV) wave (with adsorption), which disfavors the hopping heterogeneous electron‐transfer mechanism that is postulated for redox‐terminated dendrimers that contain flexible tethers. The selectivity of these Sonogashira reactions allows the synthesis of an arene‐cored dendron ( 2 c ) that contains both ethynylferrocenyl and 1,2,3,4,5‐pentamethyl‐ferrocenylethynyl redox groups, thus leading to the construction of a dendrimer ( 7 c ) that contains both types of differently substituted ferrocenyl groups with two well‐separated reversible CV waves. Upon selective oxidation, this mixed dendrimer ( 7 c ) leads to a class‐II mixed‐valence dendrimer, 7 c [PF₆]₃, as shown by Mössbauer spectroscopy, whereas oxidation of the related fully pentamethylferrocenylated dendrimer ( 7 a ) leads to the all‐ferricinium dendrimer, 7 a [PF₆]₆.     

Accelerated methods of synthesis of phosphorus-containing dendrimers

In order to shorten the long and tedious synthesis of dendrimers, several improvements have been proposed. This paper is a review of the improved methods recently published concerning the synthesis of phosphorus-containing dendrimers. It describes first the synthesis of hyperbranched polymers and their comparison with real dendrimers obtained from the same monomer. Then, the influence of the modification of the core of dendrimers is shown. In a third part, the use of dendrons is illustrated by several examples; they allow for instance to built a generation 8 directly from a generation 3 dendrimer. The last part describes the use of branched monomers of types AB₂ and CD₂, in which A reacts only with D and B reacts only with C. These reactions do not need any protecting groups, and the only by-products are H₂O and N₂. Using these monomers, the 4th generation is obtained in only four steps, instead of 8 for classical methods. This method has been improved by using more branched monomers AB₅ and CD₅, built from the cyclotriphosphazene. In this case, a dendrimer having 750 end groups is obtained in only three steps. The A (NH₂), B (PPh₂), C (N₃) and D (CHO) functions are identical in all cases, and they allow a real “Lego” chemistry, as shown by the synthesis of CA₂ and DB₂ monomers, also used for the accelerated synthesis of dendrimers.     

Synthesis of Novel Biodegradable Cationic Dendrimers

Summary: Dendrons and dendrimers with cationic amino groups at their periphery were successfully synthesized up to the third and second generation, respectively. The results obtained by ¹H NMR spectroscopy and gel permeation chromatography analysis supported the formation of the targeted dendrons and dendrimers. The dendrons were grown via ester linkages, which endowed them with biodegradability in D₂O at 37 °C. The degradation rate depends upon the steric hindrance and reactivity caused by the bulkiness and compact structure of the dendrons. All of the synthesized dendrons were degraded within a month, while 60% of the ester groups in the sterically crowded dendrimers were degraded over the same time period. The cytotoxicity of the dendrons was evaluated by the MTT assay on a 293T cell line which indicated that the obtained dendrons were completely non‐toxic. These non‐toxic, biodegradable cationic dendrons and dendrimers are believed to have potential applications in the biomedical field.

Synthetic procedure of dendrons and dendrimers.