Synthesis of oligomeric urethane dimethacrylates with carboxylic groups and their testing in dental composites

Carboxyl urethane dimethacrylate oligomers with poly(ethylene oxide) sequences in the structure were synthesized and examined in photopolymerizable resins that could better adhere to various kinds of materials, including tooth substrates. Aspects of the morphogenesis of dental composites formed through a photochemically initiated radical copolymerization of the carboxylic derivatives, in addition to other partners encountered frequently in such materials, were studied comparatively with the corresponding urethane dimethacrylate monomer. The effect of a small quantity of a carboxylic macromer (ca. 10%) on the formation of a network with a non‐carboxyl urethane dimethacrylate oligomer (90%) as a potential substitute for diglycidyl methacrylate of bisphenol A and a filler (1/1 70% Aerosil/glass) was visualized by fluorescence spectroscopy with a pyrene methanol probe. The results showed the following: (1) the degree of conversion in the formulations into which carboxyl urethane dimethacrylate was incorporated decreased with increasing poly(ethylene oxide) chain length, (2) the formation of excimers was inhibited in the derived composites, and (3) an important quenching of the monomer fluorescence emission with the UV–vis irradiation time was observed in the formulation containing a filler (Aerosil+Zr/Sr glass). Preliminary testing of the resin composites suggested that all urethane oligomers containing carboxylic acid could lead to dental materials with reduced polymerization shrinkage and good mechanical properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1956–1967, 2007     

Studies on thermal behavior of some antibacterial copper (II) complex compounds with a dibiguanide derivative ligand

The thermal behavior of six complex compounds of Cu(II) with chlorhexidine as ligand was investigated. The complexes are obtained from chlorhexidine diacetate and copper (II) chloride, bromide and acetate, respectively, in metal:ligand molar ratio 1:1 and 2:1. Thermal decomposition evidenced several well-defined steps as desolvation, anionic moieties release and the ligand cleavage for all complexes. The final residue is in all cases copper (II) oxide.     

Aggregation of imine-based metallo-supramolecular architectures through pi-pi interactions

The design of supramolecular architectures based on isoquinoline-imine ligand systems is described. The isoquinoline affords an extended pi surface and the use of this surface to obtain self-recognition and consequent pi-pi aggregation is investigated. The approach is effective in that each of four complexes is observed to aggregate through these interactions. Other pi-pi interactions can interfere with the aggregation indicating that a larger pi-surface may be required to obtain complete control over the aggregation of the units.     

Using noncovalent intra-strand and inter-strand interactions to prescribe helix formation within a metallo-supramolecular system

The effect of inter-strand and intra-strand interactions is explored in a metallo-supramolecular system in which the metal-ligand coordination requirements may be satisfied by more than one different supramolecular architecture. This is achieved by introducing alkyl substituents onto the spacers of readily prepared bis(pyridylimine) ligands. The alkyl substituents induce twisting within the ligand strand and this intra-strand effect favours formation of helical architectures. The alkyl substituents also introduce inter-strand CH.pi interactions into the system. For the smaller methyl group these are most effectively accommodated in a trinuclear circular helicate architecture. A solution mixture of dinuclear double-helicate and trinuclear circular helicate results from which, for copper(I), the trinuclear circular helicate crystallises. The CH.pi interactions endow the circular helicate with a bowl-shaped conformation and the triangular unit aggregates into a tetrahedral ball-shaped array. Low-temperature NMR studies indicate that the CH.pi interactions also confer a bowl-shaped conformation on the triangle in solution. The larger ethyl groups can sustain intra-strand CH.pi interactions in the lower nuclearity double-helical system and this is the unique architecture for that ligand system in both solution and the solid state. Crystal structures are described for both the copper(I) and silver(I) complexes. Thus we show that intra-strand interactions may be used to induce helicity within this system, while the nuclearity of the array can be prescribed by the inter-strand interactions.     

Simple and fast spectrophotometric determination of H(2)O(2) in photo-Fenton reactions using metavanadate

This work proposes a spectrophotometric method for the determination of hydrogen peroxide during photodegradation reactions. The method is based on the reaction of H₂O₂ with amonium metavanadate in acidic medium, which results in the formation of a red-orange color peroxovanadium cation, with maximum absorbance at 450 nm. The method was optimized using the multivariate analysis providing the minimum concentration of vanadate (6.2 mmol L⁻¹) for the maximum absorbance signal. Under these conditions, the detection limit is 143 μmol L⁻¹. The reaction product showed to be very stable for samples of peroxide concentrations up to 3 mmol L⁻¹ at room temperature during 180 h. For higher concentrations however, samples must be kept refrigerated (4 °C) or diluted. The method showed no interference of Cl⁻ (0.2-1.3 mmol L⁻¹), NO₃⁻ (0.3-1.0 mmol L⁻¹), Fe³⁺ (0.2-1.2 mmol L⁻¹) and 2,4-dichlorophenol (DCP) (0.2-1.0 mmol L⁻¹). When compared to iodometric titration, the vanadate method showed a good agreament. The method was applied for the evaluation of peroxide consumption during photo-Fenton degradation of 2,4-dichlorophenol using blacklight irradiation.     

Biomaterials of Poly(vinyl alcohol) and Natural Polymers

Polysaccharides and proteins are abundantly found in nature and are highly recommended for developing eco-friendly materials due to their special properties (biodegradability, biocompatibility, non-toxicity, low cost, etc.). However, they sometimes fail to meet specific requirements due to poor mechanical and physical properties. Poly(vinyl alcohol) (PVA) is one of the promising synthetic polymers with superior properties that can be blended with natural polymers for obtaining novel biomaterials with improved performances. This review addresses recent advance in PVA/polysaccharides and PVA/proteins biocomposites design and fabrication, mainly for the past two decades.     

Binding sites on the outside of metallo-supramolecular architectures; engineering coordination polymers from discrete architectures

Aggregation of metallo-supramolecular architectures through additional coordination is explored by introducing metal-binding units onto the outside of the supramolecular architectures. This is achieved within the framework of our imine-based approach to supramolecular architecture, by replacing the pyridylimine units with pyrazylketimine units. An advantage of the design is that it retains the ease-of-synthesis which characterises our imine-based approach. Silver(I) complexes of three pyrazylketimine ligand systems are described. The complexes demonstrate that introducing pyrazine donor units does indeed allow higher-order assembly of the distinct supramolecular architectures into engineered coordination polymers. Two distinct types of aggregation are observed. In the first, the donors on the outside of one architecture bind to the metals of another to link the units into a polymeric array. In the second type, the donors on the outside of the architectures bind to separate metal centres which are themselves not part of the architectures, and these separate metal centres link the units to form the macromolecular array. The weaker donor nature of the pyrazine nitrogens (compared to pyridine) also introduces an additional element into the design; higher coordination numbers are favoured and this can lead to arrays with higher connectivity than those observed in the discrete pyridylimine architectures.     

A short and efficient synthesis of crocetin-dimethylester and crocetindial

In this paper we describe an efficient six-step synthesis of crocetin-dimethylester that could be further reduced to a "four-step" synthesis through the use of in situ procedures. The simplicity of the whole process, the ready availability of starting materials, and the high overall yield render this strategy a very attractive synthesis of this very important compound, which is the key intermediate for the synthesis of several carotenoids and other polyene natural products.     

Qualitative Identification of Metal Ions in Honey by Two-Dimensional Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - Two-dimensional thin-layer chromatography (2D TLC) has been used as a screening method for detection of the metal ions Al3+, Cr3+,...