Stabilisation of Natural Colourants and Lignocellulosic Textiles

<p>The lignocellulosic fibres extracted from the leaves of New Zealand flax, Phormium tenax, have been used as the principal textile fibre by Maori since pre- European times. Variations of antifungal activity were observed in Phormium fibres of different cultivars. The most resistant cultivars of P. tenax in an aqueous antifungal assay also possessed the greatest variety of naturally-occurring 7-hydroxycoumarins as identified by mass spectroscopy, ESI-MS. In addition to antifungal effects, coumarins function as fluorescent whitening agents in Phormium fibres and play a role in the fibre’s photodegradation. Ultraviolet irradiation (350 – 400 nm) of the fibre resulted in a substantial loss of the blue fluorescence originating from a number of 7-hydroxycoumarins present, together with the formation of new fluorophores absorbing and emitting at longer wavelengths, which contribute to the photoyellowing of the fibre. The photolysis of two standard 7-hydroxycoumarins in aqueous solution was examined and two primary photoproducts were elucidated by ESI-MS: a photodimer containing a linking cyclobutane ring and a monomeric photooxidation product. The formation of at least some of the photoproducts is associated with the coumarin-sensitised generation of reactive oxygen species, hydrogen peroxide and superoxide. The fluorescence properties and photodegradation of Chinese handmade papers were also investigated. Papers manufactured by traditional methods were found to be more photostable than that produced from chemically-facilitated techniques.</p>

Stabilisation of Natural Colourants and Lignocellulosic Textiles

<p>The lignocellulosic fibres extracted from the leaves of New Zealand flax, Phormium tenax, have been used as the principal textile fibre by Maori since pre- European times. Variations of antifungal activity were observed in Phormium fibres of different cultivars. The most resistant cultivars of P. tenax in an aqueous antifungal assay also possessed the greatest variety of naturally-occurring 7-hydroxycoumarins as identified by mass spectroscopy, ESI-MS. In addition to antifungal effects, coumarins function as fluorescent whitening agents in Phormium fibres and play a role in the fibre’s photodegradation. Ultraviolet irradiation (350 – 400 nm) of the fibre resulted in a substantial loss of the blue fluorescence originating from a number of 7-hydroxycoumarins present, together with the formation of new fluorophores absorbing and emitting at longer wavelengths, which contribute to the photoyellowing of the fibre. The photolysis of two standard 7-hydroxycoumarins in aqueous solution was examined and two primary photoproducts were elucidated by ESI-MS: a photodimer containing a linking cyclobutane ring and a monomeric photooxidation product. The formation of at least some of the photoproducts is associated with the coumarin-sensitised generation of reactive oxygen species, hydrogen peroxide and superoxide. The fluorescence properties and photodegradation of Chinese handmade papers were also investigated. Papers manufactured by traditional methods were found to be more photostable than that produced from chemically-facilitated techniques.</p>

Investigation of the Antioxidant and Antitumour Properties of Some Cyclobutane Ring Containing 2,5-Thiophene Diacyl Compounds

In this research, the effect of thiophene derivatives on the (MDA) concentration which is an indicator of lipid peroxidation, antioxidant vitamins A, E and in vitro antioxidant activity and antitumor activity, were investigated in cell culture media. In the comparison done among groups, it was observed that MDA and vitamin A concentrations were statistically (P<0.05) changed. Looking at the measured parameters during the experiment, the number of live cells, the compounds is an effective antitumor activity in the L 1210 cell types. The oxidative stress parameters are used for all compounds.

Supramolecular construction of a cyclobutane ring system with four different substituents in the solid state

Methods to form cyclobutane rings by an intermolecular [2 + 2] cross-photoreaction (CPR) with four different substituents are rare. These reactions are typically performed in the liquid phase, involve multiple steps, and generate product mixtures. Here, we report a CPR that generates a cyclobutane ring with four different aryl substituents. The CPR occurs quantitatively, without side products, and without a need for product purification. Generally, we demonstrate how face-to-face stacking interactions of aromatic rings can be exploited in the process of cocrystallization and the field of crystal engineering to stack and align unsymmetrical alkenes in CPRs to afford chiral cyclobutanes with up to four different aryl groups via binary cocrystals. Overall, we expect the process herein to be useful to generate chiral carbon scaffolds, which is important given the presence of four-membered carbocyclic rings as structural units in biological compounds and materials science.

Honeycomb molecular network based upon a hydrate of 4,6-dichlororesorcinol and the photoproduct rtct-tetrakis(pyridin-4-yl)cyclobutane

The formation of a self-interpenetrated honeycomb molecular network based upon 4,6-dichlororesorcinol (4,6-diCl res), a water molecule, and the photoproduct rtct-tetrakis(pyridin-4-yl)cyclobutane ( rtct -TPCB) is reported. Interestingly, only three of the four pyridine rings on the central cyclobutane ring are found to engage in O—H...N hydrogen bonds with either the 4,6-diCl res or an included water molecule, resulting in a three-connected net. Notably, the solid (4,6-diCl res)·( rtct -TPCB)·(H2O), C6H4Cl2O2·C24H20N4·H2O, contains channels that run along the crystallographic b axis, which are found to be interpenetrated. Although rtct -TPCB has been employed as a bridging ligand in the formation of numerous metal–organic materials, surprisingly neither the single-component X-ray structure nor any multi-component molecular solids based upon this stereoisomer have been reported previously. Lastly, the single-crystal X-ray structure of the photoproduct rtct -TPCB is also reported.

Synthetic Strategies for the (+)-Grandisol, the Main Constituent of Boll Weevil Pheromone

: This paper presents a short review of synthetic approaches aiming to synthesise (+)-Grandisol, the main constituent of grandlure, a pheromone mixture released by the boll weevil which is proven to exhibit significant biological activity. (+)-Grandisol 1 is among the components of the male-produced pheromone of the boll weevil Anthonomuns grandis, an important pest of cotton crops in Mesoamerica (from the south USA to Argentina). As a result of its biological activity and unique structure, several synthetic approaches have been reported. The aim is to explore remarkable methodologies towards the synthesis of (+)-Grandisol 1. Several methodologies have been applied towards the synthesis of (+)-Grandisol 1, including classical methods for cyclobutane ring construction, which promoted substantial improvements to access this pheromone, as well as better comprehension of its biological profile.

Oxidative Repair of Pyrimidine Cyclobutane Dimers by Nitrate Radicals (NO3•): A Kinetic and Computational Study

Pyrimidine cyclobutane dimers are hazardous DNA lesions formed upon exposure of DNA to UV light, which can be repaired through oxidative electron transfer (ET). Laser flash photolysis and computational studies were performed to explore the role of configuration and constitution at the cyclobutane ring on the oxidative repair process, using the nitrate radical (NO3•) as oxidant. The rate coefficients of 8–280 × 107 M−1 s−1 in acetonitrile revealed a very high reactivity of the cyclobutane dimers of N,N’-dimethylated uracil (DMU), thymine (DMT), and 6-methyluracil (DMU6-Me) towards NO3•, which likely proceeds via ET at N(1) as a major pathway. The overall rate of NO3• consumption was determined by (i) the redox potential, which was lower for the syn- than for the anti-configured dimers, and (ii) the accessibility of the reaction site for NO3•. In the trans dimers, both N(1) atoms could be approached from above and below the molecular plane, whereas in the cis dimers, only the convex side was readily accessible for NO3•. The higher reactivity of the DMT dimers compared with isomeric DMU dimers was due to the electron-donating methyl groups on the cyclobutane ring, which increased their susceptibility to oxidation. On the other hand, the approach of NO3• to the dimers of DMU6-Me was hindered by the methyl substituents adjacent to N(1), making these dimers the least reactive in this series.

The head-to-head photodimer of indenoindene

Irradiation of 1-(1-benzocyclobutenylidene)benzocyclobutene gives indenoindene and its head-to-head photodimer nonacyclo[9.7.7.72,10.01,11.02,10.03,8.012,17.019,24.026,31]dotriaconta-3,5,7,12,14,16,19,21,23,26,28,30-dodecaene, C32H24. The molecule is built from four essentially planar indane units attached to an elongated cyclobutane ring. In the crystal, C—H...π interactions connect molecules into layers parallel to the bc plane.