Coumarins in polymers: From light harvesting to photo-cross-linkable tissue scaffolds

Poly(e-caprolactone) (PCL) with a pendent coumarin group was prepared by solution polycondensation from 7-(3,5-dicarboxyphenyl) carbonylmethoxycoumarin dichloride and α, ω-dihydroxy terminated poly(e-caprolactone) with molecular weights of 1250, 3000, and 10,000 g/mol. These photosensitive polymers underwent a rapid reversible photocrosslinking upon exposure to irradiation with alternating wavelengths (>280/254 nm) without a photoinitiator. The thermal and mechanical properties of the photocrosslinked films were examined by means of differential scanning calorimetry and stress–strain measurements. The crosslinked films exhibited elastic properties above the melting temperature of the PCL segment along with significant decrease in the ultimate tensile strength and Young's modulus. Shape-memory properties such as strain fixity ratio (Rf) and strain recovery ratio (Rr) were determined by means of a cyclic thermomechanical tensile experiments under varying maximum strains (em = 100, 300, and 500%). The crosslinked ICM/PCL-3000 and -10,000 films exhibited the excellent shape-memory properties in which both Rf and Rr values were 88–100% for tensile strain of 100–500%; after the deformation, the films recovered their permanent shapes instantaneously. In vitro degradation was performed in a phosphate buffer saline (pH 7.2) at 37 °C with or without the presence of Pseudomonas cepacia lipase. The presence of the pendent coumarin group and the crosslinking of the polymers pronouncedly decreased the degradation rate. The crosslinked biodegradable PCL showing a good shape-memory property is promising as a new material for biomedical applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2422–2433, 2009

Synthesis and characterization of photocrosslinked poly(ε‐caprolactone)s showing shape‐memory properties

The emergence of fungal infections due to the increase in the number of immunocompromised patients has become a matter of concern. Among the available sources for treating fungal infections, natural products can play a significant role. In this article, we have tried to categorize the different sources and chemical classes of fungitoxic agents as following: (1) animal sources such as defensins and other peptides, (2) plant sources such as terpenoids, flavonoids, and coumarins, (3) fungal metabolites like fatty acids, sugar derivatives and polyenes and (4) bacterial sources such as amino acids. The potentials of coumarins, which are mainly distributed in four plant families, Umbelliferae, Rutaceae, Leguminosae and Compositae, have been uncovered in this respect. In addition to antifungal property, the other bioactivities of coumarins include: anticoagulant, antibacterial, antiparasitie, anticancer, photodynamic, edema relieving, anti-inflammatory, radical scavenging, lipolytic, antiplatelet, and anti-allergic properties. Studies in structure-antifungal activity relationships of coumarins, which is presented here, reveal the essential strucutral features for their activity. In order to have a better understanding of the mode of action of coumarins, the cellular sites and the interactions of coumarins with biological systems have been explained. Effects on the enzymes gyrase and topoisomerase, and photodynamic reaction with lipids, proteins and DNA are among the main issues discussed. In this respect, morphological changes of Candida albicans cells due to coumarins, which are studied by scanning electron microscopy (SEM), support their biochemical effects.

Coumarins, the bioactive structures with antifungal property

A series of new cyclic tetramethyltetrasiloxanes with coumarin units were synthesized. By a comparative study with their related vinyl terminated precursors, the liquid crystalline properties of the cyclic tetramethyltetrasiloxanes were investigated. The results show that the thermal properties of the cyclic tetramethyltetrasiloxanes are stabilised through their increasing clearing temperatures and broadening mesophases. The thermal properties of the cyclic tetramethyltetrasiloxanes show that introduction of a tail group at the 3 position of the coumarin unit increases the thermal stability of the liquid crystalline order. Increasing the length of the tail group causes the clearing temperatures of the cyclic tetramethyltetrasiloxanes to decrease. The photochemical behavior of spin-coated films of the cyclic tetramethyltetrasiloxanes indicates the photo-crosslinking of the coumarin units in the thin films.

Liquid crystalline cyclic tetramethyltetrasiloxanes containing coumarin moieties

Summary
The effects of weed removal at five dates after planting the crop were examined and compared with weed-free and unweeded controls. The results revealed that the total weed population increased up to 6 weeks after planting and then decreased drastically in both the years. Total dry weight of weeds (at weeding and at haulm-cutting) was greatest in the unweeded control, followed by weeding at 10 weeks after planting. In both years, maximum yield was obtained where plots were kept weed-free, followed by weeding at 4 and 6 weeks after planting. The remaining treatments, including weeding at 2 weeks after planting, resulted in significant reductions in tuber yield. In unweeded control plots the tuber yield of potato was reduced by 40–43%.

Effect of time of weed removal on growth and yield of potato

Synthesis, characterization and biological activity of some poly(coumarin ethylene)s

The occurrence of total 113 geomagnetic storms during declining phase of Solar Cycle 24 (2015–2017) subdivided as about 105 moderate storms (
 $$\hbox {Dst} = -50\, \hbox {nT}$$
 to $$-100$$
 nT), 6 intense storms (
 $$\hbox {Dst} = -100\, \hbox {nT}$$
 to $$-200$$
 nT) and 2 severe storms (
 $$\hbox {Dst} < -200\, \hbox {nT}$$
 ) has been diagnosed on the basis of 5 day active window through the CACTus (Computer aided CME tracking) software. A detailed study has been carried out for the 6 intense and 2 severe storms. It is inferred that CMEs are the major source of geomagnetic storms to occur. Out of the 6 intense and 2 severe storms, only 1 has been observed with the origin of CIR. Thus, all analyzed intense geomagnetic storms are due to coronal mass ejection at the Sun. Most of our results are in good accordance with other reported results.

Causes responsible for intense and severe storms during the declining phase of Solar Cycle 24

Poly (3-substituted coumarin methylene)s (PCM1–7) were prepared by reacting salicyl-aldehyde-formaldehyde polymer (SAL-F) under Wittig. Knoevenagel and Perkin reaction conditions. All the polymers were characterized by elemental analysis, IR spectral studies and thermogravimetric analysis (TGA). The polymers were also screened for their antifungal and antibacterial activity.

Synthesis, Characterization and Biological Activity of some Poly(Coumarin Methylene)s

In a field trial conducted at the Haryana Agricultural University, Hissar during the Kharif season of 1976 and 1977 one hand weeding given at 2 to 12 weeks after sowing was compared with no weeding and weed free control in seed crop of okra. At 8-week stage of the crop the weed population was maximum, whereas the dry weight of weeds per unit area was maximum at 10 weeks after sowing. However, the most critical period for crop-weed competition fell between 2 to 6-week stage of the crop.

Effect of Time of Weeding on Growth and Seed Yield of Okra

. Multiflash whistler-like event in the ELF-band, observed during March 1998 at low latitude station Jammu, is reported. The most prominent feature of these events is the multiflash nature along with the decrease in frequency within a very short span of time resembling similar to terrestrial whistlers. The events have a significantly smaller time duration (0.5–3.5 s) than those reported earlier from high, mid and low latitudes and also display a diurnal maximum occurring around 09:30 h (IST). There have been similar reportings from other latitudes, but whistlers in the ELF-band with a multiflash nature along with a precursor emission have never been reported. Lightning seems to be the dominant source for the ELF whistlers reported here.

/pdf/multiflash-whistlers-in-elf-band-observed-at-low-latitude-oaui9lij76.pdf

S. B. Singh

Papers

Synthesis, characterization and biological activity of some poly(coumarin ethylene)s

Causes responsible for intense and severe storms during the declining phase of Solar Cycle 24

Synthesis, Characterization and Biological Activity of some Poly(Coumarin Methylene)s

Effect of Time of Weeding on Growth and Seed Yield of Okra

Multiflash whistlers in ELF-band observed at low latitude