Melamine sensing through riboflavin stabilized gold nanoparticles

Melamine (M) sensing has been achieved through supramolecular assembly with riboflavin (R) via H-bonding in the platform of R stabilized gold nanoparticles (R-Au NPs), by colorimetric as well as UV-vis techniques

Effect of complementary small molecules on the properties of bicomponent hydrogel of riboflavin

Three new bicomponent hydrogels of riboflavin (R) with salicylic acid (S), dihydroxybenzoic acid (B) and acetoguanamine (D) in 1:1 molar ratio have been reported. FTIR and UV-vis spectra suggest formation of H-bonded complexes in 1:1 molar ratio of the components. The network consists of tape, bar and helical tubes for RB11, RS11 and RD11 systems, respectively. Reversible first order phase transition and invariant storage modulus (G') with angular frequency (ω) characterise the systems as forming thermoreversible hydrogels. The RD11 gel has the highest gel melting temperature and highest critical strain compared to other gels. WAXS study indicates different crystal structures for different gels. NMR spectra reveals higher shielding of protons in RD11 gel suggesting better p-stacking compared to RS11 and RB11 gels. RD11 gel shows two-fold enhancement of photoluminescence (PL) intensity with a substantial red shift of emission peak but RB11 and RS11 gels show PL-quenching. The gels exhibit a small decrease in lifetime and the PL property is very much temperature and pH dependent. So the complementary molecules have a pronounced effect on morphology, structure, stability and optical property of riboflavin gels

Two-component thermoreversible hydrogels of melamine and gallic acid

A new two-component hydrogel of melamine and gallic acid is reported for three different compositions of the components. Optical and scanning electron microscopy indicate the fibrillar network structure of the gel, and the DSC study indicates a reversible first-order phase transition in the system. The storage modulus (G') versus frequency plot is linear and invariant at 35 and 50 °C but not at 70 °C, where it is in the sol state. The rheological melting point of 58 °C is close to the gel melting point obtained from DSC. The system shows a strong influence of pH on gelation. An FTIR study indicates H-bond formation between the >C-O group of gallic acid and the -NH2 group of melamine. 1H NMR spectra indicate the presence of π-π stacking in the gel. The UV-vis peak positions of gallic acid remain unaffected during complexation; however, the normalized absorption intensity is higher in the GM13 sol compared to that of other complexes. The photoluminescence (PL) spectra of the gels are interesting, showing a two-order increase in intensity in the gel state compared to that in the sol state. Three different structures of the complexes are proposed for the three different compositions of the components

Time sensitive, temperature and pH responsive photoluminescence behaviour of a melamine containing bicomponent hydrogel

Melamine (M) produces supramolecular complexes MQ31, MQ11 and MQ13 with 6,7-dimethoxy-2,4[1H,3H]-quinazolinedione (Q) (numbers indicate respective molar ratios of components) and they produce thermoreversible hydrogels [≥0.1% (w/v)] at 30 °C. Optical microscopy shows fibrillar network morphology and on irradiation with 300 nm light, the fibrils emit blue light. DSC results indicate a thermoreversible first order phase transition and the storage modulus (G') is invariant with frequency supporting the formation of thermoreversible hydrogel. The magnitude of G' follows the order MQ11 > MQ13 > MQ31 and a probable cause is attributed to number of H-bonds, which follows the same order in the nanofibers. FTIR-spectra suggest H-bonding interaction between components and WAXS results indicate a different crystalline structure of the complexes. The UV-vis spectra of the MQ systems shows red shift of both π-π and n-π∗ bands and a maximum red shift is observed for the MQ13 system. The PL intensity decreases with increase in M concentration and lifetime data indicates PL quenching due to the formation of less fluorescent complexes. The PL property of the gel depends on aging time. A gradual development of a new emission peak at the expanse of an initial peak suggests the formation of an initial metastable state, which transforms into the stable state after 24 h of aging. The gel is stable in the pH range 6-9, above or below which the gel breaks down showing a significant PL-quenching and a blue shift of the emission peak. With increase of temperature, the emission peak intensity increases at first up to 45 °C, followed by an abrupt decrease at ≥55 °C. Possible reasons are attributed to the gradual disassembly of the complexes converting thinner fibers and finally melting

Variation of physical and mechanical properties in the bicomponent hydrogels of melamine with positional isomers of hydroxybenzoic acid

The positional isomers of hydroxybenzoic acid have a significant influence on the physical and mechanical properties of their bicomponent hydrogels with melamine (M) produced at 1:1 molar composition. In the bicomponent hydrogels of salicylic acid (s), meta-hydroxy benzoic acid (m) and para-hdroxy benzoic acid (p), a gradation of morphology of the xerogels from tape to fibre occurs. WAXS study suggests different structures of the gels. FTIR spectra indicate that H-bonded complexes are produced in the gels. The aromatic protons in the gels become upfielded suggesting π-π stacking that follows the order Mp > Ms ≈ Mm. The UV-vis spectrum indicates better H-type aggregate formation in Mp than those in Ms and Mm systems. The photoluminescence (PL) intensity of the gels has increased by 200, 25 and 350 times those of pure acids for Ms, Mm and Mp gels, respectively. With the increase of temperature the PL intensity decreases and at 30 °C the highest PL intensity is observed at pH 6.8 but at pH 4 and 9.2 PL the intensity is drastically reduced due to breaking of the gel network. The melting point values suggest that the thermal stability of the gels follow the order Mp > Ms > Mm and both storage modulus (G') and critical strain also follow the same order. In G' vs. temperature plots, the Mp system exhibits a linear variation whereas the Ms and Mm systems exhibit peaks at 82 and 63 °C, respectively. This is attributed to the disaggregation of the gel macromolecule at high temperature forming a microgel and shear assisted aggregates

A STUDY ON ETHNO-MEDICINAL USE OF SOME COMMONLY AVAILABLE PLANTS FOR WOUND HEALING AND RELATED ACTIVITIES IN THREE SOUTHERN DISTRICTS OF WEST BENGAL, INDIA

The information of ethno-medicinal uses as haemostatic, antiseptic wound healer and anti-dermatitic properties containing plants in human and animals were collected from three districts of southern West Bengal, India, viz. Paschim Medinipur, Purba Medinipur, and Murshidabad which are situated in different agro-climatic conditions. Presently twenty one such plants were recognized and most of them are new claim regarding the said treatments. The plants were properly identified with the help of relevant literatures, photographed and available relevant previous information about the medicinal properties or uses were also searched out from the earlier literatures and were enlisted for comparison