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[en] Highlights: • Standard enthalpies of formation of nitrogen-containing compounds were calculated. • Isodesmic reactions at the CCSD(F12∗)(T) level were used for ureas and s-triazines. • HEAT protocols were applied to methanimine and methylamine. • Good agreement with experimental data, where available, was achieved. Gas-phase standard enthalpies of formation of selected ureas and s-triazines were calculated at the CCSD(F12∗)(T)/cc-pVTZ-F12//ωB97X-D/cc-pVTZ level of theory by employing isodesmic reactions. The following values were obtained (T = 298.15 K, units: kJ mol−1, estimated confidence interval 95%): urea, −231.9 ± 2.8; biuret, −430.0 ± 4.5; triuret, −620.3 ± 6.3; cyanuric acid, −451.6 ± 6.3; ammelide, −303.9 ± 6.4; ammeline, −106.5 ± 6.2; melamine, 70.1 ± 7.0. The standard enthalpies of formation of methanimine and methylamine, which were required for the isodesmic reactions, were calculated from atomization reactions by using several variants of the HEAT approach. The following results were considered most reliable (T = 298.15 K, units: kJ mol−1, estimated confidence interval 95%): methanimine, 89.0 ± 1.0; methylamine, −20.7 ± 1.0.
[en] Arylmethylenemalonitriles were synthesized in the presence of melamine through the Knoevenagel condensation of aldehydes with malononitrile in ethanol. Two strategies such as the conventional stirring and ultrasound-assisted method were performed in this work, and improvements were observed by carrying out the reactions under ultrasound irradiation. The effect of frequency and power of ultrasound on the yields was investigated, and the optimum frequency and power was 45 kHz and 240 W, respectively. The Knoevenagel reaction was carried out smoothly under the optimum conditions with the yields of 80-99% within short time. The melamine catalyst showed high activity and reusability, and exhibited no substantial loss of activity over up to four reaction cycles. This work demonstrated that short reaction times and high yields of arylmethylenemalonitriles can be obtained with the facile operation in the presence of the low-toxic, cheap and reusable melamine catalyst. (author)
[en] The synthesis of Trimethylol Melamine (TMM) precondensate was carried out by the controlled reaction of formaldehyde with melamine, which belonging to class of partially methylolated thermosetting resins. The product was clear, transparent, viscous and miscible with water. The refractive index, density and maximum absorption of the synthesized TMM was determined. The dyed (C.I. Direct Red 2) cotton and rayon specimens were impregnated with synthesized precondensate (TMM) and Fix M-3 (commercially available trimethylol melamine of BSF product), cured at 150 deg. C for 3 min using curing catalyst. The performance of the synthesized and Fix M-3 evaluated using rubbing, washing and light fastness tests. The rubbing fastness to crocking, color fastness to washing and light fastness is reported and found to be dependent on the fixing efficiency of fixer. The fastness to light is found to be dependent on the aromatic character of melamine ring which obviously due to the preferably absorption in the UV region. (author)
[en] A structural compaction model is used to correlate NSWC quasi-static compaction data on porous beds of six (6) different materials, i.e., four (4) ball powders, melamine, and Teflon. Initial densities of the porous beds ranged from 44 percent solid theoretical maximum density (TMD) to 70 percent TMD. Maximum compacted densities were about 90 percent TMD except for Teflon which was compacted to approximately 98 percent TMD. Pressures calculated by the model, plotted as a function of percent TMD, agree well with the NSWC data
[en] Edible birds nest (EBN) is widely consumed as a health food product. In recent years, adulteration of EBN is quite familiar due to high economic value and limited supply of natural authentic EBN. Authentication and assessment of EBN quality demands highly labour cost and time consuming sequential analytical measurements to confirm that the product quality meets technical and regulatory requirements. Mid-Infrared - Attenuated Total Reflectance (IR-ATR) spectroscopy is used in this study as an alternative approach to conduct rapid, cheap and non-destructive spectroscopic measurements. The samples used were authentic processed EBNs of different grades (2A, 3A, 4A and 5A) from the swiftlet species Aerodramus fuciphagus supplied by Ministry of Health, Malaysia. Similarly, adulterants commonly used in EBN namely agar, Karaya gum, bovine gelatine, fish gelatine, melamine and porcine collagen were also characterized. Adulterant mixtures were prepared gravimetrically at concentrations of 1, 5 and 10% m/m by combining appropriate quantities of adulterants with an authentic EBN sample. The samples then were analysed by the IR-ATR spectroscopy. The results showed 50 % of the EBN samples were adulterated at 5 and 10 % w/w level. This included the common adulterant Karaya gum, porcine gelatine and melamine. The analysis was less sensitive toward bovine gelatine only detecting the 10% w/w adulterated level and the fish gelatine was not detected at the 1, 5 or 10% w/w level. The IR-ATR spectroscopy technique is useful tool and rapid technique for the authentication of EBN produced in Malaysia. Further work is required to validate the approach for a wider range of adulterants including flavour enhancers and preservatives. (author)
[en] A new method based on absolutely localized molecular orbitals (ALMOs) is proposed to measure the degree of intermolecular electron density delocalization (charge transfer) in molecular complexes. ALMO charge transfer analysis (CTA) enables separation of the forward and backward charge transfer components for each pair of molecules in the system. The key feature of ALMO CTA is that all charge transfer terms have corresponding well defined energetic effects that measure the contribution of the given term to the overall energetic stabilization of the system. To simplify analysis of charge transfer effects, the concept of chemically significant complementary occupied-virtual orbital pairs (COVPs) is introduced. COVPs provide a simple description of intermolecular electron transfer effects in terms of just a few localized orbitals. ALMO CTA is applied to understand fundamental aspects of donor-acceptor interactions in borane adducts, synergic bonding in classical and nonclassical metal carbonyls, and multiple intermolecular hydrogen bonds in a complex of isocyanuric acid and melamine. These examples show that the ALMO CTA results are generally consistent with the existing conceptual description of intermolecular bonding. The results also show that charge transfer and the energy lowering due to charge transfer are not proportional to each other, and some interesting differences emerge which are discussed. Additionally, according to ALMO CTA, the amount of electron density transferred between molecules is significantly smaller than charge transfer estimated from various population analysis methods
[en] Acrylated melamines, a class of radiation curable oligomers, which were considered reactive diluents or impregnating resins, are investigated with regard to their synthesis. It is attempted to attribute the properties and the radiation curing behaviour to the specific synthetic procedure and to the data of the reaction products. Both the molecular mass and the double bond content indicate the formation of more-ring systems. Hexa(methoxymethyl)-melamine and hydroxyalkyl acrylates of a defined quality together with an accurate control of the preparation provide oligomers of a relatively high reactivity resulting in rather hard coatings or impregnations when cured by irradiation. (Author)
[en] This study synthesized nFe0 on the substrate of porous organic polymer (POM) which was prepared by glutaraldehyde and melamine. The POM-nFe0 composites were characterized by scanning electron microscopy, Brunner-Emmet-Teller, Fourier transform infrared spectrum, thermogravimetric analysis, powder X-ray diffraction, and X-ray photoelectron spectroscopy. The introduction of POM contributed to enhance the stability of U(IV) nanoparticles which is liable to be oxidized to mobile U(VI) under aerobic condition. According to the batch experiment, the maximum U(VI) removal capacity of POM-nFe0 was 230 mg/g, which shows great potential in wastewater treatment. (author)
[en] A new chiral stationary phase is proposed that is based on the supramolecular structure of melamine self-assembled in the mode of the induction of chirality. Induction is achieved via mechanical stirring in accordance with the Kondepudi effect in order to form a layer of a supramolecular structure with predominantly one type of chiral supramolecular domains on the surface of the sorbent. The resulting inert support with 1% melamine is used for the gas chromatographic separation of enantiomers of 2-butanol, 1‑methoxy-2-propanol, 2-bromobutane, 2-chlorobutane, and 2-bromopentane. The coefficients of selectivity and the separation of enantiomers are calculated. No separation of enantiomers is observed on a column conditioned at 100°C. After conditioning the column at 200°C, a series of successful separations of racemates is obtained in the 60–110°C range of temperatures. The highest coefficient of selectivity for haloalkanes is obtained at 70–75°C, so 2-bromobutane has α = 1.62 at 70°C, 2-chlorobutane has α = 1.23 at 75°C, and 2‑bromopentane has α = 1.68 at 70°C. The coefficients of selectivity for 2-butanol and 1-methoxy-2-propanol are highest at 80 and 100°C (α = 1.45 and 2.24), respectively. It is assumed that the ability of the suprastructure of melamine to exhibit enantioselectivity is associated with the formation of cavities capable of chiral recognition.
[en] Melamine-formaldehyde molding compounds have found different industrial applications. This is due to their good mechanical properties such as hardness, gloss and high modulus and strength. One of the major components of these compounds is α-cellulose fiber and has a major effect on the mechanical properties. Although this fiber is being used in these compounds for a long time, there is not much data available of α-cellulose fibers on the physical and mechanical properties of melamine-formaldehyde molding compounds being investigated. Results show that although the microstructures of these two fibers are quite different from each other, but they do not have any effect on the mechanical properties of the molding. Whereas, it has a significant effect on the wettability (processing condition) and glossiness of the mol dings. Since this latter property is very important in house wares applications, the darker mol dings can not be used in domestic applications