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[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] Measurements are reported for the radiation pressure and gas drag forces acting on a single melamine-formaldehyde microsphere. The radiation pressure force coefficient q, which would be unity if all incident photons were absorbed, has the value q=0.94±0.11. For argon, the Epstein gas drag force coefficient δ, which would be unity if impinging molecules underwent specular reflection, has the value δ=1.26±0.13 as measured with our single-particle laser acceleration method, or δ=1.44±0.19 as measured using the vertical resonance method
[en] Engineering and tuning multi-component supramolecular self-assemblies on surfaces is one of the challenges of nanotechnology. We use scanning tunneling microscopy to investigate the influence of molecular ratio on the self-assembly of PTCDA-melamine structures on Au(111)-(22x√3). Our observations reveal that three different chiral supramolecular networks having a PTCDA:melamine ratio of 3:2, 1:2, 1:4 can be selectively created by tuning the ratio of molecules deposited on the surface. The 1:2 ratio network having melamine in excess has been observed previously but the 1:4 network has not yet been reported. In comparison, the multi-component 3:2 network having PTCDA in excess is a completely new structure.
[en] The influence of a plasma environment on melamine formaldehyde particles is studied. High-precision measurements of the vertical confinement frequency with a phase-resolved resonance method indicate that the particle mass is affected in two ways: the deposition of sputtered material at the particle leads to a mass gain, whereas the outgassing of water causes a mass loss.
[en] Melamine (2,4,6 triamino-s-triazine) is a starting material for the manufacture of polymeric resins, thermosetting plastics, and housewares. The uptake, bioaccumulation and elimination of uniform triazine-labelled [14C]-melamine was determined in fingerling rainbow trout. Uptake into tissues was monitored in a static exposure system (water conc. = 89-91 ppb) until the steady state of melamine was reached in the fish tissues. The bioconcentration factor (BCF) was determined for muscle and viscera at the steady state. Uptake of [14C] melamine was low for both muscle and viscera, achieving levels only as high as 10 ppb in either compartment. Steady state was reached in the viscera within 48 hours and in muscle after only 16 hours. The BCF for muscle (0.03 to 0.11) and viscera (0.5-0.11) was less than unity, indicating a propensity of this compound to resist partitioning into the fish or fish tissues. This may be related to high hydrophilicity or a strong solute-solute interaction of malamine. In depuration studies, the half-life of malamine was found to be relatively short +1/2 viscera = 8.06 found to be relatively short (+1/2 muscle = 8.79 hrs), consistent with the rapid achievement of steady state and low BCF
[en] Radiation sensitive polymers comprising from about 1 to 100 mole % of a polymerized maleimide monomer consisting of a hydrocarbon group having from 2 to 20 carbon atoms, preferably a bridged hydrocarbon group having from 6 to 10 carbon atoms and from 0 to about 99 mole % of at least one additional polymerized ethylenically unsaturated monomer are described. The polymers are soluble in organic solvents, possess desirably high glass transition temperatures and are capable of undergoing a photochemical reaction to yield polymers having isocyanate and oxy-substituted cyclopropane moieties which are capable of crosslinking in the presence of active hydrogen-containing compounds. The polymers are useful in radiation sensitive compositions and elements containing same
[en] We present the results of experimental researches of the behavior of dust structures formed by particles with different properties (material densities, sizes, forms) under the external influences (applied magnetic field). Only monolayers in structures of a complex geometrical form are used in the experiments. The parameters that can affect the structure and the properties of a glow discharge are selected. The strength of a magnetic field, at which the rotation direction changes the sign, depends linearly on the gas pressure and is independent of the discharge current.
[en] Full text: Micron-sized melamine formaldehyde particles were introduced into argon plasma. As a result, the particles were negatively charged due to collision with the electrons within the plasma. With the right conditions, these particles formed a stable macroscopic crystal lattice, known as dust plasma crystal. In our experiment we conduct at Flinders University, we apply an external axial magnetic field to various configurations of dust plasma crystal. These configurations include small crystal lattices consisting of one to several particles, and large crystal lattices with many hundreds of particles. The magnetic field strength ranged from 0-32G and was uniform over the extent of the crystal. The crystals were observed to be rotating collectively in the left-handed direction under the influence of the axial magnetic field. In the case of the large crystals, the angular velocity was about 2 complete rotations per minute and was proportional to the applied magnetic field. The angular velocity changes only slightly depending on the plasma conditions. Neither radial variance in the angular velocity nor shear velocity in the vertical direction was observed in the crystal's rotational motion. In the case of the small crystals, we managed to rotate 2-6 particles (whether they are planar, 2 layers or tetrahedral). We discovered that the ease and the uniformity of the rotation of the different crystals increase as its rotational symmetry increases. Also an increase in the magnetic field strength will correspond to an increase in the angular velocity. Crystals in the shape of an annulus were also tested for theoretical reasons. The poster presentation will contain the experimental procedures, a detailed analysis and an explanation for such dust plasma crystal rotational motion
[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] 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)