Papers by Keyword: NMR

Abstract: DL-valinium maleate [DLVM] compound was grown as single crystals at room temperature by gradual evaporation from an aqueous solution. The classical nucleation theory was examined to maximize the growth conditions for producing high-quality crystals, Nucleation kinetics studies reveal that the crystal has been grown at room temperature 313 K for which predicted critical supersaturation is 6.19. The grown compound DLVM crystallized in a triclinic system with a centrosymmetric space group P1, according to single crystal and powder X-ray diffraction experiments. The lattice parameters were calculated as a= 6.17 Å, b= 9.68 Å, c= 10.59 Å, α= 105.75°, β = 105.67º and γ = 104.69° with unit cell volume 548.2 ų. The presence of functional groups in the grown compound has been identified by using Fourier Transform Infrared [FTIR] experiments. NMR studies were used to examine the structural features of DLVM compounds. Since the grown material belongs to the centrosymmetric space group, the material has been found to exhibit third-order NLO property. The Z-scan technique was used to analyse the third-order nonlinear behaviour of the grown crystal. The technique was very useful in evaluating the nonlinear refractive index n₂, absorption co-efficient β, and nonlinear optical susceptibility χ⁽³⁾ of the grown material. Hence, the grown crystal finds useful applications in optoelectronics. The antibacterial activity of the title compound was also studied by using the Agar disc diffusion method against the standard bacteria Klebsiella pneumonia, Staphylococcus aureus and Enterococcus faecalis. The results of the antibacterial activity experiment show that the synthesized DLVM crystal will be a good option for the creation of antibiotic medicines that will combat the tested bacterial strains.

Abstract: The development of biosensors is essential while determining the inside body assaying and assessing implants in-vivo applications. Researchers are doing remarkable studies in certain areas, but output for receiving, adaptability and circulation of nutrients are also essential. For examining the similar functionality, multi-walled carbon nanotube epoxy-composite with varying filler percentages is examined and compared using electromechanical and morphological assessment. Mechanical investigations like tensile and flexural tests were performed in addition to the hardness of specimens. The DC conductivity test is performed to determine the charge conductivity along with NMR for measuring the signal responses. The surface characterization is performed to determine the morphological properties of specimens. It is observed that the mechanical properties increased and decreased after exceeding the filler composition to addition to 2% of total weight. In comparison, the conductivity and magnetic resonance enhance to a further extent showing proportional to addition of nanofillers, thus making them potential applications for flexible organic bioelectronics products.

Abstract: The effect of substitution of alkaline earth metals for sodium on the structure of alkali borosilicate glasses had been studied using the solid-state ¹¹B and ²⁹Si NMR spectroscopy. NMR spectra enable to evaluate the relative mole fractions of different silicon and boron structural units in studied samples. The obtained results demonstrate that alkaline earth metals increase the polymerization degree of the silicon structural units at the expense of de-polymerization of the boron units. The reason for these changes is preferential coordination of sodium and alkaline earth metals to the boron units, that increases strongly for the studied alkaline earth metals.

Abstract: The quartenizeid chloride derivative of natural polyaminosaccharide chitosan was synthesized in two stages with acetate aldehyde and methyl iodide chemical reaction and ion replacement, which could be soluble in the water and wide pH ranges. The synthesis of the homopolymer was initially carried out with acetate aldehyde in Schiff reaction, and reduction was held on with the presence of NaBH₄. The quaternization was accomplished in the acetonitrile medium with methyl iodine by continuous exposure of N₂.7-8% quartenized N,N-diethyl, N-methyl chitosan iodine were synthesized with 89-91% yield, obtained by deprotonation of amine groups, with reaction of CH₃J and N,N-diethyl chitosan. The ion exchange was carried out at 10% NaCl solution during 24 hours and N,N-diethyl, N-methyl chitosan chloride was obtained. Synthesis was performed with simpler and chemically effective methods compared to previous studies. The structure of product was characterized by FT-IR, UV-Vis, NMR, SEM, TGA, DTA and elemental analysis was determined. Functional changes in the structure of macromolecules were monitored with NMR and UV-Vis, and it was proved that, the main intermediate product was composed to be N,N-diethyl carbocation carrying >C=N-chromophore group. The increasing percent of carbon in content while alkylation is depeering and the presence of halogenated ions (Cl^- or J^-) after quaternization were observed. It has been determined that, the solubility of N,N-diethyl,N-methyl chitosan chloride or iodide in water and in pH =1-10 increased frequently. Key words. Chitosan; alkylation; diethylmethyl chitosan iodine; quartenization; UV-Vis; NMR

Abstract: Controlling the hydration rate of cement can influence the properties of cement hydrates. Many commercial cement retarders are mainly adopted for slowing down the rate of cement hydration. In this study, the surface of the cement particles was modified by an organic sulfoxide to retard the rate of cement hydration. The organic sulfoxide, octyl phenyl sulfoxide (OPS), was firstly synthesized by mixing 1-dodecanethiol with aryl iodide to produce organic sulfide, and then organic sulfide was oxidized to the corresponding sulfoxide. The organic sulfoxide was identified by Nuclear Magnetic Resonance Spectroscopy (NMR). Hydrates of cement and cement modified with OPS were characterized by Fourier Transform Infrared Spectrometer (FTIR), Optical Microscope (OM), Scanning Electron Microscope (SEM) and powder X-Ray Diffraction (pXRD). Experimental results showed that OPS successfully reduced the rate of cement hydration and had positive effect on the long term microstructures of the harden cement paste.

Abstract: Silver nanoprisms, a kind of silver nanoparticles (NPs) synthesized by chemical reduction in water phase and treated with the light irradiation, have special optical properties and can be used as optoelectronic materials. However the hydrophilic property of silver nanoprisms suppresses their applications. In this study, thiols were used to modify the surface of the silver nanoprism to enhance its hydrophobicity. The ultraviolet-visible spectrometry (UV-Visible) was used to explore the surface properties of the NPs. Experimental results showed that the addition of a long chain thiol (pure 1-undecanthiol) to the water solution of silver nanoprisms gave a red shift in the absorption spectra in comparing with that of original silver nanoprisms colloid. It is due to the absorption of the thiol to surfaces of the NPs. The absorption of the long chain thiols can turn the hydrophilic surface to be hydrophobic. The NPs treated with the cracking rubber oil had the similar results. It is believed that the cracking rubber oil can be a feasible agent to enhance the surface hydrophobicity of silver nanoprisms.

Abstract: Gallium (Ga) is a critical element for the electronic industry, however, its long-term supply is not assured. Thus, the recovery of Ga from industrial wastewaters is important. Selective sorption is a recommended technology for the recovery of Ga from industrial wastewaters, however, selective sorbents are elusive. Desferrioxamine B (DFOB), a hydroxomate siderophore that is known to be highly selective towards Fe³⁺, is tested for its ability to complex Ga. This study demonstrated that DFOB forms 1:1 complex with Ga and the maximum Q_e-Ga is 124.4 mg of Ga complexed per g of DFOB. Further, the complexation mechanism of Ga³⁺ and Fe³⁺ with DFOB is similar, as indicated by NMR, suggesting that the selectivity of DFOB towards Fe³⁺ will be extended to Ga³⁺ as well. Thus, DFOB seems to be a suitable candidate for the sorption of Ga from industrial wastewaters.

Abstract: An important phase of the MgO-SiO₂-Al₂O₃ system, α-cordierite was studied for its catalytic transesterification activity in preparing palm biodiesel. The prime drawback of such solid catalyst is its low activity. To overcome this problem, the transesterification was combined with microwave irradiation. The effect of reaction time and catalyst loading on biodiesel yield was investigated in a batch reaction mode. The synthesis of biodiesel was confirmed by ¹H NMR spectroscopy. It reveals that an enhanced yield of biodiesel was obtained, whereas the maximum yield was reached in less than 30 min regardless the catalyst loading. As a solid type catalyst, this result becomes a platform to develop the flow mode reaction unit using a cordierite based structured catalyst without modifying surface chemistry of cordierite.

Abstract: Development of covalent organic polymer (COP) is a potential new class of adsorbent for gas separation due to their good hydrothermal stability, chemical tuning flexibility and low cost. COP-1 was prepared via one-step polycondensation of cyanuric chloride and piperazine under catalyst free and N₂ atmosphere condition. The properties of COP-1 were characterized using several analytical methods such as Fourier Transform Infra-Red (FTIR), solid Nuclear Magnetic Resonance (s-NMR), Thermal gravimetric analysis (TGA) and N₂ adsorption and desorption measurement. The C-N bond of COP-1 which has non-rigid framework was successfully linked in this study. It is found that COP-1 has low thermal degradation temperature i.e. 483 K. As compared to literature, lower surface area (75.5 m²/g) and slightly large pore size (8 nm) are noticed. The difference of physical properties of COP-1 synthesized between in this study and literature revealed the challenge of reproducibility for COP-1.

Abstract: Polymethylvinylsiloxane (PMVS) were prepared by pre-hydrolysis/condensation of several silicon compounds: methylvinydichlorosilane (MVDCS) and dimethyldichlorosilane (DMDCS) followed by catalysis equilibrium copolymerization by dibutyltin dilaurate (DBTDL). All manipulations in the experiments were performed under ambient condition. The PMVS were characterized by Fourier transform infrared spectroscopy (FTIR). This method has provided information about the structure of the polymer. The ¹³C NMR techniques give two sets of carbons at 1.77 ppm and 136.0 ppm consist of signals from carbons of both ligand groups, whereas ²⁹Si NMR signals of the-22.49 ppm and-35.98 ppm region are due to silicon sites bearing the methyl and vinyl ligand groups; the ²⁹Si signals of the - 109 ppm region are due to silicon sites without ligand groups attached.Keywords: Polymethylvinylsiloxane, copolymerization, NMR