SciCombinator

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Concept: Ultraviolet-visible spectroscopy

169

BACKGROUND: The new combination of moxifloxacin HCl and cefixime trihydrate is approved for the treatments of lower respiratory tract infections in adults. At initial formulation development and screening stage a fast and reliable method for the dissolution and release testing of moxifloxacin and cefixime were highly desirable. The zero order overlaid UV spectra of moxifloxacin and cefixime showed >90% of spectra are overlapping. Hence, simple, accurate precise and validated two derivative spectrophotometric methods have been developed for the determination of moxifloxacin and cefixime. METHODS: In the first derivative spectrophotometric method varying concentration of moxifloxacin and cefixime were prepared and scanned in the range of 200 to 400 nm and first derivative spectra were calculated (n = 1). The zero crossing wavelengths 287 nm and 317.9 nm were selected for determination of moxifloxacin and cefixime, respectively. In the second method the first derivative of ratio spectra was calculated and used for the determination of moxifloxacin and cefixime by measuring the peak intensity at 359.3 nm and 269.6 nm respectively. RESULTS: Calibration graphs were established in the range of 1–16 mug /mL and 1–15 mug /mL for both the drugs by first and ratio first derivative spectroscopic methods respectively with good correlation coefficients. Average accuracy of assay of moxifloxacin and cefixime were found to be 100.68% and 98 93%, respectively. Relative standard deviations of both inter and intraday assays were less than 1.8%. Moreover, recovery of moxifloxacin and cefixime was more than 98.7% and 99.1%, respectively. CONCLUSIONS: The described derivative spectrophotometric methods are simple, rapid, accurate, precise and excellent alternative to sophisticated chromatographic techniques. Hence, the proposed methods can be used for the quality control of the cited drugs and can be extended for routine analysis of the drugs in formulations.

Concepts: Spectroscopy, Ultraviolet, Respiratory system, Upper respiratory tract, Accuracy and precision, Lower respiratory tract, Ultraviolet-visible spectroscopy, Spectrophotometry

28

Three new molecular building blocks 1 a-c for supramolecular polymerization are described that feature two dipolar merocyanine dyes tethered by p-xylylene spacers. Concentration- and temperature-dependent UV/Vis spectroscopy in chloroform combined with dynamic light scattering, capillary viscosimetry and atomic force microscopy investigations were applied to elucidate the mechanistic features of the self-assembly of these strongly dipolar dyes. Our detailed studies reveal that the self-assembly is very pronounced for bis(merocyanines) 1 a,b bearing linear alkyl chains, but completely absent for bis(merocyanine) 1 c bearing sterically more bulky ethylhexyl substituents. Both temperature- and concentration-dependent UV/Vis data provide unambiguous evidence for a cooperative self-assembly process for bis(merocyanines) 1 a,b, which was analyzed in detail by the Meijer-Schenning-Van-der-Schoot model (applicable to temperature-dependent data) and by the Goldstein-Stryer model (applicable to concentration-dependent data). By combining both methods all parameters of interest to understand the self-assembly process could be derived, including in particular the nucleus size (8-10 monomeric units), the cooperativity factor (ca. 0.006), and the nucleation and elongation constants of about 10(3) and 10(6)  M(-1) in chloroform at room temperature, respectively.

Concepts: Spectroscopy, Fundamental physics concepts, Scientific techniques, Ultraviolet-visible spectroscopy, Light scattering, Dynamic light scattering, Rayleigh scattering, Stokes radius

28

A set of chiral discotic phenylacetylenes have been synthesized by 3-fold Sonogashira coupling between different ethynylbenzenes and triiodobenzenes. The resultant bulk materials are fully characterized by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction. The octopolar nature of the target compounds is studied by UV-vis absorption spectroscopy and hyper-Raleigh scattering in solution. Optimization of the donor-acceptor substitution yields both high hyperpolarizability values and appreciable mesomorphic properties. A simple thin film device for second harmonic generation has been prepared from the nitro-substituted liquid crystalline derivative.

Concepts: Crystal, Optics, Electromagnetic radiation, Differential scanning calorimetry, Absorption spectroscopy, Ultraviolet-visible spectroscopy, Birefringence, Liquid crystal

28

A new family of pi-extended tetrathiafulvalene (exTTF) donor-acceptor chromophores has been synthesized by [2+2] cycloaddition of TCNE with exTTF substituted alkynes, and subsequent cycloreversion. X-ray data and theoretical calculations, performed at the B3LYP/6-31G** level, show that the new chromophores exhibit highly distorted non-planar molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. The electronic and optical properties, investigated by UV/vis spectroscopy and electrochemical measurements, are significantly modified when the TCBD acceptor unit is substituted with a donor phenyl group, which increases the twisting of the TCBD units and reduces the conjugation between the two dicyanovinyl subunits. The introduction of phenyl substituents hampers the oxidation and reduction processes and, at the same time, largely increases the optical band gap. An effective electronic communication between the donor and acceptor units, although limited by the distorted molecular geometry, is evidenced both in the ground and in the excited electronic states. The electronic absorption spectra are characterized by low- to medium-intense charge-transfer bands that extend to the near-infrared.

Concepts: Spectroscopy, Electromagnetic radiation, Redox, Electrochemistry, Absorption spectroscopy, Ultraviolet-visible spectroscopy, Infrared spectroscopy, Electron acceptor

27

In the present work, we describe the synthesis of gold nanoparticles using an aqueous root extract of Morinda citrifolia. UV-vis spectroscopy, XRD, FTIR, FE-SEM, EDX and TEM were performed to characterize the formation of gold nanoparticles. The synthesized gold nanoparticles were characterized by a peak at 540 nm in the UV-vis spectrum. The XRD peaks at 38°, 44°, 64° and 77° can be indexed to the (111), (200), (220) and (311) Bragg’s reflections of cubic structure of metallic gold, respectively. The FTIR result showed that extract containing protein might be responsible for the formation of the nanoparticles and may play an important role in the stabilization of the formed nanoparticles. FESEM images revealed that the particles were triangle and mostly spherical in shape. TEM images clearly revealed the size of the nanoparticles were 12.17-38.26 nm in size.

Concepts: Spectroscopy, Nanoparticle, Gold, Absorption spectroscopy, Ultraviolet-visible spectroscopy, Play, Noni, Morinda

27

The syntheses of the transition metal complexes cis-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)2 MX2 ] (1, M=Pd, X=Cl; 2, M=Pd, X=Br; 3, M=Pd, X=I; 4, M=Pt, X=Cl), cis-[{2,6-(Me2 NCH2 )2 C6 H3 SnCl}2 MX2 ] (5, M=Pd, X=I; 6, M=Pt, X=Cl), trans-[{2,6-(Me2 NCH2 )2 C6 H3 SnI}2 PtI2 ] (7) and trans-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)PdI2 ]2 (8) are reported. Also reported is the serendipitous formation of the unprecedented complexes trans-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)2 Pt(SnCl3 )2 ] (10) and [(4-tBu-2,6-{P(O) (OiPr)2 }2 C6 H2 SnCl)3 Pt(SnCl3 )2 ] (11). The compounds were characterised by elemental analyses, (1) H, (13) C, (31) P, (119) Sn and (195) Pt NMR spectroscopy, single-crystal X-ray diffraction analysis, UV/Vis spectroscopy and, in the cases of compounds 1, 3 and 4, also by Mössbauer spectroscopy. All the compounds show the tin atoms in a distorted trigonal-bipyramidal environment. The Mössbauer spectra suggest the tin atoms to be present in the oxidation state III. The kinetic lability of the complexes was studied by redistribution reactions between compounds 1 and 3 as well as between 1 and cis-[{2,6-(Me2 NCH2 )2 C6 H3 SnCl}2 PdCl2 ]. DFT calculations provided insights into both the bonding situation of the compounds and the energy difference between the cis and trans isomers. The latter is influenced by the donor strength of the pincer-type ligands.

Concepts: Spectroscopy, Diffraction, X-ray, Valence electron, X-ray crystallography, Absorption spectroscopy, Ultraviolet-visible spectroscopy, Protein nuclear magnetic resonance spectroscopy

27

Monodisperse hollow carbon nanocapsules (<200 nm) with mesoporous shells were synthesized by coating their outer shells with silica to prevent aggregation during their high-temperature annealing. Monodispersed silica nanoparticles were used as starting materials and octadecyltrimethoxysilane (C18TMS) was used as a carbon source to create core-shell nanostructures. These core-shell nanoparticles were coated with silica on their outer shell to form a second shell layer. This outer silica shell prevented aggregation during calcination. The samples were characterized by TEM, SEM, dynamic light scattering (DLS), UV/Vis spectroscopy, and by using the Brunauer-Emmett-Teller (BET) method. The as-synthesized hollow carbon nanoparticles exhibited a high surface area (1123 m(2)  g(-1) ) and formed stable dispersions in water after the pegylation process. The drug-loading and drug-release properties of these hollow carbon nanocapsules were also investigated.

Concepts: Spectroscopy, Nanoparticle, Sol-gel, Scientific techniques, Ultraviolet-visible spectroscopy, Light scattering, Dynamic light scattering, Rayleigh scattering

26

Nine new mononuclear and polynuclear Cu(ii) complexes [Cu(H2L(2))Cl]Cl·3H2O (), [Cu(H2L(3))Cl]Cl·H2O (), [Cu(H2L(4))Cl]Cl·2.5H2O (), [Cu3(μ(3)-L(1))2(H2O)3](ClO4)2·H2O (), [Cu4(μ-HL(1))4](ClO4)8·CH3OH·5H2O (), [Cu2(HL(3))2](ClO4)2·2H2O (), [Cu2(μ-HL(3))2](ClO4)2·H2O (), [Cu2(μ-HL(3))(L(3))Cu(teta)](ClO4)3·2H2O () and [Cu2(H2L(3))2(ox)](ClO4)2·2H2O·2MeOH () containing [5-(2-pyridine-2-yl)-1,2,4-triazole-3-yl]alkanes (H2L(n), n = 1-4) in combination with other ligands, such as chlorido, aqua, triethylenetetramine (teta) and/or oxalato (ox(2-)), were synthesized and characterized by various techniques such as elemental analysis, FTIR, NMR and UV-Vis spectroscopy. X-ray structures of H2L(3) and H2L(4) as well as complexes were determined. The X-ray structures revealed that relatively small composition and structural changes in the H2L(n) ligands have a substantial impact on the coordination geometries of the complexes themselves as well as on their resulting magnetic properties. It has been found that the geometries of the complexes vary from square-pyramidal to trigonal-bipyramidal (with τ ranging from 0.00 to 0.96) and, moreover, that the trigonal bipyramidal geometry becomes more preferable with the increase in the length of the polymethylene chain within the corresponding H2L(n) ligand. The magnetic properties of the polynuclear compounds , , , and were analysed using the spin Hamiltonian formalism, which revealed the presence of antiferromagnetic exchange in the polynuclear systems mediated by the title ligands. The significant effect of the geometric parameters on the CuCu exchange interactions in the polynuclear complexes is discussed.

Concepts: Spectroscopy, Magnetism, Ferromagnetism, Geometry, Ligand, Ultraviolet-visible spectroscopy, Ethylenediamine, Triethylenetetramine

25

In the present study, densely dispersed silver nanoparticles (Ag NPs) were rapidly green synthesized in the presence of Rumex dentatus aqueous extract, followed by UV-irradiation reduction. The Ag NPs were characterized using UV-vis spectroscopy, FTIR, XRD, and TEM. Then, the Ag NPs were incorporated into interpenetrating polymeric networks based on cationic trimethyl chitosan (TMCS) and anionic poly(acrylamide-co-sodium acrylate) copolymer to develop a new series of composite nanoparticles as potential antibacterial agents. Both TMCS and poly(acrylamide-co-sodium acrylate) were prepared in the study, and characterized using FTIR, DSC, and SEM. The synthesized Ag NPs showed high purity and uniform particle size distribution with particle size ranged between 5 and 30 nm. The composite nanoparticles demonstrated homogeneous spherical shape with size in the range of 378-402 nm. Both Ag NPs and the composite nanoparticles showed promising bactericidal activity as compared with the control. Moreover, the antibacterial activity of the composite nanoparticles increased along with increasing the concentrations of Ag NPs and the TMCS.

Concepts: Present, Spectroscopy, Particle size distribution, Sphere, Absorption spectroscopy, Ultraviolet-visible spectroscopy, Particle size, Rumex

23

Boron subphthalocyanines (SubPcs) are powerful chromophoric heterocycles that can be synthetically modified at both axial and peripheral positions. Acetylenic scaffolding offers the possibility of building large, unsaturated carbon-rich frameworks that can exhibit excellent electron-accepting properties, and when combined with SubPcs it presents a convenient method for preparing interesting chromophore-acceptor architectures. Here we present synthetic methodologies for the post-functionalization of the relatively sensitive SubPc chromophore via acetylenic coupling reactions. By gentle AlCl3-mediated alkynylation at the axial boron position, we managed to anchor two SubPcs to the geminal positions of a tetraethynylethene (TEE) acceptor. Convenient conditions that allow for stepwise desilylations of trimethylsilyl (TMS) and triisopropylsilyl (TIPS) protected SubPc-decorated acetylenes using silver(i) fluoride were developed. The resulting terminal alkynes were successfully used as coupling partners in metal-catalyzed couplings, providing access to larger acetylenic SubPc scaffolds and multiple chromophore systems. Moreover, conditions allowing for the conversion of a terminal alkyne into an iodoalkyne in the presence of SubPc were developed, and the product was subjected to cross-coupling reactions affording unsymmetrical 1,3-butadiynes. The degree of interactions between two SubPc units as a function of the acetylenic bridge was studied by UV-Vis absorption spectroscopy and cyclic voltammetry. A TEE bridging unit was found to strongly influence the reductions and oxidations of the two SubPc units, while a more flexible bridge had no influence.

Concepts: Spectroscopy, Alkyne, Absorption spectroscopy, Ultraviolet-visible spectroscopy, Aldehyde, Sonogashira coupling, Cadiot-Chodkiewicz coupling, Trimethylsilyl