Search results for "Infrared"
showing 10 items of 2110 documents
The reluctant polymorph: investigation into the effect of self-association on the solvent mediated phase transformation and nucleation of theophylline
2015
Little is known concerning the pathway of the crystallization of the thermodynamically stable polymorph of theophylline, form IV. Here we study the reasons why the thermodynamically stable theophylline form IV can be obtained only by slow, solvent mediated phase transformation (SMPT) in specific solvents, and whether the presence of prenucleation aggregates affect the polymorphic outcome. Solution concentration, polymorphic composition and morphology were monitored over time during the transformation from form II to form IV in several solvents. NMR and FTIR spectroscopy were used to detect prenucleation molecular aggregates present in the solutions. It was determined that theophylline self-…
Formation of HXeO in a xenon matrix: Indirect evidence of production, trapping, and mobility of XeO (1 1Σ+) in solid Xe
2004
IR spectroscopy, laser induced fluorescence (LIF), and thermoluminescence (TL) measurements have been combined to monitor trapping, thermal mobility, and reactions of oxygen atoms in solid xenon. HXeO and O(3) have been used as IR active species that probe the reactions of oxygen atoms. N(2)O and H(2)O have been used as precursors for oxygen atoms by photolysis at 193 nm. Upon annealing of matrices after photolysis, ozone forms at two different temperatures: at 18-24 K from close O ...O(2) pairs and at approximately 27 K due to global mobility of oxygen atoms. HXeO forms at approximately 30 K reliably at higher temperature than ozone. Both LIF and TL show activation of oxygen atoms around 3…
Organotin(IV) complexes ofN-[(2Z)-3-hydroxy-1-methyl-2-butenylidene]glycine
2003
Organotin(IV) derivatives of N-[(2Z)-3-hydroxy-1-methyl-2-butenylidene]glycine have been synthesized and characterized by 1H, 13C, 119Sn NMR, 119Sn Mossbauer, and IR spectroscopy along with elemental analyses. The di- and triorganotin(IV) complexes were readily obtained from the reactions of organotin halides and sodium/potassium N-[(2Z)-3-hydroxy-1-methyl-2-butenylidene]glycinate. The diorganotin compound reacted with Ph3SnCl in refluxing benzene to give the mixed organotin dinuclear complex of composition Ph2Sn(2-OC(CH3)-C(H)C(CH3)NCH2COO)·Ph3SnCl, which was characterized by single crystal X-ray structure determination. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:149–154, 2003; Publ…
Structural study of ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates: conformation and transmission of substituent effects acro…
2001
Nine new ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates were prepared by a [4 + 2] cycloaddition and their FTIR, 1H, 13C and 15N NMR spectra were measured and assigned. Single crystals were grown for five compounds and their X-ray data were obtained. The electronic structure and the conformations were calculated by the semi-empirical AM1 method. Using correlations between the spectral, empirical and theoretical structural data, the transmission of substituent effects and the preferential conformation connected with the consecutive double nitrogen inversion and regarding the mutual orientation of NH and CO bonds were investigated. The results are compared with those f…
Synthesis and Crystal Structure of Ln3(OH)(CrO4)4 · 3.5H2O (Ln = Pr, Nd) and Ln2(OH)2(CrO4)2 (Ln = Tb, Gd): Thermal Behavior and Infrared Spectra of …
1993
Abstract Crystal structures of Ln 2 (OH) 2 (CrO 4 ) 2 ( Ln = Gd, Tb) and Ln 3 (OH)(CrO 4 ) 4 · 3.5H 2 O ( Ln = Pr, Nd) were determined by a conventional single-crystal X-ray diffraction technique. Crystals of Ln 2 (OH) 2 (CrO 4 ) 2 ( Ln = Gd, Tb) are monoclinic, space group P 2 1 / c (no. 14) with lattice parameters a = 8.2454(4) A, b = 11.3834(5) A, C = 12.1420(8) A, and β = 136,590(5)°, Z = 4, D x = 4.92 mg · m -3 for Gd 2 (OH) 2 (CrO 4 ) 2 and a = 8.214(1) A, b = 11.348(1) A, c = 12.094(2) A, and β = 136.59(1)°, Z = 4, D x = 5.01 Mg · m -3 for Tb 2 (OH) 2 (CrO 4 ) 2 . Crystals of Ln 3 (OH)(CrO 4 )) 4 · 3.5H 2 O ( Ln = Pr, Nd) are monoclinic, space group C 2/ c (No. 15) with lattice param…
Low-cost set-up for Fourier-transform infrared spectroscopy in diamond anvil cell from 4000 to 400 cm−1
2011
An experimental set-up for Fourier-transform infrared (FTIR) studies at high pressure in the mid-IR region (400–4000 cm−1) is constructed using a compact TEO-400 FTIR interferometer module and an external microscopic optical bench with cassegrain focusing objectives. Cassegrain-type reflective objectives act as an excellent beam condenser that facilitates the interfacing between FTIR spectrometer and diamond anvil cell. This set-up is capable of recording transmission and reflection infrared spectra at high pressure. Preliminary results are reported both in the reflection (pressure dependence of polar phonons in CuWO4) and transmission configuration (polarized light absorption of polar phon…
The ways to the trace level analysis in infrared spectroscopy
2020
The future of infrared (IR) spectroscopy as an analytical technique is assured due to its versatility and its numerous advantages; such as the possibility to obtain molecular specific information for virtually any sample in any state with no treatment or minimal sample preparation. However, spectroscopists are not satisfied with relegating IR spectroscopy just to major and minor component analysis and have been looking at analysis at the trace level too. This review is the recognition of the brilliant research performed during the past two decades and the advances achieved in this area, which have made possible the analysis of contaminants at parts per billion (ppb) levels by IR in differen…
Application of infrared spectroscopy as Process Analytics Technology (PAT) approach in biodiesel production process utilizing Multivariate Curve Reso…
2019
Abstract Process Analytical Technology means at-line collection of analytical information from the process when the reaction is in progress. Obtained information enables process engineers to better control the Critical Process Parameters and direct the reaction to desirable routs. Near-infrared spectroscopy due to its analytical features, as well as the high capability of automation, versatile sampling and spectral acquisition methods is a useful tool in process monitoring when coupled to chemometrics. The Multiple Scatter Correction preprocessing technique and Alternative Least Square method can extract spectral and concentration information of a reaction mixture simultaneously, were emplo…
Effect of the Al/Si atomic ratio on surface and structural properties of sol-gel prepared aluminosilicates
2003
Abstract A series of aluminosilicates with an Al/Si ratio ranging from 0 to ∞ (0 for pure silica and ∞ for pure alumina) was prepared by sol–gel process and characterized by surface and structure techniques. Aluminum tri sec butoxide and tetramethylorthosilicate were used as precursors for the sol–gel synthesis. The acidic properties of the oxides were studied by determination of the zero point charges, through mass titration method, and, for selected samples, by FT-IR spectroscopy of adsorbed pyridine used as a probe for both Bronsted and Lewis acidity. A dependence of the acidity on the Al/Si atomic ratio was found. According to the X-ray diffraction patterns, all the oxides have an amorp…
Recent advances in on-line liquid chromatography - infrared spectrometry (LC-IR)
2010
We review advances in isocratic and gradient liquid chromatography hyphenated on-line with infrared spectrometry (LC-IR). We place special emphasis on chemometric background correction and other applications of chemometric algorithms used to improve the sensitivity and the resolution of LC-IR signals. We also comment on recent technical advances, (e.g., dedicated flow-cells and new light sources) and review applications in the technological, cosmetics, environmental and food sectors.