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Vibrational Spectroscopy (vibrational + spectroscopy)
Selected AbstractsProbing Vibrational Anisotropy with Nuclear Resonance Vibrational Spectroscopy,ANGEWANDTE CHEMIE, Issue 26 2010Jeffrey Sondierung der Lage: Eine resonanzschwingungsspektroskopische Einkristallstudie lieferte detaillierte Informationen zu den In-Plane-Schwingungen eines Nitrosyl-Eisenporphyrinats, [Fe(oep)(NO)] (siehe Bild; oep=Octaethylporphyrin). Der axiale Nitrosyl-Ligand bestimmt die Richtung der In-Plane-Bewegung des Eisenzentrums. [source] ChemInform Abstract: Structure Studies of Dimeric [Pt2(CN)10]4- Pentacyanoplatinum(III) and Monomeric Pentacyanoplatinum(IV) Complexes by EXAFS, Vibrational Spectroscopy, and X-Ray Crystallography.CHEMINFORM, Issue 27 2002Farideh Jalilehvand Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Vibrational Spectroscopy of a Tetraureidocalix[4]arene Based Molecular Capsule.CHEMINFORM, Issue 17 2002Joerg Dormann Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: M(SCN)2 (M: Eu, Sr, Ba): Crystal Structure, Thermal Behavior, Vibrational Spectroscopy.CHEMINFORM, Issue 42 2001Claudia Wickleder Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Crystal Structures and Vibrational Spectroscopy of [NBu4][Cu(CN)X] (X: Br, I) and [NBu4][Cu3(CN)4]×CH3CN.CHEMINFORM, Issue 2 2001Graham A. Bowmaker Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Chemical Tailoring of Porous Silica Xerogels: Local Structure by Vibrational SpectroscopyCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2004Alexandra Fidalgo Abstract Monolithic porous silica xerogels were synthesized by the sol,gel process, and their local structure was analysed by vibrational spectroscopy. The silica alcogels were prepared by a two-step hydrolytic polycondensation of tetraethoxysilane (TEOS) in isopropanol, with a water/TEOS molar ratio of 4. The hydrolysis step was catalysed by hydrochloric acid (HCl), with different HCl/TEOS molar ratios (ranging from 0.0005 to 0.009), and the condensation step was catalysed by ammonia (NH3), with different NH3/HCl molar ratios (ranging from 0.7 to 1.7). After appropriate ageing, the alcogels were washed with isopropanol and subcritically dried at atmospheric pressure. The diffuse reflectance infrared Fourier transform (DRIFT) spectra were analysed in terms of the main siloxane rings that form the silica particles, taking into account the splitting of the ,asSiOSi mode into pairs of longitudinal and transverse optic components, by long-range Coulomb interactions. It was proven that the proportion of residual silanol groups (which correlates with hydrophilicity), and the fraction of siloxane 6-rings (which correlates with porosity) may be tailored by adequate catalytic conditions, mostly by the hydrolysis pH. This was explained in terms of the reactions' mechanisms taking place in the two-step sol,gel process followed. [source] Establishing quantitative in-line analysis of multiple solid-state transformations during dehydrationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2008Karin Kogermann Abstract The aim of the study was to conduct quantitative solid phase analysis of piroxicam (PRX) and carbamazepine (CBZ) during isothermal dehydration in situ, and additionally exploit the constructed quantitative models to analyze the solid-state forms in-line during fluidized bed drying. Vibrational spectroscopy (near-infrared (NIR), Raman) was employed for monitoring the dehydration and the quantitative model was based on partial least squares (PLS) regression. PLS quantification was confirmed experimentally using isothermal thermogravimetric analysis (TGA) and X-ray powder diffractometry (XRPD). To appraise the quality of quantitative models several model parameters were evaluated. The hot-stage spectroscopy quantification results were found to be in reasonable agreement with TGA and XRPD results. Quantification of PRX forms showed complementary results with both spectroscopic techniques. The solid-state forms observed during CBZ dihydrate dehydration were quantified with Raman spectroscopy, but NIR spectroscopy failed to differentiate between the anhydrous solid-state forms of CBZ. In addition to in situ dehydration quantification, Raman spectroscopy in combination with PLS regression enabled in-line analysis of the solid-state transformations of CBZ during dehydration in a fluidized bed dryer. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4983,4999, 2008 [source] Synthesis, Structure, and Physico-optical Properties of Manganate(II)-Based Ionic LiquidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2010Slawomir Pitula Dr. Abstract Several ionic liquids (ILs) based on complex manganate(II) anions with chloro, bromo, and bis(trifluoromethanesulfonyl)amido (Tf2N) ligands have been synthesized. As counterions, n- alkyl-methylimidazolium (Cnmim) cations of different chain length (alkyl=ethyl (C2), propyl (C3), butyl (C4), hexyl (C6)) were chosen. Except for the 1-hexyl-3-methylimidazolium ILs, all of the prepared compounds could be obtained in a crystalline state at room temperature. However, each of the compounds displayed a strong tendency to form a supercooled liquid. Generally, solidification via a glass transition took place below ,40,°C. Consequently, all of these compounds can be regarded as ionic liquids. Depending on the local coordination environment of Mn2+, green (tetrahedrally coordinated Mn2+) or red (octahedrally coordinated Mn2+) luminescence emission from the 4T(G) level is observed.1 The local coordination of the luminescent Mn2+ centre has been unequivocally established by UV/Vis as well as Raman and IR vibrational spectroscopies. Emission decay times measured at room temperature in the solid state (crystalline or powder) were generally a few ms, although, depending on the ligand, values of up to 25,ms were obtained. For the bromo compounds, the luminescence decay times proved to be almost independent of the physical state and the temperature. However, for the chloro- and bis(trifluoromethanesulfonyl)amido ILs, the emission decay times were found to be dependent on the temperature even in the solid state, indicating that the measured values are strongly influenced by nuclear motion and the vibration of the atoms. In the liquid state, the luminescence of tetrahedrally coordinated Mn2+ could only be observed when the tetrachloromanganate ILs were diluted with the respective halide ILs. However, for [C3mim][Mn(Tf2N)3], in which Mn2+ is in an octahedral coordination environment, a weak red emission from the pure compound was found even in the liquid state at elevated temperatures. [source] Nitroamino Triazoles: Nitrogen-Rich Precursors of Stable Energetic SaltsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2008Yangen Huang Abstract 1-Nitroamino-1,2,3-triazole (5) was synthesized and its zwitterionic structure was established using single-crystal X-ray diffraction. The calculated detonation properties for 4-nitroamino-1,2,4-triazole (2) (P = 33.4 GPa, vD = 8793 m/s) and 1-nitroamino-1,2,3-triazole (5) (P = 33.0 GPa, vD = 8743 m/s) are comparable with RDX. A new family of energetic salts 7,21 based on either the 1-nitroamino-1,2,3-triazolate or the 4-nitroamino-1,2,4-triazolate anion were prepared and characterized by vibrational spectroscopy (IR), multinuclear NMR spectra, elemental analyses, density, TGA and DSC. The heats of formation (,fH°298) and detonation properties for these stable salts were calculated using Gaussian 03 and Cheetah 4.0, respectively. Comparison of the properties of the 1,2,3- and 1,2,4-triazolate salts indicates that while the 1,2,4-derivatives are more stable thermally, the 1,2,3-analogs invariably have higher heats of formation. In contrast to its salts, 1-nitroamino-1,2,3-triazole (5) is extremely shock-sensitive with an impact sensitivty of <1 J. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Solid-State Adducts between C60 and DecamethylferroceneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2003Aldo Arrais Abstract Co-deposition from concentrated solutions of C60 and Fe[C5(CH3)5]2 affords two solid products in different yields. The major product 1, in the form of regular shaped crystals, has been investigated by X-ray diffraction, 13C CPMAS NMR and vibrational spectroscopy, which showed it to be a co-crystalline adduct of C60 and Fe[C5(CH3)5]2 with no significant electron charge transfer between the two building blocks. The minor product 2, in the form of an amorphous powder, has been investigated by vibrational techniques. Both IR and Raman spectra are consistent with a solid structure in which electron transfer between the two units appears to be possible. ((© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Use of vibrational spectroscopy to study protein and DNA structure, hydration, and binding of biomolecules: A combined theoretical and experimental approachINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2006K. J. Jalkanen Abstract We report on our work with vibrational absorption, vibrational circular dichroism, Raman scattering, Raman optical activity, and surface-enhanced Raman spectroscopy to study protein and DNA structure, hydration, and the binding of ligands, drugs, pesticides, or herbicides via a combined theoretical and experimental approach. The systems we have studied systematically are the amino acids (L -alanine, L -tryptophan, and L -histidine), peptides (N -4271 acetyl L -alanine N,-methyl amide, N -acetyl L -tryptophan N,-methyl amide, N -acetyl L -histidine N,-methyl amide, L -alanyl L -alanine, tri- L -serine, N -acetyl L -alanine L -proline L -tyrosine N,-methyl amide, Leu-enkephalin, cyclo-(gly- L -pro)3, N -acetyl (L -alanine)nN,-methyl amide), 3-methyl indole, and a variety of small molecules (dichlobenil and 2,6-dochlorobenzamide) of relevance to the protein systems under study. We have used molecular mechanics, the SCC-DFTB, SCC-DFTB+disp, RHF, MP2, and DFT methodologies for the modeling studies with the goal of interpreting the experimentally measured vibrational spectra for these molecules to the greatest extent possible and to use this combined approach to understand the structure, function, and electronic properties of these molecules in their various environments. The application of these spectroscopies to biophysical and environmental assays is expanding, and therefore a thorough understanding of the phenomenon from a rigorous theoretical basis is required. In addition, we give some exciting and new preliminary results which allow us to extend our methods to even larger and more complex systems. The work presented here is the current state of the art to this ever and fast changing field of theoretical spectroscopic interpretation and use of VA, VCD, Raman, ROA, EA, and ECD spectroscopies. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Label-free biochemical characterization of stem cells using vibrational spectroscopyJOURNAL OF BIOPHOTONICS, Issue 11 2009James W. Chan Abstract Raman and infrared (IR) spectroscopy are two complementary vibrational spectroscopic techniques that have experienced a tremendous growth in their use in biological and biomedical research. This is, in large part, due to their unique capability of providing label-free intrinsic chemical information of living biological samples at tissue, cellular, or sub-cellular resolutions. This article reviews recent developments in applying these techniques for the characterization of stem cells. A discussion of the potential for these methods to address some of the major challenges in stem cell research is presented, as well as the technological and scientific advancements that are needed to progress the knowledge in the field. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conformational polymorphism in aripiprazole: Preparation, stability and structure of five modificationsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2009Doris E. Braun Abstract Five phase-pure modifications of the antipsychotic drug aripiprazole were prepared and characterized by thermal analysis, vibrational spectroscopy and X-ray diffractometry. All modifications can be produced from solvents, form I additionally by heating of form X° to ,120°C (solid,solid transformation) and form III by crystallization from the melt. Thermodynamic relationships between the polymorphs were evaluated on the basis of thermochemical data and visualized in a semi-schematic energy/temperature diagram. At least six of the ten polymorphic pairs are enantiotropically and two monotropically related. Form X° is the thermodynamically stable modification at 20°C, form II is stable in a window from about 62,77°C, and form I above 80°C (high-temperature form). Forms III and IV are triclinic (), I and X° are monoclinic (P21) and form II orthorhombic (Pna21). Each polymorph exhibits a distinct molecular conformation, and there are two fundamental N,HO hydrogen bond synthons (catemers and dimers). Hirshfeld surface analysis was employed to display differences in intermolecular short contacts. A high kinetic stability was observed for three metastable polymorphs which can be categorized as suitable candidates for the development of solid dosage forms. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2010,2026, 2009 [source] Analysis of solid-state transformations of pharmaceutical compounds using vibrational spectroscopyJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 8 2009Andrea Heinz Abstract Objectives Solid-state transformations may occur during any stage of pharmaceutical processing and upon storage of a solid dosage form. Early detection and quantification of these transformations during the manufacture of solid dosage forms is important since the physical form of an active pharmaceutical ingredient can significantly influence its processing behaviour, including powder flow and compressibility, and biopharmaceutical properties such as solubility, dissolution rate and bioavailability. Key findings Vibrational spectroscopic techniques such as infrared, near-infrared, Raman and, most recently, terahertz pulsed spectroscopy have become popular for solidstate analysis since they are fast and non-destructive and allow solid-state changes to be probed at the molecular level. In particular, Raman and near-infrared spectroscopy, which require no sample preparation, are now commonly used coupled to fibreoptic probes and are able to characterise solid-state conversions in-line. Traditionally, uni- or bivariate approaches have been used to analyse spectroscopic data sets; however, recently the simultaneous detection of several solid-state forms has been increasingly performed using multivariate approaches where even overlapping spectral bands can be analysed. Summary This review discusses the applications of different vibrational spectroscopic techniques to detect and monitor solid-state transformations possible for crystalline polymorphs, hydrates and amorphous forms of pharmaceutical compounds. In this context, the theoretical basis of solid-state transformations and vibrational spectroscopy and common experimental approaches are described, including recent methods of data analysis. [source] Flexibility of paramagnetic (d1) organometallic dithiolene complex [Cp2Mo(dmit)]+, studied by Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Roman, wietlik Abstract We report on the experimental and theoretical studies of the flexible organometallic complex Cp2Mo(dmit) which often exhibits a folding in the solid state. Raman spectra of charge-transfer salts formed by Cp2Mo(dmit) with various anions (Br,, BF4,, PF6,, SbF6,, ReO(dmit)2,, TCNQF4,) were measured at room temperature using red (632.8 nm) and near-infrared (780 nm) excitations. The influence of the folding of the MoS2C2 metallacycle in [Cp2Mo(dmit)]+, cation on the Raman spectra was investigated. Due to folding of [Cp2Mo(dmit)]+,, the bands related to the CC and some CS stretching vibrations shift toward lower wavenumbers by about 0.5,0.6 cm,1deg,1. The bond lengths, charge distribution on atoms, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, and dipole moments for neutral and ionized complex with various folding angles were calculated by density functional theory (DFT) methods. Additionally, the normal vibrational modes and theoretical Raman spectra were calculated and compared with experimental data. Our results indicate that vibrational spectroscopy can be applied for investigation of complex deformations in the solid state. Copyright © 2009 John Wiley & Sons, Ltd. [source] Identification and characterisation of the E951 artificial food sweetener by vibrational spectroscopy and theoretical modellingJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Niculina Peica Abstract Aspartame (E951), a very well-known dipeptide sweetener, approximately 150,200 times sweeter than sugar, is widely used in a variety of applications, especially in soft drinks. A drawback of E951 is its relatively low stability at high pH values and at high temperatures, thereby limiting its use. The changes observed in the very strong bands from the 1600,1300 cm,1 spectral region, characteristic to the ,(CO) mode coupled with the NH bending mode, allows to establish the species present in the Raman and SERS solutions at different concentrations and pH values. More exactly, a molecule protonation at the amino group was detected on going from basic to acidic pH values. The DFT calculated geometry, harmonic vibrational modes and Raman scattering activities of E951 were in good agreement with the experimental data and helped establish its SERS behaviour on silver surfaces. According to the DFT calculations performed, E951 can give rise to an intramolecular hydrogen bonding network, with lengths in the same range as the hydrogen bonds in the peptide unit moieties. Copyright © 2009 John Wiley & Sons, Ltd. [source] FT-Raman, FTIR and density functional theory studies of a hydrogen-bonded formamide:pyridine complexJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2009Filipe S. F. Jacinto Abstract Raman and IR experiments have been carried out on formamide (FA) and pyridine (Py) mixtures at different compositions. The appearance of a new Raman band at 996 cm,1 (,1 region of Py), whose intensity depends on the FA concentration, is assigned to an FA:Py adduct and this result is in excellent agreement with those of other authors who employed noisy light-based coherent Raman scattering spectroscopy (I(2) CARS). Another band at 1587 cm,1 (,8 region of Py) has been observed for the first time by using Raman and IR spectroscopies. Its intensity shows the same dependence on the FA concentration and this fact allows us to also attribute it to an FA:Py adduct. The good relationship between the Raman and IR data demonstrates the potential of the vibrational spectroscopy for this kind of study. Owing to higher absolute Raman scattering cross section, the ,1 region of Py has been chosen for the quantitative analysis and a stoichiometry of 1:1 FA:Py is reported. The experimental data are very well supported by the density functional theory (DFT) calculation, which was employed for the first time to the present system. Furthermore, the actual investigation shows an excellent agreement with those reported from computational calculations for similar systems. A comparison with our previous studies confirms that the solvent dielectric constant determines the stoichiometry of a given Lewis acid,base adduct in the infinite dilution limit. Copyright © 2009 John Wiley & Sons, Ltd. [source] Observation of SERS effect in Raman optical activity, a new tool for chiral vibrational spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2006Salim Abdali Abstract A new tool for chiral vibrational spectroscopy is reported here. A surface enhanced effect was observed using Raman optical activity (ROA). This observation opens new possibilities for ROA as a tool for vibrational spectroscopy. The combination of surface enhanced effect (SE) and ROA into surface enhanced Raman optical activity (SEROA) takes this tool to another level, where a single molecule may be studied with respect to chirality, secondary structure and fold determination. ROA has been able to provide information about important dynamics in molecular understanding. Until recently, however, ROA measurements required a longer exposure and higher concentration of the sample. With SEROA these obstacles can be overcome because both studies on single molecule, i.e. very low concentration, and faster acquisition of the signal can be carried out. In the present, work silver colloids were mixed with solution, in which a pentapeptide, Met-Enkephalin, was dissolved. SEROA signals were recorded and the results are reported here. Copyright © 2006 John Wiley & Sons, Ltd. [source] Para -halogenated benzaldehyde molecules included in cyclodextrins: a combined spectroscopic and thermal analysisJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2006Paulo J. A. Ribeiro-Claro Abstract The inclusion complexes of 4-X-benzaldehyde guests (X = F, Cl, Br) in ,-, ,-and ,-cyclodextrins (,CD, ,CD and ,CD) were prepared and characterized by means of thermogravimetry, differential scanning calorimetry (DSC) and vibrational spectroscopy. The stoichiometry of the inclusion complexes ranges from 2:1 to 1:2, depending on the cavity size of the host. Sensitive vibrational modes such as CO and ring CH stretching modes were used to monitor the effects of the inclusion process and to assess the preferred inclusion geometry for each host-guest pair. On the whole, the spectral observations suggest that the small ,CD cavity imposes important structural restrictions on the guest molecule, while the larger ,CD cavity allows ,liquid-type' intermolecular contacts. Copyright © 2005 John Wiley & Sons, Ltd. [source] Experimental and theoretical vibrational spectroscopic study on symmetric and asymmetric halo-bridged complexes of palladium(II) and platinum(II)JOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2001E. Kessenich The symmetric chloro-bridged complexes [(Et3P)2PtCl(µ-Cl)]2, [(Et3P)2Pt(µ-Cl)]22+ and [(C3H5)Pd(µ-Cl)]2 and the asymmetric complexes [(C3H5)Pd(µ-Cl)2Pt(PEt3)2]+ and [(C3H5)Pd(µ-Cl)2Pt(PEt3)Cl] were studied by means of vibrational spectroscopy (infrared, Raman) and computational chemistry. Assignments of all normal modes associated with skeletal stretching are suggested and their displacement vectors are discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Mass-selective vibrational spectroscopy of vanadium oxide cluster ionsMASS SPECTROMETRY REVIEWS, Issue 4 2007Knut R. Asmis Abstract A corner stone in the study of the size-dependent properties of cluster ions in the gas phase is their structural characterization. Over the last 10 years, significant progress has been in this research field because of significant advances in the gas phase vibrational spectroscopy of mass-selected ions. Using a combination of modern experimental and quantum chemical approaches, it is now in most cases possible to uniquely identify the geometric structure of cluster ions, based on the comparison of the experimental and simulated infrared spectra. In this article, we highlight the progress made in this research area by reviewing recent infrared photodissociation (IR-PD) experiments on small and medium sized (up to 30 atoms) vanadium oxide ions. © 2007 Wiley Periodicals, Inc., Mass Spec Rev. [source] Applications of Free-Electron Lasers in the Biological and Material Sciences,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2005G. S. Edwards ABSTRACT Free-Electron Lasers (FELs) collectively operate from the terahertz through the ultraviolet range and via intracavity Compton backscattering into the X-ray and gamma-ray regimes. FELs are continuously tunable and can provide optical powers, pulse structures and polarizations that are not matched by conventional lasers. Representative research in the biological and biomedical sciences and condensed matter and material research are described to illustrate the breadth and impact of FEL applications. These include terahertz dynamics in materials far from equilibrium, infrared nonlinear vibrational spectroscopy to investigate dynamical processes in condensed-phase systems, infrared resonant-enhanced multiphoton ionization for gas-phase spectroscopy and spectrometry, infrared matrix-assisted laser-desorption-ionization and infrared matrix-assisted pulsed laser evaporation for analysis and processing of organic materials, human neurosurgery and ophthalmic surgery using a medical infrared FEL and ultraviolet photoemission electron microscopy for nanoscale characterization of materials and nanoscale phenomena. The ongoing development of ultraviolet and X-ray FELs are discussed in terms of future opportunities for applications research. [source] Understanding surfaces and buried interfaces of polymer materials at the molecular level using sum frequency generation vibrational spectroscopyPOLYMER INTERNATIONAL, Issue 5 2007Zhan Chen Abstract This paper reviews recent progress in the studies on polymer surfaces/interfaces using sum frequency generation (SFG) vibrational spectroscopy. SFG theory, technique, and some experimental details have been presented. The review is focused on the SFG studies on buried interfaces involving polymer materials, such as polymer,water interfaces and polymer,polymer interfaces. Molecular interactions between polymer surfaces and adhesion promoters as well as biological molecules such as proteins and peptides have also been elucidated using SFG. This review demonstrates that SFG is a powerful technique to characterize molecular level structural information of complicated polymer surfaces and interfaces in situ. Copyright © 2006 Society of Chemical Industry [source] Synthesis and Characterization of a New Class of Energetic Compounds , Ammonium NitriminotetrazolatesPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 6 2008Thomas Abstract 1-Methyl-5-nitriminotetrazole (1) and 2-methyl-5-nitraminotetrazole (2) obtained by nitration of 1-methyl-5-aminotetrazole (3) and 2-methyl-5-aminotetrazole (4) were deprotonated using aqueous ammonia solution yielding the energetic compounds, ammonium 1-methyl-5-nitriminotetrazolate (5) and ammonium 2-methyl-5-nitriminotetrazolate (6). The nitrogen-rich salts were tested and characterized comprehensively using vibrational spectroscopy (Infrared (IR) and Raman), multinuclear (1H, 13C, 14N, and 15N) NMR spectroscopy, and elemental analysis. The molecular structures in the crystalline state were determined using low temperature single crystal X-ray diffraction. The thermal behavior and the decompositions were investigated using differential scanning calorimetry (DSC) and gas IR spectroscopy. The heats of formation were calculated using bomb calorimetric measurements. In addition, the relevant detonation parameters, like the detonation pressure and velocity of detonation were calculated using the software EXPLO5 outperforming the values of TNT. Last but not least the sensitivities were determined using BAM methods showing moderate values against impact and friction (drophammer and friction tester) and the long-term stabilities were tested using Flexy Thermal safety calorimetry (TSC). X-ray crystallography: 5: monoclinic, P21/c, a=370.06(2),pm, b=2079.06(9),pm, c=859.69(5),pm, ,=99.120(5)°, V=65306(6),pm3, Z=4, ,calc=1.639,g cm,3; 6: monoclinic, P21, a=365.39(2),pm, b=,788.82(5),pm, c=1124.95(7),pm, ,=91.818(6), V=32408(3),pm3, Z=2, ,calc=1.651,g cm,3. [source] Quinoidal Oligothiophenes: Towards Biradical Ground-State SpeciesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2010Ortiz Dr., Rocío Ponce Abstract A family of quinoidal oligothiophenes, from the dimer to the hexamer, with fused bis(butoxymethyl)cyclopentane groups has been extensively investigated by means of electronic and vibrational spectroscopy, electrochemical measurements, and density functional calculations. The latter predict that the electronic ground state always corresponds to a singlet state and that, for the longest oligomers, this state has biradical character that increases with increasing oligomer length. The shortest oligomers display closed-shell quinoidal structures. Calculations also predict the existence of very low energy excited triplet states that can be populated at room temperature. Aromatization of the conjugated carbon backbone is the driving force that determines the increasing biradical character of the ground state and the appearance of low-lying triplet states. UV/Vis, Raman, IR, and electrochemical experiments support the aromatic biradical structures predicted for the ground state of the longest oligomers and reveal that population of the low-lying triplet state accounts for the magnetic activity displayed by these compounds. [source] Chemical Tailoring of Porous Silica Xerogels: Local Structure by Vibrational SpectroscopyCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2004Alexandra Fidalgo Abstract Monolithic porous silica xerogels were synthesized by the sol,gel process, and their local structure was analysed by vibrational spectroscopy. The silica alcogels were prepared by a two-step hydrolytic polycondensation of tetraethoxysilane (TEOS) in isopropanol, with a water/TEOS molar ratio of 4. The hydrolysis step was catalysed by hydrochloric acid (HCl), with different HCl/TEOS molar ratios (ranging from 0.0005 to 0.009), and the condensation step was catalysed by ammonia (NH3), with different NH3/HCl molar ratios (ranging from 0.7 to 1.7). After appropriate ageing, the alcogels were washed with isopropanol and subcritically dried at atmospheric pressure. The diffuse reflectance infrared Fourier transform (DRIFT) spectra were analysed in terms of the main siloxane rings that form the silica particles, taking into account the splitting of the ,asSiOSi mode into pairs of longitudinal and transverse optic components, by long-range Coulomb interactions. It was proven that the proportion of residual silanol groups (which correlates with hydrophilicity), and the fraction of siloxane 6-rings (which correlates with porosity) may be tailored by adequate catalytic conditions, mostly by the hydrolysis pH. This was explained in terms of the reactions' mechanisms taking place in the two-step sol,gel process followed. [source] | ||||||||||||||||||||||||||||