FTIR study of water clusters in water–triethylamine solutions

The FTIR study presented in this work, on water dissolved in triethylamine (TEA), reveals the formation of water clusters in the TEA liquid phase at tenths of water molar concentrations. In the OH stretching region, the FTIR spectra of water in TEA show, at high frequencies, a narrow band at 3682 cm⁻¹ and, at low frequencies, a wide band that can be resolved into four peaks with maxima at 3249 cm⁻¹, 3348 cm⁻¹, 3440 cm⁻¹ and 3545 cm⁻¹. The results have been rationalised assuming the formation of clusters containing tens of three- and four-coordinated water molecules. TEA molecules surrounding the clusters are hydrogen bonded to one OH of the water molecules at the surface, leaving dangling protons. Further, the analyses of the spectra suggest that, in the used range, the water cluster mean size does not depend strongly on the water concentration.     

Vibrational spectroscopy of the sorosilicate mineral hemimorphite Zn4(OH)2Si2O7 · H2O

Raman spectroscopy complimented by infrared spectroscopy has been used to study the mineral hemimorphite from different origins. The Raman spectra show consistently similar spectra with only one sample showing additional bands due to the presence of smithsonite. Raman bands observed at 3510–3565 and 3436–3455 cm⁻¹ are assigned to OH stretching vibrations. Using a Libowitzky type formula, these OH bands provide hydrogen bond distances of 0.2910, 0.2825, 0.2762 and 0.2716 pm. Water bending modes are observed in the Raman spectrum at 1633 cm⁻¹. An intense Raman band at 930 cm⁻¹ is attributed to SiO symmetric stretching vibration of the Si₂O₇ units. Raman bands observed at 451 and 400 cm⁻¹are attributed to out-of-plane bending vibrations of the Si₂O₇ units. Raman bands at 330, 280, 168 and 132 cm⁻¹ are assigned to ZnO and OZnO vibrations.     

Characterization of methylcellulose produced from sugar cane bagasse cellulose: Crystallinity and thermal properties

In the present work, methylcellulose produced from sugar cane bagasse was characterized by FTIR, WAXD, DTA and TGA techniques. Two samples were synthesized: methylcellulose A and methylcellulose B. The only difference in the process was the addition of fresh reactants during the preparation of methylcellulose B. The ratio between the absorption intensities of the C-H stretching band at around 2900 cm⁻¹ and O-H stretching at around 3400 cm⁻¹ for methylcellulose B is higher than for methylcellulose A, indicating that methylcellulose B showed an increase in the degree of substitution (DS). Methylcellulose A presents a more heterogeneous structure, which is similar to the original cellulose as seen through FTIR and DTA. Methylcellulose B showed thermal properties similar to commercial methylcellulose. The modification of methylcellulose preparation method allows the production of a material with higher DS, crystallinity and thermal stability in relation to the original cellulose and to methylcellulose A.     

Thermal properties and stability of cassava starch films cross-linked with tetraethylene glycol diacrylate

The thermal stability of starch cross-linked with tetraethylene glycol diacrylate was studied under nitrogen atmosphere by thermogravimetry (TG) and infrared spectroscopy (FTIR). The cross-linking reaction was confirmed by the increase in intensity of the absorption band at ca. 3330 cm⁻¹ indicating the reinforcement of hydrogen bonds and the appearance of a new band at 1726 cm⁻¹ associated with the carbonyl group of the cross-linking agent. After cross-linking the solubility of starch in water decreased to the range 9%-16%. The thermogravimetric curves of pure and cross-linked starches showed an initial stage of degradation (up to ca. 150 °C) associated with the loss of water. The main stage of degradation occurred in the range 250-400 °C corresponding to ca. 60%-70% mass loss. The activation energy (E) for the degradation process increased from 145 kJ mol⁻¹ (pure starch) to 195 kJ mol⁻¹ and 198 kJ mol⁻¹ for starch treated for 60 min by UV (30 °C) and at 90 °C, suggesting high stability after cross-linking. A higher value (240 kJ mol⁻¹) was obtained for starch treated by UV for 120 min. The main volatile products determined by FTIR which correspond to hydrocarbons and carbonyl groups are apparently associated with the scission of weak bonds in the chain (probably branched groups) and the scission of stronger bonds (glycosidic linkages), respectively.     

Application of UV–Vis,near-infrared and mid-infrared spectroscopy to the study of Mn-bearing humites

The combination of electronic and vibrational spectra has been applied to correlate the spectral properties, with composition, structure and cation substitutions such as Mn, Fe, Ca and Zn for Mg in humites: norbergite, alleghanyite, leucophoenicite and sonolite with increasing number of silicate layers, 1, 2, 3 and 4. The observation of two broad bands in the visible range, near 550 and 450 nm (18 180 and 22 220 cm⁻¹) and one sharp band around 410 nm (24 390 cm⁻¹) is characteristic of Mn²⁺ in alleghanyite and leucophoenicite. The study of UV–Vis (electronic) spectral features confirms Mn as a major substituent in these two samples. Cation impurities like Zn and Ca as revealed from EDX analysis might be the cause for the absence of Mn-type spectrum in sonolite. The first observation is the near-infrared spectra of all four minerals in the first fundamental overtone OH-stretching mode are different and each mineral is characterized by its NIR spectrum. The feature in the range 7180–6600 cm⁻¹ [1393–1515 nm or 1.39–1.52 μm] corresponds to the overtones of OH stretching vibrational modes of the humite groups observed in their IR spectra over the range, 3680–3320 cm⁻¹. The infrared spectra of the hydrous components of OH and SiO₄ groups in the mineral structure act as an aid to distinguish the minerals of the humite mineral group. A band at 541 cm⁻¹ is assigned to MnO stretching mode.     

Influence of the chain and layer structure of Fe(III) and In(III) aqua-pentachloro-complexes on the bending vibrations of water molecules

Studies of IR and Raman spectra of monohydrates M^I₂[M^IIICl₅(H₂O)] (where M^I=K⁺, Rb⁺, Cs⁺ and M^III=Fe³⁺, In³⁺) at 1400-1900 cm⁻¹ have been carried out. The medium intensity band, detected in the region 1580-1595 cm⁻¹ was assigned to bending vibrations of water molecules (δHOH). The shift of the δHOH band towards low wavenumbers (1580-1595 cm⁻¹) is a main sign of the water molecule interactions in the chain hydrates. Additionally in the IR and Raman spectra of these salts, the appearance of the low intensity band between 1750 and 1810 cm⁻¹ (ν_x(H₂O)) was observed. In the presented paper we also discuss the influence of M^I and M^III cations on the position and splitting of these bands.     

The structure of mimetite,arsenian pyromorphite and hedyphane – A Raman spectroscopic study

The minerals mimetite Pb₅(AsO₄)₃Cl, arsenian pyromorphite Pb₅(PO₄,AsO₄)₃Cl and hedyphane Pb₃Ca₂(AsO₄)₃Cl have been studied by Raman spectroscopy complimented with infrared spectroscopy. Mimetite is characterised by a band at 812–3 cm⁻¹ attributed to the A_g mode. For the arsenian pyromorphite this band is observed at 818 cm⁻¹ and for hedyphane at 819 cm⁻¹. For mimetite and hedyphane bands at 788 and 765 cm⁻¹ are attributed to A_u and E_1u vibrational modes and are both Raman and infrared active. For the arsenian pyromorphite, Raman bands at 917–1014 cm⁻¹ are attributed to phosphate stretching vibrations. Raman spectroscopy clearly identifies bands attributable to isomorphous substitution of arsenate by phosphate. The observation of low intensity bands in the 3200–3550 cm⁻¹ region are assigned to adsorbed water and OH units, thus indicating some replacement of chloride ions with hydroxyl ions.     

On the specificity of the amide VI band for the secondary structure of proteins

In this work we analyzed the specificity of the amide VI band for different types of secondary structure elements in protein structures. This band involves the bending motion of the CO group of the peptide chain that is typically observed in the spectral region from 590 to 490 cm⁻¹. The infrared absorbance spectra of a set of polypeptide model compounds of well known secondary structure was obtained at defined pH, including poly (l-lysine), poly (l-tyrosine), poly (l-alanine) and poly (l-histidine). In addition spectra of membrane proteins from the respiratory chain, namely the NADH:ubiquinone oxidoreductase, the cytochrome c oxidase and its Cu_A fragment, the cytochrome bc₁ complex, a Rieske-type protein and in addition myoglobin, have been comparatively investigated. The systematic analysis of the amide VI band of the polypeptides and the proteins allowed correlating the signal appearing at ∼525 cm⁻¹ to α-helical structures and signals at ∼545 cm⁻¹ to β-sheet contributions. Random coils have been found to contribute at ∼535 cm⁻¹ while the β-turns were observed at ∼560 cm⁻¹.     

Non-ohmic electrical conductivity of β-rhombohedral boron in high electric fields

The low-field conductivity of β-rhombohedral boron follows Mott's law of variable-range hopping. Recent improvements in the energy band scheme attribute the hopping centers to specific, partly occupied states in the band gap, evoked by structural defects, in particular unoccupied B(13) sites. Band type conductivity is also possible, after valence electrons have been excited into unoccupied gap states. An experimental tool to gain an insight into the transport mechanism of semiconductors is the field-dependence of the electrical conductivity. For the interpretation of such experiments various theories are at disposal: the classical model of hot electrons, the Poole-Frenkel model, models of non-thermally activated hopping by Mott and Shklovskii, the Model of the field-dependence of small polarons mobility, the model of space-charge-limited currents. New measurements of the electrical conductivity in the temperature range 187-303 K at field strength up to 8 k V cm⁻¹ are presented and discussed according to the above-mentioned theories together with a critical review of the previous measurements of other authors. Three ranges are to be distinguished. (i) Up to about 200 V cm⁻¹: ohmic behavior; (ii) between about 200 V cm⁻¹ and about 20 kV cm⁻¹: non-ohmic behavior with a temperature-dependent field-dependence; (iii) above the “electrical breakdown” at about 20 kV cm⁻¹: non-ohmic behavior with I:E² independent of temperature.     

A Raman spectroscopic study of the phosphate mineral pyromorphite Pb5(PO4)3Cl

A series of selected pyromorphite minerals Pb₅(PO₄)₃Cl from different Australian localities has been studied by Raman spectroscopy complemented with selected infrared spectroscopy. The Raman spectrum of unsubstituted pyromorphite shows a single band at around 920 cm⁻¹ but for the natural minerals two bands at 919 and ∼932 cm⁻¹ attributed to the ν₁ (PO₄)³⁻ stretching vibration. The observation of multiple bands is attributed to the non-equivalence of phosphate units in the pyromorphite structure and the reduction in symmetry of the (PO₄)³⁻ units. This symmetry reduction is confirmed by the observation of multiple bands in both the ν₄ bending region (500–595 cm⁻¹) and the ν₂ bending region (350–500 cm⁻¹). The presence of isomorphic substitution of (PO₄)³⁻ by (AsO₄)³⁻ units is identified by the ν₁ symmetric stretching bands at around 824 and 851 cm⁻¹ and the ν₂ bending region around 331 and 354 cm⁻¹. Contrary to expectation Raman bands in the 3320–3700 cm⁻¹ region are observed and assigned to OH stretching bands of OH units resulting from the substitution of chloride anions in the pyromorphite structure. This study brings in to question the actual formula of natural pyromorphite as it is better represented as Pb₅(PO₄,AsO₄)₃(Cl,OH) · xH₂O.     

Aurichalcite – An SEM and Raman spectroscopic study

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise the vibrational spectrum of aurichalcite a zinc/copper hydroxy carbonate (Zn,Cu²⁺)₅(CO₃)₂(OH)₆. XRD patterns of all specimens show high orientation and indicate the presence of some impurities such as rosasite and hydrozincite. However, the diffraction patterns for all samples are well correlated to the standard reference patterns. SEM images show highly crystalline and ordered structures in the form of micron long fibres and plates. EDAX analyses indicate variations in chemical composition of Cu/Zn ratios ranging from 1/1.06 to 1/2.87. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band at 1072 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for aurichalcite at 1506, 1485 and 1337 cm⁻¹. Multiple Raman bands are observed in 800–850 cm⁻¹ and 720–750 cm⁻¹ regions and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. An intense Raman band at 1060 cm⁻¹ is attributed to the δ OH deformation mode.     

Transition metal complexes with squarate anion and the pyridyl-donor ligand 1,3-bis(4-pyridyl)propane (BPP): Synthesis,crystal structure and spectroscopic investigation

Synthesis, crystal structure and the vibrational spectra of coordination polymers with 1,3-bis(4-pyridyl)propane (BPP) and squarate ion ligands and transition metal ions (M = Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) are described. All compounds are isostructural, and the BPP is not coordinated to metal site since it is in cationic form due to protonation of N atoms from pyridyl rings. The metal is coordinated to two squarate ions and two water molecules in an octahedral distorted geometry. The two water molecules are involved in medium hydrogen bonds with squarate ligands and the average of O?O distance is 2.679(3) Å. Squarate ions adopt the 1,3-bis(monodentate) coordination mode bridging two metal centers giving rise to a 2D arrangement with (4,4) topology. The four-member ring is slightly distorted and the M–M distances are respectively 8.024 and 8.111 Å. The cationic form of BPP molecules are located inside of four-member ring cavity, presenting two different orientations, in which one molecule is inverted comparing to another. Vibrational spectra of all compounds are very similar, in agreement to crystal data. In all infrared spectra of the compounds a medium band at 1640 cm⁻¹ is observed, assigned to the in plane deformation mode of NH bond, indicative of the formation of cationic BPP. In the Raman spectra of the investigated compounds is observed a weak band around 1800 cm⁻¹, assigned to the stretching mode of free CO bond, whereas the medium band observed around 1600 cm⁻¹ is tentatively assigned to coordinated CO stretching mode. At last, a very important achievement of this investigation refers to the coordination geometries of all the investigated compounds, which are governed only by the ligands, independently of the different electronic properties of the metal ions.     

2-D analysis of Ge implanted SiO2 surfaces by laser-induced breakdown spectroscopy

2-D elemental distribution of Ge in silicon oxide substrates with differing implantation doses of between 3 × 10¹⁶ cm^− 2 and 1.5 × 10¹⁷ cm^− 2 has been investigated by Laser-Induced Breakdown Spectroscopy (LIBS). Spectral emission intensity has been optimized with respect to time, crater size, ablation depth and laser energy. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) coupled with Energy-Dispersive X-Ray Spectroscopy (EDX) have been utilized to obtain crater depth, morphology and elemental composition of the sample material, respectively. LIBS spectral data revealed the possibility of performing 2-D distribution analysis of Ge atoms in silicon oxide substrate. EDX analysis results confirmed that LIBS is capable to detect Ge atoms at concentrations lower than 0.2% (atomic). LIBS as a fast semi-quantitative analysis method with 50 µm lateral and 800 nm depth resolution has been evaluated. Results illustrate the potential use of LIBS for rapid, on-line assessment of the quality of advanced technology materials during the manufacturing process.     

The structure and spectra of 1,1-bis(trimethylsilylethynyl)-cyclopropane: a priori calculated force field and vibrational effects

The molecular structure of 1,1-bis(trimethylsilylethynyl)cyclopropane has been studied by the gas electron diffraction method, by vibrational spectroscopic methods and by ab initio calculations at the RHF and MP2 levels. A scaled quantum-chemical force field was used for band assignment in the experimental IR (4000-100 cm⁻¹) and Raman (4000-200 cm⁻¹) spectra. The root-mean-square vibrational amplitudes and harmonic shrinkage corrections were calculated taking into account non-linear relations between Cartesian and internal vibrational coordinates at the level of first-order perturbation theory (h1) and with the use of the traditional scheme (h0).     

The molecular structure of selected minerals of the rosasite group – An XRD,SEM and infrared spectroscopic study

Minerals in the rosasite mineral group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite have been studied by powder X-ray diffraction, scanning electron microscopy and infrared spectroscopy. X-ray diffraction shows the minerals to be complex mixtures with more than one rosasite mineral observed in each sample. SEM analysis shows the minerals to be fibrous in nature and the use of EDAX enabled the chemical composition of the minerals to be determined. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the molecular structure is similar to malachite. A comparison is made with the spectrum of malachite. The rosasite mineral group is characterised by two OH stretching vibrations at ∼3401 and 3311 cm⁻¹. Two intense bands observed at ∼1096 and 1046 cm⁻¹ are assigned to ν₁ (CO₃)²⁻ symmetric stretching vibration and the δ OH deformation mode. Multiple bands are found in the 800–900 and 650–750 cm⁻¹ regions attributed to the ν₂ and ν₄ bending modes confirming the symmetry reduction of the carbonate anion in the rosasite mineral group as C_2v or C_s. A band at ∼560 cm⁻¹ is assigned to a CuO stretching mode.     

Synthesis and vibrational spectroscopic characterisation of nickel containing aurichalcite

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise a synthetic nickel substituted aurichalcite a zinc/nickel hydroxy carbonate, (Zn²⁺, Cu²⁺, Ni²⁺)₅(CO₃)₂(OH)₆. XRD patterns show high orientation and indicate the presence of some minor impurities. The diffraction patterns for the Ni-aurichalcite are well correlated with the standard reference patterns. EDAX analyses indicate variations in chemical composition of Zn/Ni ratios of ∼20:1. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band for the Ni-aurichalcite at 1070 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for Ni-aurichalcite at 1372, 1480 and 1543 cm⁻¹. Multiple Raman bands are observed in the regions from 800 to 850 cm⁻¹ and 720 to 750 cm⁻¹, and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. This research proves that nickel containing aurichalcites can be synthesised in the laboratory thus mimicing the natural nickel containing aurichalcites.     

The structure of mimetite,arsenian pyromorphite and hedyphane – A near-infrared spectroscopic study

Electronic and vibrational spectra of mimetite, arsenian pyromorphite and hedyphane minerals have been analysed and the spectra related to the mimetite and arsenian pyromorphite and hedyphane mineral structure. The chief spectral feature in the electronic spectra at ∼10 000 cm⁻¹ (1.00 μm) with variable band position and intensity results from the ferrous ion. The splitting of Fe(II) band is large in mimetites with a separation of 1415 cm⁻¹. An additional band shown by arsenian pyromorphite at 10 735 cm⁻¹ (0.93 μm) is assigned to Cu(II) dd-transition. The substitution of Fe(II) causes a blue shift for Cu(II) band in mimetites and the intensity of this band is enhanced at ∼11 140 cm⁻¹ (0.90 μm). The change in colour from brown to orange-yellow relates to the amount of Cu and/or Fe impurities in the mimetite minerals.     

Determination of solubility parameters of cross-linked macromonomeric initiators based on polypropylene glycol

A new type macromonomeric azo initiators also named macroinimers, MIMs, based on polypropylene glycol, PPG, with molecular weight 400 and 2000, were synthesized. Self-condensing radical polymerization of the macroinimers gave cross-linked polypropylene glycols. The solubility parameters of the cross-linked polymers determined using swelling experiments in a series of solvents have been reported. Crosss-linked PPG-400 and cross-linked PPG-2000 indicated the same solubility parameter value. But their swelling ratios were different because of the differences of the chain lengths in between of the cross-points (Mc) of the gels. Therefore, while the largest swelling ratio exhibited by a cross-linked PPG-2000 in tetrahydrofurane was being 19.48, this ratio was 6.84 for the cross-linked PPG-400 in the same solvent. The solubility parameters and constant α for these cross-linked polymers were obtained as δ_{cross-linked PPG-400} = 9.56 (cal cm⁻³)^1/2, α = 0.123 cm³ cal⁻¹ and δ_{cross-linked PPG-2000} = 8.95 (cal cm⁻³)^1/2, α = 0.107 cm³ cal⁻¹ by using the least squares regression method.     

Natural rubber nanocomposites with SiC nanoparticles and carbon nanotubes

Single-walled carbon nanotubes (SWNTs) and SiC nanoparticles were dispersed in natural rubber (NR) polymer solution and subsequently evaporated the solvent to prepare NR nanocomposites. Using this technique, nanoparticles can be better dispersed in the NR matrix. The influence of nano-fillers on the mechanical properties of the resulting nanocomposites was quantified.Mechanical test results show an increase in the initial modulus with nanoscale reinforcements for up to 50% strain compared to pure NR. The modulus and strength of natural rubber with 1.5% SiC nanoparticles appear to be superior to those of SWNTs with the same filler content. In addition to mechanical testing, these nanocomposites were studied using the SEM and Raman spectroscopy techniques in order to understand the morphology of the resulting system and the load transfer mechanism, respectively. The Raman spectrum of the SWNT/NR system is characterized by a strong band at 1595 cm⁻¹ (G mode—C-C stretching) and other two bands at 1300 cm⁻¹ (D mode-disorder induced) and 2590 cm⁻¹ (D* band). A shift of the 2590 cm⁻¹ Raman band to the lower wavenumber was observed after subjecting SWNT/NR sample to cyclic stress testing. Ageing SWNT/NR specimen in distilled water for 30 days also provided a similar result. The Raman shift in aged samples indicates internal stress transfer from the natural rubber matrix to the SWNTs implying the existence of bonding at the interface.     

Vibrational spectra and reinvestigation of the crystal structure of a polymeric copper(II)-orotate complex, [Cu(μ-HOr)(H2O)2]n: The performance of new DFT methods, M06 and M05-2X, in theoretical studies

The crystal and molecular structure of a polymeric Cu(II)-orotate complex, [Cu(μ-HOr)(H₂O)₂]_n, has been reinvestigated by single crystal X-ray diffraction. It is shown that several synergistic interactions: two axial Cu-O interactions; intramolecular and intermolecular hydrogen bonds; and π-π stacking between the uracil rings contribute to the stability of the crystal structure. The Raman and FT-IR spectra of the title complex are reported for the first time. Comprehensive theoretical studies have been performed by using three unrestricted DFT methods: B3LYP; and the recently developed M06, and M05-2X density functionals. Clear-cut assignments of all the bands in the vibrational spectra have been made on the basis of the calculated potential energy distribution, PED. The very strong Raman band at 1219 cm⁻¹ is diagnostic for the N1-deprotonation of the uracil ring and formation of the copper-nitrogen bond, in this complex. The Cu-O (carboxylate) stretching vibration is observed at 287 cm⁻¹ in the IR spectrum, while the Cu-N (U ring) stretching vibration is assigned to the strong Raman band at 263 cm⁻¹. The molecular structure and vibrational spectra (frequencies and intensities) calculated by the M06 functional method are very similar to the results obtained by the B3LYP method, but M06 performs better than B3LYP in calculations of the geometrical parameters and vibrational frequencies of the interligand O-H?O hydrogen bonding. Unfortunately, the M05-2X method seriously overestimates the strength of interligand hydrogen bond.