Structure and Reactivity of the <Emphasis Type="BoldItalic">N</Emphasis>-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-acetyl-cysteine followed by the homolytic cleavage of the S–NO bond in the gas phase. IRMPD spectroscopy coupled with DFT calculations revealed that for the radical cation the radical migrates from its initial position on the sulfur atom to the α-carbon position, which is 2.5 kJ mol^–1 lower in energy. The radical migration was confirmed by time-resolved ion-molecule reactions. These results are in contrast with our previous study on cysteine methyl ester radical cation (Osburn et al., Chem. Eur. J. 2011 , 17, 873–879) and the study by Sinha et al. for cysteine radical cation (Phys. Chem. Chem. Phys. 2010 , 12, 9794–9800) where the radical was found to stay on the sulfur atom as formed. A similar approach allowed us to form a hydrogen-deficient radical anion of N-acetyl-cysteine, (M – 2H) ^•– . IRMPD studies and ion-molecule reactions performed on the radical anion showed that the radical remains on the sulfur, which is the initial and more stable (by 63.6 kJ mol^–1) position, and does not rearrange.     

Thermal characterization of starch-based polymers produced by <Emphasis Type="Italic">Ophiostoma</Emphasis> spp

The thermal behavior of modified starches (MS) produced by biosynthetic pathway is described based on a comparative analysis with native starches (NS). MS were produced by fermentation in presence of Ophiostoma spp. cultures. Thermogravimetric analysis (TG) with successive derivatives (DTG) and differential scanning calorimetry (DSC) were used for this study. NS results showed a single peak dominating both the TG (DTG) and DSC plots. A double thermal transition event was detected in samples of MS. The procedural decomposition temperature (T _i–T _f; lowest onset temperature of initial and final mass change) was carried out within a narrow interval of temperatures for NS (610–640 °C). This interval could not be reached within the 1,000 °C range in MS. Residues higher than 10% were recorded for MS at this temperature. The presence of the double thermal transition in MS is discussed.     

Structure characterization and spectroscopic investigation of ciprofloxacin drug

Ciprofloxacin (CPF, C₁₇H₁₈FN₃O₃) drug is used in the treatment of some bacterial infectious diseases. The drug was investigated using thermal analysis (TA) measurements (TG/DTG) and electron impact mass spectral (EI-MS) fragmentation at 70 eV techniques. Furthermore, the drug was characterized and investigated by other spectroscopic tools as IR, UV–Vis, ¹H-, and ¹³C-NMR. Semi-empirical MO calculation using PM3 procedure has been carried out on neutral molecule and positively charged species. The calculations included, bond length, bond order, bond strain, partial charge distribution, ionization energy, and heat of formation (ΔH _f). The PM3 procedure provides a basis for fine distinction among sites of initial bond cleavage, which is crucial to the rationalization of subsequent fragmentation of the molecule. The mass spectra and thermal analysis fragmentation pathways were proposed and compared to each other to select the most suitable scheme representing the correct fragmentation of this drug. From EI-MS, the main primary cleavage site of the charged molecule is that due to C–COOH bond cleavage with H-rearrangement to skeleton and CO₂ loss which can further decompose by piperazine loss. Thermal analysis of the neutral form of the drug reveals the high response of the drug to the temperature variation with very fast rate. Thermal decomposition has carried out in several sequential steps in the temperature range 40–650 °C. The initial thermal decomposition is similar to that obtained by mass spectrometric fragmentation (C–COOH fragment) but differ in that a rearrangement occurs by OH and CO loss. Therefore, comparison between MS and TA helps in selection the proper pathway representing the fragmentation of this drug. This comparison successfully confirmed by MO calculation. Finally, the effect of fluorine atom on the stability of the drug was discussed.     

Kinetic investigation on thermal decomposition of organophosphorous compounds

In this paper, the thermal behaviours of two organophosphorous compounds, N,N-dimethyl-N′,N′-diphenylphosphorodihydrazidic (NDD) and diphenyl amidophosphate (DPA), were studied by thermogravimetery (TG), differential thermal analysis (DTA) and differential scanning calorimetery (DSC) techniques under non-isothermal conditions. The results showed that NDD melts about 185 °C before it decomposes. NDD decomposition occurs in two continuous steps, in the 190–410 °C temperature range. First thermal degradation stage for NDD results a broad exothermic peak in the DTA curve that is continued with a small exothermic peak at the end of decomposition process. On the other hand, applying TG-DTA techniques indicates that DPA melts about 150 °C before it decomposes. This compound decomposes in the temperature range of 230 to 330 °C in two steps. These steps are endothermic and exothermic, respectively. Activation energy and pre-exponential factor for the first step of decomposition of each compound were found by means of Kissinger method and were verified by Ozawa–Flynn–Wall method. Activation energy obtained by Kissinger method for the first stage of NDD and DPA decompositions are 138 and 170 KJ mol⁻¹, respectively. Finally, the thermodynamic parameters (ΔG ^#, ΔH ^# and ΔS ^#) for first step decomposition of investigated organophosphorous were determined.     

Three-propeller-blade-shaped electride: remarkable alkali-metal-doped effect on the first hyperpolarizability

Significant alkali-metal-doped effects on the structure and the first hyperpolarizability (β ₀) of effective multi-nitrogen complexant tris[(2-imidazolyl)methyl]amine (TIMA) are investigated. Three imidazoles of TIMA like three blades of propeller connect with methyls by the C–C single bonds. Because of the three C–C single-bond cooperative rotations, the TIMA behaves with great flexibility, and it is a high-performance multi-nitrogen complexant for the alkali metal doping. Thus, the new complexes A_m-TIMA (A_m = Li, Na, and K) with electride characteristic have diffuse excess electron than the reported electride-type system due to the strong interaction between the complexant TIMA and alkali metal. For the first hyperpolarizability, three engaging electrides A_m-TIMA with the diffuse excess electrons exhibit considerably large β ₀ values using the MP2 (full) method and the β ₀ values of new electrides are greatly larger (3,464–29,705 times) than that (338 au) of TIMA. Surprisingly, the K-TIMA sets a new record β ₀ value to be 1.00 × 10⁷ au which far exceeds than that (3,694–76,978 au) of the reported electride-type system Li@calix[4]pyrrole (J Am Chem Soc 127:10977–10981, 2005) and Li_n−H−(CF₂−CH₂)₃−H (n = 1, 2) (J Am Chem Soc 129:2967–2970, 2007) and 31,123 au of the organometallic system (J Am Chem Soc 121:4047–4053, 1999) Ru(trans-4,4′-diethylaminostyryl-2,2′-bipyridine)₃²⁺, as well as 1.23 × 10⁶ au of the large donor-CNT systems (Nano Lett 8:2814–2818, 2008). Clearly, the alkali-metal-doped effect on the first hyperpolarizability is very dramatic for the high-performance multi-nitrogen complexant TIMA. Considering simple possibility from molecule to material, the β ₀ values of optimized Li-TIMA-dimer and Li-TIMA-tetramer are investigated by BHandHLYP method. Interestingly, results show that the order of β ₀ value is Li-TIMA-monomer < Li-TIMA-dimer < Li-TIMA-tetramer. So the new three-propeller-blade-shaped electrides can be considered as candidates for high-performance nonlinear optical materials.     

Thermal analysis of high-temperature fast reactions in energetic materials

To get round two main difficulties of the kinetic study of fast reactions of high-temperature decomposition of energetic materials (EM) (spatial non-isothermality and self-inflammation) two new methods for sample preparation called “mechanical dilution” and “thermal dilution” were applied. In the first part of the presentation, some experimental and theoretical data on kinetics of fast high-temperature decomposition of some typical homogeneous and heterogeneous energetic materials (including pyroxylin, ammonia copper chromate, ammonium perchlorate, solid rocket propellants, and others) are given. In a number of cases, kinetic constants of fast reactions dominating at high temperatures were shown to significantly differ from those of low-temperature reactions. The second part of the presentation deals with a new method of thermal analysis—electrothermal analysis (ETA). By using a multi-channel high-speed optical pyrometer, variation of the temperature field in an electrically heated sample of conductive energetic material (or its mixture with metal powder) during its heating followed by thermal explosion is registered. Due to application of this method in the ETA-100 (allowing one to measure kinetic data at the temperature up to 3800 K with a time step as short as 0.1 ms, i.e., for full conversion times as short as 10⁻³ s) some important patterns of mechanisms of gasless combustion and explosion in SHS-mixtures (Si + C, Ni + Al, and Ti + C) were identified. More details regarding these and some additional important aspects can be found in [1, 2].     

Thermal characteristics of bitumen pyrolysis

The pyrolysis behavior of bitumen was investigated using a thermogravimetric analyzer–mass spectrometer system (TG–MS) and a differential scanning calorimeter (DSC) as well as a pyrolysis-gas chromatograph/mass spectrometer system (Py-GC/MS). TG results showed that there were three stages of weight loss during pyrolysis—less than 110, 110–380, and 380–600 °C. Using distributed activation energy model, the average activation energy of the thermal decomposition of bitumen was calculated at 79 kJ mol⁻¹. The evolved gas from the pyrolysis showed that organic species, such as alkane and alkene fragments had a peak maximum temperature of 130 and 480 °C, respectively. Benzene, toluene, and styrene released at 100 and 420 °C. Most of the inorganic compounds, such as H₂, H₂S, COS, and SO₂, released at about 380 °C while the CO₂ had the maximum temperature peaks at 400 and 540 °C, respectively. FTIR spectra were taken of the residues of the different stages, and the results showed that the C–H bond intensity decreased dramatically at 380 °C. Py-GC/MS confirmed the composition of the evolved gas. The DSC revealed the endothermic nature of the bitumen pyrolysis.     

Thermal studies of cobalt,iron and tin metalloporphyrins

A free-base tetraphenyl porphyrin (TPP) and its corresponding metalloporphyrins (MTPP) where M = Co, Fe and Sn were synthesized and characterized by UV–visible spectroscopy, FTIR and ¹Hnmr spectroscopy. Thermal studies of these porphyrins were carried out in synthetic air from room temperature to 800 °C using thermal analyser. The residues of MTPP after thermal treatment were qualitatively analysed, which showed the presence of corresponding metal oxides. Further, the above MTPP were subjected to thermogravimetry–evolved gas and mass spectrometry (TG–EGA–MS) analysis for the detailed information about evolved gases at their corresponding decomposition temperatures. This information may be used to predict the probable mechanism for ring opening of the macromolecular porphyrins.     

Mass spectra of gliclazide drug at various ion sources temperature

Gliclazide (GL, C₁₅H₂₁N₃O₃S) drug is used as non-insulin-dependant diabetes mellitus. The drug was investigated using thermal analysis (TA) measurements (TG/DTG) and electron impact mass spectral (EI–MS) fragmentation at 70 eV techniques. The mass spectra of GL at different values of ion source temperatures (400, 416, 425, and 440 K) are recorded and investigated. Semiempirical MO calculation, using PM3 procedure, has been carried out on neutral molecule and positively charged species. These calculations included bond length, bond order, bond strain, partial charge distribution, ionization energy, and heats of formation (ΔH _f). PM3 procedure provides a basis for fine distinction among sites of initial bond cleavage, which is crucial to the rationalization of subsequent fragmentation of the molecule. The primary fragmentation pathway in both TA and MS (at different values of ion source temperature) is initiated by S–N bond rupture. TA and DTG show one main weight loss at 250.38 °C and four peaks at 271.6, 360.99, 427.93 and 479.17 °C in DTA, which may be attributed to various fragments. Also, the rate constant (K′) of thermal degradation has been tested isothermally at 210 and 600 °C. The calculated rate values are 9.6 × 10⁻³ and 0.33 × 10⁻³ s⁻¹, respectively, and discussed. In MS, the effect of ion source temperature on mass spectral fragmentation processes is discussed on the basis of energy considerations using quasi equilibrium theory.     

Thermal Analysis of the Poly(Siloxane)–Poly(Tetrafluoroethylene) Coating System

Thermal properties of poly(siloxane)–poly(tetrafluoroethylene) (SIL–PTFE) system were investigated, using Perkin Elmer DSC-7 differential scanning calorimeter and TGA-7 thermogravimetric analyzer. For SIL–PTFE compositions, one glass transition temperature T _g has been found, in accordance with the reciprocal rule up to about 40 mass% of PTFE. However, for higher PTFE contents, T _g values about –118 to –112°C were observed that can be ascribed to motions of cross-linked SIL structures. Endo- and exothermic transitions, found in the range from 70 to 290°C, not observed for pure SIL and PTFE components, are considered as specific ones for the SIL–PTFE semi-IPN structures. The SIL–PTFE system, as well as its components, is thermally stable, if degradation reactions are considered; the temperatures of decomposition at the maximum decomposition rate were above 530°C. It has been found that the thermal stability of the SIL–PTFE system is increasing with the increase of the PTFE content. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal behavior of drugs

Data on the thermal stability of drugs was required to obtain information for handling, storage, shelf life and usage. In this study, the thermal stability of two nonsteroidal anti-inflammatory drugs (NSAIDs) was determined by differential scanning calorimetry (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the naproxen and celecoxib occurs in the temperature ranges of 196–300 and 245–359 °C, respectively. The TG/DTA analysis of compounds indicates that naproxen melts (at about 158.1 °C) before it decomposes. However, the thermal decomposition of the celecoxib started about 185 °C after its melting. The influence of the heating rate (5, 10, 15, and 20 °C min⁻¹) on the DSC behavior of the both drug samples was verified. The results showed that, as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the values of activation energy obtained by various methods, the following order for the thermal stability was noticed: naproxen > celecoxib. Finally, the values of ΔS ^#, ΔH ^#, and ΔG ^# of their decomposition reaction were calculated.     

Solid-state mechanical properties of crystalline drugs and excipients

Thermal mechanical analysis (TMA) of crystalline drugs and excipients in their pre-melt temperature range performed in this study corroborate their newly found linear dielectric conductivity properties with temperature. TMA of crystalline active pharmacy ingredients (APIs) or excipients shows softening at 30–100 °C below the calorimetric melting phase transition, which is also observed by dielectric analysis (DEA). Acetophenetidin melts at 135 °C as measured calorimetrically by DSC, but softens under a low mechanical stress at 95 °C. At this pre-melting temperature, the crystals collapse under the applied load, and the TMA probe shows rapid displacement. The mechanical properties yield a softening structure and cause a dimensionally slow disintegration resulting in a sharp dimensional change at the melting point. In order to incorporate these findings into a structure–property relationship, several United States Pharmacopeia (USP) melting-point standard drugs were evaluated by TMA, DSC, and DEA, and compared to the USP standard melt temperatures. The USP standard melt temperature for vanillin (80 °C) [1], acetophenetidin (135 °C) [2], and caffeine (235 °C) [3] are easily verified calorimetrically via DSC. The combined thermal analysis techniques allow for a wide variety of the newly discovered physical properties of drugs and excipients.     

Thermal decomposition mechanism and quantum chemical investigation of hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO)

The thermal decomposition mechanism of hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO) compound was studied by means of differential scanning calorimetry (DSC), thermogravimetry and derivative thermogravimetry (TG-DTG), and the coupled simultaneous techniques of in situ thermolysis cell with rapid scan Fourier transform infrared spectroscopy (in situ thermolysis/RSFTIR). The thermal decomposition mechanism is proposed. The quantum chemical calculation on HNTO was carried out at B3LYP level with 6-31G+(d) basis set. The results show that HNTO has two exothermic decomposition reaction stages: nitryl group break first away from HNTO molecule, then hydrazine group break almost simultaneously away with carbonyl group, accompanying azole ring breaking in the first stage, and the reciprocity of fragments generated from the decomposition reaction is appeared in the second one. The C–N bond strength sequence in the pentabasic ring (shown in Scheme 1) can be obtained from the quantum chemical calculation as: C3–N4 > N2–C3 > N4–C5 > N1–C5. The weakest bond in NTO⁻ is N7–C3. N11–N4 bond strength is almost equal to N4–C5. The theoretic calculation is in agreement with that of the thermal decomposition experiment.      

Application of TA–MS combined with PulseTA for characterization of materials

The thermal behavior of the anticancer drug-irinotecan was measured by Thermogravimetry–Differential thermal analysis (TG–DTA) to explore the application of TG–DTA in nanomedicine firstly. The TG–DTA result showed that the irinotecan was oxidized completely before 700 °C. When irinotecan was loaded onto nanosized mesoporous silica spheres, the loading capacity for irinotecan measured by TG–DTA was about 9.11% in the irinotecan/mesoporous SiO₂ composite, similar to the typical UV–Vis spectra results (10.5%), which showed that TG–DTA characterization provided an alternative method to determine the drug loading amount on inorganic carriers. Secondly, Thermogravimetry–Differential scanning calorimetry–Mass Spectrometry coupling techniques (TG–DSC–MS) were used to characterize the hydrogen adsorption temperature and capacity of TiCr_1.2 (V-Fe)_0.6 alloy. The MS result showed that the released region of hydrogen was 250–500 °C, which was consistent with the TG–DSC results. Lastly, TA–MS combined with pulse thermal analysis (PulseTA) were used for a simultaneous characterizing study in the changes of mass, determination and quantitative calibration of the evolved nitrogen formed during the thermal decomposition of the InN powder. The results showed that relative error of this method between measured value and theoretical value was 2.67% for the quantitative calibration of evolved N₂. It shows that TA–MS combined with PulseTA techniques offer a good tool for the quantification of the evolved nitrogen in the InN powder.     

Study on thermal decomposition of calix[6]arene and calix[8]arene

Thermal decomposition kinetics of calix[6]arene (C6) and calix[8]arene (C8) were studied by Thermogravimetry analysis (TG) and Differential thermal analysis (DTA). TG was done under static air atmosphere with dynamic heating rates of 1.0, 2.5, 5.0, and 10.0 K min⁻¹. Model-free methods such as Friedman and Ozawa–Flynn–Wall were used to evaluate the kinetic parameters such as activation energy (E _a) and pre-exponential factors (ln A). Model-fitting method such as linear regression was used for the evaluation of optimum kinetic triplets. The kinetic parameters obtained are comparable with both the model-free and model-fitting methods. Within the tested models, the thermal decomposition of C6 and C8 are best described by a three dimensional Jander’s type diffusion. The antioxidant efficiency of C6 and C8 was tested for the decomposition of polypropylene (PP).     

The architecture and the Jones polynomial of polyhedral links

In this paper, we first recall some known architectures of polyhedral links (Qiu and Zhai in J Mol Struct (THEOCHEM) 756:163–166, 2005; Yang and Qiu in MATCH Commun Math Comput Chem 58:635–646, 2007; Qiu et al. in Sci China Ser B Chem 51:13–18, 2008; Hu et al. in J Math Chem 46:592–603, 2009; Cheng et al. in MATCH Commun Math Comput Chem 62:115–130, 2009; Cheng et al. in MATCH Commun Math Comput Chem 63:115–130, 2010; Liu et al. in J Math Chem 48:439–456 2010). Motivated by these architectures we introduce the notions of polyhedral links based on edge covering, vertex covering, and mixed edge and vertex covering, which include all polyhedral links in Qiu and Zhai (J Mol Struct (THEOCHEM) 756:163–166, 2005), Yang and Qiu (MATCH Commun Math Comput Chem 58:635–646, 2007), Qiu et al. (Sci China Ser B Chem 51:13–18, 2008), Hu et al. (J Math Chem 46:592–603, 2009), Cheng et al. (MATCH Commun Math Comput Chem 62:115–130, 2009), Cheng et al. (MATCH Commun Math Comput Chem 63:115–130, 2010), Liu et al. (J Math Chem 48:439–456, 2010) as special cases. The analysis of chirality of polyhedral links is very important in stereochemistry and the Jones polynomial is powerful in differentiating the chirality (Flapan in When topology meets chemistry. Cambridge Univ. Press, Cambridge, 2000). Then we give a detailed account of a result on the computation of the Jones polynomial of polyhedral links based on edge covering developed by Jin, Zhang, Dong and Tay (Electron. J. Comb. 17(1): R94, 2010) and, at the same time, by using this method we obtain some new computational results on polyhedral links of rational type and uniform polyhedral links with small edge covering units. These new computational results are helpful to judge the chirality of polyhedral links based on edge covering. Finally, we give some remarks and pose some problems for further study.     

The highly crosslinked dimethacrylic/divinylbenzene copolymers

The thermal stability of the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium bromide, [BMIM]Br, and 1-n-octyl-3-methylimidazolium bromide, [OMIM]Br, was evaluated through thermogravimetry (TG). Long-term isothermal TG studies revealed that both of these ILs exhibit appreciable decomposition even at temperatures significantly lower than the onset decomposition temperature, previously determined from fast scan TG experiments. The long-term TG studies of both the ILs showed linear mass loss as a function of time at each temperature of 10 °C interval in the range 533–573 K over a period of 10 h. The kinetics of isothermal decomposition of ILs was analyzed using pseudo-zero-order rate expression. The activation energies for the isothermal decomposition of [BMIM]Br and [OMIM]Br under nitrogen atmosphere are 219.86 and 212.50 kJ mol⁻¹, respectively. The moisture absorption kinetics of these ILs at 25 °C and 30% relative humidity (RH) and at 85 °C and 85% RH were also studied. Water uptake of ILs exposed at 25 °C/30%RH follows a simple saturation behavior in agreement with Weibull model while that at 85 °C/85%RH fortuitously fit into the Henderson–Pabis model.     

Thermal unimolecular decomposition mechanism of 2,4,6-trinitrotoluene: a first-principles DFT study

Simple C–NO₂ homolysis, 4,6-dinitroanthranil (DNAt) production by dehydration, and the nitro-nitrite rearrangement–homolysis for gas-phase TNT decomposition were recently studied by Cohen et al. (J Phys Chem A 111:11074, 2007), based on DFT calculations. Apart from those three pathways, other possible initiation processes were suggested in this study, i.e., CH₃ removal, O elimination, H escape, OH removal, HONO elimination, and nitro oxidizing adjacent backbone carbon atom. The intermediate, 3,5-dinitro-2(or 4)-methyl phenoxy, is more favor to decompose into CO and 3,5-dinitro-2(or 4)-methyl-cyclopentadienyl than to loss NO following nitro-nitrite rearrangement. Below ~1,335 K, TNT condensing to DNAt by dehydration is kinetically the most favor process, and the formations of substituted phenoxy and following cyclopentadienyl include minor contribution. Above ~1,335 K, simple C–NO₂ homolysis kinetically dominates TNT decomposition; while the secondary process changes from DNAt production to CH₃ removal above ~2,112 K; DNAt condensed from TNT by dehydration yields to that by sequential losses of OH and H above ~1,481 K and to nitro-nitrite rearrangement–fragmentation above ~1,778 K; O elimination replaces DNAt production above ~2,491 K, playing the third role in TNT decomposition; H escaping directly from TNT thrives in higher temperature (above ~2,812 K), as the fourth largest process. The kinetic analysis indicates that CH₃ removal, O elimination, and H escape paths are accessible at the suggested TNT detonation time (~100–200 fs), besides C–NO₂ homolysis. HONO elimination and nitro oxidizing adjacent backbone carbon atom paths are negligible at all temperatures. The calculations also demonstrated that some important species observed by Rogers and Dacons et al. are thermodynamically the most favor products at all temperatures, possibly stemmed from the intermediates including 4,6-dinitro-2-nitroso-benzyl alcohol, 3,5-dinitroanline, 2,6-dinitroso-4-nitro-phenylaldehyde, 3,5-dinitro-1-nitrosobenzene, 3,5-dinitroso-1-nitrobenzene, and nitrobenzene. All transition states, intermediates, and products have been indentified, the structures, vibrational frequencies, and energies of them were verified at the uB3LYP/6-311++G(d,p) level. Our calculated energies have mean unsigned errors in barrier heights of 3.4–4.2 kcal/mol (Lynch and Truhlar in J Phys Chem A 105:2936, 2001), and frequencies have the recommended scaling factors for the B3-LYP/6-311+G(d,p) method (Andersson and Uvdal in J Phys Chem A 109:2937, 2005; Merrick et al. in J Phys Chem A 111:11683, 2007). All calculations corroborate highly with the previous experimental and theoretical results, clarifying some pertinent questions.     

Synthesis of electrospun BaSrTiO<Subscript>3</Subscript>/PVP nanofibers

Ba_1−x Sr _x TiO₃(x = 0–0.5, BST) nanofibers with diameters of 150–210 nm were prepared by using electrospun BST/polyvinylpyrrolidone (PVP) composite fibers by calcination for 2 h at temperatures in the range of 650–800 °C in air. The morphology and crystal structure of calcined BST/PVP nanofibers were characterized as functions of calcination temperature and Sr content with an aid of XRD, FT-IR, and TEM. Although several unknown XRD peaks were detected when the fibers were calcined at temperatures less than 750 °C, they disappeared with increasing the temperature (above 750 °C) due to its thermal decomposition and complete reaction in the formation of BST. In addition, the FT-IR studies of BST/PVP fibers revealed that the intensities of the O–H stretching vibration bands (at 3430 and 1425 cm⁻¹) became weaker with increasing the calcination temperature and a broad band at 540 cm⁻¹, Ti–O vibration, appeared sharper and narrower after calcination above 750 °C due to the formation of metal oxide bonds. However, no effect of Sr content on the crystal structure of the composites was detected.     

Thermal decomposition and antimicrobial activity of zinc(II) 2-bromobenzoates with organic ligands

New zinc(II) 2-bromobenzoate complex compounds with general formula Zn(2-BrC₆H₄COO)₂·nL·xH₂O (where L = urea, nicotinamide, N-methylnicotinamide, N,N-diethylnicotinamide, isonicotinamide, phenazone n = 0–2, x = 0–2) were prepared and characterized by elemental analysis, IR spectroscopy and thermal analysis. The thermal decomposition of hydrated compounds started with dehydration process. During the thermal decomposition organic ligand, carbon dioxide and bis(2-bromophenyl)ketone were evolved. The solid intermediates and volatile products of thermal decomposition were proved by IR spectroscopy and mass spectrometry. The final solid product of the thermal decomposition heated up to 1073 K was zinc oxide. Antimicrobial activity of the prepared compounds was tested against various strains of bacteria, yeasts and filamentous fungi (E. coli, S. aureus, C. albicans, R. oryzae, A. alternate and M. gypseum). It was found that the selected bacteria were more sensitive to the studied zinc(II) complex compounds than the yeast and the filamentous fungi.