A Density Functional Theory Study on Paracetamol-Oxalic Acid Co-Crystal

Paracetamol (PCA) has two well-known polymorphic forms, monoclinic (form I) and orthorhombic (form II). The parallel packing of flat hydrogen bonded layers in the metastable form II results in compaction properties superior to the thermodynamic stable form I which contains corrugated hydrogen bonded layers of molecules. In this study, the structure of Paracetamol (PCA)-Oxalic acid (OXA) co-crystal has been analyzed and found layered structure similar to PCA form II which enhance ability to form tablet. The Density Functional Theory (DFT) has been conducted to find some physicochemical properties of co-crystal. It was observed that the lattice energy of co-crystal is more than that of PCA form II showing more stability on co-crystal. The energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO gap) in co-crystal was found less than PCA form II showing bigger enhancement of reactivity.

Transition of Sulphide Self-Heating from Stage A to Stage B

Previous work has shown that sulphide self-heating occurs in three distinct stages, referred to as Stage A, Stage B and Stage C. In this publication, the focus is the transition from Stage A to Stage B which occurs at ca. 100 °C. Background literature hints that the transition corresponds to the transformation of the rhombic form of elemental sulphur to the more reactive monoclinic form that occurs at 96 °C. A test apparatus is modified for adiabatic heating to track the transition. The results support this transformation of sulphur as being key to the transition, and the transition temperature is thus modified to 96 °C. Variations in a sample’s response under adiabatic conditions are observed and possible reasons are discussed. Testing in adiabatic mode provides new insights into the sulphide self-heating process that complements the test designed to identify propensity to self-heat.

Synthesis and Structure of [Fe(TPA)Cl2](ClO4) and [{Fe(TPA)Cl}2O](ClO4)2 Where TPA = Tris-(2-pyridylmethyl)amine

[Fe(TPA)Cl2](ClO4), where TPA is tris-(2-pyridylmethyl)amine, crystallizes in the orthorhombic space group P212121 with Z = 4, a = 8.6264(10) Å, b = 15.459(3) Å, and c = 16.008(3) Å. The structure was determined at 110 K from 4333 reflections (3520 observed) with R = 0.041 (Rw = 0.082). The iron is pseudo-octahedral with the two chloride ions cis. The Fe-Cl bond trans to the tertiary amine is shorter. [{Fe(TPA)Cl}2O](ClO4)2 exhibits two polymorphic monoclinic forms, and the monohydrate also crystallizes in a monoclinic form. For the P21/c polymorph, Z = 2, a = 10.839(2) Å, b = 15.956(3) Å, c = 12.416(2) Å, β = 107.024(10)°, and the structure was determined at 95 K from 6514 reflections (3974 observed) with R = 0.052 (Rw = 0.099). For the C2/c polymorph, Z = 4, a = 20.5023(17) Å, b = 15.2711(13) Å, c = 16.1069(11) Å, β = 124.465(4)°, and the structure was determined at 161 K from 6250 reflections (3130 observed) with R = 0.0632 (Rw = 0.1229). For the hydrate, P21/n, Z = 4, a = 16.201(2) Å, b = 16.980(3), c = 16.451(3), β = 112.234(5)°, and the structure was determined at 100 K from 12,745 reflections (6600 observed) with R = 0.097 (Rw = 0.190). In each of the [{Fe(TPA)Cl}2O]2+ units, each iron is pseudo-octahedral with the chloride and oxide ions cis. The oxide bridge is linear, and the two chlorides are anti. The Fe-N distance for the pyridyl ring trans to the oxide bridge is quite long due to the trans influence of the oxide. Graphic Abstract The X-ray structures of [Fe(TPA)Cl2](ClO4), where TPA is tris-(2-pyridylmethyl)amine, and three polymorphs of dimeric [{Fe(TPA)Cl}2O](ClO4)2 are presented and discussed.

Two new polymorphic forms of combretastatin A-4, an antitumour agent

Two new polymorphic forms of combretastatin A-4 {systematic name: 2-methoxy-5-[(E)-2-(3,4,5-trimethoxyphenyl)ethenyl]phenol, C18H20O5, CA-4}, an inhibitor of tubulin polymerization at the colchicine binding site, were identified. A number of crystallization attempts led to the orthorhombic form, with two molecules in the asymmetric part of the unit cell; obtaining a different form required the experiment to be moved to another laboratory. None of the attempts resulted in the monoclinic form described earlier. The three different forms contain molecules of significantly different geometries, which can be related to conformational freedom, postulated as the result of biological studies. In addition, the packing modes in all three forms are basically different. The structural differences at both the molecular and the supramolecular level have also been studied via calculations of energies and a topological analysis of the electron density. The results confirm the role of weak interactions in the determination of crystal architecture and additionally hint at an explanation for the results of crystallization attempts: the new monoclinic form has significantly lower energy than the form reported earlier.

Study on degradation of diesel pollutants in seawater by composite photocatalyst MnO2/ZrO2

In this paper, the effectiveness of the composite photocatalyst was studied by using manganese dioxide (MnO2)/zirconium dioxide (ZrO2) to degrade diesel pollutants in seawater under visible light.The MnO2/ZrO2 photocatalyst was prepared by co-precipitation and characterized by scanning electron microscopy, X-ray powder diffraction, energy-dispersive spectroscopy and UV-Vis diffuse reflectance spectroscopy analysis. This is the first report on a comprehensive analytical study on the effect of various physio-chemical parameters on diesel degradation using the synthesized MnO2/ZrO2 photocatalysts. The effects of doping ratio of MnO2/ZrO2, dosage, initial diesel concentration, calcination temperature, concentration of H2O2 solutions and illumination time on the diesel degradation were investigated. The degradation of diesel pollution in seawater was optimized by orthogonal experiment. According to the results, the prepared samples were monoclinic form and the MnO2 was successfully doped into the bulk ZrO2. The absorption edge of the MnO2/ZrO2 photocatalysts exhibited red shift, and this red shifts imply enhanced photon absorption under visible light compared with the pure ZrO2. The results showed that under optimum reaction conditions, the degradation rate can reach 92.92%. The result of this study will enable ZrO2 to make more effective use of sunlight and improve the actual value of photocatalytic technology in the field of contaminant treatment.

Structural and Morphological of Pulsed Laser Deposited Magnesium Phthalocyanine (MgPc) Thin Film

Magnesium Phthalocyanine (MgPc) was deposited on a glass substrate by pulsed laser deposition (PLD) using Q-Switching Nd: YAG laser with wavelength 1064(nm), (6Hz) Repetition rate, in addition to different laser energies (200,300,400 and 500 mJ) at room temperature under vacuum condition with (10-3torr). All films were annealed at (298K) for 1hour to attain crystallinity. X-ray diffraction of MgPc powder indicated the fact that MgPc crystallizes in polycrystalline with a monoclinic structure While comparing the MgPc of films, it’s found the intensity of characteristic peak is high as the number and energy of laser pulses increase and the crystallize is monoclinic form is observed in β-form. Miller indices, hkl, values for every one of the diffraction peaks in the spectrum of the XRD have been computed. The characteristic peak of Phthalocyanine (MgPc) is found at 2θ value 6.9137o with the hkl value of {100} for both MgPc powder and deposited thin film. The surface morphology of the films showed more uniform sized grains. EDX and FESEM analysis has shown that there has been an enhancement in the crystallinity and surface morphology as a result of the increase of laser energies and for finding the optimum parameters for which film provides more efficient structural characteristics.

Are Zirconia Bioceramics and Ceramics Intended to Come in Contact with Skin Inert?

Generally speaking, ceramic materials are insensitive to corrosion, compared to most other materials. The present study questions the fact that ceramics are inert. Two major aspects are to be considered: the stability of zirconia over time, the stable tetragonal phase transforming into an unstable monoclinic form; the multitude of manufacturing methods, using various additives, sintering additives, oxides mixing, impurities, grain boundaries, and porosities which strongly influence the corrosion behavior and chemical degradation. In case of the investigated ceramics two paths were pursued:a) Dissolutions of ceramics in a mixture of HNO3 60% and HF 40% ultrapure medium.b) Release of cations from ceramics in various mediums:dental bioceramics in a 0.07 M HCl medium and a 0.1% NaF+0.1% KF medium; ceramics used in jewelry and watchmaking applications in a HCl 0.07 M medium and an artificial sweat medium. By inductively coupled plasma-optical emission spectrometry/mass spectrometry (ICP-OES/MS), traces of significant chemical elements were assessed: Hf, Cr, Y, As, Pb, Al, Fe, Cu, Se, Sb, La, Ni, Co, Sb, Ta, Te, Ba, Sm, Nb, Hg, Cd, Sr, As and Se. In ceramics used in jewelry and watchmaking applications the concentrations found vary from one ceramic to another, including toxic elements such as Te, Ba, As, Pb, Sm, Hg and Cd, therefore being technical zirconia ceramics which are not intended for the medical field. For ceramics used in jewelry and watchmaking applications a screening identification test for Ni, Co, Cu and Fe with strips of type Merckoquant® (Merck, Kenilworth, NJ, USA) was also performed. The obtained data prove that the zirconia ceramics in question are far from being “inert”.

Unprecedented Water Effect as a Key Element in Salicyl-Glycine Schiff Base Synthesis

Salens, as chelating, double Schiff base ligands, are an important group utilized in transition metal catalysis. They have been used to build interesting functional metal-organic frameworks (MOFs). However, salens interacting with amino acids have also found applications in receptors. Here, we intended to form a “green” glycine-derived salen fragment, but the available literature data were contradictory. Therefore, we optimized the synthetic conditions and obtained the desired product as two different crystallographic polymorphs (orthorhombic Pcca and monoclinic P21/c space groups). Their structures differ in conformation at the glycine moiety, and the monoclinic form contains additional, disordered water molecules. Despite the high stability of Schiff bases, these newly obtained compounds hydrolyze in aqueous media, the process being accelerated by metal cations. These studies, accompanied by mechanistic considerations and solid-state moisture and thermal analysis, clarify the structure and behavior of this amino acid Schiff base and shed new light on the role of water in its stability.

Structural elucidation of triclinic and monoclinic SFCA-III – killing two birds with one stone

A part of the system CaO-SiO2–Al2O3–Fe2O3–MgO which is of relevance to iron-ore sintering has been studied in detail. For a bulk composition corresponding to 10.45 wt% CaO, 5.49 wt% MgO, 69.15 wt% Fe2O3, 13.37 wt% Al2O3 and 1.55 wt% SiO2 synthesis runs have been performed in air in the range between 1100 and 1300°C. Products have been characterized using reflected-light microscopy, electron microprobe analysis and diffraction techniques. At 1250°C, an almost phase-pure material with composition Ca2.99Mg2.67Fe3+ 14.58Fe2+ 0.77Al4.56Si0.43O36 has been obtained. The compound corresponds to the first Si-containing representative of the M 14+6n O20+8n polysomatic series of so-called SFCA phases (Silico-Ferrites of Calcium and Aluminum) with n = 2 and is denoted as SFCA-III. Single-crystal diffraction investigations using synchrotron radiation at the X06DA beamline of the Swiss Light Source revealed that the chemically homogenous sample contained both a triclinic and monoclinic polytype. Basic crystallographic data are as follows: triclinic form: a = 10.3279 (2) Å, b = 10.4340 (2) Å, c = 14.3794 (2) Å, α = 93.4888 (12)°, β = 107.3209 (14)° and γ = 109.6626 (14)°, V = 1370.49 (5) Å3, Z = 2, space group P{\overline 1}; monoclinic form: a = 10.3277 (2) Å, b = 27.0134 (4) Å, c = 10.4344 (2) Å, β = 109.668 (2)°, V = 2741.22 (9) Å3, Z = 4, space group P21/n. Structure determination of both modifications was successful using diffraction data from the same allotwinned crystal. A description of the observed polytypism within the framework of OD-theory is presented. Triclinic and monoclinic SFCA-III actually correspond to the two possible maximum degree of order structures based on OD-layers containing three spinel (S) and one pyroxene (P) modules (〈S3P〉). The existence of SFCA-III in industrial iron-ore sinters has yet to be confirmed. Polytypism is likely to occur in other SFCA-members (SFCA, SFCA-I) relevant to sintering as well, but has so far been neglected in the characterization of industrial samples. Our results shed light on this phenomenon and may therefore be also helpful for better interpretation of the powder diffraction patterns that are used for phase analysis of iron-ore sinters.