Optimization of process parameters of γ-polyoxymethylene synthesis

Two procedures for γ-polyoxymethylene production are considered: the existing commercial procedure and high-efficiency perspective procedure, differing in the chain-transfer agents and catalysts used. Mathematical models of the dependences of the yield and weight-average particle size of γ-polyoxymethylene on the synthesis process parameters for the commercial and perspective technologies are constructed using the method of optimum experiment design. The mathematical models were used for determining the optimum synthesis parameters allowing preparation of γ-polyoxymethylene with the weight-average particle size d ≤ 14 μm in maximal yields.     

Use of polyethylene glycol in the process of sol–gel encapsulation of Burkholderia cepacia lipase

Lipases from Burkholderia cepacia were encapsulated using polyethylene glycol (PEG, M _w 1500) at various concentrations (0.5–3.0 %, w/v) as an additive during the sol–gel immobilisation process. Matrixes immobilized in the presence and absences of additives were characterized by thermal analysis [thermogravimetric (TG) and differential scanning calorimetry (DSC)], scanning electron microscopy (SEM), enzymatic activity, and total activity recovery yield (Ya). The addition of PEG increased the activity values, with Ya just above 1.0 % (w/v) in the presence of PEG. The additional of 1.0 % (w/v) PEG increased enzyme activity from 33.98 to 89.91 U g^?1 and the values of recovery yield were 43.0–91.4 %, compared to values of the samples without PEG. PEG enhanced the thermal stability of the matrix structure in the temperature range 50–200 °C, as confirmed by TG and DSC analyses. This was influenced by the presence of water bound to the matrix. The SEM micrographs clearly showed an increase in the number of deposits on the material surface, producing matrices with greater porosity.     

‘Apples’ and ‘oranges’: comparing the structural aspects of biomineral- and ice-interaction proteins

The title of this review describes structural comparisons of protein classes whose task is to identify and interact with biological solids (minerals and ice). To date, the following trends have been noted: (1) biomineral-interaction proteins typically adopt unfolded, open conformations, and, where mineral binding motifs have been identified, these sequences exhibit structural trends towards extended, random coil, or other unstable secondary structures; (2) ice-interaction proteins typically adopt folded structures, featuring stable secondary structure preferences (α-helix, β-sheet, β-helix, etc.) and stable, planar ice binding motifs that exploit hydrophobicity and van der Waals’ interactions for ice binding.     

‘Verification’ versus ‘validation’: a terminological comparison

The present diversity in the definitions and relations of ‘verification’ and ‘validation’ is impractical for such transdisciplinary concepts. General dictionaries, international special language vocabularies and minor lists show that the respective recent formulations by the International Organization for Standardization (ISO) and the Joint Committee for Guides in Metrology (JCGM) are the most quoted. The characteristics of these concepts are elucidated terminologically, and separate concept systems are made for ISO and JCGM to arrive at a preference for a generic rather than an associative relation.     

The meaning of ‘concentration’

Terminology within a small laboratory community can be informal without danger of misunderstanding, but communication with a wider audience and not least in publications, needs unequivocal terms for defined concepts. As an example, the many meanings of “concentration” are explored to present a systematic nomenclature, including a concept diagram.

Green process of fuel production under porous γ-Al2O3 catalyst: Study of activation and deactivation kinetic for MTD process

One of the methods of industrial dimethyl ether production is the catalytic dehydration of methanol. In this research work, methanol dehydration reactor has been modeled using continuous model and its results have been compared with experimental works and Voronoi pore network model. A 1D heterogeneous dispersed plug flow model was utilized to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether. The mass and heat transfer equations are numerically solved for the reactor. The concentration of the reactant and products and also the temperature varies along the reactor, therefore the effectiveness factor would also change in the reactor. We used the the effectiveness factor that was simulated according to the diffusion and reaction in the catalyst pellet as a Voronoi pore network model. Sensitivity analysis was performed to determine the influence of T, P and weight hourly space velocity on performance of the chemical reactor. Acceptable agreement was reached between the measured and the model data. The results showed that the maximum reaction conversion was obtained about 90 % at WHSV = 10 h^?1 and T = 560 K, while the inlet temperature (T_inlet) had a greater effect on methanol conversion. In addition, the effect of water in the feed on methanol conversion was quantitatively studied. Also, the deactivation kinetics of γ-Al₂O₃ heterogeneous-acidic catalyst in methanol to dimethyl ether dehydration process was studied using integral analysis method. Based on independent deactivation kinetics, a second order was found that accurately fitted the experimental conversion time data. The main reaction activation energies and catalyst deactivation energies were 143.1 and ?102.1 kJ/mol, respectively.     

‘Bad’ distributions of good data: unusual statistics of structural databases

Structural Chemistry - Distributions of data taken from crystal structure databases, display unusual statistical properties like non-Gaussian shape, polymodality, and heavy tails. These features,...     

Thermal investigation of ‘molten starch’

Detailed thermal analysis studies have shown that a ‘molten starch’ phase is obtained during controlled heating of starch. Before the ‘molten’ stage, depolymerisation of starch produces lower molecular weight compounds like dextrins, oligo, di- and monosaccharides, as well as other types of compounds. These compounds should have ideal properties for plasticizing starches because of the similarities of the molecules, helping lower phase changes in collaboration with molecular weight decrease. Interestingly, it was found previously that these materials only act as adhesives in a narrow temperature range around 523 K (250 °C) (Shuttleworth et al. J Mater Chem 19(45):8589–8593, 2009). Materials were investigated using thermal and mechanical analyses of single lap joints.     

Influence of process parameters on the sol–gel synthesis of nano hydroxyapatite using various phosphorus precursors

Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ has attracted widespread interest from both orthopedic and dental fields due to its excellent biocompatibility and tissue bioactivity properties. Since nanophase materials can mimic the dimensions of constituent components of natural tissues, the implants developed from nanophase material could serve as a successful alternative. However, the defects of hydroxyapatite ceramics, mainly brittleness and low fracture toughness, have been overcome by the use of nanophase hydroxyapatite coatings on the implant surfaces that integrate the good mechanical properties of metals and the bioactivity of hydroxyapatite. In the present investigation, Sol?Cgel hydroxyapatite was prepared from two different phosphorus precursors such as triethyl phosphate and phosphorus pentoxide respectively with calcium nitrate tetrahydrate as a calcium precursor. The effects of pH and liquid P³¹ Nuclear Magnetic Resonance spectroscopy for the solution aged at different periods were investigated and the synthesized hydroxyapatite powder was characterized by Transmission electron microscopy, X-ray Powder Diffraction, Fourier transform infrared spectroscopy and thermal analysis respectively. In order to fully understand the bioactivity of the synthesized materials, they were coated on 316L Stainless Steel implant surface by spin coating method at the spin speed of 2,000 Revolutions per minute. The effect of nanoparticles on the surface of 316L Stainless Steel implant was studied by adhesive strength measurements. The corrosion resistance property of the hydroxyapatite coatings was evaluated by electrochemical impedance analysis. From the results, it was observed that the hydroxyapatite coatings obtained from different precursors have very high resistance to corrosion with higher adhesive strength.     

Photo-oxidative degradation of polyethylene: Effect of polymer characteristics on chemical changes and mechanical properties. Part 1—Quenched polyethylene

Photo-oxidative degradation of quenched samples of linear low density (LLD), medium density (MD) and two kinds of high density (HD) polyethylene (PE) films was studied using a medium-pressure mercury lamp. Greater amounts of crosslinking and build up of oxidation products were noticed in LLDPE than the other samples. The primary products of interaction between dienes and oxygen are considered to participate in the initiation of the photo-oxidation reactions. Using the FT-IR difference spectrum technique, the amount of branch concentration in the photo-irradiated PE samples was determined. Oxidation damage at the boundary region between crystalline and amorphous phases is considered to be important in determining the embrittlement time.     

Low generational polyamidoamine dendrimers to enhance the solubility of folic acid:A‘‘dendritic effect’’investigation

Low generational(G0–G2,G for generation) polyamidoamine(PAMAM) dendrimers were investigated as enhancers to improve the aqueous solubility of folic acid at pH 11 and pH 5.In these two cases,the solubility of folic acid increases with both the dendrimer concentration and generation.However,the solubilization mechanism is different.The electrostatic interaction between the primary amines of dendrimers and the ionized carboxylic groups of folic acid dominates the dissolution process at pH 11 while the increase of the solubility of folic acid at pH 5 is attributed to the hydrophobic encapsulation inside the dendrimer molecules.In addition,for comparison ethylenediamine was used as a small molecule control to examine the ‘‘dendritic effect' in the dendrimer-related solubilization process.Interestingly,PAMAM dendrimers exhibit,at pH 5,a significant superiority over ethylenediamine in enhancing solubility,whereas this ‘‘dendritic effect' cannot be observed under the basic condition.     

Kinetics and optimisation of process parameters for electrochemical generation of uranous ions in nitric acid–hydrazine media

For the quantitative generation of uranous from uranyl ions in the presence of hydrazine in nitric acid medium, electrochemical reduction was carried out in divided and undivided cells. The influence of process conditions, viz. current density, concentration of nitric acid and hydrazine was studied for 50, 100 and 150 g/l of U(VI) solutions. The performance of the cathodes (titanium and platinum) was evaluated by calculating the conversion efficiencies in the reduction process using these electrodes for the reduction of 100 g/l U(VI) at 6 mA/cm² as the cathodic current density. Batch mode experiments using Ti cathode revealed the reduction reaction of U(VI) to follow zero order kinetics and the simultaneous reduction of nitric acid to follow first order kinetics. From the temperature dependence, the activation energy for the reduction of U(VI) was determined to be 4.05 kJ/mol. The chemical stability of U(IV) in nitric acid–hydrazine medium, under ambient conditions of temperature and pressure was established from the amount of U(VI) produced from U(IV) by aerial oxidation over a period of 16 weeks.     

Synthesis and Crystal Structure of N—（1‘’‘’—Phenyl—2‘’‘’—hydroxyethyl）—2,3—naphthylenedicarboximide

IntroductionThe design and the synthesis of new chiral ox-azoline[1,2 ] and C2 symmetric bis( oxazoline) ligandsand the application of their metal complexes inasymmetric catalytic reactions have inspired manyscientists to great exertions in recent years[3— 8] .Our interest has been focussed on the studies ofenantioselective transition metal catalysis ofhetero-cyclic ligands[9— 11] . In the synthesis of our new de-signed ligands,what is crucial is to select a rigidcyclic backbone. Bis( oxazo…     

Formation of crystalline Na2V6O16·3H2O ribbons into belts and rings

Single-crystalline nanobelts and nanorings of Na(2)V(6)O(16)·3H(2)O structures have been facilely synthesized through a direct hydrothermal reaction between NaVO(3) and H(3)PO(4), without the addition of any harmful solvents or surfactants. The analytical techniques of scanning electron microscopy, transmission electron microscopy (TEM), powder X-ray diffraction, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, Fourier transform infrared, high-resolution TEM, and selected-area electron diffraction have been used to characterize the morphology, composition, and structure of the synthesized products. The Na(2)V(6)O(16)·3H(2)O nanobelts are up to several hundreds of micrometers in length and 100-300 nm in thickness, and for nanorings, the diameters are 4.5-6.5 μm. H(3)PO(4) plays a key role in maintaining the pH of the solution as well as producing PO(4)(3-) ions in solution. The chemical reactions and a possible growth mechanism involved in the formation of Na(2)V(6)O(16)·3H(2)O nanobelts and nanorings are briefly discussed.