Strategy To Modify the Crystallization Behavior of EVOH32 through Interactions with Low-Molecular-Weight Molecules

Elements, Atoms, and Electrons Matter and Elements Atoms Atomic Structure Isotopes The Periodic Table Electron Structure of Atoms Covalent Bonding and Molecules Interactions between Atoms Covalent Bonds Are Formed by Sharing Outer Electrons Formulae of Compounds Covalent Bonds Formed by Combining Atomic Orbitals Single Overlap, the Sigma-Bond Double Overlap, the Pi-Bond Molecules with s- and p-Bonds Hybrid Molecular Orbitals Forces Within and Between Molecules Ionic Bonding Polar Covalent Bonds Dipole-Dipole Forces The Hydrogen Bond van der Waals Forces The Hydrophobic Effect Coordinate Bonds Chemical Reactions Rates of Reaction Factors Affecting Rate of Reaction Rate Equations Integrated Forms of Rate Equations Zero-Order Reactions Integrated Form of the Zero-Order Rate Equation First-Order Reactions The Integrated Form of the First-Order Rate Equation Second-Order Reactions Integrated Forms of Second-Order Rate Equations Pseudo-First-Order Reactions Reversible Reactions Equilibrium Water The Water Molecule Ice Water Solutions The Mole Concept Calculating Molar Masses Molarity Colloidal Solutions Diffusion and Osmosis Acids, Bases, and Buffers Ionisation of Water The Hydrogen Ion Acids and Bases Strong Acids and Strong Bases Weak Acids and Weak Bases Ka and Kb Relationship between Ka and Kb pH, pOH, pKw, pKa, pKb Solutions of Weak Acids and Bases Salts and Salt Hydrolysis Buffer Systems Calculating the pH Values of Buffers Indicators Titrations Gases Pressure Measurement of Pressure Ideal Gas Laws Partial Pressures Solubility of Gases Diffusion in Gases Aliphatic Carbon Compounds Simple Molecules Containing Carbon Organic Compounds Alkanes and Alkyl Groups Alkenes Alcohols Thiols Aldehydes and Ketones Carboxylic Acids Amines Lipids, Sugars, and Linkages between Reactive Groups Fatty Acids Esters Glycerol Esters Hemiacetals and Hemiketals Simple Sugars Chirality in Simple Sugars Straight-Chain Sugars Spontaneously Form Rings Sugar Hydroxyls Can Be Chemically Modified Sugars Are Joined Together by Glycosidic Bonds Aromatic Carbon Compounds and Isomerism Benzene Bioactive Aromatic Compounds Isomerism Structural Isomerism Chain, Positional, and Functional Group Isomerism Tautomerism Stereoisomerism Geometrical Isomerism Optical Isomerism Organic and Biological Reaction Mechanisms Reactive Sites and Functional Groups Describing Reaction Mechanisms Bimolecular Nucleophilic Substitution Electrophilic Addition to a Nonpolar Double Bond Elimination to Form an Alkene Nucleophilic Addition to a Polar Double Bond Free Radical Reactions Carbon-Carbon Bond Formation in Biosynthesis Sulphur and Phosphorus The Electron-Shell Structure and Valency of Phosphorus and Sulphur Sulphur The Thiol Group and Thiol Esters Phosphate, Pyrophosphate, and Polyphosphate Phosphate Esters The Role of Phosphate Esters and ATP in Cellular Energy Metabolism Oxidation and Reduction Reactions Oxidation Is Linked to Reduction The Chemical Changes in the REDOX Process Splitting REDOX Reactions Standardising REDOX Half-Reactions Predicting Electron Flow Free Energy and Standard Reduction Potentials Redox Reactions and Nonstandard Conditions Metals in Biology General Properties of Metals in Biology Some Properties of Alkali Metals The Alkaline Earth Metals Transition Metals Role of Metal as Oxygen Carrier Metals Facilitate Biocatalysis The Role of Metal Ions as Charge Carriers The Toxicity of Metals Energy The First Law of Thermodynamics Units of Energy Measurement of Energy Internal Energy, U, and Enthalpy, H Calorimetry Hess's Law Enthalpies of Formation The Second Law of Thermodynamics Free Energy Interaction of DeltaH with TDeltaS Reactions and Equilibrium DeltaG and Equilibrium Activation Energy The Effect of the Temperature on Reaction Rate The Arrhenius Equation Catalysis Enzyme Catalysis Kinetics of Enzyme Reactions Finding Vmax and KM Light Light Is Part of the Electromagnetic Spectrum Wavelength and Frequency The Quantum Theory of Light The Absorption of Light The Relationship between Light Absorption and Concentration The Spectrophotometer The Fate of Absorbed Light Appendix: Derivations of Equations Index

Heating-Induced Phase Transition of Bupropion Hydrobromide Polymorphs

The effects of annealing temperatures at 150, 200 and 240 °C were investigated on the povidone–silica nanocomposite film as a gate dielectric. The thermal gravimetric (TGA) and differential thermal (DTA) analyses showed that the decomposition rate of the nanocomposite increased from around 220 °C. The formation of hydrogen and covalent bonds between the elements of nanocomposite was proved via Fourier transform infrared spectroscopy (FTIR). All the films had low root mean square (0.047–0.12 nm) and leakage current densities (1.32 × 10−5–3.95 × 10−8 A/cm2 at 15 V). The results of deconvoluted X-ray photoelectron spectroscopy (XPS) spectra of the O1s orbital indicated that the Si–OH hydrogen bonds dominating the film were not annealed (55.9%). The Si–OH hydrogen bonds decreased (18%) and the Si–O–Si covalent bonds became dominant (80.36%) in the film annealed at 150 °C. The percentage of Si–O–Si bonds decreased by further increasing the temperature (200 °C) and these bonds disappeared in the film annealed at 240 °C. A peak also appeared at the binding energy which is about 1 eV less than that of the Si–O–Si bonds in the films annealed at 200 and 240 °C. The capacitance and leakage current density of fabricated FETs based on nanocomposite dielectric film annealed at 150 and 200 °C decreased. The degradation of cross-linked structure in the dielectric film annealed at 240 °C and the presence of polar Si–OH groups in the nanocomposite dielectric film which was not annealed increased the capacitance and leakage current densities.

The influence of different synthetic pathways on the phase transition and side-chain crystallization behavior of cellulose ethers was systematically investigated by a combination of differential scanning calorimetry (DSC), small and wide-angle X-ray scattering (SAXS, WAXS) and Fourier transform infrared spectroscopy (FTIR) techniques. DSC investigation indicated that the melting temperature and crystallization temperature, respectively, of cellulose derivatives that were synthesized by homogeneous reactions in cellulose solutions differed from those of cellulose aggregates in a swollen state synthesized by heterogeneous reactions; this implies that the synthetic pathway had a strong effect on the side-chain crystallization behavior in comb-like polymers. WAXS results showed that the cellulose ethers prepared by homogeneous reaction packed into hexagonal crystals, while those prepared by heterogeneous reaction exhibited multiple crystals. These phenomena may be understood as a result of the effect of the regularity of the main chain and the difference in hydrogen bonding interactions in the two kinds of cellulose ethers. For the latter, the presence of free –OH groups at the C-6 position in the samples obtained via the heterogeneous reaction is considered to contribute critically to intermolecular hydrogen bonds that promote crystallization of the system.

Molecular mobility of imidazoles in molten state as a key factor to enhance proton conductivity

Surface hydroxyl groups on TiO2 play an important role for the photoinduced hydrophilicity as well as for photocatalytic reactions. Adsorbed species such as water and organic compounds are expected to affect the hydroxyl group behaviour on the TiO2 surface, however, their influences have to date not been clearly determined. Herein, a detailed investigation of H2O and D2O adsorption on the TiO2 surface (anatase) in the dark and under UV(A) irradiation is reported using ATR-FTIR spectroscopy. The adsorption and photocatalytic degradation of acetate on the TiO2 surface was also investigated in H2O and D2O. Adsorption of H2O with different ratios of D2O revealed an isotopic exchange reaction occurring on the surface of TiO2 in the dark. This isotopic exchange leads to a change in the behaviour of acetate with the intensity of the OH bending band between the carboxylate and the OH group at 900 cm-1 decreasing and ultimately disappearing in the dark. Upon illumination with UV(A) light both, OH and OD groups are formed, which in turn increase the hydrophilicity of the TiO2 surface. The amount of OH and OD groups was found to increase in the presence of molecular oxygen. This increase is most likely caused by the photoadsorption of H2O and D2O due to photoinduced charge transfer processes [1]. On the other hand, the investigations show that during UV(A) irradiation the acetate molecules can adsorb again on the TiO2 surface which is explained by an increased surface area due to a de-aggregation of the particles agglomerates [2]. Based upon the observed correlation between the carboxylate and the OH and/or OD groups at neutral pH (pH ≈ pHzpc) it is obvious that acetate preferentially adsorbs on the positively charged anatase in a monodentate structure. As an in-situ technique, ATR-FTIR studies provide evidence of the adsorption behaviour of water and D2O on TiO2 surfaces thus yielding new insights into the mechanism of photoinduced hydrophilicity and of photocatalytic reactions.

Effects of organic nucleating agents and zinc oxide nanoparticles on isotactic polypropylene crystallization

Neighbouring groups can be strategically located to polarise HO.OH intramolecular hydrogen bonds in an intended direction. A group with a unique hydrogen-bond donor or acceptor character, located at hydrogen-bonding distance to a particular OH group, has been used to initiate the hydrogen-bond network and to polarise a HO.OH hydrogen bond in a predicted direction. This enhanced the donor character of a particular OH group and made it a cooperative hydrogen-bond centre. We have proved that a five-membered-ring intramolecular hydrogen bond established between an amide NH group and a hydroxy group (1,2-e,a), which is additionally located in a 1,3-cis-diaxial relationship to a second hydroxy group, can be used to select a unique direction on the six-membered-ring intramolecular hydrogen bond between the two axial OH groups, so that one of them behaves as an efficient cooperative donor. Talose derivative 3 was designed and synthesised to prove this hydrogen-bonding network by NMR spectroscopy, and the mannopyranoside derivatives 1 and 2 were used as models to demonstrate the presence in solution of the 1,2-(e,a)/five-membered-ring intramolecular hydrogen bond. Once a well-defined hydrogen-bond is formed between the OH and the amido groups of a pyranose ring, these hydrogen-bonding groups no longer act as independent hydrogen-bonding centres, but as hydrogen-bonding arrays. This introduces a new perspective on the properties of carbohydrate OH groups and it is important for the de novo design of molecular recognition processes, at least in nonpolar media. Carbohydrates 1-3 have shown to be efficient phosphate binders in nonpolar solvents owing to the presence of cooperative hydroxy centres in the molecule.

The crystallization and multiple melting behavior of poly(phenylene sulfide) (PPS) and its blends with amorphous thermoplastic bisphenol A polysulfone (PSF) and phenolphthalein poly(ether ketone) (PEK-C), crystalline thermoplastic poly(ether ether ketone) (PEEK), and thermosetting bismaleimide (BMI) resin were investigated by a differential scanning calorimeter (DSC). The addition of PSF and PEK-C was found to have no influence on the crystallization temperature (Tc) and heat of crystallization (ΔHc) of PPS. A significant increase in the value of Tc and the intensity of the Tc peak of PPS was observed and the crystallization of PPS can be accelerated in the presence of the PEEK component. An increase in the Tc of PPS can also be accelerated in the BMI/PPS blend, but was no more significant than that in the PEEK/PPS blend. The Tc of PPS in the PEEK/PPS blends is dependent on the maximum temperature of the heating scans and can be divided into three temperature regions. The addition of a second component has no influence on the formation of a multiple melting peak. The double melting peaks can also be observed when PPS and its blends are crystallized dynamically from the molten state. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 637–644, 1998

The dissolution temperature of the crystalline platelets of polyacrylonitrile in propylene carbonate bears a linear relationship with the crystallization temperature Tc. The step heights ζ of the crystalline platelets measured by electron microscopy increase with increase in crystallization temperature, in accordance with the current theory of high polymer crystallization in dilute solution. The step heights were found to be 100, 130, and 150 A. for Tc of 95, 116, and 125°C., respectively. By extrapolating the experimental values of Ts to the value at ζ = ∞, a characteristic constant (Tm)∞ is obtained. The (Tm)∞ was 175°C. for the sample studied in propylene carbonate. The interfacial free energy, σe, calculated from the melting point and the step height is of the order of 1950 cal./mole of emerging chain repeat unit, or 45 ergs/cm.2 as compared to 1900 cal./mole or 70 ergs/cm.2 for polyethylene. It appears that the surface free energies of various organic polymers are remarkably similar. Although the degree of crystalline perfection of polyacrylonitrile is inferior to that of organic crystals with three‐dimensional order, polyacrylonitrile displays a crystallization behavior similar to other semicrystalline polymers; this conclusion is supported by the linear relationship between Ts and Tc, the variation of the step height with the crystallization temperature, and the sigmoid relationship of the fractional change in specific volume as a function of time during crystallization.

Reactivite du dimethylcyanamide vis a vis des groupements o- et N-epoxyde et hydroxyle

The release of ubiquitin from attachment to other proteins and adducts is critical for ubiquitin biosynthesis, proteasomal degradation and other cellular processes. De-ubiquitination is accomplished in part by members of the UCH (ubiquitin C-terminal hydrolase) family of enzymes. We have determined the 2.25 A resolution crystal structure of the yeast UCH, Yuh1, in a complex with the inhibitor ubiquitin aldehyde (Ubal). The structure mimics the tetrahedral intermediate in the reaction pathway and explains the very high enzyme specificity. Comparison with a related, unliganded UCH structure indicates that ubiquitin binding is coupled to rearrangements which block the active-site cleft in the absence of authentic substrate. Remarkably, a 21-residue loop that becomes ordered upon binding Ubal lies directly over the active site. Efficiently processed substrates apparently pass through this loop, and constraints on the loop conformation probably function to control UCH specificity.

PutA is a novel flavoprotein in Escherichia coli that switches from a transcriptional repressor to a membrane-bound proline catabolic enzyme. Previous crystallographic studies of the PutA proline dehydrogenase (PRODH) domain under oxidizing conditions revealed that FAD N(5) and the ribityl 2'-OH group form hydrogen bonds with Arg431 and Arg556, respectively. Here we identify molecular interactions in the PutA PRODH active site that underlie redox-dependent functional switching of PutA. We report that reduction of the PRODH domain induces major structural changes in the FAD cofactor, including a 22 degrees bend of the isoalloxazine ring along the N(5)-N(10) axis, crankshaft rotation of the upper part of the ribityl chain, and formation of a new hydrogen bond network involving the ribityl 2'-OH group, FAD N(1), and Gly435. The roles of the FAD 2'-OH group and the FAD N(5)-Arg431 hydrogen bond pair in regulating redox-dependent PutA-membrane associations were tested using FAD analogues and site-directed mutagenesis. Kinetic membrane binding measurements and cell-based reporter gene assays of modified PutA proteins show that disrupting the FAD N(5)-Arg431 interaction impairs the reductive activation of PutA-membrane binding. We also show that the FAD 2'-OH group acts as a redox-sensitive toggle switch that controls PutA-membrane binding. These results illustrate a new versatility of the ribityl chain in flavoprotein mechanisms.

Isotactic Polypropylene (iPP) is a widely used polymer due to its excellent mechanical and thermal properties, as well as its chemical resistance. The crystallization behavior of polypropylene is influenced by several factors, such as temperature, cooling rate, and pressure. The effect of pressure is significant for both scientific and technological points of view, since in important industrial processing techniques the polymer solidifies under high pressures. In this paper, the study of the effect of pressure on the crystallization kinetics of iPP was conducted using a dilatometer in the pressure range from 100 to 600 bar and under two cooling rates: 0.1 and 1 °C/s. The morphology of the samples was characterized using DSC, optical microscopy, and X-ray diffraction. The results showed that pressure had a larger effect on specific volume changes at higher temperatures (in the melt state) than at lower temperatures (in the solid state). The polymer crystallization, which determined the transition between the melt and solid state, occurred at higher temperatures with increasing pressure. The cooling rate affected the crystallization process, with higher cooling rates leading to crystallization at lower temperatures. The size of the spherulites decreased with increasing cooling rates. The crystallinity evolution curves showed a linear relationship between the crystallization temperature and pressure. The study used a Kolmogoroff–Avrami–Evans model to describe the evolution into isotropic structures, and the predictions of the model accurately described the effect of pressure and cooling rates on the final spherulite radii.

Experimental and first-principles study of the interactions between graphene oxide and carbon nanotube