An analysis of fractal geometry of macromolecular gelation

With fractal geometry theory and based on experiments, an analysis of fractal geometry behavior of gelation of macromolecules was carried out. Using the cross-linking copolymerization of styrene-divinylbenzene (DVB) as an example, through the determinations of the evolution of the molecular weight, size and the dependence of scattering intensity on the angle of macromolecules by employing laser and synchrotron small angle X-ray scattering, respectively, this chemical reaction was described quantitatively, its fractal behavior was analyzed and the fractal dimension was also measured. By avoiding the complex theories on gelation, this approach is based on modern physical techniques and theories to perform the analysis of the behavior of fractal geometry of macromolecular gelation and thus is able to reveal the rules of this kind of complicated gelation more essentially and profoundly.     

Multielement analysis of foods by neutron capture prompt γ-ray activation analysis

A method is described for the determination of H, B, Cl, K, Na, S, Ca, and Cd in foods using in-beam neutron capture prompt -ray activation analysis. Special calibration procedures were necessary because of matrix-related thermal neutron scattering-induced sensitivity and background enhancements. Detection limits and sensitivities are presented for best-case and worst-case irradiation conditions. The method was applied to multielement analysis of 41 foods and to B, Cl, and K analysis of 13 orange juice produts in conjunction with analysis by inductively coupled plasma atomic emission spectrometry. The purpose of the latter application was to study B losses during acid digestion.     

Excitation-emission-lifetime analysis of multicomponent systems—I. Principal component factor analysis

This paper defines methods and notation for the application of principal component factor analysis (PCFA) to porphyrin excitation-emission-lifetime data obtained from luminescence spectroscopy. We are able to determine non-exponential decay kinetics and the spectra of individual chemical species in impure or mixed samples with this technique. A data array of intensities, I(excitation wavelengths) × J(emission wavelengths) × K(times), is reduced to a P × P × P array by projection onto the principal components. The spectra of the emitting species are obtained by iteration from an initial guess, which is made by reference to the projections of the observed spectra onto a plane in the three-dimensional principal component vector space. It is shown that weighting the data with the variances speeds convergence of the iteration process.     

Determination of selectivity of HPLC systems by correspondence factor analysis

Correspondence factor analysis （CFA） was employed to study the selectivity of 14 HPLC systems. The tested LC systems were classified as reversed-phase （RP）, ion-exchange （IE） and hydrophilic interaction chromatography （HILIC） modes. It was found that the retentions of the hydrophilic solutes on HILIC column were significantly influenced by the second-order effects besides their hydrophilic properties. Organic modifiers and residue silanol groups on silica surface both participated in retention. HypersilTM amino column performed separation in the HILIC mode at appropriate conditions, and its retention mechanism was more similar to that of HILIC silica column than that of HILIC column coating poly（aspartamide） groups.     

NMR-based analysis of protein–ligand interactions

Physiological processes are mainly controlled by intermolecular recognition mechanisms involving protein–protein and protein–ligand (low molecular weight molecules) interactions. One of the most important tools for probing these interactions is high-field solution nuclear magnetic resonance (NMR) through protein-observed and ligand-observed experiments, where the protein receptor or the organic compounds are selectively detected. NMR binding experiments rely on comparison of NMR parameters of the free and bound states of the molecules. Ligand-observed methods are not limited by the protein molecular size and therefore have great applicability for analysing protein–ligand interactions. The use of these NMR techniques has considerably expanded in recent years, both in chemical biology and in drug discovery. We review here three major ligand-observed NMR methods that depend on the nuclear Overhauser effect—transferred nuclear Overhauser effect spectroscopy, saturation transfer difference spectroscopy and water–ligand interactions observed via gradient spectroscopy experiments—with the aim of reporting recent developments and applications for the characterization of protein–ligand complexes, including affinity measurements and structural determination.     

Evolved gas analysis–ion attachment mass spectrometric analysis of decacarbonyl dimanganese pyrolysis

Evolved gas analysis?Cion attachment mass spectrometric analysis of the principal species produced by the pyrolysis of Mn₂(CO)₁₀ in an infrared image furnace indicated the presence of Mn(CO)₅ in the gas phase. This observation indicates that Mn₂(CO)₁₀ was in equilibrium with Mn(CO)₅. We also studied the temperature dependence of the mass spectrum to obtain information about the kinetics of the Mn₂(CO)₅ dissociation reaction. From the temperature dependence of the peak for Mn(CO)₅Li⁺ (m/z 202), we calculated the apparent activation energy of Mn(CO)₅ dissociation from solid Mn₂(CO)₁₀. The calculated activation energy (274.57?kJ/mol) is compared with previously reported experimental and calculated values of Mn?CMn bond dissociation energies.     

Thermal analysis of the improved Hummers’ synthesis of graphene oxide

Journal of Thermal Analysis and Calorimetry - The improved Hummers’ synthesis of graphene oxide (GO) from graphite is investigated to monitor how the functional groups form during the...     

Profile analysis of infrared absorption of NH stretching band

The shape of the infrared NH stretching band of N-methyl aniline in different solvents has been studied. Carbon tetrachloride, tetrachloroethylene, carbon disulfide, benzene, anisole, chloroform, dioxane and di-n-butyl ether were used as solvents. Band shapes observed show self-association of N-methyl aniline in dioxane, di-n-butyl ether and chloroform solutions.Moments analysis and time autocorrelation function calculations have been performed. The frequencies of the band maximum are more sensible to the solvent than the half band width and the band shape. Moments values depend strongly on the integration interval. The correlation function shows non-exponential decays in a short time range (0–0.16 ps) for any solutions, and this indicates that the molecular motions do not obey a simple rotational diffusion model. Exponential decays show at times longer than 0.16 ps. Relaxation times are linearly related with the solvents viscosity.     

Nmr analysis of α-methyl branched organic acids

A methode for analyzing α-methyl branched organic acids has been developed using NMR spectroscopy. The composition is determined in terms of α,α-dimethyl, α-methyl-α-alkyl and α-methyl strnetures. Peak assignmunts were made on the basis of model compound studies. This technique has been successfully used in analyzing Koch acid synthesis mixtures.     

Thermal analysis of protein–metallic ion systems

Advanced thermal analysis methods, such as temperature modulated DSC (differential scanning calorimetry) and quasi-isothermal TMDSC were used to analyze the protein–metallic ion interactions in silk fibroin proteins. The precise heat capacities were measured and theoretically predicted in this study. To remove bound water and simplify the system, a thermal cycling treatment through both standard DSC and TMDSC was used to detect the underlying heat capacity and reveal the phase transitions of the silk–metallic salts system. Results show that K⁺ metallic salts play the role of plasticizer in silk fibroin proteins, which reduces the glass transition (T_g) of the pure silk protein and negatively affects its structural thermal stability. On the other hand, Ca²⁺ metallic salts act as an anti-plasticizer, and increase the glass transition and the thermal stability of the silk protein structure. This indicates that the thermal analysis methods offer a new pathway to study protein–metallic ion systems, yielding very fruitful information for the study of protein structures in the future.     

Modeling and conformation analysis of β-cyclodextrin complexes

Summary A series of -cyclodextrin complexes containing various guest molecules was studied using computer-aided molecular modeling and conformation analysis techniques. The geometry of each complex was studied using crystallographic data. The positions of the glycosidic O4 atoms indicate that the -cyclodextrin molecules are elliptically distorted. This distortion can be related to the van der Waals volume of the guest molecules. This correlation is different for aromatic and non-aromatic guest compounds. Rigid body docking experiments demonstrated that in crystal structures the guest molecule occupies a position in the cavity of nearly minimum interaction energy when there are no other molecules having interactions with the guest molecule. From the crystallographic data several rules could be deduced which seem to determine the conformation of -cyclodextrin molecules in complexes. A procedure was developed to construct -cyclodextrin molecules that are able to encompass guest molecules having a given van der Waals volume.     

Determination of thorium with DBF-arsenaz by flow-injection analysis

A sensitive,selective,rapid,simple,and convenient method for the determination of thoriumwas developed.The method was based on the color reaction of thorium with DBF-arsenazo in astrong acidic medium (4 mol/L HCI).The flow-injection technique was used with an automated flow-injection analyzer.Beer's law was obeyed in the range of 0—1.4 μg/mL.The relative standarddeviations were less than 1%.     

Bifurcation analysis of reaction–diffusion Schnakenberg model

Bifurcations of spatially nonhomogeneous periodic orbits and steady state solutions are rigorously proved for a reaction–diffusion system modeling Schnakenberg chemical reaction. The existence of these patterned solutions shows the richness of the spatiotemporal dynamics such as oscillatory behavior and spatial patterns.     

CFD analysis of a TG–DSC apparatus

A ThermoGravimetric analyser with differential scanning calorimetry (TG–DSC) has been studied during the fusion of an indium sample using both an experimental procedure and a CFD simulation. To do so, a CAD model of the real device was built and meshed in detail, in order to take into account the small scale processes which occur inside the crucibles. Several theoretical models, some previously existing in the CFD software used and others developed ad hoc, were applied to simulate the whole facility. Therefore, realistic boundary conditions and a PID-based control system already developed for previous studies had to be used. The validation of the CFD model was done by comparing the outcome of the resulting simulation to the results obtained by experimental procedure in a case where natural convection is the main heat and mass transfer mechanism. This comparison was made for two different heating rates inside the furnace. Typical characteristics of phase change process inside a TG-DSC as thermal lag, onset temperature or heat flow exchange during the fusion could be analysed. As well, a more detailed approach to physical phenomena taking place inside the furnace could be done, since CFD simulations allow to obtain data which is not achievable experimentally. Besides, a valid CFD model for a TG-DSC could be later used in further CFD simulations.     

Sequential analysis of dimethyl sulfur compounds in seawater

A sequential method for the determination of dimethyl sulfur compounds, including dimethylsulfide （DMS）, dimethylsulfonio- propionate （DMSP） and dimethylsulfoxide （DMSO）, in seawater samples has been developed. Detection limit of 2.5 pmol of DMS in 25 mL sample, corresponding to 0.10 nmol/L, was achieved. Recoveries for dimethyl sulfur compounds were in the range of 68.6- 78.3%. The relative standard deviations （R.S.D.s） for DMS, DMSP and DMSO determination were 3.0, 5.4 and 7.4%, respectively.     

Thermal analysis of Vectran® fibers and films

Vectra^® liquid crystalline polymers (LCP's) were introduced as commercial products in the mid-1980's. The first of these (Vectra A130) was a wholly aromatic thermotropic copolyester ofp-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. Vectra A130 is a thermotropic LCP that can be melt spun into filaments that on heat treatment are characterized by high strength and high modulus. Vectra resin can also be extruded into films. In the fiber or film form this material is commercially known as Vectran^®. Heat treatment enhances the tensile strength of Vectran fiber variants. Because of this, the elucidation of the physical transformations taking place in the internal structure of the material during heating has always been an important subject. Several thermal techniques are used to indicate clearly that what is observed as a glass transition is unlike the conventional glass transition in typical semicrystalline polymers. There is also an indication of the presence of multiple states of mesophase aggregation that collapse into a single state when taken to high enough temperatures.     

Sedimentation analysis of organic–inorganic hybrid colloids

Hybrid organic–inorganic latex particles are synthesized to combine the beneficial properties of the constituents which thus lead to synergistic improvement in the properties. The properties of hybrid particles are dependent on the successful hybridization process, thus controlling or tuning of such processes by effective characterization is immensely important. Analytical ultracentrifugation provides these characterization possibilities owing to its high statistical capability and ability to characterize multiple parameters. The use of different detection methodologies can help in generating valuable information on the overall size and density distributions of the particles. Apart from that, it is also possible to quantify the presence of any free polymer and inorganic particles in the hybrid latex which would affect the properties of hybrid latexes. By following the densities of the pure and hybrid particles, it is also possible to quantify the amounts of the constituent phases in the hybrid particles. The density gradients generated in preparative ultracentrifugation also provide additional possibilities for the characterization of the hybrid particles which have densities higher than the measurable range in the analytical ultracentrifuge. Evolution of hybrid particles can also be studied as a function of time. It also provides advantage of separation of the various fractions for further characterization.     

Vibrational analysis of substituted nitrobenzenes. I—Vibrational spectra,normal coordinate analysis and transferability of force constants of some chlorinated nitrobenzenes

The Raman and Fourier transform infrared spectra of 2,3-dichloro-, 2,4-dichloro-, 2,5-dichloro-, 3,4-dichloro-, 3,5-dichloro-, 2,3,4-trichloro-, 2,4,5-trichloro-, 2,4,6-trichloro-, 2,3,5,6-tetrachloro- and pentachloronitrobenzene were recorded. Raman polarization measurements were made wherever possible. A normal coordinate analysis was carried out for both the in-plane and out-of-plane vibrations of these molecules using a 59-parameter modified valence force field. The force constants were refined using an Overlay least-squares technique employing 352 frequencies of 10 molecules. The reliability of the force constants so obtained was tested by making a zero-order calculation for p-, m- and o-dinitrobenzenes, 1-fluoro-, 1-chloro- and 1-bromo-, 2,4-dinitrobenzenes, 2,4-difluoro- and 2,5-difluoro- and 2,5-dibromonitrobenzenes. Unambiguous vibrational assignments of all the fundamentals were made using the potential energy distribution and eigen vectors.     

‘Lab-in-reaction-cell’ cyclic injection analysis as an opportunity for the miniaturization of flow analysis

The method of cyclic injection analysis in the ‘lab-in reaction-cell’ mode has been proposed for the miniaturization of flow analysis; the hydraulic scheme of this mode assumes the formation of the analytical forms of the analytes and their detection directly in the reaction cell of the cyclic injection analyzer through the combination of the latter with the measurement cuvette of a fiber optic spectrophotometer. The possibilities of the proposed solution are illustrated by the example of the determination of ‘active chlorine’ in aqueous media. A procedure has been developed for the automated photometric determination of ‘active chlorine’ in the range from 0.2 to 1.3 mg/L in aqueous media in a 125 μL sample, the duration of one analysis being 2.5 min.