A novel approach to determination of carbonyl groups in DMAc/LiCl-insoluble pulps by fluorescence labeling

The CCOA method for profiling of carbonyl groups by fluorescence labeling has meanwhile become an established procedure for dissolving pulps and rag papers. High molecular weight pulps, such as certain paper pulps, could not be analyzed so far due to their limited solubility in DMAc/LiCl. The new approach presented in this paper is based on the heterogeneous carbonyl-selective fluorescence labeling with CCOA (2), which is subsequently released with triflic acid from the labeled pulp in a quantitative manner, and the concentration of CCOA and CCOA-derived products is determined by HPLC. The procedure requires material in the mg range only. Calibration was performed against DMAc/LiCl-soluble standard pulps. Comparison of the data obtained by the novel approach correlated well with data from the established CCOA procedure.     

Comparison of Aqueous and Non-Aqueous Treatments of Cellulose to Reduce Copper-Catalyzed Oxidation Processes

Summary. The present paper examines oxidative degradation of cellulose catalyzed by presence of Cu¹⁺and Cu²⁺ ions in the context of historic paper conservation treatments. Aqueous treatments of degraded papers further spread transition metal ions, such as copper, across the fibre matrix, and therefore augment the detrimental effect of these ions. In the paper industry, the inhibiting effects of magnesium ions on metal-catalyzed degradation of cellulose contaminated with metal impurities have been observed. Also, magnesium compounds dissolved in alcoholic or aqueous solutions are generally used in paper conservation as deacidification agents. Paper samples with artificially produced copper corrosion served as mock-ups for examination and comparison of different treatments which focused on the inhibiting effect of magnesium and antioxidants. Analytical examination of molecular weight distribution, carbonyl content, carboxyl content, and surface pH was performed. Results show an inhibiting effect of magnesium on copper-catalyzed cellulose degradation, although less pronounced than expected.     

Iron gall ink-induced corrosion of cellulose: aging,degradation and stabilization. Part 1: model paper studies

Cellulose in historic paper documents is often damaged by the writing media used, especially iron gall ink or copper pigments. Degradation induced by iron gall ink is suggested to be a synergistic process comprising both hydrolytic and oxidative reactions. These processes were studied on very low sample amounts according to the CCOA and FDAM method, i.e. by fluorescence labeling of carbonyl and carboxyl groups in combination with GPC-MALLS, respectively. This study focused on preventive means to stop the deterioration induced by iron gall ink of cellulose and to prevent further damage, keeping in mind that a suitable conservation treatment has to hinder both, hydrolytic and oxidative processes, at the same time. A combination of the complexing agent calcium phytate and calcium hydrogencarbonate in aqueous solution was proved to give optimum results. To gain insight into long term stability, an aging step was performed after treatment and different ink modifications were tested. Recording the molecular weight distributions and the carbonyl group content over time GPC analysis verified for the first time the preventive effect of this treatment. This effect was not only seen for the ink-covered areas, but extended also to areas remote from the ink lines. Ink containing copper ions responded equally positively to the calcium phytate/hydrogencarbonate treatment as the iron gall ink papers did. Gelatine, sometimes used in a similar way due to an alleged cellulose-stabilizing effect did not have a beneficial influence on cellulose integrity when metal ions were present.     

On the Nature of Carbonyl Groups in Cellulosic Pulps

Apart from the reducing end groups, most celluloses contain small amounts of carbonyl groups in the mol/g range, which are introduced into the material by a variety of preparation, processing and purification steps. By a combination of carbonyl-selective fluorescence labeling (CCOA method) and UV resonance Raman spectroscopy it was demonstrated that carbonyls in celluloses are not only present as a C=O structure with an sp²-hybridized carbon, but also to a significant extent in sp³-hybridized form as hydrates or hemiacetals.     

Iron gall ink-induced corrosion of cellulose: aging,degradation and stabilization. Part 2: application on historic sample material

Degradation of cellulose in historic paper by iron gall ink is a synergistic process of both, acid hydrolysis caused by acidic ink ingredients and oxidation catalyzed by free iron and/or copper ions. The interplay of both reactions was studied according to the CCOA method on historic paper samples. Only minute amounts (few mg) of the samples were required to obtain profiles of naturally present and oxidatively introduced carbonyl groups, which was done by group-selective fluorescence labeling in combination with determination of the molecular weight distribution by GPC-MALLS. In the present study naturally occurring degradation pathways in historic sample papers have been investigated. Different extents of oxidatitive degradation were shown for paper with and without ink. A typical pattern of the molecular weight distribution in naturally aged papers was identified, the peculiar feature being a distinctive shoulder in the region of low molecular weight, roughly between 25,000 and 5,000 g/mol corresponding to a DP between 150 and 30. This pattern was a typical attribute of degraded natural samples: any artificial aging procedures aimed at modeling natural aging processes must thus attempt to reproduce this feature. Although the historic samples had been more severely oxidized than model papers, the inhibition of further oxidation and hydrolysis by the calcium phytate/hydrogen carbonate treatment was evident and could be proven for the first time on the molecular level. Also on plain paper without ink application the oxidation was suppressed and the molecular weight was stabilized on a high level.     

Studies into the Early Degradation Stages of Cellulose by Different Iron Gall Ink Components

Selective fluorescence labelling of oxidized cellulose functionalities followed by GPC-MALLS was used to get a deeper insight into ink-induced degradation processes. As the method is very sensitive towards oxidation and molecular weight changes, slight variations at the very beginning of aging processes, e.g. during ink corrosion of cellulose, can be studied. Five different ink modifications were applied on model papers and underwent mild accelerated aging at 55 °C and cycling humidity (7 days) followed by a short period of static humid aging at 80 °C (2 days). Pure ink constituents like tannic acid or iron sulphate do not result in the same degree of oxidation or chain scission as complete inks. Balanced ink degrades paper more than single compounds, but less than unbalanced inks. Interestingly, some degradation occurs already during or shortly after the application process of unbalanced inks on paper. It could be demonstrated that this oxidation proceeded in a rather high Mw area, while the subsequent aging steps affected predominantly regions of shorter cellulose chains.     

A simplified approach to vapor–liquid equilibria calculations with the group-contribution lattice-fluid equation of state

Equations of state that are based on the lattice-statistics approach use Guggenheim's quasi-chemical approximation to describe the non-randomness in the mixture due to the energetic interactions between the molecules. For ternary and higher-component systems the non-randomness expression is complex and requires an iterative calculation procedure. We have shown that the non-randomness parameters play a negligible role in the application of the GCLF-EoS model (based on the Panayiotou–Vera EoS) for predicting vapor–liquid equilibria. Omission of the non-randomness parameters from such calculations can significantly improve the computation efficiency. Binary, ternary, and quaternary vapor–liquid equilibria predictions were made including polystyrene, polyvinyl acetate, polyethylene, and polypropylene in polar and non-polar solvents to test the theory.     

A topological stochastic approach to the study of multidimensional potential energy surfaces of chemical reactions

In this article we propose a new approach for investigating the properties of multidimensional potential energy surfaces in chemical reactions, based on relations of each multidimensional surface to its one-dimensional image which is the chemical reaction tree. This approach makes it possible to find a common number of independent channels in chemical reactions for complex systems and to construct the probable models.     

A molecular dynamics approach to examine the kinetics of the capillary imbibition of a polymer at nanoscale

A molecular dynamics (MD) approach was employed to simulate the imbibition of a designed nanopore by a polymer. The length of imbibition as a function of time for various interactions between the polymer and the pore wall was recorded for this system (i.e., polymer and nanopore). By and large, the kinetics of imbibition was successfully described by the Lucas–Washburn (LW) equation, although deviation from it was observed in some cases. This nonuniformity contributes to the neglect of the dynamic contact angle (DCA) in the LW equation. Two commonly used models (i.e., hydrodynamic and molecular–kinetic models) were thus employed to calculate the DCA. It is demonstrated that none of the evaluated models is able to justify the simulation results in which are not in good agreement with the simple LW equation. Further investigation of the MD simulation data revealed an interesting fact that there is a direct relationship between the wall–polymer interaction and the speed of the capillary imbibition. More evidence to support this claim will be presented.     

A new approach to the prediction of RP-HPLC retention times in gradient elution from isocratic data

Summary A general chromatographic model has been set up starting from a set of equations based on the concept of the velocity of a solute along the column. The composition of the mobile phase is taken into account solely as a numerical factor entering into suitable equations and totally independent of the chemical-properties of the constituents. A few isocratic experimental runs are necessary as input data, and subsequently a small amount of computational effort is sufficient to make predictions of retention times under gradient elution conditions for solutes of whatever chemical structure. The prediction errors are dependent on the steepness of the linear gradient chosen but are, in any case, acceptably low.     

Fluoropolyethers end‐capped by polar functional groups. IV. A novel approach to the evaluation of reactivities of hydroxy‐terminated ethoxylated fluoropolyethers in the tin(IV)‐catalyzed reactions with isophorone diisocyanate

The effect of catalyst dibutyltin dilaurate (DBTDL) on the kinetics of urethane formation reactions of α,ω‐bis(hydroxy)‐terminated fluoropolyethers Fomblin® Z‐DOL TXs (FPEs) of various molecular weights and poly(oxyethylene) glycol PEG‐400 with isophorone diisocyanate (IPDI) in hexafluoroxylene (HFX) and tetrahydrofuran (THF) at 40 °C and NCO:OH = 2:1 have been studied in a broad range of catalyst (0.10–9.00) ×10^?4 M and total reagents (10.0–60.1 wt %) concentrations. The rate of tin‐catalyzed second‐order reactions (with respect to diol and diisocyanate) was found to be proportional to the square root of catalyst concentration [DBTDL]^0.5 both in low polar (HFX) and polar (THF) solvents. Effect of catalyst saturation was revealed for all the reaction systems at higher DBTDL concentrations as well as the appearance of the limiting catalyst concentrations C_lim below which the rates of reaction were close to zero. Based on these findings new effective rate coefficients have been derived k = k_cat/(C ? C) that are independent of the total reagent concentration in the range of 10.0–60.1 wt % ([OH] = 0.10–0.91 equiv/L). This new approach highlights that the rate of the tin‐catalyzed urethane formation reactions of α,ω‐bis(hydroxy)‐terminated fluoropolyethers Z‐DOL TXs with IPDI in HFX at 40 °C and NCO:OH = 2:1 increases significantly with increasing MW of FPE from 776 up to 3405. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5354–5371, 2004     

A novel approach to the qualitative and quantitative assay of HPTLC plates: Second and fourth derivative recording of spectrophotodensitograms

One of the limitations due to lack of resolution for a given pair of analytes in TLC or HPTLC is the need to optimize the system. In Practice this requires time, rerunning of the sample in different developing solvents, and a great deal of expertise on the part of the analyst. In our experience, application of first and second derivative recording techniques to HPTLC facilitates and speeds the whole process, permitting qualitative and quantitative assay of most unresolved spots. Consequently, we have now extended our instrumental capabilities to fourth derivative measurements. For this purpose, we have added a homemade electronic unit in series with the one previously used for first and second order derivatives. Thus, we have been able to evaluate the potential advantages of higher order derivatives for HPTLC analysis of unresolved components in various pharmaceutical products. A comparison of second and fourth order derivative measurements of seriously overlapping HPTLC components in a sample of preservatives used in the pharmaceutical industry suggests that the lower order derivatives might be a better choice in view of the higher accuracy and precision of the corresponding data. This is supported by the results of other applications, such as the assay of a commercial colorant, and a syrup formulation. The observed lack of precision of fourth order measurements stems from the fact that although the second and higher order derivatives produce narrower bandwidths, thus contributing to improved resolution, the signal to noise ratio decreases and satellite peak interactions increase, thus rendering correct discrimination of the fine structural detail of overlapping components more difficult.     

A density‐functional theory approach to the separation of K2ZrF6 and K2HfF6 via fractional crystallization

Because of the low absorption cross‐section for thermal neutrons of zirconium (Zr) as opposed to hafnium (Hf), Zr‐metal must essentially be Hf‐free (<100 ppm Hf) to be suitable for use in nuclear reactors. However, Zr and Hf always occur together in nature, and due to very similar chemical and physical properties, their separation is particularly difficult. Separation can be achieved by traditional liquid–liquid extraction or extractive distillation processes, using Zr(Hf)Cl₄ as feedstock. However, the production of K₂Zr(Hf)F₆ via the plasma dissociation route, developed by the South African Nuclear Energy Corporation Limited (Necsa), could facilitate the development of an alternative separation process. In this theoretical study, the results of density‐functional theory (DFT) simulations of K₂Zr_(1‐z)Hf_zF₆ solid solutions [using Cambridge Serial Total Energy Package (CASTEP)] are presented, for which the supercell approach was applied in an attempt to determine whether solid solution formation during crystallization from aqueous solutions (fractional crystallization) is thermodynamically possible, which would hinder the separation efficiency of this method. Consequently, the calculated thermodynamic properties of mixing were used to evaluate the separation efficiency of Zr and Hf by fractional crystallization using a thermodynamic model to calculate the relative distribution coefficients. The small mixing enthalpies that were calculated from the DFT results, indicates that lattice substitution of Zr(IV) by Hf(IV) in K₂ZrF₆ could occur with relative ease. This is not surprising, considering the close similarities between Zr and Hf, and it was therefore concluded that K₂Zr_(1‐z)Hf_zF₆ solid solution formation might well restrict the separation efficiency of Zr and Hf by fractional crystallization of K₂Zr(Hf)F₆. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

A new approach to the synthesis of lactams of muramic,isomuramic and normuramic acids via intramolecular O-alkylation: Stereochemical features of the intramolecular nucleophilic substitution

The title compounds were synthesized from the selectively protected N-acylated d-glucosamine derivatives, containing α-halo carboxylic acid moieties, via intramolecular 3-O-alkylation. It was found that if the starting compound contains asymmetric electrophilic center, isomuramic acid derivatives were mainly formed, regardless of the configuration of the electrophilic carbon atom. An explanation for the observed stereochemical results was proposed on the basis of the analysis of steric interactions in the molecules of the starting compounds, as well as using the concept of anchimeric assistance. It was shown that N-acetylation of the obtained lactam derivatives and subsequent methanolysis under mild conditions led to the selective cleavage of δ-lactam ring resulting in the formation of the corresponding ester derivatives of N-acetylmuramic acid or its analogues in high yields.     

Identification of potential inhibitor and enzyme-inhibitor complex on trypanothione reductase to control Chagas disease

Chagas is a parasitic disease with major threat to public health due to its resistance against commonly available drugs. Trypanothione reductase (TryR) is the key enzyme to develop this disease. Though this enzyme is well thought-out as potential drug target, the accurate structure of enzyme-inhibitor complex is required to design a potential inhibitor which is less available for TryR. In this research, we aimed to investigate the advanced drug over the available existing drugs by designing inhibitors as well as to identify a new enzyme-inhibitor complex that may act as a template for drug design. A set of analogues were designed from a known inhibitor Quinacrine Mustard (QUM) to identify the effective inhibitor against this enzyme. Further, the pharmacoinformatics elucidation and structural properties of designed inhibitor proposed effective drug candidates against Chagas disease. Molecular docking study suggests that a designed inhibitor has higher binding affinity in both crystal and modeled TryR and also poses similar interacting residues as of crystal TryR-QUM complex structure. The comparative studies based on in silico prediction proposed an enzyme-inhibitor complex which could be effective to control the disease activity. So our in silico analysis based on TryR built model, Pharmacophore and docking analysis might play an important role for the development of novel therapy for Chagas disease. But both animal model experiments and clinical trials must be done to confirm the efficacy of the therapy.