Definition and detection of data-based uniqueness in evaluating bilinear (two-way) chemical measurements

Multivariate curve resolution methods, frequently used in analyzing bilinear data sets, result in ambiguous decomposition in general. Implementing the adequate constraints may lead to reduce the so-called rotational ambiguity drastically, and in the most favorable cases to the unique solution. However, in some special cases, non-negativity constraint as minimal information of the system is a sufficient condition to resolve profiles uniquely. Although, several studies on exploring the uniqueness of the bilinear non-negatively constrained multivariate curve resolution methods have been made in the literature, it has still remained a mysterious question. In 1995, Manne published his profile-based theorems giving the necessary and sufficient conditions of the unique resolution. In this study, a new term, i.e., data-based uniqueness is defined and investigated in details, and a general procedure is suggested for detection of uniquely recovered profile(s) on the basis of data set structure in the abstract space. Close inspection of Borgen plots of these data sets leads to realize the comprehensive information of local rank, and these argumentations furnish a basis for data-based uniqueness theorem. The reported phenomenon and its exploration is a new stage (it can be said fundament) in understanding and describing the bilinear (matrix-type) chemical data in general.     

Thermal behavior of holo- and hemicellulose obtained from rice straw and bagasse

Thermal gravimetric analysis, and differential thermal behavior of holo- and hemicelluloses obtained from rice straw and bagasse were investigated. Degradation was found to be of first order reaction. The activation energy values and the rate constants were calculated from the kinetic of weight loss. Hemicellulose was found to be less stable than holocellulose, and the stability of the samples was arranged in the order, rice straw holo- > bagasse holo- > rice straw hemi- > bagasse hemicellulose. Degradation of rice straw (holo- as well as hemicellulose) was performed via two exothermic processes, whereas bagasse hemicellulose combustion was completed through three exothermic processes. The magnitude and the shape of the exotherms depend, mainly, on the chemical composition of the sample.     

Spectrophotometric study of interaction of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone with diaza-18-crown-6 and diaza-15-crown-5 in acetonitrile and chloroform solutions

Interactions of diaza-18-crown-6 and diaza-15-crown-5, as electron donors, with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), as an electron acceptor, have been investigated spectrophotometrically in acetonitrile and chloroform solutions. The results indicated immediate formation of an electron donor-electron acceptor complex DA: [reaction in text] which is followed by two relatively slow consecutive reactions: [reaction in text]. The pseudo-first-order rate constants for the formation of the ionic intermediate and the final product have been evaluated at various temperatures by computer fitting of the absorbance time data to appropriate equations. The formation constants of the resulting DA complexes have also been determined. The influences of both the azacrown's structure and the solvent properties on the formation of DA complexes and the rates of subsequent reactions are discussed.     

Structure–retardation factor relationship of natural amino acids in two different mobile phases of RP-TLC

Abstract

Separation of amino acids (AAs) and their simple and inexpensive determination/identification is an interesting topic in biological and protein science, different food industries, and drug factories. Also, the presentation of the chromatographic behavior of compounds in a predictive model can be effective to estimate the structural/chemical properties of analyte and mobile phases. In this work for the first time, retardation factor (R_F) of 42 AAs in reversed-phase thin layer chromatography (RP-TLC) was modeled. Acetonitrile-sodium azide solution and 1,2 dioxane-sodium azide solution were two mobile phases which have been studied in this work. Results showed that the values of R_F are correlated with the structural properties of AAs and these properties had some similarities and differences in two noted mobile phases. For the TLC data in two mobile phases, five parametric linear models were suggested (R²_train = 0.93 and 0.97; R²_test = 0.93 and 0.99). The models were also evaluated with different statistical approaches. It was shown that increasing the sum of geometrical distances between N and O in AAs causes decreasing their R_F in RP-TLC using both mobile phases. Other structural effects of AAs on their separation in the desired RP-TLC system were also discussed.     

Conductance study of ammonium complexes with several crown ethers and cryptands in nitrobenzene,acetonitrile and dimethylformamide solutions

The formation of ammonium complexes with several crown ethers and cryptands in nitrobenzene, acetonitrile and dimethylformamide solutions was investigated by conductometry at 25°C. Stability constants of the resulting 1:1 complexes sere determined from the molar conductance-mole ratio data and found to vary in the order DC18C6>18C6>DB30C10>DB21C7>DB24C8>DB18C6>15C5>B15C5>12C4, in the case of crown complexes, and in the order C222>C221>C211>C22>C21 for the ammonium cryptates. The stabilities of the complexes varied inversely with the Gutmann donicity of the solvents. Influences of the number of members in the macrocycle, nature of the substituents in the polyether ring, cavity size and dimensionality, conformations of the free and complexed ligands and number of N⁺–H bonds available for hydrogen bonding are discussed.     

Conductance study of the thermodynamics of ammonium ion complexes with several crown ethers in acetonitrile solution

A conductance study concerning the interaction between ammonium ion and several crown ethers in acetonitrile solution has been carried out at different temperatures. The stability constants of the resulting 11 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order DC18C6>18C6>DB30C10>DB21C7>DB24C8>DB18C6>15C5>B15C5. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The influence on the thermodynamic data of different parameters such as cavity size and dimensionality of crown ethers, nature of substituents in the polyether ring, conformations of the free and complexed ligands, solvent-ligand interaction and number of N–H bonds available for hydrogen bonding are discussed.     

Proposed Mechanism for the Antitrypanosomal Activity of Quercetin and Myricetin Isolated from Hypericum afrum Lam.: Phytochemistry,In Vitro Testing and Modeling Studies

The in vitro activity of L. donovani (promastigotes, axenic amastigotes and intracellular amastigotes in THP1 cells) and T. brucei, from the fractions obtained from the hydroalcoholic extract of the aerial part of Hypericum afrum and the isolated compounds, has been evaluated. The chloroform, ethyl acetate and n-butanol extracts showed significant antitrypanosomal activity towards T. brucei, with IC₅₀ values of 12.35, 13.53 and 12.93 µg/mL and with IC₉₀ values of 14.94, 19.31 and 18.67 µg/mL, respectively. The phytochemical investigation of the fractions led to the isolation and identification of quercetin (1), myricitrin (2), biapigenin (3), myricetin (4), hyperoside (5), myricetin-3-O-β-d-galactopyranoside (6) and myricetin-3’-O-β-d-glucopyranoside (7). Myricetin-3’-O-β-d-glucopyranoside (7) has been isolated for the first time from this genus. The chemical structures were elucidated by using comprehensive one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopic data, as well as high-resolution electrospray ionization mass spectrometry (HR-ESI–MS). These compounds have also been evaluated for their antiprotozoal activity. Quercetin (1) and myricetin (4) showed noteworthy activity against T. brucei, with IC₅₀ and IC₉₀ values of 7.52 and 5.71 µM, and 9.76 and 7.97 µM, respectively. The T. brucei hexokinase (TbHK1) enzyme was further explored as a potential target of quercetin and myricetin, using molecular modeling studies. This proposed mechanism assists in the exploration of new candidates for novel antitrypanosomal drugs.     

Study of flame-retardant finishing of cellulose fibres: Organic–inorganic hybrid versus conventional organophosphonate

The aim of this study was to introduce a non-formaldehyde inorganic–organic hybrid sol–gel flame-retardant precursor (SiOP) containing phosphorous, nitrogen, and silicon and to compare its functional properties with those of the conventional formaldehyde-containing organic flame-retardant agent, organophosphonate (OP). SiOP was used at concentrations of 2%, 4%, and 8%, and OP was used at a concentration of 200 g/dm³. Both agents were applied to 100% cotton (CO) woven fabric by the pad-dry-cure method under the appropriate conditions. The presence of the SiOP and OP coatings on the CO fabric was confirmed by scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. The results of the vertical tests of flammability and the thermogravimetric analyses showed that the presence of the SiOP coating changed the thermal degradation pathway of the CO fabric and resulted in an increase in the thermo-oxidative stability of the cellulose fibres. The thermo-oxidative stability was enhanced by the addition of higher amount of dry solids. At comparable dry solids contents, OP preserved significantly greater flame retardancy and thermo-oxidative stability than did SiOP. These results indicated that the SiOP precursor could not act as an effective alternative to the OP agent in the flame-retardant protection of CO fabric.     

Nanosized cationic and anionic manganese porphyrins as mesoporous catalysts for the oxidation of olefins: Nano versus bulk aggregates

In this study, catalytic activity of bulk and nano‐sized meso‐tetrakis(4‐sulfonatophenyl)porphyrinatomanganese(III) acetate, MnTPPS₄(OAc), (ammonium salt) and meso‐tetrakis(3‐methylpyridyl)porphyrinatomanganese(III) acetate, MnT(3‐MePy)P(OAc) (tosylate salt) for the oxidation of olefins with tetra‐n‐butylammonium Oxone has been studied and compared with that of the bulk counterparts. The nanoparticles were prepared by mixing solvent techniques using water, (triethyleneglycol) monomethyl ether and dimethylsulfoxide or acetonitrile. The formation of nano‐sized catalysts was confirmed by UV‐Vis spectroscopy, DLS and AFM. Nitrogen porosimetry measurements indicated the homogeneous pore size distribution in the bulk and nano‐sized manganese porphyrins. In spite of the high oxidizability of Oxone, the heterogenized manganese porphyrins showed a significantly higher oxidative stability relative to their homogeneous counterparts within a reaction time of 6 h. The increase in the catalytic activity induced by the formation of nano‐sized catalysts was more pronounced in the case of MnT(3‐MePy)P(OAc). MnT(3‐MePy)P(OAc) may be recovered and reused for at least 4 times without any significant decrease in the catalyst efficiency. In the case of MnTPPS₄(OAc) a large decrease in the catalytic activity was observed after the first use of the catalyst. The latter was attributed to higher degrees of catalyst degradation in the case of MnTPPS₄(OAc).