Methylation of Chitosan with Iodomethane: Effect of Reaction Conditions on Chemoselectivity and Degree of Substitution

N,N,N‐trimethylchitosan (TMC) was prepared by reacting purified chitosan with iodomethane, in the presence of sodium hydroxide, water and sodium iodide, at room temperature. The reaction medium was N‐methyl‐2‐pyrrolidone. Different samples of TMC were obtained by adding to the reaction medium a fixed volume (5.5 mL) of aqueous NaOH solutions at different concentrations (15, 20, 30 and 40 wt.‐%) and carrying out the reactions for 9 or 24 h. The features observed in the ¹H and ¹³C NMR spectra of these chitosan derivatives, in respect of the chemical shift, number and relative intensity of the signals, depended strongly on the excess of NaOH and H₃CI added to the reaction medium, but when the lowest excess was employed, the characteristics of the derivative were not affected by the reaction time to the same extent. The average degree of quaternization of these N‐methylated derivatives of chitosan ranged from 10.5% to 44.8%, according to the reaction conditions. Increasing the excess of NaOH, in reactions carried out for 9 h, resulted in TMC samples with progressively higher content of trimethylated sites however, the reaction yields were correspondingly lower and O‐alkylation was favored in these cases.

¹H NMR spectrum of sample [A_X]^24h dissolved in D₂O (C_p = 10 g/L).     

Structural and Transport Properties of Mg1−xMnxMn2O4±δ Spinels

The synthesis and structural properties of Mg_1−xMn_2+xO₄, for 0≤x≤1 are described. Complete miscibility in the solid state exists for this system. For the material with the correct stoichiometry, i.e. MgMn₂O₄, the effect of temperature on the cation distribution was investigated= above 600°C the inversion degree (m) starts increasing. The electrical conductivity shows a small dependence on P(O₂) which is consistent with the small oxygen non-stoichiometry determined by means of thermogravimetry. The main contribution to the transport properties arises from the inversion equilibrium. Two distinct conductivity regimes, below and above the inversion threshold, can be assumed to explain the electrical conductivity and thermoelectric power results.     

1H-NMR Investigation of the Binding of 2-Methylnaphthalene to α-Cyclodextrin in D2O Solutions

As -cyclodextrin (-CD) was added to D₂Osolutions of 2-methylnaphthalene, its proton signals shifted to lower fieldsat low concentrations of -CD. At 2.0 × 10^-2 moldm^-3 of -CD, however, a reverse, higher-field shift wasobserved for the H-8 signal, indicating the formation of 1 : 1 and 2 : 1-CD–2-methylnaphthalene inclusion complexes. Intrinsic chemicalshift differences of all the protons in 2-methylnaphthalene have beenevaluated for both the 1 : 1 and the 2 : 1-CD–2-methylnaphthalene inclusion complexes. These intrinsicchemical shift differences suggest that the first -CD molecule has noselectivity in accommodating one end of uncomplexed 2-methylnaphthalene;-CD binds to a methyl group, as well as a naphthalene ring-end havingno methyl group, to form the 1 : 1 inclusion complex, resulting in theformation of two kinds of 1 : 1 complexes.     

Etude de l’isotherme 25°C du système quasi quaternaire H2O-Zn(NO3)2·6H2O-Cu(NO3)2·3H2O-NH4NO3;I- Isoplèthes 4 masse% NH4NO3, 8 ma

The solid-liquid equilibria of the quasi-quaternary system H₂O-Zn(NO₃)₂·6H₂O-Cu(NO₃)₂·3H₂O-NH₄NO₃ were studied at 25°C by using a synthetic method based on conductivity measurements. Three isoplethic sections has been established at 25°C and the stable solid phases which appear are: NH₄NO₃(IV), Zn(NO₃)₂·6H₂O, anhydrous Cu(NO₃)₂, Cu(NO₃)₂·3H₂O and metastable Cu(NO₃)·2.5H₂O. Neither double salts, nor mixed crystals are observed at these temperatures and composition range.     

EPR parameters and local geometry for Cr3+ and V2+ ions in HfS2 crystals

From the high-order perturbation formulas of EPR parameters (zero-field splitting D, g factors gparallel, gperpendicular and hyperfine structure constants Aparallel, Aperpendicular) based on the two spin-orbit coupling parameter model for 3d3 ions in trigonal symmetry, the EPR parameters of Cr3+ and V2+ ions in HfS2 crystals are calculated. From the calculations, it is found that the local trigonal distortion angle theta of impurity center in HfS2:Cr3+ is smaller than that in HfS2:V2+. The dominant cause of the small zero-field splitting |D| and g-anisotropy |Deltag|=|gparallel-gperpendicular| in HfS2:Cr3+ (compound to HfS2:V2+) is due to the small local trigonal distortion angle theta rather than to the small impurity-ligand distance R in HfS2:Cr3+.     

Mass transfer determining parameter in facilitated transport through di-(2-ethylhexyl) dithiophosphoric acid activated composite membranes

Activated composite membranes (ACMs) containing di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier have been found to facilitate the transport and separation of several cations. This paper describes an approach to the chemical characterisation of the transport phenomena of Zn²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Sn²⁺ and In³⁺ by an ACM. The selectivity of D2EHDTPA based ACM towards different metal ions is presented and discussed focusing in Zn²⁺ and Cd²⁺ transport and recovery. Selectivity demonstrates that zinc ions are removable from mixtures due to the different extraction strength of D2EHDTPA. Such selectivity is based on the differences of the dynamic behaviour of the metal ions transport. In addition, a correlation of the chemical behaviour of those ACM systems with the corresponding solvent extraction systems has been found.     

Speciation analysis of platinum antitumoral drugs in impacted tissues

Chemical compounds containing platinum have been employed since 1978 as drugs to beat certain type of tumours. Nevertheless, besides of their exceptional antitumoral properties, these drugs also have important deleterious side effects, such as, nephrotoxicity and ototoxicity.A study of Pt accumulation and a speciation analysis has been performed by ICP-MS in samples from kidney and inner ear in a controlled population of Wistar rats treated with, either, cisplatin, carboplatin or oxaliplatin. The results on Pt accumulation point out to drug structure and not only to Pt content as the responsible for the alteration of organ functionality.Speciation studies in the samples from kidney and inner ear were performed coupling two-dimensional liquid chromatography (2D-LC) to ICP-MS. Size exclusion (SEC) and anion exchange fast protein liquid chromatography (FPLC) was employed for 2D orthogonal separation. After these separations, free drug peaks were not observed in any of the samples.The binding of Pt to biomolecules was demonstrated by SEC and, independently of the drug used, Pt eluted as two main bands with molecular weights of 12 kDa and 25-65 kDa for inner ear samples, and as two different bands with 20 kDa and 50-60 kDa in the samples from kidney. However, the relative band intensity presented important differences for the three drugs. Using the same chromatographic conditions, it was shown that a metallothionein (MT) standard eluted in the same position as some of the cytosolic Pt-biomolecules.High Pt-containing fractions eluting from the SEC column were analysed by anion exchange FPLC after a preconcentration step. Among the different preconcentration methods tested, sample focusing on the head of the FPLC column shows main advantages. In this way, the separation by 2D chromatography of the high molecular Pt-species has been considerably improved.     

Synthesis of pyrrolidine-substituted benzamides via iodocyclization of β-enaminoesters

Novel 2-, and N-substituted 5-methylene-pyrrolidine benzamides and 2-, 3-, and N-substituted 5-methylene-2-pyrroline benzamides were synthesized for the first time in a straightforward manner and in good yields via iodocyclization of γ- and α-alkenyl-β-enaminoesters, respectively. The key step in the process is the synthesis of the methylene-pyrrolidine iodide and methylene-2-pyrroline iodide intermediates. Functional group inter-conversion of these iodides to their amino analogs, and their subsequent coupling to benzoic acids via EDC, afforded the above pyrrolidine/2-pyrroline-substituted benzamides in yields of around 75%.     

Methods for the Synthesis of Isogramines and Their Chemical Properties. (Review)

Published data on methods for the synthesis of indole derivatives (isogramines) containing a dimethylamino group at positions 1, 2 and also at various positions of the benzene ring in the indole bicycle and their chemical properties are reviewed.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 483–504, April, 2005.     

Crystal Structures of Twisted Di(2-Pyridyl)ketone and Planar Azo-di(2-Pyridine) and Their Discussion Based on PM3 Enthalpy Hypersurfaces for the Isoelectronic Molecules

Single crystal structure determinations prove the two pyridine substituents in di(2-pyridyl)ketone (H₄C₄NC)₂C=O to be twisted out of the carbonyl skeleton plane by torsion angles (OCCN) of 41° and –163°, in contrast to their planar arrangement in azo-di(2-pyridine) H₄C₄NC)-N=N-(CNC₄H₄). In order to rationalize the surprising difference between the two isoelectronic molecules, approximate PM3 enthalpy of formation hypersurfaces have been calculated for each of the two ring torsions, which are assumed to be the dominant ones among the 3N – 6 = 60 degrees of freedom. For both the ketone and the azo derivative, global minima are calculated, the torsion angles of which deviate from the crystal structure results, and, therefore, support the assumption that both the experimentally determined twisting of di(2-pyridyl)ketone as well as the flattening of azo-di(2-pyridine) might be affected by the crystal packing.