Anticancer anthrapyrazoles. Improved syntheses of clinical agents CI-937, CI-941, and piroxantrone hydrochloride

Improved processes for the synthesis of bulk quantities of the anthrapyrazole clinical agents CI-937, CI-941, and piroxantrone hydrochloride are reported. Reported also are detailed analytical and spectroscopic data for these agents and intermediates of the synthetic sequences.     

Effect of structure on properties of polypyromellitimide films

Polypyromellitimides were prepared by the reaction of di(4-aminophenyl) ether (E)/di (4-aminophenyl) methane (M), and pyromellitic dianhydride in dimethylformamide, followed by thermal cyclization in a nitrogen atmosphere. Copolyimides were obtained by taking different molar ratios of diamines in the initial monomer feed. Differential scanning calorimetric, thermogravimetric analysis, and thermally stimulated current studies were carried out on these samples. It was concluded that the dielectric relaxation in these copolymers is due to trapping of the charge carriers. The dielectric relaxation parameters and activation energies were also calculated.     

Complex permittivity,complex permeability and microwave absorption properties of ferrite–polymer composites

The complex permittivity (ε′–jε″), complex permeability (μ′–jμ″) and microwave absorption properties of ferrite–polymer composites prepared with different ferrite ratios of 50%, 60%, 70% and 80% in polyurethane (PU) matrix have been investigated in X-band (8.2–12.4 GHz) frequency range. The M-type hexaferrite composition BaCo⁺²_0.9Fe⁺²_0.05Si⁺⁴_0.95Fe⁺³_10.1O₁₉ was prepared by solid-state reaction technique, whereas commercial PU was used to prepare the composites. At higher GHz frequencies, ferrite's permeabilities are drastically reduced, however, the forced conversion of Fe⁺³ to Fe⁺² ions that involves electron hopping, could have increased the dielectric losses in the chosen composition. We have measured complex permittivity and permeability using a vector network analyzer (HP/Agilent model PNA E8364B) and software module 85071. All the parameters ε′, ε″, μ′ and μ″ are found to increase with increased ferrite contents. Measured values of these parameters were used to determine the reflection loss at various sample thicknesses, based on a model of a single-layered plane wave absorber backed by a perfect conductor. The composite with 80% ferrite content has shown a minimum reflection loss of −24.5 dB (>99% power absorption) at 12 GHz with the −20 dB bandwidth over the extended frequency range of 11–13 GHz for an absorber thickness of 1.6 mm. The prepared composites can fruitfully be utilized for suppression of electromagnetic interference (EMI) and reduction of radar signatures (stealth technology).     

Preparation and thermal decomposition of some oxomolybdenum(VI) oxalates

Anionic oxomolybdenum(VI) oxalates having the general formula A₂[Mo₂O₆(C₂O₄)], where A = K⁺ and NH⁺₄, are prepared and characterized by chemical analysis and IR spectra, and their thermal decomposition studied using TG and DTA techniques. Both the compounds are anhydrous and the decomposition of oxalate takes place in a single step. The ammonium compound decomposes between 255 and 320°C to give MoO₃ as the end product, while the potassium compound decomposes between 300 and 380°C to give K₂Mo₂O₇ as the end product. Both the products were characterized by chemical analysis, IR and X-ray studies. The X-ray diffraction patterns of the two oxalato complexes confirm that they are crystalline compounds.     

A general and convenient method of synthesizing dihydridoplatinum(II) complexes with bulky phosphine ligands

Platinum(II) dihydrides containing bulky phosphine ligands, trans-PtH₂L₂ (L = PCy₃, P-i-Pr₃, P-n-Bu-t-Bu₂, PMe-t-Bu₂), have been prepared conveniently and in excellent yield from the reaction of the corresponding peroxycarbonato complexes with NaBH₄. A similar reduction of the dioxygen platinum(II) complexes also affords the dihydrides but less readily. All these dihydrides react with highly activated acetylenes to form the trans-hydridovinyl complexes.     

Preparation of sodium dimolybdate by the pyrolysis of sodium oxomolybdenum (VI) oxalate

Thermal studies on various oxalato complexes have been of immense interest as they yield finely divided, highly reactive oxides which are usually obtained at a much lower temperature than that required in the conventional method of preparation, i.e., heating a mixture of two or more constituents [1]. A survey of the literature reveals that the compounds having the general formula A₂[Mo₂O₅(C₂O₄)₂(H₂O)₂], where A = K⁺, NH⁺₄[2] and A = Cs⁺ [3], have been prepared and their thermal decomposition is studied, but no such information is available regarding the preparation and characterisation of Na₂[Mo₂O₅(C₂O₄)₂(H₂O)₂] (SMO), which forms the subject of study of this paper. Sodium dimolybdate (Na₂Mo₂O₇), the decomposition product of SMO, is obtained at 280°C, a temperature much lower than that required in the conventional method of preparation of heating a mixture of Na₂MoO₄ and MoO₃ [4].     

Structure of short polymers at interfaces: a combined simulation and theoretical study

The structure of polymers confined between surfaces is studied using computer simulation and a density functional approach. The simple model system considers the polymer molecule as a pearl necklace of freely jointed hard spheres, having attractions among the beads, confined between attractive surfaces. This approach uses the universality of the free-energy functional to obtain the self-consistent field required in the single chain simulation. The second-order direct correlation function for the uniform bulk fluid required as input has been calculated from the reference interaction site model integral equation theory using mean spherical approximation. The theoretical results are shown to compare well with the Monte Carlo simulation results for varying densities, chain lengths, and with different attractive interaction parameters. The simulation results on the conformational properties give important indications regarding the behavior of chains as they approach the surfaces.     

Design of Peptides with α,β-Dehydro-Residues: Syntheses and Crystal Structures of (i) N-Tertiarybutyloxycarbonyl-L-Ala-ΔPhe-L-Ala-OCH3 and (ii) N-Tertiarybutyloxycarbonyl-L-Leu-ΔPhe-L-Leu-OCH3

In order to contribute to design rules with α,β-dehydro amino acid residues, two peptides (i) Boc-Ala-ΔPhe-Ala-OCH₃ and (ii) Boc-Leu-ΔPhe-Leu-OCH₃ were synthesized and their crystal structures were determined. Peptide (i) with Ala residues on both sides of ΔPhe adopted a type II β-turn conformation with dihedral angles of two corner residues, φ₁ = ?62.6(4)^°, ψ₁ = 138.9(5)^°, φ₂ = 76.3(4)^° and ψ₂ = 13.1(3)^°, while the peptide (ii) with Leu residues formed an unfolded conformation with dihedral angles, φ₁ = ?81.9(5)^°, ψ₁ = ?28.3(4)^°, φ₂ = 56.7(5)^° and ψ₂ = 42.6(4)^°. The structure of peptide (i) was stabilized by an intramolecular 4→1 hydrogen bond between Ala³ NH and BOC carbonyl oxygen atom, whereas that of peptide (ii) was stabilized by van der Waals forces involving the side chains of two Leu residues.