Determination of Poly (Diallyldimethylammonium Chloride ) via Spectrophotometric Titration with Coomassie Brilliant Blue G Dye

Poly(diallyldimethylammonium chloride) (PDDA) is used as organic coagulant in water purification and auxiliary agent in paper production. Determination of PDDA in aqueous solutions is carried out usually by means of polyelectrolyte titration using streaming current detector or o-Toluidine Blue dye for endpoint recognition. The proposed method of PDDA assay takes advantage of Coomassie Brilliant Blue G dye having strong affinity to cationic macromolecules. Titration of PDDA solution with the dye is carried out measuring absorbance at 585 nm. Inflection points of the obtained zigzag photometric curves have good repeatability provided that titration rate is low enough to attain endpoint for 1 hour or more. The method assures rectilinear calibration (R2=0.999 5) in the broad range of PDDA concentrations from 0.3 to 9.6 mg·dm-3.     

Guest-Editorial

Editorial Introduction

Guest-Editorial     

Nitration of 2-substituted pyrimidine-4,6-diones,structure and reactivity of 5,5-gem-dinitropyrimidine-4,6-diones

Nitration of some 2-substituted pyrimidine-4,6-diones in sulfuric acid was studied, which afforded previously unknown 5,5-gem-dinitropyrimidine-4,6-diones in high yields. The gem-dinitro products were easily attacked by nucleophiles with concomitant formation of gem-dinitroacetyl derivatives, which in turn could be further hydrolyzed to salts of dinitromethane and triureas.     

Cationic beta-cyclodextrin bilayer vesicles

Cationic amphiphilic beta-cyclodextrins, substituted with hydrophobic n-alkylthio chains at the primary hydroxyl side and hydrophilic omega-amino-oligo(ethylene glycol) units at the secondary side, form bilayer vesicles with a diameter of 30-35 nm (when alkyl = hexadecyl) or nanoparticles with a diameter of ca. 120 nm (when alkyl = hexyl) in water.     

Synthesis of a highly enantiomerically enriched silyllithium compound

The highly enantiomerically enriched silyllithium compound lithiomethylphenyl(1-piperidinylmethyl)silane (4) reacts stereospecifically with chlorosilanes, but over a period of several hours slow racemization in solution at room temperature occurs, which can be suppressed by a transmetalation reaction with MgBr2(thf)4.     

Localization and Spread of the Particle in a Box

The most basic example of a quantum mechanical problem, the one-dimensional particle in a box, is revisited. Three aspects are treated. 1. It is shown that a number of textbooks give an incorrect result for the expectation value of x², and, therefore, do not obtain the correct spread x. Consequently, the verification of the Heisenberg relation is also in error. 2. It is found that textbooks do not mention the origin dependence of expectation values, which is a nuisance, as the problem is evidently treated in the literature with two choices of origin. 3. Superposition of an infinite number of even (cosine) solutions of the one-dimensional particle in the box allows for an analytical demonstration of complete localization of the particle (x = 0).     

Preparation of N-alkylated pyridones via selective N-alkylation of 2-alkoxypyridines on solid phase

Regioselective solid-phase synthesis of N-alkylated 2-pyridones has been carried out starting from 2-halopyridines. Variously substituted 2-halopyridines were linked to a Wang resin in quantitative yields to afford 2-alkoxypyridines. The coupled products were then reacted with a variety of alkyl halides, resulting in tandem alkylation and cleavage from the resin to generate N-alkylated pyridones with no detectable traces of O-alkylated products. The scope and limitations of this exceptionally selective reaction have been studied.     

Fluorescent 1,10-phenanthroline-containing oligonucleotides distinguish between perfect and mismatched base pairing

[structure: see text] A fluorescent deoxyuridine analogue is sensitive to the polarity of its environment and exhibits a distinct emission profile in single- vs double-stranded oligonucleotides. Emission-monitored denaturation curves of internally modified dU(phen) duplexes are characteristic of the base opposite dU(phen) and distinguish between perfect and mismatched complementary oligonucleotides.     

In Vitro Degradation of Trimethylene Carbonate Based (Co)polymers

Trimethylene carbonate (TMC) was copolymerized with D ,L ‐lactide (DLLA) or with ε‐caprolactone (CL), and the degradation of melt‐pressed solid copolymer films in phosphate‐buffered saline at pH 7.4 and 37 °C was followed for a period of over two years. The parent homopolymers were used as reference materials. The degradation profile of TMC‐DLLA‐ and TMC‐CL based copolymers was similar and was best described by autocatalyzed bulk hydrolysis, preferentially of ester bonds. The hydrolysis rates varied by two orders of magnitude, depending on polymer composition and physical characteristics under the degradation conditions. TMC‐DLLA copolymers degraded faster than the parent homopolymers. The copolymers lost their tensile strength in less than five months, after which mass loss occurred. Copolymers with 50 or 80 mol‐% of TMC underwent total degradation in eleven months. For TMC‐CL copolymers, a slow and gradual decrease in molecular weight and deterioration of the mechanical performance was observed. These copolymers maintained suitable mechanical properties for seventeen months or longer. Chain scission in the semicrystalline copolymers resulted in an increase in crystallinity. In comparison with the CL homopolymer, the introduction of a small amount of TMC (10 mol‐%) significantly reduced the increase in crystallinity during degradation. Poly(TMC) specimens were dimensionally stable and showed a negligible decrease in molecular weight. A 60% decrease in the initial tensile strength of the polymer samples was observed after two years.