Characterization of internal structure of hydrated agar and gelatin matrices by cryo‐SEM

There has been a considerable interest in recent years in developing polymer gel matrices for many important applications such as 2DE for quantization and separation of a variety of proteins and drug delivery system to control the release of active agents. However, a well‐defined knowledge of the ultrastructures of the gels has been elusive. In this study, we report the characterization of two different polymers used in 2DE: Gelatin, a naturally occurring polymer derived from collagen (protein) and agar, a polymer of polysaccharide (sugar) origin. Low‐temperature SEM is used to examine the internal structure of these gels in their frozen natural hydrated states. Results of this study show that both polymers have an array of hollow cells that resembles honeycomb structures. While agar pores are almost circular, the corresponding Gaussian curve is very broad exhibiting a range of radii from nearly 370 to 700 nm. Gelatin pores are smaller and more homogeneous reflecting a narrower distribution from nearly 320 to 650 nm. Overall, these ultrastructural findings could be used to correlate with functions of the polymers.     

Unusual synthesis of azines and their oxidative degradation to carboxylic acid using iodobenzene diacetate

Reaction of 3-hydrazonobutan-2-one oxime with aromatic aldehydes resulted in the formation of 1,2-bis(arylidene)hydrazine commonly referred as azine as an unexpected product, instead of expected product 3-(aryl)methylenehydrazonobutan-2-one oxime, which were subsequently oxidized to corresponding aromatic acids with an ecofriendly oxidizing agent iodobenzene diacetate. Azines and carboxylic acids were characterized by IR and NMR (¹H, ¹³C, HMBC, and HMQC) studies.     

1,1′‐Methylenedipyridinium tetrachloridocuprate(II) and bis[tetrachloridoaurate(III)] hybrid salts by X‐ray powder diffraction

In order to explore the potential propensity of the 1,1′‐methylenedipyridinium dication to form organic–inorganic hybrid ionic compounds by reaction with the appropriate halide metal salt, the organic–inorganic hybrid salts 1,1′‐methylenedipyridinium tetrachloridocuprate(II), (C₁₁H₁₂N₂)[CuCl₄], (I), and 1,1′‐methylenedipyridinium bis[tetrachloridoaurate(III)], (C₁₁H₁₂N₂)[AuCl₄]₂, (II), were obtained by treatment of 1,1′‐methylenedipyridinium dichloride with CuCl₂ and Na[AuCl₄], respectively. Both hybrid salts were isolated as pure compounds, fully characterized by multinuclear NMR spectroscopy and their molecular structures confirmed by powder X‐ray diffraction studies. The crystal structures consist of discrete 1,1′‐methylenedipyridinium dications and [CuCl₄]²⁻ and [AuCl₄]⁻ anions for (I) and (II), respectively. As expected, the dications form a butterfly shape; the Cu^II centre of [CuCl₄]²⁻ has a distorted tetrahedral configuration and the Au^III centre of [AuCl₄]⁻ shows a square‐planar coordination. The ionic species of (I) and the dication of (II) each have twofold axial symmetry, while the two [AuCl₄]⁻ anions are located on a mirror‐plane site. Both crystal structures are stabilized by intermolecular C—H...Cl hydrogen bonds and also by Cl...π interactions. It is noteworthy that, while the average intermolecular centroid–centroid pyridinium ring distance in (I) is 3.643 (8) Å, giving strong evidence for noncovalent π–π ring interactions, for (II), the shortest centroid–centroid distance between pyridinium rings of 5.502 (9) Å is too long for any significant π–π ring interactions, which might be due to the bulk of the two [AuCl₄]⁻ anions.     

Diverse Reactivity of Dienes with Pentaphenylborole and 1-Phenyl-2,3,4,5-Tetramethylborole Dimer

The reactions of a monomeric borole and a dimeric borole with 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene were investigated. The monomeric borole reacted at ambient temperature whereas heat was required to crack the dimer to form the monomer and induce reactivity. 2,3-Dimethyl-1,3-butadiene reacts to give diverse products resulting from a cycloaddition process with the B−C moiety of the boroles acting as a dienophile, followed by rearrangements to furnish bicyclic species. For 1,3-cyclohexadiene, a [4+2] process is observed in which 1,3-cyclohexadiene serves as the dienophile and the boroles as the diene partner. The experimental results are corroborated with mechanistic theoretical calculations that indicate boroles can serve as either a diene or dienophile in cycloaddition reactions with dienes.