Controlled stacking of charged block copolymer micelles

Using poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene (PAA-b-PMA-b-PS) triblock copolymers or a mixture of different molecular weight PAA-b-PS diblock copolymers, stacks of polymeric micellar assemblies, such as disks and Y-shaped cylinders, were formed through intermicellar interactions. Whereas micelles hierarchically stacked together, micellar interactions within the stack defined a uniform micelle geometry and size for up to micrometers in length. The kinetic pathway dependence and stability of the stacked assemblies were studied, and possible intermicellar interactions between micelles within the stacks are proposed.     

Ion-molecule chemistry within boron tribromide clusters: experiment and theory

Molecular clusters of BBr3 were subjected to electron ionization and mass analysis in a reflectron time-of-flight mass spectrometer. Five series of cluster ions were observed, with formulas corresponding to each of the possible fragment ions of BBr3 being solvated by neutral BBr3 molecules. Geometry optimizations on the observed cluster ions using density functional theory (B3LYP/6-31G*) predict that fragment ions smaller than BBr3+ undergo reactions with neutral BBr3 molecules to form covalently bound adduct species that function as core ions within the clusters. Once all boron atoms are saturated, the reactions cease, and larger cluster ions consist of BBr3 molecules loosely bound to the core ions. Divalent bromine atoms are present in at least three of the cluster ions, and most of the intermolecular contact within the clusters is between Br atoms. Enthalpies of formation, addition reactions, and BBr3 elimination from the cluster ions were derived from B3LYP and MP2 calculations at the B3LYP/6-31G* geometries using both the 6-31G* and the 6-311++G(2df,2p) basis sets. The results are compared to limiting expectations based on known bulk thermochemistry.     

Curcumin-Loaded Microspheres Are Effective in Preventing Oxidative Stress and Intestinal Inflammatory Abnormalities in Experimental Ulcerative Colitis in Rats

Curcumin’s role in the treatment of ulcerative colitis (UC) has been proven by numerous studies, but its preventive administration, with the aim of reducing the remission episodes that are characteristic of this disease, must be further investigated. This study investigates the effects of a novel curcumin-loaded polymeric microparticulate oral-drug-delivery system for colon targeting (Col-CUR-MPs) in an experimental model of UC. Male Wistar rats (n = 40) were divided into five groups (n = 8), which were treated daily by oral gavage for seven days with a 2% aqueous solution of carboxymethylcellulose sodium salt (CMCNa) (healthy and disease control), free curcumin powder (reference), Col-CUR-MPs (test) and prednisolone (reference) prior to UC induction by the intrarectal administration of acetic acid (AA), followed by animal sacrification and blood and colonic samples’ collection on the eighth day. Col-CUR-MPs exhibited an important preventive effect in the severity degree of oxidative stress that resulted following AA intrarectal administration, which was proved by the highest catalase (CAT) and total antioxidant capacity (TAC) levels and the lowest nitrites/nitrates (NOx), total oxidative status (TOS) and oxidative stress index (OSI) levels. Biochemical parameter analysis was supported by histopathological assessment, confirming the significant anti-inflammatory and antioxidant effects of this novel colon-specific delivery system in AA-induced rat models of UC. Thus, this study offers encouraging perspectives regarding the preventive administration of curcumin in the form of a drug delivery system for colon targeting.     

Synthesis and linear and nonlinear optical properties of metal-terminated bis(dioxaborine) polymethines

Rh(III) and Ir(III) can be complexed to bipyridine groups attached to the termini of bis(dioxaborine)-capped heptamethines; these chromophores exhibit large third-order polarisabilities at 1.55 μm, while retaining good film-forming properties and linear optical transparency in the near infrared.     

4Fe4S]2+ clusters exhibit ground-state paramagnetism

Two proteins involved in nitrogen fixation contain ferredoxin-type [4Fe4S] clusters that exist in paramagnetic ground state upon oxidation, a property never observed since the discovery of ferredoxins 50 years ago. This unique characteristic suggests a specific coupling in these clusters necessary for nitrogen fixation and implies an evolutionary connection between the clusters in the two proteins.     

Cyanine‐Like Dyes with Large Bond‐Length Alternation

Herein, the synthesis and properties of alkyne‐bridged carbocations, which are analogous in structure to cyanine dyes, are reported. An alkene‐bridged dye, linked at the third position of the indole, was also synthesized as a reference compound. These new carbocations are stable under ambient conditions, allowing characterization by UV/Vis and NMR (¹H and ¹³C) spectroscopies. These techniques revealed a large degree of delocalization of the positive charge, similar to a previously reported porphyrin carbocation. The linear and nonlinear optical properties are compared with cyanine dyes and triarylmethyl cations, to investigate the effects of the bond‐length alternation and the overall molecular geometry. The value of Re(γ), the real part of the third‐order microscopic polarizability, of ?1.3×10^?33 esu for the alkyne‐linked cation is comparable to that of a cyanine dye of similar length. Nondegenerate two‐photon absorption spectra showed that the alkene‐bridged dye exhibited characteristics of cyanines, whereas the alkyne‐bridged dye is reminiscent of octupolar chromophores, such as the triarylmethyl carbocation brilliant green. Such attributes were confirmed and rationalized by quantum chemical calculations.     

Sphere Packing, IV. Detailed Bounds

This paper is the fourth in a series of six papers devoted to the proof of the Kepler conjecture, which asserts that no packing of congruent balls in three dimensions has density greater than the face-centered cubic packing. In a previous paper in this series, a continuous function f on a compact space was defined, certain points in the domain were conjectured to give the global maxima, and the relation between this conjecture and the Kepler conjecture was established. The function f can be expressed as a sum of terms, indexed by regions on a unit sphere. In this paper detailed estimates of the terms corresponding to general regions are developed. These results form the technical heart of the proof of the Kepler conjecture, by giving detailed bounds on the function f. The results rely on long computer calculations.