Exceptional gas permeation selectivity of a glued Langmuir-Blodgett bilayer by pH control

The monolayer properties of 5,11,17,23,29,35-hexakis[(N,N,N-trimethylamonium)-N-methyl-37,38,39,40,41,42-hexakis-n-hexadecyloxy-calix[6]arene hexachloride (1) have been characterized over aqueous solutions of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) as a function of pH. At high pH values (e.g., pH 10), such monolayers show relatively low surface viscosities. At low pH (e.g., pH 4.4), these monolayers exhibit relatively high surface viscosities. The barrier properties of single Langmuir-Blodgett bilayers of 1, which have been ionically cross-linked (i.e., "glued together") with PAA were found to correlate with changes in surface viscosity. Thus, bilayers that were fabricated under low pH conditions exhibited high permeation barriers and high permeation selectivity with respect to He and N(2). Given the extreme thinness of these glued bilayers (ca. 6 nm), the optimized He/N(2) selectivity of ca. 1000 is extraordinary. These results, taken together, demonstrate the feasibility of fine tuning the surface viscosity of monolayers of 1, and also the barrier properties of corresponding glued bilayers, by adjusting the pH of an aqueous subphase that contains a weak polyacid.     

Photosensitizers in dermatology

Systemic injection of hematoporphyrin derivative (HpD) in contribution with visible light (red or blue-green) delivered by laser was used to treat a patient with psoriasis. The psoriatic lesions responded vigorously to laser treatments, forming eschars by 1 week post irradiation. In contrast, only minimal erythema was observed in the noninvolved, clinically normal appearing skin. Two approaches for localized HpD administration were investigated in the guinea-pig and minipig models as a means of achieving local photodynamic effects. Intracutaneous injection of HpD produced localized cutaneous photosensitization with either UVA or red light. Azone increased percutaneous penetration of HpD in human skin in vitro. Topical application of HpD and irradiation with UVA produced localized cutaneous photosensitivity and inhibition of epidermal DNA synthesis.     

A quantitative assessment of the influence of permanent kinks on the mixing behavior of phospholipids in cholesterol-rich bilayers

The mixing behavior of a phospholipid containing a cis-cyclopropyl moiety (1) with one that contains two myristoyl groups (3a) has been investigated in fluid bilayers via the nearest-neighbor recognition (NNR) method. In the absence of cholesterol, these lipids mix ideally. In the presence of cholesterol, they show a modest preference for homo-phospholipid association. A trans-form of 1 (i.e., 2) was found to have similar behavior, except that the influence of cholesterol in promoting homo-phospholipid association was greater. Similar results have been found in membranes in which 3a is replaced with a phospholipid bearing two palmitoyol chains (3b). In this case, the effect of the kink is approximately twice as great. The implications of these findings, with respect to the "trans-fatty acid debate", are briefly discussed     

Classification of all noncommutative polynomials whose Hessian has negative signature one and a noncommutative second fundamental form

Every symmetric polynomial p = p(x) = p(x ₁,..., x _g ) (with real coefficients) in g noncommuting variables x ₁,..., x _g can be written as a sum and difference of squares of noncommutative polynomials:

Isometric representations of some quotients ofH ∞ of an annulus

Let denote an annulus,E a finite subset of with at least three elements, and the ideal of functions in which vanish at the points ofE. The quotient does not have a completely isometric representation on a finite dimensional Hilbert space. This complements a result of [11] which implies that the quotient has an isometric representation on a Hilbert space of dimension twice the cardinality ofE.     

Incorporation of poly(2‐acrylamido‐2‐methyl‐N‐propanesulfonic acid) segments into block and brush copolymers by ATRP

2‐Acrylamido‐2‐methyl‐N‐propanesulfonic acid (AMPSA) was successfully polymerized via atom transfer radical polymerization (ATRP) using a copper chloride/2,2′‐bipyridine (bpy) catalyst complex after in situ neutralization of the acidic proton in AMPSA with tri(n‐butyl)amine (TBA). A 5 mol % excess of TBA was required to completely neutralize the acid and prevent protonation of the bpy ligand, as well as to avoid side reactions caused by large excess of TBA. The use of activators generated by electron transfer (AGET) ATRP with ascorbic acid as reducing agent resulted in both increased conversion of the AMPSA monomer during polymerization (up to 50% with a 0.8 [ascorbic acid]/[Cu(II)] ratio) and much shorter polymerization times (<30 min). Block copolymers and molecular brushes containing AMPSA side chains were prepared using this method, and the solution and surface behavior of these materials were investigated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5386–5396, 2009     

Development of a microfluidic paper-based analytical device for the determination of salivary aldehydes

A low cost, disposable and easy to use microfluidic paper-based analytical device (μPAD) was developed for simple and non-invasive determination of total aldehydes in saliva with a potential to be used in epidemiological studies to assess oral cancer risk. The μPAD is based on the colour reaction between aldehydes (e.g. acetaldehyde, formaldehyde), 3-methyl-2-benzothiazolinone hydrazone (MBTH) and iron(III) to form an intense blue coloured formazan dye. The newly developed μPAD has a 3D design with two overlapping paper layers. The first layer comprises 15 circular detection zones (8 mm in diameter), each impregnated with 8 μL of MBTH, while the second layer contains 15 reagent zones (4 mm in diameter). Two μL of iron(III) chloride are added to each one of the second layer zones after the addition of sample to the detection zones in the first layer. All hydrophilic zones of the μPAD are defined by wax printing using a commercial wax printer.