Interaction of nonionic surfactants with copolymer microgel particles of NIPAM and acrylic acid

Binding of the nonionic surfactants Triton X-100 and Triton X-405 onto linear copolymers of N-isopropylacrylamide (NIPAM) and acrylic acid and to cross-linked microgel particles of similar composition but differing in their cross-link densities has been studied. The binding capacities vary for each of these polymeric systems, being smallest for the linear copolymer. The binding is also significantly less in all cases for the more hydrophilic surfactant, namely, Triton X-405. By comparing estimates of the pore or "cage" size within the microgel particles with the dimensions of the free micelles in solution, it is concluded that micelles of Triton X-100 form within the microgel particles more readily for the lower cross-linked microgel particles. However, micelles do not form as easily inside either microgel for Triton X-405. The swelling/deswelling behavior of each of the two microgels, in the presence of the surfactants, has been explained in terms of their relative binding behavior and how this contributes to the osmotic pressure difference inside and outside the microgel particles and also in terms of micelle "bridging" of the polymer network, causing shrinkage.     

A series of novel lanthanide polyoxometalates: condensation of building blocks dependent on the nature of rare earth cations

A series of novel lanthanide polyoxomolybdates was synthesized by reaction of lanthanide cations with the Anderson type anion (TeMo(6)O(24))(6-). The polyoxometalates K(6n)(TeMo(6)O(24))(n)[(Ln(H(2)O)(7))(2)(TeMo(6)O(24))](n)[middle dot]16nH(2)O (Ln = Eu, Gd) and K(3n)[Ln(H(2)O)(5)(TeMo(6)O(24))](n)[middle dot]6nH(2)O (Ln = Tb, Dy, Ho, Er) were characterized by X-ray structure analysis, elemental analysis and IR spectroscopy. We found that the solid-state structures of Ln/(TeMo(6)O(24))(6-) compounds are strongly dependent on the lanthanide cations, and therefore represent a rare example for different arrangements of building units depending on the nature of the rare earth cations. While the Eu(3+) and Gd(3+) cations achieve ninefold coordination by seven water molecules and two terminal oxygen atoms of the (TeMo(6)O(24))(6-) anions, the Tb(3+), Dy(3+), Ho(3+) and Er(3+) cations are coordinated by five water molecules, two terminal oxygen atoms and one molybdenum-bridging oxygen atom belonging to the (TeMo(6)O(24))(6-) anion. The europium and gadolinium substituted compounds contain infinite one-dimensional [(Ln(H(2)O)(7))(2)(TeMo(6)O(24))](n) chains; the terbium, dysprosium, holmium and erbium compounds contain infinite one-dimensional [Ln(H(2)O)(5)(TeMo(6)O(24))](n)(3n-) chains.     

2-Aminopurine: a probe of structural dynamics and charge transfer in DNA and DNA:RNA hybrids

Spectroscopic techniques are employed to probe relationships between structural dynamics and charge transfer (CT) efficiency in DNA duplexes and DNA:RNA hybrids containing photoexcited 2-aminopurine (Ap). To better understand the variety of interactions and reactions, including CT, between Ap and DNA, the fluorescence behavior of Ap is investigated in a full series of redox-inactive as well as redox-active assemblies. Thus, Ap is developed as a dual reporter of structural dynamics and base-base CT reactions in nucleic acid duplexes. CD, NMR, and thermal denaturation profiles are consistent with the family of DNA duplexes adopting a distinct conformation versus the DNA:RNA hybrids. Fluorescence measurements establish that the d(A)-r(U) tract of the DNA:RNA hybrid exhibits enhanced structural flexibility relative to that of the d(A)-d(T) tract of the DNA duplexes. The yield of CT from either G or 7-deazaguanine (Z) to Ap in the assemblies was determined by comparing Ap emission in redox-active G- or Z-containing duplexes to otherwise identical duplexes in which the G or Z is replaced by inosine (I), the redox-inactive nucleoside analogue. Investigations of CT not only demonstrate efficient intrastrand base-base CT in the DNA:RNA hybrids but also reveal a distance dependence of CT yield that is more shallow through the d(A)-r(U) bridge of the A-form DNA:RNA hybrids than through the d(A)-d(T) bridge of the B-form DNA duplexes. The shallow distance dependence of intrastrand CT in DNA:RNA hybrids correlates with the increased conformational flexibility of bases within the hybrid duplexes. Measurements of interstrand base-base CT provide another means to distinguish between the A- and B-form helices. Significantly, in the A-form DNA:RNA hybrids, a similar distance dependence is obtained for inter- and intrastrand reactions, while, in B-DNA, a more shallow distance dependence is evident with interstrand CT reactions. These observations are consistent with evaluations of intra- and interstrand base overlap in A- versus B-form duplexes. Overall, these data underscore the sensitivity of CT chemistry to nucleic acid structure and structural dynamics.     

Distribution of CdSe quantum dots within swollen polystyrene microgel particles using confocal microscopy

CdSe quantum dots (QDs) are semiconducting nanoparticles that fluoresce when stimulated by visible light. This property has been exploited in their use as tracer particles in biomedical applications. In this study, confocal microscopy has been used to determine the distribution of QDs within polystyrene microgel particles, dispersed in an organic solvent. It was found that the extent of microgel swelling affected the penetration of the QDs into the particles. Only when the microgel particles were swollen to their maximum extent were the QDs able to penetrate into the central core region of the particles.     

Zur Bestimmung von Ammoniak in Lebensmitteln

Zusammenfassung In einer Vakuumapparatur mit modifizierter Destilliervorlage wurden die für ein schonendes Verfahren optimalen Destillationsbedingungen zur quantitativen Freisetzung geringer Ammoniakmengen ermittelt, wobei sich z.B. eine Alkalisierung auf mindestens pH 9 ergab.Die Anwendung dieser Methode auf proteinhaltige Lebensmittel liefert ebenfalls — wenn auch nur in geringem Maße — Ammoniakabspaltungen, die wieder von der Art der Substanzen, der Alkalität der Lösung und der Destillationsdauer abhängig sind. Veränderungen im Verhältnis von Einwaagemenge zu Alkalisierungsmittel liefern daher über Alkalitätsverschiebungen auch jeweils etwas unterschiedliche Ammoniakausbeuten.Diese Vakuumdestillation im Makromaßstab ist bei Ammoniakbestimmungen in Substanzgemischen mit empfindlichen organischen Stickstoffverbindungen der Wasserdampfdestillation bei Normaldruck zwar überlegen, sie kann jedoch nicht als zuverlässige Methode empfohlen werden.

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Determination of ammonia in foodII. Examination of the vacuum distillation

In a vacuum apparatus with modified receiver the optimum conditions for a careful procedure for the quantitative liberation of small amounts of ammonia were tested. An alkalinity of at least pH 9 was necessary.Using this method with foods containing protein, ammonia was released too, though only in small amounts. These are depending not only on the type of substances, but also on the alkalinity of solution and the duration of distillation. Therefore, variations in the relationship between the amount of sample and the solution for alkalisation effect a change of alkalinity and thereby different yields of ammonia.For determinations of ammonia in mixtures of substances with instable nitrogen compounds the macrovacuum-apparatus is superior to the steam distillation applying normal pressure, but cannot be recommended as an reliable method.

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I. Mitteilung: diese Z. 244, 379 (1969).

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Auszug aus der Dissertation W. Sturm: Zur Bestimmung von Ammoniak in Getreidemehlen und Backwaren. Techn. Univ. Braunschweig 1967.     

Selective Cross-Coupling of Unsaturated Substrates on AlI

The Al^I compound NacNacAl ( 1 , NacNac = [ArNC(Me)CHC(Me)NAr]⁻, Ar = 2,6-iPr₂C₆H₃) serves as a template for the chemoselective coupling between carbonyls (benzophenone, fenchone, isophorone, p-tolyl benzoate, N,N-dimethylbenzamide, (1-phenylethylidene)aniline) and pyridine. With the CH-acidic ketone (1R)-(+) camphor, the reaction affords a hydrido alkoxide compound of Al, formed as the result of enolization, whereas an enolizable imine, (1-phenylethylidene)aniline, and the bulky ketone isophorone, still chemoselectively couple with pyridine. In contrast, reaction with the ester p-tolyl benzoate results in cleavage of the ester bond together with replacement of the alkoxy group by a hydrogen atom of the pyridine moiety. This study demonstrates that for carbonyl substrates featuring phenyl substituents, the reaction proceeds via intermediate formation of η²(C,X)-coordinated (X = O, N) carbonyl adducts, whereas the reaction of 1 with (R)-(−)-fenchone in the absence of pyridine leads to CH activation in the pendant isopropyl group of the Ar substituent of the NacNac ligand.     

Neurofibrillary tangles and plaques are not accompanied by white matter pathology in aged triple transgenic-Alzheimer disease mice

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is the most common cause of dementia in aging populations. Although senile plaques and neurofibrillary tangles are well-established hallmarks of AD, changes in cerebral white matter correlate with cognitive decline and may increase the risk of the development of dementia. We used the triple transgenic (3xTg)-AD mouse model of AD, previously used to show that white matter changes precede plaque formation, to test the hypothesis that MRI detectable changes occur in the corpus callosum, external capsule and the fornix. T₂-weighted and diffusion tensor magnetic resonance imaging and histological stains were employed to assess white matter in older (11–17 months) 3xTg-AD mice and controls. We found no statistically significant changes in white matter between 3xTg-AD mice and controls, despite well-developed neurofibrillary tangles and beta amyloid immunoreactive plaques. Myelin staining was normal in affected mice. These data suggest that the 3xTg-AD mouse model does not develop MRI detectable white matter changes at the ages we examined.