Effect of the Temperature on the Stoichiometry of Borane Dimethyl Sulfide Reduction of Secondary and Tertiary Amides

A simple procedure has been described for the reduction of secondary and tertiary amides to amines using borane-dimethyl sulfide in theoretical amounts.     

Synthesis of N2 2'-deoxyguanosine adducts formed by 1-nitropyrene

[reaction: see text] Synthesis of N(2) 2'-deoxyguanosine adducts formed by the ubiquitous carcinogen, 1-nitropyrene, is reported. Various conditions of Buchwald-Hartwig palladium-catalyzed amination are examined. The most convenient synthetic approach involved a straightforward coupling between protected 2'-deoxyguanosine and bromonitropyrenes, which, upon reductive deprotection, provided excellent yield of the two 1-nitropyrene adducts.     

Templated Formation of Discrete RNA and DNA:RNA Hybrid G‐Quadruplexes and Their Interactions with Targeting Ligands

G‐rich RNA and DNA oligonucleotides derived from the human telomeric sequence were assembled onto addressable cyclopeptide platforms through oxime ligations and copper‐catalyzed azide‐alkyne cycloaddition (CuAAc) reactions. The resulting conjugates were able to fold into highly stable RNA and DNA:RNA hybrid G‐quadruplex (G4) architectures as demonstrated by UV, circular dichroism (CD), and NMR spectroscopic analysis. Whereas rationally designed parallel RNA and DNA:RNA hybrid G4 topologies could be obtained, we could not force the formation of an antiparallel RNA G4 structure, thus supporting the idea that this topology is strongly disfavored. The binding affinities of four representative G4 ligands toward the discrete RNA and DNA:RNA hybrid G4 topologies were compared to the one obtained with the corresponding DNA G4 structure. Surface plasmon resonance (SPR) binding analysis suggests that the accessibility to G4 recognition elements is different among the three structures and supports the idea that G4 ligands might be shaped to achieve structure selectivity in a biological context.     

Exploration of high‐resolution ultrasonic spectroscopy as an analytical tool to study demixing and remixing in poly(N‐isopropyl acrylamide)/water solutions

The ultrasonic properties of poly(N‐isopropyl acrylamide) (PNIPAM)/water solutions, determined with high‐resolution ultrasonic spectroscopy (HR‐US), change during demixing and remixing. All HR‐US measurements are discussed with respect to modulated temperature differential scanning calorimetry results. The lower critical solution temperature type of phase behavior, in combination with the glass‐transition/composition curve of PNIPAM/water, determines the evolution of the ultrasonic signals. Three different temperature regions can be distinguished: a homogeneous region and a heterogeneous region, the latter subdivided into zones without and with interference of partial vitrification of the PNIPAM‐rich phase. During phase separation, the ultrasonic velocity decreases because of a change in the hydration structure around the polymer chains, whereas the ultrasonic attenuation increases as aggregation sets in. Isothermal measurements clearly show time dependence for both the velocity and the attenuation. The observed timescales are different and can be related to a changing polymer/water interphase and aggregate formation, respectively. Partial vitrification of the PNIPAM‐rich phase slows the demixing kinetics and especially the remixing kinetics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1283–1295, 2005