Cyclic Ethers as Synthetic Equivalents of ω-Alkyn-1-ols

ω -Alkyn-1-ols were obtained by treatment of thiophenyl α-sustituted tetrahydrofuranes under KAPA Acetylenic Zipper conditions.     

An Improved Bound for the Crossing Number of C<Subscript><Emphasis Type="Italic">m</Emphasis></Subscript>C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>: a Self–Contained Proof Using Mostly Combinatorial Arguments

We present some surprisingly elementary arguments to prove that for every >0, if m is sufficiently large, then the crossing number of the Cartesian product C_m×C_n is at least (0.8–)mn, for every nm. The self–contained proof we give involves only one (rather elementary) geometrical result. The rest of the proof involves purely combinatorial arguments.Supported by CONA-CYT (Grant J32168E) and by FAI-UASLPFinal version received: July 14, 2003     

The assessment of viability in isolated rat hepatocytes subjected to cold or subzero non-freezing preservation protocols using a propidium iodide modified test

A rapid and simple assay (6 min, two steps) is described for determination of cell viability of hepatocytes subjected to cold preservation protocols. In this method, cells are incubated with the fluorescent marker propidium iodide (PI) and the fluorescence intensity is measured before (direct fluorescence--Fd) and after (total fluorescence--Ft) addition of digitonin, which allows the dye to enter the hepatocytes. The Fd originated from non-viable cells that have membrane damage and taken up PI. The Ft originated from all cells in the sample. The ratio between the two fluorescence values is used as an indicator of cell viability. The assay was challenged versus two classical viability tests: LDH retention and Trypan Blue exclusion. Our assay shows good correlation only with Trypan Blue test. In addition, a fluorescence confocal microscopy protocol was used to evaluate the possible toxicity of PI in hepatocyte suspensions.     

Peripheral substitution of a near-IR-absorbing soluble phthalocyanine using "click" chemistry

A series of near-IR-absorbing soluble phthalocyanines (Pcs) with eight alkyne moieties as side chains of the chromophore have been synthesized. One of these Pcs has been used as a scaffold for functional group modification using alkyne-azide click chemistry with various azides. This led to a small library of Pcs with photo and thermal crosslinkable, dendritic, and hydrophilic moieties starting from a single Pc molecule. A patterned thin film was fabricated by photocrosslinking one of these Pc derivatives.