PubMed · 4434139
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1974-12-07. Editorial: Outmoded barbiturates.. https://pubmed.ncbi.nlm.nih.gov/4434139/
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The amplification of supramolecular chirality has been studied in dynamic chiral hydrogen-bonded assemblies 1(3).(CA)(6) using "Sergeants and Soldiers" experiments. Previously, we have shown that chiral centers present in either the dimelamine component 1 or the cyanurate component CA quantitatively induce one handedness (M or P) in the assembly. This offers the possibility to study the amplification of chirality under two different kinetic regimes. When chiral dimelamines 1 are used, the exchange of chiral components and (M/P)-interconversion, i.e., interconversion between the (M)- and (P)-isomers of assembly 1(3).(CA)(6), take place via identical pathways (condition A). When chiral cyanurates CA are used, the exchange of chiral components occurs much faster than (M/P)-interconversion (condition B). Experimentally, a much stronger chiral amplification is observed under condition B. For example, the observed chiral amplification for a mixture of chiral and achiral components (40:60) is 46% under condition B and 32% under condition A. Kinetic models were developed to fit the experimental data and to simulate chiral amplification in dynamic systems in general. These simulations show that it is theoretically possible that the diastereomeric excess in a dynamic system is more than 99% with less than 1% chiral component present!
Recent developments in microfluidics have enabled the design of a lab-on-a-chip system capable of measuring cellular membrane potential. The chip accesses liquid samples sequentially by sipping from a microplate through a capillary, mixes the samples with cells flowing through a microchannel, contacts the cells with potential-sensitive dyes, and reads out cellular responses using fluorescence detection. The rate of cellular uptake of membrane-permeable, ionic fluorophores by THP-1 cells was found to depend strongly on membrane potential. The ratio of the fluorescence of the anionic dye DiBAC(4)(3) and the cationic dye Syto 62 taken up by cells was found to double for every 33 mV change in membrane potential. The utility of this approach was demonstrated by assaying ion channel activity in human T lymphocytes. Because of the high sensitivity, low cellular and reagent consumption, and high data quality obtained with the microfluidic device, the lab-on-a-chip system should be widely applicable in high-throughput screening and functional genomics studies.
New and improved methods to determine the membrane potential (Delta Psi) and the Delta pH in methanogenic archaea were developed and tested in Methanobacterium thermoautotrophicum strain Delta H. The Delta pH measurements took advantage of the pH-dependent fluorescence properties of coenzyme F(420), the major intracellular electron carrier in the organism. The protonophore p-nitrophenol did not show any interference with the F(420) fluorescence spectra and was therefore suitable to equalize internal and external pH. The method developed allowed the determination of the intracellular pH with an error of less than 0.05 pH units.Membrane potentials could easily be assessed using the fluorescent probe bis-(1,3-dibutylbarbituric acid)trimethine oxonol (DiBAC(4)(3)) with an accuracy of approximately 10 mV. Both methods were tested with cell suspensions of M. thermoautrophicum incubated at medium pH values between 5.5 and 8. It was found that Delta Psi and Delta pH values remained constant under these conditions. Membrane potentials were about -160 mV and Delta pH was kept at 0.35 pH units (inside minus outside) resulting in a total proton motive force of about -180 mV (inside negative).