Abstract. Algorithmic cooling (AC) is a method to purify quantum systems, such as ensembles of nuclear spins, or cold atoms in an optical lattice. When applied to spins, AC produces ensembles of highly polarized spins, which enhance the signal strength in nuclear magnetic resonance (NMR). According to this cooling approach, spin-half nuclei in a constant magnetic field are considered as bits, or more precisely quantum bits, in a known probability distribution. Algorithmic steps on these bits are then translated into specially designed NMR pulse sequences using common NMR quantum computation tools. The algorithmic cooling of spins is achieved by alternately combining reversible, entropy-preserving manipulations (borrowed from data compression algorithms) with selective reset, the transfer of entropy from selected spins to the environment. In theory, applying algorithmic cooling to sufficiently large spin systems may produce polarizations far beyond the limits due to conservation of Shannon entropy. Here, only selective reset steps are performed, hence we prefer to call this process "heat-bath" cooling, rather than algorithmic cooling. We experimentally implemented two consecutive steps of selective reset, thus transferring entropy from two selected spins to the environment. We performed such cooling experiments, with commercially available labeled molecules, on standard liquid-state NMR spectrometers. We report in particular on our original experiment, unpublished until now except on the arXiv (quant-ph/0511156) in 2005, which was, to the best of our knowledge, the world's first experiment that yielded polarizations results that bypassed Shannon's entropy-conservation bound, so that the entire spin-system was cooled.

Heat-bath cooling is a component of practicable algorithmic cooling of spins, an approach which might be useful for in vivo 13 C spectroscopy, in particular for prolonged metabolic processes where substrates that are hyperpolarized ex-vivo are not effective. We applied heat-bath cooling to 1,2-13 C 2 -amino acids, using the α protons to shift entropy from selected carbons to the environment. For glutamate and glycine, both carbons were cooled by about 2.5-fold, and in other experiments the polarization of C1 nearly doubled while all other spins had equilibrium polarization, indicating reduction in total entropy. The effect of adding Magnevist R , a gadolinium contrast agent, on heat-bath cooling of glutamate was investigated.

The 19F NMR Ca(2+)-indicator molecule 5,5'-difluoro-1,2-bis(o- aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (5-FBAPTA) was used in a procedure that enhances its range of applications to measuring free Ca2+ concentrations in buffer solutions and human erythrocytes. Even if the signal from the Ca-5-FBAPTA complex was not visible, the concentration of the complex could be calculated from saturation transfer spectra. This was demonstrated with well characterized buffer solutions in vitro and shown to also apply to concentrated haemolysates. The analysis required a precise estimate of the dissociation rate constant of the complex; this was found to be 295/s at 37 degrees C and the corresponding association rate constant was 4.1 x 10(8) L/mol/s. These values differ from those obtained previously in different buffer conditions and by two different NMR methods. A series of spectra were acquired from haemolysates containing 5-FBAPTA, in which saturating irradiation was applied at a frequency that was progressively off-set from the carrier frequency. Saturation transfer to the free 5-FBAPTA was seen from irradiation at frequencies different from that of Ca-5-FBAPTA, thus suggesting the presence of complexes with proteins.

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We present new data obtained by 23Na nuclear magnetic resonance spectroscopy, which can distinguish free intracellular sodium from cell-bound sodium, showing that the intracellular concentration of Na+ the halophilic eubacterium Vibrio costicola is only 5 to 20% of that in the extracellular medium. Previous methods could not distinguish free intracellular Nn.' from that bound to cell structures, and it was believed that in halophilic eubacteria the total monovalent cation concentration inside matched that of the NaCl outside. Information obtained by the newer technology raises fundamental questions about the ways in which these organisms and others which live in hypersaline environments function and cope with osmotic stress.Halophilic bacteria belong to two major kingdoms. The archaebacterial extreme halophiles generally require 2 to 3 M NaCl and can grow in saturated brines (16,25). The composition of their cell envelopes differs from that of eubacterial cells, and they have high proportions of negatively charged proteins in their membranes, ribosomes, and other cell components. They are known to accumulate intracellular potassium ions to balance the extracellular sodium concentrations (16,25).The second group, the eubacterial halophiles, are far more widely distributed, both environmentally and among families and genera (19,22,32), and they are of great ecological and economic importance in agriculture, food industry, and other more specialized processes. The eubacterial halophiles also show more wide-ranging salt requirements and tolerances, i.e., they are more adaptable. The mechanisms and components which enable them to grow over such a wide range (from 3-to 10-fold, according to species) of salt concentrations are still largely unknown. One of the most important questions still unresolved involves the true intracellular ion concentrations relative to those in the medium and how the organisms deal with the osmotic and ionic gradients across their cell membranes. This problem has been highlighted by studies which showed that in vitro protein-synthesizing systems from such organisms (35) and most of their intracellular enzymes were inhibited by NaCl concentrations at which the cells had been grown (12,17,35). On the other hand, earlier studies of intracellular salt concentrations in such organisms suggested that the total concentration of intracellular cations was more or less equal to the cation concentration in the extracellular milieu (3,5,15,20,23,27,28,33