Hydrides modulation

The Ergenics unit is modular in construction and portable. Applications include storage for fuel cells and electrolyzers as well as hydride modules for compressors and heat pumps. 

Figure 1. The MHHP modular sorber diagram 1 - tubular case of the hydride module 2 -corrugated heat-conducting insert 3 - hydrogen ceramic collector-filter 4 - metal hydride 5 - tip of a metal hydride bed 6 - hydrogen manifold 7 - spacer plate 8 - heat exchanger shroud 9 - union 10 - flange-cover of a heat exchanger. Heat exchanger thermal insulation is not shown conditionally.

There have been numerous studies with the objective of gaining an understanding of the factors that influence the stability, stoichiometry, and H-site occupation in hydride phases. Stability has been correlated with cell volume [7] or the size of the interstitial hole in the metal lattice [8] and the free energy of the a p phase conversion. This has been widely exploited to modulate hydride phase stability, as discussed in Sec. 7.2.2.1. 

Homocitrate acting as a leaving group modulating the reduction potential of Mo and opening up coordination sites for hydrides... 

Chondroitin 6-sulfate, 4 706 Chondroitin sulfates, 20 456 Chopped strand mat (CSM), 26 751 Chopper pumps, 21 78 Chop-stx number, for boron hydrides, 4 183 Chorinated trisodium phosphate, 4 52 Christmas tree module design, 15 835 Chromacity diagrams, 7 313-315 Chromaphores, 19 379 Chromate coatings, 9 827 Chromate conversion coatings, 16 218 Chromated copper arsenate, 3 276 ... 

Nickel formate dihydrate, 77 117 Nickel halides, 77 109-110 Nickel-hydride battery modules, 7 7 95... 

The minimal functional module in [NiFe] hydrogenases always contains the NiFe(CN)2(CO) site plus the proximal [4Fe-4S] cluster. The active site in [Fe] hydrogenases consists of the Fe-Fe site linked to a [4Fe-4S] cluster. Oxidation of the hydride is either an action of the dinuclear site alone, or a concerted action of this site plus the proximal cluster. 

We do not know exactly where the hydrogen binds at the active site. We would not expect it to be detectable by X-ray diffraction, even at 0.1 nm resolution. EPR (Van der Zwaan et al. 1985), ENDOR (Fan et al. 1991b) and electron spin-echo envelope modulation (ESEEM) (Chapman et al. 1988) spectroscopy have detected hyperfine interactions with exchangeable hydrous in the NiC state of the [NiFe] hydrogenase, but have not so far located the hydron. It could bind to one or both metal ions, either as a hydride or H2 complex. Transition-metal chemistry provides many examples of hydrides and H2 complexes (see, for example. Bender et al. 1997). These are mostly with higher-mass elements such as osmium or ruthenium, but iron can form them too. In order to stabilize the compounds, carbonyl and phosphine ligands are commonly used (Section 6). 

Bio)chemical reactions may take place prior to or after the continuous separation module and are intended to enhance or facilitate mass transfer, detection or both. The earliest and simplest approach to integrated analytical steps in continuous-flow systems involves a combination of chemical reactions and continuous separations [4,5]. Such is the case with the formation of soluble organic chelates of metal ions in liquid-liquid extractions with the ligand initially dissolved in the organic stream [6], the formation and dissolution of precipitates [7], the formation of volatile reaction products in gas difiusion [8] and that of volatile hydrides in atomic absorption spectro-... 

The main units of installation are sorbers forming two units of a metal hydride heat pump. Sorbers of the first unit are modular-type. Modules of the first unit sorbers have seven thin-walled steel tubes 25 mm in diameter. When installation works, water is run through a sorber case and flow around external surface of modules heating or cooling them. 

Fig. 4.1. Hydride and cold mercury vapour separators. (A) Sandwich-type. (B) Tubular-type. (C) Modified Vijan-type. (D) Commercial-type (Perkin-Elmer FIAS-200 module). (E) With direct introduction of the stripping gas into the separator. (F) Dismountable separator for solid samples. (Reproduced with permission of the Royal Society of Chemistry and Perkin-Elmer.)...

Pre-steady-state kinetic studies established that the appearance of the NADH chromophore on addition of substrate was a two-step process, and these steps can now be identified as closure of the active site and hydride transfer. This study indicated that the on-enzyme equilibrium for addition of water or homocysteine to the enone was close to unity (and the value in free solution), whereas the equilibrium for oxidation of NAD by bound adenosine was 10 times more favourable than in free solution. The focusing of the catalytic power of the enzyme on the oxidation step avoids the formation of abortive complexes by hydride transfer between enone and NADH, yielding 4,5-dehydroadenosine and NAD ". This happens about 10 " times faster than productive hydride transfer at the beginning and end of the catalytic cycle, with the slow rate (close to that of model reactions) apparently arising from a conformationally modulated increase in the distance the hydride has to be transferred. 

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