Search

The world’s demand of energy is projected to double by 2050 in accordance with population growth and with the industrialization of developing countries. The supply of fossil fuel could be limited and even worse is concentrated in a few regions of world, while demand is growing everywhere. One promising alternative to fossil fuel is hydrogen which is abundant and generously distributed through the world without regard for national boundaries. The aim of this paper is to explore this early market opportunity for fuel cell cogeneration systems in buildings and to determine the conditions under which they might compete with the alternative of purchased power. It is suitable to identify and to provide solutions for problems encountered in adapting these systems to buildings through a process which involve three steps: - Determination of buildings energy annual demand compiled by a data acquisition system or logged daily by operators - Characterization of a specific fuel cell in terms of amount of heat flow available and its temperature level, based on the power output of the system - Calculation of annual energy costs (natural gas fuel and possibly purchased electrical energy) for providing power, heat and air conditioning and comparison with operating costs of existing buildings. The energy cost savings provided by the various cogeneration systems were used to provide estimates of what capital costs for each of these systems might be economically justified A numerical model is developed to perform a fuel cell cogeneration system, coupled with a Thermal Energy Storage (TES), in accordance with energy requirements of a single-family residence. The objective of the mathematical model is to calculate the energy allocation for each system component and to determine fuel use of the system on hour basis. The operation of the cogeneration system is dependent on the temperature of TES (TTS ) which varies during the hours. If the tank is hot enough (TTS ≥ Thwx temperature limit for electric domestic water heating) it can supply the entire domestic water load, otherwise if the tank is too hot (TTS ≥ Tfcx temperature limit for external heat rejection from the fuel cell) the heat transfer from the fuel cell will be limited. Two conventional systems connected to public grid are investigated as alternatives to the cogeneration ones.

New 1,1'-biphenylsulfonamides were synthesized and evaluated as inhibitors of the ubiquitous human carbonic anhydrase isoforms I, II, IX, XII, and XIV using acetazolamide (AAZ) as reference compound. The sulfonamides 1-21 inhibited all the isoforms, with Ki values in the nanomolar range of concentration, and were superior to AAZ against all of them. X-ray crystallography and molecular modeling studies on the adducts that compound 20, the most potent hCA XIV inhibitor of the series (Ki = 0.26 nM), formed with the five hCAs, provided insight into the molecular determinants responsible for the high affinity of this molecule toward the target enzymes. The results pave the way to the development of 1.1'-biphenylsulfonamides as a new class of highy potent hCA XIV inhibitors.

Hydroxylamine-O-sulfonamide, a molecule incorporating two zinc-binding groups (ZBGs), has been investigated as a carbonic anhydrase inhibitor (CAI) by means of kinetic, crystallographic and Raman spectroscopy studies, highlighting interesting results on its mechanism of action. These data can be exploited to design new, effective and selective CAIs.

Recent mutagenic and molecular modelling studies suggested a role for glycine 84 in the putative oxyanion loop of the carboxylesterase EST2 from Alicyclobacillus acidocaldarius. A 114 times decrease of the esterase catalytic activity of the G84S mutant was observed, without changes in the thermal stability. The recently solved three-dimensional (3D) structure of EST2 in complex with a HEPES molecule permitted to demonstrate that G84 (together with G83 and A156) is involved in the stabilization of the oxyanion through a hydrogen bond from its main chain NH group. The structural data in this case did not allowed us to rationalize the effect of the mutation, since this hydrogen bond was predicted to be unaltered in the mutant. Since the mutation could shed light on the role of the oxyanion loop in the HSL family, experiments to elucidate at the mechanistic level the reasons of the observed drop in k cat were devised. In this work, the kinetic and structural features of the G84S mutant were investigated in more detail. The optimal temperature and pH for the activity of the mutated enzyme were found significantly changed (T = 65°C and pH = 5.75). The catalytic constants K M and Vmax were found considerably altered in the mutant, with ninefold increased K M and 14-fold decreased Vmax, at pH 5.75. At pH 7.1, the decrease in k cat was much more dramatic. The measurement of kinetic constants for some steps of the reaction mechanism and the resolution of the mutant 3D structure provided evidences that the observed effects were partly due to the steric hindrance of the S84-OH group towards the ester substrate and partly to its interference with the nucleophilic attack of a water molecule on the second tetrahedral intermediate. Proteins 2008. © 2007 Wiley-Liss, Inc.

Esterase 2 (EST2) from the thermophilic eubacterium Alicyclobacillus acidocaldarius is a thermostable serine hydrolase belonging to the H group of the esterase/lipase family. This enzyme hydrolyzes monoacylesters of different acyl-chain length and various compounds with industrial interest. EST2 displays an optimal temperature at 70 °C and maximal activity with p NP-esters having acyl-chain bearing from six to eight carbon atoms. EST2 mutants with different substrate specificity were also designed, generated by site-directed mutagenesis, and biochemically characterized. To better define at structural level the enzyme reaction mechanism, a crystallographic analysis of one of these mutants, namely M211S/R215L, was undertaken. Here we report its three-dimensional structure at 2.10 A resolution. Structural analysis of the enzyme revealed an unexpected dimer formation as a consequence of a domain-swapping event involving its N-terminal region. This phenomenon was absent in the case of the enzyme bound to an irreversible inhibitor having optimal substrate structural features. A detailed comparison of the enzyme structures before and following binding to this molecule showed a movement of the N-terminal helices resulting from a trans – cis isomerization of the F37–P38 peptide bond. These findings suggest that this carboxylesterase presents two distinct structural arrangements reminiscent of the open and closed forms already reported for lipases. Potential biological implications associated with the observed quaternary reorganization are here discussed in light of the biochemical properties of other lipolytic members of the H group.