Adsorption and Desorption Behaviors of Ammonia on Zeolites at 473 K by the Pressure-Swing Method.

Adsorption and desorption behaviors of ammonia on the zeolites were investigated using the pressure-swing method to utilize the ammonia adsorbent at 473 K. For various (Y, A, L, and mordenite) types of zeolites, the effects of their pore sizes, countercation species, and number of adsorption sites on the ammonia adsorption behavior were evaluated. The adsorption capacity increased with increasing the pore size. The differences in the countercation species and the number of adsorption sites contributed to the ammonia adsorption process on the zeolites. Sodium cations strongly adsorb ammonia molecules. The adsorption/desorption of ammonia expanded and shrunk the zeolite crystal, suggesting that the pores in the zeolite were enlarged by the adsorption of ammonia molecules. Despite repetitive lattice expansion and shrinkage, the morphologies of the zeolite particles were not degraded. These results confirm that the zeolite showed high durability for the adsorption and desorption of ammonia at 473 K.

Hydration of LiOH and LiCl-Near-Infrared Spectroscopic Analysis.

The hydration behavior of LiOH, LiOH·H2O, and LiCl was observed by near-infrared (NIR) spectroscopy. Anhydrous LiOH showed two absorption bands at 7340 and 7171 cm-1. These NIR bands were assigned to the first overtone of surface hydroxyls and interlayer hydroxyls of LiOH, respectively. LiOH·H2O showed two absorption bands at 7137 and 6970 cm-1. These NIR bands were assigned to the first overtone of interlayer hydroxyls and H2O molecules coordinated with Li+, respectively. The interlayer OH- and the coordinated H2O of LiOH·H2O were not modified even when the LiOH·H2O was exposed to air. In contrast, anhydrous LiOH was slowly hydrated for several hours, to form LiOH·H2O under ambient conditions (RH 60%). Kinetic analysis showed that the hydration of the interlayer OH- of LiOH proceeded as a second-order reaction, indicating the formation of intermediate species-[Li(H2O) x (OH)4]3- (x = 1 or 2). However, the hydration of the LiOH surface did not follow a second-order reaction because the chemisorption of H2O molecules onto the defect sites of the LiOH surface does not need to crossover the energy barrier. Furthermore, we succeeded in observing the hydration of deliquescent LiCl, including the formation of LiCl solution for several minutes by NIR spectroscopy.

Fourier-transform infrared and X-ray diffraction analyses of the hydration reaction of pure magnesium oxide and chemically modified magnesium oxide.

The magnesium hydroxide/magnesium oxide (Mg(OH)2/MgO) system is a promising chemical heat storage system that utilizes unused heat at the temperature range of 200-500 °C. We have previously reported that the addition of lithium chloride (LiCl) and/or lithium hydroxide (LiOH) promotes the dehydration of Mg(OH)2. The results revealed that LiOH primarily catalyzed the dehydration of the surface of Mg(OH)2, while LiCl promoted the dehydration of bulk Mg(OH)2. However, the roles of Li compounds in the hydration of MgO have not been discussed in detail. X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) techniques were used to analyze the effects of adding the Li compounds. The results revealed that the addition of LiOH promoted the diffusion of water into the MgO bulk phase and the addition of LiCl promoted the hydration of the MgO bulk phase. It was also observed that the concentration (number) of OH- affected hydration. The mechanism of hydration of pure and LiCl- (or LiOH)-added MgO has also been discussed.

Effect of Lithium Compound Addition on the Dehydration and Hydration of Calcium Hydroxide as a Chemical Heat Storage Material.

Many studies on calcium hydroxide [Ca(OH)2] as a chemical heat storage material have been conducted. Generally, calcium hydroxide undergoes a dehydration reaction (heat storage operation) efficiently at about 400 °C or higher. In this study, we aimed to lower the dehydration reaction temperature and increase the dehydration reaction rate to expand the applicability of calcium hydroxide as a chemical heat storage material. For the purpose of improving the dehydration reactivity, calcium hydroxide with added lithium compounds was prepared, and the dehydration/hydration reactivities were evaluated. From the results, it was confirmed that the addition of the lithium compounds lowered the dehydration reaction temperature of calcium hydroxide and enhanced the reaction rate. The dehydration reaction of Ca(OH)2 with Li compounds proceeded efficiently even at 350 °C, and the reversibility of the dehydration/hydration reaction was confirmed. The reason for the improvement of the calcium hydroxide dehydration reactivity upon the addition of a lithium compound was examined from the viewpoint of its crystal structure. It was presumed that when lithium ions enter the calcium hydroxide crystals, the crystals became fragile and the dehydration reaction was accelerated.

Comparison of the Effect of Coaddition of Li Compounds and Addition of a Single Li Compound on Reactivity and Structure of Magnesium Hydroxide.

Mg(OH)2 is a chemical heat storage material that is studied for the utilization of 300-350 °C waste heat. In this study, LiCl and LiOH were coadded to Mg(OH)2, and the reactivity and structural evolution were investigated. In the hydration of samples at 200 °C subsequent to dehydration at 270 °C, Mg(OH)2 with coadded LiCl and LiOH showed excellent hydration reactivity, with a heat output density of 1053 kJ kg-1. The coaddition of LiCl and LiOH enhanced both the dehydration and the hydration reactivity of Mg(OH)2. X-ray diffraction analysis indicated that the addition of LiOH to Mg(OH)2 promoted the decomposition of Mg(OH)2 and the diffusion of water on the surface of Mg(OH)2, whereas the addition of LiCl to Mg(OH)2 promoted these processes in the bulk phase of Mg(OH)2.

Characterization of a restriction modification system from the commensal Escherichia coli strain A0 34/86 (O83:K24:H31).

BACKGROUND: Type I restriction-modification (R-M) systems are the most complex restriction enzymes discovered to date. Recent years have witnessed a renaissance of interest in R-M enzymes Type I. The massive ongoing sequencing programmes leading to discovery of, so far, more than 1 000 putative enzymes in a broad range of microorganisms including pathogenic bacteria, revealed that these enzymes are widely represented in nature. The aim of this study was characterisation of a putative R-M system EcoA0ORF42P identified in the commensal Escherichia coli A0 34/86 (O83: K24: H31) strain, which is efficiently used at Czech paediatric clinics for prophylaxis and treatment of nosocomial infections and diarrhoea of preterm and newborn infants. RESULTS: We have characterised a restriction-modification system EcoA0ORF42P of the commensal Escherichia coli strain A0 34/86 (O83: K24: H31). This system, designated as EcoAO83I, is a new functional member of the Type IB family, whose specificity differs from those of known Type IB enzymes, as was demonstrated by an immunological cross-reactivity and a complementation assay. Using the plasmid transformation method and the RM search computer program, we identified the DNA recognition sequence of the EcoAO83I as GGA(8N)ATGC. In consistence with the amino acids alignment data, the 3' TRD component of the recognition sequence is identical to the sequence recognized by the EcoEI enzyme. The A-T (modified adenine) distance is identical to that in the EcoAI and EcoEI recognition sites, which also indicates that this system is a Type IB member. Interestingly, the recognition sequence we determined here is identical to the previously reported prototype sequence for Eco377I and its isoschizomers. CONCLUSION: Putative restriction-modification system EcoA0ORF42P in the commensal Escherichia coli strain A0 34/86 (O83: K24: H31) was found to be a member of the Type IB family and was designated as EcoAO83I. Combination of the classical biochemical and bacterial genetics approaches with comparative genomics might contribute effectively to further classification of many other putative Type-I enzymes, especially in clinical samples.

Quick identification of Type I restriction enzyme isoschizomers using newly developed pTypeI and reference plasmids.

Although DNA-recognition sequences are among the most important characteristics of restriction enzymes and their corresponding methylases, determination of the recognition sequence of a Type-I restriction enzyme is a complicated procedure. To facilitate this process we have previously developed plasmid R-M tests and the computer program RM search. To specifically identify Type-I isoschizomers, we engineered a pUC19 derivative plasmid, pTypeI, which contains all of the 27 Type-I recognition sequences in a 248-bp DNA fragment. Furthermore, a series of 27 plasmids (designated 'reference plasmids'), each containing a unique Type-I recognition sequence, were also constructed using pMECA, a derivative of pUC vectors. In this study, we tried those vectors on 108 clinical E. coli strains and found that 48 strains produced isoschizomers of Type I enzymes. A detailed study of 26 strains using these 'reference plasmids' revealed that they produce seven different isoschizomers of the prototypes: EcoAI, EcoBI, EcoKI, Eco377I, Eco646I, Eco777I and Eco826I. One strain EC1344 produces two Type I enzymes (EcoKI and Eco377I).

Four new type I restriction enzymes identified in Escherichia coli clinical isolates.

Using a plasmid transformation method and the RM search computer program, four type I restriction enzymes with new recognition sites and two isoschizomers (EcoBI and Eco377I) were identified in a collection of clinical Escherichia coli isolates. These new enzymes were designated Eco394I, Eco826I, Eco851I and Eco912I. Their recognition sequences were determined to be GAC(5N)RTAAY, GCA(6N)CTGA, GTCA(6N)TGAY and CAC(5N)TGGC, respectively. A methylation sensitivity assay, using various synthetic oligonucleotides, was used to identify the adenines that prevent cleavage when methylated (underlined). These results suggest that type I enzymes are abundant in E.coli and many other bacteria, as has been inferred from bacterial genome sequencing projects.

The recognition and modification sites for the bacterial type I restriction systems KpnAI, StySEAI, StySENI and StySGI.

Using an in vivo plasmid transformation method, we have determined the DNA sequences recognized by the KpnAI, StySEAI, StySENI and StySGI R-M systems from Klebsiella oxytoca strain M5a1, Salmonella eastbourne, Salmonella enteritidis and Salmonella gelsenkirchen, respectively. These type I restriction-modification systems were originally identified using traditional phage assay, and described here is the plasmid transformation test and computer program used to determine their DNA recognition sequences. For this test, we constructed two sets of plasmids, pL and pE, that contain phage lambda and Escherichia coli K-12 chromosomal DNA fragments, respectively. Further, using the methylation sensitivities of various known type II restriction enzymes, we identified the target adenines for methylation (listed in bold italics below as A or T in case of the complementary strand). The recognition sequence and methylation sites are GAA(6N)TGCC (KpnAI), ACA(6N)TYCA (StySEAI), CGA(6N)TACC (StySENI) and TAAC(7N)RTCG (StySGI). These DNA recognition sequences all have a typical type I bipartite pattern and represent three novel specificities and one isoschizomer (StySENI). For confirmation, oligonucleotides containing each of the predicted sequences were synthesized, cloned into plasmid pMECA and transformed into each strain, resulting in a large reduction in efficiency of transformation (EOT).

New restriction enzymes discovered from Escherichia coli clinical strains using a plasmid transformation method.

The presence of restriction enzymes in bacterial cells has been predicted by either classical phage restriction-modification (R-M) tests, direct in vitro enzyme assays or more recently from bacterial genome sequence analysis. We have applied phage R-M test principles to the transformation of plasmid DNA and established a plasmid R-M test. To validate this test, six plasmids that contain BamHI fragments of phage lambda DNA were constructed and transformed into Escherichia coli strains containing known R-M systems including: type I (EcoBI, EcoAI, Eco124I), type II (HindIII) and type III (EcoP1I). Plasmid DNA with a single recognition site showed a reduction of relative efficiency of transformation (EOT = 10(-1)-10(-2)). When multiple recognition sites were present, greater reductions in EOT values were observed. Once established in the cell, the plasmids were subjected to modification (EOT = 1.0). We applied this test to screen E.coli clinical strains and detected the presence of restriction enzymes in 93% (14/15) of cells. Using additional subclones and the computer program, RM Search, we identified four new restriction enzymes, Eco377I, Eco585I, Eco646I and Eco777I, along with their recognition sequences, GGA(8N)ATGC, GCC(6N)TGCG, CCA(7N)CTTC, and GGA(6N)TATC, respectively. Eco1158I, an isoschizomer of EcoBI, was also found in this study.

Restriction enzyme recognition sequence search program.

A critical and difficult part of characterizing restriction enzymes and methylases is the identification of recognition sequences. To simplify this process, we have developed a plasmid transformation method along with a computer program named RM search that determines the exact recognition sequences for given restriction and modification systems.

Influence of local duplex stability and N6-methyladenine on uracil recognition by mismatch-specific uracil-DNA glycosylase (Mug).

To maintain genomic integrity, DNA repair enzymes continually remove damaged bases and lesions resulting from endogenous and exogenous processes. These repair enzymes must distinguish damaged bases from normal bases to prevent the inadvertent removal of normal bases, which would promote genomic instability. The mechanisms by which this high level of specificity is accomplished are as yet unresolved. One member of the uracil-DNA glycosylase family of repair enzymes, Escherichia coli mismatch-specific uracil-DNA glycosylase (Mug), is reported to distinguish U:G mispairs from U:A base pairs based upon specific contacts with the mispaired guanine after flipping the target uracil out of the duplex. However, recent studies suggest other mechanisms for base selection, including local duplex stability. In this study, we used the modified base N6-methyladenine to probe the effect of local helix perturbation on Mug recognition of uracil. N6-Methyladenine is found in E. coli as part of both the mismatch repair and restriction-modification systems. In its cis isomer, N6-methyladenine destabilizes hydrogen bonding by interfering with pseudo-Watson-Crick base pairing. It is observed that the selection of uracil by Mug is sequence dependent and that uracil residues in sequences of reduced thermostability are preferentially removed. The replacement of adenine by N6-methyladenine increases the frequency of removal of the uracil residue paired opposite the modified adenine. These results are in accord with suggestions that local helix stability is an important determinant of base recognition by some DNA repair enzymes and provide a potential strategy for identifying the sequence location of modified bases in DNA.