Crosslinked Gel Polymer Electrolyte from Trimethylolpropane Triglycidyl Ether by In Situ Polymerization for Lithium-Ion Batteries

Electrolytes play a critical role in battery performance. They are associated with an increased risk of safety issues. The main challenge faced by many researchers is how to balance the physical and electrical properties of electrolytes. Gel polymer electrolytes (GPEs) have received increasing attention due to their satisfactory properties of ionic conductivity, mechanical stability, and safety. Herein, we develop a gel network polymer electrolyte (GNPE) to address the challenge mentioned earlier. This GNPE was formed by tri-epoxide monomer and bis(fluorosulfonyl)imide lithium salt (LiFSI) via an in situ cationic polymerization under mild thermal conditions. The obtained GNPE exhibited a relatively high ionic conductivity (σ) of 2.63 × 10-4 S cm-1, lithium transference number (tLi+, 0.58) at room temperature (RT), and intimate electrode compatibility with LiFePO4 and graphite. The LiFePO4/GNPE/graphite battery also showed a promising cyclic performance at RT, e.g., a suitable discharge specific capacity of 127 mAh g-1 and a high Coulombic efficiency (>97%) after 100 cycles at 0.2 C. Moreover, electrolyte films showed good mechanical stability and formed the SEI layer on the graphite anode. This study provides a facile method for preparing epoxy-based electrolytes for high-performance lithium-ion batteries (LIBs).

Cross-Linked Gel Polymer Electrolyte Based on Multiple Epoxy Groups Enabling Conductivity and High Performance of Li-Ion Batteries

The low ionic conductivity and unstable interface of electrolytes/electrodes are the key issues hindering the application progress of lithium-ion batteries (LiBs). In this work, a cross-linked gel polymer electrolyte (C-GPE) based on epoxidized soybean oil (ESO) was synthesized by in situ thermal polymerization using lithium bis(fluorosulfonyl)imide (LiFSI) as an initiator. Ethylene carbonate/diethylene carbonate (EC/DEC) was beneficial for the distribution of the as-prepared C-GPE on the anode surface and the dissociation ability of LiFSI. The resulting C-GPE-2 exhibited a wide electrochemical window (of up to 5.19 V vs. Li⁺/Li), an ionic conductivity (σ) of 0.23 × 10^-3 S/cm at 30 °C, a super-low glass transition temperature (T_g), and good interfacial stability between the electrodes and electrolyte. The battery performance of the as-prepared C-GPE-2 based on a graphite/LiFePO₄ cell showed a high specific capacity of ca. 161.3 mAh/g (an initial Coulombic efficiency (CE) of ca. 98.4%) with a capacity retention rate of ca. 98.5% after 50 cycles at 0.1 C and an average CE of about ca. 98.04% at an operating voltage range of 2.0~4.2 V. This work provides a reference for designing cross-linking gel polymer electrolytes with high ionic conductivity, facilitating the practical application of high-performance LiBs.

Synthesis and Characterization of Gel Polymer Electrolyte Based on Epoxy Group via Cationic Ring-Open Polymerization for Lithium-Ion Battery

The polymer electrolytes are considered to be an alternative to liquid electrolytes for lithium-ion batteries because of their high thermal stability, flexibility, and wide applications. However, the polymer electrolytes have low ionic conductivity at room temperature due to the interfacial contact issue and the growing of lithium dendrites between the electrolytes/electrodes. In this study, we prepared gel polymer electrolytes (GPEs) through an in situ thermal-induced cationic ring-opening strategy, using LiFSI as an initiator. As-synthesized GPEs were characterized with a series of technologies. The as-synthesized PNDGE 1.5 presented good thermal stability (up to 150 °C), low glass transition temperature (Tg < −40 °C), high ionic conductivity (>10−4 S/cm), and good interfacial contact with the cell components and comparable anodic oxidation voltage (4.0 V). In addition, PNGDE 1.5 exhibited a discharge capacity of 131 mAh/g after 50 cycles at 0.2 C and had a 92% level of coulombic efficiency. Herein, these results can contribute to developing of new polymer electrolytes and offer the possibility of good compatibility through the in situ technique for Li-ion batteries.

Enhancing co-metabolic degradation of trichloroethylene with toluene using Burkholderia vietnamiensis G4 encapsulated in polyethylene glycol polymer

The biodegradation potential of Burkholderia vietnamiensis G4 (B. vietnamiensis G4) was evaluated under encapsulation in comparison with direct exposure to trichloroethylene (TCE) (0.1, 0.5, 1 and 5 mg/L) and toluene (10 and 50 mg/L), maintaining aerobic conditions. B. vietnamiensis G4 was encapsulated in polyethylene glycol (PEG) polymer. Under suspended conditions, the degradation rate decreased as the initial TCE concentration increased, even with a higher amount of substrate available. However, the encapsulated systems were less suppressed, presumably by mitigated toxicity, and completely removed TCE with 50 mg/L of toluene. The transformation yield (Ty) was as high as 0.427 mg-TCE/mg-toluene for the encapsulated cultures and 0.1007 mg-TCE/mg-toluene for the suspended cultures. The Ty value for the encapsulated cultures was one to two orders higher than what has been reported in the literature. The higher Ty values in the encapsulated cultures compared with those from suspended cultures showed that the PEG encapsulation provided more a favourable environment for efficient substrate use.

Responses of intracellular cofactors to single and dual substrate limitations

The highly systematic responses of cellular cofactors to controlled substrate limitations of electron donor, electron acceptor, and both (dual limitation) were quantified using continuous-flow cultures of Pseudomonas putida. The results showed that the NADH concentration in the cells decreased gradually as the specific rate of electron-donor utilization (-q(d)) fell or increased systematically as oxygen limitation became more severe for fixed -q(d), while the NAD concentration was invariant. The NAD(H) responses demonstrated a common strategy; compensation for a low concentration of an externally supplied substrate by increasing (or decreasing) the concentration of its internal cosubstrate (or coproduct). The compensation was dramatic, as the NAD/NADH ratio showed a 24-fold modulation in response to depletion of dissolved oxygen (DO) or acetate. In the dual-limitation region, the compensating effects toward depletion of one substrate were damped, because the other substrate was simultaneously at low concentration. However, the NAD(H) responses minimized the adverse impact from substrate depletion on overall cell metabolism. Cellular contents of ATP, ADP, and P(i) were mostly affected by -q(d), such that the phosphorylation potential, ATP/ADP . P(i), increased as -q(d) fell due to depletion of acetate, DO, or both. Since the respiration rate should be slowed by high ATP/ADP . P(i), the cellular response seems to amplify an unfavorable environmental condition when oxygen is depleted. The likely reason for this apparent disadvantageous response is that the response of phosphorylation potential is more keenly associated with other aspects of metabolic control, such as for synthesis, which requires P(i) for production of phospholipids and nucleotides. (c) 1996 John Wiley & Sons, Inc.

Phase II study of irinotecan, 5-fluorouracil (5-FU) and leucovorin combination chemotherapy in taxane and cisplatin-based chemotherapy-refractory metastatic gastric cancer

e15599

Background: The role of the second line chemotherapy in advanced gastric cancer was not clear, but possibility of prolongation of survival is open question. Irinotecan is promising agents in gastric cancer and this phase II study evaluated the efficacy and safety of combination chemotherapy with irinotecan, high dose of 5-fluorouracil (5-FU) and leucovorin in taxane and cisplatin based chemotherapy refractory metastatic gastric cancer. Methods: Eligible criteria were as followed; histologic confirmed adenocarcinoma of stomach, previously treated with taxane and cisplatin, age≥18, Eastern Clinical Oncology Group (ECOG) performance status of 1 or less, adequate organ function. Irinotecan (150 mg/m2) as a 30-min infusion and leucovorin (200 mg/m2) as a 15-min infusion were given on day 1, followed by 5-FU 400 mg/m2bolus infusion then 5-FU 2,400 mg/m2 as a 48-hour continuous infusion. This cycle was repeated every 2 weeks until disease progression or unacceptable toxicities. Results: Thirty-four patients were enrolled. The median age was 57 years (range 27–73 years), and the ECOG performance status of all patients was 1. All patients were evaluable for safety and survival and twenty seven patients (79.4%) were evaluable for tumor response. The overall response rate was 18.5% (95% CI: 3.9–33.1). The median progression free survival and overall survival were 4.6 (95% CI: 2.4–6.9) and 9.3 months (95% CI: 5.2–13.4), respectively. Greater than grade 3 haematological toxicities were neutropenia in nine (26.5%), febrile neutropenia in one (2.9%) and thrombocytopenia in one patient (2.9%). The major non-haematological toxicity was asthenia, but most of patients showed grade 1 or 2. Greater than grade 3 non- haematological toxicities were elevated AST/ALT in four (11.8%), hyperbilirubinemia in two (5.9%), nausea in two patients (5.9%). Conclusions: This results showed that the combination chemotherapy with irinotecan, 5-FU and leucovorin was well tolerated and active in taxane and cisplatin refractory patients.

No significant financial relationships to disclose.

Phase II study of S-1 monotherapy in taxane, cisplatin refractory gastric cancer

4551

Background: S-1 is a fourth-generation oral fluoropyrimidine that was developed to mimic protracted continuous infusion of 5-fluorouracil (5-FU). In previous study, S-1 demonstrated promising activity which is comparable to combination chemotherapy in advanced gastric cancer. This phase II study evaluated the efficacy and safety of S-1 salvage chemotherapy, in patients with taxane and cisplatin refractory gastric cancer. The primary end point was progression free survival and secondary end points were overall survival, safety and clinical benefit. Methods: Patients were eligible if they had histologically documented gastric adenocarcinoma previously treated with taxane (docetaxel or paclitaxel) and cisplatin; age≥18; Eastern Clinical Oncology Group (ECOG) performance status of 2 or less; adequate organ function; no evidence of gastrointestinal obstruction or passage disturbance. S-1 treatment was performed according to BSA as followed; < BSA 1.25, 80 mg/day, 1.25 ≤ BSA < 1.5, 100 mg/day; BSA ≥ 1.5, 120 mg/day. Every dosage was delivered divided two times and administered for 4 weeks followed by 2 weeks of resting period. Treatment continued until progression of disease or life-threatening adverse events were occurred. Results: Fifty-four patients were enrolled in this study and of the patients, forty-eight patients were evaluable. A total 194 chemotherapy cycles were administered and median number of cycles was three. Four (8.3%) patients had a partial response and 18 (37.5%) patients had stable disease. The median progression free survival and overall survival were 3.8 and 10.2 months, respectively. Grade III/IV hematologic toxicities included neutropenia in 6 patients (12.5%) and there was no febrile neutropenia. Most of nonhematologic toxicities were diarrhea, asthenia, and mucositis, and there was no grade 3 or grade 4 except two patients, who developed grade 3 anorexia and diarrhea, respectively. The clinical benefit response was observed in 16 patients (33.3%). Conclusions: This results showed that S-1 monotherapy was active and safe salvage chemotherapy in patients with advanced gastric cancer previously treated with taxane and cisplatin.

No significant financial relationships to disclose.

Long-term follow-up results of endoscopy-assisted breast surgery (EBS) for early breast cancer

Abstract #4145

Introduction: Although endoscopy-assisted breast surgery(EBS) for early breast cancer had shown the excellent cosmetic outcomes, the application of ESSB is still controversial because of the scanty evidence of long-term safety and feasibility. This study is to evaluate the long-term outcome of endoscopy-assdisted breast surgery compared to conventional breast surgery for early breast cancer.&#x2028; Patients and Methods: Between January 2002 through December 2006, 76 patients(Group E) who had diagnosed breast cancer underwent EBS at Sungkyunkwan University Kangbuk Samsung Hospital. 52 patients(Group O) not greater than stage 2A who had undergone conventional breast surgery during same period were enrolled in this study. The clinicopathologic characteristics, postoperative outcomes, hospital courses, and long-term outcomes including cancer recurrence and 5 year survival were retrospectively compared between two groups. The survivals of all the patients were confirmed with 58.4 month median follow up duration. Results: Tumor sizes were larger in Group O than in Group E(p=0.000). Harvested lymph nodes were more in Group O than in Group E(p=0.000). Postoperative recovery was significantly faster in the Group E; drain was removed earlier(p=0.001) and the postoperative hospital stay was shorter(p=0.001). The mean operation time was significantly longer in the Group E(p=0.000). There were no differences in the operation related morbidity and mortality between the two groups. In comparison of adjuvant therapy, Group O were received more chemotherapy than Group E(p=0.018), but there were no statistical differences of radiotherapy and hormonal therapy between two groups. Subjective cosmetic results were excellent in 63.6% and good in 18.2% more than 1 year after surgery. There was follow-up loss in 3 cases. Cancer-related death occurred in only 1 patient(0.7%) in Group O. The overall 5-year survival rate(5YSR) of the Group O and Group E were 98.2% and 100% , repectively. The disease-free 5YSR of Group O and Group E was 91.3% and 86.9%, repectively. There were no statistical differences on the overall and disease-free 5YSR between the two groups(p=0.446, p=0.205). Cancer recurrence occurred in 5 cases including 2 local recurrences, 2 distant metastases, and 1 second non-breast primary cancer in Group O and 6 cases including 2 local recurrences, 2 regional recurrences, 1 distant metastasis and 1 second non-breast primary cancer in Group E and there was no statistical significance between two groups(p=0.787).&#x2028; Conclusions: Although the number and the qualification of the patients were so limited, our data suggest that endoscopy-assisted skin sparing breast surgery for early breast cancer is feasible and safe comparing to conventional breast surgery. We expect the results of the present study to be confirmed by prospective randomized analysis.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 4145.

Comparison of influence of free ammonia and dissolved oxygen on nitrite accumulation between suspended and attached cells

The shortcut biological nitrogen removal (SBNR) hybrid (suspended cells combined with attached cells) process is an innovative technology that nitrosofies ammonium to nitrite and then denitrifies nitrite to nitrogen gas. Theoretically, this results in a 25% savings of the oxygen needed for nitrification and a 40% of savings in carbon source needed for denitrification. In this study, the influences of free ammonia (FA) and dissolved oxygen (DO) concentrations on nitrite accumulation were investigated to find the optimal operational factors for stable nitrite accumulation over a long period. The maximum specific utilization rates for ammonium (qa) and nitrite (qn) were determined for suspended and attached cells taken from a bench-scale SBNR reactor and a pilot-scale livestock wastewater treatment plant reactor. For the ammonium and nitrite oxidations in both reactors, the attached cells were more resistant to the FA concentration, but were more significantly influenced by the DO concentration than the suspended cells. In addition, the effect of the DO concentration was more significant than that of the FA concentration for both types of cells from both reactors. In this SBNR hybrid system, a simultaneous manipulation of DO concentration (<1.5 mg l(-1)) and FA concentration (10-20 mg l(-1)) was required for maintaining high levels of nitrite accumulation.

Evaluation of predominant reaction mechanisms for the Fenton process in textile dyeing wastewater treatment

This research quantitatively evaluated the predominant reactions in a large-scale Fenton process that treated dyeing wastewaters and suggested an economical and effective treatment process. Through plant analysis, it was found that a great part of the COD was removed by ferric coagulation. The comparative evaluation of Fenton oxidation and ferric coagulation revealed that ferric coagulation was the predominant mechanism to remove COD and colour. In Fenton oxidation, the removal efficiencies of SCOD and colour were 67.7% and 84.7%, respectively. In ferric coagulation, those of SCOD and colour were 60.8% and 62.0%, respectively. A combined process with iron coagulation/precipitation and Fenton oxidation reduced the hydrogen peroxide dosage by over 40% compared to a conventional dosage.

Optimal operational factors for nitrite accumulation in batch reactors

The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture. A batch reactor with 50 mg-N/l of ammonia was used. The pH, temperature and dissolved oxygen concentration were varied. The concentration of unionized free ammonia also changed with the oxidation of ammonia and the variation of pH and temperature. The accumulation of nitrite was affected sensitively by pH and temperature. A higher nitrite concentration was observed at pH 8-9 or temperature around 30 degrees C. The dissolved oxygen also affected, giving the highest nitrite accumulation at around 1.5 mg/l. These were the favored conditions for nitrite production. The free ammonia concentration influenced the nitrite accumulation also, by inhibiting nitrite oxidation. The inhibition became apparent at a concentration of approximately 4 mg/l or above, but insignificant at below 1 mg/l. Thus, simultaneously high free ammonia concentration and maximum specific ammonia-oxidation rate (above 15 x 10(-3) mg-N/mg-VSS x h) were needed for a significant nitrite accumulation. When the two conditions were met, then the highest accumulation was observed when the ratio of the maximum specific oxidation rate of ammonia to the maximum specific oxidation rate of nitrite (ka/kn) was highest. Under the optimal operating conditions of pH 8, 30 degrees C and 1.5 mg/l of dissolved oxygen, as much as 77% of the removed ammonia accumulated in nitrite.

Application of membrane-coupled anaerobic volatile fatty acids fermentor for dissolved organics recovery from coagulated raw sludge

To investigate the treatment performance of membrane-coupled anaerobic volatile fatty acids fermentor system, the effects of operational parameters for volatile fatty acids production were evaluated through experiments and a mathematical model. The volatile fatty acids recovery ratio was largely affected by the change of hydraulic retention time, reaching its maximum value at 12 hrs. Over the range of hydraulic retention time 8 to 96 hrs, the volatile fatty acids recovery ratio decreased with the increase of hydraulic retention time above 12 hrs, while the ratio of mineralization and gasification increased. Hydraulic retention time and membrane filtration ratio should be maintained less than 1 day and above 0.9, respectively, to attain over 40% of organic materials recovery ratio at 10 days of solids retention time. When the hydrolysis rate constant was 0.01 hr-1, the organic loading rate should be maintained at above 1.0 (kgC/m3/day) to attain over 45% of volatile fatty acids recovery ratio. Based on experimental and simulated results, membrane-coupled anaerobic volatile fatty acids fermentor system was thought to be effective for dissolved organics recovery from coagulated sewage sludge.

Genetic engineering of Escherichia coli for enhanced uptake and bioaccumulation of mercury

Synthetic phytochelatins (ECs) are a new class of metal-binding peptides with a repetitive metal-binding motif, (Glu-Cys)(n)Gly, which were shown to bind heavy metals more effectively than metallothioneins. However, the limited uptake across the cell membrane is often the rate-limiting factor for the intracellular bioaccumulation of heavy metals by genetically engineered organisms expressing these metal-binding peptides. In this paper, two potential solutions were investigated to overcome this uptake limitation either by coexpressing an Hg(2+) transport system with (Glu-Cys)(20)Gly (EC20) or by directly expressing EC20 on the cell surface. Both approaches were equally effective in increasing the bioaccumulation of Hg(2+). Since the available transport systems are presently limited to only a few heavy metals, our results suggest that bioaccumulation by bacterial sorbents with surface-expressed metal-binding peptides may be useful as a universal strategy for the cleanup of heavy metal contamination.

Enhanced bioaccumulation of heavy metals by bacterial cells displaying synthetic phytochelatins

A novel strategy using synthetic phytochelatins is described for the purpose of developing microbial agents for enhanced bioaccumulation of toxic metals. Synthetic genes encoding for several metal-chelating phytochelatin analogs (Glu-Cys)(n)Gly (EC8 (n = 8), EC11 (n = 11), and EC20 (n = 20)) were synthesized, linked to a lpp-ompA fusion gene, and displayed on the surface of E. coli. For comparison, EC20 was also expressed periplasmically as a fusion with the maltose-binding protein (MBP-EC20). Purified MBP-EC20 was shown to accumulate more Cd(2+) per peptide than typical mammalian metallothioneins with a stoichiometry of 10 Cd(2+)/peptide. Cells displaying synthetic phytochelatins exhibited chain-length dependent increase in metal accumulation. For example, 18 nmoles of Cd(2+)/mg dry cells were accumulated by cells displaying EC8, whereas cells exhibiting EC20 accumulated a maximum of 60 nmoles of Cd(2+)/mg dry cells. Moreover, cells with surface-expressed EC20 accumulated twice the amount of Cd(2+) as cells expressing EC20 periplasmically. The ability to genetically engineer ECs with precisely defined chain length could provide an attractive strategy for developing high-affinity bioadsorbents suitable for heavy metal removal.

Escherichia coli CspA-family RNA chaperones are transcription antiterminators

CspA, the major cold-shock protein of Escherichia coli, is an RNA chaperone, which is thought to facilitate translation at low temperature by destabilizing mRNA structures. Here we demonstrate that CspA, as well as homologous RNA chaperones CspE and CspC, are transcription antiterminators. In vitro, the addition of physiological concentrations of recombinant CspA, CspE, or CspC decreased transcription termination at several intrinsic terminators and also decreased transcription pausing. In vivo, overexpression of cloned CspC and CspE at 37 degrees C was sufficient to induce transcription of the metY-rpsO operon genes nusA, infB, rbfA, and pnp located downstream of multiple transcription terminators. Similar induction of downstream metY-rpsO operon genes was observed at cold shock, a condition to which the cell responds by massive overproduction of CspA. The products of nusA, infB, rbfA, and pnp-NusA, IF2, RbfA, and PNP-are known to be induced at cold shock. We propose that the cold-shock induction of nusA, infB, rbfA, and pnp occurs through transcription antitermination, which is mediated by CspA and other cold shock-induced Csp proteins.

Characterization of Escherichia coli cspE, whose product negatively regulates transcription of cspA, the gene for the major cold shock protein

Escherichia coli contains nine members of the CspA protein family from CspA to Cspl. To elucidate the cellular function of CspE, we constructed a delta cspE strain. CspE is highly produced at 37 degrees C. The synthesis level of CspE transiently increased during the growth lag period after dilution of stationary-phase cells into the fresh medium at 37 degrees C. This is consistent with the delta cspE phenotype of the longer growth lag period after dilution. The protein synthesis patterns of the delta cspE strain and the wild-type strain were compared using two-dimensional gel electrophoresis. In the delta cspE strain, the synthesis of a number of proteins at 37 degrees C was found to be altered and cspA was derepressed. The derepression of cspA in the delta cspE strain was at the level of transcription in a promoter-independent fashion but was not caused by stabilization of the cspA mRNA, which was shown to be a major cause of CspA induction after cold shock. In vitro transcription assays demonstrated that both CspE and CspA enhanced transcription pause at the region immediately downstream of the cold box, a putative repressor binding site on the cspA mRNA. In a cell-free protein synthesis system using S-30 cell extracts, CspA production was specifically inhibited by the addition of CspE. These results indicate that CspE functions as a negative regulator for cspA expression at 37 degrees C, probably by interacting with the transcription elongation complex at the cspA cold box region.

Glutathione as a matrix for the synthesis of CdS nanocrystallites

GSH-capped CdS nanocrystallites were synthesized by reacting Cd(II)-GSH with aqueous sodium sulfide using specific initial sulfide/Cd(II) ratios. Spectroscopic analyses of fractions obtained from a size exclusion column showed varying absorption spectra indicating a significant dispersion in size-distribution of nanocrystallites at lower sulfide/Cd(II) ratios. However, size distribution of the nanocrystallites was narrower at initial sulfide/Cd(II) ratios that exceeded 1.0. An ethanol precipitation procedure was used to remove free Cd(II)-GSH complexes and selectively isolate GSH-capped nanocrystallites in a very narrow size range. Size exclusion chromatography indicated similar chemical compositions and overlapping spectral profiles of ethanol-precipitated samples suggesting apparent uniformity in both the size and the cap content. All of the GSH-capped CdS nanocrystallites with varying cap contents degraded p-nitrophenol upon irradiation at 366 nm. However, photocatalytic degradation of p-nitrophenol was significantly higher in samples with higher sulfide/Cd ratio and less capping material. The addition of H2O2 enhanced levels of photo-oxidation of p-nitrophenol.

CspA, the major cold shock protein of Escherichia coli, negatively regulates its own gene expression

When the gene for CspA, the major cold shock protein of Escherichia coli, was disrupted by a novel positive/negative selection method, the deltacspA cells did not show any discernible growth defect at either 37 or 15 degrees C. By two-dimensional gel electrophoresis, total protein synthesis was analyzed after temperature downshift in the deltacspA strain. The production of the CspA homologs CspB and CspG increased, and the duration of their expression was prolonged, suggesting that both CspB and CspG compensate for the function of CspA in the absence of CspA during cold shock adaptation. Interestingly, the production of the 159-base 5'-untranslated region (5'-UTR) of cspA from the chromosomal cspA::cat gene, detected by primer extension, failed to be repressed after cold shock. When an independent system to produce CspA was added to the deltacspA strain, the 5'-UTR production for the cspA::cat gene was significantly reduced compared to that of the deltacspA strain. By examining the expression of translationally fused cspA and cspB genes to lacZ in the deltacspA strain, it was found that cspA is more strongly regulated by CspA than cspB is. We showed that the increased expression of the 5'-UTR of the cspA mRNA in the deltacspA strain occurred mainly at the level of transcription and, to a certain extent, at the level of mRNA stabilization. The mRNA stabilization in the deltacspA strain was observed for other mRNAs, supporting the notion that CspA functions as an mRNA chaperone to destabilize secondary structures in mRNAs.

Characteristics of glutathione-capped ZnS nanocrystallites

The titration of increasing equivalents of inorganic sulfide into preformed Zn-glutathione led to the appearance of UV/VIS spectral features attributable to ZnS nanocrystallites. Glutathione-ZnS complexes upon irradiation caused reduction of methylviologen confirming their semiconductor properties. Size-fractionation of glutathione-ZnS samples on a gel filtration column showed the formation of a range of complexes whose spectral properties were correlated with the sulfide content. The stoichiometry of Zn:glutathione increased from 1:2 to a maximum of about 7:1 as the sulfide/Zn ratios increase from 0 to approximately 1.0 in Zn-glutathione complex indicating up to 14-fold increase in the Zn-binding capacity of glutathione upon sulfide incorporation. Spectral characteristics of GSH-capped ZnS nanocrystallites were significantly influenced by pH and by the stoichiometry of Zn, sulfide and glutathione in the complex. Samples containing least glutathione and highest sulfide showed maximal luminescence at pH 6, whereas those with higher glutathione and lower sulfide content showed maximal luminescence at pH 11.

Promoter-independent cold-shock induction of cspA and its derepression at 37 degrees C by mRNA stabilization

The gene for CspA, the major cold-shock protein of Escherichia coli is known to be dramatically induced upon temperature downshift. Here, we report that three-base substitutions around the Shine-Dalgarno sequence in the 159-base 5'-untranslated region of the cspA mRNA stabilizes the mRNA 150-fold, resulting in constitutive expression of cspA at 37 degrees C. This stabilization was found to be at least partially due to resistance against RNase E degradation. The cold-shock induction of cspA was also achieved by exchanging its promoter with the non-cold-shock Ipp promoter. The results presented indicate that the cspA gene is efficiently transcribed even at 37 degrees C. However, the translation of the cspA mRNA is blocked because of its extreme instability at 37 degrees C. The presented results also demonstrate that the cspA gene is constitutively transcribed at all temperatures; however, its expression at 37 degrees C is prevented by destabilizing its mRNA.

A structured model of dual-limitation kinetics

A structured model of substrate-utilization kinetics that encompasses dual-limitation conditions, caused by simultaneously low concentrations of the electron donor and the electron acceptor, is developed by incorporating the internal cofactor responses into the kinetic variables. The structured model is based on an assumption that the maximum specific electron-donor-oxidation rate (q(md)) is not a constant, but is linearly controlled by the intracellular chemical potentials, log(NAD/NADH) and log(ATP/ADP . P(i)). Determination of the kinetic parameters for the dual-limitation model, using experimental data from the companion article, verifies that q(md) varies and demonstrates that the NAD/NADH ratio affects q(md) in a positive direction; thus, an increase of the ratio increases the rate of electron-donor utilization. Because the internal NAD/NADH ratio rises with an increase in S(ar) the specific electron-donor-utilization rate is accelerated by high S(a). Since the ratio also increases as the specific electron-donor-utilization rate falls, the specific rate is intrinsically accelerated by the cofactor response when it becomes low due to a depletion of electron donor. Because the cofactor responses upon changes of the external substrate concentrations are systematic, the dual-limitation model can be expressed as a function of only external concentrations of electron donor and electron acceptor, which results in a multiplicative (double-Monod) form. Thus, dual limitation by both substrates reduces the overall reaction rate below the rate expected from single limitation by only one, the most severely limiting, substrate. (c) 1996 John Wiley & Sons, Inc.

Responses of intracellular cofactors to single and dual substrate limitations

The highly systematic responses of cellular cofactors to controlled substrate limitations of electron donor, electron acceptor, and both (dual limitation) were quantified using continuous-flow cultures of Pseudomonas putida. The results showed that the NADH concentration in the cells decreased gradually as the specific rate of electron-donor utilization (-q(d)) fell or increased systematically as oxygen limitation became more severe for fixed -q(d), while the NAD concentration was invariant. The NAD(H) responses demonstrated a common strategy; compensation for a low concentration of an externally supplied substrate by increasing (or decreasing) the concentration of its internal cosubstrate (or coproduct). The compensation was dramatic, as the NAD/NADH ratio showed a 24-fold modulation in response to depletion of dissolved oxygen (DO) or acetate. In the dual-limitation region, the compensating effects toward depletion of one substrate were damped, because the other substrate was simultaneously at low concentration. However, the NAD(H) responses minimized the adverse impact from substrate depletion on overall cell metabolism. Cellular contents of ATP, ADP, and P(i) were mostly affected by -q(d), such that the phosphorylation potential, ATP/ADP . P(i), increased as -q(d) fell due to depletion of acetate, DO, or both. Since the respiration rate should be slowed by high ATP/ADP . P(i), the cellular response seems to amplify an unfavorable environmental condition when oxygen is depleted. The likely reason for this apparent disadvantageous response is that the response of phosphorylation potential is more keenly associated with other aspects of metabolic control, such as for synthesis, which requires P(i) for production of phospholipids and nucleotides. (c) 1996 John Wiley & Sons, Inc.