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At least 739 records · Page 41Linked to original sources
PubMed2004

Direct analysis of oxidizing agents in aqueous solution with attenuated total reflectance mid-infrared spectroscopy and diamond-like carbon protected waveguides.

A novel approach for the direct detection of oxidizing agents in aqueous solution is presented using diamond-like carbon (DLC) protected waveguides in combination with attenuated total reflectance (ATR) mid-infrared spectroscopy. Pulsed laser deposition was applied to produce high-quality DLC thin films on ZnSe ATR crystals with thicknesses of a few 100 nm. Scanning electron microscopy and X-ray photoelectron spectroscopy has been used to investigate the surface properties of the DLC films including the sp(3)/sp(2) hybridization ratio of the carbon bonds. Beside excellent adhesion of the DLC coatings to ZnSe crystals, these films show high chemical stability against strongly oxidizing agents. IR microscopy was utilized to compare differences in the chemical surface modification of bare and protected ATR waveguides when exposed to hydrogen peroxide, peracetic acid, and peroxydisulfuric acid. The feasibility of DLC protected waveguides for real-time concentration monitoring of these oxidizing agents was demonstrated by measuring calibration sets in a concentration range of 0.2-10%. Additionally, principal component regression has been applied to analyze multicomponent mixtures of hydrogen peroxide, acetic acid, and peracetic acid in aqueous solution. Due to high chemical stability and accurate monitoring capabilities, DLC protected waveguides represent a novel approach for directly detecting oxidizing agents in aqueous solution with promising potential for industrial process analysis.

Journal Article↗
PubMed2004

Attenuated total reflectance FTIR detection and quantification of low concentrations of aqueous polyatomic anions.

Development of a new quantitative method for determining low concentrations of aqueous polyatomic anions using attenuated total reflectance (ATR) FTIR spectroscopy is described. Evaporated thin-film coatings of anion-selective tetraalkylated ferrocenium salts were applied to the surface of ATR crystals, which enabled anion detection limits to be lowered up to 23 000-fold below those achieved using the commercially available spectrometer with identical uncoated ATR crystals. Linear calibration curves based on d(absorbance)/dt, which is related to the rate of anion exchange in the thin film, were established in the 0.04-30 microM range. Limits of detection (10-min analyses) for perchlorate, chlorate, trifluoromethanesulfonate, perfluoro-n-butanesulfonate, perfluoro-n-octanesulfonate, tetrafluoroborate, hexafluorophosphate, and pinacolylmethylphosphonate in aqueous solution were 0.03, 0.2, 0.05, 0.07, 0.06, 0.06, 0.6, and 0.7 microM, respectively, using the thin-film coatings. This simple detection/quantification method afforded good reproducibility with relatively fast detection times.

Calibration↗
PubMed2003

An infrared reflection-absorption spectroscopy study of the secondary structure in (KL4)4K, a therapeutic agent for respiratory distress syndrome, in aqueous monolayers with phospholipids.

KLLLLKLLLLKLLLLKLLLLK (KL(4)) has been suggested to mimic some aspects of the pulmonary surfactant protein SP-B and has been tested clinically as a therapeutic agent for respiratory distress syndrome in premature infants [Cochrane, C. G., and Revak, S. D. (1991) Science 254, 566-568]. It is of obvious interest to understand the mechanism of KL(4) function as a guide for design of improved therapeutic agents. Attenuated total reflection (ATR) IR measurements have indicated that KL(4) is predominantly alpha-helical with a transmembrane orientation in lipid multilayers (1), a geometry quite different from the originally proposed peripheral membrane lipid interaction. However, the lipid multilayer model required for ATR may not be the best experimental paradigm to mimic the in vivo function of KL(4). In the current experiments, IR reflection-absorption spectroscopy (IRRAS) was used to evaluate peptide secondary structure in monolayers at the air/water interface, the physical state that best approximates the alveolar lining. In contrast to the ATR-IR results, KL(4) (2.5-5 mol %) films with either DPPC or DPPC/DPPG (7/3 mol ratio) adopted an antiparallel beta-sheet structure at all surface pressures studied > or =5 mN/m, including pressures physiologically relevant for lung function (40-72 mN/m). In contrast, in DPPG/KL(4) films, the dominant conformation was the alpha-helix over the entire pressure range, a possible consequence of enhanced electrostatic interactions. IRRAS has thus provided unique molecular structure information and insight into KL(4)/lipid interaction in a physiologically relevant state. A structural model is proposed for the response of the peptide to surface pressure changes.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2003

Direct monitoring of soil and water nitrate by FTIR based FEWS or membrane systems.

The development of silver halide fibers that transmit with minimal loss into the mid-IR (MIR) paved the way to their successful utilization as effective ATR (Attenuated Total Reflectance) elements, promoting the implementation of Fiberoptic Evanescent Wave Spectroscopy (FEWS) for direct monitoring of nitrate in environmental systems. Samples containing nitrate in water, soil extracts, and pastes were used for the determination of nitrate concentration with a common ATR ZnSe crystal and with silver halide fibers (FEWS). Spectra of soil pastes and suspensions and those of phosphate, carbonate, sulfate, ammonium, and soil organic constituents were collected to study possible interference with nitrate determination. The standard error of estimate (SEE) and R2 values obtained with flat fibers, using the simple single-point correlation method, were superior to those obtained for cylindrical FEWS and ZnSe ATR crystals in pure water. A significant improvement in the SEE and R2 was achieved in most soil pastes by applying the simple mode of the Cross Correlation method. Direct transmission of MIR radiation through ion-exchange membranes, partially loaded with nitrate or carbonate, was found an effective alternative for MIR-FTIR determination of these ions. Further development and modification of the FEWS devices should allow in-situ and online determination of nitrate in soil and environmental systems.

Agrochemicals↗
PubMed2005

Novel polysilsesquioxane-I-/I3- ionic electrolyte for dye-sensitized photoelectrochemical cells.

A new sol-gel precursor, based on 1-methyl-3-[3-(trimethoxy-lambda(4)-silyl)propyl]imidazolium iodide (MTMSPI(+)I(-)), was synthesized and investigated as a potential novel quasi-solid-state ionic liquid redox electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of the Graetzel type. MTMSPI(+)I(-) was hydrolyzed with acidified water, and the reaction products of the sol-gel condensation reactions were assessed with the help of (29)Si NMR and infrared spectroscopic techniques. Results of time-dependent analyses showed the formation of a positively charged polyhedral cubelike silsesquioxane species, which still contained a small amount of silanol end groups that were removed after heating at 200 degrees C. After cooling, the material formed was a tough, yellowish, and transparent solid, consisting mainly of ladderlike polysilsesquioxane species. The specific conductivity (sigma) of the nonhydrolyzed MTMSPI(+)I(-) (no I(2)) was 0.23 mS/cm, while the activation energy (E(a)), determined from the Vogel-Tamman-Fulcher (VTF) relation, was 0.29 kJ/mol. After 56 days of aging the sigma value of the hydrolyzed MTMSPI(+)I(-) dropped to 0.11 mS/cm but the viscosity had already increased to 7500 Pa.s after 17 days, demonstrating that a quasi solid state was attained. Apparent diffusion coefficients (D(app)) of I(-) and I(3)(-) obtained from the voltammetric measurements were approximately 10(-7) cm(2)/s and decreased to approximately 10(-8) cm(2)/s after 15 days of sol aging. Time-dependent vibrational spectra, which served in assessing the hydrolysis and condensation reactions of MTMSPI(+)I(-), were measured with the help of the attenuated total reflectance (ATR) IR spectroscopic technique. The results revealed that, in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to a shift of the vibrational band position in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined, and the results are applied in this work.

Iodides↗
PubMed2004

Elucidation of functional groups on gram-positive and gram-negative bacterial surfaces using infrared spectroscopy.

Surface functional group chemistry of intact Gram-positive and Gram-negative bacterial cells and their isolated cell walls was examined as a function of pH, growth phase, and growth media (for intact cells only) using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Infrared spectra of aqueous model organic molecules, representatives of the common functional groups found in bacterial cell walls (i.e., hydroxyl, carboxyl, phosphoryl, and amide groups), were also examined in order to assist the interpretation of the infrared spectra of bacterial samples. The surface sensitivity of the ATR-FTIR spectroscopic technique was evaluated using diatom cells, which possess a several-nanometers-thick layer of glycoprotein on their silica shells. The ATR-FTIR spectra of bacterial surfaces exhibit carboxyl, amide, phosphate, and carbohydrate related features, and these are identical for both Gram-positive and Gram-negative cells. These results provide direct evidence to the previously held conviction that the negative charge of bacterial surfaces is derived from the deprotonation of both carboxylates and phosphates. Variation in solution pH has only a minor effect on the secondary structure of the cell wall proteins. The cell surface functional group chemistry is altered neither by the growth phase nor by the growth medium of bacteria. This study reveals the universality of the functional group chemistry of bacterial cell surfaces.

Bacillus↗
PubMed2005

Influence of electrostatic interactions on the surface adsorption of a viral protein cage.

The Cowpea chlorotic mottle virus (CCMV) provides a useful protein-cage architecture that can be used for the size- and shape-constrained chemistry of nanomaterials. The control of surface assembly is necessary for the realization of many applications of these nanoscale reaction vessels. Electrostatic interactions provide a useful (and reversible) method for controlled surface assembly. CCMV absorption behavior was studied on Formvar, bare Si, Formvar-coated Si, and Si modified by aminopropyltriethoxysilane (APS). Transmission electron microscopy (TEM), atomic force microscopy (AFM), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) were used to characterize the CCMV surface adsorption. Combined AFM and ATR-FTIR data indicated that the viral coverage on the modified surfaces was approximately 84% of the jamming limit predicted by the random sequential adsorption (RSA) model. According to the ATR-FTIR results, surface coverage was not increased at higher ionic strengths nor at a pH near the isoelectric point (pI) of the virus. The Langmuir model was used to provide a description of the kinetic absorption behavior.

Adsorption↗
PubMed2006

CO adsorption and oxidation at the catalyst-water interface: an investigation by attenuated total reflection infrared spectroscopy.

Adsorption of carbon monoxide and oxidation of preadsorbed carbon monoxide from gas and aqueous phases were studied on a platinum catalyst deposited on a ZnSe internal reflection element (IRE) using attenuated total reflection infrared (ATR-IR) spectroscopy. The results of this study convincingly show that it is possible to prepare platinum metal layers strongly attached to an IRE, which are stable for over 3 days in aqueous-phase experiments. It is shown that ATR-IR spectroscopy is a suitable technique to study adsorption and catalytic reactions occurring at the interface of a solid catalyst in an aqueous reaction mixture, even with an extreme low-surface-area catalyst. Clearly, ATR-IR spectroscopy allows for a direct comparison of reactions on a catalytic surface in gas and liquid phases on the same sample. CO was found to adsorb both linearly and bridged on the platinum metal layer when adsorbed from the gas phase, but only linear CO was detected in aqueous solution, although with 5 times higher intensity. Oxidation of preadsorbed CO on platinum occurs in both gas phase, wetted gas, and aqueous media and was found to be 2 times faster in the aqueous phase compared to gas-phase oxidation because of a promoting effect of water. Moreover, during oxidation at room temperature, CO2 adsorbed on Pt/ZnSe was detected in both gas and aqueous phases.

Journal Article↗
PubMed2001

A phase II study of oral eniluracil/fluorouracil in patients with anthracycline-refractory or anthracycline- and taxane-refractory advanced breast cancer.

BACKGROUND: Eniluracil is an effective inactivator of dihydropyrimidine dehydrogenase, the initial and rate limiting enzyme in the catabolism of fluorouracil. The current study was done to determine the objective tumour response of a 28-day oral regimen of eniluracil-fluorouracil in patients with advanced breast cancer. PATIENTS AND METHODS: This was a multicentre, phase II study in patients with anthracycline-refractory (AR) or anthracycline- and taxane-refractory (ATR) advanced breast cancer. Oral eniluracil (10 mg/m2) and fluorouracil (1 mg/m2) were taken twice daily for 28 days of each 35-day treatment course. RESULTS: In this study, 106 patients received treatment: 62 patients in the AR stratum and 44 patients in the ATR stratum. The objective tumour response rate in the intent-to-treat population was 18% (95% confidence intervals (CI): 11%-27%), including three complete responses. The response rate was similar in both strata: 19% in the AR and 16% in the ATR stratum. The overall median duration of response was 23.6 weeks. The treatment was well tolerated with a low incidence of grade 3 or 4 toxicities that were considered attributable to study medication. CONCLUSION: Treatment with oral eniluracil-fluorouracil was well tolerated by patients with advanced breast cancer. The efficacy data were comparable with those of other published studies in this group of refractory patients.

Administration, Oral↗
PubMed1997

Clear cornea sutureless phacoemulsification and astigmatic decay after two years.

PURPOSE: To determine whether clear cornea temporal sutureless sections lead to astigmatic decay over a 2 year period. METHOD: The difference between (a) pre-operative keratometric cylinder and keratometric cylinder at final follow-up, and (b) spectacle cylinder at 1 month post-operation and final follow-up, was calculated for 43 eyes. RESULTS: The mean difference in keratometric cylinder between pre-operation and final follow-up was 0.12 D with the rule (WTR) or against the wound. The range was from 0.7 D WTR to 0.4 D against the rule (ATR). Eighty-two per cent of eyes did not change by more than 0.3 D. The mean change in spectacle prescription between 1 month post-operation and final follow-up was 0.05 D ATR, range 0.5 D WTR to 1.0 D ATR. At final follow-up 93% of eyes were seeing 20/40 or better unaided. CONCLUSION: A carefully constructed temporal wound can remain astigmatically neutral.

Adult↗
PubMed2002

Dextran sodium sulphate-induced colitis perturbs muscarinic cholinergic control of colonic epithelial ion transport.

1. Neuronal cholinergic input is an important regulator of epithelial electrolyte transport and hence water movement in the gut. 2. In this study, colitis was induced by treating mice with 4% (w v(-1)) dextran sodium-sulphate (DSS)-water for 5 days followed by 3 days of normal water. Mid-colonic segments were mounted in Ussing chambers and short-circuit current (Isc, indicates net ion movement) responses to the cholinergic agonist, carbachol (CCh; 10(-4) M)+/-tetrodotoxin, atropine (ATR), hexamethonium (HEX), naloxone or phenoxybenzamine were assessed. 3. Tissues from mice with DSS-induced colitis displayed a drop in Isc in response to CCh (-11.3+/-3.3 microA/cm(2)), while those from control mice showed a transient increase in Isc (76.3+/-13.0 microA/cm(2)). The DeltaIsc in colon from DSS-treated mice was tetrodotoxin-sensitive, atropine-insensitive and was reversed by hexamethonium (HEX+CCh=16.7+/-7.8 microA/cm(2)), indicating involvement of a nicotinic receptor. 4. CCh induced a drop in Isc in tissues from controls only when they were pretreated with the cholinergic muscarinic receptor blocker, atropine: ATR+CCh=-21.3+/-7.0 microA/cm(2). Nicotine elicited a drop in Isc in Ussing-chambered colon from both control and DSS-treated mice that was TTX-sensitive. 5. The drop in Isc evoked by CCh challenge of colonic tissue from DSS-treated mice or ATR+CCh challenge of control tissue was not significantly affected by blockade of opiate or alpha-adrenergic receptors by naloxone or phenoxybenzamine, respectively. 6. The data indicate that DSS-colitis reveals a nicotinic receptor that becomes important in cholinergic regulation of ion transport.

Animals↗
PubMed2003

Nitric oxide promotes p53 nuclear retention and sensitizes neuroblastoma cells to apoptosis by ionizing radiation.

Nitric oxide (NO) is a potent activator of the p53 tumor suppressor protein. However, the mechanisms underlying p53 activation by NO have not been fully elucidated. We previously reported that a rapid downregulation of Mdm2 by NO may contribute to the early phase of p53 activation. Here we show that NO promotes p53 nuclear retention and inhibits Mdm2-mediated p53 nuclear export. NO induces phosphorylation of p53 on serine 15, which does not require ATM but rather appears to depend on the ATM-related ATR kinase. An ATR-kinase dead mutant or caffeine, which blocks the kinase activity of ATR, effectively abolishes the ability of NO to cause p53 nuclear retention, concomitant with its inhibition of p53 serine 15 phosphorylation. Of note, NO enhances markedly the ability of low-dose ionizing radiation to elicit apoptotic killing of neuroblastoma cells expressing cytoplasmic wild-type p53. These findings imply that, through augmenting p53 nuclear retention, NO can sensitize tumor cells to p53-dependent apoptosis. Thus, NO donors may potentially increase the efficacy of radiotherapy for treatment of certain types of cancer.

Active Transport, Cell Nucleus↗
PubMed2003

Protein kinase inhibitor 2-aminopurine overrides multiple genotoxic stress-induced cellular pathways to promote cell survival.

2-Aminopurine (2-AP) is an adenine analog shown to cause cells to bypass chemical- and radiation-induced cell cycle arrest through as-yet unidentified mechanisms. 2-AP has also been shown to act as a kinase inhibitor. Tumor suppressor p53 plays an important role in the control of cell cycle and apoptosis in response to genotoxic stress. We were interested in examining the effect of 2-AP on p53 phosphorylation and its possible consequences on checkpoint control in cells subjected to various forms of DNA damage. Here, we show that 2-AP suppresses p53 phosphorylation in response to gamma radiation, adriamycin, or ultraviolet treatment. This is partly explained by the ability of the kinase inhibitor to inhibit ATM or ATR activities in vitro and impair ATM- or ATR-dependent p53 phosphorylation in vivo. However, 2-AP is also capable of inhibiting p53 phosphorylation in cells deficient in ATM, DNA-PK, or ATR suggesting the existence of multiple pathways by which this kinase inhibitor modulates p53 activation. Biologically, the 2-AP-mediated inhibition of p53 stabilization enables wild-type p53-containing cells to bypass adriamycin-induced G(2)/M arrest. In the long term, however, 2-AP facilitates cells to resist DNA damage-induced cell death independently of p53.

2-Aminopurine↗
PubMed2004

Disruption of the Rad9/Rad1/Hus1 (9-1-1) complex leads to checkpoint signaling and replication defects.

The checkpoint sliding-clamp complex, Rad9/Rad1/Hus1, plays a critical role during initiation of checkpoint signals in response to DNA damage and replication disruption. We investigated the impact of loss of Rad1 on checkpoint function and on DNA replication in mammalian cells. We show that RAD1 is an essential gene for sustained cell proliferation and that loss of Rad1 causes destabilization of Rad9 and Hus1 and consequently disintegration of the sliding-clamp complex. In Rad1-depleted cells, Atr-dependent Chk1 activation was impaired whereas Atm-mediated Chk2 activation was unaffected, suggesting that the sliding clamp is required primarily in Atr-dependent signal activation. Disruption of sliding-clamp function also caused a major defect in S-phase control. Rad1-depleted cells exhibited an RDS phenotype, indicating that damage-induced S-phase arrest was compromised by Rad1 loss. Furthermore, lack of Rad1 also affected the efficiency of replication recovery from DNA synthesis blockage, resulting in a prolonged S phase. These deficiencies may perpetually generate DNA strand breakage as we have found chromosomal abnormalities in Rad1-depleted cells. We conclude that the Rad9/Rad1/Hus1 complex is essential for Atr-dependent checkpoint signaling, which may play critical roles in the facilitation of DNA replication and in the maintenance of genomic integrity.

Cell Cycle↗
PubMed2001

Fate and movement of atrazine, cyanazine, metolachlor and selected degradation products in water resources of the deep Loess Hills of Southwestern Iowa, USA.

The environmental fate and movement of herbicides widely used for weed control in corn are assessed for a deep loess soil in southwestern Iowa. Beginning in the early 1980s, the herbicide-based weed control program emphasized the application of atrazine (ATR) or cyanazine (CYN) and metolachlor (MET) for both broadleaf and grass control. Between 1992 and 1995, concentrations of ATR, desethylatrazine (DEA), desisopropylatrazine (DIA), CYN and MET were measured in rainwater, both shallow and deep vadose zone water, and well water. Results show that the frequency of herbicide detections and the range and distribution of occurrences are dependent upon both landscape position and temporal inputs of recharge water from rainfall. Generally, DIA was observed more frequently and in higher mean concentration in well water than DEA, while DEA was observed more frequently than DIA in vadose zone groundwater. A chromatographic analogy is suggested to explain the occurrence patterns observed for both parent herbicide and degradation products within the unsaturated zone water. Analysis of rainwater samples collected during this time also revealed low concentrations of ATR, CYN and MET, with the timing of the detections indicative of non-local transport. Results show that the deep loess soil conducts both water and agricultural chemicals relatively rapidly and as such represents a production system which is vulnerable to contamination of shallow groundwater by herbicide-derived chemicals. Results also illustrate the importance of including major herbicide degradation products in water resource impact assessment studies.

Acetamides↗
PubMed2003

Monitoring of apoptosis of HL60 cells by Fourier-transform infrared spectroscopy.

Fourier-transform infrared (FTIR) spectroscopy is a vibrational technique that gives information on the chemical composition of a sample, providing a "molecular fingerprint" of it. It is a powerful approach to study intact cells. The aim of the present study was to analyse and quantify apoptotic cells by using a FTIR approach based on attenuated total reflection (ATR). We incubated human HL60 leukaemic cells with camptothecin, a cytotoxic drug, and monitored apoptosis induction over a period of time. Several ATR-FTIR spectral changes occurred during the apoptotic process. In particular, we observed that the apoptotic index was inversely correlated with the spectral area in the region 1200-900 cm(-1), assigned to the absorption of nucleic acids. We therefore propose that ATR-FTIR spectral features may be used as a diagnostic marker of apoptotic cells.

Amino Acid Chloromethyl Ketones↗
PubMed1996

Internal pH crisis, lysine decarboxylase and the acid tolerance response of Salmonella typhimurium.

Salmonella typhimurium possesses an adaptive response to acid that increases survival during exposure to extremely low pH values. The acid tolerance response (ATR) includes both log-phase and stationary-phase systems. The log-phase ATR appears to require two components for maximum acid tolerance, namely an inducible pH homeostasis system, and a series of acid-shock proteins. We have discovered one of what appears to be a series of inducible exigency pH homeostasis systems that contribute to acid tolerance in extreme acid environments. The low pH-inducible lysine decarboxylase was shown to contribute significantly to pH homeostasis in environments as low as pH 3.0. Under the conditions tested, both lysine decarboxylase and sigma s-dependent acid-shock proteins were required for acid tolerance but only lysine decarboxylase contributed to pH homeostasis. The cadBA operon encoding lysine decarboxylase and a lysine/cadaverine antiporter were cloned from S. typhimurium and were found to be 79% homologous to the cadBA operon from Escherichia coli. The results suggest that S. typhimurium has a variety of means of fulfilling the pH homeostasis requirement of the ATR in the form of inducible amino acid decarboxylases.

Acids↗
PubMed2002

Autoinduction of the ompR response regulator by acid shock and control of the Salmonella enterica acid tolerance response.

Salmonella enterica serovar Typhimurium periodically experiences acid stress in a variety of host and non-host environments. An encounter with non-lethal acid stress (pH > 4) induces an assortment of physiological changes, called the acid tolerance response (ATR), that helps the cell to tolerate extreme low pH (pH 3). These physiological changes differ in log phase and stationary phase cells and are controlled by different regulatory proteins. OmpR is an acid-induced response regulator critical to the stationary phase ATR but not to the log phase ATR. As OmpR also controls the expression of the acid-induced virulence operon ssrAB, acid shock induction of ompR was examined to gain insight into how Salmonella links virulence with survival at extreme acid pH. The results indicate that acid pH induces ompR from a promoter different from that used for basal expression. Transcription from this promoter is repressed by the histone-like protein H-NS and requires OmpR-P for induction. The classic sensor kinase EnvZ and acetyl phosphate collaborate to produce the optimum level of OmpR-P needed for autoinduction. Although OmpR-P is required for acid-induced expression of ompR in wild-type cells, OmpR is not needed for ompR transcription in the absence of H-NS. Thus, the role of OmpR-P in autoinduction is to help to counteract repression by H-NS. This evidence, combined with the finding that relaxing DNA supercoiling with novobiocin also increased ompR transcription, suggests that acid stress induces ompR by altering local DNA topology, not by changing the phosphorylation status of OmpR.

Anti-Bacterial Agents↗