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Hepatocellular carcinoma (HCC) is auxotrophic for the semi-essential amino acid arginine, depletion of which leads to tumor death. In humans, arginine is not an essential amino acid since many adult somatic cells can re-synthesize it from other sources, such as citrulline. Enzymes capable of depleting arginine in vitro include the urea cycle enzyme arginase, which is found in abundance in human liver. For over three decades, arginase has not been considered as a potential drug candidate because of its low substrate affinity, short circulatory half-life and sub-optimal enzymatic activity at physiological pH, though its in vitro anti-tumor activities in certain tumors have been amply reported. Arginine deiminase, a bacterial enzyme from Mycoplasma hominus has been shown to induce HCC remission through the mechanism of arginine depletion. We report here an innovative treatment approach for the treatment of locally advanced and metastatic HCC with transhepatic arterial embolisation (TAE) of the liver tumor with lipiodol and gel foam as a means of inducing a leakage of hepatic arginase from the liver into the circulation. Hepatic arginase released into the systemic circulation rapidly depleted plasma arginine. High-dose insulin was included to induce a state of hypoaminoacidaemia to augment arginine depletion. With this protocol, we have treated seven patients with locally advanced and/or metastatic HCC. Five patients achieved arginine depletion, ranging from 0 to 20 microM (normal plasma level 100-120 microM); all had varying degrees of tumor remission in their primary tumors and extra-hepatic sites in the lymph nodes, lungs and bones, suggesting systemic anti-cancer effect of arginine depletion. The two non-responders did not show significant reduction in plasma arginine. Based on our findings, we propose that the urea cycle enzyme, arginase, is a good drug candidate for the treatment of HCC.

The modeling of photodecoloration of a nonbiodegradable azo dye, Reactive Red 2 (RR2), in a cocktail mixture of acetone (ACE) and triethylamine (TEA) solution, was investigated. It was found that the cocktail photolysis system was capable of completely decolorizing the azo dye in a very short treatment time, and the overall dye degradation followed pseudo-first-order decay kinetic. Three distinct stages were observed in the cocktail photolysis profiles. A lag phase was observed at the commencement of the degradation, but its duration was gradually reduced with the increment of the TEA concentration and the incident light intensity. Subsequently, a fast decay of RR2 was observed, in which over 80% of the dyes were reduced and it was interesting to find a tailing stage after 90-95% of the color was removed. A quantitative estimation of RR2 in the cocktail photolysis system was also studied. The differential equation consisting of two parallel reactions was solved to predict the concentration of RR2 at any reaction time with very good agreements. Furthermore, the sensitivity analysis indicated that the photosensitization process (contributed by ACE) was the dominant mechanism in the cocktail photolysis system, while the presence of a hydrogen source (TEA) did not contribute a major decay pathway but promoted the reaction rate of photosensitization by offering an add-on effect.

Degradation of a dye, C.I. Reactive Red 120, in dyeing wastewater by the process of UV/H2O2/US was studied with a bench-scale reactor under the continuous mode of operation. The effects of dyeing wastewater flow rate and the feeding rate of an oxidant, H2O2, on the color removal efficiency of the process were investigated. The significance of ultrasonic (US) combined with UV irradiation was also investigated and the performances of the process on color removal were evaluated. The results showed that the decoloration process followed a pseudo first-order kinetic model and the UV light is the most significant factor on dye removal. Besides, at higher flow rates, incomplete color removal was observed due to relatively insufficient irradiation time (low degradation rate). In order to achieve a higher degradation rate, the feeding rate of H2O2 should be increased.

The photodegradation (at λ = 253.7 nm) of a typical anthraquinone disperse dye (DO11) in a solution containing acetone and triethylamine (TEA) has been investigated. Anthraquinone disperse dyes are known to have very low photodecay rates in the natural environment because of their low solubility. Acetone (ACE) acts not only as a solvent to increase the dye's solubility, but also as a photosensitizer to enhance the dye's photodecay rate. The photodegradation of DO11 follows pseudo first-order decay via photoreduction. In general, the decay quantum yield increases with the increase of ACE/H2O ratios and pH levels, except at very high ACE/H2O ratios or pH levels. Under these circumstances, photoreaction will be retarded because of light attenuation by excess acetone and formation of intramolecular hydrogen bonds within the dye molecules. Adding a low concentration of TEA to the aqueous acetone can further enhance the reaction because TEA can be used as an additional hydrogen source. However, an overdose of T...

The photodegradation of hydrophobic disperse dyes with different chromophores in the presence of acetone (ACE) was investigated. In this study, the photodecay of dyes was carried out in the Rayonet™ RPR-200 merry-go-round photoreactor, with 253.7 nm monochromatic ultraviolet (UV) lamps. A typical azo disperse dye (CI disperse yellow 7 – DY7) and an anthraquinone disperse dye (CI disperse orange – DO11) were used as the probe compounds. The results demonstrate that the addition of acetone increases the solubility of hydrophobic disperse dyes and enhances the photosensitization reaction simultaneously. More than ten times of quantum yield enhancement is observed in the presence of ACE photosensitizer than in water alone. The photodegradation of DY7 and DO11 is dominated by photoreduction, which follows pseudo first-order decay, and the rate constants strongly depend on the solvent system (i.e., ACE/H 2 O ratios) and the initial pH levels. The decay quantum yields of dyes are normally observed with the increase of the ACE/H 2 O ratio. The optimum quantum yields of DY7 and DO11 were determined at 0.5 (v/v) and 0.25 (v/v), respectively, in alkaline conditions. A further increase in the ACE/H 2 O ratio reduces the quantum yields, possibly due to light attenuation by excess acetone.

Recently, photochemical reaction became more important in view of using UV in textile dyeing wastewater treatment processes, in which neither chemical sludges nor toxic residues are left in the treated effluent. The photodegradation of hydrophobic dye (Palanil Yellow 5R, PY-5R) in the presence of acetone, which performs as a solvent and/or a photo-sensitizer, was investigated in this study. The results demonstrated that photochemical reaction in the presence of acetone could rapidly and effectively enhance color removal at a wavelength of 253.7 nm. The photodegradation follows pseudo first-order decay. The rate constants and decay quantum yields of dye degradation by UV depend on the solution pH and solvent system, (i.e., acetone to water ratio). The photosensitization of the disperse dye was found to be optimized at pH 9 and in 0.5 (v:v) acetone-water ratio.

DNA sequencing upstream of the Salmonella enterica serovar Typhi pilV and rci genes previously identified in the ca. 118-kb major pathogenicity island (X.-L. Zhang, C. Morris, and J. Hackett, Gene 202:139‐146, 1997) identified a further 10 pil genes apparently forming a pil operon. The product of the pilS gene, prePilS protein (a putative type IVB structural prepilin) was purified, and an anti-prePilS antiserum was raised in mice. Mutants of serovar Typhi either lacking the whole pil operon or with an insertion mutation in the pilS gene were constructed, as was a strain in which the pilN to pilV genes were driven by the tac promoter. The pil 1 strains synthesized type IVB pili, as judged by (i) visualization in the electron microscope of thin pili in culture supernatants of one such strain and (ii) the presence of PilS protein (smaller than the prePilS protein by removal of the leader peptide) on immunoblotting of material pelleted by high-speed centrifugation of either the culture supernatant or sonicates of pil 1 strains. Control pil mutants did not express the PilS protein. A pilS mutant of serovar Typhi entered human intestinal INT407 cells in culture to levels only 5 to 25% of those of the wild-type strain, and serovar Typhi entry was strongly inhibited by soluble prePilS protein (50% inhibition of entry at 1.4 mM prePilS). Earlier, it was reported that the major pathogenicity island of Salmonella enterica serovar Typhi, which is ca. 118 kb in size (11), contained pilV and rci genes, which were cloned and sequenced (22). The Rci gene product was shown to be a site-specific recombinase, active to invert DNA in the C-terminal region of the pilV gene, so that two PilV proteins could be synthesized. Comparisons with database sequences indicated that the two possible pilV genes might code for pilus-tip adhesins, as the serovar Typhi PilV sequence was similar to that of PilV proteins encoded by the Escherichia coli R64 plasmid. In R64-bearing strains, different PilV proteins, borne on type IV pili, select various recipients in liquid mating (the R64-bearing cell is the donor) (10). Both serovar Typhi PilV proteins were seen when the two pilV genes were transcribed from the T7 promoter. The discovery of the serovar Typhi pilV and rci genes in the ca. 118-kb pathogenicity island (henceforth in this work termed the large pathogenicity island) suggested that serovar Typhi might synthesize thin pili belonging to the type IV pilin family (9). As type IV pili, encoded in a Vibrio cholerae pathogenicity island (7, 8) are used by V. cholerae as mediators of adhesion to human cells (13, 18), it was of interest to ask (i) if serovar Typhi also synthesizes type IV pili and (ii) if such pili are important in adherence to or invasion of human intestinal cells. These topics are the subject of this paper. MATERIALS AND METHODS Materials. All reagents were of molecular biology grade. Enzymes active on DNA were obtained from either GibcoBRL or Boehringer Mannheim and were

The decolorisation of reactive dyeing wastewater with ultraviolet radiation and ultrasonic vibration in the presence of hydrogen peroxide was investigated by a batch operation system. Kinetic studies of the reactive dye were conducted on the effects of pH and peroxide dosage, and the performance of ultrasonic vibration on the oxidation process was also investigated. It was found that the degradation of the reactive dye followed a pseudo-first-order kinetic model at different pH and peroxide dosages. The relationships between the rate constants and pH, as well as peroxide concentration, were established.

Calibrated electroluminescence (EL) measurements have been made on GaAs/AlGaAs and InGaAs/GaAs p–i–n quantum-well (QW) photodiodes at temperatures between 200 and 300 K. The calibrated spectra are compared with a theoretical model. In both cases the model shows the QW electron–hole quasi-Fermi level separation (Δ φ f ) to be suppressed with respect to the applied bias. For the InGaAs/GaAs sample, the barrier luminescence is shown to be consistent with Δ φ f equal to the applied bias. The discrepancy between Δ φ f in the QW and barrier is attributed to an irreversible carrier escape process.

We have measured electroluminescence (EL) spectra of GaAs/InGaAs and AlGaAs/GaAs single quantum well (QW) p-i-n photodiodes at temperatures between 200 and 300 K and forward biases close to the open circuit voltage. Integrated EL spectra vary like eqV/nkT with an ideality factor n=1.05±0.05 over five decades, indicating purely radiative processes. The spectra are calibrated into absolute units enabling comparison to be made with the predictions of a theoretical model. For each temperature and bias we calculate the EL spectrum and radiative current expected in the detailed balance limit, integrating the theoretical emission spectrum over the surface of the device, in order to establish the quasi-Fermi potential separation, Δφf, in the QW and, where possible, in the host material. For the GaAs/InGaAs cell we are able to model emission from the QW and the host material simultaneously. We find that, in all cases, the QW emission is overestimated by theory if it is assumed that Δφf=V. QW emission corresponds instead to a value of Δφf which a few tens of mV less than V. In contrast, emission from the host material, where visible, is well fitted by the model with Δφf=V at all biases and temperatures. We attribute the variation in Δφf to irreversible thermally assisted escape from the QWs.

We have studied the variation with applied bias and temperature of steady state photoluminescence (DCPL) and photoconductivity (DCPC) from a series of GaAs/AlGaAs single quantum well, p-i-n structures with different well widths. We present the DCPC and DCPL results, which when combined, allow us to assess how significant nonradiative recombination is in the samples and hence the quality of the material. We discuss the qualitative features in the light of a new theoretical approach presented here for the first time. This includes contributions from escape (of both electrons and holes) and makes it possible to extract from the experimental data two parameters, each reflecting the competition between escape and one of the recombination processes (radiative or nonradiative) in the absence of the other. We further comment qualitatively on the bias and temperature dependence of these different processes.

An experimental study of carrier escape in a series of p - i - n asymmetric double quantum well (ADQW) structures using time-resolved photoluminescence is presented. By performing complementary continuous-wave photoluminescence and photocurrent measurements the carrier escape times were extracted as a function of temperature and perpendicular applied electric field and compared with a quantitative model which includes the mechanisms of tunnelling, thermally assisted tunnelling and thermionic emission. Holes were found to dominate the escape rate, and in the light of this it is shown that if narrow wells are grown next to wider wells and nearer the p region a significantly enhanced carrier escape rate can result. This is explained by resonant hole tunnelling and may have implications in the design of QW modulator and solar cell devices with improved performance.

Time-resolved photoluminescence (TRPL), continuous-wave photoluminescence (PL) and photocurrent (PC) measurements have been performed on a single quantum well (SQW) embedded in a p - i - n diode and, by combining these measurements, unambiguous carrier escape times have been extracted as a function of perpendicular applied electric field and temperature. The experimental data are compared with a quantitative model based on the competition between escape and recombination lifetimes which includes direct tunnelling, thermally assisted tunnelling and thermionic emission processes and which has no free fitting parameters. Good agreement was found for the escape times with the radiative recombination rate being determined by the carriers with the faster escape rate and hence the lowest steady-state concentration. These are holes in this sample.

Spectra of the electroluminescence emanating from narrow windows in the top contact stripes of GaAs/AlGaAs separate confinement heterostructure double (2*25 AA) quantum well lasers operating in the spontaneous high-injection regime have been measured as a function of the injection current. The devices have been chosen because they are of interest for the assessment of the effects of barrier size and quality upon laser performance. In this paper the integrated relative luminescence intensities from the well and barrier regions are plotted against the quasi-Fermi level separation, which has been determined from the spectra themselves; this facilitates comparisons between devices, and with calculations based on a simple model in which the carrier populations in the wells and barriers are specified by a common quasi-Fermi level. Reasonable agreement is found between the electroluminescence characteristics and theory using a carrier temperature close to that of the lattice, which indicates that electron capture into the well does not present a significant rate-limiting step in the steady-state operation of the lasers studied. Moreover, the quasi-Fermi level separations relative to the effective band gaps of the quantum wells in all the devices are found to be very similar at lasing threshold, which leads to the conclusion that differences observed in the externally measured current are largely due to non-radiative processes in the barriers or carrier leakage.

In calculations of recombination rates and optical gain in semiconductors it is necessary to relate the quasi-Fermi level positions for electrons and holes at a given injection level. Usually this is done by requiring the volume densities of electrons and holes to be equal but when this charge neutrality condition is applied to a quantum well a charge imbalance is implied in the barrier regions. A more satisfactory approach is to require the whole active region, comprising wells and barriers, to be neutral overall; nevertheless, the band bending implied by both of these models is inconsistent with the use of spatially constant band edge energies. The authors have explored the range of validity of these two neutrality conditions and their influence upon the calculated gain-current characteristic for a 25 AA wide GaAs quantum well with Al0.35Ga0.65As barriers. While the choice of neutrality condition influences the individual electron and hole densities at a given quasi-Fermi level separation the radiative recombination rate, which depends upon the (np) product, is not significantly changed. Similarly, the gain as a function of spontaneous current is not strongly affected, though the calculation of other recombination currents which depend primarily upon the density of only one type of carrier, such as recombination via traps and Auger recombination, are influenced by the choice of charge neutrality condition.

Previously, it was shown that type IVB pili encoded by the Salmonella enterica serovar Typhi pil operon are used to facilitate bacterial entry into human intestinal epithelial cells in vitro and that such entry is inhibited by purified prepilin (pre-PilS) protein (X.-L. Zhang, I. S. M. Tsui, C. M. C. Yip, A. W. Y. Fung, D. K.-H. Wong, X. Dai, Y. Yang, J. Hackett, and C. Morris, Infect. Immun. 68:3067-3073, 2000). The pil operon concludes with a simple shufflon, and a recombinase gene product (Rci) inverts DNA in the C-terminal region of the pilV gene to allow synthesis of two distinct PilV proteins, PilV1 and PilV2, which are presumptive minor pilus proteins. We show here that the type IVB pili mediate bacterial self-association, but only when the PilV1 and PilV2 proteins are not expressed. This may be achieved in wild-type serovar Typhi by rapid DNA inversion activity of the shufflon. We show that the inversion activity inhibits the expression of genes inserted between the 19-bp inverted repeats used for Rci-mediated recombination and that the activity of Rci increases when DNA is supercoiled. The data suggest that serovar Typhi self-associates under conditions (such as low oxygen tension in the gut) that favor DNA supercoiling. These results explain (i) the function of the serovar Typhi shufflon and (ii) why there are only two possible shufflon states, in contrast to the many possible states of other shufflon systems. The data further indicate that a very early step in serovar Typhi pathogenesis may be type IVB pilus-mediated self-association of bacteria in the anaerobic human small intestine prior to invasion of the human gut epithelium. The suggested type IVB pilus-dependent step in typhoid fever pathogenesis may partially explain the enhanced invasiveness of serovar Typhi for humans.

The photodegradation of azo reactive dye (RR2) in the presence of acetone (ACE) or triethylamine (TEA) via indirect photolysis was investigated. Photolytic experiments were conducted in a merry-go-round photoreactor with 253.7-nm monochromatic UV lamps. The photodegradation of RR2 in aqueous ACE or TEA solution was found to be kinetically controlled by pseudo-first- and zero-order kinetics, respectively. Typically, the photodegradation reaction is more favorable at higher pH. In the presence of TEA, the rate enhancement primarily is a result of the electron transfer from TEA to RR2 and results in the photoreduction of dye chromophore. Photosensitization is likely the dominant mechanism in the presence of ACE. With respect to the decoloration rate, ACE proved to be a promising rate enhancer at elevated concentrations, and the solution color faded rapidly within 5 minutes of retention time. The photodecoloration of RR2 was found to co-occur with photodechlorination and was followed by photodesulfonation at a later stage in which the mineralized end products, including hydrogen, chloride, and sulphorate ions, were detected in approximately stoichiometric amounts.

The photodegradation of textile azo dyes in aqueous solution containing acetone (ACE) photosensitizer was investigated at 253.7 nm. In this study, a typical azo reactive dye (C I Reactive Red 2-RR2) is used as the probe compound. ACE is a powerful photosensitizer that possesses high triplet energy, and the presence of ACE significantly enhances the overall photodegradation reaction through simultaneous sensitization. In the UV/ACE system, at the optimum conditions, over 97% of RR2 can be successfully decomposed and decolored within 300 seconds of retention time. The photodegradation mechanisms of RR2 involve both photodechlorination and photoreduction, which follow pseudo first-order decay kinetics. The quantum yield of the photolysis system has been evaluated as a function of ACE concentration and the initial pH. RR2 contains the chlorotriazinyl group, which undergoes hydrolysis and results in the formation of hydrochloric acid, indicating that the photodechlorination process is the dominant reaction mechanism. The photo-product, H+, is likely to retard the quantum yield of dye decay, suggesting that the initial pH is a critical factor in changing the photodecolorization rates of dye. Generally, this system is more favorable at higher pH levels.

Degradation of a dye, C. I . Reactive Red 120, in dyeing waatewater by the process o UV/H2O2/US was studied with a bench-scale reactor under the continuous mode of operation. The effects of dyeing wastewater flow rate and the feeding rate of an oxidant, H2O2, on the color removal efficiency of the process were investigated. The significance of ultrasonic (US) combined with UV irradiation was also investigated and the performances of the process on color removal were evaluated. The results showed that the decoloration process followed a pseudo first-order kinetic model and the UV light is the most significant factor on dye removal. Besides, at higher flow rates, incomplete color removal was observed due to relatively insufficient irradiation time (low degradation rate). In order to achieve a higher degradation rate, the feeding rate of H2O2 should be increased.

Recently, photochemical reaction became more important in view of using UV in textile dyeing wastewater treatment processes, in which neither chemical sludges nor toxic residues are left in the treated effluent. The photodegradation of hydrophobic dye (Palanil Yellow 5R, PY-5R) in the presence of acetone, which performs as a solvent and/or a photo-sensitizer, was investigated in this study. The results demonstrated that photochemical reaction in the presence of acetone could rapidly and effectively enhance color removal at a wavelength of 253.7 nm. The photodegradation follows pseudo first-order decay. The rate constants and decay quantum yields of dye degradation by UV depend on the solution pH and solvent system, (i.e., acetone to water ratio). The photosensitization of the disperse dye was found to be optimized at pH 9 and in 0.5 (v:v) acetone-water ratio.

In this paper we discuss the potential advantages of quantum wells (QWs) for enhancing solar cell efficiency. We present recent experimental results which show that the open-circuit voltage (Voc) of the quantum well solar cell (QWSC) is enhanced over that of comparable conventional cells formed from the well material, by more than the change in the absorption edge. We also report on theoretical and experimental studies which seek to determine the quasi-Fermi level separation in quantum wells inside a p-i-n system in order to understand the voltage behaviour of QWSCs and to be able to estimate the efficiency enhancements which may be achieved in the radiative limit. We discuss QWSCs in the InPInGaAs lattice matched system and present results which show that QWSCs in this deep well system have a better variation of efficiency with temperature than conventional cells made from either the well or barrier material. This is important for applications involving concentrated sunlight. We also consider the advantages of quantum well cells in the area of thermophotovoltaics (TPV).

It is known that quantum well solar cells (QWSCs) can enhance short circuit current and power conversion efficiency in comparison with similar, conventional solar cells made from the quantum well (QW) barrier material alone. In this article we report measurements of the dark‐current and open‐circuit voltage (Voc) of a number of quantum well cells in three different lattice‐matched material systems, namely, Al0.35Ga0.65As/GaAs, GaInP/GaAs, and InP/InGaAs. We also present the results obtained from comparable control cells without wells formed either from the material of the barriers or the well material alone. Our results clearly demonstrate in all three cases that, at fixed voltage, QWSC dark currents are systematically lower than would be expected from control cells with the same effective absorption edge. Measurements of Voc in a white‐light source show that the open‐circuit voltages of the QWSCs are higher than those of control cells formed from the well material. Furthermore, this enhancement is more t...

Salmonella enterica serovar Typhi expresses type IVB pili. We show that the prePilS protein (the soluble precursor form of the structural pilin) interacts with a 15-mer peptide representing the first extracellular domain of the cystic fibrosis transmembrane conductance regulator (CFTR), a recognized human epithelial cell receptor for serovar Typhi (G. B. Pier et al., Nature 393:79-82, 1998). This indicates that after mediating bacterial self-association (C. Morris et al., Infect. Immun. 71:1141-1146, 2003), the pili then act to attach the bacterial clumps to CFTR in the membrane of gut epithelial cells. These sequential type IVB pilus-mediated events cannot be performed by (for example) S. enterica serovar Typhimurium, which may explain why only serovar Typhi causes epidemics of enteric fever in humans.

We used electro-optic voltage probing to map the potential distributions along a degenerate single quantum well that exhibited current oscillations when subjected to high fields at low temperatures. The results given here were obtained over a wide range of field strengths at room temperature. The potential profiles were found to contain some very unusual features which might be indicative of the poor quality of the barrier material in this sample.

The Hall mobility in semi‐insulating GaAs has been measured by probing the Hall voltage dropped across the thickness of the sample optically. This is achieved by exploiting the linear electro‐optic (Pockels) effect in the material. The method only involves two electrical contacts to the sample which gives a distinct advantage over the conventional Hall or Van der Pauw techniques. It permits, in principle, the direct measurement of the time evolution of carrier populations, a useful corollary to transient photoconductivity. It also makes possible the measurement of a Hall voltage dropped across the width of a quantum well.

Calibrated electroluminescence spectra of GaAs/InGaAs and AlGaAs/GaAs single and double quantum well (QW) p-i-n devices, at various temperatures (200-300 K) and biases (0.8-1.5 V), have been compared to theory to extract the quasi-Fermi level separation, /spl Delta//spl phi//sub f/, in the QWs and where possible in the host material. Emission from the host material for the GaAs/InGaAs cell is well fitted with /spl Delta//spl phi//sub f/=V/sub app/ at all biases and temperatures. In contrast, emission from the QW in both GaAs/InGaAs and AlGaAs/GaAs cases requires a value of /spl Delta//spl phi//sub f/ which is a few tens of meV less than V/sub app/. We attribute the variations in /spl Delta//spl phi//sub f/ to irreversible thermally assisted escape from the QWs and detail some preliminary results from double QW samples.