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The study was conducted to establish a population pharmacokinetic (PPK) model of valsartan in Chinese healthy subjects and investigate potential covariate impacts on the pharmacokinetics (PK) parameters. Data from a bioequivalence study with 78 Chinese healthy subjects were retrospectively analyzed to develop a PPK model of valsartan. Phoenix NLME 8.1 was used to build a PPK model and quantify the effects of covariates, such as demographic data and biochemical, on the PK parameters of valsartan. For the healthy Chinese population, valsartan conformed to the two-compartment model with an absorption lag time. In the final PPK model, food affected the absorption rate constant, while aspartate aminotransferase, alanine aminotransferase, and creatinine affected the clearance of the central compartment. The final PPK model was verified to be reproducible, and it can be used to evaluate the PK parameters. This is the first research describing the PPK profile of valsartan in healthy Chinese subjects, and it is expected to provide relevant PK parameters for further study of valsartan.

UVA-induced deleterious effect of thiopurine prodrugs including azathioprine, 6-mercaptopurine and 6-thioguanine (6-TG) increases the risk of cancer development due to the incorporation of 6-TG in patients' DNA. The catalytic mechanism by which thiobases act as a sustained oxidant producer has yet to be explored, especially through the Type I electron transfer pathway that produces superoxide radicals (O2˙-). Under Fenton-like conditions O2˙- radicals convert to extremely reactive hydroxyl radicals (˙OH), thus carrying even higher risk of biological damage than that induced by the well-studied type II reaction. By monitoring 6-TG/UVA-induced photochemistry in mass spectra and superoxide radicals (O2˙-) via nitro blue tetrazolium (NBT) reduction, this work provides two new findings: (1) in the presence of reduced glutathione (GSH), the production of O2˙-via the type I reaction is enhanced 10-fold. 6-TG thiyl radicals are identified as the primary intermediate formed in the reaction of 6-TG with O2˙-. The restoration of 6-TG and concurrent generation of O2˙- occur via a 3-step-cycle: 6-TG type I photosensitization, O2˙- oxidation and GSH reduction. (2) In the absence of GSH, 6-TG thiyl radicals undergo oxygen addition and sulfur dioxide removal to form carbon radicals (C6) which further convert to thioether by reacting with 6-TG molecules. These findings help explain not only thiol-regulation in a biological system but chemoprevention of cancer.

The adsorption separation of gaseous olefin/paraffin using porous materials has been extensively studied from both experimental and molecular simulation perspectives, while the adsorption separation of liquid-phase olefin/paraffin has been much less studied. One of the most important reasons for this is that it is difficult to measure the actual adsorption capacity of liquid-phase adsorption separation directly through experiments, and the simulation results of most studies are compared to gas-phase measurements. In this paper, the selective adsorption of linear α-olefins from three binary liquid-phase olefin/paraffin mixtures, 1-hexene/n-hexane (C6), 1-octene/n-octane (C8), and 1-decene/n-decane (C10), by zeolite adsorbents was systematically investigated using batch adsorption experiments and configurational-bias grand canonical Monte Carlo (CB-GCMC) simulations. In the batch experiments, based on the liquid-phase measurement method of the actual adsorption capacity that we developed, a modified commercial 5A zeolite with a relatively large pore volume and surface area was used for adsorption. The results showed that the modified 5A zeolite had larger actual adsorption capacities for C6 and C8 linear α-olefins, which increased by 51% and 56%, respectively, than the standard 5A zeolite that was used in our previous work. The adsorption isotherms of C6, C8, and C10 in the 5A and 13X zeolites were calculated by CB-GCMC simulations. The visualized results of density profiles showed that the olefin molecules were densely distributed at the edge of the zeolite cages and that there were cases where a single molecule was adsorbed over two adjacent cages. The good agreement between the experimental and simulated data proves the completeness of the liquid-phase measurement method that we developed and the reliability of the simulation prediction.

Whereas extensive studies have examined the effectiveness of inquiry-based learning in chemistry education, few have tracked undergraduate performance throughout the college chemistry curricula. In this study, we describe an instructional model of conceptual learning and inquiry-based practices (CLIP) and assess students’ transformation of knowledge about precision and accuracy in the laboratory components of Introductory Chemistry, Analytical Chemistry, Instrumental Analysis, and Physical Chemistry. Student performance in written laboratory reports reveals that repetition of concepts and specific feedback from instructors are essential in constructing knowledge about precision and accuracy. We observed a distinct gap between students’ perception of their understanding and their ability to determine precision and accuracy in data sets. This gap decreases as students move from introductory to advanced chemistry laboratories, but loss of student participants throughout the study increases the uncertainty in the significance. In contrast to traditional teaching, enhanced learning was observed in Introductory Chemistry I Laboratories thought CLIP, with the support of concept/skill training, specific feedback, and student-centered activities. This study benefits members of the community who are engaged in supporting students’ mastery of theory with practice.

The COVID-19 outbreak has altered chemistry laboratory instruction and forced us to reconsider the balance between face-to-face and online teaching. Our students preferred face-to-face teaching (sc...

The adsorption separation of gaseous olefin/paraffin using porous materials has been extensively studied from both experimental and molecular simulation perspectives, while the adsorption separation of liquid-phase olefin/paraffin has been much less studied. One of the most important reasons for this is that it is difficult to measure the actual adsorption capacity of liquid-phase adsorption separation directly through experiments, and the simulation results of most studies are compared to gas-phase measurements. In this paper, the selective adsorption of linear α-olefins from three binary liquid-phase olefin/paraffin mixtures, 1-hexene/

It is both challenging and desirable to have drug sensitizers released at acidic tumor pH for photodynamic therapy in cancer treatment. A pH-responsive carrier was prepared, in which fumed silica-attached 5,10,15,20-tetrakis(4-trimethylammoniophenyl)porphyrin (TTMAPP) was encapsulated into 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) nanocomposite liposomes. The sizes of agglomerates were determined by dynamic light scattering to be 115 nm for silica and 295 nm for silica-TTMAPP-DOPC liposomes. Morphological changes were also found in TEM images, showing liposome formation at pH 8.5 but collapse upon silanol protonation. TTMAPP release is enhanced from 13% at pH 7.5 to 80% at pH 2.3, as determined spectrophotometrically through dialysis membranes. Fluorescence emission of TTMAPP encapsulated in the dry film of liposomes was reduced to half at pH 8.6 when compared to that at pH 5.4, while the production of singlet oxygen was quintupled at pH 5.0 compared to pH 7.6. Upon treatment of human prostate cancer cells with liposomes containing 6.7 μM, 13 μM, 17 μM and 20 μM TTMAPP, the cell viabilities were determined to be 60%, 18%, 20% and 5% at pH 5.4; 58%, 30%, 25% and 10% at pH 6.3; and 90%, 82%, 68% and 35% at pH 7.4, respectively. Light-induced apoptosis in cancerous cells was only observed in the presence of liposomes at pH 6.3 and pH 5.4 but not at pH 7.4, as indicated by chromatin condensation.

Selective dimension enlarging integrated with numbering-up is of great importance for microfluidics. However, its feasibility for photochemical processes remains unclear due to the strict requirements of uniform irradiation. Herein, a novel method for selective dimension enlarging in photochemical production was developed by introducing microbubbles. A membrane dispersion microreactor was employed to generate microbubbles for efficient mixing and uniform absorption of photons. With an increased channel size from 0.6 mm to 4 mm, it allowed a 41-fold increase in productivity while maintaining the microscale effect. The yield of was increased by 44−70 % with 83−86 % less side products, compared with those of the homogeneous and segmented flow systems. In addition, a theoretical method combining CFD simulation was developed to predict the change of mixing time with device scales, which could be used to assess the practicality by selective dimension enlarging for different photochemical microfluidic processes.

Herein we describe the design, efficient synthesis, and photophysical properties of two macrocycle dyes for cancer theranostics. This study compares a glycosylated chlorin with a glycosylated phthalocyanine designed to specifically target cancer, wherein the photophysical properties enable both fluorescence imaging and the sensitization of the formation of reactive oxygen species (ROS) for photodynamic therapy. Both the compounds show low darktoxicity (IC50 > 100 μM). The glycosylated phthalocyanine showed low phototoxicity (IC50 > 100 μM) while glycosylated chlorin showed high phototoxicity (IC50 = 1–2 μM). ZnPcGlc8 has low solubility and also form aggregates in aqueous media, thus resulting in minimal uptake in two different human breast cancer cell lines: MDA-MB-231 and MCF-7. The glycosylated chlorin however was efficiently taken up by these two cell lines, thus allows fluorescence imaging in cells and in xenograft tumor model in mice. In this study, we find that the chlorin conjugate is the more promising theranostic agent.

The separation of gaseous olefin/paraffin mixtures by physical adsorption and π-complexation chemical adsorption has been widely investigated, while studies on the adsorption of liquid olefin/paraffin are much rarer. One of the most important reasons is that it is difficult to determine the actual adsorption capacity of liquid phase adsorption directly through experiments, and the study of liquid olefin/paraffin mixtures adsorption capacities has not been sufficiently systematic. In this paper, the adsorption of C6, C8 and C10 linear α-olefins onto 5A and 13X molecular sieves from binary liquid olefin/paraffin mixtures in batch and fixed bed column systems was systematically investigated. In batch experiments, a measurement method of actual adsorption capacity was established, and the actual adsorption capacities of 5A and 13X were determined by the liquid phase concentration difference and pore volume correction with the help of gas chromatography (GC) and physisorption apparatus. The adsorption selectivity was obtained through experimental data and the binary liquid adsorption theory. Experimental data were fitted to the Freundlich and Langmuir isotherms to determine the adsorption characteristics. The adsorption kinetics were well fitted with pseudo-second-order and Crank models. In the fixed bed column experiments, breakthrough curves were obtained and the dynamic adsorption characteristics were analyzed through breakthrough curves. The effects of operational conditions, such as adsorbents, flow rate and feed concentration on the column dynamics were examined. Both Thomas and Yoon-Nelson models gave satisfactory fits to the experimental data of dynamic adsorption in a fixed bed column.

In a typical chemistry instrumentation laboratory, students learn analytical techniques through a well-developed procedure. Such an approach, however, does not engage students in a creative endeavor. To foster the intrinsic motivation of students’ desire to learn, improve their confidence in self-directed learning activities and enhance their problem-solving skills, students’ self-designed, research-based analytical chemistry projects have been developed within the course of Advanced Chemical Methods for junior and senior undergraduates at SUNY College at Old Westbury. In addition to a series of manual-based laboratories held on a regular basis, students also do a literature search to formulate their own ideas that are tested using appropriate analytical instruments. By participating in self-designed projects, students independently go through the key components of analytical chemistry with greater engagement: from literature survey, problem identification, experimental design, sample preparation, measure...

Thiopurines were examined for their ability to produce singlet oxygen ((1)O(2)) with UVA light. The target compounds were three thiopurine prodrugs, azathioprine (Aza), 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG), and their S-methylated derivatives of 6-methylmercaptopurine (me6-MP) and 6-methylthioguanine (me6-TG). Our results showed that these thiopurines were efficient (1)O(2) sensitizers under UVA irradiation but rapidly lost their photoactivities for (1)O(2) production over time by a self-sensitized photooxidation of sulfur atoms in the presence of oxygen and UVA light. The initial quantum yields of (1)O(2) production were determined to be in the range of 0.30-0.6 in aqueous solutions. Substitution of a hydrogen atom with a nitroimidazole or methyl group at S decreased the efficacy of photosensitized (1)O(2) production as found for Aza, me6-MP and me6-TG. (1)O(2)-induced formation of 8-oxo-7,8-dihydro-2'-dexyguanosine (8-oxodGuo) was assessed by incubation of 6-methylthiopurine/UVA-treated calf thymus DNA with human repair enzyme 8-oxodGuo DNA glycosylase (hOGG1), followed by apurinic (AP) site determination. Because more 8-oxodGuo was formed in Tris D(2)O than in Tris H(2)O, (1)O(2) is implicated as a key species in the reaction. These findings provided quantitative information on the photosensitization efficacy of thiopurines and to some extent revealed the correlations between photoactivity and phototoxicity.

The incorporation of 6-thioguanine (6-TG) into DNA increases the risk of (1)O(2)-initiated skin cancer. We herein provide the first report on quantitative characterization of the photoactivity of 6-thioguanines including 6-TG and 6-thioguanosine. Time-resolved singlet oxygen luminescence was observed directly for the first time after UVA irradiation of 6-thioguanines in both CHCN(3) and aqueous solutions. Their photosensitization was characterized by the quantum yield of singlet oxygen production, showing a dramatic decrease over time from the initial 0.49-0.58 to zero. Experiments performed on both 6-TG and 6-thioguanosine did not show any significant difference in the quantum yield of singlet oxygen production, indicating that there was no potential participation of 7H- and 9H-tautomers. Our findings provide a primary basis for a better understanding of molecular events of thiopurine drugs in biological systems.

The facile synthesis and photophysical properties of three nonhydrolyzable thioglycosylated porphyrinoids are reported. Starting from meso-perfluorophenylporphyrin, the nonhydrolyzable thioglycosylated porphyrin (PGlc₄), chlorin (CGlc₄), isobacteriochlorin (IGlc₄), and bacteriochlorin (BGlc₄) can be made in 2-3 steps. The ability to append a wide range of targeting agents onto the perfluorophenyl moieties, the chemical stability, and the ability to fine-tune the photophysical properties of the chromophores make this a suitable platform for development of biochemical tags, diagnostics, or as photodynamic therapeutic agents. Compared to the porphyrin in phosphate buffered saline, CGlc₄ has a markedly greater absorbance of red light near 650 nm and a 6-fold increase in fluorescence quantum yield, whereas IGlc₄ has broad Q-bands and a 12-fold increase in fluorescence quantum yield. BGlc₄ has a similar fluorescence quantum yield to PGlc₄ (10%), but the lowest-energy absorption/emission peaks of BGlc₄ are considerably red-shifted to near 730 nm with a nearly 50-fold greater absorbance, which may allow this conjugate to be an effective PDT agent. The uptake of CGlc₄, IGlc₄, and BGlc₄ derivatives into cells such as human breast cancer cells MDA-MB-231 and K:Molv NIH 3T3 mouse fibroblast cells can be observed at nanomolar concentrations. Photobleaching under these conditions is minimal.

Singlet oxygen ( 1 O 2 ) signals observed upon illumination at 532 nm are a consequence of TiO 2 excitation in a two-photon process, and at 355 nm in a one-photon pathway. After corrections for light reflectance, the relative quantum yields of 1 0 2 production are 0.23 ± 0.01 and 0.22 ± 0.02 for 532 and 355 nm excitation, respectively. Total quenching rate constants of 1 O 2 removal by TiO 2 particles are near the diffusion-controlled rate limit. By employing 1 O 2 , as a probe, we have established an efficient and simple method to elucidate the nature of TiO 2 photoexcitation.

Indigo is a unique organic compound in terms of its blue color and its multiple conjugated functional groups contained therein. We ask whether the enthalpy of its cleavage reaction into two isatin molecules reflects the novelty of either this color and/or the conjugated functionalities contained therein.

We suggest that singlet molecular oxygen [1O2 (1Δg)] is formed upon irradiation of indigo 1 [in air or O2-saturated DMSO and DMSO (0.5% H2SO4)] and indigo carmine 2 [in air or O2-saturated CH3OH, D2O, and 1-butyl-3-methylimidazolium tetrafluoroborate (BmIm–BF4)]. The quantum yield for production of 1O2 is estimated to be 0.6 for 1 and 0.3–0.5 for 2. The rates of reaction of 1O2 with 1 and 2 were determined by monitoring the emission of 1O2 at 1270 nm over time. Low molar absorptivities (at 532 nm) and rapid physical quenching caused by 1 and 2 limit their utility as 1O2 photosensitizers in solution. Compounds 1 and 2 degrade slowly during the photolysis due to a self-sensitized (type I or II) photooxidation reaction. Oxidative cleavage of 1 by singlet oxygen and superoxide, and 2 by superoxide has been noted before (Kuramoto, N.; Kitao, T. J. Soc. Dyers Color. 1979, 95, 257–261; Kettle, A. J.; Clark, B. M.; Winterbourn, C. C. J. Biol. Chem. 2004, 279, 18521–18525).

The chemistry of singlet oxygen with a variety of arylphosphines has been studied. Rates of singlet oxygen removal by para -substituted arylphosphines show good correlation with the Hammett σ parameter ( ρ =−1.53 in CDCl 3 ), and with the Tolman electronic parameter. The only products for the reactions of these phosphines with singlet oxygen are the corresponding phosphine oxides. Conversely, for ortho -substituted phosphines with electron-donating substituents, there are two products, namely a phosphinate formed by intramolecular insertion and phosphine oxide. Kinetic analyses demonstrate that both products are formed from the same intermediate, and this allows determination of the rate ratios for the competing pathways. Increasing the steric bulk of the phosphine leads to an increase in the amount of insertion product. VT NMR experiments show that peroxidic intermediates can only be detected for very hindered and very electron-rich arylphosphines.

We prepared the primary adduct for the reaction of singlet dioxygen ( 1 O 2 ) with an arylphosphine by using the sterically hindered arylphosphine tris( o -methoxyphenyl)phosphine. The resulting phosphadioxirane has a dioxygen molecule triangularly bound to the phosphorus atom. Olefin trapping experiments show that the phosphadioxirane can undergo nonradical oxygen atom–transfer reactions. Under protic conditions, two different intermediates are formed during the reaction of singlet dioxygen with tris( o -methoxyphenyl)phosphine, namely, the corresponding hydroperoxy arylphosphine and a hydroxy phosphorane. Experiments with other arylphosphines possessing different electronic and steric properties demonstrate that the relative stability of the tris( o -methoxyphenyl)phosphadioxirane is due to both steric and electronic effects.

Reactions of excess electrons in TiO 2 nanocrystallites produced by radiolysis have been studied by both steady state and pulse radiolysis techniques. The TiO 2 electrons were produced by γ or pulse radiolysis of 2-propanol or t -butanol aqueous solutions in acid pH's. The effects of various materials, including such that are often present in photocatalytic systems such as hydrogen peroxide, oxygen, nitrate and perchlorate on the decay of the TiO 2 electron absorption was followed, using two nanocrystallite sizes with average diameters of 1.0 and 4.7 nm. The rates of electron reactions depend on particle size. Several scavengers including Cu 2+ , ClO 2 − , ClO 3 − , NO 2 − , and NO 3 − show decay of the TiO 2 electron predominantly by single pseudo-first order process. The rate of reaction of the above ions in the large nanocrystallites systems is 2–10 times faster than in the respective small particle systems. Hydrogen peroxide and oxygen show a multi-exponential decay, which is supposedly related to different kinds of adsorption. Large particles show reduction rates 2–3 orders faster for H 2 O 2 and 10–20 times faster for O 2 , compared to the small particles. The reaction of the electron with ClO 4 − ions is first order in [ClO 4 − ] but second order with respect to the TiO 2 electron. In the large particle system the rate was found to depend on the number of electrons per particle. (No similar information is available for the small particles). The rates of reduction of the different scavengers, tend to increase with the driving force, although not always. Deviations from linear dependency of log k on the driving force are large. The mechanisms and role of adsorption are discussed.

Reactions of the hydrated electron, H atoms, 2-propanol, and methanol radicals with the TiO 2 nano-particles have been studied either directly or by competition kinetics. The radicals were produced by radiolysis of 2-propanol, t -butanol, or methanol aqueous solutions in acid pH's. The reactions involve electron injection to the conduction band. As expected, the t -butanol radical is inert towards TiO 2 under our conditions, while the other reducing radicals react with TiO 2 . The reactivity decreases in the order: e aq − >H>CH 3 COHCH 3 >CH 2 OH. Two TiO 2 nanocrystallite sizes, with average diameters of 1.0 and 4.7 nm were compared. For equal concentrations (in terms of TiO 2 molecules), the rate of electron injection shows relatively little dependency on particle size. The rates of interfacial electron transfer and transfer coefficient are also reported.

The yield of hydroxyl radicals has been determined by illumination of TiO 2 layers immersed in air saturated aqueous methanol solutions. This yield is equal to half the measured formaldehyde yield in the pH range 7-13. A detailed mechanism is proposed, accounting for the lack of accumulation of hydrogen peroxide. The effect of changing methanol concentration, pH and light intensity (the latter by three orders of magnitude) is in agreement with a very simple mechanism. In contrast to hydroxyl radicals, which react via hydrogen abstraction, leading to formation of HCHO, there is no sign for reaction of methanol with mobile holes. Thus, the limiting quantum yield observed at high methanol concentration is related to the maximum yield of ○OH ads under air saturated conditions at the given pH and light intensity. The effect of light intensity shows the expected inverted square root dependency. The yield of ○OH ads is nearly constant in the range 7 < pH < 12. This system may be useful for comparative tests of different TiO 2 preparations.

A triply bridged fused diporphyrin appended with six thioglucose units is reported. This new, chemically, and photochemically stable amphiphilic compound is taken up by breast cancer cells and causes cell death upon light exposure. Photophysical studies reveal absorption bands in the near IR region, and photosensitized formation of singlet oxygen in high quantum yields.

[reaction--see text] The chemistry of singlet oxygen with all three isomers of tris(methoxyphenyl)phosphine has been studied. For the severely hindered ortho isomer, intramolecular rearrangement to form phenyl diphenyl phosphinate is preferred to formation of phosphine oxide at low concentration in aprotic solvents. In protic solvents, no intramolecular reactivity is observed. A detailed kinetic analyses has been undertaken. There is no physical quenching, regardless of solvent. Mechanistic implications of these findings are discussed.

This work involves an experimental study of the optical properties of excess electrons in solvated TiO2 nanoparticles. The excess electrons were produced by γ irradiation of deaerated 2-propanol solutions containing TiO2 nanoparticles in acidic pH. The irradiation produced propanol radicals and hydrated electrons, which react with TiO2 sols and produce the blue color of excess TiO2 electrons. Results are provided for the maximum loading of electrons on the TiO2 nanoparticles for both Q-particles and large nanocrystallites, and for the extinction coefficients, which were determined by titration. Discussion of the electron spectra in the light of earlier work is presented. In addition, we find that the high local concentration of electrons enables reduction of H2O2 and ClO4- by simultaneous two-electron transfer.

A voltammetric procedure is described which allows determination of rate constants for reactions of hydroxyl radicals. Hydroxyl radicals, generated by reaction of an iron-EDTA complex with H 2 O 2 in the presence of ascorbic acid, attack deoxyribose to form products that, upon heating with thiobarbituric acid under acid conditions, yield a pink chromogen with second order derivative cathodic wave at −0.88 V vs SCE. Added hydroxyl radical `scavengers' compete with deoxyribose for the hydroxyl radicals produced and diminish chromogen formation. The electrochemical behavior of the chromogen has been determined using voltammetry and cyclic voltammetric techniques. A rate constant for reaction of the scavenger with hydroxyl radical can be deduced from the inhibition of chromogen formation. For a wide range of compounds, the results fit well with rate constants previously obtained with other methods. It is suggested that voltammetric deoxyribose assay is a simple and cheap alternative for determination of rate constants for reaction of most biological molecules with hydroxyl radicals. Rate constants for reactions of six kinds of active compounds extracted from rheum, a traditional Chinese herb, have been determined by this method. Reaction mechanism has also been discussed.

The autoxidation of pyrogallol was investigated in the presence of EDTA or DETAPAC (diethylenetriaminepentaacetic acid) in the pH range 7.87 to 9.10. Pyrogallol reacts with dioxygen in weakly alkaline solutions to form several intermediate products which are electroactive substance and can be detected by electroanalytical methods. The focus here was putted on the effect of pH on the autoxidation rate of some intermediate products produced in pyrogallol autoxidation, which gives sensitive second-order derivative cathodic waves at −0.20, −0.96 and −1.45 V vs. SCE, respectively. Reaction mechanism was discussed. The paper also presented a convenient electroanalytical assay for superoxide dismutase enzyme activity.

A new ultraviolet spectrophotometric method for hexavalent chromium in water based on the oxidation of chromotropic acid by Cr(VI) in 0.12 mol/liter HCl medium is described. The molar absorptivity is 1.76 × 10 4 liters·mol −1 cm −1 . The detection limit is 0.024 μg ml −1 Cr. This sensitive and very simple ultraviolet spectrophotometric method for microquantitative determination of Cr(VI) in water has good precision and accuracy.

Many biomolecules contain photoactive reducing agents, such as reduced nicotinamide adenine dinucleotide (NADH) and 6-thioguanine (6-TG) incorporated into DNA through drug metabolism. These reducing agents may produce reactive oxygen species under UVA irradiation or act as electron donors in various media. The interactions of C60 fullerenes with biological reductants and light energy, especially via the Type-I electron-transfer mechanism, are not fully understood although these factors are often involved in toxicity assessments. The two reductants employed in this work were NADH for aqueous solutions and 6-TG for organic solvents. Using steady-state photolysis and electrochemical techniques, we showed that under visible light irradiation, the presence of reducing agents enhanced C60 -mediated Type-I reactions that generate superoxide anion (O2(.-)) at the expense of singlet oxygen ((1)O2) production. The quantum yield of O2(.-) production upon visible light irradiation of C60 is estimated below 0.2 in dipolar aprotic media, indicating that the majority of triplet C60 deactivate via Type-II pathway. Upon UVA irradiation, however, both C60 and NADH undergo photochemical reactions to produce O2(.-), which could lead to a possible synergistic toxicity effects. C60 photosensitization via Type-I pathway is not observed in the absence of reducing agents.

A water soluble zinc(II) phthalocyanine symmetrically appended with eight thioglucose units was synthesized from commercially available hexadecafluorophthalocyaninatozinc(II) by controlled nucleophilic substitution of the peripheral fluoro groups. The photophysical properties and cancer cell uptake studies of this nonhydrolysable thioglycosylated phthalocyanine are reported. The new compound has amphiphilic character, is chemically stable, and can potentially be used as a photosensitizer in photodynamic therapy.

A pH-responsive, TiO2-attached sensitizer was prepared based on the adsorption of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) onto TiO2 nanoparticles. This colloidally dispersed TiO2-attached TCPP behaves as a single-phase colloidal sensitizer at pH 1.0-3.3 with quantum yields of singlet oxygen production (Phi(Delta)) between 0.20 and 0.25, as a heterogeneous particle sensitizer at pH 3.5-6.0 with Phi(Delta) between 0.25 and 0.50, and as homogeneous free TCPP molecules in alkaline solutions with Phi(Delta) = 0.53. The changes in Phi(Delta) are fully consistent with pH-dependent adsorption of TCPP onto the TiO2 surface. Recovery yields of 99.8% for TCPP and 98.8% for TiO2 were obtained from 1.4 mM TiO2-attached TCPP. We attribute its photosensitization ability to retaining TCPP solubility on the TiO2 surface and, hence, activity. This novel system shows a potential to bridge the gap between easily recoverable and highly efficient sensitizers.

Single-walled carbon nanotubes (SWNTs) functionalized with -COOH (along with some sulphonation and nitration), and/or modified with chitosan were prepared and tested for their singlet oxygen ((1)O(2)) production. The emission from (1)O(2) observed upon SWNT irradiation at 532 nm was due to a two-photon process, while (1)O(2) production via excitation at 355 nm occurred through a conventional one-photon pathway. The relative quantum yield of (1)O(2) production at excitation wavelength of 532 nm was found to be 0.00, 0.07-0.13 and 0.24-0.54 for highly-functionalized, partially-functionalized and non-functionalized SWNT samples respectively. The nanotube-mediated generation of (1)O(2) may find applications in both targeted destruction of tumor cells and selective degradation of drug molecules. Our research provides a practical approach to modulate the production of reactive oxygen species from SWNTs via surface functionalization/modification.

Singlet molecular oxygen [1O2 (1Deltag)] is generated cleanly in aqueous solution upon irradiation of a heterogeneous complex, meso-tetra(N-methyl-4-pyridyl)porphine (1) adsorbed onto porous Vycor glass (PVG). The cationic photosensitizer 1 tightly binds onto PVG and gives a stable material, which does not dissociate 1 into the surrounding aqueous phase. The production of 1O2 was measured by monitoring the time-resolved 1O2 (1Deltag) phosphorescence at 1270 nm. Indirect analysis of 1O2 generation was also carried out with the photooxidation of trans-2-methyl-2-pentenoate anion, which afforded the corresponding hydroperoxide. Sensitizer-1-impregnated PVG gives rise to a new singlet oxygen generator but more importantly provides a heterogeneous system for use in water.

Intelligent Route Control (IRC) technologies allow multihomed networks to dynamically select egress links based on performance measurements. TCP congestion control, on the other hand, dynamically adjusts the send-window of a connection based on the current path's available bandwidth. Little is known about the complex interactions between IRC and TCP congestion control. In this paper, we consider a simple dual-feedback model in which both controllers react to packet losses, either by switching to a better path (IRC) or by reducing the offered load (TCP congestion control). We first explain that the IRC-TCP interactions can be synergistic as long as IRC operates on larger timescales than TCP ("separation of timescales"). We then examine the impact of sudden RTT changes on TCP, the behavior of congestion control upon path changes, the effect of IRC measurement delays, and the conditions under which IRC is beneficial under two path impairment models: short-term outages and random packet losses.

Singlet oxygen reacts with binaphthyl phosphine derivatives such as 1,1'-binaphthyl di-tert-butyl phosphine to form the corresponding binaphthyl-2-oxide phosphine oxides. This new intramolecular arene epoxidation reaction proceeds with complete retention of stereochemistry. The binaphthyl-2-oxide di-tert-butyl phosphine oxide undergoes a slow "NIH-rearrangement" to form the corresponding hydroxylated product. A transient phosphadioxirane intermediate has been directly observed by low-temperature NMR. Kinetic analyses show that all of the phosphadioxirane intermediate is converted to product. [reaction: see text]

In INterdomain Ingress Traffic Engineering (INITE), a “target” Autonomous System (AS) aims to control the ingress link at which the traffic of one or more upstream source networks enters that AS. In practice, ISPs often manipulate, mostly in a trial-and-error manner, the length of the AS-Path attribute of upstream routes through a simple technique known as prepending (or padding). In this paper, we focus on prepending and propose a polynomial-time algorithm (referred to as OPV) that determines the optimal padding for an advertised route at each ingress link of the target network. Specifically, given a set of “elephant” source networks and some maximum load constraints on the ingress links of the target AS, OPV determines the minimum padding at each ingress link so that the load constraints are met, when it is feasible to do so. OPV requires as input an AS-Path length estimate from each source network to each ingress link. We describe how to estimate this matrix, leveraging the BGP Looking Glass Servers. To deal with unavoidable inaccuracies in the AS-Path length estimates, and also to compensate for the generally unknown BGP tie-breaking process in upstream networks, we also develop a robust variation (RPV) of the OPV algorithm.

Models for network topology form a crucial component in the analysis of protocols. This paper systematically investigates a variety of evolutionary models for autonomous system (AS) level Internet topology. Evolution-based models produce a topology incrementally, attempting to reflect the growth patterns of the actual topology. While evolutionary models are appealing, they have generally not agreed as closely with measurements of real data as non-evolutionary models. We attempt to understand what factor contributes to a "good" evolutionary model. Our systematic study consists of a relatively generic evolutionary model framework, which we populate with different choices for the components. This allows us to compare a variety of instances of models to measurements from real data sets. We study issues such as the initial topology, the type of preferential connectivity used when adding edges, and the role of "growth" edges added between existing nodes. We find that appropriate instantiation of the framework can provide topologies that agree closely with real data. We also use our work to highlight several crucial open problems in topology modeling.

The need to service populations of high diversity in the face of high disparity affects all aspects of network operation: planning, routing, engineering, security, and accounting. We analyze diversity/disparity from the perspective of selecting a boundary between mice and elephants in IP traffic aggregated by route, e.g., destination AS. Our goal is to find a concise quantifier of size disparity for IP addresses, prefixes, policy atoms and ASes, similar to the oft-quoted 80/20 split (e.g., 80% of volume in 20% of sources). We define crossover as the fraction c of total volume contributed by a complementary fraction 1-c of large objects. Studying sources and sinks at two Tier 1 backbones and one university, we find that splits of 90/10 and 95/5 are common for IP traffic. We compare the crossover diversity to common analytic models for size distributions such as Pareto/Zipf. We find that AS traffic volumes (by byte) are top-heavy and can only be approximated by Pareto with α=0.5, and that empirical distributions are often close to Weibull with shape parameter 0.2–0.3. We also find that less than 20 ASes send or receive 50% of all traffic in both backbones’ samples, a disparity that can simplify traffic engineering. Our results are useful for developers of traffic models, generators and simulators, for router testers and operators of high-speed networks.

We report the singlet oxygen sensitization properties of a series of bis-cyclometalated Ir(III) complexes (i.e., (bt)2Ir(acac), (bsn)2Ir(acac), and (pq)2Ir(acac); bt = 2-phenylbenzothiazole, bsn = 2-(1-naphthyl)benzothiazole, pq = 2-phenylquinoline, and acac = acetylacetonate). Complexes with acetylacetonate ancillary ligands give singlet oxygen quantum yields near unity (PhiDelta = (0.7-1.0) +/- 0.1), whether exciting the ligand-based state or the lowest energy excited state (MLCT + 3LC). The singlet oxygen quenching rates for these beta-diketonate complexes were found to be small [(5 +/- 2) x 105 to (6 +/- 0.2) x 106 M-1 s-1], roughly 3 orders of magnitude slower than the corresponding phosphorescence quenching rate. Similar complexes were prepared with glycine or pyridine tethered to the Ir(III) center (i.e., (bsn)2Ir(gly) and (bt)2Ir(py)Cl; gly = glycine and py = pyridine). The glycine and pyridine derivatives give high singlet oxygen yields (PhiDelta = (0.7-1.0) +/- 0.1).

Singlet oxygen reacts with Ir(I) and Rh(I) thiolato complexes to form the corresponding Ir(III) and Rh(III) peroxo thiolato complexes which do not undergo intramolecular oxidation of the thiolate moiety.

Singlet oxygen reacts with Ir(I) and Rh(I) thiolato complexes to form the corresponding Ir(III) and Rh(III) peroxo thiolato complexes which do not undergo intramolecular oxidation of the thiolate moiety.