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A π-conjugated copolymer based on a pyrene diimide unit (P(PyDI-T2)) was synthesized using the Suzuki–Miyaura cross-coupling reaction between 4,5,9,10-pyrene diimide-2,7-diboronic ester and 2,2′-di...

Ozone is known to be present within the surface ice of Jupiter’s moon Ganymede as well as Saturn’s moons Dione and Rhea. Given the ubiquity of solar photons incident on these water-ice-dominated su...

The presence of sulfur dioxide on the trailing hemisphere of Europa’s surface is well-established, and both its presence and its chemistry are influenced by sulfur ion implantation. Particle irradi...

A computational study of the direct arylation reaction was undertaken to understand the origin of nonselective β-couplings observed in thiophene-based polymers prepared by direct (hetero)arylation polymerization (DHAP). The reactivities and selectivities of C–H bond activations were studied for the concerted metalation–deprotonation mechanism on model thiophene substrates using density functional theory (DFT) and domain-based local pair natural orbital coupled cluster with singles, doubles, and perturbative triples (DLPNO-CCSD(T)). Substituent effects are shown to control experimentally observed regioselectivities. Electron-rich or -deficient thiophene substrates with multiple C–H bonds possess an intrinsic selectivity for bond activation at the α-position, while halogens in the α-position substantially reduce coupling selectivities by activating the adjacent Cβ–H bonds. Therefore, the halogenated monomer is responsible for the reported poor selectivities in DHAP. The effect of the substrate undergoing ox...

Organic molecules are emerging candidates for the next generation of cost-effective active materials of Li-ion batteries. Small diimide building blocks such as pyromellitic diimide (PMDI) have attracted much attention because of their high theoretical capacity. Many strategies have been undertaken to limit the well-known phenomenon of dissolution of the active material in the electrolyte. Such strategies include the preparation of salts and the synthesis of polyimides or macrocycles. Since dibromopyromellitic dimiide exhibits almost no sp2 cross-coupling polymerization reaction by conventional synthetic routes (Suzuki–Miyaura or Migita–Stille), we used PMDI as an aromatic C–H bond-bearing unit for direct (hetero)arylation polymerization (DHAP) with 1,4-dibromobenzene as comonomer as a new stabilization strategy. DHAP proved to be an effective tool in the preparation of this polymer, yielding a number-average molecular weight of up to 31 kDa. We studied the effect of side-chain engineering using variable c...

Chloride salts have been proposed to exist on the surface of Europa based on some geochemical predictions of the ocean composition as well as some interpretations of data from the Galileo spacecraft. To help elucidate our understanding of Europa’s surface composition, we have conducted a study of frozen chloride salt brines prepared under simulated Europa surface conditions (vacuum and temperature) using both near-infrared (NIR) and Raman spectroscopies. The latter was used to determine the hydration states of various chloride salts as a function of the temperature, while NIR spectroscopy of identically prepared samples was used to provide reference reflectance spectra of the identified hydrated salts. We further investigated the stability of the formed hydrated salts under vacuum and ultraviolet (UV) irradiation. Our results indicate that, at temperatures ranging from 80 to 233 K, (i) NaCl·2H2O is formed from the freezing of NaCl brines, (ii) freezing of KCl solutions does not form KCl hydrates, (iii) fr...

Vapor intrusion (VI) investigations often require sampling of indoor air for evaluating occupant risks, but can be confounded by temporal variability and the presence of indoor sources. Controlled pressure methods (CPM) have been proposed as an alternative, but temporal variability of CPM results and whether they are indicative of impacts under natural conditions have not been rigorously investigated. This study is the first involving a long-term CPM test at a house having a multiyear high temporal resolution indoor air data set under natural conditions. Key observations include (a) CPM results exhibited low temporal variability, (b) false-negative results were not obtained, (c) the indoor air concentrations were similar to the maximum concentrations under natural conditions, and (d) results exceeded long-term average concentrations and emission rates under natural conditions by 1-2 orders of magnitude. Thus, the CPM results were a reliable indicator of VI occurrence and worst-case exposure regardless of day or time of year of the CPM test.

Laser desorption is an attractive technique for in situ sampling of organics on Mars given its relative simplicity. We demonstrate that under simulated Martian conditions (~2.5 Torr CO(2)) laser desorption of neutral species (e.g., polycyclic aromatic hydrocarbons), followed by ionization with a simple ultraviolet light source such as a discharge lamp, offers an effective means of sampling organics for detection and identification with a mass spectrometer. An electrodynamic ion funnel is employed to provide efficient ion collection in the ambient Martian environment. This experimental methodology enables in situ sampling of Martian organics with minimal complexity and maximum flexibility.

Aquifer physical model experiments were performed to investigate if diffusive emissions from nonaqueous phase liquid (NAPL)-impacted low-permeability layers into groundwater moving through adjacent NAPL-free high-permeability layers can be reduced by creating an aerobic biotreatment zone at the interface between the two, and if over time that leads to reduced emissions after treatment ceases. Experiments were performed in two 1.2-m long × 1.2-m high × 5.4 cm wide stainless steel tanks; each with a high-permeability sand layer overlying a low-permeability crushed granite layer containing a NAPL mixture of indane and benzene. Each tank was water-saturated with horizontal flow primarily through the sand layer. The influent water was initially deoxygenated and the emissions and concentration distributions were allowed to reach near-steady conditions. The influent dissolved oxygen (DO) level was increased stepwise to 6.5-8.5 mg/L and 17-20 mg/L, and then decreased back to deoxygenated conditions. Each condition was maintained for at least 45 days. Relative to the near-steady benzene emission at the initial deoxygenated condition, the emission was reduced by about 70% when the DO was 6.5-8.5 mg/L, 90% when the DO was 17-20 mg/L, and ultimately 60% when returning to low DO conditions. While the reductions were substantial during treatment, longer-term reductions after 120 d of elevated DO treatment, relative to an untreated condition predicted by theory, were low: 29% and 6% in Tank 1 and Tank 2, respectively. Results show a 1-2 month lag between the end of DO delivery and rebound to the final near-steady emissions level. This observation has implications for post-treatment performance monitoring sampling at field sites.

Current vapor intrusion (VI) pathway assessment heavily weights concentrations from infrequent (monthly-seasonal) 24 h indoor air samples. This study collected a long-term and high-frequency data set that can be used to assess indoor air sampling strategies for answering key pathway assessment questions like: "Is VI occurring?", and "Will VI impacts exceed thresholds of concern?". Indoor air sampling was conducted for 2.5 years at 2-4 h intervals in a house overlying a dilute chlorinated solvent plume (10-50 μg/L TCE). Indoor air concentrations varied by 3 orders of magnitude (

The ability of small interfering RNA (siRNA) to efficiently silence the expression of specific genes provides the basis for exciting new therapies based on RNA interference (RNAi). The efficient intracellular delivery of siRNA from cell uptake through the endosomal trafficking pathways into the cytoplasm remains a significant challenge. Previously we described the synthesis of a new family of diblock copolymer siRNA carriers using controlled reversible addition fragmentation chain transfer (RAFT) polymerization. The carriers were composed of a positively-charged block of dimethylaminoethyl methacrylate (DMAEMA) to mediate siRNA binding and a second pH-responsive endosome releasing block composed of DMAEMA and propylacrylic acid (PAA) in roughly equimolar ratios, and butyl methacylate (BMA). Here we describe the development of a new generation of siRNA delivery polymers based on this design that exhibit enhanced transfection efficiency and low cytotoxicity. This design incorporates a longer endosomolytic block with increased hydrophobic content to induce micelle formation. These polymers spontaneously form spherical micelles in the size range of 40 nm with CMC (critical micelle concentration) values of approximately 2 μg/ml based on dynamic light scattering (DLS), 1H-NMR, electron microscopy, and selective partitioning of the small molecule pyrene into the hydrophobic micelle core. The siRNA binding to the cationic shell block did not perturb micelle stability or significantly increase particle size. The self-assembly of the diblock copolymers into particles was shown to provide a significant enhancement in mRNA knockdown at siRNA concentrations as low as 12.5 nM. Under these conditions the micelle--based systems showed an 89 % reduction in GAPDH mRNA levels as compared to only 23 % (10 nM siRNA) for the non-micelle system. The reduction in mRNA levels becomes nearly quantitative as the siRNA concentration is increased to 25 nM and higher. Flow cytometry analysis of fluorescent-labeled siRNA showed uptake in 90% of cells and a 3-fold increase in siRNA per cell compared to a standard lipid transfection agent. These results demonstrate the potential utility of this carrier design for siRNA drug delivery.

The fragmentation of the copper(I) guanidinate [Me(2)NC(NiPr)(2)Cu](2) (1) has been investigated with time-of-flight mass spectrometry (TOF MS), matrix-isolation FTIR spectroscopy (MI FTIR spectroscopy), and density functional theory (DFT) calculations. Gas-phase thermolyses of 1 were preformed in the temperature range of 100-800 degrees C. TOF MS and MI FTIR gave consistent results, showing that precursor 1 starts to fragment at oven temperatures above 150 degrees C, with a close to complete fragmentation at 260 degrees C. Precursor 1 thermally fragments to Cu((s)), H(2)(g), and the oxidized guanidine Me(2)NC(=NiPr)(N=CMe(2)) (3). In TOF MS experiment, 3 was clearly indentified by its molecular ion at 169.2 u. Whereas H(2)(+) was detected, atomic Cu was not found in gas-phase thermolysis. In addition, the guanidine Me(2)NC(NiPr)(NHiPr) (2) was detected as a minor component among the thermolysis products. MI thermolysis experiments with precursor 1 were performed, and species evolving from the thermolysis oven were trapped in solid argon at 20 K. These species were characterized by FTIR spectroscopy. The most indicative feature of the resulting spectra from thermolysis above 150 degrees C was a set of intense and structured peaks between 1600 and 1700 cm(-1), an area where precursor 1 does not have any absorbances. The guanidine 2 was matrix-isolated, and a comparison of its FTIR spectrum with the spectra of the thermolysis of 1 indicated that species 2 was among the thermolysis products. However, the main IR bands in the range of 1600 and 1700 cm(-1) appeared at 1687.9, 1668.9, 1635.1, and 1626.6 cm(-1) and were not caused by species 2. The oxidized guanidine 3 was synthesized for the first time and characterized by (1)H NMR and FTIR spectroscopy. A comparison of an FTIR spectrum of matrix isolated 3 with spectra of the thermolysis of 1 revealed that the main IR bands in the range of 1600 and 1700 cm(-1) are due to the presence of 3. The isomers exhibit the NMe(2) group cis or trans to the iPr group, with cis-3 being significantly less stable than trans-3. At higher temperature secondary thermal fragments had been observed. For example at 700 degrees C, TOF MS and MI FTIR data showed that species 2 and 3 both eliminate HNMe(2) to give the carbodiimides iPrNCNiPr (CDI) and iPrNCN[C(=CH(2))Me] (4), respectively. A DFT study of the decomposition of compound 1 was undertaken at the B3LYP/6-31+G(d,p) level of theory employing dispersion-correcting potentials (DCPs). The DFT study rationalized both carbodiimide deinsertion and beta-hydrogen elimination as exergonic decomposition pathways (DeltaG = -44.4 kcal/mol in both cases), but experiment showed beta-hydrogen elimination to be the favorable route.

While numerous detection methods exist for environmental heavy metal monitoring, easy-to-use technologies combining rapidity with in vivo measurements are lacking. Multiwell systems exploiting transgenic tadpoles are ideal but require time-consuming placement of individuals in wells. We developed a real-time flow-through system, based on Fountain Flow cytometry, which measures in situ contaminant-induced fluorescence in transgenic amphibian larvae immersed in water samples. The system maintains the advantages of transgenic amphibians, but requires minimal human intervention. Portable and self-contained, it allows on-site measurements. Optimization exploited a transgenic Xenopus laevis bearing a chimeric gene with metal responsive elements fused to eGFP. The transgene was selectively induced by 1 microM Zn(2+). Using this tadpole we show the continuous flow method to be as rapid and sensitive as image analysis. Flow-through readings thus accelerate the overall process of data acquisition and render fluorescent monitoring of tadpoles suitable for on-site tracking of heavy metal pollution.

The use of compound-specific isotope analysis (CSIA) as a diagnostic tool for MTBE biodegradation in aquifers was tested at the Port Hueneme, CA site. There, a 1500-m long dissolved MTBE plume and associated engineered aerobic flow-through biobarrier have been well-studied, leading to delineation of regions of known significant and limited bioattenuation. This allowed comparison of field-scale CSIA results with a priori knowledge of aerobic MTBE biodegradation, leading to conclusions concerning the utility of CSIA as a diagnostic tool for other aerobic biodegradation sites. Groundwater samples were collected and analyzed for both 13C and 2H (D) in MTBE through the bioactive treatment zone and within the larger MTBE plume. For reference, the 13C enrichment factor for MTBE biodegradation in laboratory-scale microcosms using site groundwater and sediments was also quantified. Aerobic microcosms showed a 13C enrichment of 5.5 to 6.4 +/- 0.2 per thousand over a two-order of magnitude concentration decrease, with an average isotope enrichment factor (epsilon(c)) of -1.4 per thousand, in agreement with other aerobic microcosm studies. Less 13C enrichment (about 25%) was observed for similar MTBE concentration reductions in groundwater samples collected within the aerobic biotreatment zone, and this enrichment was comparable to the scatter in delta13C values within the source zone. Increasing enrichment with decreasing MTBE concentration seen in microcosm data was not evident in either the 13C or D field data. The discrepancy between field and laboratory data may reflect small-scale (1 m) spatial heterogeneity in MTBE biodegradation activity and the mixing of water from adjacent strata during groundwater sampling; for example, relatively nonattenuated MTBE-impacted water from one stratum could be mixed with highly attenuated/low-MTBE concentration from another, and this could produce a sample with both reduced MTBE concentration and low enrichment. Overall, the results suggest that 13C data alone may produce inconclusive results at sites where MTBE undergoes aerobic biodegradation, and that even with two-dimensional CSIA (13C and D), an increase in the confidence of data interpretation may only be possible with data sets larger than those typically collected in practice.

Modeling and field study results suggest that, in the case of a building overlying an aerobically biodegradable vapor source (i.e., petroleum-impacted soil), the significance of vapor intrusion into the building depends on the source vapor concentration, the relative position of the vapor source and building, and the rate of O2 transport from the atmosphere to the soil gas beneath the building. This work quantified the latter at a house having about a 250 m2 slab-on-grade foundation footprint. It was constructed on 1.5 m of clean fill overlying a petroleum hydrocarbon-impacted soil layer undergoing methanogenesis. Soil gas O2 and CH4 profiles adjacent to and beneath the foundation were measured and then the soil gas beneath the slab was rapidly displaced with N2. The natural replenishment of O2 was monitored for 90 days using in situ O2 sensors, and the responses with time were similar, independent of location. The O2 replenishment rate was about 2500 g-O2/d immediately after the N2 flood and then it declined to 200-500 g-O2/d over 30 days. Weather events affected the O2 replenishment rate; an increase occurred during a strong wind period (3 m/s), and a decrease occurred during a heavy rainfall event. The spatial and temporal patterns in the O2 sensor responses and quantified O2 replenishment rates could not be accounted for by simple mechanistic hypotheses involving lateral diffusion or advection through the bulk soil, and instead the data suggest rapid replenishment immediately below the foundation followed by downward diffusion.

Steady-state vapor intrusion scenarios involving aerobically biodegradable chemicals are studied using a three-dimensional multicomponent numerical model. In these scenarios, sources of aerobically biodegradable chemical vapors are placed at depths of 1-14 m beneath a 10 m x 10 m basement or slab-on-grade construction building, and the simultaneous transport and reaction of hydrocarbon and oxygen vapors are simulated. The results are presented as Johnson and Ettinger attenuation factors alpha (predicted indoor air hydrocarbon concentration/source vapor concentration), and normalized contour plots of hydrocarbon and oxygen concentrations. In addition to varying the vapor source depth, the effects of source concentration (2-200 mg chemical/L vapor) and oxygen-limited first-order reaction rates (0.018-1.8 h(-1)) are studied. Hydrocarbon inputs were specific to benzene, although the relevant properties are similar to those for a range of hydrocarbons of interest. Overall, the results suggest that aerobic biodegradation could play a significant role in reducing vapor intrusion into buildings (decreased alpha-values) relative to the no-biodegradation case, with the significance of aerobic biodegradation increasing with increasing vapor source depth, decreasing vapor source concentration, and increasing first-order biodegradation rate. In contrast to the no-biodegradation case, differences in foundation construction can be significant in some settings. The significance of aerobic biodegradation is directly related to the extent to which oxygen is capable of migrating beneath the foundation. For example, in the case of a basement scenario with a 200 mg/L vapor source located at 3 m bgs, oxygen is consumed before it can migrate beneath the foundation, so the attenuation factors for simulations with and without aerobic biodegradation are similar for all first-order rates studied. For the case of a 2 mg/L vapor source located at 8 m bgs, the oxygen is widely distributed beneath the foundation, and the attenuation factor for the biodegradation case ranges from about 3 to 18 orders-of-magnitude less than that for the no-biodegradation case.

As part of an ongoing effort to explore the utility of high-resolution electrospray ionization ion mobility spectrometry (ESI-IMS) for the detection and identification of organic molecules on other planetary bodies, pursuant to NASA objectives, the reduced ion mobilities of 14 amino acids that have been identified in meteoritic material were determined in both N2 and CO2 drift gases. A (12,4) hard core potential model of the ion−neutral interaction was applied to a combined data set of amino acid mobilities from the present work (abiotic) and an earlier investigation of twenty common biotic amino acids (Beegle, L. W.; Kanik, I.; Matz, L.; Hill, H. H. Anal. Chem. 2001, 73, 3028−3034). The model was used to investigate the protonated amino acid mass−mobility correlation to extract details of the ion−neutral interaction and to gain insight into the structural details of these ions.

In situ bioaugmentation and biostimulation experiments were conducted at the USN Hydrocarbon National Environmental Test Site at Port Hueneme, CA (PH), where the dissolved MTBE groundwater plume is over 1500 m long. Laboratory microcosm experiments prepared with PH groundwater showed that MTBE was rapidly metabolized (t1/2 ≤ 2 weeks) after inoculation with a high-activity MTBE-degrading bacterial consortium (MC-100). Microcosm studies also showed that natural ether degraders were present at PH; however, the rates were 3−5 times slower than with the bioaugmented treatment. The field pilot test was conducted to assess the efficacy of creating an MTBE biobarrier by inoculating with MC-100 and maintaining well-oxygenated conditions. Three test plots located in the MTBE-only portion of the plume included control (no treatment), O2-only (intermittent O2 gas injection), and O2 + bioaugmented (MC-100) zones. Initial MTBE and dissolved oxygen (DO) concentrations in the plots prior to treatment varied from 2 to 9 m...

Laboratory-scale two-dimensional aquifer physical model studies were conducted to qualitatively assess how changes in air injection rate, air injection pulsing, and chemical type affect the rate and extent of removal by in situ air sparging. In this work, the treatment of immiscible-phase source zones in coarse media has been simulated. To provide a basis for comparison, equivalent unsaturated-soil soil vapor extraction-like simulation experiments were also conducted. Results suggest that, (1) initially, removal occurs from within saturated zone air flow channels at rates similar to those observed for soil vapor extraction, (2) during this initial period, removal rates are proportional to air flow rate and equilibrium chemical vapor concentrations, (3) while increased air injection rates improve volatilization rates in the short-term, the long-term cumulative removal efficiency may not be affected unless the saturated zone air flow distribution changes significantly with flow rate, (4) pulsing the air injection can improve the long-term cumulative removal efficiency, and (5) while short-term removal efficiency improves with increasing flow rate and vapor pressure, the long-term removal efficiency appears to improve with increasing solubility.

Knowledge of the effective vapor-phase porous medium diffusion coefficient is important for many applications, including risk-based volatilization and vapor migration calculations and remediation performance estimates. A procedure for measuring the effective vapor-phase porous medium diffusion coefficient in situ is presented here. The approach utilizes transient changes in volume-averaged concentrations of an inert tracer gas, rather than changes in point concentration measurements, to determine the effective vapor-phase porous medium diffusion coefficient Dveff. Measurements are made over intermediate time frames (minutes − hours), and the procedure is easily altered to probe scales ranging from approximately 0.1−1 m. The data reduction leads to the determination of Dveff/(θv)1/3, where θv denotes the air-filled porosity. Given this reduced dependence on θv (relative to approaches based on transient point concentration changes), in many settings it would not be necessary to make independent measurements...

In situ air sparging refers to a process in which clean air is injected directly into an aquifer formation to treat contaminant source zones, remediate dissolved contaminant plumes, or provide barriers to dissolved contaminant plume migration. This paper presents a theoretical analysis of the mechanisms and factors contributing to the overall performance of in situ air sparging systems. By examining processes occurring at the microscale, the significance of volatilization, biodegradation, bulk water flow, chemical concentrations, partitioning parameters, and air distribution are assessed. The analysis indicates that (a) if aerobic biodegradation occurs, it only enhances performance relative to the case of volatilization when dissolved contaminant concentrations are 2 cm/d toward the air channels occurs; (c) performance is expected to be significantly better for dissolved plumes than in sources containing immiscible phase contaminants; (d) the chemical property most affecting performance in source zones is solubility; and (e) in situ air sparging has significant potential for remediating spills of very soluble, but slowly degrading fuel oxygenates, such as MTBE.

Selected 15-, 32-, and 15,32-substituted lanosterol analogs are shown here to display time-dependent inactivation and lanosterol 14 alpha-methyl demethylase. These molecules are competitive with respect to substrate and require NADPH and O2 in order to display time dependence, thus supporting the premise that they are mechanism-based inactivators. Structural features required for lanosterol demethylation by the lanosterol demethylase such as nuclear double bond location and availability of an abstractable 15 alpha-proton are also essential elements for time-dependent inactivation. 32-(S)-Vinyllanost-8-en-3 beta,32-diol is a potent time-dependent inactivator (Kinact/Ki = 0.36 min-1 microM-1), while the 32-(R)-vinyllanost-8-en-3 beta,32-diol functions solely as a competitive demethylase inhibitor. These results support the premise that stereoselective oxidation occurs during lanosterol demethylation and that the 32-pro-S proton is abstracted during the demethylation reaction.

A variety of analogues of 1-[4-methoxy-3,5-dimethylbenzyl]-4-[3-(ethylamino)-2-pyridyl]piperazine hydrochloride (U-80493E) were synthesized and evaluated for their inhibition of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). Replacement of the substituted aryl moiety with various substituted indoles provided bis(heteroaryl)piperazines (BHAPs) that were 10-100-fold more potent than U-80493E. The pyridyl portion of the lead molecule was found to be very sensitive to modifications. Extensive preclinical evaluations of several of these compounds led to the selection of 1-[(5-methoxyindol-2-yl)carbonyl]-4-[3-(ethylamino)-2- pyridyl]piperazine methanesulfonate (U-87201E, atevirdine mesylate) for clinical evaluation.

The intrusion into and subsequent accumulation of contaminant vapors in buildings and family dwellings is of concern for health and safety reasons. When preparing environmental and health risk assessments, one must be able to quantify this exposure pathway in order to decide if site-specific conditions correspond to unacceptable indoor contaminant vapor concentrations. For cases in which contaminated-site specific conditions, a related problem is the determination of residual contaminant levels below which associated adverse health effect risks are deemed negligible. Unfortunately, there are currently no accepted models for predicting vapor intrusion rates, and there is considerable debate over which transport mechanisms govern the process. This paper presents a heuristic model for screening-level calculations. It incorporates both convective and diffusive mechanisms, as well as contaminant soil, and building foundation properties. Sample calculations are presented for a range of parameter values to illustrate use of the model and the relative contributions of individual transport mechanisms.

Recombinant hirudin (r-hirudin), unlike the naturally occurring leech protein, lacks a sulfate ester on Tyr-63 which reduces its binding affinity to thrombin by 3-10-fold. We demonstrate that nitration or iodination of Tyr-63 restores hirudin-thrombin affinity to levels similar to or exceeding that of the natural inhibitor. In contrast, nitration of Tyr-3 reduces the affinity of hirudin for thrombin. These chemical modifications results in multiple reaction products that are readily separated by reverse-phase HPLC. The mechanism of the observed changes in thrombin affinity may involve a reduction in the pK of the hydroxyl group of tyrosine due to substitution of the electrophilic iodo or nitro group on the phenyl ring, resulting in an increased negative charge at neutral pH. For Tyr-63, this effect mimics the sulfatotyrosine of natural hirudin, leading to an increased thrombin affinity at the anion-binding exosite. For Tyr-3, the increased polarity may destabilize its interaction within the apolar-binding site of thrombin. Substitution of the highly conserved Tyr-3 residue with Phe or Trp not only enables specific and quantitative chemical modification at Tyr-63 but also independently increases hirudin-thrombin affinity. Kinetic analysis of thrombin inhibition showed that enhanced binding by r-hirudin(nitro-Tyr-63) is due to an increase in the association rate between hirudin and thrombin whereas the reduced binding of r-hirudin(nitro-Tyr-3) results from a large increase in the dissociation rate. These observations indicate that specific segments within both the amino- and carboxy-terminal regions of hirudin interact with thrombin.

On montre que la formation reversible d'un complexe donneur-accepteur entre les polymeres heterocycliques [poly(benzimidazole-benzophenanthroline), poly(p-phenylene benzobisoxazole), poly(p-phenylene benzobisthiazole] et des acides de Lewis permet leur dissolution pour donner des solutions visqueuses qui sont etudiees par spectroscopie et viscosimetrie. Des films et des materiaux de revetement peuvent etre prepares a partir de ces solutions, ces films ont une structure identique a celle de la pristine

The diffusivity of ozone in water was determined experimentally by measuring the rate of ozone absorption into an aqueous laminar liquid jet. Penetration theory was used to interpret the results. Experiments were conducted over the temperature range of 10 °C to 45 °C. The results for diffusivity were correlated by an Arrhenius function for temperature dependence with a maximum deviation of ±3.3%: D/m2·s-1 = 1.10 × 10-6 exp[−1896/(T/K)].

A combined room-tempepature x-ray and neutron diffraction study of the bis(triphenylphosphine)iminium salt of the (Cr/sub 2/(CO)/sub 10/(..mu..-H))/sup -/ monoanion has been performed to investigate the effects of crystal packing on the anion and Cr--H--Cr geometry. A comparison with the earlier work on the (Et/sub 4/N)/sup +/ salt has shown that the pseudo-D/sub 4h/ geometry of the anion's nonhydrogen framework is maintained. This result indicates that the (Cr/sub 2/(CO)/sub 10/(..mu..-H))/sup -/ anion is considerably less susceptible than the tungsten analogue to a twisting deformation from a linear, eclipsed to a bent, staggered configuration. ((Ph/sub 3/P)/sub 2/N)/sup +/(Cr/sub 2/(CO)/sub 10/(..mu..-H))/sup -/ crystallizes with four molecules in a monoclinic unit cell of symmetry C2/c with x-ray-determined lattice parameters of a = 21.377(6) A, b = 16.285 (4) A, c = 16.186 (5) A, and ..beta.. = 128.68 (2)/sup 0/. The ((Ph/sub 3/P)/sub 2/N)/sup +/ cation lies along the twofold rotation axis which bisects the P--N--P bond angle of 154.8 (4)/sup 0/; the (Cr/sub 2/(CO)/sub 10/(..mu..-H))/sup -/ anion resides on the crystallographic center of symmetry. Only one position for the bridging hydrogen atom was resolved from the neutron diffraction data with the corresponding maximum negative nuclear density at the center of symmetry. However, themore » highly anisotropic character of its thermal ellipsoid strongly favors our interpretation that the observed anion structure is consistent with the slightly bent (Cr/sub 2/(CO)/sub 10/(..mu..-H))/sup -/ anion of C/sub 2v/-2mm geometry (previously observed for the (Et/sub 4/N)/sup +/ salt) being disordered among four equivalent sites and with the off-axis placement of the bridging hydrogen atom. 48 references, 4 figures, 7 tables.« less

Effets de la temperature et de l'empechement sterique sur les produits de la condensation (du type aldolique) des dianions avec l'heptanal, benzaldehyde, isobutanal, acetone, cyclopentanone

The complex (CH/sub 3/C/sub 5/H/sub 4/)/sub 2/Hf(BH/sub 4/)/sub 2/ can be prepared by the reaction of (CH/sub 3/C/sub 5/H/sub 4/)/sub 2/CfCl/sub 2/ with LiBH/sub 4/ in benzene.The bonding, molecular dynamics, and structure of this compound have been studied by infrared and Raman vibrational spectroscopy, dynamic nuclear magnetic resonance spectroscopy, and single-crystal neutron diffraction. Vibrational spectra reveal the perturbation of the B-containing ligand from a free BH/sub 4//sup -/ ion to be less in this complex than in most covalent tetrahydroborate transition metal complexes. The compound crystallizes from toluene/pentane in the monoclinic space group C2/c with four molecules in a unit cell of dimensions a = 14.566 (3), b = 6.839 (1), c = 13.959 (3) A, and ..beta.. = 102.31 (2)/sup 0/. Full-matrix least-squares refinement gave a final value of R(F/sub 0//sup 2/) = 0.107 for 1022 reflections. The molecular structure consists of monomeric (eta/sup 5/-CH/sub 3/C/sub 5/H/sub 4/)/sub 2/Hf(BH/sub 4/)/sub 2/ units having C/sub 2/ symmetry and bidentate tetrahydroborate ligands. The ring centroid--Hf--ring centroid angle is 128.5 (3)/sup 0/. The average Hf--C(ring) bond distance is 2.491 (9) A. The coordination of each tetrahydroborate group is markedly unsymmetrical with crystallographically independent Hf--H(bridge) distances of 2.069 (7) and 2.120 (8) A.more » The lengths of the two B--H(bridge) bonds mirror, inversely, the Hf--H distances:. The B--H(terminal) distances are 1.186 (16) and 1.198 (15) A, and the Hf--B distance is 2.553 (6) A. Important bond angles are B--Hf--B = 101.4 (3)/sup 0/, H(bridge)--B--H(bridge) = 108.4 (6)/sup 0/, and H(terminal)--B--H(terminal) = 115.4 (10)/sup 0/. The anisotropy of the hydrogen atom thermal parameters within the tetrahydroborate groups may reflect motion along the bridge-terminal hydrogen interchange reaction coordinate. The nature of the (CH/sub 3/C/sub 5/H/sub 4/)/sub 2/Hf--tetrahydroborate interaction can be understood in terms of those bonding factors which govern ligand-to-metal charge donation.« less

The main structural findings reported here, which bear on the diminished electrical conductivity of (NH/sub 4/)/sub 2/(Pt(CN)/sub 4/)Cl/sub 0/./sub 3/ . 3H/sub 2/O compared to prototype K/sup 2/(Pt(CN)/sub 4/)Br/sub 0/./sub 3/ . 3H/sub 2/O, are that while the intrachain Pt-Pt spacings are shorter and are of equal length (2.88(1)A) in the K+ salt, they are longer and are of different length (2.910(5) and 2.930(5)A x rays) in the NH/sub 4//sup +/ salt. Thus the formation of alternately long and short Pt-Pt separations (dimerization) in NH/sub 4/CP(Cl) is likely one of the most important factors contributing to its electrical conduction properties. A factor which supports hypothesis is that in RbCP(Cl), the Pt-Pt distances are also of unequal length (2.924(8) and 2.877(8)A), and Rb CP(Cl) has lower room temperature conductivity than KCP(Br). The complete explanation for the structure-conductivity relationships in those POTCP complexes is obviously much more complicated, because although a Rb/sup +/ ion has nearly the same cation radius as NH/sub 4//sup +/ and RbCP(Cl) and NH/sub 4/CP(Cl) are isostructural, the low-temperature electrical conductivity (NH/sub 4/CP(Cl)<< RbCP(Cl)) is vastly different.

Solubilisation du PBT dans des solvants aprotiques (nitroalcane, nitrobenzene) par formation reversible de complexes avec des acides de Lewis. Solutions cristallines liquides a concentrations elevees. Etude spectroscopique, viscocimetrique, microscopique des solutions. Etude spectroscopique et thermique des films de PBT prepares a partir de ces solutions