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Solid imidazolium-based poly(ionic liquid)s with variable molecular weights that contain the poly[2-(1-butylimidazolium-3-yl)ethyl methacrylate] (BIEMA) cation and different counter anions were evaluated in terms of CO2 capture and compared with classical ionic liquids with similar counter anions. In addition to poly(ionic liquid)s with often-applied ions such as BF4 (-) , PF6 (-) , NTf2 (-) , trifluoromethanesulfonate (OTf(-) ) and Br(-) , for the first time [BIEMA][acetate] was synthesised, which revealed a remarkably high CO2 sorption performance that exceeded the poly(ionic liquid)s studied previously on average by a factor of four (12.46 mg gPIL (-1) ). This study provides an understanding of the factors that affect CO2 sorption and a comparison of the CO2 capture efficiency with the frequently used sorbents. Moreover, all the studied sorbents were reusable if regenerated under carefully selected conditions and can be considered as suitable candidates for CO2 sorption.

The study of conformational transitions of peptides has obtained considerable attention recently because of their importance as a molecular key event in a variety of degenerative diseases. However, the study of peptide self-assembly into beta-sheets and amyloid beta (Abeta) fibrils is strongly hampered by their difficult synthetic access and low solubility. We have recently developed a new concept termed switch-peptides that allows the controlled onset of polypeptide folding and misfolding at physiologic conditions. As a major feature, the folding process is initiated by chemically or enzyme triggered O,N-acyl migration in flexible and soluble folding precursors containing Ser- or Thr-derived switch (S)-elements. The elaborated methodologies are exemplified for the in situ conversion of NPY- and Cyclosporine A-derived prodrugs, as well as for the onset and reversal of alpha and beta conformational transitions in Abeta peptides. In combining orthogonally addressable switch-elements, the consecutive switching on of S-elements gives new insights into the role of individual peptide segments (hot spots) in early processes of polypeptide self-assembly and fibrillogenesis. Finally, the well-known secondary structure disrupting effect of pseudoprolines (PsiPro) is explored for its use as a building block (S-element) in switch-peptides. To this end, synthetic strategies are described, allowing for the preparation of PsiPro-containing folding precursors, exhibiting flexible random-coil conformations devoid of fibril forming propensity. The onset of beta-sheet and fibril formation by restoring the native peptide chain in a single step classify PsiPro-units as the most powerful tool for inhibiting peptide self-assembly, and complement the present methodologies of the switch-concept for the study of fibrillogenesis.

A simple three-step procedure converted the readily accessible (2-bromo-1,1-difluoroethyl)arenes into a-aryl-a,a-difluoroacetaldehydes. Subsequent hydrocyanation, hydrolysis, oxidn. and again hydrolysis afforded b-aryl-b,b-difluoro-a-oxopropionic acids. Reductive amination transformed the oxo acids into a separable mixt. of a-hydroxy acids and racemic b,b-difluoro-b-phenylalanine derivs.. Enantiomerically pure b,b-difluorophenylalanine was obtained when a,a-difluoro-a-phenylacetaldehyde was condensed with homochiral 1-phenylethylamine, hydrogen cyanide added to the resulting imine, the diastereomeric mixt. thus produced hydrolyzed to the carboxamides which were found to be separable by fractional crystn. or chromatog. The pKa values of the b-aryl-b,b-difluoroalanines were measured and biol. profile of the latter probed. 3-(4-Chlorophenyl)-3,3-difluoro-2-oxopropionic acid proved to be a potent (Ki 27 mM) and selective inhibitor of arogenate dehydratase, a key enzyme catalyzing the last step of the phenylalanine biosynthesis. [on SciFinder (R)]

To better understand the relationship between lead speciation and bioavailability in natural freshwaters, the interaction of lead with the freshwater alga Chlorella kesslerii was studied in the presence of the Suwannee River fulvic acid (SRFA). Special attention was paid to direct interactions of the fulvic acid on the algae, as well as potential physiological (membrane permeability and algal metabolism) influences. Lead-free ion concentration measurements were carried out using a novel ion-selective electrode. Pb uptake decreased in the presence of SRFA with respect to noncomplexed Pb, but uptake fluxes, cellular Pb, Pb bound to the transport sites, and total adsorbed Pb were all higher than predicted from Pb2+ activities, in accordance with the free ion activity model (FIAM). The discrepancies between the observed values and those predicted by the FIAM in the presence and absence of synthetic ligands increased with increasing concentration of SRFA. Several hypotheses were examined to explain the observed differences. No contributions of labile and/ or hydrophobic Pb-SRFA complexes were found. Furthermore, direct biological effects, including variations in membrane permeability or algal metabolism, could not account for the observations. On the other hand, changes in the algal surface charge due to SRFA adsorption seemed to account, at least partially, for the observed increase in lead uptake in the presence of SRFA as compared to that corresponding to the same Pb2+ concentration in the presence of synthetic ligands.

A new indicator is proposed for determining if tropospheric ozone production in a specifiacr eai s limitedb yV OC or NOx.T he indicato1r 9= r•ø•C/•oød•Xes cribeths e ratio of the lifetimes of OH against the losses by reacting with VOC and NOx. Whereas •oøx• c anb e obtainebdy c onventionmale asurementthse, n ewp umpa ndp robeO H approach which is described in part one of this publication makes it now possible to obtain also ß_ov •o c ßI ndicator values above a thresholdv alue of 0.2 __+50 % are representativeo f NOx-saturatedc onditionsw here an increaseo f NOx emissionsc auses lower ozone production.F or valuesb elow 0.01 the ozone productioni s very insensitivet o changeso f VOC emissionsT. he robustnesso f this indicator againsts everalp arameters sucha s temperature,h umidity,p hotolysisa, nd initial ozone concentrationsis tested in a box model and comparedt o the robustnesso f other earlier proposedi ndicators.I n contrast to earlier proposed indicators, this new one is not based on photochemically producedl ong-liveds peciesb ut describest he instantaneousr egime of an air parcel. Three-dimensionasl imulations howst hat this indicator is quite successfuiln estimatingt he impact of increasedo r reducede missionso n the ozone concentrationsfo r each location in the modeling area. This will make it a very helpful tool for developing ozone abatement strategies.

A de-trending technique was developed for short-term and annual variations to identify long-term trends in primary and secondary pollutants. With this approach, seasonal and annual variations are removed using a mean year; the residual meteorol. short-term variation is removed using a multiple linear regression model. This method was used to de-trend O3, NOx, volatile org. compd. (VOC) and CO concns. in Switzerland. Primary pollutants (NOx, VOC, CO) at urban and suburban stations exhibited a downward trend over the last decade which correlates well with redns. in estd. Swiss emissions. Despite large decreases achieved in precursor emissions, summer peak O3 concns. did not show any statistically significant trend over the last decade. Applying this method to O3 concns. measured at the Jungfraujoch (3580 m above sea level) also showed no trend over the last 10 yr. De-trended summer O3 correlated well with European Union gross national product and industrial prodn. growth rates. These results suggested that if substantial redns. in summer peak O3 in Switzerland are desired, emissions redn. strategies must be part of control programs involving a much larger region.

Purpose: The present study was initiated to det. the conditions under which a single photodynamic treatment would induce maximal damage to a tumor with no or at least minimal reversible damage to a normal striated muscle. Methods and Materials: The technique of interstitial light delivery was used after prior 0.5 mg/kg tetra(m-hydroxyphenyl)chlorin administration in a hamster model. After having estd. the threshold light doses required for minimal muscle damage, the same light doses were applied to squamous cell carcinomas to evaluate the efficiency of interstitial photodynamic therapy. Sixteen and 96 h after the injection, irradn. at 650 nm was performed on the thigh muscle of the left hind leg. The applied light doses ranged between 0.3-15 J and were delivered at an intensity of 44 mW per cm of diffuser length. Results: The threshold of muscle damage was obtained using light doses of 1.5-3 J at two drug-light intervals of 16 and 96 h, resp. More than 85% of the tumor mass was destroyed when lesions were illuminated using these threshold conditions. In terms of immediate short-term tumor response, this means that for the given irradn. conditions, a relatively low threshold energy of only 1.5 or 3 J, depending on the drug-light interval, is sufficient to induce massive tumor destruction with minimal muscle damage. Conclusion: These results have implications for evaluating interstitial PDT for squamous cell cancers in unfavorable localization in the oral cavity or pharynx, such as at the base of the tongue.

(2,6-Dichlorophenyl)- and (2,6-dibromophenyl)trialkylsilanes undergo hydrogen/metal interconversion preferentially at the 4- rather than 3-position. However, the organometallic species generated by such a "meta metalation" are thermodynamically less stable (i.e., more basic) than those that would result from an ordinary "ortho metalation". This was demonstrated by equilibration experiments based on permutational halogen/metal interconversion. A new buttressing effect can explain the unprecedented regioselectivity. It is supported by X-ray structures that reveal marked deformations of the benzene ring in halophenylsilanes. [structure: see text]

To optimize photodynamic therapy (PDT) and photodetection of cancer with second-generation photosensitizers, knowledge of important variables such as the uptake of the dye and the dye contrast between normal and tumoral tissue after injection is necessary. The pharmacokinetics of a second-generation photosensitizer, tetra(meta-hydroxyphenyl)chlorin (mTHPC), is presented. To study this in a clinical context, an apparatus based on fluorescence spectroscopy and a non-invasive optical fiber probe has been used. The mTHPC fluorescence is induced at 2 excitation wavelengths (420 and 520 nm) with different penetration depth. The pharmacokinetics of mTHPC in patients with a squamous-cell carcinoma in the oral cavity show a signal selectivity as high as 16 about 3 hr after i.v. injection for the more advanced carcinomas. The magnitude of this selectivity appears to correlate with the staging of the cancer, the more invasive tumors showing the highest selectivity. Results obtained at 420 and 520 nm show little difference. These pharmacokinetics can be used directly for optimizing photodetection with mTHPC. However, complementary information on the localization of the drug by fluorescence microscopy, and a correlation of this data with tumor necrosis efficacy, are needed to optimize PDT timing.

We present a systematic study of the time-integrated fluorescence of native bacteriorhodopsin, as a function of excitation wavelength across the visible absorption band. While the fluorescence maximum is unaffected, the spectrum broadens on the high-energy side, with decreasing excitation wavelengths. In addition, there is no mirror image relation between emission and absorption, even for the longest excitation wavelengths. By comparison with the retinal cation in solution, we attribute these observations to vibrationally hot emission, and to the topology of the excited state surface on the way to isomerization.

16-Membered meta, para-cyclophanes mimicking the vancomycin binding pocket (D-O-E ring) are designed and synthesized. The structural features of these biaryl ether containing macrocycles are: a) the deletion of the carboxyl group of vancomycin's central amino acid (amino acid D); b) the elongation of the N-terminal; c) the presence of lipidated aminoglucose at the D-ring. Cycloetherification by way of an intramolecular nucleophilic aromatic substitution reaction (S(N)Ar) is used as a key step for the construction of the macrocycle. Minimum inhibitory concentrations for all of the derivatives are measured using a standard microdilution assay. Compounds 2a-2c and 3a-3c displayed weak activities against resistant strain Enterococcus faecalis L560 and were inactive against Enterococcus faecium resistant strain L2215.

Studies on designed peptides that exhibit high tendencies for medium-induced conformational transitions have recently attracted much attention because structural changes are considered as molecular key processes in degenerative diseases. The experimental access to these events has been limited so far mainly due to the intrinsic tendency of the involved polypeptides for self-association and aggregation, e.g. amyloid ? plaque formation, thought to be at the origin of Alzheimer's disease. We have developed a new concept termed 'switch-peptides' which allows the controlled onset of polypeptide folding and misfolding in vitro and in vivo, starting from a soluble, non-toxic precursor molecule. As a major feature, the folding process is initiated by enzyme-triggered N,O-acyl migrations restoring the native peptide backbone in situ. As the folding is set off in the moment of creating the bioactive molecule ('in statu nascendi', ISN), our concept allows for the first time the investigation of the early steps of protein misfolding as relevant in degenerative diseases, opening new perspectives for the rational design of therapeutically relevant compounds.

A visible-pump/UV-probe transient absorption is used to characterize the ultrafast dynamics of bacteriorhodopsin with 80-fs time resolution. We identify three spectral components in the 265- to 310-nm region, related to the all-trans retinal, tryptophan (Trp)-86 and the isomerized photoproduct, allowing us to map the dynamics from reactants to products, along with the response of Trp amino acids. The signal of the photoproduct appears with a time delay of ≈250 fs and is characterized by a steep rise (≈150 fs), followed by additional rise and decay components, with time scales characteristic of the J intermediate. The delayed onset and the steep rise point to an impulsive formation of a transition state on the way to isomerization. We argue that this impulsive formation results from a splitting of a wave packet of torsional modes on the potential surface at the branching between the all-trans and the cis forms. Parallel to these dynamics, the signal caused by Trp response rises in ≈200 fs, because of the translocation of charge along the conjugate chain, and possible mechanisms are presented, which trigger isomerization.

The title cyclophanes, such as I, were prepd. via a Ugi-4CR four component reaction and subsequent macrocyclization of the resulting amides using intramol. SNAr reactions. [on SciFinder (R)]

A comparative study of absorption spectroscopy at 100 K has been performed on three-dimensional crystals of bacteriorhodopsin extd. from a lipidic cubic phase and on native purple membrane. A modified microspectrophotometer has been designed which yields absorption data with a high signal-to-noise ratio and remarkable reproducibility. Excellent agreement of the absorption spectra of the three-dimensional crystals and the purple membrane is obsd. provided that a rigorous crystal-handling procedure is followed. This result supports the equivalence of the protein structure in both the cubic phase crystals and the native purple membrane. On the other hand, it is shown that dramatic deviations of the crystal spectrum can be induced by minor changes in the extn. method. Exposure to air at room temp. can lead within a short time to an irreversible dehydration manifested by a distinct species with an absorption max. at 500 nm. Exposure of the crystals to a buffer with lower ionic strength than the crystn. soln. produces a different spectral form with an absorption max. at 477 nm, which was assigned to a distorted protein conformation induced by osmotic stress. The extreme sensitivity of these crystals to exptl. conditions is relevant for x-ray structural studies, in particular as different exptl. treatments are implemented to trap the intermediates of the protein's photocycle. [on SciFinder (R)]

Cyclic peptides I (R = benzyl, allyl; R1 = NO2, NH2, H), which contain the macrocyclic aryl ether skeleton of some naturally occurring alkaloids such as pandamine, were prepd. Key to the synthetic strategy was the cyclocondensation of the linear peptides II [NR2 = NHBOC, N(benzyl)2, N(allyl)2; R2 = SiMe2CMe3, H] to form macrocycles I. Thus, II [NR2 = N(allyl)2, R2 = H] in a DMF soln. was treated with Bu4N+F- in the presence of mol. sieves to form I (R = allyl, R1 = NO2), which was subsequently converted first to the amine I (R = allyl, R1 = NH2) and then to the target macrocycle I (R = allyl, R1 = H). [on SciFinder (R)]

The reactivityo f hydroxyrl adical (OH) with total volatile organicc ompounds (VOC), Z kvoc[VOC ], is directly obtained in the planetary boundary layer (PBL). The method is basedo n a perturbationt echniquew here high initial OH concentrationsa re createdb yf lashp hotolysoisf ozonea nds ubsequerneta ctiono f O(•D) withH 20. Laserinduced fluorescence is used to measure the residual OH concentration at different time delays after the perturbation (

Protein Engineering, 14 (12), ISSN:0269-2139, ISSN:1460-213X

A review. Manipulation of the quantum properties of matter can influence the course of biochem. reactions. Can biol. functions, such as vision or photosynthesis, that are driven by incoherent phenomena have anything to do with quantum mechanics, where the wave properties of matter play a key role. The answer is yes, and on page 1257 of this issue, Prokhorenko et al. show that biol. processes can be manipulated by means of coherent control. The work of Prokhorenko et al. goes beyond the specifics of biol. systems: It shows that for a quantum system in a fluctuating bath, one can manipulate the outcome of the reaction by creating constructive or destructive interferences along the reaction coordinate. Their investigation of the phase dependence of isomerization is quite revealing of the coherent nature of their control, and it is hoped that future studies will demonstrate the phase sensitivity of coherent control for mols. in liqs. as well. [on SciFinder (R)]

To characterize the catalytic mechanism for zinc-dependent histone deacetylases (HDAC), we have carried out d. functional theory (DFT) QM/MM studies on the deacetylation reaction catalyzed by a histone-deacetylase-like protein (HDLP). The calcn. results do not support the previous mechanistic hypothesis, but suggest a lower protonation state for the active site as well as a 4-fold zinc coordination during the reaction process. To characterize such mechanistic difference is not only significant for our fundamental understanding of its inner workings but also crucial for the design of HDAC inhibitors. [on SciFinder (R)]

Our research group is working towards understanding the fundamental physicochemical mechanisms of trace metal biouptake by aquatic microorganisms in natural systems. Research is currently focused on identifying under what conditions uptake fluxes are limited by physical (e.g. diffusion) as opposed to biological (transfer across biological membrane) processes. In addition, the complexation of the trace metals is being examined from both a thermodynamic (stability) and kinetic (lability) perspective in order to elucidate its effect on the overall uptake flux. Up-to-date information on the group, including a current publication list can be found at http://www.unige.ch/cabe/wilkinson.

Bromine contg. compds. are thought to play an important role in the O3 destruction in various regions of the atm. Recent studies of atm. Br chem. suggest that HOBr is one of the important Br compds. The rapid photolysis of HOBr in daytime releases Br atoms and OH radicals, which causes ozone destruction. In this study, the reactivity of HOBr with solid alkali metal halides is reported which affords insights into the importance of heterogeneous reactions of HOBr with salt, which in the atm. act as substrate particles for the reactions. The heterogeneous reactions of HOBr with solid cryst. NaCl [HOBr(g) + NaCl(s) -> BrCl(g) + NaOH(s)] and KBr [HOBr(g) + KBr(s) -> Br2(g) + KOH(s)] substrates at ambient temp. have been investigated using a Teflon coated Knudsen cell reactor. Powder, grain, and spray-deposited salt substrates were used for the measurement of the HOBr reactivity. The obsd. uptake probability depends on the total external surface area of the salt substrates. For NaCl substrates, Br2 and BrCl are obsd. as products; for KBr substrates, Br2 is obsd. as the sole product. In both cases, a dependence of the initial uptake probability g0 on HOBr flow rate has been obsd. The initial uptake is large at low flow rate and 10 times smaller at high flow rate. Values of g0 ? (6.5 +- 2.5) * 10-3 for NaCl and g0 ? 0.18 +- 0.04 for KBr are obtained under our exptl. conditions of limiting low flow rates akin to atm. conditions. The prodn. of Br2 is obsd. even for HOBr interacting on solid NaNO3, a non-halogen contg. substrate. The yield measurements imply that a HOBr self-reaction occurs on salt surfaces according to 2HOBr -> Br2 + H2O + 1/2O2. The decrease in Br2 yield with increasing HOBr flow rate from 100 to 50% indicates that a competition between the heterogeneous reaction of HOBr with NaCl or KBr and the self-reaction of HOBr takes place on the solid salt surface under lab. exptl. conditions. The decrease of g0 with time indicates that approx. 5-10% of the Br atoms on a KBr surface interact with HOBr.

Photodynamic therapy (PDT) with Foscan (mTHPC) is used to cure early cancers of the esophagus or the tracheobronchial tree. However, fixed PDT parameters (drug dose, light dose, etc.) do not permit an accurate prediction of the tissue damage. Large interpatient fluctuations in tissue drug level, at the time of light application, suggest that the light dose must be adjusted to the drug dose shortly before the PDT. This drug dose can be measured endoscopically by light-induced fluorescence spectroscopy, but this measurement is inconvenient and somewhat difficult. A better test site, yielding comparable information, is needed. The oral cavity seems ideal. However, it first had to be established to what extent the estimation of the drug dose was dependent upon the location of the measurement and the pressure applied to the probe. These measurements prove to be not only correlated to similar measurements in the esophagus or the bronchi but also more consistent and less sensitive to the location and the applied pressure. The buccal mucosa is therefore recommended as a test site for measuring the Foscan fluorescence signal at the time of PDT in the esophagus or the bronchi. This measurement is accurate enough for use in light-dose adjustment.

Review with 199 refs. Recent studies addressing vancomycin-resistance phenomena are surveyed. Besides leading semi-synthetic glycopeptides: BI-397 and LY 333328, other new synthetic derivs. are also presented. Rational design based on the known mode of action is seen in recent research from both industrial and academic groups. Thus, Biosearch Italia SpA worked on new synthetic glycopeptides with a modified binding pocket in order to find drugs active against both vancomycin-sensitive and -resistant strains. Eli Lilly & Co. and research groups at Stanford, Cambridge and Harvard synthesized covalently linked dimers in order to copy the dimerization and membrane anchoring effects. Both directions proved to be rewarding and some interesting compds. with potent in vitro activity against vancomycin-resistant enterococci (VRE) were found from these investigations. A new mechanistic proposal that can account for the bioactivity of LY 333328 against VRE was summarized. Research on new agents with modes of action different to that of glycopeptide antibiotics have also been successful and recent investigations related to RP-59500, SCH-27899 and U-100766 are presented. [on SciFinder (R)]

A comparative study of the efficiencies of W, Mg, Mg + Pd, Ir + Mg and Ir + W + PO43- as chem. modifiers for the thermal stabilization of Pb and Sn in slurries was performed. The Ir + Mg modifier contributes more than the others to minimizing matrix effects and preventing double peak formation. The influences of slurry concn., amt. of modifier and pyrolysis step on the integrated absorbance signals for Pb and Sn in sediment slurry were studied. The potential of fractional factorial design was explored to evaluate the effect on the absorbance signals of different factors such as drying and pyrolysis times, pyrolysis and atomization temps., presence of modifier and incorporation of a cool-down step in the electrothermal program. The Pb and Sn integrated absorbance signals are increased by lower and higher pyrolysis and atomization temps., resp. The Ir + Mg modifier also increases the absorbance signal for Sn. The use of an Ir + Mg modifier and ultrasonic agitation in the direct introduction of slurries into the graphite atomizer provides a consistent performance with good sensitivity, precision and anal. recovery. [on SciFinder (R)]

A polemic in answer to U. Schmidt (ibid. 1074). [on SciFinder (R)]

Eulerian photochem. grid models are widely used in the making of policy decisions concerning emission controls. However, significant uncertainties persist in a host of crucial input parameters. Quantifying and understanding their implications have become imperative from both the scientific and policy perspectives. Meteorol. uncertainties have a special significance because efforts to quantify them using conventional techniques based on expert ests. have failed to account for the complex correlations in their nonlinear spatial and temporal evolution. A comprehensive effort to quantify meteorol. uncertainties has been accomplished by subjecting a mesoscale meteorol. model to Monte Carlo simulations based on uncertainties in key base input parameters for the 3-day summer smog POLLUMET episode over the Swiss plateau. Monte Carlo uncertainty anal. based on the resulting meteorol. input uncertainties was then carried out using a photochem. grid model. Preliminary post-simulation anal. and statistics on the uncertainties in peak ozone estn. and the significance of considering correlations among inputs in sampling are presented.

Formation of vanadia species during the calcination of ball milled mixt. of V2O5 with TiO2 was studied by Raman spectroscopy in situ and at ambient conditions. Calcination in air leads to fast (1-3 h) spreading of vanadia over TiO2 followed by a slower process giving a monolayer vanadia. The calcinated catalyst showed higher activity during toluene oxidn. than the uncalcinated one, but the selectivity towards C7-oxygenated products (benzaldehyde and HOBz) remains unchanged. The activity of the catalysts is ascribed to the formation of vanadia species in the monolayer. The details of the parallel-consecutive reaction scheme of toluene oxidn. are presented from steady-state and transient kinetics studies. Different O species seem to participate in the deep and partial oxidn. of toluene. Coke formation was obsd. during the reaction presenting an av. compn. C2nH1.1n. The amt. of coke on the catalyst was not dependent on the calcination step and the V content in the catalyst. Coke formation is responsible for the deactivation of the catalyst. [on SciFinder (R)]

Hydroxyl radicals dominate daytime tropospheric chem., responsible for reactive removal of most trace gases (e.g., volatile org. compds.[VOC]), and is an active participant in the NO and NO2 cycle. Pump-and-probe LIDAR was used to examine the OH- chem. in the planetary boundary layer. This method consists of a high OH- concn. prodn. by a first laser beam (pump), including a flash photolysis of O3: O3 + hv (256 nm) -> O(1D) + O2, and the reaction, O(1D) + H2O -> 2OH. Its relaxation is followed by measuring the time evolution of the radical by laser-induced fluorescence (probe beam). A simulation of this expt. showed that in a short delay time, a direct est. of the total hydrocarbon reactivity defined as SVOC was obtained. The pump-and-probe technique allows measurements which can distinguish between locations where O3 formation mainly depends on NOx concns. and those where it mainly depends on VOC concns.

An in vitro method of assocg. proteins with the nucleic acid encoding them in the selection of novel variants is described. This method can be used for evolutionary selection of polypeptides in vitro. The inventive method makes it possible to allocate nucleic acids to the polypeptides coded thereby and to select and isolate nucleic acids coding for polypeptides with selected properties. The method involves manuf. of the protein of interest in vitro in a coupled transcription-translation system. The protein is manufd. as a fusion protein with a nucleic acid-binding protein that will bind to the nucleic acid upon appearance of the translation product. The transcription-translation systems are compartmented by incorporating them into a water-in-oil emulsion. The nucleic acid-binding protein is preferably a (cytosine-5)-Me transferase. This binds to DNA, and by use of a suicide inhibitor base analog, such as 5-fluorocytosine, incorporated into the DNA, a covalent complex can be formed. Sites contg. the label lie outside the gene for the fusion protein. The complexes can then be captured, e.g. using an affinity label, and screened for the desired property and the gene recovered for further processing. The use of the method to manuf. fusion proteins of HaeIII methylase labeled with hexahistidine and FLAG peptides is demonstrated. Use of calmodulin as an affinity label is also demonstrated. [on SciFinder (R)]

Preliminary work confirmed the important contribution of regional scale processes on pollutant concns. obsd. at local scales. For Grenoble, France, the model domain for simulations discussed, was selected considering the topog., urban area distribution, boundary conditions, and possible constraints in terms of computing time. The nesting technique used involved calcns. over a larger domain which contained the smaller domain. Two of the most important components of these models are the chem. mechanism and transport algorithm. The field campaign objective was to develop the necessary database to use for initial model conditions. Lidar and differential optical absorption spectroscopy observations provided essential inputs to develop the appropriate models. Results showed that even in very complex topog. areas, atm. models can be used to assess air pollution abatement strategy.

As the need for lower mol. wt. acrylates for specialty and molding applications increases, industry is looking for substitute prodn. processes. An alternative to the increasing of initiator and chain transfer agent concn. is working at higher temps. However, the high temp. polymn. of acrylates is a rather complex process with various new aspects to investigate, among others depropagation and thermal initiation. Addnl., all equipment has to be designed for this temp. range. In the scope of this work, the radical polymn. of Me methacrylate (MMA) is investigated for temps. between 140 DegC and 180 DegC in a continuous pilot scale tubular reactor. The reaction kinetics were detd. in batch expts. and implemented in a PREDICI model for the simulation of the continuous process. This model includes the initiation by MMA peroxides, which can form in the monomer from dissolved mol. oxygen, as well as a high temp. gel effect model and the depolymn. of the living chains. The pilot plant consist of Sulzer SMXL equipped DN20 tubes and has a max. throughput of 10kg/h. The first part is a loop reactor with a recycle ratio of approx. 45:1, which is followed by a tubular part. Both reaction zones contain high temp. ultrasound probes for inline conversion measurement. A micro-dosing pump allows further addn. of initiator or stabilizers into the process between the two reaction zones. For devolatilization of the polymer, a one-step flash chamber with a two-phase preheater is employed. The process is evaluated with respect to final monomer conversion, mol. wt. distribution and residual volatiles' concn. (VOC) of the produced polymer. First runs with the pilot plant have led to satisfying results, which show the feasibility of the high temp. polymn. and the agreement with the modeling. Final monomer conversion was limited to 60% by the choice of an appropriate initiator and mol. wts. between 150.000 and 200.000 g/mol were obtained.

The links between air pollution gas phase chem., aerosol chem. processes, and solar radiation are calcd. to improve air quality models. Air quality models are used to simulate pollutant content of the city plumes such as for Los Angeles.

An extensive random mutagenesis study on the function of nine residues in the subunit binding site of FimC was conducted to evaluate the mol. mechanisms of subunit binding by FimC and the contribution of chaperone surface residues. Five plasmid libraries of FimC variants with amino acid replacements in one or two of the nine residues were constructed to transform an Escherichia coli FimC null mutant. The assembly of type 1 pili was affected by the amino acid replacements at the subunit site of FimC; these did not completely eliminate the chaperone function. The amino acid replacements affect the interaction with different pilus subunits. The changes in the subunit binding site of FimC not only affect the pilus length and pilus no., but also the subunit compn. of type 1 pili. These findings revealed a fine-tuned affinity of pilus chaperones for the individual pilus subunits which detd. both the initiation of pilus assembly, stoichiometry and morphol. [on SciFinder (R)]

A review on various methods for the selection of catalysts using phage display. The different approaches (selection of catalysts by binding and direct selections for catalytic activity) are presented. Metallo-beta -lactamase BCII from Bacillus cereus was used as model enzyme. [on SciFinder (R)]

In a mode of nude mice bearing a human colon carcinoma xenograft, the biodistribution and tumor localization of metatetrahydroxyphenylchlorin (m-THPC) coupled to polyethylene glycol (PEG) were compared with those of the free form of this photosensitizer used in photodynamic therapy (PDT). At different times after i.v. injection of both forms of 125I-labeled photosensitizer, m-THPC-PEG gave on average a 2-fold higher tumor uptake than free m-THPC. In addition, at early times after injection, m-THPC-PEG showed a 2-fold longer blood circulating half-life and a 4-fold lower liver uptake than free m-THPC. The tumor to normal tissue ratios of radioactivity concentrations were always higher for m-THPC-PEG than for free m-THPC at any time point studied from 2 to 96 hr post-injection. Significant coefficients of correlation between direct fluorescence measurements and radioactivity counting were obtained within each organ tested. Fluorescence microscopy studies showed that m-THPC-PEG was preferentially localized near the tumor vessels, whereas m-THPC was more diffusely distributed inside the tumor tissue. To verify whether m-THPC-PEG conjugate remained phototoxic in vivo, PDT experiments were performed 72 hr after injection and showed that m-THPC-PEG was as potent as free m-THPC in the induction of tumor regression provided that the irradiation does for m-THPC-PEG conjugate was adapted to a well-tolerated 2-fold higher level. The overall results demonstrate first the possibility of improving the in vivo tumor localization of a hydrophobic dye used for PDT by coupling it to PEG and second that a photosensitizer conjugated to a macromolecule can remain phototoxic in vivo.

Reversal of amyloid formation through a controlled induced transformation from beta-sheet to sol. alpha-helix structures through the use of a switch element S could have an important consequences understanding the mechanisms of amyloid formation and clearance.

Laser-induced CVD has been used to produce Pt lines on pyrex glass substrates by means of platinum bis(hexafluoroacetylacetonate) as precursor. The effect that writing speed has on the line geometry and resistivity was studied, as well as the influence of writing speed, precursor vapor pressure, and laser power on periodic structure formation. The results are discussed in terms of laser beam residence time and radiation-induced temp. increase. It is possible to obtain lines with a resistivity very close to that of pure Pt under optimum exptl. conditions.

Efficient stirring is needed to realize heat flow anal. with a thermally homogeneous medium. Because dispersion polymn. with supercrit. fluids can be destabilized under stirring, a preliminary target has been to find a compromise between synthesis and basic reaction calorimetry requirements. This paper describes the use of poly(dimethylsiloxane) macromonomer with a mol. wt. 5000 g/mol as stabilizer for the dispersion polymn. of Me methacrylate in supercrit. carbon dioxide. The effect of stirring speed and stabilizer concn. has been examd. This study has shown that PMMA can be produced at high yield and mol. wt. using 10 wt. % (with respect to monomer) PDMS macromonomer at stirring speeds up to 600 rpm. A polymn. enthalpy of -57.6+-2 kJ/mol has been calcd. being in good agreement with previously reported data. Thus, preliminary results for the heat balance using the newly developed high pressure reaction calorimeter for supercrit. fluid applications have shown the important potential of reaction calorimetry to promote supercrit. fluid technologies at industrial scale allowing for the detn. of kinetics and thermodn. and safety data, resp.

In view of the uncertainty of the origin of the secular increase of N2O, we studied heterogeneous processes that contribute to formation of N2O in an environment that comes as close as possible to exhaust conditions containing NO and SO2, among other constituents. The N2O formation was followed using electron capture gas chromatography (ECD-GC). The other reactants and intermediates (SO2, NO, NO2 and HONO) were monitored using gas phase UV-VIS absorption spectroscopy. Experiments were conducted at 298 and 368 K as well as at dry and high humidity (approaching 100% rh) conditions. There is a significant heterogeneous rate of N2O formation at conditions that mimic an exhaust plume from combustion processes.The simultaneous presence of NO, SO2, O2 in the gas phase and condensed phase water, either in the bulk liquid or adsorbed state has been confirmed to be necessary for the production of significant levels of N2O. The stoichiometry of the overall reaction is: 2 NO+SO2+H2O → N2O+H2SO4. The maximum rate of N2O formation occurred at the beginning of the reaction and scales with the surface area of the condensed phase and is independent of its volume. A significant rate of N2O formation at 368 K at 100% rh was also observed in the absence of a bulk substrate. The diffusion of both gas and liquid phase reactants is not rate limiting as the reaction kenetics is dominated by the rate ofN2O formation under the experimental conditions used in this work. The simultaneous presence of high humidity (90–100% rh at 368 K) and bulk condensed phase results in the maximum rate and final yield of N2O approaching 60% and 100% conversion after one hour in the presence of amorphous carbon and fly-ash, respectively.

The kinetics of the adsorption of human serum albumin (HSA) onto spherical resin beads (Blue Sepharose CL-6B) in a closed stirred tank have been investigated. The differential equation with appropriate boundary conditions at the grain outer surface may be solved numerically or to various degrees of approxn. Using the Laplace transform technique to solve the equation of interest, we are able to obtain the exact soln. to the problem, in the Laplace domain. We assume that equil. is described by a linear absorption isotherm and that the adsorption rate is very rapid compared to diffusion in the adsorbent particles. A functional description of the exptl. data in the time domain allows us to computer the corresponding Laplace transform and fit it to the exact soln., to obtain the film mass transfer coeff., kf, and the effective diffusion coeff., De. The main advantage of this Laplace transform technique is that time-consuming numerical approaches are not needed. The two parameters are rapidly and easily found via two algebraic fits, one in the time domain followed by another in the Laplace domain. Using the parameters thus obtained, a numerical soln. of the problem is in good agreement with the exptl. data. [on SciFinder (R)]

A novel concept of a recycle loop reactor is developed with structured filamentous catalysts integrated as trays in a staged bubble column. The reactor can be operated in batch or continuous mode. Woven fabrics of activated carbon fibers (ACF) were used as support for the Pd catalyst. The loop reactor was tested in the 2-butyne-1,4-diol hydrogenation showing selectivity up to 97% towards 2-butene-1,4-diol at conversions up to 80%. The reactor behavior was described quant. assuming an ideally mixed reactor and Langmuir-Hinshelwood kinetics with weak hydrogen adsorption. Catalyst reuse was demonstrated in multiple runs over a period of 6 mo with more than 375 h on stream. [on SciFinder (R)]

National audience; Les étapes décisives de la photoperception cellulaire sont caractérisées et suivies en temps réel par spectroscopie laser jusqu'à l'échelle de quelques dizaines de femtosecondes. Les protéines photoactives étudiées dans cet article sont impliquées dans des phénomènes naturels majeurs comme la vision (protéines de rétinal modélisées par la bactériorhodopsine), la photomotilité de microorganismes (protéine jaune photoactive et oxyblépharisminoprotéine) et le phototropisme des plantes (cryptochrome). On montre également que la protéine verte fluorescente (GFP) peut être utilisée, en amont de la thérapie génique, comme sonde temporelle de la solubilité cytoplasmique de fragments d'anticorps auxquels elle est fusionnée.