International audienc
The ability of a model-based real-time optimization (RTO) scheme to converge to the plant optimum relies on the ability of the underlying process model to predict the plant’s necessary conditions of optimality (NCO). These include the values and gradients of the active constraints, as well as the gradient of the cost function. Hence, in the presence of plant−model mismatch or unmeasured disturbances, one could use (estimates of) the plant NCO to track the plant optimum. This paper shows how to formulate a modifed optimization problem that incorporates such information. The so-called modifiers, which express the difference between the measured or estimated plant NCO and those predicted by the model, are added to the constraints and the cost function of the modified optimization problem and are adapted iteratively. Local convergence and model-adequacy issues are analyzed. The modifier-adaptation scheme is tested experimentally via the RTO of a three-tank system.
International audienceIn this work, a group contribution-associating equation of state namely GCA-EoS, is extended to model the phase behavior of alkyl amine + hydrocarbon and alkyl amine + alcohol systems while considering the association of functional groups. A generalized routine has been implemented to quantify the association effects through functional groups with associating sites. The predictions of the model are found in good agreement with experimental data reported in the literature. The model parameters were estimated in the temperature range 218-428 K and pressures up to 735 kPa
We present an experiment that allows for a straightforward assignment of NMR resonances, even in large and/or challenging proteins. A single 3D double-TROSY experiment provides three pairs of sequential correlations between two alpha carbons, two amide protons, and two nitrogen nuclei. Thus, all correlated nuclei can readily be visualized within all dimensions of the resulting spectrum, and chain elongation of sequential amino acids can be effected with this single data set. This resolves ambiguities occurring in traditional methods which involve time-consuming and cumbersome strip comparisons obtained with series of triple-resonance spectra. The experiment makes use of the double TROSY technique to account for signal intensity losses during transfer and evolution periods and was tested on a 500 microM sample of the 33 kDa nonribosomal peptide synthetase protein EntB.
We have observed the photoactivatable fluorescent protein IrisFP in a transient dark state with near-atomic resolution. This dark state is assigned to a radical species that either relaxes to the ground state or evolves into a permanently bleached chromophore. We took advantage of X-rays to populate the radical, which presumably forms under illumination with visible light by an electron-transfer reaction in the triplet state. The combined X-ray diffraction and in crystallo UV-vis absorption, fluorescence, and Raman data reveal that radical formation in IrisFP involves pronounced but reversible distortion of the chromophore, suggesting a transient loss of pi conjugation. These results reveal that the methylene bridge of the chromophore is the Achilles' heel of fluorescent proteins and help unravel the mechanisms of blinking and photobleaching in FPs, which are of importance in the rational design of photostable variants.
Laulimalide is a structurally unique 20-membered marine macrolide displaying microtubule stabilizing activity similar to that of paclitaxel and the epothilones. The use of atom-economical transformations such as a Rh-catalyzed cycloisomerization to form the endocyclic dihydropyran, a dinuclear Zn-catalyzed asymmetric glycolate aldol reaction to prepare the syn 1,2-diol, and an intramolecular Ru-catalyzed alkene-alkyne coupling to build the macrocycle enabled us to synthesize laulimalide via an efficient and convergent pathway. The designed synthetic route also allowed us to prepare an analogue of the natural product that possesses significant cytotoxic activity.
Quantitative analysis of the staining of cell membranes with the cationic amphiphile, octadecyl rhodamine B (R18), is confounded by probe aggregation and changes to the probes' absorption cross section and emission quantum yield. In this paper, flow cytometry, quantum-dot-based fluorescence calibration beads, and FRET were used to examine real-time transfer of R18 from water to two limiting models of the cellular plasma membrane, namely, a single-component disordered membrane, dioleoyl-L-alpha-phosphatidylcholine (DOPC), and a ternary mixture of DOPC, cholesterol, and sphingomyelin (DSC) membranes, reconstituted on spherical and monodisperse glass beads (lipobeads). The quenching of R18 was analyzed as the probe concentration was raised from 0 to 10 mol % in membranes. The data show a > 2-fold enhancement in the quenching level of the probes that were reconstituted in DSC relative to DOPC membranes at the highest concentration of R18. We have parametrized the propagation of concentration-dependent quenching as a function of real-time binding of R18 to lipobeads. In this way, phenomenological kinetics of serum-albumin-mediated transfer of R18 from the aqueous phase to DOPC and DSC membranes could be evaluated under optimal conditions where the critical aggregation concentration (CAC) of the probe is defined as 14 nM. The mass action kinetics of association of R18 with DOPC and DSC lipobeads are shown to be similar. However, the saturable capacity for accepting exogenous probes is found to be 37% higher in DOPC relative to that for DSC membranes. The difference is comparable to the disparity in the average molecular areas of DOPC and DSC membranes. Finally, this analysis shows little difference in the spectral overlap integrals of the emission spectrum of a fluorescein derivative donor and the absorption spectrum of either monomeric or simulated spectrum of dimeric R18. This approach represents a first step toward a nanoscale probing of membrane heterogeneity in living cells by analyzing differential local FRET among sites of unique receptor expression in living cells.
We report the functionalization of cross-linked poly(divinylbenzene) (pDVB) microspheres using both thiol-ene chemistry and azide-alkyne click reactions. The RAFT technique was carried out to synthesize SH-functionalized poly(N-isopropylacrylimide) (pNIPAAm) and utilized to generate pNIPAAm surface-modified microspheres via thiol-ene modification. The accessible double bonds on the surface of the microspheres allow the direct coupling with thiol-end functionalized pNIPAAm. In a second approach, pDVB microspheres were grafted with poly(2-hydroxyethyl methacrylate) (pHEMA). For this purpose, the residual double bonds on the microspheres surface were used to attach azide groups via the thiol-ene approach of 1-azido-undecane-11-thiol. In a second step, alkyne endfunctionalized pHEMA was used to graft pHEMA to the azide-modified surface via click-chemistry (Huisgen 1,3-dipolar cycloaddition). The surface-sensitive characterization methods X-ray photoelectron spectroscopy, scanning-electron microscopy and FT-IR transmission spectroscopy were employed to characterize the successful surface modification of the microspheres. In addition, fluorescence microscopy confirms the presence of grafted pHEMA chains after labeling with Rhodamine B
Three new pregnanes, ptilosteroid A (1), ptilosteroid B (2), and ptilosteroid C (3), and two new pregnane glycosides, ptilosaponoside A (4) and ptilosaponoside B (5), were isolated from the marine sponge Ptilocaulis spiculifer collected in the Solomon Islands. The structures were determined by spectroscopic methods. Biological tests of these compounds showed that they are not cytotoxic against KB cells.
Six unreported aromatic compounds, 1-6, were isolated, along with the known compounds dehydrocurcuphenol and manoalide, from a sample of Plakortis sp., which was the main component of a Pacific sponge consortium. The new molecules were chemically characterized by spectroscopic methods. Compounds 1-4 contain a six-membered cyclic peroxide, whereas 5 and 6 display a terminal methyl ketone. The new metabolites were tested for antifungal and antibacterial properties. Compounds 1 and 4 were weakly active against S. aureus.