Naupliolide, a sesquiterpene lactone with a novel tetracyclic skeleton from Nauplius graveolens subsp. odorus

The aerial parts of Nauplius graveolens subsp. odorus (Schousb) Wikl. afforded a novel sesquiterpene lactone (1) named naupliolide together with the known 6,7,9,10-tetradehydroasteriscanolide 2 and asteriscunolides A-D 3a-d. The structure of compound 1 corresponds to a novel skeleton of 14,15-dimethyl-7,13-dioxotricyclic[6.4.0.0^9,11]dodeca-12,13-olide, and was established on the basis of spectroscopic methods including 2D-NMR. The coexistence of naupliolide 1 together with the structurally related sesquiterpene lactones asterisculolides A-D (3a-d) and 6,7,9,10-tetradehydroasteriscanolide 2, seems to indicate their biosynthetic relationship.     

Time-limited polling systems with batch arrivals and?phase-type service times

In this paper, we develop a general framework to analyze polling systems with either the autonomous-server or the time-limited service discipline. According to the autonomous-server discipline, the server continues servicing a queue for a certain period of time. According to the time-limited service discipline, the server continues servicing a queue for a certain period of time or until the queue becomes empty, whichever occurs first. We consider Poisson batch arrivals and phase-type service times. It is known that these disciplines do not satisfy the well-known branching property in polling systems. Therefore, hardly any exact results exist in the literature. Our strategy is to apply an iterative scheme that is based on relating in closed-form the joint queue-lengths at the beginning and the end of a server visit to a queue. These kernel relations are derived using the theory of absorbing Markov chains.     

Role of protein structure and the role of individual fingers in zinc finger protein–DNA recognition: a molecular dynamics simulation study and free energy calculations

Molecular dynamics and MM_GBSA energy calculations on various zinc finger proteins containing three and four fingers bound to their target DNA gave insights into the role of each finger in the DNA binding process as part of the protein structure. The wild type Zif 268 (PDB code: 1AAY) gave a ΔG value of ??76.1 (14) kcal/mol. Zinc fingers ZF1, ZF2 and ZF3 were mutated in one experiment and in another experiment one finger was cut and the rest of the protein was studied for binding. The ΔΔG values for the Zinc Finger protein with both ZF1 and ZF2 mutated was +?80 kcal/mol, while mutating only ZF1 the ΔΔG value was +?52 kcal/mol (relative to the wild type). Cutting ZF3 and studying the protein consisting only of ZF1 linked to ZF2 gave a ΔΔG value of +?68 kcal/mol. Upon cutting ZF1, the resulting ZF2 linked to ZF3 protein gave a ΔΔG value of +?41 kcal/mol. The above results shed light on the importance of each finger in the binding process, especially the role of ZF1 as the anchoring finger followed in importance by ZF2 and ZF3. The energy difference between the binding of the wild type protein Zif268 (1AAY) and that for individual finger binding to DNA according to the formula: ΔΔG_{linkers, otherstructuralfactors}?=?ΔG_zif268???(ΔG_F1+F2+F3) gave a value?=???44.5 kcal/mol. This stabilization can be attributed to the contribution of linkers and other structural factors in the intact protein in the DNA binding process. DNA binding energies of variant proteins of the wild type Zif268 which differ in their ZF1 amino acid sequence gave evidence of a good relationship between binding energy and recognition and specificity, this finding confirms the reported vital role of ZF1 in the ZF protein scanning and anchoring to the target DNA sequence. The role of hydrogen bonds in both specific and nonspecific amino acid-DNA contacts is discussed in relation to mutations. The binding energies of variant Zinc Finger proteins confirmed the role of ZF1 in the recognition, specificity and anchoring of the zinc finger protein to DNA.     

A dynamic liquid-liquid interfacial pressure detector for the rapid analysis of surfactants in a flowing organic liquid

Design and development of a dynamic interfacial pressure detector (DIPD) is reported. The DIPD measures the differential pressure as a function of time across the liquid-liquid interface of organic liquid drops (i.e., n-hexane) that repeatedly grow in water at the end of a capillary tip. Using a calibration technique based on the Young-Laplace equation, the differential pressure signal is converted, in real-time, to a relative interfacial pressure. This allows the DIPD to monitor the interfacial tension of surface active species at liquid-liquid interfaces in flow-based analytical techniques, such as flow injection analysis (FIA), sequential injection analysis (SIA) and high performance liquid chromatography (HPLC). The DIPD is similar in principle to the dynamic surface tension detector (DSTD), which monitors the surface tension at the air-liquid interface. In this report, the interfacial pressure at the hexane-water interface was monitored as analytes in the hexane phase diffused to and arranged at the hexane-water interface. The DIPD was combined with FIA to analytically measure the interfacial properties of cholesterol and Brij^®30 at the hexane-water interface. Results show that both cholesterol and Brij^®30 exhibit a dynamic interfacial pressure signal during hexane drop growth. A calibration curve demonstrates that the relative interfacial pressure of cholesterol in hexane increases as the cholesterol concentration increases from 100 to 10,000 μg ml⁻¹. An example of the utility of the DIPD as a selective detector for a chromatographic separation of interface-active species is also presented in the analysis of cholesterol in egg yolk by normal-phase HPLC-DIPD.     

Correction to: Densitometric high‑performance thin‑layer chromatography methods for the quantification of oleuropein in Olea europaea leaves and pharmaceutical preparation utilizing normal‑ and reversed‑phase silica gel plates

JPC – Journal of Planar Chromatography – Modern TLC - A correction to this paper has been published: https://doi.org/10.1007/s00764-021-00100-0     

Mathematical analysis of radionuclides displacement in porous media with nonlinear adsorption

This paper is devoted to the mathematical analysis of the miscible displacement of a set of radionuclides in a flow occurring in a heterogeneous porous medium. The flow is governed by Darcy's law, and the motion of the chemical species is given by a nonclassical advection-diffusion-reaction equations system. The novelty of the model lies in the adsorption phenomenon that leads to a time derivative of a nonlinear term in these equations. A semi-discretization method is used to establish the existence of weak solutions to this system. Uniform L^∞-estimates on the solutions are specified.     

Magnetic ordering in Mg−Zn ferrites

The magnetic ordering of a series of magnesium-zinc ferrite, Zn_0.3Mg _x Fe_2.7?x O_4±δ (0.5≤x≤1.1; 0≤δ≤0.2) has been investigated using Mössbauer measurements in the temperature range 295–620 K. The samples were found to be magnetic at room temperature with a hyperfine field at each site which increases with iron content. The Curie temperature was also observed to increase in a similar manner. The slope of this increase forB _hf andT _c is steeper forx≤0.6 thanx≥0.7. It has also been observed that Mg²⁺ substitution by Zn²⁺ in MgFe₂O₄ affects the magnetic ordering and the internal hyperfine field. The Curie temperature decreases by ～200 K andB _hf by ～20%.     

Ultrasonic diffraction grating spectroscopy and characterization of fluids and slurries

The ultrasonic diffraction grating is formed by machining triangular grooves, 300 microns apart, on a stainless steel surface. The grating surface is in contact with the liquid or slurry. The ultrasonic beam, traveling in the solid, strikes the back of the grating and produces a transmitted m=1 beam in the liquid. The angle of this beam in the liquid increases with decreasing frequency and the critical frequency FCR occurs when the angle is 90 degrees. At frequencies below FCR, this m=1 wave does not exist and its energy is shared with other types of waves. The signal of the reflected m=0 wave is observed and an increase is observed at FCR. This information yields the velocity of sound in the liquid and particle size.     

Macrocycles. XXVIII. Cyclic poly(benzonitrile ether)s derived from bisphenol A

Bisphenol A was polycondensed with 2,6‐dichlorobenzonitrile, 2,6‐difluorobenzonitrile, 2,4‐difluorobenzonitrile, and 3,5‐difluorobenzonitrile in sulfolane. With 2,6‐and 2,4‐difluorobenzonitrile, quantitative conversions were achieved, and matrix‐assisted laser desorption/time‐of‐flight mass spectra revealed a nearly quantitative formation of cyclic oligoethers and polyethers. Furthermore, O,O′‐bistrimethylsilyl bisphenol A was polycondensed with the aforementioned dihalobenzonitriles in dry N‐methylpyrrolidone (promoted by potassium carbonate). Both the temperature and time were optimized. Only with 2,6‐difluorobenzonitrile were nearly quantitative conversions achieved, and this resulted in high molecular weights and high cycle contents. Size exclusion chromatography elution curves exhibited a tendency toward a bimodal character when larger fractions of cycles were present. Calibration with polystyrene standards indicated number‐average molecular weights of up to 10⁵ Da and weight‐average molecular weights of up to 2.3 × 10⁵ Da. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3838–3846, 2003     

Cosynthesis, coexistence, and self-organization of alpha- and beta-cobalt hydroxide based on diffusion and reaction in organic gels

We report the cosynthesis of highly stable laminated single crystal alpha- and beta-Co(OH) 2 using the reaction and diffusion of a hydroxide solution into a gel containing Co(II). The obtained alpha-Co(OH) 2, which is known to be thermodynamically unstable and transforms in a short period of time to the beta form, has been stabilized in the gel medium for weeks. The system also exhibits Liesegang banding where complicated spatial dynamics during the formation of the two polymorphs are shown to take place.