Central Ring Structure Research Articles

Luminescent Tetranuclear Copper(I) and Gold(I) Heterobimetallic Complexes: A Phosphine Acetylide Amidinate Orthogonal Ligand Framework for Selective Complexation.

The synthesis of phosphine acetylide amidinate stabilized copper(I) and gold(I) heterobimetallic complexes was achieved by reacting ligand [{Ph2PC≡CC(NDipp)2}Li(thf)3] (Dipp=2,6-N,N'-diisopropylphenyl) with CuCl and Au(tht))Cl, yielding the eight membered ring [{Ph2PC≡CC(NDipp)2}2Cu2] and the twelve membered ring [{Ph2PC≡CC(NDipp)2}2Au2]. {Ph2PC≡CC(NDipp)2}2Cu2] features a Cu2 unit, which is bridged by two amidinate ligands, served as a metalloligand to synthesize the heterobimetallic CuI/AuI complexes [{(AuX)Ph2PC≡CC(NDipp)2}2Cu2] (X=Cl, C6F5). In these reactions, the central ring structure is retained. In contrast, when the twelve membered ring [{Ph2PC≡CC(NDipp)2}2Au2] was reacted with CuX (X=Cl, Br, I and Mes), the reaction led to the rearrangement of the central ring structure to give [{(AuX)Ph2PC≡CC(NDipp)2}2Cu2] (X=Cl, Br, I and Mes), which feature the same the eight membered Cu2 ring as above. These compounds were also synthesized by a one-pot reaction. The luminescent heterobimetallic complexes were further investigated for their photophysical properties.

Unraveling the Impact of Flexibility and Solvent Effects on the UV-Vis Absorption Spectrum of Subphthalocyanine in Liquid Chloroform within the Born-Oppenheimer Molecular Dynamics Approach.

A study based on Born-Oppenheimer molecular dynamics (BOMD) of the subphthalocyanine (SubPc) with a chloride attached to the central boron atom was carried out. The BOMD simulation is used to access the dynamic evolution of the SubPc in liquid chloroform, and the electronic absorption spectrum is calculated using the Time-Dependent Density Functional Theory (TDDFT) considering explicit solvent models. We show that the conformational changes and solvent effects produce a red shift of the Q-band, where the largest contribution is due to the geometry changes of the symmetric structure of SubPc. A large splitting (0.2 eV) of the first electronic transition is also described, and it originates as a shoulder in the Q-band, which according to previous experimental studies is attributed to a vibronic origin. The red shift is obtained in agreement with experiment within less than 0.1 eV. The splitting is a consequence of the symmetry breaking in the SubPc central ring structure occurring during the molecular dynamics, with a significant contribution to the large red shift and the broadening of the spectrum.

Stereoselective Mannich reaction catalyzed by tetrahydroindolo[3,2-b]indole under solvent-free conditions

A series of indole-based organocatalysts (4b,9b-aryl-4b,5,9b,10-tetrahydroindolo[3,2-b]indole derivatives) (2a-2f) have been designed and synthesized for the three-component direct Mannich reaction of aromatic aldehydes and aromatic amines with ketones. Significantly, the organocatalyst 2a delivered excellent catalytic stereoselectivity (up to >99:1) with good yields (up to 88 %) for above reaction process under the solvent-free conditions at room temperature. X-ray diffraction analysis reveals that organocatalyst 2a is of eight-membered central ring structure with interesting strained quadricyclic ring connectivity. The characteristic rigid V-shape indole ring structure contained in 2a and the formed hydrogen-bonding interaction between 2a and intermediate prefer to the anti-stereoselective product.

Quad-Band 3D Rectenna Array for Ambient RF Energy Harvesting

This paper presents a quad-band, 3D mountable rectenna module for ambient energy harvesting. With the aim of powering up Internet of Things (IoT) nodes in practical ambient environments, a hybrid approach of combining power, both at RF and DC, is adopted using 98 MHz FM band, GSM900 (Global System for Mobile Communications), GSM1800, and Wi-Fi 2.4 GHz band. A dual polarized cross-dipole antenna featuring asymmetric slots as well as central ring structure enables multiband response and improved matching at the higher three frequency bands, whereas a loaded monopole wire antenna is used at the lower FM band. Four identical multiband antennas are placed in a 3D cubic arrangement that houses a 4-to-1 power combiner and matching circuits on the inside and the FM antenna on the top. In order to maintain stable rectenna output at varying input power levels and load resistances, a novel transmission line based matching network using closed form equations is proposed. Integrated in form of a 10 × 10 × 10 cm3 cube using standard FR4 substrate, the rectenna generates a peak output voltage of 2.38 V at −10 dBm input power. The RF to DC conversion efficiency is 70.28%, 41.7%, 33.37%, and 27.69% at 98 MHz, 0.9 GHz, 1.8 GHz, and 2.4 GHz, respectively, at −6 dBm. The rectenna also exhibits a measured conversion efficiency of 31.3% at −15 dBm for multitone inputs in ambient environment. The promising results in both indoor and outdoor settings are suitable to power low power IoT devices.

Zoning of REE Mineralization of the Udzha Region, Republic of Sakha (Yakutia)

On the basis of combined analysis of data on a geological survey on a scale of 1 : 200 000 (1959–1960) and exploration works (1980–1990), it was found that the zones of higher radioactivity and related rich La–Ce ores are localized along linear faults 10–15 km long parallel to the axis of the Udzha Anticline. The HREE mineralization of the Y–Yb group is concentrated in sandstones and gravelstones of the Vendian Tomtor Formation, which unconformably overlap the Udzha Anticline on its wings. This indicates that the volatile flow has a deep (transmagmatic) origin rather than separation from magma. A carbonatite body with sulfide veinlets and dissemination is described with respect to a zone of high contents of La–Ce ores. The complex character of the Tomtor ores is explained by the juxtaposition of mineralization phases of various ages and composition: Nb and Sc–Th mineralization paragenetically related to the central ring structure of the intrusion and to the external rischorrite zone, respectively.

Studies on neuraminidase inhibition

AbstractNeuraminidase (NA) inhibitors are a class of antiviral drugs developed to target the influenza virus— a highly contagious virus that can cause severe respiratory illness and death. Although several NA inhibitors have been developed in the last decade, it is still poorly understood how they interact in the active site of the enzyme and which chemical and structural features potentiate their inhibitory activity. Taking this into account, we analyze in this article the inhibitory activity of 236 known NA inhibitors using molecular docking simulations. The protocol performed in this work, based on AutoDock, demonstrated to be very efficient in differentiating NA inhibitors with ΔGbinding above −11.7 kcal·mol−1. The results have shown that the best inhibitors are those that closely resemble the structure of the natural substrate, but explore additional areas of the active site with which they interact strongly and, therefore, potentiate their inhibitory activity. The best NA inhibitors are characterized by a central saturated six‐member ring filling almost completely the space available in the active site pocket. In addition, they contain both a carboxylate and an acetamide group, bound to the central ring structure, which allow them to interact with five arginines, organized in a triad (Arg371, Arg118, Arg292) and a pair (Arg151, Arg152). These interactions are very strong and act as two anchors that fix the compounds in the active site. The inhibitory activity of the compounds is improved if they have hydrophobic groups pointing toward a hydrophobic region of the active site, where Ile222 is located, and when they have amine or guanidine groups pointing toward three glutamates (Glu277, Glu276, Glu227). The studies performed here lay the foundations for the rational design of new and more efficient drugs to fight the influenza virus.

Variations in the composition and origin of hydrocarbon gases from inclusions in minerals of the Khibiny and Lovozero plutons, Kola Peninsula, Russia

Relationships between methane and its homologues mainly contained in fluid microinclusions have been studied in 332 monomineralic fractions from the Khibiny and Lovozero alkaline plutons. Hydrocarbon gases (HCG) were extracted for subsequent chromatographic analysis using the bulk method of sample comminution. The molecular weight distribution (MWD) of gaseous alkanes in the same and associated minerals is different depending on geological setting of the samples. The molecular mass of HCG increases (i) with decrease in temperature and capture of fluid inclusions in the course of transformation of primary magmatic minerals and the formation of late minerals as products of intensified postmagmatic processes; (ii) in the direction from khibinite at the margin and foyaite in the core of the Khibiny pluton to the central ring structure; and (iii) from the bottom to top of the differentiated complex in the Lovozero pluton. The results obtained coupled with other geochemical data suggest multistage generation and transformation of hydrocarbons from the magmatic to the final low-temperature hydrothermal stage. The MWD of hydrocarbon components in gases occluded by minerals can serve as an indicator of conditions characteristic of rock and ore formation, as well as of the consecutive formation and transformation of associated minerals revealing ambiguous and controversial relationships.

The origin of Patom Crater, East Siberia, from geological and geochemical data

A multidisciplinary expedition of geologists‐ geochemists, geophysicists, and astronomers studied Patom Crater in Bodaibo District, north of Irkutsk oblast, in 2006. This paper presents new geological and geochemical data evidencing an endogenous origin of the crater. As was discovered, it represents a central ring structure with a cone of clastic material of limestone and other rocks. The structure appeared to have a zoned pattern created by consequent formation of early stage ring swell, late stage ring swell, ring trench, and central mound. Hence, it took quite some time to form Patom Crater, and it could not have been produced by a single event like meteorite collapse. The whole amount of analyzed stone samples within and around the crater gives no evidence of meteorite substance or any geochemical anomalies that could be related to it. Hypogene fluids and gases played important role in the formation of Patom Crater affecting the rocks of the cone. Along with oxidized fluids (H 2 O and CO 2 ), some reduced gases (CO, H 2 ) were found in the rocks of the crater. This points to a quite deep source of fluids. Patom Crater is not meteoritic, but was formed by endogenous processes, the most important being an outbreak of fluid substance from great depth, which led to the formation of a clastic cone.

Central ring structure identified in one of the world's best-preserved impact craters

Seismic refraction and reflection data were acquired in 2000 and 2003 to study the morphology and sedimentary fill of the remote El'gygytgyn crater (Chukotka, northeastern Siberia; diameter 18 km). These data allow a first insight into the deeper structure of this unique impact crater. Wide-angle data from sonobuoys reveal a five-layer model: a water layer, two lacustrine sedimentary units that fill a bowl-shaped apparent crater morphology consisting of an upper layer of fallback breccia with P-wave velocities of ∼3000 m/s, and a lower layer of brecciated bedrock (velocities >3600 m/s). The lowermost layer shows a distinct anticline structure that, by analogy with other terrestrial and lunar craters of similar size, can be interpreted as a central ring structure. The El'gygytgyn crater exhibits a well-expressed morphology that is typical of craters formed in crystalline target rocks.

Third-order optical nonlinearities of near-infrared dyes

Near-infrared dyes – di- and tri-indocarbocyanine dyes and nickel dithiolenes – were synthesized and their third-order optical nonlinearities in solutions were investigated by using the degenerate four-wave mixing technique. Large third-order nonlinear optical susceptibilities with γ values of up to 10 −29 esu were observed. The γ value of the indocarbocyanine dyes increases with increase of conjugation length of the polymethine chain. The central ring structure in the chromophore lowers the γ value of the indocarbocyanine dyes. With change of the substituents on the benzene ring an increase in γ value is observed for all the asymmetric nickel dithiolenes. The order of increase of nonlinear hyperpolarizability is as follows: H<Cl<CH 3<C 2H 5<CH(CH 3) 2.

Synthesis of two peptides of α-bungarotoxin and the participation of the amino acid residue Trp-28 of the neurotoxin in the antigenicity of the molecule

Using the method of solid-phase peptide synthesis, two peptides have been synthesized, one of which corresponds to the central ring structure of α-bungarotoxin (α-BTX), while the second has in position 28 a Gly residue in place of the Trp in the first peptide, and their interrelationship with antitoxin antibodies has been investigated. It has been shown that the amino acid residue Trp-28 of α-BTX, which is the contact residue in binding with the acetylcholine receptor, also participates directly in binding with the active centers of antibodies to α-BTX.

Two Monomeric Ruthenium Complexes Containing Bidentate Bis(diphenylphosphino) Ligands

The crystal structures of chloro­(η5-cyclopentadienyl)[methylenebis(diphenylphosphine-P)]ruthenium–chloroform (1/1), [RuCl(C5H5)(C25H22P2)].CHCl3, (A), and chloro(η5-cyclopentadienyl)[1,2-ethanediylbis(diphenylphosphine-P)] ruthenium–chloroform (1/1), [RuCl(C5H5)(C26H24P2)].CHCl3, (B), are reported. Both molecules contain a central ring structure in which a pair of P atoms, linked by a –CH–2–[in (A)] or a –C2H4– [in (B)] group, are bonded to a central Ru atom. The P—Ru—P bond angle undergoes expansion from 72.07 (2)° in (A) to 83.48 (2)° in (B). The bond distances around the Ru center are compared with values reported for similar compounds. Both structures include a chloroform solvent molecule in addition to the ruthenium complex. The chloroform molecule in (A) was found to be disordered.

Degradation and inactivation of human atrial natriuretic peptide by human pulmonary plasma membranes

Atrial natriuretic peptide (ANP) is extracted from plasma during its passage through the lungs. ANP is metabolized in rat lung membrane preparations by the enzyme neutral endopeptidase-24.11 (EC 3.4.24.11), but the hydrolysis of ANP in human lung has not been characterized. In the present study synthetic human atrial natriuretic peptide 1–28 (α-hANP) was separately incubated with human pulmonary plasma membranes from two non-smoking patients, and the major degradation products were separated from α-hANP by reverse-phase high pressure liquid chromatography. The degradation products were identified by sequence analysis and by mass-spectrometry, and biological activity was studied in vitro by exposing precontracted rabbit pulmonary arteries to α-hANP and the degradation products. The initial cleavage appeared, with membrane preparations from both patients, in the central ring structure between Arg 14 and Ile 15, followed by a cleavage of the bond Arg 3-Arg 4 at the N-terminal region of the peptide. The biological activity of this ring-opened product was about 1 500 of the activity of uncleaved α-hANP. Cleavage of the Arg 3-Arg 4 or Arg 14-Ile 15 bonds could not be inhibited by EDTA, iodoacetamide, benzamidine hydrochloride or pepstatin A. Neither did phosphoramidon (1 μM) or thiorphan (1 μM) inhibit the hydrolysis, indicating the presence in human lung of an ANP-degrading enzyme different from endopeptidase-24.11.

The effect of a bar on the kinematics of a central ring structure in NGC 4736

We analyze the kinematics of the gaseous ring in the central region of NGC 4736 considering an ejection mechanism for the formation of the ring in a non-axisymmetric potential. A barred spiral of strength 10 or 25 per cent of the axisymmetric background is consistent with van der Kruit (1974) observational data.

Degradation and inactivation of rat atrial natriuretic peptide 1–28 by neutral endopeptidase-24.11 in rat pulmonary membranes

Atrial natriuretic peptide (ANP), a 28-residue peptide with cardiovascular and renal effects, is rapidly cleared from the circulation. Beside renal clearance, an extra-renal metabolism by the enzyme neutral endopeptidase-24.11 (NEP-24.11) has been proposed, since specific NEP-24.11-inhibitors increase endogenous plasma-ANP. NEP-24.11 is present in rat lung but its significance for ANP hydrolysis within the lung is unclear. The aim of this study was to investigate a possible degradation of rat ANP in a membrane preparation from rat lung. Hydrolysis products of ANP were separated by HPLC and further characterized by a pulmonary artery bioassay, by radio-immunoassay with different antisera, by peptide sequencing and by masspectrometry. Rat pulmonary membranes degraded ANP to one main metabolite lacking biological activity and with poor cross-reactivity to an antiserum recognising the central ring-structure of the peptide. Formation of the hydrolysis product was prevented by the NEP-24.11-inhibitor phosphoramidon (1 μM). Peptide sequencing of the metabolite revealed a cleavage between Cys 7 and Phe 8, which was confirmed by mass-spectrometry. The metabolite had an HPLC elution time identical to that of the product formed by purified porcine NEP-24.11. These findings suggest that ANP is metabolized and inactivated by endopeptidase-24.11 in rat lungs, the first organ exposed to ANP released from the heart.

Ultrastructure of papain and pepsin digestion fragments of human IgM globulins.

The ultrastructure of papain and pepsin-digested products of human IgM globulins has been analyzed. Papain digestion was performed both in the presence and absence of cysteine. The Fcmicro fragment was found to represent the central ring structure in the intact IgM molecule, plus a minor part of the appendages extending from the ring. The Fcmicro ring structure was occasionally seen to be composed of dimers of short rods, probably identical with the endpieces of two micro-chains. Such dimeric structures, released from the intact Fcmicro rings, had a tendency to aggregate sidewise, producing complexes of varying size. The dimensions of the Fcmicro fragments were: outer diameter approximately 85 A, inner diameter about 40 A. The length of the protrusions varied from 20-30 A. The Fabmicro preparations contained long strands of sidewise aggregated, short rod-shaped fragments. No aggregates were seen in the F(ab'')(2)micro preparations. The two Fab''micro units in the dimeric F(ab'')(2)micro fragments were usually parallel to each other. The dimensions of the Fabmicro and F(ab'')(2)micro fragments were 50-80 A x 30 A and 75-80 A x 55 A, respectively. These findings provide morphological evidence that the C-terminal ends of the micro-chains (the Fcmicro fragment) make up the central ring structure in the IgM molecule. They further indicate that the F(ab'')(2)micro fragments constitute about (3/4) of the appendages extending from this ring structure.