Mesoscopic organization reveals the constraints governing C. elegans nervous system

One of the biggest challenges in biology is to understand how activity at the cellular level of neurons, as a result of their mutual interactions, leads to the observed behavior of an organism responding to a variety of environmental stimuli. Investigating the intermediate or mesoscopic level of organization in the nervous system is a vital step towards understanding how the integration of micro-level dynamics results in macro-level functioning. In this paper, we have considered the somatic nervous system of the nematode Caenorhabditis elegans, for which the entire neuronal connectivity diagram is known. We focus on the organization of the system into modules, i.e., neuronal groups having relatively higher connection density compared to that of the overall network. We show that this mesoscopic feature cannot be explained exclusively in terms of considerations, such as optimizing for resource constraints (viz., total wiring cost) and communication efficiency (i.e., network path length). Comparison with other complex networks designed for efficient transport (of signals or resources) implies that neuronal networks form a distinct class. This suggests that the principal function of the network, viz., processing of sensory information resulting in appropriate motor response, may be playing a vital role in determining the connection topology. Using modular spectral analysis, we make explicit the intimate relation between function and structure in the nervous system. This is further brought out by identifying functionally critical neurons purely on the basis of patterns of intra- and inter-modular connections. Our study reveals how the design of the nervous system reflects several constraints, including its key functional role as a processor of information.Comment: Published version, Minor modifications, 16 pages, 9 figure

Hydrogen generating Ru/Pt bimetallic photocatalysts based on phenyl-phenanthroline peripheral ligands

Recent studies on hydrogen generating supramolecular bimetallic photocatalysts indicate a more important role of the peripheral ligands than expected, motivating us to design a Ru/Pt complex with 4,7‐diphenyl‐1,10‐phenanthroline peripheral ligands. Photoinduced intra‐ and inter‐ligand internal conversion processes have been investigated using transient absorption spectroscopy, spanning the femto‐ to nanosecond timescale. After photoexcitation and ultrafast intersystem crossing, triplet states localised on either the peripheral ligands or on the bridging ligand/catalytic unit are populated in a non‐equilibrated way. Time‐resolved photoluminescence demonstrates that the lifetime for the Ru/Pt dinuclear species (795±8 ns) is significantly less than that of the mononuclear analogue (1375±20 ns). The photocatalytic studies show modest hydrogen turnover numbers, which is possibly caused by the absence of an excited state equilibrium. Finally, we identify challenges that must be overcome to further develop this class of photocatalysts and propose directions for future research

Highly Sensitive Optical Sensor for Selective Detection of Fluoride Level in Drinking Water: Methodology to Fabrication of Prototype Device

Excess consumption of fluoride through drinking water and its detrimental effects on human health have been a serious global concern. Therefore, frequent monitoring as well as quantitative determination of fluoride ion (F-) concentration in aqueous media is of vital importance. Herein, we have developed a facile and highly sensitive spectroscopic technique for selective detection of F- in aqueous media using aluminium phthalocyanine chloride (AlPc-Cl) as a sensor. The absorbance as well as steady-state fluorescence intensity of AlPc-Cl has been found to decrease in presence of F- which has been used as a marker for the determination of fluoride ion concentration in water. The structural change in AlPc-Cl after addition of F- has been thoroughly studied by using 19F NMR (Nuclear Magnetic Resonance) spectroscopy. Our detailed steady-state as well as time-resolved fluorescence studies reveal that the quenching mechanism is static in nature due to ground state complexation in between F- and AlPc-Cl molecules. The response of the sensor is found to be linear over the F- concentration regime from 0 to 6 parts per million (ppm) with a detection limit of 0.05 ppm. Additionally, it shows an excellent selectivity as well as an insignificant change in sensitivity even in the presence of interfering iron and aluminium ions. Based on the detailed photophysical study, we have further developed a low cost and portable prototype device which shows an excellent sensitivity with the detection limit of 0.10 ppm. This prototype device has a high prospect for real-time monitoring of fluoride ion concentration especially in remote areas.</p

Re‐Dichalcogenides: Resolving Conflicts of Their Structure–Property Relationship

Abstract ReX2 (X = S, Se) remains a copious source of controversies and unanswered questions due to its widely contrasting experimental and theoretical results. With the help of comparative first‐principles electronic structure and phonon calculations, the correct structures for both systems are established, which minimize the apparent divergence of different experimental results. It is demonstrated that ReS2 and ReSe2 are neither iso‐structural nor iso‐electronic. The contributions of the in‐plane and out‐of‐plane orbitals at the band‐edges of the bulk and monolayers are coordinated with their anisotropic optical response. Under moderately high pressure, both of these systems are observed to undergo a semiconductor to metal transition. With the help of a combined full‐potential density functional theory and multiplet ligand field theory (DFT+MLFT) approach, the X‐ray spectral properties of these two systems are analyzed in the light of their intricate differences of optimized structures and electronic correlations

Bioactive Flavaglines and Other Constituents Isolated from <i>Aglaia perviridis</i>

Eight new compounds, including two cyclopenta­[<i>b</i>]­benzopyran derivatives (<b>1</b>, <b>2</b>), two cyclopenta­[<i>b</i>]­benzofuran derivatives (<b>3</b>, <b>4</b>), three cycloartane triterpenoids (<b>5</b>–<b>7</b>), and an apocarotenoid (<b>8</b>), together with 16 known compounds, were isolated from the chloroform-soluble partitions of separate methanol extracts of a combination of the fruits, leaves, and twigs and of the roots of <i>Aglaia perviridis</i> collected in Vietnam. Isolation work was monitored using human colon cancer cells (HT-29) and facilitated with an LC/MS dereplication procedure. The structures of the new compounds (<b>1</b>–<b>8</b>) were determined on the basis of spectroscopic data interpretation. The Mosher ester method was employed to determine the absolute configurations of <b>5</b>–<b>7</b>, and the absolute configuration of the 9,10-diol unit of compound <b>8</b> was established by a dimolybdenum tetraacetate [Mo₂(AcO)₄] induced circular dichroism procedure. Seven known rocaglate derivatives (<b>9</b>–<b>15</b>) exhibited significant cytotoxicity against the HT-29 cell line, with rocaglaol (<b>9</b>) being the most potent (ED₅₀ 0.0007 μM). The new compounds <b>2</b>–<b>4</b> were also active against this cell line, with ED₅₀ values ranging from 0.46 to 4.7 μM. The cytotoxic compounds were evaluated against a normal colon cell line, CCD-112CoN. In addition, the new compound perviridicin B (<b>2</b>), three known rocaglate derivatives (<b>9</b>,<b> 11</b>, <b>12</b>), and a known sesquiterpene, 2-oxaisodauc-5-en-12-al (<b>17</b>), showed significant NF-κB (p65) inhibitory activity in an ELISA assay