Dynamic solvation in phosphonium ionic liquids: comparison of bulk and micellar systems and considerations for the construction of the solvation correlation function, C(t)

Dynamic solvation of the dye coumarin 153 is studied in a phosphonium ionic liquid: hexadecyltributylphosphonium bromide, [(C4)3C16P+][Br-]. It forms micelles in water, and the bulk also exists as a liquid under our experimental conditions. This system permits a comparison with an imidazolium ionic liquid studied earlier, which also formed micelles in water (J. Phys. Chem. A 2006, 110, 10725-10730). We conclude that our analysis of the comparable situation in a phosphonium liquid is not as definitive as we had proposed earlier, i.e., that the majority of the early-time solvation arises from the organic cation. Part of the difficulty in performing this analysis is most likely due to the amount of water that is associated with the micelle. In the course of this work, we have focused on the calculation of the solvation correlation function, C(t), and investigated how it depends upon the methods with which the "zero-time" spectrum is constructed.     

Maristentorin, a novel pigment from the positively phototactic marine ciliate Maristentor dinoferus, is structurally related to hypericin and stentorin

The photoreceptor pigment of the heterotrich ciliate, Maristentor dinoferus, has been characterized. It is structurally similar to those of Stentor coeruleus and Blepharisma japonicum but differs significantly in that it bears no aromatic hydrogens. The structure of the pigment, maristentorin, is based upon the hypericin skeleton, and its spectra are nearly identical to those of hypericin but shifted toward the red. Within experimental error, its fluorescence lifetime is identical to that of hypericin, approximately 5.5 ns in dimethylsulfoxide. It is remarkable that while the pigments are structurally similar in S. coeruleus and M. dinoferus, in the former there is an abrupt photophobic response, whereas in the latter there is a slow response toward light. The roles of the hypericin-like pigments in the heterotrich ciliates are discussed as potentially analogous in Maristentor.     

Characterization of the interactions of fluorescent probes with proteins: coumarin 153 and 1,8-ANS in complex with holo- and apomyoglobin

In order to provide a thorough characterization of a system with which to study the dielectric response of a protein, a well-defined system complex of a fluorescent probe and protein is required. We have argued that such a system is provided by coumarin 153 and apomyoglobin (Photochem. Photobiol. 79, 440-446 [2004]). In order to demonstrate further that coumarin 153 exhibits negligible nonspecific binding to the surface of apomyoglobin, we study its interactions with both the apo and holo proteins. We further make a similar comparison with 8-anilino-l-naphthalenesulfonic acid, for which an NMR structure with apomyoglobin has been obtained. Our results confirm the appropriateness of the system of coumarin 153 and apomyoglobin for the investigation of solvation by the protein matrix.     

Synthesis of pyrimidines from ketones using microwave irradiation

A simple, high yielding synthesis of pyrimidines from ketones in the presence of HMDS and formamide is described. Under microwave irradiation, heteroaromatic, aryl, aliphatic, and cyclic ketones cyclized to give pyrimidines in good yields.     

Pushback: A hidden Markov model based scheme for energy efficient data transmission in sensor networks

In sensor networks, application layer QoS requirements are critical to meet while conserving energy. One of the leading factors for energy wastage is failed transmission attempts due to channel dynamics and interference. Existing techniques are unaware of the channel dynamics and lead to suboptimal channel access patterns. We propose a MAC layer solution called pushback, that appropriately delays packet transmissions to overcome periods of poor channel quality and high interference, while ensuring that the throughput requirement of the node is met. It uses a hidden Markov model (HMM) based channel model that is maintained without any additional signaling overhead. The pushback algorithm is shown to improve the packet success rate by up to 71% and reduce the number of transmissions needed by up to 38% while ensuring the same throughput.     

Detection of Nontrivial Topology Driven by Charge Density Wave in a Semi-Dirac Metal

The presence of electron correlations in a system with topological order can lead to exotic ground states. Considering single crystals of LaAgSb₂ which has a square net crystal structure, one finds multiple charge density wave transitions (CDW) as the temperature is lowered. Large planar Hall (PHE) signals are found in the CDW phase, which are still finite in the high-temperature phase though they change sign. Optimizing the structure within first-principles calculations, one finds an unusual chiral metallic phase. This is because as the temperature is lowered, the separation between the Ag/Sb atoms on different layers decreases, leading to stronger repulsions between electrons associated with atoms on different layers. This leads to successive layers sliding with respect to each other, thereby stabilizing a chiral structure in which inversion symmetry is also broken. The large Berry curvature associated with the low-temperature structure explains the low-temperature PHE. At high temperature, the PHE arises from the changes induced in the anisotropic Dirac cone in presence of a magnetic field. This work represents a route toward detecting and understanding the mechanism in a correlation-driven topological transition through electron transport measurements, complemented by ab-initio electronic structure calculations.