Direct observation of metal nanoparticles as heterogeneous nuclei for the condensation of supersaturated organic vapors: Nucleation of size-selected aluminum nanoparticles in acetonitrile and n-hexane vapors

This work reports the direct observation and separation of size-selected aluminum nanoparticlesacting as heterogeneous nuclei for the condensation of supersaturated vapors of both polar and nonpolar molecules. In the experiment, we study the condensation of supersaturated acetonitrile and n-hexane vapors on charged and neutral Al nanoparticles by activation of the metalnanoparticles to act as heterogeneous nuclei for the condensation of the organic vapor.Aluminum seed nanoparticles with diameters of 1 and 2 nm are capable of acting as heterogeneous nuclei for the condensation of supersaturated acetonitrile and hexane vapors. The comparison between the Kelvin and Fletcher diameters indicates that for theheterogeneous nucleation of both acetonitrile and hexane vapors, particles are activated at significantly smaller sizes than predicted by the Kelvin equation. The activation of the Alnanoparticles occurs at nearly 40% and 65% of the onset of homogeneous nucleation of acetonitrile and hexane supersaturated vapors, respectively. The lower activation of the chargedAl nanoparticles in acetonitrile vapor is due to the charge-dipole interaction which results in rapid condensation of the highly polar acetonitrile molecules on the charged Al nanoparticles.The charge-dipole interaction decreases with increasing the size of the Al nanoparticles and therefore at low supersaturations, most of the heterogeneous nucleation events are occurring on neutral nanoparticles. No sign effect has been observed for the condensation of the organic vapors on the positively and negatively charged Al nanoparticles. The present approach of generating metal nanoparticles by pulsed laser vaporization within a supersaturated organic vapor allows for efficient separation between nucleation and growth of the metal nanoparticlesand, consequently controls the average particle size, particle density, and particle size distribution within the liquid droplets of the condensing vapor. Strong correlation is found between the seed nanoparticle\u27s size and the degree of the supersaturation of the condensing vapor. This result and the agreement among the calculated Kelvin diameters and the size of the nucleating Al nanoparticles determined by transmission electron microscopy provide strong proof for the development of a new approach for the separation and characterization of heterogeneous nuclei formed in organic vapors. These processes can take place in the atmosphere by a combination of several organic species including polar compounds which could be very efficient in activating charged nanoparticles and cluster ions of atmospheric relevance

Vapor phase nucleation on neutral and charged nanoparticles: Condensation of supersaturated trifluoroethanol on Mg nanoparticles

A new technique is described to study the condensation of supersaturated vapors on nanoparticles under well-defined conditions of vapor supersaturation, temperature, and carrier gas pressure. The method is applied to the condensation of supersaturated trifluoroethanol (TFE) vapor on Mg nanoparticles. The nanoparticles can be activated to act as condensation nuclei at supersaturations significantly lower than those required for homogeneous nucleation. The number of activated nanoparticles increases with increasing the vapor supersaturation. The small difference observed in the number of droplets formed on positively and negatively charged nanoparticles is attributed to the difference in the mobilities of these nanoparticles. Therefore, no significant charge preference is observed for the condensation of TFE vapor on the Mg nanoparticles

Effects of Amiodarone and N-desethylamiodarone on Cardiac Voltage-Gated Sodium Channels

Amiodarone (AMD) is a potent antiarrhythmic drug with high efficacy for treating atrial fibrillation and tachycardia. The pharmacologic profile of AMD is complex. AMD possesses biophysical characteristics of all of class I, II, III, and IV agents. Despite its adverse side effects, AMD remains the most commonly prescribed antiarrhythmic drug. AMD was described to prolong the QT interval and can lead to torsades de pointes. Our goal was to study the effects of AMD on peak and late sodium currents (INa,P and INa,L) and determine whether these effects change as AMD is metabolized into N-Desethylamiodarone (DES). We hypothesized that AMD and DES block both INa,P and INa,L with similar profiles due to structural similarities. Given the inherent small amounts of INa,L in NaV1.5, we screened AMD and DES against the Long QT-3-causing mutation, ∆KPQ, to better detect any drug-mediated effect on INa,L. Our results show that AMD and DES do not affect WT or ∆KPQ activation; however, both drugs altered the apparent valence of steady-state fast-inactivation. In addition, AMD and DES preferentially block ∆KPQ peak conductance compared to WT. Both compounds significantly increase INa,L and window currents. We conclude that both compounds have pro-arrhythmic effects on NaV1.5, especially ∆KPQ; however, DES seems to have a greater pro-arrhythmic effect than AMD

Regulation of mRNA translation by a photoriboswitch.

Optogenetic tools have revolutionized the study of receptor-mediated processes, but such tools are lacking for RNA-controlled systems. In particular, light-activated regulatory RNAs are needed for spatiotemporal control of gene expression. To fill this gap, we used in vitro selection to isolate a novel riboswitch that selectively binds the trans isoform of a stiff-stilbene (amino-tSS)-a rapidly and reversibly photoisomerizing small molecule. Structural probing revealed that the RNA binds amino-tSS about 100-times stronger than the cis photoisoform (amino-cSS). In vitro and in vivo functional analysis showed that the riboswitch, termed Werewolf-1 (Were-1), inhibits translation of a downstream open reading frame when bound to amino-tSS. Photoisomerization of the ligand with a sub-millisecond pulse of light induced the protein expression. In contrast, amino-cSS supported protein expression, which was inhibited upon photoisomerization to amino-tSS. Reversible photoregulation of gene expression using a genetically encoded RNA will likely facilitate high-resolution spatiotemporal analysis of complex RNA processes

Metagenomic profiling of microbial metal interaction in Red Sea deep-anoxic brine pools

Extreme environmental conditions induce evolution of microbiomes and shape microbial abundance. Different geochemical studies reported high metal abundance in Red Sea deep-anoxic brine pools, especially in Atlantis II Deep, which has the highest metals content. Brine pools show wide diversity of biologically essential and non-essential metals. Several metals known for their toxicity to biological life were detected in these pools. Yet, previous microbiome analyses of the pools demonstrated vast microbiological diversity. In this study, we compare metal-resistant prokaryotic microbiomes in different metal-rich brine water samples from Atlantis II lower convective layer (ATII-LCL), Atlantis II upper convective layer (ATII-UCL), Discovery Deep (DD) and Kebrit Deep (KD). Moreover, we investigate genome evolution of microbial communities in response to such excessive metal abundance. Using 16S rRNA pyrotags and shot-gun 454-pyrosequencing, we perform a comparative analyses of (i)-taxonomic assignment of operational taxonomic units to major bacterial and archaeal groups and (ii)-metal resistant protein-coding genes, of the microbial communities and metagenomes. The ATII-LCL, ATII-UCL, DD and KD brine pools metagenomes protein-coding genes involved in microbial-metal interaction and resistances were assessed for abundance and diversity. We report specific microbial richness of these three brine pools. Functional analyses of the metagenomes revealed different metal resistance mechanisms and different modes of mutual interaction between dissolved metals/sediments and microbial communities. This was supported by the strong correlation between specific high metal/s concentration in selected brine water, where; metal resistance, enrichment of metals metabolism and transport were revealed. As expected, ATII-LCL showed the highest relative abundance of genes involved in microbial-metal interaction. Additionally, we report significant abundance of peroxidases-encoding genes, mainly in ATII-LCL, and we hypothesize that generation of hydrogen peroxide (H2O2) occurs through interaction of pyrite deposits. Moreover, we suggest that genus Paenibacillus, which is highly abundant in ATII-LCL has a role in increasing concentration of dissolved iron in brine water. DD and KD showed relatively lower enrichment of genes involved in microbial-metal interaction. However, geochemistry of these environments together with unique microbial abundance give an inference about mechanisms of microbial metal interaction and metabolism taking place there. Eventually, we successfully identified free living metal-resistant prokaryotic communities, showed how prokaryotes tolerate and induce changes to the surrounding environment, and highlighted how geochemical conditions affected microbial abundance and induced evolution of microbiomes in brine pools

Power Amplifiers and Antennas for Implantable Biomedical Transceivers

Recently, there has been a strong trend in medicine to use implanted electronic devices for diagnostic and/or therapeutic purposes. These devices usually involve a one- or twoway communication link, allowing communication with the implant. One revolutionary implanted system that was recently launched into the healthcare market is the wireless imaging capsule for monitoring the gastrointestinal tract. Among the application-specific design challenges of such a wireless system are the severe constraints on low power and on small physical size. Besides, the allowed power levels of signals due to in-body radiating devices are restricted to very low values due to human safety concerns. To meet the requirements of such a wireless system, highly efficient, small-size, low-power transmitting radio frequency (RF) blocks are needed. This thesis focuses on the design, implementation and measurements of the last two blocks in the transmitter, namely the antenna and the power amplifier (PA). Three PA circuits have been designed and measured, all of class AB topology. The first two PAs operate at 2.4 GHz, while the third is designed for 405-MHz operation. All designs are fully integrated and realized in a standard mixed-signal 0.18 ~m complementary metaloxide- semiconductor (CMOS) process. Measurement results show that at a supply voltage of 1.4 V, the circuits have a maximum drain efficiency of 32% and 40.7% for the 2.4-GHz and the 405-MHz designs, respectively, while providing an output power of 7.2 and 8 dBm to the load. These results greatly outperform similar designs in the literature, proving that class AB PAs, if properly designed, are well-suited for low-power biotelemetry application. A simple layout design approach was developed to minimize the parasitic effects of on-silicon interconnections that cause significant degradation in the performance of RF integrated circuits (RF ICs ). This approach was used to design the layouts of the three PA circuits presented in this work, and the approach was tested on a low-noise amplifier (LNA) operating at 5 GHz, since at such a high frequency the parasitics become more pronounced. Measurements on the LNA circuit show good agreement with simulations. Thus, next to allowing for optimized circuit performance, this approach can shorten the design time of RF ICs by providing very good predictions of performance characteristics. The last part of this thesis deals with the analysis and design of efficient in-body antennas. A study of the use of loop antennas in medical implants was conducted. Simulations and measurements have been used to characterize the radiation performance of loop antennas in terms of their radiation resistance, transmitting bandwidth and biocompatibility. At 405 MHz, the antenna has proven to be efficient in the dissipative biological tissues, to have a wide transmitting bandwidth, and a specific absorption rate (SAR) distribution that is well below the safety limits. To further verify its suitability for in-body operation, a miniature loop antenna was fabricated and measured at 405 MHz and 2.4 GHz. For measurement purposes, two body simulating chemical solutions were prepared in-house to provide the necessary radiation environment. Measurements show that small loop antennas are well matched in the medium and are thus good in-body radiators. ThesisMaster of Applied Science (MASc