Superfast motion of catalytic microjet engines at physiological temperature

There is a great interest in reducing the toxicity of the fuel used to self-propel artificial nanomachines. Therefore, a method to increase the efficiency of the conversion of chemicals into mechanical energy is desired. Here, we employed temperature control to increase the efficiency of microjet engines while simultaneously reducing the amount of peroxide fuel needed. At physiological temperatures, i.e. 37 °C, only 0.25% H(2)O(2) is needed to propel the microjets at 140 μm s(-1), which corresponds to three body lengths per second. In addition, at 5% H(2)O(2), the microjets acquire superfast speeds, reaching 10 mm s(-1). The dynamics of motion is altered when the speed is increased; i.e., the motion deviates from linear to curvilinear trajectories. The observations are modeled empirically.     

Generalised expressions for the association and dissociation rate constants of molecules with multiple binding sites

ABSTRACT

Many proteins exhibit multiple binding patches. A patch may harbour a key chemical modification site, but may also simply act as a trap for the binding to another site. Here we consider the scenario in which one molecule (enzyme) binds another molecule (substrate) which contains two sites. We present microscopic expressions for the rate at which the enzyme binds to a particular site on the substrate, both for the scenario in which the enzyme directly binds the site without first visiting the other site, and for the case in which it may visit the other site an arbitrary number of times before binding to the site of interest. We also present the expressions for the corresponding dissociation reactions. These expressions can be used to compute in a single rare-event simulation of the dissociation pathway not only both the intrinsic and effective dissociation rate constants but also both association rate constants.     

Nonenzymatic Rubylation and Ubiquitination of Proteins for Structural and Functional Studies

Uncovering the mechanisms that allow conjugates of ubiquitin (Ub) and/or Ub‐like (UBL) proteins such as Rub1 to serve as distinct molecular signals requires the ability to make them with native connectivity and defined length and linkage composition. A novel, effective, and affordable strategy for controlled chemical assembly of fully natural UBL–Ub, Ub–UBL, and UBL–UBL conjugates from recombinant monomers is presented. Rubylation of Ub and Rub1 and ubiquitination of Rub1 was achieved without E2/E3 enzymes. New residue‐specific information was obtained on the interdomain contacts in naturally‐occurring K48‐linked Rub1–Ub and Ub–Rub1, and K29‐linked Rub1–Ub heterodimers, and their recognition by a K48‐linkage‐specific Ub receptor. The disassembly of these heterodimers by major deubiquitinating enzymes was examined and it was discovered that some deubiquitinases also possess derubylase activity. This unexpected result suggests possible crosstalk between Ub and Rub1/Nedd8 signaling pathways.     

Microwave mediated synthesis of non-carboxylic analogues of ibuprofen with improved pharmacological activity

A series of 1,2,4-triazolo[3,4-b]-thiadiazoles were synthesized following microwave irradiation method and also by conventional method.Newly synthesized compounds were evaluated for their anti-inflammatory and analgesic activities.     

Ultrafast Raman loss spectroscopy (URLS): instrumentation and principle

In this paper, we report on the concept and the design principle of ultrafast Raman loss spectroscopy (URLS) as a structure‐elucidating tool. URLS is an analogue of stimulated Raman scattering (SRS) but more sensitive than SRS with better signal‐to‐noise ratio. It involves the interaction of two laser sources, namely, a picosecond (ps) Raman pump pulse and a white‐light (WL) continuum, with a sample, leading to the generation of loss signals on the higher energy (blue) side with respect to the wavelength of the Raman pump unlike the gain signal observed on the lower energy (red) side in SRS. These loss signals are at least 1.5 times more intense than the SRS signals. An experimental study providing an insight into the origin of this extra intensity in URLS as compared to SRS is reported. Furthermore, the very requirement of the experimental protocol for the signal detection to be on the higher energy side by design eliminates the interference from fluorescence, which appears on the red side. Unlike CARS, URLS signals are not precluded by the non‐resonant background and, being a self‐phase‐matched process, URLS is experimentally easier. Copyright © 2011 John Wiley & Sons, Ltd.     

Light-Driven Continual Oscillatory Rocking of a Polymer Film

Achieving oscillatory motion in polymers without requiring on/off switching of stimuli is a current challenge. Hereby, a free-standing liquid crystal polymer (LCP) is demonstrated to undergo a sustained oscillatory motion when triggered by light, moving back and forth, resembling the motion of a rocking-chair. Two polymer films having different azobenzene photo-switches have been studied, revealing photoswitch requirements as well as illumination conditions necessary to sustain oscillations. The motion presented here shows how feedback loops involving light-triggered actuation, self-shadowing and a shifting center of gravity can be utilized to achieve self-sustained motion in free-standing polymers.     

Metal Sulfide Nanoparticles: Precursor Chemistry

Fascination with and the need for evermore increasing efficiency, power, or strength have been the cornerstones for developing new materials and methods for their creation. Higher solar cell conversion efficiencies, increased battery storage power, and lightweight strong materials are some that have been at the forefront of attention for these efforts. Materials created for most applications start as simple chemical compounds. A study of how these chemicals have been used in the past can be used to create new materials and new methods of production. Herein, a class of materials that are valuable in a multitude of applications, metal sulfide nanoparticles, are examined, along with how they are being produced and how new methods can be established that will help to standardize and increase production capabilities. Precursor–solvent combinations that can be used to create metal sulfide nanoparticles in the gas phase are also explored.     

Ultrafast Raman loss spectroscopy

This paper deals with a new form of nonlinear Raman spectroscopy called ‘ultrafast Raman loss spectroscopy (URLS)’. URLS is analogous to stimulated Raman spectroscopy (SRS) but is much more sensitive than SRS. The signals are background (noise) free unlike in coherent anti‐Stokes Raman spectroscopy (CARS) and it provides natural fluorescence rejection, which is a major problem in Raman spectroscopy. In addition, being a self‐phase matching process, the URLS experiment is much easier than CARS, which requires specific phase matching of the laser pulses. URLS is expected to be alternative if not competitive to CARS microscopy, which has become a popular technique in applications to materials, biology and medicine. Copyright © 2009 John Wiley & Sons, Ltd.     

Non‐Invasive Monitoring of Osteogenic Differentiation on Microtissue Arrays under Physiological Conditions Using Scanning Electrochemical Microscopy

In this paper, we present a non‐invasive assay using scanning electrochemical microscopy (SECM) for detecting osteogenic differentiation at physiological conditions (pH 7.5) on arrays of C2C12 microtissues. Upon exposure to bone morphogenic protein 2 (BMP‐2), C2C12 microtissues differentiate and express alkaline phosphatase (ALP), which is indirectly detected through an enzymatic assay producing an electroactive species. The latter is detected using SECM by scanning at constant height over live microtissues at physiological pH (7.5) as well as more alkaline pH (8.5). As a control, expression of ALP is confirmed using a standard colorimetric assay. Detecting differentiation on live samples at physiological conditions represents a significant improvement for continuous monitoring of tissue differentiation or further use of the microtissues for, e.g., regenerative medicine.     

Electronic Transport and Thermopower in 2D and 3D Heterostructures—A Theory Perspective

The impact of interfaces and heterojuctions on the electronic and thermoelectric transport properties of materials is discussed herein. Recent progress in understanding electronic transport in heterostructures of 2D materials ranging from graphene to transition metal dichalcogenides, their homojunctions (grain boundaries), lateral heterojunctions (such as graphene/MoS₂ lateral interfaces), and vertical van der Waals heterostructures is reviewed. Work on thermopower in 2D heterojunctions, as well as their applications in creating devices such as resonant tunneling diodes (RTDs), is also discussed. Last, the focus turns to work in 3D heterostructures. While transport in 3D heterostructures has been researched for several decades, here recent progress in theory and simulation of quantum effects on transport via the Wigner and non‐equilibrium Green's functions approaches is reviewed. These simulation techniques have been successfully applied toward understanding the impact of heterojunctions on transport properties and thermopower, which finds applications in energy harvesting, and electron resonant tunneling, with applications in RTDs. In conclusion, tremendous progress has been made in both simulation and experiments toward the goal of understanding transport in heterostructures and this progress will soon be parlayed into improved energy converters and quantum nanoelectronic devices.