No abstract

The mechanism of micelle formation of surfactants sodium dodecyl sulfate (SDS), n-hexyldecyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) in heavy water solutions was studied by 1H NMR (chemical shift and line shape) and NMR self-diffusion experiments. 1H NMR and self-diffusion experiments of these three surfactants show that their chemical shifts (delta) begin to change and resonance peaks begins to broaden with the increase in concentration significantly below their critical micelle concentrations (cmc's). At the same time, self-diffusion coefficients ( D) of the surfactant molecules decrease simultaneously as their concentrations increase. These indicate that when the concentrations are near and lower than their cmc's, there are oligomers (premicelles) formed in these three surfactant systems. Carefully examining the dependence of chemical shift and self-diffusion coefficient on concentration in the region just slightly above their cmc's, one finds that the pseudophase transition model is not applicable to the variation of physical properties (chemical shift and self-diffusion coefficient) with concentration of these systems. This indicates that premicelles still exist in this concentration region along with the formation of micelles. The curved dependence of chemical shift and self-diffusion coefficient on the increase in concentration suggests that the premicelles grow as the concentration increases until a definite value when the size of the premicelle reaches that of the micelle, i.e., the system is likely dominated by the monomers and micelles. Additionally, the approximate values of premicelle coming forth concentration (pmc) and cmc were obtained by again fitting chemical shifts to reciprocals of concentrations at a different perspective, and are in good accordant with experimental results and literature values and prove the former conclusion.

The Crab Nebula is a bright source of gamma-rays powered by the Crab Pulsar's rotational energy, through the formation and termination of a relativistic electron-positron wind. We report the detection of γ-rays from this source with energies from 5 × 10−4 to 1.1 petaelectronvolts (PeV), with a spectrum showing gradual steepening over three energy decades. The ultra-high-energy photons imply the presence of a PeV electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. We constrain the pevatron's size between 0.025 and 0.1 pc, and magnetic field ≈110 μG. The production rate of PeV electrons, 2.5 × 1036 erg s−1, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of PeV protons to the production of the highest energy γ-rays.

Recently, much attention has been focused on the development of second near‐infrared window (NIR‐II, 1000–1700 nm) fluorescence imaging because of its reduced scattering, minimal absorption, and negligible autofluorescence. NIR‐II bioimaging allows the visualization of deep anatomical features with an unprecedented degree of clarity. In addition to the construction of a variety of new NIR‐II fluorophores, using a fluorescence tail emission greater than 1000 nm for conventional NIR‐I dyes represents a promising strategy for developing an NIR‐II imaging technique. Herein, the authors report tailoring a supramolecular assembly of human serum albumin (HSA) protein complexed with a sulfonated NIR‐I organic dye (IR820) to produce a brilliant 21‐fold increase in fluorescence for NIR‐II imaging. In vivo NIR‐II imaging with IR820–HSA allows noninvasive and dynamic visualization and monitoring of physiological and pathological conditions of the vascular system, lymphatic drainage system, and tumor‐bearing mice, as well as image‐guided tumor resection with high spatial and temporal resolution. Furthermore, photoacoustic imaging (PAI) of IR820–HSA in mouse tumor models also demonstrate good tumor accumulation. Overall, an IR820–protein complex with high biocompatibility can be easily constructed using a conventional NIR‐I dye that provides a new theranostic tool with high clinical translation potential.