Zinc Cations Uniquely Stabilize Cell Membrane for Cell Cryopreservation.

We report, for the first time, merely using a small amount of (0.039% w/w) Zn(II) instead of very high concentration (25%-50% w/w) of conventional cryoprotective agents (CPAs), i.e., glycerol, during the cryopreservation of red blood cells (RBCs) can lead to a comparable post-thaw recovery rate of ∼95% while avoiding the tedious gradient washout process for the removal of CPA afterward. The result is remarkable, since Zn(II) does not have the ice-controlling ability reported to be critical for CPA. It benefits from its moderate interaction with lipid molecules, facilitating the formation of small and dynamic lipid clusters. Consequently, the membrane fluidity is maintained, and the cells are resilient to osmotic and mechanical stresses during cryopreservation. This study first reports the ion-specific effect on stabilizing the cell membrane; meanwhile, reversibly tuning the structure of biological samples against injuries during the cooling and rewarming provides a new strategy for cryopreservation.

Role of an Ice Surface in the Photoreaction of Coumarins.

Ice affects many chemical reactions in nature, which greatly influences the atmosphere, climate, and life. However, the exact mechanism of ice in these chemical reactions remains elusive. For example, it is still an open question as to whether ice can act as a catalyst to greatly enhance the reactivity and selectivity, which is essential for the production of some natural compounds in our planet. Here, we discover that ice can lead to high efficiency and stereoselectivity of the [2 + 2] photodimerization of coumarin and its derivatives. The conversion of the [2 + 2] photodimerization of coumarins enhanced by ice is dozens of times higher than that in the unfrozen saturated solution, and the reaction displays a high syn-head-head stereoselectivity (>95%) in comparison with those in the absence of the ice. Note that almost no reaction occurs in the crystal powder and melt of the coumarins, indicating that the role of ice in the photodimerization reaction is not simply due to the usual mechanisms found in the freezing concentration. We further reveal that the reaction rate is found to be proportional to the total area of the ice surface and follows Michaelis-Menten-like kinetics, indicating that the ice surface catalyzes the reaction. Molecular dynamics simulations demonstrate that ice surfaces can induce reactants to form a two-dimensional liquid-crystal-ordered layer with a suitable intermolecular distance and unique side-by-side packing, facilitating stereoselective photodimerization for syn-head-head dimers. These findings give evidence that ice-surface-induced molecular assembly may play an important role in atmospheric heterogeneous photoreaction processes.

Hydrogen polarity of interfacial water regulates heterogeneous ice nucleation.

Using all-atomic molecular dynamics (MD) simulations, we show that the structure of interfacial water (IW) induced by substrates characterizes the ability of a substrate to nucleate ice. We probe the shape and structure of ice nuclei and the corresponding supercooling temperatures to measure the ability of IW with various hydrogen polarities for ice nucleation, and find that the hydrogen polarization of IW even with the ice-like oxygen lattice increases the contact angle of the ice nucleus on IW, thus lifting the free energy barrier of heterogeneous ice nucleation. The results show that not only the oxygen lattice order but the hydrogen disorder of IW on substrates are required to effectively facilitate the freezing of top water.

Simultaneous measurement of refractive index, strain, and temperature based on a Mach-Zehnder interferometer with hybrid structure optical fiber.

An optical fiber sensor based on a Mach-Zehnder interferometer with hybrid structure optical fiber for simultaneous measurement of refractive index (RI), strain, and temperature is proposed and demonstrated. The proposed structure is a hybrid structure based on a non-core fiber combined with few-mode fiber. The possibility of simultaneously measuring RI, strain, and temperature relies on the different sensitivity responses of three resonance peaks in the transmission spectrum. Thus, simultaneous measurement of RI, strain, and temperature is realized by calculating the wavelength shift of the three resonance peaks. The experimental results show that the sensitivities of RI are 22.9 pm/RIU, 24.6 pm/RIU, and 97 pm/RIU when RI changes from 1.3707 to 1.39809, respectively. The sensitivities of strain are $ - {3.5}\,\, \text{pm}/ \unicode{x00B5}\unicode{x03B5}$-3.5pm/µÎµ, $ - {1.9}\,\, \text{pm}/ \unicode{x00B5} \unicode{x03B5}$-1.9pm/µÎµ, and $ - {4.1}\,\, \text{pm}/ \unicode{x00B5} \unicode{x03B5}$-4.1pm/µÎµ in the range from 0 to 1400 pm/µ$\unicode{x03B5}$ε. The sensitivities of temperature ranging from 35°C to 55°C are 162 pm/°C, 194 pm/°C, and 162 pm/°C, respectively. The proposed sensor, with advantages of simple configuration, compact structure, and high sensitivity, exhibits great potential in fields of multi-parameter measurement.

Matching optimization for SFS-structured interferometers with step-index fibers.

Axial-aligned SFS-structured interferometers with step-index fibers hold advantages of easy fabrication, high stability, and extremely low cost, while low extinction ratio of the interferometer remains challenging. Here, we investigate the influence of core radius and refractive index of the fibers adopted in the interferometer on its extinction ratio and coupling loss, aiming to achieve the extinction ratio above 15dB - this criterion is applicable for practical use. The improvement of extinction ratio values presented in experiment was from 2dB to 7dB, which match perfectly with theoretical values, therefore demonstrates the effectiveness of the theoretical conclusion.

A Jump-from-Cavity Pyrophosphate Ion Release Assisted by a Key Lysine Residue in T7 RNA Polymerase Transcription Elongation.

Pyrophosphate ion (PPi) release during transcription elongation is a signature step in each nucleotide addition cycle. The kinetics and energetics of the process as well as how it proceeds with substantial conformational changes of the polymerase complex determine the mechano-chemical coupling mechanism of the transcription elongation. Here we investigated detailed dynamics of the PPi release process in a single-subunit RNA polymerase (RNAP) from bacteriophage T7, implementing all-atom molecular dynamics (MD) simulations. We obtained a jump-from-cavity kinetic model of the PPi release utilizing extensive nanosecond MD simulations. We found that the PPi release in T7 RNAP is initiated by the PPi dissociation from two catalytic aspartic acids, followed by a comparatively slow jump-from-cavity activation process. Combining with a number of microsecond long MD simulations, we also found that the activation process is hindered by charged residue associations as well as by local steric and hydrogen bond interactions. On the other hand, the activation is greatly assisted by a highly flexible lysine residue Lys472 that swings its side chain to pull PPi out. The mechanism can apply in general to single subunit RNA and DNA polymerases with similar molecular structures and conserved key residues. Remarkably, the flexible lysine or arginine residue appears to be a universal module that assists the PPi release even in multi-subunit RNAPs with charge facilitated hopping mechanisms. We also noticed that the PPi release is not tightly coupled to opening motions of an O-helix on the fingers domain of T7 RNAP according to the microsecond MD simulations. Our study thus supports the Brownian ratchet scenario of the mechano-chemical coupling in the transcription elongation of the single-subunit polymerase.

Detailed study of bending effects in large mode area segmented cladding fibers.

This paper studies the bending effects on segmented cladding fibers (SCFs) in detail. Rod-type SCFs have offered large effective mode areas (EMAs) very successfully. The low-index segments in the design also enable the optical fibers to be bend-resistant. In this paper, the bending performance of the SCFs has been investigated by using the finite element method. The results indicate that SCFs can provide low-loss effective single-mode operation in a wide bandwidth under a bent configuration, due to the leakage losses of the higher-order modes (HOMs). A large ratio between the HOMs and the fundamental mode losses can be ensured, over a wide range of duty cycle, refractive index difference, and bending radius. Therefore, the required fabrication accuracy decreases. The mode loss ratio and EMA are independent of the bending orientation. Operating at 1550 nm and 10 cm bend radius, large EMA (754 µm2) is achievable with a large loss ratio (>30). The trade-offs between loss, EMA, and bending are studied. The structure has potential for compact high power fiber lasers, amplifiers, and beam delivery applications.

Ultrasensitive temperature fiber sensor based on Fabry-Pérot interferometer assisted with iron V-groove.

A fiber extrinsic Fabry-Pérot interferometer (EFPI) assisted with iron V-groove for temperature measurement is proposed and investigated by means of both numerical simulation and experiment for the first time to our best knowledge. The main temperature sensing component is acted by the iron V-groove whose coefficient of linear thermal expansion (CLTE) is much higher than that of the silica glass. Two fibers are stuck to the V-groove with two glued points, respectively. Maximum sensitivity of 260.7 nm/°C, which is the highest value for a fiber interferometric sensor up to now, has been achieved experimentally. It is worth noting that the temperature sensitivity of this sensor can be improved limitlessly via implementing a smaller gap size of the EFPI, longer distance between the two glued points or material with higher CLTE of the V-groove, theoretically.

[Investigation on wild resources of Dendrobium officinale distribution and ecological envirment in Anhui].

The wild resources of Dendrobium officinale in Anhui province were studied by textural research, data collection, interview survey and regional survey, in order to investigate the resources distribution and ecological characters and provide the reference for Anhui Dendrobium industry. In this paper, a part of producing areas of wild D. officinale in Anhui province was selected to analyze the ecological characters. As a result, we find that the wild resources of D. officinale in Anhui distributed only sporadic and the conditions of growth environment were harsh. Our findings may provide some suggestions on wild resources protection and artificial cultivation in suitable environments because the wild resources of D. officinale in Anhui are decreasing rapidly and facing an endangered situation.

Ion-Specific Effects on the Growth of Single Ice Crystals.

Understanding the effects of soluble impurities or suspended particles on ice growth is of significant importance from Earth science to materials engineering. Ions are common impurities with ice in a wide range of fields, but their effects on ice growth remain largely elusive. Here, we studied the ion-specific effects on single ice crystal growth in various electrolyte and polyelectrolyte solutions and found F- and NH4+ show remarkable abilities of inducing single ice crystals to form hexagonal shapes and reducing the growth rates of ice crystals. Molecular dynamics simulations reveal the accumulation of F- around the ice/solution interface that plays a key role in the shapes and growth rates of single ice crystals. The understanding of ion-specific effects on ice growth opens up more possibilities for improving related fields, e.g., freeze desalination and cryopreservation.

Identifying metastable states of biomolecules by trajectory mapping and density peak clustering.

Efficiently and accurately analyzing high-dimensional time series, such as the molecular dynamics (MD) trajectory of biomolecules, is a long-standing and intriguing task. Two different but related techniques, i.e., dimension reduction methods and clustering algorithms, have been developed and applied widely in this field. Here we show that the combination of these techniques enables further improvement of the analyses, especially with very complicated data. Specifically, we present an approach that combines the trajectory mapping (TM) method, which constructs slow collective variables of a time series, with density peak clustering (DPC) [A. Rodriguez and A. Laio, Science 344, 1492 (2014)SCIEAS0036-807510.1126/science.1242072], which identifies similar data points to form clusters in a static data set. We illustrate the application of the TMDPC approach with hundreds of microseconds of all-atomic MD trajectories of two proteins, the villin headpiece and protein G. The results show that TMDPC is a powerful tool for achieving the metastable states and slow dynamics of these high-dimensional time series due to the efficient consideration of the time successiveness and the geometric distances between data points.

Imaging Metastable States and Transitions in Proteins by Trajectory Map.

It has been a long-standing and intriguing issue to develop robust methods to identify metastable states and interstate transitions from simulations or experimental data to understand the functional conformational changes of proteins. It is usually hard to define the complicated boundaries of the states in the conformational space using most of the existing methods, and they often lead to parameter-sensitive results. Here, we present a new approach, visualized Trajectory Map (vTM), to identify the metastable states and the rare interstate transitions, by considering both the conformational similarity and the temporal successiveness of conformations. The vTM is able to give a nonambiguous description of slow dynamics. The case study of a ß-hairpin peptide shows that the vTM can reveal the states and transitions from all-atom MD trajectory data even when a single observable (i.e, one-dimensional reaction coordinate) is used. We also use the vTM to refine the folding/unfolding mechanism of HP35 in explicit water by analyzing a 125 µs all-atom MD trajectory and obtain folding/unfolding rates of about 1/µs, which are in good agreement with the experimental values.