Giant Tunability of Intersubband Transitions and Quantum Hall Quartets in Few-Layer InSe Quantum Wells.

A two-dimensional (2D) quantum electron system is characterized by quantized energy levels, or subbands, in the out-of-plane direction. Populating higher subbands and controlling the intersubband transitions have wide technological applications such as optical modulators and quantum cascade lasers. In conventional materials, however, the tunability of intersubband spacing is limited. Here we demonstrate electrostatic population and characterization of the second subband in few-layer InSe quantum wells, with giant tunability of its energy, population, and spin-orbit coupling strength, via the control of not only layer thickness but also the out-of-plane displacement field. A modulation of as much as 350% or over 250 meV is achievable, underscoring the promise of InSe for tunable infrared and THz sources, detectors, and modulators.

Natural IgG against S-Protein and RBD of SARS-CoV-2 Do Not Bind and Hydrolyze DNA and Are Not Autoimmune.

Since the onset of the COVID-19 pandemic, numerous publications have appeared describing autoimmune pathologies developing after a coronavirus infection, with several papers reporting autoantibody production during the acute period of the disease. Several viral diseases are known to trigger autoimmune processes, and the appearance of catalytic antibodies with DNase activity is one of the earliest markers of several autoimmune pathologies. Therefore, we analyzed whether IgG antibodies from blood plasma of SARS-CoV-2 patients after recovery could bind and hydrolyze DNA. We analyzed how vaccination of patients with adenovirus Sputnik V vaccine influences the production of abzymes with DNase activity. Four groups were selected for the analysis, each containing 25 patients according to their relative titers of antibodies to S-protein: with high and median titers, vaccinated with Sputnik V with high titers, and a control group of donors with negative titers. The relative titers of antibodies against DNA and the relative DNase activity of IgGs depended very much on the individual patient and the donor, and no significant correlation was found between the relative values of antibodies titers and their DNase activity. Our results indicate that COVID-19 disease and vaccination with adenoviral Sputnik V vaccine do not result in the development or enhancement of strong autoimmune reactions as in the typical autoimmune diseases associated with the production of anti-DNA and DNA hydrolyzing antibodies.

Self-Assembled Particles Combining SARS-CoV-2 RBD Protein and RBD DNA Vaccine Induce Synergistic Enhancement of the Humoral Response in Mice.

Despite the fact that a range of vaccines against COVID-19 have already been created and are used for mass vaccination, the development of effective, safe, technological, and affordable vaccines continues. We have designed a vaccine that combines the recombinant protein and DNA vaccine approaches in a self-assembled particle. The receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 was conjugated to polyglucin:spermidine and mixed with DNA vaccine (pVAXrbd), which led to the formation of particles of combined coronavirus vaccine (CCV-RBD) that contain the DNA vaccine inside and RBD protein on the surface. CCV-RBD particles were characterized with gel filtration, electron microscopy, and biolayer interferometry. To investigate the immunogenicity of the combined vaccine and its components, mice were immunized with the DNA vaccine pVAXrbd or RBD protein as well as CCV-RBD particles. The highest antigen-specific IgG and neutralizing activity were induced by CCV-RBD, and the level of antibodies induced by DNA or RBD alone was significantly lower. The cellular immune response was detected only in the case of DNA or CCV-RBD vaccination. These results demonstrate that a combination of DNA vaccine and RBD protein in one construct synergistically increases the humoral response to RBD protein in mice.

Synthesis and Antiviral Properties of Camphor-Derived Iminothiazolidine-4-Ones and 2,3-Dihydrothiazoles.

A set of heterocyclic products was synthesized from natural (+)-camphor and semi-synthetic (-)-camphor. Then, 2-Imino-4-thiazolidinones and 2,3-dihydrothiazoles were obtained using a three-step procedure. For the synthesized compounds, their antiviral activity against the vaccinia virus and Marburg virus was studied. New promising agents active against both viruses were found among the tested compounds.

Triterpenic Acid Amides as Potential Inhibitors of the SARS-CoV-2 Main Protease.

Although the incidence and mortality of SARS-CoV-2 infection has been declining during the pandemic, the problem related to designing novel antiviral drugs that could effectively resist viruses in the future remains relevant. As part of our continued search for chemical compounds that are capable of exerting an antiviral effect against the SARS-CoV-2 virus, we studied the ability of triterpenic acid amides to inhibit the SARS-CoV-2 main protease. Molecular modeling suggested that the compounds are able to bind to the active site of the main protease via non-covalent interactions. The FRET-based enzyme assay was used to reveal that compounds 1e and 1b can inhibit the SARS-CoV-2 main protease at micromolar concentrations.

Synthesis and In Vitro Study of Antiviral Activity of Glycyrrhizin Nicotinate Derivatives against HIV-1 Pseudoviruses and SARS-CoV-2 Viruses.

When developing drugs against SARS-CoV-2, it is important to consider the characteristics of patients with different co-morbidities. People infected with HIV-1 are a particularly vulnerable group, as they may be at a higher risk than the general population of contracting COVID-19 with clinical complications. For such patients, drugs with a broad spectrum of antiviral activity are of paramount importance. Glycyrrhizinic acid (Glyc) and its derivatives are promising biologically active compounds for the development of such broad-spectrum antiviral agents. In this work, derivatives of Glyc obtained by acylation with nicotinic acid were investigated. The resulting preparation, Glycyvir, is a multi-component mixture containing mainly mono-, di-, tri- and tetranicotinates. The composition of Glycyvir was characterized by HPLC-MS/MS and its toxicity assessed in cell culture. Antiviral activity against three strains of SARS-CoV-2 was tested in vitro on Vero E6 cells by MTT assay. Glycyvir was shown to inhibit SARS-CoV-2 replication in vitro (IC502-8 µM) with an antiviral activity comparable to the control drug Remdesivir. In addition, Glycyvir exhibited marked inhibitory activity against HIV pseudoviruses of subtypes B, A6 and the recombinant form CRF63_02A (IC50 range 3.9-27.5 µM). The time-dependence of Glycyvir inhibitory activity on HIV pseudovirus infection of TZM-bl cells suggested that the compound interfered with virus entry into the target cell. Glycyvir is a promising candidate as an agent with low toxicity and a broad spectrum of antiviral action.

Impact of Surfactants on the Formation and Properties of Droplet Clusters.

A levitating cluster of condensed microdroplets can form over the heated area of a water layer. The thermocapillary (TC) flow at the surface of the water layer combined with the convective flow in the layer often prevents a cluster's stability due to disturbances that it creates in the gas flow over the water surface. The TC flow can be suppressed by introducing small amounts of surfactants into the water layer. We conduct a systematic study of the effect of a surfactant on the cluster. We show experimentally that the introduction of the surfactant sodium laureth sulfate with concentrations of 0.05-0.5 g/L can suppress the TC convection. It is shown that the amount of surfactant does not affect the condensational growth of droplets and the structure of the cluster. In the absence of the surfactant, a ring-shaped cluster is formed, which is reported in this paper for the first time.

Self-Arranged Levitating Droplet Clusters: A Reversible Transition from Hexagonal to Chain Structure.

Water microdroplets condense over locally heated water-vapor interfaces and levitate in an ascending vapor-air flow forming self-assembled ordered monolayer clusters. The droplets do not coalesce due to complex aerodynamic interactions between them. The droplet cluster formation is governed by the condensation/evaporation balance and by coupling of heat flux and vapor flow with aerodynamic forces. Here, we report the observations of a reversible structural transition from the ordered hexagonal-structure cluster to the chain-like structure and provide an explanation of its mechanism and conditions under which the transition occurs. The phenomenon provides new insights on the fundamental physical and chemical processes with microdroplets including their role in reaction catalysis in nature and their potential for aerosol and microfluidic applications.

Raman Spectroscopy, Photocatalytic Degradation, and Stabilization of Atomically Thin Chromium Tri-iodide.

As a 2D ferromagnetic semiconductor with magnetic ordering, atomically thin chromium tri-iodide is the latest addition to the family of two-dimensional (2D) materials. However, realistic exploration of CrI3-based devices and heterostructures is challenging due to its extreme instability under ambient conditions. Here, we present Raman characterization of CrI3 and demonstrate that the main degradation pathway of CrI3 is the photocatalytic substitution of iodine by water. While simple encapsulation by Al2O3, PMMA, and hexagonal BN (hBN) only leads to modest reduction in degradation rate, minimizing light exposure markedly improves stability, and CrI3 sheets sandwiched between hBN layers are air-stable for >10 days. By monitoring the transfer characteristics of the CrI3/graphene heterostructure over the course of degradation, we show that the aquachromium solution hole-dopes graphene.

Engineering of novel hemagglutinin biosensors for rapid detection and drug screening of Influenza A H7N9 virus.

New pathogenic influenza virus strains are constantly emerging, posing a serious risk to both human health and economic growth. To effectively control the spread of this virus, there is an urgent need for early, rapid, sensitive, simple, and cost-effective detection technologies, as well as new and effective antiviral drugs. In this study, we have successfully achieved a significant milestone by successfully fusing the H7N9 influenza virus hemagglutinin (HA) protein with the nano-luciferase component, resulting in the development of a novel set of biosensors. This remarkable achievement marks the first instance of utilizing this biosensor technology for influenza antibody detection. Our biosensor technology also has the potential to facilitate the development of antiviral drugs targeting specific epitopes of the HA protein, providing a promising avenue for the treatment of H7N9 influenza virus infections. Furthermore, our biosensors have broad applications beyond H7N9 influenza virus detection, as they can be expanded for the detection of other pathogens and drug screening applications in the future. By providing a novel and effective solution to the detection and treatment of influenza viruses, our biosensors have the potential to revolutionize the field of infectious disease control.

Biochemical Properties of a Promising Milk-Clotting Enzyme, Moose (Alces alces) Recombinant Chymosin.

Moose (Alces alces) recombinant chymosin with a milk-clotting activity of 86 AU/mL was synthesized in the Kluyveromyces lactis expression system. After precipitation with ammonium sulfate and chromatographic purification, a sample of genetically engineered moose chymosin with a specific milk-clotting activity of 15,768 AU/mg was obtained, which was used for extensive biochemical characterization of the enzyme. The threshold of the thermal stability of moose chymosin was 55 °C; its complete inactivation occurred after heating at 60 °C. The total proteolytic activity of moose chymosin was 0.332 A280 units. The ratio of milk-clotting and total proteolytic activities of the enzyme was 0.8. The Km, kcat and kcat/Km values of moose chymosin were 4.7 µM, 98.7 s-1, and 21.1 µM-1 s-1, respectively. The pattern of change in the coagulation activity as a function of pH and Ca2+ concentration was consistent with the requirements for milk coagulants for cheese making. The optimum temperature of the enzyme was 50-55 °C. The introduction of Mg2+, Zn2+, Co2+, Ba2+, Fe2+, Mn2+, Ca2+, and Cu2+ into milk activated the coagulation ability of moose chymosin, while Ni ions on the contrary inhibited its activity. Using previously published data, we compared the biochemical properties of recombinant moose chymosin produced in bacterial (Escherichia coli) and yeast (K. lactis) producers.

Pre-Pandemic Cross-Reactive Immunity against SARS-CoV-2 among Siberian Populations.

In December 2019, a new coronavirus, SARS-CoV-2, was found to in Wuhan, China. Cases of infection were subsequently detected in other countries in a short period of time, resulting in the declaration of the COVID-19 pandemic by the World Health Organization (WHO) on 11 March 2020. Questions about the impact of herd immunity of pre-existing immune reactivity to SARS-CoV-2 on COVID-19 severity, associated with the immunity to seasonal manifestation, are still to be resolved and may be useful for understanding some processes that precede the emergence of a pandemic virus. Perhaps this will contribute to understanding some of the processes that precede the emergence of a pandemic virus. We assessed the specificity and virus-neutralizing capacity of antibodies reacting with the nucleocapsid and spike proteins of SARS-CoV-2 in a set of serum samples collected in October and November 2019, before the first COVID-19 cases were documented in this region. Blood serum samples from 799 residents of several regions of Siberia, Russia, (the Altai Territory, Irkutsk, Kemerovo and Novosibirsk regions, the Republic of Altai, Buryatia, and Khakassia) were analyzed. Sera of non-infected donors were collected within a study of seasonal influenza in the Russian Federation. The sample collection sites were located near the flyways and breeding grounds of wild waterfowl. The performance of enzyme-linked immunosorbent assay (ELISA) for the collected sera included the usage of recombinant SARS-CoV-2 protein antigens: full-length nucleocapsid protein (CoVN), receptor binding domain (RBD) of S-protein and infection fragment of the S protein (S5-6). There were 183 (22.9%) sera reactive to the S5-6, 270 (33.8%) sera corresponding to the full-length N protein and 128 (16.2%) sera simultaneously reactive to both these proteins. Only 5 out of 799 sera had IgG antibodies reactive to the RBD. None of the sera exhibited neutralizing activity against the nCoV/Victoria/1/2020 SARS-CoV-2 strain in Vero E6 cell culture. The data obtained in this study suggest that some of the population of the analyzed regions of Russia had cross-reactive humoral immunity against SARS-CoV-2 before the COVID-19 pandemic started. Moreover, among individuals from relatively isolated regions, there were significantly fewer reliably cross-reactive sera. The possible significance of these data and impact of cross-immunity to SARS-CoV-2 on the prevalence and mortality of COVID-19 needs further assessment.

SARS-CoV-2 RBD Conjugated to Polyglucin, Spermidine, and dsRNA Elicits a Strong Immune Response in Mice.

Despite the rapid development and approval of several COVID vaccines based on the full-length spike protein, there is a need for safe, potent, and high-volume vaccines. Considering the predominance of the production of neutralizing antibodies targeting the receptor-binding domain (RBD) of S-protein after natural infection or vaccination, it makes sense to choose RBD as a vaccine immunogen. However, due to its small size, RBD exhibits relatively poor immunogenicity. Searching for novel adjuvants for RBD-based vaccine formulations is considered a good strategy for enhancing its immunogenicity. Herein, we assess the immunogenicity of severe acute respiratory syndrome coronavirus 2 RBD conjugated to a polyglucin:spermidine complex (PGS) and dsRNA (RBD-PGS + dsRNA) in a mouse model. BALB/c mice were immunized intramuscularly twice, with a 2-week interval, with 50 µg of RBD, RBD with Al(OH)3, or conjugated RBD. A comparative analysis of serum RBD-specific IgG and neutralizing antibody titers showed that PGS, PGS + dsRNA, and Al(OH)3 enhanced the specific humoral response in animals. There was no significant difference between the groups immunized with RBD-PGS + dsRNA and RBD with Al(OH)3. Additionally, the study of the T-cell response in animals showed that, unlike adjuvants, the RBD-PGS + dsRNA conjugate stimulates the production of specific CD4+ and CD8+ T cells in animals.

Branched droplet clusters and the Kramers theorem.

Scaling laws inherent for polymer molecules are checked for the linear and branched chains constituting two-dimensional (2D) levitating microdroplet clusters condensed above the locally heated layer of water. We demonstrate that the dimensionless averaged end-to-end distance of the droplet chain r[over ¯] normalized by the averaged distance between centers of the adjacent droplets l[over ¯] scales as r[over ¯]/l[over ¯]∼n^{0.76}, where n is the number of links in the chain, which is close to the power exponent ¾, predicted for 2D polymer chains with excluded volume in the dilution limit. The values of the dimensionless Kuhn length b[over ̃]≅2.12±0.015 and of the averaged absolute value of the bond angle of the droplet chains |θ|[over ¯]=22.0±0.5^{0} are determined. Using these values we demonstrate that the predictions of the Kramers theorem for the gyration radius of branched polymers are valid also for the branched droplets' chains. We discuss physical interactions that explain both the high value of the power exponent and the applicability of the Kramers theorem including the effects of the excluded volume, surrounding droplet monomers, and the prohibition of extreme values of the bond angle.

SOI-FET Sensors with Dielectrophoretic Concentration of Viruses and Proteins.

Quick label-free virus screening and highly sensitive analytical tools/techniques are becoming extremely important in a pandemic. In this study, we developed a biosensing device based on the silicon nanoribbon multichannel and dielectrophoretic controlled sensors functionalized with SARS-CoV-2 spike antibodies for the use as a platform for the detection and studding of properties of viruses and their protein components. Replicatively defective viral particles based on vesicular stomatitis viruses and HIV-1 were used as carrier molecules to deliver the target SARS-CoV-2 spike S-proteins to sensory elements. It was shown that fully CMOS-compatible nanoribbon sensors have the subattomolar sensitivity and dynamic range of 4 orders. Specific interaction between S-proteins and antibodies leads to the accumulation of the negative charge on the sensor surface. Nonspecific interactions of the viral particles lead to the positive charge accumulation. It was shown that dielectrophoretic controlled sensors allow to estimate the effective charge of the single virus at the sensor surface and separate it from the charge associated with the binding of target proteins with the sensor surface.

Antibodies to the Spike Protein Receptor-Binding Domain of SARS-CoV-2 at 4-13 Months after COVID-19.

Identification of factors behind the level and duration of persistence of the SARS-CoV-2 antibodies in the blood is assumed to set the direction for studying humoral immunity mechanisms against COVID-19, optimizing the strategy for vaccine use, antibody-based drugs, and epidemiological control of COVID-19. Objective: This study aimed to study the relationship between clinical and demographic characteristics and the level of IgG antibodies to the RBD of SARS-CoV-2 spike protein after COVID-19 in the long term. Residents of the Altai Region of Western Siberia of Russia, Caucasians, aged from 27 to 93 years (median 53.0 years), who recovered from COVID-19 between May 2020 and February 2021 (n = 44) took part in this prospective observational study. The titer of IgG antibodies to the RBD of SARS-CoV-2 spike protein was measured repeatedly in the blood at 4-13 months from the beginning of the clinical manifestation of COVID-19 via the method of enzyme-linked immunosorbent assay. The antibody titer positively correlated with age (p = 0.013) and COVID-19 pneumonia (p = 0.002) at 20-40 and 20-24 weeks from the onset of COVID-19 symptoms, respectively. Age was positively associated with antibody titer regardless of history of COVID-19 pneumonia (beta regression coefficient p = 0.009). The antibody titer decreased in 15 (34.1%) patients, increased in 10 (22.7%) patients, and did not change in 19 (43.2%) patients from the baseline to 48-49 weeks from the onset of COVID-19 symptoms, with seropositivity persisting in all patients. Age and COVID-19 pneumonia are possibly associated with higher IgG antibodies to the spike protein RBD of SARS-CoV-2 following COVID-19 in the long term. Divergent trends of anti-RBD IgG levels in adults illustrate inter-individual differences at 4-13 months from the onset of COVID-19 symptoms.

Light sources with bias tunable spectrum based on van der Waals interface transistors.

Light-emitting electronic devices are ubiquitous in key areas of current technology, such as data communications, solid-state lighting, displays, and optical interconnects. Controlling the spectrum of the emitted light electrically, by simply acting on the device bias conditions, is an important goal with potential technological repercussions. However, identifying a material platform enabling broad electrical tuning of the spectrum of electroluminescent devices remains challenging. Here, we propose light-emitting field-effect transistors based on van der Waals interfaces of atomically thin semiconductors as a promising class of devices to achieve this goal. We demonstrate that large spectral changes in room-temperature electroluminescence can be controlled both at the device assembly stage -by suitably selecting the material forming the interfaces- and on-chip, by changing the bias to modify the device operation point. Even though the precise relation between device bias and kinetics of the radiative transitions remains to be understood, our experiments show that the physical mechanism responsible for light emission is robust, making these devices compatible with simple large areas device production methods.

Optimization of In Vivo Electroporation Conditions and Delivery of DNA Vaccine Encoding SARS-CoV-2 RBD Using the Determined Protocol.

Vaccination against SARS-CoV-2 and other viral infections requires safe, effective, and inexpensive vaccines that can be rapidly developed. DNA vaccines are candidates that meet these criteria, but one of their drawbacks is their relatively weak immunogenicity. Electroporation (EP) is an effective way to enhance the immunogenicity of DNA vaccines, but because of the different configurations of the devices that are used for EP, it is necessary to carefully select the conditions of the procedure, including characteristics such as voltage, current strength, number of pulses, etc. In this study, we determined the optimal parameters for delivery DNA vaccine by electroporation using the BEX CO device. BALB/c mice were used as a model. Plasmid DNA phMGFP was intramuscular (I/M) injected into the quadriceps muscle of the left hind leg of animals using insulin syringes, followed by EP. As a result of the experiments, the following EP parameters were determined: direct and reverse polarity rectangular DC current in three pulses, 12 V voltage for 30 ms and 950 ms intervals, with a current limit of 45 mA. The selected protocol induced a low level of injury and provided a high level of GFP expression. The chosen protocol was used to evaluate the immunogenicity of the DNA vaccine encoding the receptor-binding domain (RBD) of the SARS-CoV-2 protein (pVAXrbd) injected by EP. It was shown that the delivery of pVAXrbd via EP significantly enhanced both specific humoral and cellular immune responses compared to the intramuscular injection of the DNA vaccine.

Comparative Immunogenicity of the Recombinant Receptor-Binding Domain of Protein S SARS-CoV-2 Obtained in Prokaryotic and Mammalian Expression Systems.

The receptor-binding domain (RBD) of the protein S SARS-CoV-2 is considered to be one of the appealing targets for developing a vaccine against COVID-19. The choice of an expression system is essential when developing subunit vaccines, as it ensures the effective synthesis of the correctly folded target protein, and maintains its antigenic and immunogenic properties. Here, we describe the production of a recombinant RBD protein using prokaryotic (pRBD) and mammalian (mRBD) expression systems, and compare the immunogenicity of prokaryotic and mammalian-expressed RBD using a BALB/c mice model. An analysis of the sera from mice immunized with both variants of the protein revealed that the mRBD expressed in CHO cells provides a significantly stronger humoral immune response compared with the RBD expressed in E.coli cells. A specific antibody titer of sera from mice immunized with mRBD was ten-fold higher than the sera from the mice that received pRBD in ELISA, and about 100-fold higher in a neutralization test. The data obtained suggests that mRBD is capable of inducing neutralizing antibodies against SARS-CoV-2.

Thickness- and Twist-Angle-Dependent Interlayer Excitons in Metal Monochalcogenide Heterostructures.

Interlayer excitons, or bound electron-hole pairs whose constituent quasiparticles are located in distinct stacked semiconducting layers, are being intensively studied in heterobilayers of two-dimensional semiconductors. They owe their existence to an intrinsic type-II band alignment between both layers that convert these into p-n junctions. Here, we unveil a pronounced interlayer exciton (IX) in heterobilayers of metal monochalcogenides, namely, γ-InSe on ε-GaSe, whose pronounced emission is adjustable just by varying their thicknesses given their number of layers dependent direct band gaps. Time-dependent photoluminescense spectroscopy unveils considerably longer interlayer exciton lifetimes with respect to intralayer ones, thus confirming their nature. The linear Stark effect yields a bound electron-hole pair whose separation d is just (3.6 ± 0.1) Å with d being very close to dSe = 3.4 Å which is the calculated interfacial Se separation. The envelope of IX is twist-angle-dependent and describable by superimposed emissions that are nearly equally spaced in energy, as if quantized due to localization induced by the small moiré periodicity. These heterostacks are characterized by extremely flat interfacial valence bands making them prime candidates for the observation of magnetism or other correlated electronic phases upon carrier doping.