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Nowadays, millions of products and services are available to the public online. Therefore, searching for the best products which meets individuals' expectations would be difficult due to the existence of too many alternative choices. One of the most reliable approaches to choose a product or service is to exploit the experience of people who have already tried them, and are expected to have reported their almost honest opinions about them. A reviewing system is a place where individuals share their experience on products and services. Individuals may read and/or write their reviews which may be neutral and professional or biased. Moreover, companies utilize reviewing systems to apply opinion mining techniques in order to improve their goods or services and may be to watch their competitors. However, the popularity of reviewing systems ignites this motivation for some people to try to influence viewers by entering their fake reviews to promote some products or defame some others. These spam reviews should be detected and eliminated to prevent misleading potential customers and unethically affect the market. Opinion mining should be adapted to locate and eliminate potential spam reviews. In this paper, some review spam detection approaches have been proposed and examined over a sample dataset. The proposed approaches consider patterns that existed in trends of reviews, as well as reviewers' behavior. The approaches depend on various strategies such as observing abnormal trends, detecting uncommon or suspicious behaviors, investigating group activities, among others. The reported test results revealed some promising outcome.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), is a new virus that emerged in China and immediately spread around the world. Evidence has been documented that the immune system is impressively involved in the pathogenesis of this disease, especially in causing inflammation. One of the important components of the immune system is the complement system whose increased activity has been shown in inflammatory diseases and consequently damage caused by the activity of its components. In the present study, serum levels of C3 and C4 factors as well as the activity level of complement system in the classical pathway were measured by CH50 test in patients with SARS-CoV-2. Participants in the study consisted of 53 hospitalized patients whose real-time PCR test was positive for SARS-CoV-2. The mean age of these patients was 42.06 ± 18.7 years, including 40% women and 60% men. The most common symptoms in these patients were cough (70%), fever (59%), dyspnea (53%) and chills (53%), respectively. Analysis of biochemical and hematological test results revealed that 26 (49%) patients had lymphopenia, 34 (64%) patients were positive for C-reactive protein (CRP) and 26 (49%) patients had ESR and LDH levels significantly higher than normal. In addition, 27 patients (51%) had vitamin D deficiency. The mean CH50 activity level in COVID-19 patients was significantly reduced compared to healthy individuals (84.9 versus 169.9 U/ml, p= < 0.0001). Comparison of the mean CH50 activity levels between different subgroups of patients indicated that COVID-19 patients with decreased peripheral blood lymphocyte count and positive CRP had a significant increase in activity compared to the other groups (p= 0.0002). The serum levels of C3 and C4 factors had no significant change between patients and healthy individuals. Conclusion: The activity level of complement system in the classical pathway decreases in COVID-19 patients compared to healthy individuals, due to increased activity of complement system factors in these patients.

Using a combination of quantum chemistry and cluster size distribution dynamics, we study the heterogeneous nucleation of n-butanol and water onto sodium chloride (NaCl)10seeds at different butanol saturation ratios and relative humidities. We also investigate how the heterogeneous nucleation of butanol is affected by the seed size through comparing (NaCl)5, (NaCl)10, and (NaCl)25seeds and by seed electrical charge through comparing (Na10Cl9)+, (NaCl)10, and (Na9Cl10)−seeds. Butanol is a common working fluid for condensation particle counters used in atmospheric aerosol studies, and NaCl seeds are frequently used for calibration purposes and as model systems, for example, sea spray aerosol. In general, our simulations reproduce the experimentally observed trends for the NaCl–BuOH–H2O system, such as the increase of nucleation rate with relative humidity and with temperature (at constant supersaturation of butanol). Our results also provide molecular-level insights into the vapor–seed interactions driving the first steps of the heterogeneous nucleation process. The main purpose of this work is to show that theoretical studies can provide molecular understanding of initial steps of heterogeneous nucleation and that it is possible to find cost-effective yet accurate-enough combinations of methods for configurational sampling and energy evaluation to successfully model heterogeneous nucleation of multicomponent systems. In the future, we anticipate that such simulations can also be extended to chemically more complex seeds.

Condensation particle counter (CPC) instruments are commonly used to detect atmospheric nanoparticles. They operate on the basis of condensing an organic working fluid on the nanoparticle seeds to grow the particles to a detectable size, and at the size of few nanometers, their efficiency depends on how well the working fluid interacts with the seeds under the measurement conditions. This study models the first steps of heterogeneous nucleation of two working fluids commonly used in CPCs (diethylene glycol (DEG) and n-butanol) onto two positively charged seeds, ammonium bisulfate and tetramethylammonium bromide. The nucleation process is modeled on a molecular level using a combination of systematic configurational sampling and density functional theory (DFT). We take into account the conformational flexibility of DEG and n-butanol and determine the key factors that can improve the efficiency of nanoparticle measurements by CPCs. The results show that hydrogen bonding between the seed and the working fluid molecules is central to the adsorption of the first DEG/n-butanol molecules onto the seeds. However, intermolecular hydrogen bonding between the adsorbed molecules can also enhance the nucleation process for the weakly adsorbing vapor molecules. Accordingly, the heterogeneous nucleation probability is higher for working fluid–nanoparticle combinations with a higher potential for hydrogen bonding; in this case, DEG and ammonium bisulfate. Moreover, conformational analysis and methodology evaluations indicate that the consideration of adsorbate conformers and step-wise addition of the vapor molecules to the seeds is not essential for qualitative modeling of heterogeneous nucleation systems, at least for systems where the adsorbate and seed chemical properties are clearly different. This is the first molecular-level modeling study reporting detailed chemical reasons for experimentally observed seed and working fluid preferences in CPCs and reproducing the experimental observations. Our presented approach can be likely used for predicting preferences in similar nucleating systems.

Heterogeneous nucleation on charged seeds has been shown to frequently prefer a given sign of electrical charge (anion or cation), at constant seed size and (apparent) chemical composition. For some systems, this sign preference can be readily understood in terms of individual chemical interactions. However, experiments are in general unable to provide satisfying molecular-level explanations for the sign preference of chemically complex systems. Here, we experimentally demonstrate a positive sign preference for charged ionic liquid seeds (CILS) with diethylene glycol vapor (DEG) and explain the physicochemical origins of this preference via quantum chemical calculations. The computational results show that all enthalpies and free energies for adsorption of DEG onto the CILS clusters are lower for the positively charged seeds compared to those for the negatively charged seeds. The main reason for this difference is the stronger hydrogen bonds in the cationic clusters originating from the ability of imidazolium-based cations to act as hydrogen bond acceptors.

A simplified model is applied for the prediction of gas/solid adsorption isotherms of pure gases (i.e., CO2, N2, SO2) on the metal–organic framework Mg-MOF-74 and then applied to flue gas mixtures with small amounts of SO2in the range 0.001–1% in weight. The model is based on periodic density functional theory (DFT) calculations and a dual-site Langmuir approach (DFT/DSL), using a mean-field approximation for the inclusion of the lateral interactions. This model not only provides reliable adsorption isotherms (P≤ 1 atm, 293 ≤ T≤ 373 K) but also isosteric heats of adsorption in good agreement with both available experimental data and more refined previous models. Moreover, the effect of SO2in the efficiency of adsorption of the other components of the mixture has been evaluated by showing that a very low presence of SO2is enough to poison the Mg-MOF-74 structure. Finally, several swing adsorption techniques have been analyzed at different operative conditions to quantify the impact of SO2poisoning in the CO2adsorption.

The effect of dust aerosols on accretion reactions of water, formaldehyde, and formic acid was studied in the conditions of earth’s troposphere at the DLPNO-CCSD(T)/aug-cc-pVTZ//ωB97X-D/6-31++G** level of theory. A detailed analysis of the reaction mechanisms in the gas phase and on the surface of mineral dust, represented by mono- and trisilicic acid, revealed that mineral dust has the potential of decreasing reaction barrier heights. Specifically, at 0 K, mineral dust can lower the apparent energy barrier of the reaction of formaldehyde with formic acid to zero. However, when the entropic contributions to the reaction free energies were accounted for, mineral dust was found to selectively enhance the reaction of water with formaldehyde, while inhibiting the reaction of formaldehyde and formic acid, in the lower parts of the troposphere (with temperatures around 298 K). In the upper troposphere (with temperatures closer to 198 K), mineral dust catalyzes both reactions and also the reaction of methanol with formic acid. Despite the intrinsic potential of mineral dust, calculation of the catalytic enhancement parameter for a likely range of dust aerosol concentrations suggested that dust aerosols will not contribute to secondary organic aerosol formation via dimerization of closed-shell organic compounds. The main reason for this is the relatively low absolute concentration of tropospheric dust aerosol and its inefficiency in increasing the effective reaction rate coefficients.

Although both atomic carbon and water are omnipresent in human life, there is a debate about the possibility of carbon reaction with water. Some low-temperature spectroscopic investigations have rejected the reaction, whereas some room-temperature experiments and theoretical studies have accepted the possibility of the reaction by reporting rate coefficients ranging from 105to 109L mol–1s–1. This study provides new lines of evidence about the reaction through exploration of the reaction mechanism using the CCSD(T) method and solving the corresponding master equation by following two main approaches. According to the results, the rate coefficient of the reaction is significantly influenced by the tunneling and hindered rotation effects, in addition to the selected total angular momentum (J). Furthermore, the total rate coefficient of the reaction increases dramatically (from 107to 1011L mol–1s–1) with the rise of temperature from 100 to 4000 K, while the total rate coefficient is insensitive to pressure (0.1–10 atm). Despite some differences between the results of the two approaches, the rate coefficients of both methods are consistent with the previously reported rate coefficients. Also, in agreement with the previous studies, the major products are 2HOC + 2H and 2HCO + 2H. In general, the findings approve the occurrence of the title reaction and indicate that the mentioned conflict is due to the sensitivity of the reaction to the investigated temperature and Jlevel. The sensitivity does not permit low-temperature spectroscopic studies to detect any products and varies the measured and calculated rate coefficients.

Hydroxyl (OH) is a radical that is distributed all over the universe including the human body, where it can be readily produced, results in oxidative damage to cellular components, and leads to several health implications. While the reaction of OH with proteins is usually addressed as the gas-phase reaction of free amino acids with OH in theoretical studies, this study questions the efficiency of such calculations by focusing on the reaction of glutamic acid (Glu) with OH. According to the results, the reaction profile alters significantly by shifting from gas-phase calculations to solvent-phase due to the zwitterionic nature of this amino acid. So that the barrier height of the N-terminal reaction path and the relative energies of the species vary considerably. Furthermore, the interconnection of all collisional energy transfer events and chemical changes through solving the reaction’s master equation and inclusion of the effect of tunneling suggests that the major product changes from vdw1-N to R-CA, R-CB, and R-CG by considering the effect of solvent on the gas-phase reaction. Despite these changes, the rate constants of both gas- and solvent-phase reactions (1.23 × 1010and 7.32 × 109L mol–1s–1, respectively, at 310 K and 1 atm) demonstrate positive temperature dependency. With respect to the rate coefficients reported in the literature, Glu, Ser, and Met are the most vulnerable amino acids to oxidative attack by OH among the Ser, Cys, Asn, β-Ala, Ala, Gly, Met, and Glu amino acids.

Metal–organic frameworks (MOFs) have been a center of interest because of their highly diverse structural and physicochemical properties. The study of many MOFs requires periodic calculations. However, isolated models have also been employed in first-principles calculations to study their mechanisms and energy profiles. Following the water adsorption properties of MOF building units, this study determines how far isolated models of MOFs can reproduce experimental observations and where they fail. According to our DFT simulations of water adsorption by 70 common metal nodes and over 110 organic linkers, the isolated models provide some opportunities and limitations. They indicate the water adsorption mechanism and energy of the individual MOF components. They give clues about the water stability of the metal nodes and the degradation pathways. Also, they predict an overall trend for the maximum water uptake capacity. However, they cannot always give an accurate insight into MOF’s water adsorption enthalpies, their water harvesting efficiency, their water uptake capacities under varying conditions, and a complete picture of the water uptake mechanism inside MOF pores.

Quasi-classical trajectory calculations and stochastic one-dimensional chemical master equation simulation methods are used to study the dynamics of the reaction of amidogen radical [NH2(2B1)] with hydroperoxyl radical [HO2(2A″)] on the lowest singlet electronic state. The title complex reaction takes place on a multi-well multichannel potential energy surface consisting of three deep potential wells and one van der Waals complex. In quasi-classical trajectory calculations a new analytical potential energy surface based on CCSD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) ab initio method was driven and used to study the dynamics of the title reaction. In quasi-classical trajectory calculations, the reactive cross sections and reaction probabilities are determined for 200–2000 K relative translational energies to calculate the rate constants. The same ab initio method was used to have the necessary data for solving the one-dimensional chemical master equation to calculate the rate constants of different channels. In solving the master equation, the Lennard-Jones potential model was used to form the collision between the collider gases. The fractional populations of different intermediates and products in the early stages of the reaction were examined to determine the role of the energized intermediates and the van der Waals complex on the dynamics of the title reaction. Although the calculated total rate constants from both methods are in good agreement with the reported experimental values in the literature, the quasi-classical trajectory simulation predicts the formation of NH2O + OH as the major channel in the title reaction in accordance with the previous studies (Sumathi and Peyerimhoff, Chem. Phys. Lett., 263:742–748, 1996), while the stochastic master equation simulation predicts the formation of HNO + H2O as the major products.

Human serum albumin (HSA) primarily functions as a transport carrier for a vast variety of natural ligands and pharmaceutical drugs. In the present study, three structurally related cationic Pt(II) complexes ([Pt(ppy)(dppe)]CF3CO2: 1, Pt(bhq)(dppe)]CF3CO2: 2, and [Pt(bhq)(dppf)]CF3CO2: 3) were used to evaluate their interaction with HSA under different experimental setups, using UV–Vis absorption spectroscopy, fluorescence and circular dichroism techniques. The spectroscopic results suggest that upon binding to HSA, the Pt(II) complexes could effectively induce structural alteration of the protein. The complexes can bind to HSA with the binding affinities of the following order: 3> 2> 1. Also, thermodynamic parameters of binding between these complexes and HSA indicated the existence of entropy-driven spontaneous interaction which primarily dominated with the hydrophobic forces. Also, docking simulation study revealed the binding details of these complexes on HSA. Complex 3with highest binding affinity for HSA indicates lowest denaturing effect on this protein. The low denaturation properties of 3appear important in the terms of lower susceptibility of this platinum complex for possible development of deleterious side effects.

In the present work, the interaction of a dimethylplatinum(II) complex (Pt(II) complex) with DNA and human serum albumin (HSA) was studied by different spectroscopic techniques, including UV–vis spectroscopy, fluorescence, and far-UV circular dichroism (CD). The Pt(II) complex exhibits strong ability in quenching the intrinsic fluorescence of HSA. The results of far-UV CD suggest that this Pt(II) complex induces significant reduction of HSA α-helical structure which was accompanied with the elevation in quantity of the other protein structures. Molecular simulation and fluorescence spectroscopic results were employed to define the van der Waals and hydrophobic interactions of this complex with HSA. Also, the half maximal cytotoxic concentration (Cc50) of the complex was found to be 17.33 and 3.95 µM for the incubation times of 24 and 48 h, respectively. The results show that this complex is a promising antiproliferative agent that can serve as a new drug with anticancer properties.

[Fe4S4] or [4S–4Fe] clusters are responsible for storing and transferring electrons in key cellular processes and interact with their microenvironment to modulate their oxidation and magnetic states. Therefore, these clusters are ideal for the metal node of chemically and electromagnetically tunable metal–organic frameworks (MOFs). To examine the adsorption-based applications of [Fe4S4]-based MOFs, we used density functional theory calculations and studied the adsorption of CO2, CH4, H2O, H2, N2, NO2, O2, and SO2onto [Fe4S4]0, [Fe4S4]2+, and two 1D MOF models with the carboxylate and 1,4-benzenedithiolate organic linkers. Our reaction kinetics and thermodynamics results indicated that MOF formation promotes the oxidative and hydrolytic stability of the [Fe4S4] clusters but decreases their adsorption efficiency. Our study suggests the potential industrial applications of these [Fe4S4]-based MOFs because of their limited capacity to adsorb CO2, CH4, H2O, H2, N2, O2, and SO2and high selectivity for NO2adsorption.

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