Reparameterization of GFN1-xTB for atmospheric molecular clusters: applications to multi-acid-multi-base systems.

Atmospheric molecular clusters, the onset of secondary aerosol formation, are a major part of the current uncertainty in modern climate models. Quantum chemical (QC) methods are usually employed in a funneling approach to identify the lowest free energy cluster structures. However, the funneling approach highly depends on the accuracy of low-cost methods to ensure that important low-lying minima are not missed. Here we present a reparameterized GFN1-xTB model based on the clusteromics I-V datasets for studying atmospheric molecular clusters (AMC), denoted AMC-xTB. The AMC-xTB model reduces the mean of electronic binding energy errors from 7-11.8 kcal mol-1 to roughly 0 kcal mol-1 and the root mean square deviation from 7.6-12.3 kcal mol-1 to 0.81-1.45 kcal mol-1. In addition, the minimum structures obtained with AMC-xTB are closer to the ωB97X-D/6-31++G(d,p) level of theory compared to GFN1-xTB. We employ the new parameterization in two new configurational sampling workflows that include an additional meta-dynamics sampling step using CREST with the AMC-xTB model. The first workflow, denoted the "independent workflow", is a commonly used funneling approach with an additional CREST step, and the second, the "improvement workflow", is where the best configuration currently known in the literature is improved with a CREST + AMC-xTB step. Testing the new workflow we find configurations lower in free energy for all the literature clusters with the largest improvement being up to 21 kcal mol-1. Lastly, by employing the improvement workflow we massively screened 288 new multi-acid-multi-base clusters containing up to 8 different species. For these new multi-acid-multi-base cluster systems we observe that the improvement workflow finds configurations lower in free energy for 245 out of 288 (85.1%) cluster structures. Most of the improvements are within 2 kcal mol-1, but we see improvements up to 8.3 kcal mol-1. Hence, we can recommend this new workflow based on the AMC-xTB model for future studies on atmospheric molecular clusters.

On the geometry dependence of the nuclear magnetic resonance chemical shift of mercury in thiolate complexes: A relativistic density functional theory study.

Thiolate containing mercury(II) complexes of the general formula [Hg(SR) n $$ {}_n $$ ] 2 - n $$ {}^{2-n} $$ have been of great interest since the toxicity of mercury was recognized. 199Hg nuclear magnetic resonance spectroscopy (NMR) is a powerful tool for characterization of mercury complexes. In this work, the Hg shielding constants in a series of [Hg(SR) n $$ {}_n $$ ] 2 - n $$ {}^{2-n} $$ complexes are therefore investigated computationally with particular emphasis on their geometry dependence. Geometry optimizations and NMR chemical shift calculations are performed at the density functional theory (DFT) level with both the zeroth-order regular approximation (ZORA) and four-component relativistic methods. The four exchange-correlation (XC) functionals PBE0, PBE, B3LYP, and BLYP are used in combination with either Dyall's Gaussian-type (GTO) or Slater-type orbitals (STOs) basis sets. Comparing ZORA and four-component calculations, one observes that the calculated shielding constants for a given molecular geometry have a constant difference of ∼ $$ \sim $$ 1070 ppm. This confirms that ZORA is an acceptable relativistic method to compute NMR chemical shifts. The combinations of four-component/PBE0/v3z and ZORA/PBE0/QZ4P are applied to explore the geometry dependence of the isotropic shielding. For a given coordination number, the distance between mercury and sulfur is the key factor affecting the shielding constant, while changes in bond and dihedral angles and even different side groups have relatively little impact.

Improved Configurational Sampling Protocol for Large Atmospheric Molecular Clusters.

The nucleation process leading to the formation of new atmospheric particles plays a crucial role in aerosol research. Quantum chemical (QC) calculations can be used to model the early stages of aerosol formation, where atmospheric vapor molecules interact and form stable molecular clusters. However, QC calculations heavily depend on the chosen computational method, and when dealing with large systems, striking a balance between accuracy and computational cost becomes essential. We benchmarked the binding energies and structures and found the B97-3c method to be a good compromise between the accuracy and computational cost for studying large cluster systems. Further, we carefully assessed configurational sampling procedures for targeting large atmospheric molecular clusters containing up to 30 molecules (approximately 2 nm in diameter) and proposed a funneling approach with highly improved accuracy. We find that several parallel ABCluster explorations lead to better guesses for the cluster global energy minimum structures than one long exploration. This methodology allows us to bridge computational studies of molecular clusters, which typically reach only around 1 nm, with experimental studies that often measure particles larger than 2 nm. By employing this workflow, we searched for low-energy configurations of large sulfuric acid-ammonia and sulfuric acid-dimethylamine clusters. We find that the binding free energies of clusters containing dimethylamine are unequivocally more stable than those of the ammonia-containing clusters. Our improved configurational sampling protocol can in the future be applied to study the growth and dynamics of large clusters of arbitrary compositions.

Current and future machine learning approaches for modeling atmospheric cluster formation.

The formation of strongly bound atmospheric molecular clusters is the first step towards forming new aerosol particles. Recent advances in the application of machine learning models open an enormous opportunity for complementing expensive quantum chemical calculations with efficient machine learning predictions. In this Perspective, we present how data-driven approaches can be applied to accelerate cluster configurational sampling, thereby greatly increasing the number of chemically relevant systems that can be covered.

Effects of ionic strength on removal of toxic pollutants from aqueous media with multifarious adsorbents: A review.

Adsorption is one of the most widely used and effective wastewater treatment methods. The role of ionic strength (IS) in shaping the adsorption performances is much necessary due to the ubiquity of electrolyte ions in water body and industrial effluents. The influences of IS on adsorption are rather complex, because electrolyte ions affect both adsorption kinetics and thermodynamics by changing the basic characteristics of adsorbents and adsorbates. For a given adsorption system, multiple or even contradictory effects of IS may coexist under identical experimental conditions, rendering the dominant mechanism recognition and net effect prediction complicated. We herein reviewed the key advancement on the interaction and mechanisms of IS, including change in number of active sites for adsorbents, ion pair for metal ions, molecular aggregation and salting-out effect for organic compounds, site competition for both inorganic and organic adsorbates, and charge compensation for adsorbent-adsorbate reciprocal interactions. The corresponding fundamental theory was thoroughly described, and the efforts made by various researchers were explicated. The structural optimization of adsorbents affected by IS was detailed, also highlighting polyamine materials with exciting "salt-promotion" effects on heavy metal removal from high salinity wastewater. In addition, the research trends and prospects were briefly discussed.

Design, Preparation, and Performance of a Novel Bilayer Tissue-Engineered Small-Diameter Vascular Graft.

In clinical practice, the need for small-diameter vascular grafts continues to increase. Decellularized xenografts are commonly used for vascular reconstructive procedures. Here, porcine coronary arteries are decellularized, which destroys the extracellular matrix structure, leading to the decrease of vascular strength and the increase of vascular permeability. A bilayer tissue-engineered vascular graft (BTEV) is fabricated by electrospinning poly(l-lactide-co-carprolactone)/gelatin outside of the decellularized vessels and functionalized by immobilizing heparin, which increases the biomechanical strength and anticoagulant activity of decellularized vessels. The biosafety and efficacy of the heparin-modified BTEVs (HBTEVs) are verified by implanting in rat models. HBTEVs remain patent and display no expansion or aneurism. After 4 weeks of implantation, a cell monolayer in the internal surface and a dense middle layer have formed, and the mechanical properties of regenerated vessels are similar to those of rat abdominal aorta. Therefore, HBTEVs can be used for rapid remodeling of small-diameter blood vessels.

Immobilization of heparin/poly-l-lysine microspheres on medical grade high nitrogen nickel-free austenitic stainless steel surface to improve the biocompatibility and suppress thrombosis.

Thrombosis formation, restenosis, and delayed endothelium regeneration continue to be a challenge for coronary artery stent therapy. To improve the hemocompatibility of cardiovascular implants and to selectively direct vascular cell behavior, a novel heparin/poly-l-lysine microsphere was developed and immobilized on a dopamine-coated surface. We chose medical grade high nitrogen nickel-free austenitic stainless steel as the stent material since it has better biocompatibility. The stability and structural characteristics of the microspheres changed with the heparin: poly-l-lysine concentration ratio. Antithrombin III binding was significantly enhanced. Furthermore, for plasma coagulation tests, the activated partial thromboplastin time and thrombin time were prolonged and depended on the heparinfunction. The modified exhibited excellent stability and anticoagulant activity, and efficiently accelerated endothelialization and anticoagulation. This work has potential application for the design of coronary artery stent surfaces tailored for vascular cell behavior.

PEG-b-PCL polymeric nano-micelle inhibits vascular angiogenesis by activating p53-dependent apoptosis in zebrafish.

Micro/nanoparticles could cause adverse effects on cardiovascular system and increase the risk for cardiovascular disease-related events. Nanoparticles prepared from poly(ethylene glycol) (PEG)-b-poly(ε-caprolactone) (PCL), namely PEG-b-PCL, a widely studied biodegradable copolymer, are promising carriers for the drug delivery systems. However, it is unknown whether polymeric PEG-b-PCL nano-micelles give rise to potential complications of the cardiovascular system. Zebrafish were used as an in vivo model to evaluate the effects of PEG-b-PCL nano-micelle on cardiovascular development. The results showed that PEG-b-PCL nano-micelle caused embryo mortality as well as embryonic and larval malformations in a dose-dependent manner. To determine PEG-b-PCL nano-micelle effects on embryonic angiogenesis, a critical process in zebrafish cardiovascular development, growth of intersegmental vessels (ISVs) and caudal vessels (CVs) in flk1-GFP transgenic zebrafish embryos using fluorescent stereomicroscopy were examined. The expression of fetal liver kinase 1 (flk1), an angiogenic factor, by real-time quantitative polymerase chain reaction (qPCR) and in situ whole-mount hybridization were also analyzed. PEG-b-PCL nano-micelle decreased growth of ISVs and CVs, as well as reduced flk1 expression in a concentration-dependent manner. Parallel to the inhibitory effects on angiogenesis, PEG-b-PCL nano-micelle exposure upregulated p53 pro-apoptotic pathway and induced cellular apoptosis in angiogenic regions by qPCR and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) apoptosis assay. This study further showed that inhibiting p53 activity, either by pharmacological inhibitor or RNA interference, could abrogate the apoptosis and angiogenic defects caused by PEG-b-PCL nano-micelles, indicating that PEG-b-PCL nano-micelle inhibits angiogenesis by activating p53-mediated apoptosis. This study indicates that polymeric PEG-b-PCL nano-micelle could pose potential hazards to cardiovascular development.