H–X (X = H, CH₃, CH₂F, CHF₂, CF₃, and SiH₃) Bond Activation by Criegee Intermediates: A Theoretical Perspective

Using theoretical calculations and Born–Oppenheimer molecular dynamics simulations, it is shown here that Criegee intermediate, which is principally produced in the olefin ozonolysis, can activate H–X (X = H, CH₃, CH₂F, CHF₂, CF₃, and SiH₃) under mild conditions, a reaction that has long been known for transition metals. The zwitterionic electronic structure of Criegee intermediate makes it an interesting metal-free system for activating enthalpically strong small molecules such as H₂, methane, silanes, and boranes. The calculated barriers for the H₂ or SiH₄ reactions of CH₂OO are significantly lower than those for the CH₄ or its fluorinated analogue reactions. The distortion-interaction energy model is found to be successful in explaining the differential reactivity of the Criegee intermediate toward activating the various H–X bonds. The canonical transition state theory calculations suggest that the CH₂OO–H₂ reaction is 9–11 orders of magnitude faster than the CH₂OO–CH₄ reaction over the 200–300 K temperature range. Considering that the laboratory synthesis of Criegee intermediate is now feasible, these findings may open up new vistas in the metal-free activation of small molecules

Reactions of Criegee Intermediates with Non-Water Greenhouse Gases: Implications for Metal Free Chemical Fixation of Carbon Dioxide

High-level theoretical calculations suggest that a Criegee intermediate preferably interacts with carbon dioxide compared to two other greenhouse gases, nitrous oxide and methane. The results also suggest that the interaction between Criegee intermediates and carbon dioxide involves a cycloaddition reaction, which results in the formation of a cyclic carbonate-type adduct with a barrier of 6.0–14.0 kcal/mol. These results are in contrast to a previous assumption that the reaction occurs barrierlessly. The subsequent decomposition of the cyclic adduct into formic acid and carbon dioxide follows both concerted and stepwise mechanisms. The latter mechanism has been overlooked previously. Under formic acid catalysis, the concerted decomposition of the cyclic carbonate may be favored under tropospheric conditions. Considering that there is a strong nexus between carbon dioxide levels in the atmosphere and global warming, the high reactivity of Criegee intermediates could be utilized for designing efficient carbon capture technologies

A Coupled Cluster Investigation of SNO Radical Isomers and Their Reactions with Hydrogen Atom: Insight into Structures, Conformers, Barriers, and Energetics

High-level coupled cluster theory with single and double excitation, and including a perturbative triples correction (CCSD­(T)) method and a series of Dunning’s augmented correlation consistent basis sets, aug-cc-pVXZ (X = D, T, Q, and 5) was applied to examine the conformational landscape of SNO radical system. The basis set has an important effect on the relative stability of SNO radical isomers; that is, at the CCSD­(T)/aug-cc-pV5Z level of theory, the NSO radical is the most stable member of SNO radical family. This is in contrast to previous density functional theory prediction suggesting SNO radical is the most stable isomer. The CCSD­(T)/aug-cc-pV5Z//CCSD­(T)/aug-cc-pVTZ results suggest that the reaction between SNO radical isomers and hydrogen atom result in the formation of their [H,N,S,O] hydrides with HNSO hydrides being the most stable ones. Subsequently, these hydrides could decompose either into SH and NO radicals or into SN and OH radicals. The former pathway is preferred due to relatively lower barriers and favorable reaction energies. The results from our calculations support the role of S-nitrosothiols as NO shuttling agent in signaling-pathways and as a new source of HS and NO radicals in the lower atmosphere of Venus. Overall, these high-level calculations will play an important role in improving our understanding about the chemistry of S-nitrosothiols that has recently become a topic of interest because of their involvement in biochemical pathways and planetary processes

The Role of Catalysis in Alkanediol Decomposition: Implications for General Detection of Alkanediols and Their Formation in the Atmosphere

Quantum chemical calculations have been carried out to investigate the gas-phase structure, stability, and decomposition of the two simplest alkanediols, methanediol and 1,1-ethanediol, in the presence of various catalysts. Three different conformers for monomeric alkanediols namely <i>cis</i>, <i>trans</i>, and <i>trans</i>′ were considered. The calculations reveal that alkanediols may exist not only as monomers but also as dimers that have high binding energies of 7–11 kcal/mol due to hydrogen bonding among the oxygenate functionalities. Some of these dimers have high dipole moments and, thus, may be more easily detected experimentally than the monomers of alkanediols. For the decomposition of alkanediols, the calculations dominantly favor dehydration over dehydrogenation. The relatively low barrier for the decomposition of 1,1-ethanediol suggests that the structure of an alkanediol plays a role in its decomposition. Though the dehydration of alkanediols with or without water catalyst involves large barriers, organic and inorganic acids, the hydroperoxyl radical catalytically influences the reaction to such an extent that the dehydration reaction either involves significantly reduced barriers or essentially becomes barrierless. Considering that alkanediols contain hydroxyl groups and their dimers have high binding energies, the gas-phase dehydration may be self-driven. Because acids are present in significant amounts in the troposphere, results suggest that diol dehydration may be facile under atmospheric conditions

HIPdb statistics: a) Targets, b) Cell lines, c) Peptide length, d) Amino acid composition.

<p>HIPdb statistics: a) Targets, b) Cell lines, c) Peptide length, d) Amino acid composition.</p

Performance of SVM by employing distinct peptide properties during 10-fold cross validation using negative dataset from UniProt.

<p>AAC, Amino Acid Composition; DPC, Di Peptide Composition; N5AAC, Amino Acid Composition of 5 N-terminal residues; C5AAC, Amino Acid Composition of 5 C-terminal residues; N5Bin, Binary pattern of 5 N-terminal residues; C5Bin, Binary pattern of 5 C-terminal residues; N5C5Bin, Binary pattern of 5 N and 5 C terminal residues; Physico, top 10 physicochemical properties; SVM, Support Vector Machine; MCC, Mathew’s correlation coefficient; AUC, Area Under the curve;</p><p>Performance of SVM by employing distinct peptide properties during 10-fold cross validation using negative dataset from UniProt.</p

Amino acid compositional comparison of quorum sensing peptides (QSPs), antiviral peptides (AVPs), cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs) with overall amino acids composition in Swiss-Prot.

<p>Amino acid compositional comparison of quorum sensing peptides (QSPs), antiviral peptides (AVPs), cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs) with overall amino acids composition in Swiss-Prot.</p

Amino acid compositional comparison of quorum sensing peptides (QSPs) and non-quorum sensing peptides (non-QSPs).

<p>Amino acid compositional comparison of quorum sensing peptides (QSPs) and non-quorum sensing peptides (non-QSPs).</p

Hexaphenylbenzene-Stabilized Luminescent Silver Nanoclusters: A Potential Catalytic System for the Cycloaddition of Terminal Alkynes with Isocyanides

A hexaphenylbenzene (HPB)-based derivative bearing thiol groups has been designed and synthesized that undergoes aggregation-induced emission enhancement in mixed aqueous media to form rodlike fluorescent aggregates. These rodlike aggregates behave as a “not quenched” probe for the detection of silver ions and further act as reactors and stabilizers for reducing-agent-free preparation of blue luminescent silver nanoclusters at room temperature. The utilization of fluorescent supramolecular aggregates for the preparation of Ag NCs in mixed aqueous media is unprecedented in the literature. Moreover, the wet chemical method that we are reporting in the present paper for the preparation of luminescent silver nanoclusters is better than the other methods reported in the literature. Further, these in situ generated Ag NCs showed exceptional catalytic activity in the preparation of pyrroles involving cocyclization of isocyanides and terminal alkynes. Interestingly, the catalytic efficiency of in situ generated Ag NCs was found to be better than the other catalytic systems reported in the literature

Amino acid compositional analysis of Quorum sensing peptides (QSPs).

<p>Comparison of percent amino acid composition of QSPs with their 5 N-terminal and 5 C-terminal residues.</p