Prebiotic Nucleoside Synthesis: The Selectivity of Simplicity

Ever since the discovery of nucleic acids 150 years ago,^[1] major achievements have been made in understanding and decrypting the fascinating scientific questions of the genetic code.^[2] However, the most fundamental question about the origin and the evolution of the genetic code remains a mystery. How did nature manage to build up such intriguingly complex molecules able to encode structure and function from simple building blocks? What conditions were required? How could the precursors survive the unhostile environment of early Earth? Over the past decades, promising synthetic concepts were proposed providing clarity in the field of prebiotic nucleic acid research. In this Minireview, we show the current status and various approaches to answer these fascinating questions.     

Targeting the Rich Conformational Landscape of N-Allylmethylamine Using Rotational Spectroscopy and Quantum Mechanical Calculations

The highly variable conformational landscape of N-allylmethylamine (AMA) was investigated using Fourier transform microwave spectroscopy aided by high-level theoretical calculations to understand the energy relationship governing the interconversion between nine stable conformers. Spectroscopically, transitions belonging to four low energy conformers were identified and their hyperfine patterns owing to the ¹⁴N quadrupolar nucleus were unambiguously resolved. The rotational spectrum of the global minimum geometry, conformer I, shows an additional splitting associated with a tunneling motion through an energy barrier interconnecting its enantiomeric forms. A two-step tunneling trajectory is proposed by finding transition state structures corresponding to the allyl torsion and NH inversion. Natural bond orbital and non-covalent interaction analyses reveal that an interplay between steric and hyperconjugative effects rules the conformational preferences of AMA.     

The spanning trees forced by the path and the star

A set S of trees of order n forces a tree T if every graph having each tree in S as a spanning tree must also have T as a spanning tree. A spanning tree forcing set for order n that forces every tree of order n. A spanning-tree forcing set S is a test set for panarboreal graphs, since a graph of order n is panarboreal if and only if it has all of the trees in S as spanning trees. For each positive integer n ≠ 1, the star belongs to every spanning tree forcing set for order n. The main results of this paper are a proof that the path belongs to every spanning-tree forcing set for each order n ∉ {1, 6, 7, 8} and a computationally tractable characterization of the trees of order n ≥ 15 forced by the path and the star. Corollaries of those results include a construction of many trees that do not belong to any minimal spanning tree forcing set for orders n ≥ 15 and a proof that the following related decision problem is NP-complete: an instance is a pair (G, T) consisting of a graph G of order n and maximum degree n - 1 with a hamiltonian path, and a tree T of order n; the problem is to determine whether T is a spanning tree of G. © 1996 John Wiley & Sons, Inc.     

General Method to Increase Carboxylic Acid Content on Nanodiamonds

Carboxylic acid is a commonly utilized functional group for covalent surface conjugation of carbon nanoparticles that is typically generated by acid oxidation. However, acid oxidation generates additional oxygen containing groups, including epoxides, ketones, aldehydes, lactones, and alcohols. We present a method to specifically enrich the carboxylic acid content on fluorescent nanodiamond (FND) surfaces. Lithium aluminum hydride is used to reduce oxygen containing surface groups to alcohols. The alcohols are then converted to carboxylic acids through a rhodium (II) acetate catalyzed carbene insertion reaction with tert–butyl diazoacetate and subsequent ester cleavage with trifluoroacetic acid. This carboxylic acid enrichment process significantly enhanced nanodiamond homogeneity and improved the efficiency of functionalizing the FND surface. Biotin functionalized fluorescent nanodiamonds were demonstrated to be robust and stable single-molecule fluorescence and optical trapping probes.     

MNDO calculations on boron–nitrogen derivatives of nonbenzenoid aromatics: I. The two fully boron–nitrogen-alternating isomers of “inorganic azulene”

Modified neglect of diatomic overlap (MNDO) calculations have been used to investigate the ground state properties of the two fully boron-nitrogen-alternating isomers of “inorganic azulene”: 1,3,4,6,8-pentaaza-2,3a, 5,7, 8a-pentaboraazulene ( 1 , 1,3,4,6,8-PAPBAZ) and 2,3a,5,7,8a-pentaaza-1,3,4,6,8-pentaboraazulene ( 2 , 2,3a,5,7,8a-PAPBAZ). Both molecules optimize to planar structures, have exothermic heats of formation (−194.4 kcal/mol and −161.4 kcal/mol, respectively), and exhibit some bond delocalization. The relationship of these two PAPBAZ isomers to their organic parent molecule, azulene, is discussed.     

Health-Promoting Properties of Medicinal Mushrooms and Their Bioactive Compounds for the COVID-19 Era—An Appraisal: Do the Pro-Health Claims Measure Up?

Many mushroom species are consumed as food, while significant numbers are also utilised medicinally. Mushrooms are rich in nutrients and bioactive compounds. A growing body of in vitro, in vivo, and human research has revealed their therapeutic potentials, which include such properties as anti-pathogenic, antioxidant, anti-inflammatory, immunomodulatory, gut microbiota enhancement, and angiotensin-converting enzyme 2 specificity. The uses of medicinal mushrooms (MMs) as extracts in nutraceuticals and other functional food and health products are burgeoning. COVID-19 presents an opportunity to consider how, and if, specific MM compounds might be utilised therapeutically to mitigate associated risk factors, reduce disease severity, and support recovery. As vaccines become a mainstay, MMs may have the potential as an adjunct therapy to enhance immunity. In the context of COVID-19, this review explores current research about MMs to identify the key properties claimed to confer health benefits. Considered also are barriers or limitations that may impact general recommendations on MMs as therapy. It is contended that the extraction method used to isolate bioactive compounds must be a primary consideration for efficacious targeting of physiological endpoints. Mushrooms commonly available for culinary use and obtainable as a dietary supplement for medicinal purposes are included in this review. Specific properties related to these mushrooms have been considered due to their potential protective and mediating effects on human exposure to the SARS CoV-2 virus and the ensuing COVID-19 disease processes.     

Ultrasonic and Raman Scattering Spectroscopy of Zinc Thiocyanate Complexes in Water at 25<Superscript>∘</Superscript>C: Kinetics of Complex Formation Determined by Multivariate Analysis

Advances have been made recently in broadening the accessible ultrasonic absorption frequency range and improving the detectability of minor species present in solution using Raman spectroscopy. Development of chemometric techniques in these areas needs to keep pace with the improvement of these experimental methods. Refinements in the analysis of ultrasonic and Raman data based on multivariable least squares and factor analysis, respectively, are examined to investigate the kinetics of zinc thiocyanate complex formation in water. Analysis of ultrasonic absorption relaxation spectra verified that the observed process in aqueous Zn(SCN)₂ involves substitution of water from the first coordination shell of Zn²⁺. Use of a multivariable least-squares error surface is described that enhances the reliability of assigned frequencies of ultrasonic absorption maxima. Factor analysis of Raman scattering data provided direct evidence that at least four complex species, such as Zn(SCN)⁺ and Zn(SCN)₂, are simultaneously present in the aqueous zinc thiocyanate solutions.     

Structural characterization of intact proteins is enhanced by prevalent fragmentation pathways rarely observed for peptides

While collisionally activated dissociation (CAD) pathways for peptides are well characterized, those of intact proteins are not. We systematically assigned CAD product ions of ubiquitin, myoglobin, and bovine serum albumin generated using high-yield, in-source fragmentation. Assignment of >98% of hundreds of product ions implies that the fragmentation pathways described are representative of the major pathways. Protein dissociation mechanisms were found to be modulated by both source declustering potential and precursor ion charge state. Like peptides, higher charge states of proteins fragmented at lower energies next to Pro, via mobile protons, while lower charge states fragmented at higher energies after Asp and Glu, via localized protons. Unlike peptides, however, predominant fragmentation channels of proteins occurred at intermediate charge states via non-canonical mechanisms and produced extensive internal fragmentation. The non-canonical mechanisms include prominent cleavages C-terminal to Pro and Asn, and N-terminal to Ile, Leu, and Ser; these cleavages, along with internal fragments, led to a 45% increase in sequence coverage, improving the specificity of top-down protein identification. Three applications take advantage of the different mechanisms of protein fragmentation. First, modulation of declustering potential selectively fragments different charge states, allowing the source region to be used as the first stage of a low-resolution tandem mass spectrometer, facilitating pseudo-MS3 of product ions with known parent charge states. Second, development and integration of automated modulation of ion funnel declustering potential allows users access to a particular fragmentation mechanism, yielding facile cleavage on a liquid chromatography timescale. Third, augmentation of a top-down search engine improved protein characterization.     

The Direct Synthesis of Hydrogen Peroxide Using Platinum‐Promoted Gold–Palladium Catalysts

The direct synthesis of hydrogen peroxide offers a potentially green route to the production of this important commodity chemical. Early studies showed that Pd is a suitable catalyst, but recent work indicated that the addition of Au enhances the activity and selectivity significantly. The addition of a third metal using impregnation as a facile preparation method was thus investigated. The addition of a small amount of Pt to a CeO₂‐supported AuPd (weight ratio of 1:1) catalyst significantly enhanced the activity in the direct synthesis of H₂O₂ and decreased the non‐desired over‐hydrogenation and decomposition reactions. The addition of Pt to the AuPd nanoparticles influenced the surface composition, thus leading to the marked effects that were observed on the catalytic formation of hydrogen peroxide. In addition, an experimental approach that can help to identify the optimal nominal ternary alloy compositions for this reaction is demonstrated.