Solution structure of a peptide nucleic acid duplex from NMR data: features and limitations

This paper describes the results of a 1D and 2D NMR spectroscopy study of a palindromic 8-base pair PNA duplex GGCATGCC in H2O and H2O-D2O solutions. The (1)H NMR peaks have been assigned for most of the protons of the six central base pairs, as well as for several amide protons of the backbone. The resulting 36 interbase and base-backbone distance restraints were used together with Watson-Crick restraints to generate the PNA duplex structure in the course of 10 independent simulated annealing runs followed by restrained molecular dynamics (MD) simulations in explicit water. The resulting PNA structures correspond to a P-type helix with helical parameters close to those observed in the crystal structures of PNA. Based on the current limited number of restraints obtained from NMR spectra, alternative structures obtained by MD from starting PNA models based on DNA cannot be ruled out and are also discussed.     

The development of an immobilized enzyme reactor containing glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma cruzi: the effect of species' specific differences on the immobilization

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) plays an important role in the life cycle of the Trypanosoma cruzi, and an immobilized enzyme reactor (IMER) has been developed for use in the on-line screening for GAPDH inhibitors. An IMER containing human GAPDH has been previously reported; however, these conditions produced a T. cruzi GAPDH-IMER with poor activity and stability. The factors affecting the stability of the human and T. cruzi GAPDHs in the immobilization process and the influence of pH and buffer type on the stability and activity of the IMERs have been investigated. The resulting T. cruzi GAPDH-IMER was coupled to an analytical octyl column, which was used to achieve chromatographic separation of NAD(+) from NADH. The production of NADH stimulated by d-glyceraldehyde-3-phosphate was used to investigate the activity and kinetic parameters of the immobilized T. cruzi GAPDH. The Michaelis-Menten constant (K(m)) values determined for d-glyceraldehyde-3-phosphate and NAD(+) were K(m) = 0.5 +/- 0.05 mM and 0.648 +/- 0.08 mM, respectively, which were consistent with the values obtained using the non-immobilized enzyme.     

Modern automated microextraction procedures for bioanalytical,environmental, and food analyses

Sample preparation frequently is considered the most critical stage of the analytical workflow. It affects the analytical throughput and costs; moreover, it is the primary source of error and possible sample contamination. To increase efficiency, productivity, and reliability, while minimizing costs and environmental impacts, miniaturization and automation of sample preparation are necessary. Nowadays, several types of liquid-phase and solid-phase microextractions are available, as well as different automatization strategies. Thus, this review summarizes recent developments in automated microextractions coupled with liquid chromatography, from 2016 to 2022. Therefore, outstanding technologies and their main outcomes, as well as miniaturization and automation of sample preparation, are critically analyzed. Focus is given to main microextraction automation strategies, such as flow techniques, robotic systems, and column-switching approaches, reviewing their applications to the determination of small organic molecules in biological, environmental, and food/beverage samples.     

New Extensions of Popoviciu’s Inequality

Popoviciu’s inequality is extended to the framework of h-convexity and also to convexity with respect to a pair of quasi-arithmetic means. Several applications are included.

     

Dependency of particle sizes and colloidal stability of polyelectrolyte complex dispersions on polyanion structure and preparation mode investigated by dynamic light scattering and atomic force microscopy

Polyelectrolyte complex (PEC) dispersions were prepared by controlled mixing of three random copolymers of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) with either t-butyl acrylamide (TBA) [P(AMPS54-co-TBA46) and P(AMPS37-co-TBA63)] or methyl methacrylate (MM) [P(AMPS52-co-MM48)] with an ionene-type polycation, containing 95 mol % N,N-dimethyl-2-hydroxypropyleneammonium chloride repeat units (PCA5), with their structural characteristics being deeply investigated by dynamic light scattering (DLS) and atomic force microscopy (AFM). Shape, size, and polydispersity of the PEC dispersions were directly observed by AFM as a function of polyanion structure, the ratio between charges, n-/n+, and the titrant addition rate (TAR). The particle sizes increased and the colloidal stability decreased with the increase of the nonionic comonomer content and with the decrease of TAR. It was demonstrated that the medium particle sizes of the complex nanoparticles adsorbed on silicon wafers measured by AFM, in the dry state, were close but always lower than those measured by DLS, both before and after the complex stoichiometry.     

Carbon nanotubes for electrochemical biosensing

The aim of this review is to summarize the most relevant contributions in the development of electrochemical (bio)sensors based on carbon nanotubes in the last years.Since the first application of carbon nanotubes in the preparation of an electrochemical sensor, an increasing number of publications involving carbon nanotubes-based sensors have been reported, demonstrating that the particular structure of carbon nanotubes and their unique properties make them a very attractive material for the design of electrochemical biosensors.The advantages of carbon nanotubes to promote different electron transfer reactions, in special those related to biomolecules; the different strategies for constructing carbon nanotubes-based electrochemical sensors, their analytical performance and future prospects are discussed in this article.     

H2O nucleation around Au+

First principles electronic structure calculations have been carried out to investigate the ground state geometry, electronic structure, and the binding energy of [Au(H2O)n]+ clusters containing up to 10 H2O molecules. It is shown that the first coordination shell of Au+ contains two H2O molecules forming a H2O-Au+-H2O structure with C2 symmetry. Subsequent H2O molecules bind to the previous H2O molecules forming stable and fairly rigid rings, each composed of 4 H2O molecules, and leading to a dumbbell structure at [Au(H2O)8]+. The 9th and the 10th H2O molecules occupy locations above the Au+ cation mainly bonded to one H2O from each ring, leading to structures where the side rings are partially distorted and forming structures that resemble droplet formation around the Au+ cation. The investigations highlight quantum effects in nucleation at small sizes and provide a microscopic understanding of the observed incremental binding energy deduced from collision induced dissociation that indicates that [Au(H2O)n]+ clusters with 7-10 H2O molecules have comparable binding energy. The charge on the Au+ is shown to migrate to the outside H2O molecules, suggesting an interesting screening phenomenon.     

Intramolecular chalcogen-tin interactions in (o-MeE-C6H4)CH2SnPh3-nCln (E = S, O; n = 0, 1, 2), characterized by X-ray diffraction and 119Sn solution and solid-state NMR

Organotin(IV) compounds of the type (o-MeE-C6H4)CH2SnPh3-nCln were synthesized, E = O, n = 0 (1), n = 1 (2), n = 2 (3) and E = S, n = 0 (4), n = 1 (5), n = 2 (6). The complexes exhibit significant trigonal bipyramidal pentacoordination at tin as a consequence of intramolecular Sn-O (1-3) and Sn-S (4-6) interactions upon substitution of the phenyl groups by chloro groups. The intramolecular Sn-O distances in 1, 2, and 3 are 83%, 75%, and 79% of the sum of the van der Waals radii. The equivalent Sn-S values for 4, 5, and 6 are 90%, 73%, and 71%, respectively. The geometry of compound 3 is complicated by intermolecular dimerization via bridging chlorines creating a distorted octahedral geometry at tin. The related dichloro sulfur compound 6 also exhibits an intermolecular association in the form of Sn-Cl-H hydrogen bonding leading to a polymeric structure in the solid state. CPMAS 119Sn NMR spectroscopy suggests that the intramolecular Sn-E interactions persist in solution and also facilitated the discovery of a new crystalline form of 4, 4', that contains a Sn-S distance which is 95% the sum of the van der Waals radii.     

Pharmacological and Therapeutic Potential of Myristicin: A Literature Review

Natural products have been used by humanity for many centuries to treat various illnesses and with the advancement of technology, it became possible to isolate the substances responsible for the beneficial effects of these products, as well as to understand their mechanisms. In this context, myristicin, a substance of natural origin, has shown several promising activities in a large number of in vitro and in vivo studies carried out. This molecule is found in plants such as nutmeg, parsley, carrots, peppers, and several species endemic to the Asian continent. The purpose of this review article is to discuss data published in the last 10 years at Pubmed, Lilacs and Scielo databases, reporting beneficial effects, toxicity and promising data of myristicin for its future use in medicine. From 94 articles found in the literature, 68 were included. Exclusion criteria took into account articles whose tested extracts did not have myristicin as one of the major compounds.     

Semisynthetic Derivatives of Selected Amaryllidaceae Alkaloids as a New Class of Antimycobacterial Agents

The search for novel antimycobacterial drugs is a matter of urgency, since tuberculosis is still one of the top ten causes of death from a single infectious agent, killing more than 1.4 million people worldwide each year. Nine Amaryllidaceae alkaloids (AAs) of various structural types have been screened for their antimycobacterial activity. Unfortunately, all were considered inactive, and thus a pilot series of aromatic esters of galanthamine, 3-O-methylpancracine, vittatine and maritidine were synthesized to increase biological activity. The semisynthetic derivatives of AAs were screened for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Ra and two other mycobacterial strains (M. aurum, M. smegmatis) using a modified Microplate Alamar Blue Assay. The most active compounds were also studied for their in vitro hepatotoxicity on the hepatocellular carcinoma cell line HepG2. In general, the derivatization of the original AAs was associated with a significant increase in antimycobacterial activity. Several pilot derivatives were identified as compounds with micromolar MICs against M. tuberculosis H37Ra. Two derivatives of galanthamine, 1i and 1r, were selected for further structure optimalization to increase the selectivity index.