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1.
Chemosphere ; 287(Pt 1): 131988, 2022 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-34523438

RESUMO

Alkali metals have been known for their intercalation properties and can be employed for the separation of stacking in sheet-like materials. In this work, alkali metals (Na, K, Rb and Cs) have been systematically incorporated in varying concentrations in g-C3N4 sheets and their effect on resulting optical, surface and photocatalytic properties have been explored in detail. It was observed that the optical, electronic and surface properties of g-C3N4 were altered upon the incorporation of different alkali metal ions. The band gap and specific surface area of resulting materials were decreased as compared to the pristine g-C3N4. In addition, the alkali metal incorporation in g-C3N4 sheets showed the formation of cyanide groups and nitrogen vacancies in the resulted materials. Further, the photocatalytic activity of g-C3N4 and alkali metal incorporated g-C3N4 was calculated by studying the degradation of acid red 94 dye under visible light irradiation. It was observed that the photocatalytic activity of pristine g-C3N4 sheets was decreased with an increase in the concentration of alkali salt used during the synthesis of alkali metal incorporated g-C3N4. This decrease in the activity could arise due to the decreased surface area, detrimental amount of nitrogen vacancies and high concentration of alkali metal ions incorporated in the structural framework of g-C3N4 sheets. This work provides a unique example of the adverse effect of alkali metal ions on photocatalytic activity of g-C3N4 and paves future directions for the improvement of the performance of g-C3N4 based materials.


Assuntos
Poluentes Ambientais , Metais Alcalinos , Catálise , Grafite , Íons , Compostos de Nitrogênio
2.
Talanta ; 234: 122674, 2021 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-34364474

RESUMO

Ambient ionization of glycans is simply and efficiently achieved by spraying from an alkali metal salt-impregnated paper surface. Monosaccharides, oligosaccharides and ring glycans easily form abundant alkali metal adduct ions, and give simple and clean high-quality mass spectra. The enhancement is specific for glycans, compared to a wide variety of non-glycan compounds present in a matrix. In addition, molecular weight of unknown glycans can be further identified based on the ion mass difference of various alkali metal adduct ions from a certain compound when using a mixed salt-impregnated paper containing five cation salts. Successful determination of glycans and glycoconjugates in plant extracts, honey, blood and urine demonstrates the practicability of this approach to complicated matrices, especially biological matrices.


Assuntos
Metais Alcalinos , Polissacarídeos , Peso Molecular , Oligossacarídeos , Espectrometria de Massas por Ionização por Electrospray , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz
3.
Chem Rec ; 21(8): 1898-1911, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-34197009

RESUMO

Biodegradable polyesters such as poly(ϵ-caprolactone) (PCL) and poly(lactic acid) (PLA) have been considered for use in several areas, such as drug delivery devices, sutures, tissue engineering, and GBR membranes, due to its bio-renewability, biodegradability, and biocompatibility. Several synthetic techniques for the preparation of polyesters have been reported in the literature, amongst which the ring-opening polymerization (ROP) of cyclic esters is the most efficient. A convenient approach to access iso-selective PLAs is polymerization of racemic lactide (rac-LA), which shows excellent stereoregularity without the need for costly chiral auxiliaries or ligands. In this personal account, we review a series of methods that have been practiced to the synthesis of biodegradable polyesters from various cyclic monomers using alkali and alkaline earth metal complexes as efficient catalysts.


Assuntos
Complexos de Coordenação/química , Metais Alcalinos/química , Metais Alcalinoterrosos/química , Poliésteres/química , Boranos/química , Catálise , Calcogênios/química , Ciclização , Ésteres/química , Poliésteres/síntese química
4.
J Mol Graph Model ; 106: 107935, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-34034048

RESUMO

Finding new materials with exceptionally large nonlinear optical response is an interesting and challenging avenue for scientific research. Here, we report the alkali metal doped Zn12O12 nanocages as inorganic electrides with excellent nonlinear optical response. Density functional theory calculations have been performed for geometric, electronic and nonlinear optical response of exo- and endohedrally alkali metal doped Zn12O12 nanoclusters. For exohedral doping, all different possible doping sites are considered for decoration of alkali metal on the nanocage. The electride nature of the complexes is highly dependent on the position of alkali metal doping. All exohedral complexes except for alkali metal doping on six membered ring (r6) are electride in nature, as revealed from frontier molecular orbital analysis. Interaction energies reveal that all doped nanoclusters except endo-K@Zn12O12 are thermodynamically stable. The exothermic encapsulation of alkali metals in Zn12O12 nanocages is in marked contradiction with other inorganic fullerenes where encapsulation is an endothermic process. The barriers for boundary crossing are also evaluated in order study the interconversion of exo- and endohedral complexes. Doping of alkali metal significantly influences the properties of nanocages. HOMO-LUMO (H-L) gap is reduced significantly whereas hyperpolarizability is increased several orders of magnitude. The NLO response of exohedrally doped complexes is higher than the corresponding endohedral complexes, which is in mark contradiction with the behavior of phosphide or nitride nanocages. The highest first hyperpolarizability of 1.0 × 105 au is calculated for K@r6-Zn12O12 complex. Third order NLO response of these complexes is calculated and compared with the best systems reported in the literature at the same level of theory.


Assuntos
Fulerenos , Metais Alcalinos , Eletrônica , Zinco
5.
J Phys Chem A ; 125(15): 3146-3158, 2021 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-33830783

RESUMO

Flavin compounds are of great interest in biochemistry because of their diverse functions in catalytic and photochemical processes. The intrinsic optical properties of flavins depend sensitively on their environment such as complexation with metal ions. Herein, we characterize the interaction of alkali metal ions (M+) with riboflavin (RF, vitamin B2). To this end, two different experimental spectroscopic approaches are employed to determine the structural, vibrational, energetic, and optical properties of M+RF complexes by comparison with density functional theory (DFT) calculations at the PBE0/cc-pVDZ level. First, infrared multiple photon dissociation (IRMPD) spectra recorded at room temperature demonstrate that M+ binds to one of the two available nucleophilic carbonyl groups (CO2, CO4) of RF, denoted O2 and O4+ isomers, as revealed by characteristic shifts of the CO stretch modes upon metalation. Second, the optical spectrum of K+RF is recorded between 428 and 529 nm in a cryogenic ion trap held at 6 K by visible photodissociation (VISPD). Analysis of the VISPD spectrum by time-dependent DFT calculations coupled to Franck-Condon simulations demonstrates that in fact only the O2 isomer of M+RF is formed by electrospray ionization, while the spectroscopic signatures of the O4+ isomer are absent. The VISPD spectrum is attributed to the S1 ← S0 (ππ*) transition of the O2 isomer, which is calculated to be much more stable than the O4+ isomer because of additional multiple interactions of M+ with the OH groups of the ribityl (sugar) side chain attached at N10 of RF. In contrast, there is no evidence for the presence of the O4+ isomer, in which M+ forms a chelate complex, with M+ binding to both O4 and N5. A comparison between RF (ribityl at N10) and lumiflavin (LF and CH3 at N10) reveals the drastic effects of the side chain on the structural, energetic, and optical properties of the flavin interaction with metal ions. While for M+LF the O2 and O4+ isomers are close in energy and both observed experimentally, for M+RF the O2 isomer is strongly favored due to the additional interaction with the side chain. Although the S1 energies of M+RF(O2) and M+LF(O2) are quite similar, because the ππ* transition is localized on the same isoalloxazine chromophore for both flavins, the vibrational structures are strongly different because the soft bending potential for the M+···flavin interaction is strongly affected by the ribityl side chain at N10. In contrast to H+RF, which prefers protonation at N1, steric repulsion of the larger M+ ions with the ribityl side chain prevents metalation at N1, leading to the formation of the O2 global minimum.


Assuntos
Metais Alcalinos/química , Riboflavina/química , Teoria da Densidade Funcional , Íons/química , Espectrofotometria Infravermelho
6.
Chemistry ; 27(37): 9514-9518, 2021 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-33909296

RESUMO

The synthesis of benzoborole dianions by alkali metal reduction of BN-naphthalene derivatives via a ring-contraction strategy has been developed. Reduction of 1-alkynyl 2,1-benzazaborine 1 a in Et2 O led to the elimination of alkynyllithium with the formation of 1-amino-1-benzoborole trilithium salt 2 a, whereas reduction of 1-phenyl 2,1-benzazaborine 1 c in THF yielded 1-phenyl-1-benzoborole dilithium salt 2 c with the elimination of ArNHLi. The trilithium and dilithium salts 2 a and 2 c have been fully characterized. Treatment of trilithium salt 2 a with Et3 NHCl led to the selective protonation of the amino lithium to afford the dilithium salt 2 aH, which could be cleanly oxidized to 1-amino-1-benzoborole 3 in an excellent yield. Reaction of 1-phenyl-1-benzoborole dilithium salt 2 c with MeI yielded the lithium borate 4 c, which is luminescent both in solution and in the solid state.


Assuntos
Metais Alcalinos , Naftalenos , Lítio
7.
Phys Chem Chem Phys ; 23(11): 6783-6790, 2021 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-33720244

RESUMO

Cryogenic ion spectroscopy was used to characterize adenine complexes containing alkali metal cations (M+A, M = Cs, Rb, K, Na, and Li) produced by electrospray ionization. The ultraviolet (UV) photodissociation spectra of the complexes stored in a cryogenic ion trap exhibited well-resolved vibronic bands near their origin bands of the S0-S1 transition. The UV-UV hole-burning and infrared ion-dip spectra showed that all the M+A ions in the ion trap were single isomers of M+A7a, where the M+ ion was not bound to canonical 9H-adenine (A9) but bound to a rare tautomer, 7H-adenine (A7). Density functional theory calculations showed lower tautomerization barriers for M+A9 than for bare A9 in aqueous solution. We suggest that M+ ions not only play a catalytic role in the tautomerization of A9 to A7 but also increase the tautomerization yield by forming stable M+A7a isomers.


Assuntos
Adenina/química , Complexos de Coordenação/química , Metais Alcalinos/química , Espectrofotometria Infravermelho , Teoria da Densidade Funcional , Água/química
8.
Molecules ; 26(5)2021 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-33652943

RESUMO

An implicit account of the solvent effect can be carried out using traditional static quantum chemistry calculations by applying an external electric field to the studied molecular system. This approach allows one to distinguish between the effects of the macroscopic reaction field of the solvent and specific solute-solvent interactions. In this study, we report on the dependence of the simulation results on the use of the polarizable continuum approximation and on the importance of the solvent effect in nonpolar solvents. The latter was demonstrated using experimental data on tautomeric equilibria between the pyridone and hydroxypyridine forms of 2,6-di-tert-butyl-4-hydroxy-pyridine in cyclohexane and chloroform.


Assuntos
Cicloexanos/química , Metais Alcalinos/química , Piridinas/química , Solventes/química , Clorofórmio , Simulação por Computador , Eletricidade , Modelos Moleculares , Teoria Quântica , Soluções/química , Termodinâmica
9.
Macromol Rapid Commun ; 42(9): e2000746, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-33644940

RESUMO

The recovery of lithium from global water resources continues to be challenging due to interfering metal ions with similar solution properties. Hence, a lithium-selective diblock copolymer system containing crown ethers (CEs) is developed. A polystyrene-block-poly(methacrylic acid) diblock copolymer is synthesized first via a one-pot solution-emulsion reversible addition-fragmentation chain transfer polymerization. A subsequent Steglich esterification yields the CE functionalized polymer. The complexation properties with different alkali metals are first investigated by liquid-liquid extraction (LLE) in dichloromethane (DCM) - water systems using free benzo-9-crown (B9C3), benzo-12-crown-4 (B12C4), and benzo-15-crown-5 (B15C5) CEs as reference components, followed by the correspondingly CE-functionalized polymers. Extraction complexation constants in the aqueous phase are determined and the impact of the complexation constants on the extractability is estimated. The B9C3 CE is especially appealing since it has the smallest cavity size among all CEs. It is too small to complex sodium or potassium ions; however, it forms sandwich complexes with a lithium-ion resulting in extraordinary complexation constants in polymer systems avoiding other interfering alkali metal ions. On this basis, a new material for the efficient extraction of lithium ion traces in global water resources is established.


Assuntos
Lítio , Metais Alcalinos , Íons , Polímeros , Sódio
10.
J Mol Graph Model ; 105: 107867, 2021 06.
Artigo em Inglês | MEDLINE | ID: mdl-33725640

RESUMO

The geometric, electronic and nonlinear properties of exohedral and endohedral single and multiple alkali metal (Li, Na and K) atom doped C24 fullerene are studied. First, the most stable orientations at the most stable spin state are evaluated. Complexes with odd metal atoms are stable at doublet spin state and complexes with even number of metal atoms are stable at singlet spin state. Thermodynamic analysis shows that Li4C24 among all complexes with highest thermodynamic stability has interaction energy of -190.78 kcal mol-1. The energy gaps (GH-L) are fairly reduced in single and multi-doped cages, and the lowest energy gap is observed for K4C24 complex. NBO analysis is performed to validate the charge transfer from alkali metal toward C24. The largest amount of charge (0.95 |e|) transfer is monitored in exohedral K2C24 complex where the highest charge transfer is for potassium (K) metal. Total density of states (TDOS) spectra of doped complexes justify the involvement of alkali metals and nanocage in new HOMO formation for the excess electrons. First hyperpolarizability is descriptor of NLO properties of single and multi-doped complexes are calculated. It is observed that doping of alkali metal atoms (Li, Na and K) greatly enhances the first hyperpolarizability. Among all the complexes of C24, Na3C24 shows the highest hyperpolarizability value of 2.74 × 105 au. The results of this study are a guideline for the computational designing of highly efficient and thermodynamically stable complexes for the optical and optoelectronic technologies.


Assuntos
Fulerenos , Metais Alcalinos , Eletrônica , Elétrons , Termodinâmica
11.
Environ Sci Technol ; 55(5): 3250-3259, 2021 03 02.
Artigo em Inglês | MEDLINE | ID: mdl-33600153

RESUMO

The partitioning of solutes into the polyamide active layers of reverse osmosis (RO) membranes is a key membrane property determining solute permeation. Quantification of partition coefficients and their dependence on feedwater pH would contribute to the development of predictive transport models of contaminant transport through RO membranes; however, neither solute partitioning nor the effect of feed solution pH on partitioning has been thoroughly characterized in the literature. Accordingly, we characterized the partitioning of all chloride salts of alkali metals (CsCl, RbCl, KCl, NaCl, and LiCl) from the aqueous phase into the polyamide active layers of five polyamide RO membranes, including one prepared in-house and four commercial membranes. We evaluated the effect of pH on the partitioning of alkali metal salts and whether the effect of pH on salt partitioning and rejection is consistent with Donnan theory predictions. Results showed that for all membranes, the partition coefficients of all salts were less than one and did not differ substantially among RO membranes. Results also indicated that for all membranes tested, Donnan theory provided an appropriate theoretical framework to estimate the effect of pH on salt partitioning (evaluated for all chloride salts of alkali metals) and salt rejection (evaluated for NaCl). Thus, we conclude that changes in salt rejection resulting from feed solution pH are primarily driven by changes in salt partitioning with comparatively small changes in salt diffusion coefficients.


Assuntos
Metais Alcalinos , Purificação da Água , Concentração de Íons de Hidrogênio , Membranas Artificiais , Nylons , Osmose , Sais , Água
12.
Anal Biochem ; 616: 114099, 2021 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-33388294

RESUMO

Precipitation of DNA is performed frequently in molecular biology laboratories for the purpose of purification and concentration of samples and also for transfer of DNA into cells. Metal ions are used to facilitate these processes, though their precise functions are not well characterized. In the current study we have investigated the precipitation of double-stranded DNA by group 1 and group 2 metal ions. Double-stranded DNAs were not sedimented efficiently by metals alone, even at high concentrations. Increasing the pH to 11 or higher caused strong DNA precipitation in the presence of the divalent group 2 metals magnesium, calcium, strontium and barium, but not group 1 metals. Group 2 sedimentation profiles were distinctly different from that of the transition metal zinc, which caused precipitation at pH 8. Analysis of DNAs recovered from precipitates formed with calcium revealed that structural integrity was retained and that sedimentation efficiency was largely size-independent above 400 bp. Several tests supported a model whereby single-stranded DNA regions formed by denaturation at high pH became bound by the divalent metal cations. Neutralization of negative surface charges reduced the repulsive forces between molecules, leading to formation of insoluble aggregates that could be further stabilized by cation bridging (ionic crosslinking).


Assuntos
Precipitação Química , DNA/química , Metais Alcalinos/química , Metais Alcalinoterrosos/química , Cátions Bivalentes/química , Cátions Monovalentes/química , Cloretos/química , DNA/isolamento & purificação , Concentração de Íons de Hidrogênio , Espectroscopia Fotoeletrônica , Zinco/química
13.
Braz. arch. biol. technol ; 64: e21200117, 2021. tab
Artigo em Inglês | LILACS | ID: biblio-1285553

RESUMO

Abstract This study evaluated the effects of three chemical pretreatments of biomass sorghum (BS): dilute alkaline (PTA1 and PTA2), dilute acid (PTB1 and PTB2) and alkaline hydrogen peroxide (PTC1 and PTC2) in the enzymatic hydrolysis and ethanol production. Among the six investigated conditions, the pretreatment with 7.36% H2O2 (PTC2) was the most efficient in the lignin removal and preservation of the polysaccharide fraction. After the enzymatic hydrolysis, increases in the glucose and xylose concentrations were observed in the pretreated BS hydrolysates, mainly in PTB1 and PTC1. All the hydrolysates obtained low concentrations of inhibitors. In the alcoholic fermentations with Pichia stiptis, the greatest ethanol yield was obtained in PTB1 hydrolysate (3.84 g L-1), corresponding to 16.15% of yield. The highest ethanol yield in PTB1 hydrolysate can be justified by the maximum concentration of xylose obtained in this hydrolysate, demonstrating the potential of P. stiptis in the fermentation of pentose to ethanol. The results indicated that biomass sorghum is an alternative lignocellulose source with potential for the production of second generation ethanol, opening up prospects for additional studies.


Assuntos
Biomassa , Etanol , Fenômenos Químicos , Peróxido de Hidrogênio , Metais Alcalinos
14.
Phys Chem Chem Phys ; 22(37): 21108-21118, 2020 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-32954397

RESUMO

To gain better understanding of the stabilizing interactions between metal ions and DNA quadruplexes, dispersion-corrected density functional theory (DFT-D) based calculations were performed on double-, triple- and four-layer guanine tetrads interacting with alkali metal cations. All computations were performed in aqueous solution that mimics artificial supramolecular conditions where guanine bases assemble into stacked quartets as well as biological environments in which telomeric quadruplexes are formed. To facilitate the computations on these significant larger systems, optimization of the DFT description was performed first by evaluating the performance of partial reduced basis sets. Analysis of the stabilizing interactions between alkali cations and the DNA bases in double and triple-layer guanine quadruplex DNA reproduced the experimental affinity trend of the order Li+< Rb+ < Na+ < K+. The desolvation and the size of alkali metal cations are thought to be responsible for the order of affinity. Nevertheless, for the alkali metal cation species individually, the magnitude of the bond energy stays equal for binding as first, second or third cation in double, triple and four-layer guanine quadruplexes, respectively. This is the result of an interplay between a decreasingly stabilizing interaction energy and increasingly stabilizing solvation effects, along the consecutive binding events. This diminished interaction energy is the result of destabilizing electrostatic repulsion between the hosted alkali metal cations. This work emphasizes the stabilizing effect of aqueous solvent on large highly charged biomolecules.


Assuntos
DNA/química , Quadruplex G , Guanina/química , Metais Alcalinos/química , DNA/genética , Teoria da Densidade Funcional , Modelos Químicos , Termodinâmica
15.
J Phys Chem A ; 124(40): 8101-8111, 2020 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-32936636

RESUMO

Guanine self-assemblies are promising supramolecular platforms for optoelectronic applications. The study (Hua et al., J. Phys. Chem. C 2012, 116, 14,682-14,689) reported that alkaline cations cannot modulate the electronic absorption spectrum of G-quadruplexes, although a cation effect is observable during electronic relaxation due to different mobility of Na+ and K+ cations. In this work, we theoretically examined whether divalent Mg2+ and Ca2+ cations and hydration might shift excited charge-transfer states of a cation-templated stacked G-quartet to the absorption red tail. Our results showed that earth alkaline cations blue-shifted nπ* states and stabilized charge-transfer ππ* states relative to those of complexes with alkaline cations, although the number of charge-separation states was not significantly modified. Earth alkaline cations were not able to considerably increase the amount of charge-transfer states below the Lb excitonic states. Hydration shifted charge-transfer states of the Na+-coordinated G-octet to the absorption red tail, although this part of the spectrum was still dominated by monomer-like excitations. We found G-octet electron detachment states at low excitation energies in aqueous solution. These states were distributed over a broad range of excitation energies and could be responsible for oxidative damage observed upon UV irradiation of biological G-quadruplexes.


Assuntos
Quadruplex G , Metais Alcalinos/química , Cátions , Teoria Quântica
16.
Artigo em Inglês | MEDLINE | ID: mdl-32731444

RESUMO

In order to investigate the adsorption characteristics of activated carbon fibers (ACFs) with improved surface morphologies towards volatile organic compounds (VOCs), a commercial low-grade ACF was surface modified by successive surface treatment (ST) and chemical activation (CA) process. O3 was used as an ST agent for the formation of oxygen-containing functional groups on the carbon matrix of ACFs. CA was carried out after ST, using a KOH solution. After the successive ST-CA process, Brunauer-Emmett-Teller (BET) surface area and average pore diameter of ACFs were increased from 1483 m2/g to 2743 m2/g and enlarged from 1.931 nm to 2.512 nm, respectively. The successive ST-CA process also resulted in the adsorption capacities of benzene, toluene, and xylene of the ACFs to increase from 0.22 g-Ben./g-ACFs, 0.18 g-Tol./g-ACFs, and 0.19 g-Xyl/g-ACFs up to 0.37 g-Ben./g-ACFs, 0.35 g-Tol./g-ACFs, and 0.38 g-Xyl/g-ACFs, respectively.


Assuntos
Carvão Vegetal , Gases/química , Metais Alcalinos , Ozônio/química , Adsorção , Fibra de Carbono
17.
J Proteome Res ; 19(8): 3176-3183, 2020 08 07.
Artigo em Inglês | MEDLINE | ID: mdl-32627559

RESUMO

Tandem mass spectrometry (MS/MS) is a highly sensitive and selective method for the detection of tumor-associated peptide antigens. These short, nontryptic sequences may lack basic residues, resulting in the formation of predominantly [peptide + H]+ ions in electrospray. These singly charged ions tend to undergo inefficient dissociation, leading to issues in sequence determination. Addition of alkali metal salts to the electrospray solvent can drive the formation of [peptide + H + metal]2+ ions that have enhanced dissociation characteristics relative to [peptide + H]+ ions. Both previously identified tumor-associated antigens and predicted neoantigen sequences were investigated. The previously reported rearrangement mechanism in MS/MS of sodium-cationized peptides is applied here to demonstrate complete C-terminal sequencing of tumor-associated peptide antigens. Differential ion mobility spectrometry (DIMS) is shown to selectively enrich [peptide + H + metal]2+ species by filtering out singly charged interferences at relatively low field strengths, offsetting the decrease in signal intensity associated with the use of alkali metal cations.


Assuntos
Espectrometria de Mobilidade Iônica , Metais Alcalinos , Cátions , Peptídeos , Espectrometria de Massas por Ionização por Electrospray , Espectrometria de Massas em Tandem
18.
Chemphyschem ; 21(18): 2112-2126, 2020 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-32643813

RESUMO

For many years, non-covalently bonded complexes of nucleobases have attracted considerable interest. However, there is a lack of information about the nature of hydrogen bonding between nucleobases when the bonding is affected by metal coordination to one of the nucleobases, and how the individual hydrogen bonds and aromaticity of nucleobases respond to the presence of the metal cation. Here we report a DFT computational study of nucleobase pairs interacting with alkali metal cations. The metal cations contribute to the stabilization of the base pairs to varying degrees depending on their position. The energy decomposition analysis revealed that the nature of bonding between nucleobases does not change much upon metal coordination. The effect of the cations on individual hydrogen bonds were described by changes in VDD charges on frontier atoms, H-bond length, bond energy from NBO analysis, and the delocalization index from QTAIM calculations. The aromaticity changes were determined by a HOMA index.


Assuntos
Pareamento de Bases , Cátions/química , DNA/química , Metais Alcalinos/química , Simulação por Computador , Ligação de Hidrogênio , Modelos Moleculares , Termodinâmica
19.
Environ Monit Assess ; 192(8): 504, 2020 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-32651666

RESUMO

The study of trace and major elements in the biosphere has traditionally focused on the transition and basic metals; the rare earth (REMs), alkaline earth (AEMs) and alkali metals (AMs) that equally constitute environmental contaminants are rarely considered especially in the tropics. The levels and spatial variation of some REMs, AEMs and AMs in the 0-50-cm layer of agricultural soils of Ikwo in southeastern Nigeria typing a humid tropical environment were studied. Soil sampling was undertaken at five zones namely north, south, east, west and centre (covering over 60% of the land area) in the 2017 dry season. Four soil samples were collected from each of the four cardinal points (with evidence of mining and agricultural activities), and two from the centre (serving as reference zone), totalling 18. Metal concentrations were determined using inductively coupled plasma atomic emission spectroscopy. The metals were grouped into REMs (Ce, La, Sm), AEMs (Ba, Ca, Mg, Sr) and AMs (Cs, K, Na, Rb). All metals increased in concentration from the north, or the south (for Ce and Sm only), towards the centre. Overall, they were reasonably similar in distribution pattern among the five zones. Cationic ratios did not vary markedly, reflecting the greater role of pedogenesis than anthropogenic activities in the area. Nevertheless, their variations showed more K, Ca, Sr and La enrichments over the other metals. Enrichment factor and pollution index of the REMs showed healthy levels of these elements in the soils. The data from this preliminary study may add to the data pool on levels and occurrence of REMs, AEMs and AMs in largely disturbed ecosystems of the humid tropics.


Assuntos
Metais Alcalinos , Metais Pesados/análise , Poluentes do Solo/análise , Ecossistema , Monitoramento Ambiental , Nigéria , Rizosfera , Solo
20.
Science ; 368(6495): 1056-1057, 2020 06 05.
Artigo em Inglês | MEDLINE | ID: mdl-32499427
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