Theoretical study of the effects of substituents (F,Cl, Br,CH<Subscript>3</Subscript>, and CN) on the aromaticity of borazine

This paper presents a theoretical study of the effects of substituents (F, Cl, Br, CH₃, and CN) on the aromaticity of borazine (B₃N₃H₆), using density functional theory (DFT) and the Hartree-Fock (HF) method. The calculations to optimize the geometries, structural properties, and vibrational frequencies were performed using the same 6–311G(d,p) and 6–311++G(d,p) basis sets, comparing the methods with experimental results. In the analysis of the NICS_ZZ values, it was found that that replacing the hydrogen atoms by halogen atoms (F, Cl, and Br) and CH₃ reduced the aromaticity of the borazine molecule, while use of the CN group resulted in NICS_ZZ values (0.9–2.0 Å) very close to those of borazine, presenting the following order of increasing aromaticity: B₃N₃H₃-(Br)₃?<?B₃N₃H₃-(Cl)₃?<?B₃N₃H₃-(F)₃?<?B₃N₃H₃-(CH₃)₃?<?B₃N₃H₆ ~ B₃N₃H₃-(CN)₃. All the spectra of the compounds showed only the presence of transition peaks distant from the UV region, reflecting the large energy difference between the HOMO and LUMO orbitals. After the substitution of the borazine ring, all the compounds presented an intensification of the spectrum, with a shift of the maximum absorbance toward red, indicative of a bathochromic effect. There was a direct inverse relation between the energy gap and the maximum wavelength of the compounds.     

The influence of Sc doping on structural,electronic and optical properties of Be<Subscript>12</Subscript>O<Subscript>12</Subscript>, Mg<Subscript>12</Subscript>O<Subscript>12</Subscript> and Ca<Subscript>12</Subscript>O<Subscript>12</Subscript> nanocages: a DFT study

Density functional theory (DFT) calculations were used to study the effect of scandium doping on the structural, energetic, electronic, linear and nonlinear optical (NLO) properties of Be₁₂O₁₂, Mg₁₂O₁₂ and Ca₁₂O₁₂ nanoclusters. Scandium (Sc) doping on nanoclusters leads to narrowing of their E _g, which enhances their conductance greatly. Also, the polarizability (α) and first hyperpolarizability (β₀) of nanoclusters were dramatically increased as Be, Mg or Ca atoms are substituted with a Sc atom. Among all clusters, α and β₀ values for Sc-doped Ca₁₂O₁₂ were the largest. Consequently, the effect of the doping atom, as well as of cluster size, on electronic and optical properties was explored. Time dependent (TD)-DFT calculations were also carried out to confirm the β₀ values; the results show that the higher value of first hyperpolarizability belongs to Sc-doped Ca₁₂O₁₂, which has the smallest transition energy (ΔEgn). The results obtained show that these clusters can be candidates for using in electronic devices and NLO materials in industry.     

Vitamin B<Subscript>12</Subscript> as a carrier for targeted platinum delivery: in vitro cytotoxicity and mechanistic studies

It is attractive to use vitamin B₁₂ as a carrier for targeted delivery of cytotoxic agents such as platinum complexes owing to the high demand for vitamin B₁₂ by fast proliferating cells. The basic {B₁₂–CN–Pt^II} conjugates are recognized by intracellular enzymes and converted to coenzyme B₁₂ in an enzymatic adenosylation assay. The reductive adenosylation of {B₁₂–CN–Pt^II} conjugates leads to the release of the Pt^II complexes; thus, {B₁₂–CN–Pt^II} conjugates can be considered as prodrugs. It is important not only to elucidate the activity of the cisplatin–B₁₂ conjugates, but also to understand the mode of action on a molecular level. Chemical reduction of {B₁₂–CN–Pt^II} conjugates with cobaltocene yielded cob(II)alamin and induced release of the corresponding Pt^II species. Kurnakov tests and coordination of 2′-deoxyguanosine or GMP to the released Pt^II complexes allowed isolation and characterization of Pt^II complexes as released during enzymatic adenosylation. The biological activity of these Pt^II complexes was evaluated. Since the cleaved Pt^II complexes show cytotoxicity, the {B₁₂–CN–Pt^II} conjugates can be used for specific targeting of cancer cells and therapeutic drug delivery. Preliminary in vitro cytotoxicity studies indicated lower activity (IC₅₀ between 8 and 88 μM) than found for pure cisplatin. Since active transport and receptor-mediated uptake limits the intracellular {B₁₂–CN–Pt^II} concentration, comparison with pure cisplatin is of limited use. We could show that the Pt^II complexes cleaved from B₁₂ exerted a cytotoxicity comparable to that of cisplatin itself. Cytotoxicity studies in vitamin B₁₂ free media showed a dependence on the addition of transcobalamin II for B₁₂–Pt(II) conjugates.     

Effects of CO/CO<Subscript>2</Subscript>/NO on elemental lead adsorption on carbonaceous surfaces

The adsorption processes of elemental lead on carbonaceous surfaces which adsorbed CO/CO₂/NO flue gases were investigated to understand the effects of CO/CO₂/NO on elemental lead adsorption on carbonaceous surfaces with density functional theory. All calculations including optimizations, energies, and frequencies were conducted at B3PW91 density functional theory level, utilizing SDD basis set for lead and 6-31G(d) Pople basis set for other atoms. The results indicate that CO, CO₂, and NO can promote the adsorption of elemental lead on the carbonaceous surface, but probably compete for adsorption sites with elemental lead. The promotion effects on adsorption can be attributed to active sites on the carbonaceous surface rather than flue gas adsorption on the carbonaceous surface. In addition, the adsorption order of three kinds of flue gas on the carbonaceous surface is CO₂?>?NO?>?CO?>?Pb on average. Furthermore, the enhancement order of three kinds of flue gas on the elemental lead adsorption on carbonaceous surfaces is CO-CS?>?CO₂-CS?>?NO-CS?>?CS in general. In particular, atomic charge and adsorption energy have good linear relationship in the process of elemental lead adsorption.

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Graphical Abstract Competitive adsorption between flue gas and elemental lead on carbonaceous surfaces.

     

Computational study of the NO,SO<Subscript>2</Subscript>, and NH<Subscript>3</Subscript> adsorptions on fragments of 3N-graphene and Al/3N graphene

The adsorption properties of common gas molecules (NO, NH₃, and SO₂) on the surface of 3N-graphene and Al/3N graphene fragments are investigated using density functional theory. The adsorption energies have been calculated for the most stable configurations of the molecules on the surface of 3N-graphene and Al/3N graphene fragments. The adsorption energies of Al/3N graphene-gas systems are ?220.5 kJ mol^?1 for Al/3NG-NO, ?111.9 kJ mol^?1 for Al/3NG-NH₃, and ?347.7 kJ mol^?1 for Al/3NG-SO₂, respectively. Compared with the 3N-graphene fragment, the Al/3N graphene fragment has significant adsorption energy. Furthermore, the molecular orbital, density of states, and electron densities distribution were used to explore the interaction between these molecules and the surface. We found that orbital hybridization exists between these molecules and the Al/3N graphene surface, which indicates that doping Al significantly increases the interaction between the gas molecules and Al/3N graphene. In addition, compared with Li, Al can more powerfully enhance adsorption of the 3N-graphene fragment. The results indicate that Al/3N graphene can be viewed as a new nanomaterial adsorbent for NO, NH₃, and SO₂.     

Salicylic acid and phenolic compounds under cadmium stress in cucumber plants (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.)

In this pot experiment, cucumbers (Cucumis sativus L.) were grown in a model soil contaminated by three different concentrations of cadmium (40, 160, and 320 mg.kg^?1) with different accompanied anions (Cl^?, SO₄ ^2?). In all variants, the most Cd (90 %) was accumulated in the roots, but higher content in the case of Cl^?. The distribution of Cd in various cucumber organs was as follows: root > stem > leaf > fruits. However, in variants with higher doses of Cd with SO₄ ^2?, the ratio was changed as follows: root > leaf > stem > fruits. In all variants, least of Cd (max. 1 %) was found in fruits. Variants with the highest Cd doses were significantly different by comparison with all other variants, but higher content was in the case of Cl^? anion. Stimulation effect on the biomass production and growth of aerial parts and roots of plants in all variants with Cd was observed. Toxicity symptoms, mainly in the presence of leaf chlorosis and yellowing, were more visible in the variants with Cl^?, in comparison with SO₄ ^2?. The amounts of phenol compounds in leaves rose almost in all variants. Only the variants with higher Cd content with SO₄ ^2? showed slight reduction. One possible explanation of reduced content may be their bounding on Cd. The content of salicylic acid was reduced in all variants with Cd treatment. However, it is difficult to conclude their role in plant defence responses to heavy metal, because their actual defence mechanism is still unclear. However, from these results, we can suggest that the accompanying anion and the form in which Cd exists may have an impact on the involvement of various antioxidant systems.     

Recent improvements in the development of A<Subscript>2B</Subscript> adenosine receptor agonists

Adenosine is known to exert most of its physiological functions by acting as local modulator at four receptor subtypes named A₁, A_2A, A_2B and A₃ (ARs). Principally as a result of the difficulty in identifying potent and selective agonists, the A_2B AR is the least extensively characterised of the adenosine receptors family. Despite these limitations, growing understanding of the physiological meaning of this target indicates promising therapeutic perspectives for specific ligands. As A_2B AR signalling seems to be associated with pre/postconditioning cardioprotective and anti-inflammatory mechanisms, selective agonists may represent a new therapeutic group for patients suffering from coronary artery disease. Herein we present an overview of the recent advancements in identifying potent and selective A_2B AR agonists reported in scientific and patent literature. These compounds can be classified into adenosine-like and nonadenosine ligands. Nucleoside-based agonists are the result of modifying adenosine by substitution at the N ⁶-, C²-positions of the purine heterocycle and/or at the 5′-position of the ribose moiety or combinations of these substitutions. Compounds 1-deoxy-1-{6-[N′-(furan-2-carbonyl)-hydrazino]-9H-purin-9-yl}-N-ethyl-β-D-ribofuranuronamide (19, hA₁ K _i = 1050 nM, hA_2A K _i = 1550 nM, hA_2B EC₅₀ = 82 nM, hA₃ K _i > 5 μM) and its 2-chloro analogue 23 (hA₁ K _i = 3500 nM, hA_2A K _i = 4950 nM, hA_2B EC₅₀ = 210 nM, hA₃ K _i > 5 μM) were confirmed to be potent and selective full agonists in a cyclic adenosine monophosphate (cAMP) functional assay in Chinese hamster ovary (CHO) cells expressing hA_2B AR. Nonribose ligands are represented by conveniently substituted dicarbonitrilepyridines, among which 2-[6-amino-3,5-dicyano-4-[4-(cyclopropylmethoxy)phenyl]pyridin-2-ylsulfanyl]acetamide (BAY-60–6583, hA₁, hA_2A, hA₃ EC₅₀ > 10 μM; hA_2B EC₅₀ = 3 nM) is currently under preclinical-phase investigation for treating coronary artery disorders and atherosclerosis.     

Reconnoitring the current characteristics of the double C<Subscript>20</Subscript> fullerene molecular device in two probe configuration

It is worth remarking that the C₂₀ cage like isomer has been the topic of concentrated theoretical research. C₂₀ single fullerene molecular devices gained a lot of popularity in the field of nano research due to their superlative doping dependent conductive properties. In this work, the double fullerene device has been considered. Here double fullerene molecular junction is created when two C₂₀ fullerene molecules, one in pristine form and other in doped form, are positioned between gold electrodes. Doping was done firstly by second period elements, boron, nitrogen, oxygen, and fluorine and then by group 14 tetragens, silicon, germanium, tin, and lead. For both the cases current characteristics were investigated. Superior conductivity was observed in the boron doped double C₂₀ molecular device while the fluorine doped device was the least conducting. Further for group 14 doping, the silicon doped double C₂₀ device showed maximum current carrying feature, whereas, least value of current was noted in tin doped C₂₀ device.     

Insight into the lithium/hydrogen bonding in (CH<Subscript>2</Subscript>)<Subscript>2</Subscript>X...LiY/HY (X: C=CH<Subscript>2</Subscript>, O,S; Y=F,Cl, Br) complexes

The nature of the lithium/hydrogen bonding between (CH₂)₂X(X: C=CH₂, O, S) and LiY/HY(Y=F, Cl, Br) have been theoretically investigated at MP2/6-311++G (d, p) level, using Bader’s “atoms in molecules (AIM)” theory and Weinhold’s “natural bond orbital (NBO)” methodology. The molecule formation density differences (MFDD) of the titled complexes are analyzed. Two kinds of geometries of the lithium/hydrogen bonded complexes are compared. As a whole, the nature of lithium bond and hydrogen bond are different. For the same electron donor and the same acceptor, lithium bond is stronger than hydrogen bond. For the same electron acceptor and different kind of donors, the interaction energies follows the n-type> π-type > pseudo-π-type order. For the same (CH₂)₂X, the interaction energy increases in the sequence of Y=F, Cl and Br for lithium bond systems while it decreases for hydrogen bond systems. Electron transfer plays an important role in the formation of lithium bond systems while it is less important in the hydrogen bond systems.     

Noble gas inserted compounds of borazine and its derivative B<Subscript>3</Subscript>N<Subscript>3</Subscript>R<Subscript>6</Subscript>: structures and bonding

Quantum chemistry computations were performed at the MP2 and B3LYP levels of theory using the basis sets aug-cc-pVDZ and def2-TZVPPD to study the noble gas (Ng) compounds formed by insertion of a Ng atom (Kr, Xe, Rn) into the B–H/F and N–H/F bonds of inorganic benzene B₃N₃H₆ and its fluorine derivative B₃N₃F₆. The geometrical structures were optimized and vibrational analysis was carried out to demonstrate these structures being local minima on the potential energy surface. The thermodynamic properties of the formation process of Ng compounds were calculated. A series of theoretical methods based on the wavefunction analysis, including NBO, AIM and ELF methods and energy decomposition analysis, was used to investigate the bonding nature of the noble gas atoms and the properties of the Ng compounds. The N–Ng bond was found to be stronger than the B–Ng bond, but the B–Ng bond is of typical covalent character and σ-donation from the Ng atom to the ring B atom makes the predominant contribution towards stability of the B-Ng bond. NICS calculation shows that these Ng-containing compounds are of weak π-aromaticity.     

Theoretical study on the functionalization of BC2N nanotube with amino groups

Using density functional theory calculations, we investigated properties of a functionalized BC₂N nanotube with NH₃ and five other NH₂-X molecules in which one of the hydrogen atoms of NH₃ is substituted by X = ?CH₃, ?CH₂CH₃, ?COOH, ?CH₂COOH and ?CH₂CN functional groups. It was found that NH₃ can be preferentially adsorbed on top of the boron atom, with adsorption energy of ?12.0 kcal mol^?1. The trend of adsorption-energy change can be correlated with the trend of relative electron-withdrawing or -donating capability of the functional groups. The adsorption energies are calculated to be in the range of ?1.8 to ?14.2 kcal mol^?1, and their relative magnitude order is found as follows: H₂N(CH₂CH₃) > H₂N(CH₃) > NH₃ > H₂N(CH₂COOH) > H₂N(CH₂CN) > H₂N(COOH). Overall, the functionalization of BC₂N nanotube with the amino groups results in little change in its electronic properties. The preservation of electronic properties of BC₂N coupled with the enhancement of solubility renders their chemical modification with either NH₃ or amino functional groups to be a way for the purification of BC₂N nanotubes.     

Studies on the viscosity behavior of concentrated alkali halides in aqueous maltose solutions

The viscosities of concentrated solutions of sodium and potassium halides (concentration range 0.125 to 3.0m) have been measured in aqueous maltose solution at 25, 30, 35, and 40°. Various equations employed for concentrated solutions of electrolytes have been tested, to ascertain the validity of the relative viscosity data. In order to elucidate the structural behavior of sodium and potassium halides in aqueous maltose solution, the molar volumes ($\text{V}$), ionic B-coefficients, and hydration numbers (n_B) of various ions have been computed. The B₊ and B_? coefficients have been interpreted in terms of solute-solvent interactions. On the basis of the data, it has been found that, in 0.5m maltose solution, the different ions show structure-breaking tendency in the order: I^? > Br^? > Cl^? > K⁺ > Na⁺.     

Noble gas supported boron-pentagonal clusters B<Subscript>5</Subscript>Ng<Subscript>n</Subscript><Superscript>3+</Superscript>: exploring the structures and bonding

A novel type of trivalent BNg five-membered cational species B₅Ng_n³⁺(Ng = He~Rn, n = 1~5) has been found and investigated theoretically using the B3LYP and MP2 methods with the def2-QZVPPD and def2-TZVPPD basis sets. The geometry, harmonic vibrational frequencies, bond energies, charge distribution, bond nature, aromaticity, and energy decomposition analysis of these structures were reported. The calculated B?Ng bond energy is quite large (the averaged bond energy is in the range of 209.2~585.76 kJ mol^-1) for heavy rare gases and increases with the Ng atomic number. The analyses of the molecular wavefunction show that in the BNg compounds of heavy Ng atoms Ar~Rn, the B?Ng bonds are of typical covalent character. Nuclear independent chemical shifts display that both B₅³⁺ and B₅Ng_n³⁺(n=1~5) have obvious aromaticity. Energy decomposition analysis shows that these BNg compounds are mainly stabilized by the σ-donation from the Ng valence p orbital to the B₅³⁺ LUMO. These findings offer valuable clues toward the design and synthesis of new stable Ng-containing compounds.     

Effect of chemical and microbial vitamin B<Subscript>12</Subscript> analogues on production of vitamin B<Subscript>12</Subscript>

Strain improvement by genetic manipulation or optimization of fermentation conditions for overproduction of vitamin B₁₂ has a drawback due to feed back inhibition. To resist the feed back inhibition by analogues of vitamin B₁₂ in Propionibacterium freudenrechii subsps. shermanii (OLP-5), we have tested with microbially separated B₁₂ analogues from three different strains. Microbial analogues were differentiated from commercially available vitamin B₁₂ by high pressure liquid chromatography and spectrophotometric method. An analogue isolated from NRRL-B-4327 was shown to increase vitamin B₁₂ concentration from 18.53 ± 0.15 to 31.67 ± 0.58 mg/l in OLP-5 strain. The presence of chemical analogue (ICH₂ Co(DH)₂ (H₂Py)₄) increased vitamin B₁₂ production from 16.13 ± 0.15 to 18.53 ± 0.15 mg/l in OLP-5. These findings revealed that addition of B₁₂ analogues in fermentation media have developed strain resistance to feed back inhibition by vitamin B₁₂.     

Si-doped graphene: an ideal sensor for NO- or NO<Subscript>2</Subscript>-detection and metal-free catalyst for N<Subscript>2</Subscript>O-reduction

Exploring and evaluating the potential applications of two-dimensional graphene is an increasingly hot topic in graphene research. In this paper, by studying the adsorption of NO, N₂O, and NO₂ on pristine and silicon (Si)-doped graphene with density functional theory methods, we evaluated the possibility of using Si-doped graphene as a candidate to detect or reduce harmful nitrogen oxides. The results indicate that, while adsorption of the three molecules on pristine graphene is very weak, Si-doping enhances the interaction of these molecules with graphene sheet in various ways: (1) two NO molecules can be adsorbed on Si-doped graphene in a paired arrangement, while up to four NO₂ molecules attach to the doped graphene with an average adsorption energy of −0.329 eV; (2) the N₂O molecule can be reduced easily to the N₂ molecule, leaving an O-atom on the Si-doped graphene. Moreover, we find that adsorption of NO and NO₂ leads to large changes in the electronic properties of Si-doped graphene. On the basis of these results, Si-doped graphene can be expected to be a good sensor for NO and NO₂ detection, as well as a metal-free catalyst for N₂O reduction.     

Bonding analysis and stability on alternant B<Subscript>16</Subscript>N<Subscript>16</Subscript> cage and its dimers

Bonding analysis is performed on alternant B₁₆N₁₆ cage based on a combined study of DFT with NBO method. The main feature of such analysis is the separation of bonding structure into two components: σ skeleton and π bond system. Each component is further decomposed into contributions from various NBOs, thus we obtain the details of bonding interactions of every BN unit. Based on these results, relative stability of four covalent dimers of B₁₆N₁₆ is predicted and this prediction is verified by DFT calculations. So the possibility of forecasting properties of oligomers just from analysis on monomer is highlighted in this way.     

Self-stability of C<Subscript>60</Subscript> nanocapsules with radio-iodide content and its interaction with calcium atoms

This paper inquires the C₆₀ capabilities to contain radio-iodide (¹³¹I₂) molecules. The encapsulation conditions are investigated applying first principles method to simulate with geometric optimizations and molecular dynamics at 310 K and atmospheric pressure. We find that the n¹³¹I₂@C₆₀ system, where n?=?1, 2, 3…, is stable if the content does not exceed three molecules of radio-iodide. The application of density functional theory allows us to determine that, the nanocapsules content limit is related with the amount of charge that is transferred from the iodine ¹³¹I₂ molecules to the carbon atoms in the fullerene surface. The Mulliken population analysis reveals that the excess of charge increases the repulsive forces between atoms and the bond length average in the C₆₀ structure. The weakened bonds easily break and will critically damage the encapsulation properties. Additionally, we test the interaction nanocapsules with different amounts of radioactive iodine diatomic molecules content with calcium atoms, and find that only the fullerene containing one radioactive iodine diatomic molecule was able to interact with up to nine atoms of calcium without disrupting or cracking. Other fullerenes with two and three radio iodine diatomic molecules cannot resist the interaction with a single calcium atom without cracking or being broken.

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Graphical Abstract Instability of 3¹³¹I₂@C₆₀ Ca.

     

Modeling zigzag CNT: dependence of structural and electronic properties on length,and application to encapsulation of HCN and C<Subscript>2</Subscript>H<Subscript>2</Subscript>

Density functional theory (B3LYP, B3LYP-D2 and wB97XD functionals) was used in finite models of zigzag carbon nanotubes (CNT), (n,0)×k with n?=?6–9 and k?=?2–4, to systematically investigate the effects of size on their structural and electronic properties. We found that the ratio between the length (L _t) and the diameter (d _t) of the pristine CNT has to be larger than 2, i.e., L _t/d _t?>?2, in order to provide the observed experimental trends of C=C bond distances, as well as to maintain the atomic charges nearly constant and zero around the center of the tube. Therefore, the concepts of useful length and volume were developed and tested for the encapsulation process of HCN and C₂H₂ into CNTs. The energies involved in these processes, as well as the changes in molecular structure and electronic properties of the dopants and the CNTs are discussed and rationalized by the amount of charge transferred between dopant and CNT.

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Graphical Abstract Illustration of zigzag CNT length and diameter ratio in order to represent C=C bond experimental trend

     

M234Glu is a component of the proton sponge in the reaction center from photosynthetic bacteria

Bacterial reaction centers use light energy to couple the uptake of protons to the successive semi-reduction of two quinones, namely Q_A and Q_B. These molecules are situated symmetrically in regard to a non-heme iron atom. Four histidines and one glutamic acid, M234Glu, constitute the five ligands of this atom. By flash-induced absorption spectroscopy and delayed fluorescence we have studied in the M234EH and M234EL variants the role played by this acidic residue on the energetic balance between the two quinones as well as in proton uptake. Delayed fluorescence from the P⁺Q_A^? state (P is the primary electron donor) and temperature dependence of the rate of P⁺Q_A^? charge recombination that are in good agreement show that in the two RC variants, both Q_A^? and Q_B^? are destabilized by about the same free energy amount: respectively ～ 100 ± 5 meV and 90 ± 5 meV for the M234EH and M234EL variants, as compared to the WT. Importantly, in the M234EH and M234EL variants we observe a collapse of the high pH band (present in the wild-type reaction center) of the proton uptake amplitudes associated with formation of Q_A^? and Q_B^?. This band has recently been shown to be a signature of a collective behaviour of an extended, multi-entry, proton uptake network. M234Glu seems to play a central role in the proton sponge-like system formed by the RC protein.