Resonance bonding in XNgY (X = F,Cl, Br,I; Ng = Kr or Xe; Y = CN or NC) molecules: an NBO/NRT investigation

Several noble-gas-containing molecules XNgY were observed experimentally. However, the bonding in such systems is still not understood. Using natural bond orbital and natural resonance theory (NBO/NRT) methods, the present work investigated bonding of the title molecules. The results show that each of the studied XNgY molecules should be better described as a resonance hybrid of ω-bonding and \( \widehat{\sigma} \)-type long-bonding structures: X:^? Ng⁺???Y, X???Ng⁺: Y^?, and X^{^}Y. The ω-bonding and long-bonding make competing contributions to the composite resonance hybrid due to the accurately preserved bond order conservation principle. We find that the resonance bonding is highly tunable for these noble-gas-containing molecules due to its dependence on the nature of the halogen X or the central noble-gas atoms Ng. When the molecule XNgY consists of a relatively lighter Ng atom, a relatively low-electronegative X atom, and the CN fragment rather than NC, the long-bonding structure X^{^}Y tends to be highlighted. In contrast, the heavy Ng atom and high-electronegative X atom will enhance the ω-bonding structure. Overall, the present work provides electronic principles and chemical insights that help understand the bonding in these XNgY species.     

A B3LYP and MP2(full) theoretical investigation into the cooperativity effect between dihydrogen-bonding and H–M∙∙∙π (M = Li, Na, K) interactions among HF, MH with the π-electron donor C2H2, C2H4 or C6H6

The DFT-B3LYP/6-311++G(3df,2p) and MP2(full)/6-311++G(3df,2p) calculations were carried out on the binary complex formed by HM (M?=?Li, Na, K) and HF or the π-electron donor (C₂H₂, C₂H₄, C₆H₆), as well as the ternary system FH???HM???C₂H₂/C₂H₄/C₆H₆. The cooperativity effect between the dihydrogen-bonding and H–M???π interactions was investigated. The result shows that the equilibrium distances R _H???H and R _M???π in the ternary complex decrease and both the H???H and H–M???π interactions are strengthened when compared to the corresponding binary complex. The cooperativity effect of the dihydrogen bond on the H–M???π interaction is more pronounced than that of the M???π bond on the H???H interaction. Furthermore, the values of cooperativity effect follow the order of FH???HNa???π?>?FH???HLi???π?>?FH???HK???π and FH???HM???C₆H₆?>?FH???HM???C₂H₄?>?FH???HM???C₂H₂. The nature of the cooperativity effect was revealed by the analyses of the charge of the hydrogen atoms in H???H moiety, atom in molecule (AIM) and electron density shifts methods.

[(B3O3H3)nM]+(n = 1, 2;M = Cu, Ag, Au): a new class of metal-cation complexes

A density functional theory (DFT) investigation into the structures and bonding characteristics of [(B₃O₃H₃)_nM]⁺(n?=?1, 2;M?=?Cu, Ag, Au) complexes was performed. DFT calculations and natural bond orbital (NBO) analyses indicate that the ΙB metal complexes of boroxine exhibit intriguing bonding characteristics, different from the typical cation–π interactions between ΙB metal-cations and benzene. The complexes of [B₃O₃H₃M]⁺ and [(B₃O₃H₃)₂?M]⁺ (M?=?Cu, Ag, and Au) favor the conformation of perfectly planar structures with the C_2v and D_2h symmetry along one of the threefold molecular axes of boroxine, respectively. Detailed natural resonance theory (NRT) and canonical molecular orbitals (CMOs) analyses show that interaction between the metal cation and the boroxine in [B₃O₃H₃M]⁺ (M?=?Cu, Ag, and Au) is mainly ionic, while the ΙB metal-cations←π donation effect is responsible for the binding site. In these complexes, boroxine serves as terminals η¹-B₃O₃H₃ with one O atom of the B₃O₃ ring. The infra-red (IR) spectra of [B₃O₃H₃M]⁺ were simulated to facilitate their future experimental characterization. The complexes all give two IR active modes at about 1,300 and 2,700 cm^?1, which are inactive in pure boroxine. Simultaneously, the B–H stretching modes of the complexes are red-shifted due to the interaction between the metal-cation and boroxine. To explore the possibility of the structural pattern developed in this work forming mesoporous materials, complexes [(B₃O₃H₃M)₆]⁶⁺ (M?=?Cu, Ag, and Au) were also studied, which appear to be unique and particular interesting: they are all true minima with D_6h symmetries and pore sizes ranging from 12.04 Å to 13.65 Å.

A comparative theoretical investigation into the strength of the trigger-bond in the Na+, Mg2+ and HF complexes involving the nitro group of R–NO2 (R = –CH3, –NH2 and –OCH3) or the C = C bond of (E)-O2N–CH = CH–NO2

A comparative theoretical investigation into the change in strength of the trigger-bond upon formation of the Na⁺, Mg²⁺ and HF complexes involving the nitro group of RNO₂ (R?=? –CH₃, –NH₂, –OCH₃) or the C?=?C bond of (E)-O₂N–CH?=?CH–NO₂ was carried out using the B3LYP and MP2(full) methods with the 6-311++G**, 6-311++G(2df,2p) and aug-cc-pVTZ basis sets. Except for the Mg²⁺?π system with (E)-O₂N–CH?=?CH–NO₂ (i.e., C₂H₂N₂O₄?Mg²⁺), the strength of the trigger-bond X–NO₂ (X?=?C, N or O) was enhanced upon complex formation. Furthermore, the increment of bond dissociation energy of the X–NO₂ bond in the Na⁺ complex was far greater than that in the corresponding HF system. Thus, the explosive sensitivity in the former might be lower than that in the latter. For C₂H₂N₂O₄?Mg²⁺, the explosive sensitivity might also be reduced. Therefore, it is possible that introducing cations into the structure of explosives might be more efficacious at reducing explosive sensitivity than the formation of an intermolecular hydrogen-bonded complex. AIM, NBO and electron density shifts analyses showed that the electron density shifted toward the X–NO₂ bond upon complex formation, leading to a strengthened X–NO₂ bond and possibly reduced explosive sensitivity.

Interplay between halogen and chalcogen bonding in the XCl∙∙∙OCS∙∙∙NH3 (X = F,OH, NC,CN, and FCC) complex

The interplay between halogen and chalcogen bonding in the XCl???OCS and XCl???OCS???NH₃ (X = F, OH, NC, CN, and FCC) complex was studied at the MP2/6-311++G(d,p) computational level. Cooperative effect is observed when halogen and chalcogen bonding coexist in the same complex. The effect is studied by means of binding distance, interaction energy, and cooperative energy. Molecular electrostatic potential calculation reveals the electrostatic nature of the interactions. Cooperative effect is explained by the difference of the electron density. Second-order stabilization energy was calculated to study the orbital interaction in the complex. Atoms in molecules analysis was performed to analyze the enhancement of the electron density in the bond critical point.     

Optical analysis of RE3+ (RE = Eu,Tb):MgLa2V2O9 nano-phosphors

Red and green rare-earth ion (RE³⁺) (RE = Eu, Tb):MgLa₂V₂O₉ micro-powder phosphors were produced utilizing a standard solid-state chemical process. The X-ray diffraction examination performed on the phosphors showed that they were crystalline and had a monoclinic structure. The particles grouped together, as shown in the scanning electron microscopy (SEM) images. Powder phosphors were examined using a variety of spectroscopic techniques, including photoluminescence (PL), Fourier-transform infrared, and energy dispersive X-ray spectroscopy. Brilliant red emission at 615 nm (⁵D₀ → ⁷F₂) having an excitation wavelength (λ_exci) of 396 nm (⁷F₀ → ⁵L₆) and green emission at 545 nm (⁵D₄ → ⁷F₅) having an λ_exci = 316 nm (⁵D₄ → ⁷F₂) have both been seen in the emission spectra of Tb³⁺:MgLa₂V₂O₉ nano-phosphors. The emission mechanism that is raised in Eu³⁺:MgLa₂V₂O₉ and Tb³⁺:MgLa₂V₂O₉ powder phosphors has been explained in an energy level diagram.     

Comparative Cytogenetics Among Allopatric Populations of the Fish, Hoplias Malabaricus. Cytotypes with 2n = 42 Chromosomes

The available chromosomal data on Hoplias malabaricus make possible the identification of three major karyotypic forms in this fish group, all of them bearing 2n = 42 chromosomes, and named as Cytotypes A, B and E in previous studies. While Cytotype A and B share a general macrokaryotypic feature, Cytotype E is well differentiated concerning the morphology and size of some chromosome pairs. On the other hand, Cytotype B presents an exclusive XX/XY sex chromosome system. Six allopatric populations, belonging to Cytotype A, were subjected to cytogenetic analysis in the present study. Despite their basic karyotypic similarity, some differences in the chromosome formulae, as well as in the heterochromatin and Ag-NORs locations, were observed among populations indicating that they no more correspond to a unit, at least in the cytogenetical level. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phase stability,elastic, anisotropic and thermodynamic properties of HoT2Al20 (T = Ti,V, Cr) intermetallic cage compounds

The structural stability, elastic properties, anisotropy, dynamics stability and thermodynamics properties were explored for pure Al and HoT₂Al₂₀ intermetallics from the first-principles method. The formation enthalpy and phonon frequencies indicate that these HoT₂Al₂₀ intermetallics maintain structural stability. The elastic constants C_ijs and moduli B, G, E and H_v indicate these intermetallics possess higher hardness and the better resistance to deformation. The values of Poisson’s ratio and B/G demonstrate that HoT₂Al₂₀ intermetallics are brittle materials. The anisotropic constants and anisotropic acoustic velocities confirm that HoT₂Al₂₀ intermetallics exhibit anisotropic properties. Importantly, the calculated thermal quantities demonstrate that these new HoT₂Al₂₀ intermetallics possess the better thermodynamic properties at high temperature.     

Structures, spectroscopic and thermodynamic properties of U2On (n = 0 ∼ 2, 4) molecules: a density functional theory study

The equilibrium structures, spectroscopic and thermodynamic parameters [entropy (S), internal energy (E), heat capacity (C _p)] of U₂, U₂O, U₂O₂ and U₂O₄ uranium oxide molecules were investigated systematically using density functional theory (DFT). Our computations indicated that the ground electronic state of U₂ is the septet state and the equilibrium bond length is 2.194 Å; the ground electronic state of U₂O and U₂O₂ were found to be $ {\tilde{X}}^3\varPhi $ and $ {\tilde{X}}^3{\sum}_{\mathrm{g}} $ with stable C _∞v and D _∞h linear structures, respectively. The bridge-bonded structure with D _2h symmetry and $ {\tilde{X}}^3{\mathrm{B}}_{1\mathrm{g}} $ state is the most stable configuration for the U₂O₄ molecule. Mulliken population analyses show that U atoms always lose electrons to become the donor and O atoms always obtain electrons as the acceptor. Molecular orbital analyses demonstrated that the frontier orbitals of the title molecules were contributed mostly by 5f atomic orbitals of U atoms. Vibrational frequencies analyses indicate that the maximum absorption peaks stem from the stretching mode of U–O bonds in U₂O, U₂O₂ and U₂O₄. In addition, thermodynamic data of U₂O_n (n?=?0?～?4) molecules at elevated temperatures of 293.0 K to 393.0 K was predicted.     

Effects of a single administration of prostaglandin F2alpha, or a combination of prostaglandin F2alpha and prostaglandin E2, or placebo on fertility variables in dairy cows 3–5 weeks post partum, a randomized, double-blind clinical trial

Background  

Delayed uterine involution has negative effects on the fertility of cows; use of prostaglandin F2alpha alone as a single treatment has not been shown to consistently improve fertility. Combined administration of PGF2alpha and PGE2 increased uterine pressure in healthy cows. We hypothesized, that the combination of both prostaglandins would accelerate uterine involution and have, therefore, a positive effect on fertility variables. In commercial dairy farming, the benefit of a single post partum combined prostaglandin treatment should be demonstrated.     

Effects of a single administration of prostaglandin F2alpha, or a combination of prostaglandin F2alpha and prostaglandin E2, or placebo on fertility variables in dairy cows 3–5 weeks post partum, a randomized, double-blind clinical trial

In female mammals, including humans, deviations from normal androgenic or estrogenic exposure during fetal development are detrimental to subsequent adult ovarian function. Androgen deficiency, without accompanying estrogen deficit, has little apparent impact on ovarian development. Fetal estrogen deficiency, on the other hand, results in impaired oocyte and follicle development, immature and abnormal adult ovaries, and excessive ovarian stimulation from endogenous gonadotropins ultimately generating hemorrhagic follicles. Complete estrogen deficiency lasting into adulthood results in partial ovarian masculinization. Fetal androgen excess, on the other hand, mediated either by direct androgen action or following androgen aromatization to estrogen, reprograms ovarian development and reproductive neuroendocrinology to mimic that found in women with polycystic ovary syndrome: enlarged, polyfollicular, hyperandrogenic, anovulatory ovaries with accompanying LH hypersecretion. Oocyte developmental competence is also compromised. Insulin is implicated in the mechanism of both anovulation and deficient oocyte development. Fetal estrogen excess induces somewhat similar disruption of adult ovarian function to fetal androgen excess. Understanding the quality of the fetal female sex steroid hormone environment is thus becoming increasingly important in improving our knowledge of mechanisms underlying a variety of female reproductive pathologies.     

A new reaction mode of germanium-silicon bond formation: insertion reactions of H2GeLiF with SiH3X (X = F, Cl, Br)

A combined density functional and ab initio quantum chemical study of the insertion reactions of the germylenoid H₂GeLiF with SiH₃X (X?=?F, Cl, Br) was carried out. The geometries of all the stationary points of the reactions were optimized using the DFT B3LYP method and then the QCISD method was used to calculate the single-point energies. The theoretical calculations indicated that along the potential energy surface, there were one precursor complex (Q), one transition state (TS), and one intermediate (IM) which connected the reactants and the products. The calculated barrier heights relative to the respective precursors are 102.26 (X?=?F), 95.28 (X?=?Cl), and 84.42 (X?=?Br) kJ mol^-1 for the three different insertion reactions, respectively, indicating the insertion reactions should occur easily according to the following order: SiH₃-Br?>?SiH₃-Cl?>?SiH₃-F under the same situation. The solvent effects on the insertion reactions were also calculated and it was found that the larger the dielectric constant, the easier the insertion reactions. The elucidations of the mechanism of these insertion reactions provided a new reaction model of germanium-silicon bond formation.     

Does the use of DM-nitrophen,nitr-5, or diazo-2 interfere with the measurement of indo-1 fluorescence?

Emission spectra of the photolabile Ca2+ chelators DM-nitrophen, nitr-5, and diazo-2 were studied alone, and in the presence of indo-1, to investigate potential interactions that would make the simultaneous manipulation and ratiometric measurement of the intracellular Ca2+ concentration difficult. Neither diazo-2 nor its photoproduct were found to be significantly fluorescent, and consequently concentrations of diazo-2 up to 20 times that of indo-1 did not distort the emission spectra of indo-1. DM-nitrophen was scarcely fluorescent, but its fluorescence did increase upon photolysis. In contrast to diazo-2 and DM-nitrophen, nitr-5 itself was found to be quite fluorescent, and this fluorescence was significantly increased upon photolysis. Thus, combined use of nitr-5 and indo-1 poses the most difficulty. The emission spectra of all the investigated compounds were used to define experimental conditions and calibration procedures that make possible simultaneous measurement and manipulation of the intracellular Ca2+ concentration.     

Metal-modified nucleobase pairs involving 7,9-dimethylguanine: trans-a2PtII analogues (a = NH3 or CH3NH2) of Watson-Crick GC and homo GG pairs

 The analogy between H-bonded nucleobase pairs and their metalated analogues is extended to the hemiprotonated pair of 7,9-dimethylguanine (7,9-DimeG) and the Watson-Crick and reversed Watson-Crick pair between 7,9-dimethylguaninium (7,9-DimeGH⁺) and 1-methylcytosine (1-MeC). The crystal structure analyses of two model compounds, trans–[Pt(CH₃NH₂)₂(7,9-DimeG-N1)₂](NO₃)₂ (1) and trans–[Pt(NH₃)₂(1-MeC-N3)(7, 9-DimeG-N1)](PF₆)₂· 2.5 H₂O (3a) are reported. Pt binding is through N1 of 7,9-DimeG and N3 of 1-MeC. In solution, 3a exists in a mixture with Watson-Crick and reversed Watson-Crick arrangements of the two bases, depending on solvent, concentration and anions. Received: 16 October 1996 / Accepted: 27 January 1997     

Formation of the Si-B bond: insertion reactions of silylenes into B-X(X = F,Cl, Br,O, and N) bonds

The insertion reactions of the silylene H₂Si with H₂BXH_n-1 (X?=?F, Cl, Br, O, N; n?=?1, 1, 1, 2, 3) have been studied by DFT and MP2 methods. The calculations show that the insertions occur in a concerted manner, forming H₂Si(BH₂)(XH_n-1). The essences of H₂Si insertions with H₂BXH_n-1 are the transfers of the σ electrons on the Si atom to the positive BH₂ group and the electrons of X into the empty p orbital on the Si atom in H₂Si. The order of reactivity in vacuum shows the barrier heights increase for the same-family element X from up to down and the same-row element X from right to left in the periodic table. The energies relating to the B-X bond in H₂BXH_n-1, and the bond energies of Si-X and Si-B in H₂Si(BH₂)(XH_n-1) may determine the preference of insertions of H₂Si into B-X bonds for the same-column element X or for the same-row element X. The insertion reactions in vacuum are similar to those in solvents, acetone, ether, and THF. The barriers in vacuum are lower than those in solvents and the larger polarities of solvents make the insertions more difficult to take place. Both in vacuum and in solvents, the silylene insertions are thermodynamically exothermic.

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Graphical Abstract The insertion process of H₂Si and H₂BXH_n-1(X?=?F, Cl, Br, O, and N; n?=?1, 1 , 1, 2, 3).

     

Protonation,alkylation, addition and redox reactions of 16, 17 and 18 valence electron [Mo(L)(NO)('S4')] complexes [L = SPh,PMe3, NO; 'S4'2– = 1,2-Bis-(2-mercaptophenylthio)ethane(2-)]

In the quest for complexes modelling functional characteristics of metal sulfur oxidoreductases, a series of molybdenum nitrosyl complexes with sulfur-dominated coordination sphere was synthesized. Treatment of the 16, 17 and 18 valence electron (VE) complexes [Mo(L)(NO)('S₄')] (1–3) [L?=?SPh (1), PMe₃ (2), NO (3), 'S₄'^2–?=?1,2-bis-(2-mercaptophenylthio) ethane(2-)] with the Brönsted acid HBF₄ resulted in formation of different types of products. 1 and 3 were reversibly protonated at one thiolate atom of the 'S₄'^2– ligand;2, however, yielded the phosphonium salt [HPMe₃]BF₄ and the dinuclear [Mo(NO)('S₄')]₂. Alkylation of 1, 2 and 3 by Me₃OBF₄ or Et₃OBF₄ uniformly resulted in high yields of [Mo(L)(NO)(R-'S₄')]BF₄ complexes [L?=?SPh: R?=?Me (5), Et (6); L?=?PMe₃: R?=?Me (7); L?=?NO: R?=?Me (8), Et (9)] in which one thiolate atom of the 'S₄'^2– ligand had become alkylated; the NMR spectra of 5, 6, 8 and 9 indicated that only one out of four theoretically possible diastereoisomers had formed. 5 and 6 were characterized also by single-crystal X-ray structure analyses. A comparison of ν(NO) bands and redox potentials (cyclic voltammetry) of parent complexes and alkylated derivatives showed that alkylation leads to a decrease in electron density at the molybdenum center and to a positive shift in redox potentials. The 16 VE complex 1 could be reduced, also chemically, to give the corresponding 17 VE anion [1]^–, and inserted elemental sulfur into the Mo-SPh bond, forming the 18 VE phenylperthio complex [Mo(η²–SSPh)(NO)('S₄')] (11) which, upon reaction with PPh₃, gave SPPh₃ and regenerated the parent complex 1. These results are discussed with regard to the sequence of proton and electron transfer steps occurring in substrate conversions catalyzed by metal sulfur oxidoreductases.     

Bcl-2 proteins: regulators of apoptosis or of mitochondrial homeostasis?

Programmed cell death (apoptosis) is used by multicellular organisms during development and to maintain homeostasis within mature tissues. One of the first genes shown to regulate apoptosis was bcl-2. Subsequently, a number of Bcl-2-related proteins have been identified. Despite overwhelming evidence that Bcl-2 proteins are evolutionarily conserved regulators of apoptosis, their precise biochemical function remains controversial. Three biochemical properties of Bcl-2 proteins have been identified: their ability to localize constitutively and/or inducibly to the outer mitochondrial, outer nuclear and endoplasmic reticular membranes, their ability to form heterodimers with proteins bearing an amphipathic helical BH3 domain, and their ability to form ion-conducting channels in synthetic membranes. The discovery that mitochondria can play a key part in the induction of apoptosis has focused attention on the role that Bcl-2 proteins may have in regulating either mitochondrial physiology or mitochondria-dependent caspase activation. Here we attempt to synthesize our current understanding of the part played by mitochondria in apoptosis with a consideration of how Bcl-2 proteins might control cell death through an ability to regulate mitochondrial physiology.