Synthesis,spectral and structural studies of oxovanadium(IV/V) complexes derived from 2-hydroxyacetophenone-3-hydroxy-2-naphthoylhydrazone: polymorphs of oxovanadium(V) complex [VOL(OCH<Subscript>3</Subscript>)]

Abstract  

Oxovanadium(IV/V) complexes of 2-hydroxyacetophenone-3-hydroxy-2-naphthoylhydrazone (H₂L) have been synthesized and characterized. The complexes were characterized by elemental analyses, IR, electronic and EPR spectra. The oxovanadium(V) complex [VOL(OCH₃)] is crystallized in two polymorphic forms, denoted by 1a and 1b, with space groups Pn2₁a and P_[`1] P_{{\bar{1}}} , respectively. Both have distorted square pyramidal structures.     

Unanimous Model for Describing the Fast Bioluminescence Kinetics of Ca2+‐regulated Photoproteins of Different Organisms

Upon binding their metal ion cofactors, Ca²⁺‐regulated photoproteins display a rapid increase of light signal, which reaches its peak within milliseconds. In the present study, we investigate bioluminescence kinetics of the entire photoprotein family. All five recombinant hydromedusan Ca²⁺‐regulated photoproteins—aequorin from Aequorea victoria, clytin from Clytia gregaria, mitrocomin from Mitrocoma cellularia and obelins from Obelia longissima and Obelia geniculata—demonstrate the same bioluminescent kinetics pattern. Based on these findings, for the first time we propose a unanimous kinetic model describing the bioluminescence mechanism of Ca²⁺‐regulated photoproteins.     

The Fer tyrosine kinase regulates interactions of Rho GDP-Dissociation Inhibitor α with the small GTPase Rac

Background  

RhoGDI proteins are important regulators of the small GTPase Rac, because they shuttle Rac from the cytoplasm to membranes and also protect Rac from activation, deactivation and degradation. How the binding and release of Rac from RhoGDI is regulated is not precisely understood.     

Syntheses of N-alkyl, N,N-dialkyl, and N-(4-substituted phenyl) O-ethyl thioncarbamates: a kinetic study

Abstract  

The kinetics of the syntheses of N-alkyl, N,N-dialkyl, and N-(4-substituted phenyl) O-ethyl thioncarbamates from sodium ethyl xanthogenacetate, ten alkylamines, and eight substituted anilines were studied at 25, 30, 35, and 40 °C. The reactions were found to follow second-order kinetics. The kinetic (Arrhenius) parameters, such as the activation energy and the frequency factor, as well as the Eyring parameters, such as the standard entropy, the standard Gibbs energy, and the standard enthalpy of activation, were calculated from the second-order rate constants. The mechanism of the reaction was postulated based on the kinetic studies presented and the optimization of the reaction mechanism using the MOPAC PM6 semi-empirical method.     

The differential modulation of USP activity by internal regulatory domains, interactors and eight ubiquitin chain types

Ubiquitin-specific proteases (USPs) are papain-like isopeptidases with variable inter- and intramolecular regulatory domains. To understand the effect of these domains on USP activity, we have analyzed the enzyme kinetics of 12 USPs in the presence and absence of modulators using synthetic reagents. This revealed variations of several orders of magnitude in both the catalytic turnover (k_cat) and ubiquitin (Ub) binding (K_M) between USPs. Further activity modulation by intramolecular domains affects both the k_cat and K_M, whereas the intermolecular activators UAF1 and GMPS mainly increase the k_cat. Also, we provide the first comprehensive analysis comparing Ub chain preference. USPs can hydrolyze all linkages and show modest Ub-chain preferences, although some show a lack of activity toward linear di-Ub. This comprehensive kinetic analysis highlights the variability within the USP family.     

Chemistry of chromium bis-acetylide complexes

Abstract  

Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)₂Cr(dmpe)₂] ⁿ⁺ (R = Ph, SiMe₃, SiEt₃, C≡C–SiMe₃ n = 0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies.     

The effect of point mutations on copper(II) complexes with peptide fragments encompassing the 106–114 region of human prion protein

Abstract  

The tetrapeptides Ac-SKHM-NH₂, Ac-TKHM-NH₂, Ac-MKHS-NH₂, Ac-S(OMe)KHM-NH₂, and Ac-MKHS(OMe)-NH₂ and the nonapeptides Ac-KTNSKHMAG-NH₂ and Ac-KTNMKHSAG-NH₂ were synthesized and their copper(II) complexes were studied by potentiometric, UV–Vis, circular dichroism (CD), and electron paramagnetic resonance (EPR) spectroscopic methods. These peptides mimic the 109–112 and 106–114 residues of the sequence of human prion protein. The imidazole-N donor atoms of histidyl residues were found to be the primary metal binding sites of all peptide fragments. This binding mode provides a good possibility for the cooperative deprotonation and metal ion coordination of two amide functions preceding histidine. The (N_im,N⁻,N⁻)-bonded species predominate in the pH range 5.5–7.0 and the free coordination sites of these species make possible the metal binding of weakly coordinating side chains. The comparison of the potentiometric and spectroscopic results revealed the stabilizing role of the oxygen donors of seryl, threonyl, or methoxyseryl residues of Ac-SKHM-NH₂, Ac-TKHM-NH₂, Ac-S(OMe)KHM-NH₂, and Ac-KTNSKHMAG-NH₂ containing the mutations in position 109. These interactions were, however, not observed in the peptides containing the specific amino acids in other locations of the peptide sequence.     

Ge-doped (4,4) armchair single-walled boron phosphide nanotube as a semiconductor: a computational study

Abstract  

Density functional theory (DFT) calculations were performed to investigate the electronic structure properties of Ge-doped boron phosphide nanotubes (BPNTs) as a semiconductor at the B3LYP/6-31G* level of theory in order to evaluate the influence of Ge doping on (4,4) armchair BPNTs. We extended the DFT calculations to predict the electronic structure properties of Ge-doped boron phosphide nanotubes, which are very important for production of solid-state devices and other applications. The isotropic (CS^I) and anisotropic (CS^A) chemical shielding parameters for the sites of various ¹¹B and ³¹P atoms, and the quadrupole coupling constant (C _Q) and asymmetry parameter (η _Q) at the sites of various ¹¹B nuclei, were calculated in pristine and Ge-doped (4,4) armchair BPNT models. The calculations indicated that, in these two forms of Ge-doped BPNTs, the binding energies are not attractive and do not characterize a chemisorption process. In comparison with the pristine model, the band gap of the two forms of Ge-doped BPNTs is reduced and increases their electrical conductance. The dipole moments of the Ge-doped BPNT structures show notable changes with respect to the pristine model. The nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) results show that the Ge_B model is a more reactive material than the pristine or Ge_P model.     

Synthesis,Structures, and Properties of Layered Quaternary Chalcogenides of the General Formula ALnEQ4 (A = K,Rb; Ln = Ce,Pr, Eu; E = Si,Ge; Q = S,Se)

Four related quaternary compounds containing rare‐earth metals have been synthesized employing the molten flux method and metathesis. The reactions of Eu and Rb₂S₅ with Si and Ge in evacuated fused silica ampoules at 725 °C for 150 h yielded RbEuSiS₄ ( I ) and RbEuGeS₄ ( II ), respectively. On the other hand, a reaction between CeCl₃ and K₄Ge₄Se₁₀ at 650 °C for 148 h has yielded KCeGeSe₄ ( III ) and KPrSiSe₄( IV ) was obtained by the reaction of elemental Pr, Si and Se in KCl flux at 850 °C for 168 h. Crystal data for these compounds are as follows: I , orthorhombic, space group P2₁2₁2₁ (#19), a = 6.392(1), b = 6.634(2), c = 17.001(3) Å, α = β = γ = 90°, Z = 4; II , monoclinic, space group P2₁/m (#11), a = 6.498(2), b = 6.689(3), c = 8.964(3) Å, β = 108.647(6)°, Z = 2; III , monoclinic, space group P2₁ (#4), a = 6.852(2), b = 7.025(2), c = 9.017(3) Å, β = 108.116(2)°, Z = 2; IV , monoclinic, space group P2₁ (#4), a = 6.736(2), b = 6.943(2), c = 8.990(1) Å, β = 108.262(2)°, Z = 2. The crystal structures of I ‐ IV contain two‐dimensional corrugated anionic layers of the general formula, [LnEQ₄]^? (Ln = Ce, Pr, Eu; E = Si, Ge and Q = S, Se) alternately piled upon layers of alkali cations. In addition to structural elucidation, Raman and UV‐visible spectroscopy, and magnetic measurements for compound III (KCeGeSe₄) are also discussed.     

Synthesis, UV–Vis spectra, and Hammett correlation of some novel bis(dihydropyrrolo[3,4-c]pyrazoles)

Abstract  

Twenty-nine novel bis(dihydropyrrolo[3,4-c]pyrazole) derivatives were obtained by reacting C,N-phenyl-substituted nitrilimines generated in situ from corresponding hydrazonyl chlorides with bismaleimides. The structures were elucidated by physical and spectroscopic methods [m.p., R _f, infrared (IR), ¹H nuclear magnetic resonance (NMR), ¹³C NMR, correlation spectroscopy (COSY), heteronuclear correlation (HETCOR), nuclear Overhauser effect (NOE), and high-resolution mass spectrometry (HRMS)]. Also, Hammett correlation graphs were obtained between Hammett constants σ _p and λ _max values of bis(pyrrolopyrazoles) carrying p-substituted phenyl-ring-bearing electron-withdrawing and electron-donating groups and discussed in terms of substituent effects.     

A facile and efficient method for synthesis of xanthone derivatives catalyzed by HBF4/SiO2 under solvent-free conditions

Abstract  

HBF₄/SiO₂ was used as an efficient, green, and inexpensive catalytic system for synthesis of 12-aryl or 12-alkyl-8,9,10,12-tetrahydro-11H-benzo[a]xanthen-11-one derivatives via a one-pot three-component reaction of aldehydes, 2-naphthol, and cyclic 1,3-dicarbonyl compounds. The reactions proceeded rapidly at 80 °C under solvent-free conditions and the desired products were obtained in good to excellent yields.     

Self-assembly of tris(2-ureidobenzyl)amines with <Emphasis Type="Italic">C</Emphasis><Subscript>1</Subscript> symmetry

Abstract  

Tris(2-ureidobenzyl)amines bearing three differentially substituted arms have been synthesized. They possess an asymmetric nitrogen atom, the pivotal one, and thus they feature C ₁ symmetry. The self-assembly of these C ₁-symmetric tris(2-ureidobenzyl)amines may potentially lead to multiple regio- and diastereoisomeric capsules coming from the pairing of the four stereoisomeric monomers with configurations (R, P), (S, P), (R, M) and (S, M). The ¹H- and ¹⁹F{¹H}-NMR spectra confirm the presence of dimeric aggregates, as a mixture of several regio- and diastereoisomeric species.     

Application of chloroaluminate ionic liquid as catalyst and medium for the dealkylation of esters

Abstract  

Dealkylation of esters to carboxylic acids was performed using chloroaluminate ionic liquids (PyHBr/AlCl₃, PyHCl/AlCl₃, Me₃NHCl/AlCl₃, Et₃NHCl/AlCl₃) as catalyst and medium. The catalytic activity of PyHBr/AlCl₃ (X(AlCl₃) = 0.67) proved to be superior to the other three ionic liquids for the dealkylation of methyl benzoate with a conversion of 97% after 3 h at 140 °C. After easy separation from the products the ionic liquid PyHBr/AlCl₃ could be reused six times without loss of its activity.     

Salt flux crystal growth of the titanyl arsenate NaTiO[AsO4]

Abstract  

The titanyl arsenate NaTiO[AsO₄] was synthesized in the form of colourless lath-shaped crystals from arsenic and titanium dioxide in a NaCl/KCl flux at 850 °C. NaTiO[AsO₄] crystallizes with the monoclinic low-temperature form LT-CaTiO[SiO₄], space group P2₁/c. The structure was refined from single crystal diffractometer data: a = 6.7170(9), b = 8.7707(12), c = 7.2447(10) ?, β = 114.77(1)°, wR2 = 0.0559, 789 F ² values, and 74 variables. NaTiO[AsO₄] is characterized by a topology common to a wide range of oxide structures of stoichiometry AMOXO₄. It consists of parallel chains of trans-corner-sharing TiO₆ octahedra, cross-linked by isolated AsO₄ tetrahedra.     

Synthesis,crystal structures,and magnetic properties of three isomorphous helical coordination polymers

Three isomorphous coordination polymers of general formula {[M(H₂bna)·(DMF)₂·(H₂O)₂]·DMF}_n (M = Co for 1, Mn for 2, Ni for 3, respectively, where H₄bna = 2,2′-dihydroxy-[1,1′]-binaphthalene-3,3′-dicarboxylate) were synthesized under solvothermal conditions and characterized by FTIR, single crystal X-ray diffraction, thermogravimetric analysis, and X-ray power diffraction analysis. All three polymers crystallize in the same monoclinic space group P2₁/n. The complexes are assembled into 1D helical chains, and each adjacent helical chain of the same chirality is further connected to form a chiral layer by hydrogen bond interactions. The layers are packed in alternating left-(M) and right-handed (P) chirality arrays. Magnetic studies reveal the presence of antiferromagnetic coupling interactions in complexes 1 and 2.     

The interaction of water-soluble α, ω-disubstituted alkanes (bolaform compounds) with polyvinylpyrrolidone in aqueous solution

Summary The published work on the interactions between polyvinylpyrrolidone (PVP) and small-molecule solutes (cosolutes) in aqueous solution has been briefly surveyed. The further information on these types of interaction which the proposed study of,-disubstituted aliphatic cosolutes, of the general type X(CH₂) _m Y (bolaform compounds), was hoped to yield has been outlined. The technique of equilibrium dialysis (employing two-compartment acrylate cells) has been used to study the interaction between PVP in aqueous solution at 25 °C and the following eight symmetrical (X=Y) bolaform cosolutes: X=SO₄ Na,m=8, 10 and 12 (A, B and C); X=CO₂ K,m=10 (D); X=N(CH₃)₃ Br,m=10 (E); X=NH₃ Cl,m=8, 10 and 12 (F, G and H). The maximum total cosolute concentrations used were between 100 and 230 millimolal. The equilibrated dialysis-cell solutions were assayed by differential refractometry; the data obtained were converted into the values ofa, the concentration of free cosolute, andr, the concurrent number of moles of cosolute bound per base mole (vinylpyrrolidone unit) of the polymer. The limit of detectable binding wasr=0.005 for all cosolutes. The results showed that of the three disulphates (A, B and C), the octamethylene compound (A) was not detectably bound while the deca- and dodecamethylene compounds (B and C) had binding isotherms of the hyperbolic (Langmuir) form:r =nKa/(1 +Ka), withK=65 (±20) molal^–1 andn=0.057 (±0.005) form=10, andK=16 (±2) molal^–1 andn=0.139 (±0.005) form=12; the other anionic cosolute (D) was not detectably bound. Of the cationic cosolutes (E, F, G and H), Decamethonium bromide (E) had a non-hyperbolic binding isotherm with a maximum ata=75 millimolal ofr~0.025; the three di(ammonium chloride)s (F, G and H) were not detectably bound. The refractive index increments and densities of the aqueous solutions of the same eight compounds have also been determined; the results did not show any anomalies which could definitely be attributed to association or micellisation, except in the case of Decamethonium bromide where ion-pairing is known to take place. The marked difference in binding behaviour between the anionic cosolutes and the cationic ones is attributed to the different environments of the positive and negative ends of the dipolar imide groups in the pyrrolidone rings of PVP; the binding data are discussed in terms of the polar (ion-dipole) and non-polar (hydrophobic) forces between cosolute and polymer, and of the relative roles played by the value of the end-to-end distance for the cosolute molecule and by any direct hydrophobic interactions in determining the dependence of binding behaviour upon cosolute chain length,m.     

Aminopeptidase B,a glucagon-processing enzyme: site directed mutagenesis of the Zn<Superscript>2+</Superscript>-binding motif and molecular modelling

Background  

Aminopeptidase B (Ap-B; EC 3.4.11.6) catalyzes the cleavage of basic residues at the N-terminus of peptides and processes glucagon into miniglucagon. The enzyme exhibits, in vitro, a residual ability to hydrolyze leukotriene A₄ into the pro-inflammatory lipid mediator leukotriene B₄. The potential bi-functional nature of Ap-B is supported by close structural relationships with LTA₄ hydrolase (LTA₄H ; EC 3.3.2.6). A structure-function analysis is necessary for the detailed understanding of the enzymatic mechanisms of Ap-B and to design inhibitors, which could be used to determine the complete in vivo functions of the enzyme.     

Occurrence and sequence of Sphaeroides Heme Protein and Diheme Cytochrome C in purple photosynthetic bacteria in the family <Emphasis Type="Italic">Rhodobacteraceae</Emphasis>

Background  

Sphaeroides Heme Protein (SHP) was discovered in the purple photosynthetic bacterium, Rhodobacter sphaeroides, and is the only known c-type heme protein that binds oxygen. Although initially not believed to be widespread among the photosynthetic bacteria, the gene has now been found in more than 40 species of proteobacteria and generally appears to be regulated. Rb. sphaeroides is exceptional in not having regulatory genes associated with the operon. We have thus analyzed additional purple bacteria for the SHP gene and examined the genetic context to obtain new insights into the operon, its distribution, and possible function.     

The 3D porous metal-organic framework constructed by Cd(II) with 2-methylimidazole-4,5-dicarboxylic acid

Abstract  

A 3D metal-organic framework, [C₆H₃CdN₂O₄]·NH₄, was synthesized solvothermally and structurally characterized by single-crystal X-ray structure determination. This compound crystallizes in the tetragonal system with the space group P42/nmc. The crystal structure presents a 3D framework and open channels, exhibiting guest-coordination sites at channel walls and strong fluorescent emission.     

Effect of precompression on isothermal decomposition kinetics of pure and doped potassium bromate

Pure and doped samples of potassium bromate (KBrO₃) were subjected to precompression and their thermal decomposition kinetics was studied by thermogravimetry at 668 K. The samples decomposed in two stages governed by the same rate law (contracting square equation), but with different rate constants, k ₁ (for a α ≤ 0.45) and k ₂ (for α ≥ 0.45), as in the case of uncompressed samples. The rate constants k ₁ and k ₂ decreased dramatically on precompression, the decrease being higher for doped samples. Cation dopants (Ba²⁺, Al³⁺) caused more desensitization effect than the anion dopants ( \textSO₄ ^2- {\text{SO}}_{4}{}^{ 2- } , PO₄ ³⁻) of the same magnitude of charge and concentration. The results favor ionic diffusion mechanism proposed earlier on the basis of doping studies.