Rational design of a novel fluorescent biosensor for beta-lactam antibiotics from a class A beta-lactamase

A rational design strategy was used to construct a sensitive "turn-on" biosensor for beta-lactam antibiotics and beta-lactamase inhibitors from a class A beta-lactamase mutant with suppressed hydrolytic activity. A fluorescein molecule was attached to the 166 position on the Omega-loop of the E166C mutant close to the active site of the beta-lactamase. Upon binding with antibiotics or inhibitors, the flexibility of the Omega-loop allows the fluorescein molecule to move out from the active site and be more exposed to solvent. This process is accompanied by an increase in the fluorescence of the labeled enzyme. The fluorescence intensity of the biosensor increases with the concentration of antibiotics or inhibitors, which can detect penicillin G at concentrations as low as 50 nM in water. This approach opens a possibility for converting highly active and nonallosteric enzymes into substrate-binding proteins for biosensing purposes.     

1,2,4,5-苯四甲酸铒配合物的合成及其晶体结构

合成了NH4^+[ErC6H2(COO)4.3H2O]^-.4H2O晶体,并测定了其晶体结构,发现稀土Er^+^3跟苯四甲酸中的五个氧原子及三个水的氧原子配位,形成八配位的配合物.配位多面体呈二帽畸变三角反棱柱.晶体结构沿着(001)面呈现一个网状结构.这种结构对研究稀土元素的结构化学、配位化学,化学键理论等提供了有用的实验数据.     

Synthesis and crystal structure of a Pb complex with ciprofloxacin

A hydrothermal reaction of ciprofloxacin with PbCl₂ · 2H₂O and Na₂S yields a metal complex [Pb₂(H-Cip)₆S]Cl₆ (I), which was characterized by elemental analysis, IR, and single crystal diffraction analyses. Complex I crystallizes in the rhombohedral system, space group $R\bar 3c$ , with lattice parameters a = 15.7800(7), c = 77.901(9) ?, V = 16799(2) ?³, Z = 12, ??_calcd = 1.646 mg/m³.     

Synthesis of a new chiral source, (1R,2S)-1-Phenylphospholane-2-carboxylic acid, via a key intermediate alpha-phenylphospholanyllithium borane complex: configurational stability and X-ray crystal structure of an alpha-monophosphinoalkyllithium borane complex

A synthetic route to enantiomerically pure (1R,2S)-1-phenylphospholane-2-carboxylic acid (1), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation-carboxylation of the 1-phenylphospholane borane complex 3 by using sBuLi/1,2-dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine-coordinated alpha-phosphinoalkyllithium borane complex 4, was investigated by employing lithiodestannylation-carboxylation of both diastereomers of the 1-phenyl-2-trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at -100 degrees C. The key intermediate, the DPE-coordinated trans-1-phenyl-2-phospholanyllithium borane complex 9, was isolated, and the structure was identified by X-ray crystal structure analysis. This is the first X-ray crystal structure determined for an alpha-monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li--C bond (2.170 A) has been confirmed. Moreover, (1)H-(7)Li HOESY and (6)Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9, its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at -100 degrees C. Finally, 1 was used as a chiral ligand in a palladium-catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity.     

Wheel-and-axle design as a source of host-guest compounds. The crystal structure of the 2:1 acetone: tetraphenyl-2,4-hexadiyne-1,6-diol complex

The title diyne-diol crystallizes with an “open” structure containing channels, roughly parallel to the long axis of the host, in which the acetone is hydrogen bonded to the anti-oriented hydroxyl groups.     

The body-centered cubic structure of methyllithium tetramer crystal: staggered methyl conformation by electrostatic stabilization via intratetramer multipolarization

The methyllithium tetramer (CH3Li)4 structure in the bcc crystal has been theoretically optimized with the use of density functional theory calculations under the periodic boundary condition. The X-ray structure shows that the methyl-group conformation in tetramer in crystal takes the staggered form rather than the eclipsed form that is taken in the isolated tetramer, i.e., the crystal packing effect, and this has been reproduced for the first time. It is concluded that the staggered form is advantageous in crystal, as a whole, due to the larger electrostatic stabilization via the induced intratetramer multipolarization, although it should cause, simultaneously, smaller destabilization in intratetramer electronic energy.     

A simple molecule with a complex crystal structure: interplay of 31P solid-state NMR spectroscopy and single-crystal x-ray diffraction in the structure determination of a ruthenium diphosphine diamine complex

A comprehensive 31P solid-state NMR study of Ru(eta1-Ph2PCH2CH2OCH3)2(eta2-en)Cl2 (en = ethylenediamine) (1), by 1D (contact time variation, inversion-recovery, SPARTAN) and 2D techniques (homonuclear J-resolved, SECSY) indicated that the crystal structure of 1 should be complex. The single-crystal x-ray structure determination confirmed the presence of eight independent molecules in the asymmetric unit, with 31P isotropic chemical shifts in the range 27.3-40.1 ppm, while the spans of the phosphorus chemical shift tensors are of the order of 170 ppm. Based on unique structural features and NMR data, one molecule has been tentatively assigned.     

Complexes of pyrene with 2,4,6-trinitroanisole. Studies of association in solution and the crystal structure of the 1:1 complex

Cyclohexane solutions of 2,4,6-trinitroanisole (A) containing excess pyrene (D) can be described in terms of a double equilibrium involving complexes DA and D₂A. Formation constants for these complexes from A and from DA respectively from three independent experiments are in good agreement, the average values being K₁= 9.7 kg mol^-1 and K₂= 1.8 kg mol^-1 at 33.5°. The crystalline complex was obtained by gel diffusion. The mw (C₂₃H₁₅N₃O₇) corresponds to 1:1 stoichiometry C₁₆H₁₀, C₇H₅N₃O₇, X-ray structure data: P2₁/c, a = 10.633(7), b= 16.336(8), c = 11.683(7) Å, β = 94.62(12)°, V = 2023 ų, F₀₀₀ = 924, μ(CuKα) = 8.3 cm^-1, Z = 4. R = 0.091 for 1572 reflexions. The crystal contains extended stacks ADADA, parallel to (101). The pyrene molecules are disordered by rotation over two sites. The majority site has an occupancy factor of 0.544(2). The angle between the normals to the mean planes of A and D is 7.0(4)°, allowing the nitro groups of A to twist out of the plane of the benzene ring by 41.0(1.0), 2.7(5) and 20.7(8)°.     

Molecular and crystal structure of a cationic dinitrosyl iron complex with 1,3-dimethylthiourea

A new dinitrosyl iron complex of the composition [Fe(SC(NHCH₃)₂)₂(NO)₂]Cl (I) is obtained by direct nitrosylation of ferrous sulfate and a hydrochloric acid solution of 1,3-dimethylthiourea. The characteristic features of the molecular and crystal structure of complex I is determined by single crystal X-ray diffraction analysis.     

Molybdenum-phosphorus triple bond stabilization by ancillary alkoxide ligation: synthesis and structure of a terminal phosphide tris-1-methylcyclohexanoxide complex

Using alcoholysis, we converted terminal phosphide PMo(N[i-Pr]Ar)3 into a new, monomeric terminal phosphide PMo(OR)3, where R = 1-methylcyclohexyl or 1-adamantyl. Dimerization of the PMo unit was observed upon alcoholysis with 2,6-dimethylphenol, and the dimer [PMo(N[i-Pr]Ar)(O-2,6-C6H3Me2)2]2 was isolated and characterized by X-ray crystallography.     

Reactivity of a triruthenium alkenyl cluster complex with conjugated diynes: Coupling of two diyne molecules via a face-capping diyne intermediate

The cluster [Ru₃(μ₃-κ²-HNNMe₂)(μ-κ²-PhCHCPh)(μ-CO)₂(CO)₆], which has a face-capping 1,1-dimethylhydrazido and an edge-bridging 1,2-diphenylethenyl ligand, reacts with diphenylbutadiyne or 2,4-hexadiyne to give the isomeric triruthenium carbonyl cluster complexes [Ru₃(μ₃-κ²-HNNMe₂)(μ-κ²-PhCHCPh){μ₃-κ⁴-RCCCC(R)C(R)CCCR}(CO)₆] (3a, R = Ph; 3b, R = Me) and [Ru₃(μ₃-κ²-HNNMe₂)(μ-κ²-PhCHCPh){μ₃-κ⁴-RCCCC(R)C(CCR)CR}(CO)₆] (4a, R = Ph; 4b, R = Me). These compounds contain a large unsaturated hydrocarbyl ligand that arises from a metal-cluster-mediated head-to-head (3) or head-to-tail (4) coupling of two diyne molecules and maintain the original hydrazido and ethenyl ligands. Metal clusters that contain a face-capping diyne coordinated through only one alkyne fragment, such as [Ru₃(μ₃-κ²-HNNMe₂)(μ-κ²-PhCHCPh)(μ₃-κ²-RCCCCR)(CO)₇], have also been isolated (2a, R = Ph; 2b, R = Me). They are the intermediates that incorporate a second diyne reagent to give 3 and 4. The structural parameters of intermediate 2b have been obtained from DFT calculations.     

Unusual crystal and molecular structure of the 1-(1-silatranylmethyl)-3,5-dimethylpyrazole complex with zinc dichloride

The crystal and molecular structure of a 1-(1-silatranylmethyl)-3,5-dimethylpyrazole complex with zinc dichloride (I) is determined by XRD. The coordination polyhedron of the zinc atom is a tetrahedron formed by two covalent Zn-Cl bonds and coordination Zn ← N and Zn ← O bonds. Compound I is the first example of how an endocyclic oxygen atom of the silatranyl fragment participates in the coordination of the metal atom with the formation of a six-membered heterocycle.     

The crystal structure of a Terbium(III) complex with 1,1-Cyclobutanedicarboxylic acid

A complex of 1,1-cyclobutanedicarboxylic acid with terbium was obtained as a pentahydrate. The salt crystallizes in the monoclinic system, space group P2₁/n with a = 15.885(3), b = 8.489(2), c = 19.189(4)?Å, β = 106.02(3)° and Z = 4. The structure was solved by direct methods and refined to R = 0.0537. The complex forms polymeric chains in which terbium(III) ions are linked by carboxylate bridges. Each terbium cation is surrounded by carboxylate oxygen atoms and two or three water oxygen atoms, giving coordination number 9. The structure is stabilized by a system of hydrogen bonds.     

A new CoII complex of diniconazole: synthesis,crystal structure and antifungal activity

A new Co^II complex of diniconazole, namely diaqua[(E)‐(RS)‐1‐(2,4‐dichlorophenyl)‐4,4‐dimethyl‐2‐(1H‐1,2,4‐triazol‐1‐yl‐κN⁴)pent‐1‐en‐3‐ol]cobalt(II) dinitrate dihydrate, [Co(C₁₅H₁₇Cl₂N₃O)₃(H₂O)₂](NO₃)₂·2H₂O, was synthesized and characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction. Crystal structural analysis shows that the centrosymmetric Co^II cation is coordinated by four diniconazole ligands and two water molecules, forming a six‐coordinated octahedral structure. There are also two free nitrate counter‐anions and two additional solvent water molecules in the structure. Intermolecular O—H...O hydrogen bonds link the complex cations into a one‐dimensional chain. In addition, the antifungal activity of the complex against Botryosphaeria ribis, Gibberella nicotiancola, Botryosphaeria berengriana and Alternariasolani was studied. The results indicate that the complex shows a higher antifungal activity for Botryosphaeria ribis and Botryosphaeria berengriana than diniconazole, but a lower antifungal activity for Gibberella nicotiancola and Alternariasolani.     

Synthesis of an octamethyl-18-crown-6 derivative and the X-ray crystal structure of its 2:1 complex with borane-ammonia

The synthesis of 2,2,3,3,11,11,12,12-octamethyl-1,4,7,10,13,16-hexaoxacyclooctadecane (2) from pinacol (3) by a sequence of reactions (3→4→5→6+5→2) involving alkylation (3→ 4), ozonolysis and reduction (4→5), tosylation (5→6), and cyclisation (5+6→2) is reported. With borane-ammonia, the octamethyl-18-crown-6 derivative 2 forms a crystalline 2:1 complex, (BH₃NH₃)₂ · 2. X-Ray crystallography reveals the two guest BH₃NH₃ molecules are hydrogen bonded in a centrosymmetric manner to the opposite faces of the host 2, which adopts an all-gauche (ag⁺a ag^-a)₃ conformation.