Spin Crossover in a Hexaamineiron(II) Complex: Experimental Confirmation of a Computational Prediction

Single crystal structural analysis of [Fe^II(tame)_2]Cl_2⋅MeOH (tame=1,1,1‐tris(aminomethyl)ethane) as a function of temperature reveals a smooth crossover between a high temperature high‐spin octahedral d^6 state and a low temperature low‐spin ground state without change of the symmetry of the crystal structure. The temperature at which the high and low spin states are present in equal proportions is T_1/2=140 K. Single crystal, variable‐temperature optical spectroscopy of [Fe^II(tame)_2]Cl_2⋅MeOH is consistent with this change in electronic ground state. These experimental results confirm the spin activity predicted for [Fe^II(tame)_2]^2+ during its de novo artificial evolution design as a spin‐crossover complex [Chem. Inf. Model . 2015 , 55 , 1844], offering the first experimental validation of a functional transition‐metal complex predicted by such in silico molecular design methods. Additional quantum chemical calculations offer, together with the crystal structure analysis, insight into the role of spin‐passive structural components. A thermodynamic analysis based on an Ising‐like mean field model (Slichter–Drickammer approximation) provides estimates of the enthalpy, entropy and cooperativity of the crossover between the high and low spin states.publishedVersio

Anaphylactic Shock A Form of Distributive Shock without Inhibition of Oxygen Consumption

Background: The pathophysiology of anaphylactic shock during anesthesia is incompletely characterized. It is described as distributive by analogy with septic shock (anaerobic metabolism, high tissue oxygen pressure [PtiO 2 ] values). The PtiO 2 profile and its metabolic consequences during anaphylaxis are not known. Methods: Ovalbumin-sensitized anaphylactic shock rats (n ‫؍‬ 11) were compared to nicardipine-induced hypotension rats (n ‫؍‬ 12) for systemic hemodynamics, PtiO 2 , sympathetic nervous system activation, skeletal muscle blood flow, and interstitial lactate and pyruvate concentrations using combined microdialysis and polarographic Clark-type oxygen probes. Results: In both groups, the time course and the magnitude of arterial hypotension were similar. The ovalbumin group but not the nicardipine group displayed decreased skeletal muscle blood flow (from 45 ؎ 6.2 ml ⅐ 100 g ؊1 ⅐ min ؊1 to 24.3

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Spin Crossover in a Hexaamineiron(II) Complex: Experimental Confirmation of a Computational Prediction

Single crystal structural analysis of [Fe^II(tame)_2]Cl_2⋅MeOH (tame=1,1,1‐tris(aminomethyl)ethane) as a function of temperature reveals a smooth crossover between a high temperature high‐spin octahedral d^6 state and a low temperature low‐spin ground state without change of the symmetry of the crystal structure. The temperature at which the high and low spin states are present in equal proportions is T_1/2=140 K. Single crystal, variable‐temperature optical spectroscopy of [Fe^II(tame)_2]Cl_2⋅MeOH is consistent with this change in electronic ground state. These experimental results confirm the spin activity predicted for [Fe^II(tame)_2]^2+ during its de novo artificial evolution design as a spin‐crossover complex [Chem. Inf. Model . 2015 , 55 , 1844], offering the first experimental validation of a functional transition‐metal complex predicted by such in silico molecular design methods. Additional quantum chemical calculations offer, together with the crystal structure analysis, insight into the role of spin‐passive structural components. A thermodynamic analysis based on an Ising‐like mean field model (Slichter–Drickammer approximation) provides estimates of the enthalpy, entropy and cooperativity of the crossover between the high and low spin states

Spin Crossover in a Hexaamineiron(II) Complex: Experimental Confirmation of a Computational Prediction

Single crystal structural analysis of [FeII(tame)₂]Cl₂·MeOH (tame = 1,1,1-tris(aminomethyl)ethane) as a function of temperature reveals a smooth crossover between a high temperature high-spin octahedral d⁶ state and a low temperature low-spin ground state without any change of the symmetry of the crystal structure. The temperature at which the high and low spin states are present in equal proportions is T1/2 = 140 K. Single crystal, variable-temperature optical spectroscopy of [FeII(tame)₂]Cl₂·MeOH is consistent with this change in electronic ground state. These experimental results confirm the spin activity predicted for [Fe(tame)₂]2+ during its de novo artificial evolution design as a spin-crossover complex [Chem. Inf.2015, 55, 1844], offering the first experimental validation of a functional transition-metal complex predicted by such in-silico molecular design methods. Additional quantum chemical calculations offer, together with the crystal structure analysis, insight into the role of spin-passive structural components. A thermodynamic analysis based on an Ising-like mean field model (Slichter-Drickammer approximation) provides us with estimates on enthalpy, entropy and cooperativity of the crossover between the high and low spin states

Kinetic and Structural Characterization of the Self-Labeling Protein Tags HaloTag7, SNAP-tag, and CLIP-tag

The self-labeling protein tags (SLPs) HaloTag7, SNAP-tag, and CLIP-tag allow the covalent labeling of fusion proteins with synthetic molecules for applications in bioimaging and biotechnology. To guide the selection of an SLP-substrate pair and provide guidelines for the design of substrates, we report a systematic and comparative study of the labeling kinetics and substrate specificities of HaloTag7, SNAP-tag, and CLIP-tag. HaloTag7 reaches almost diffusion-limited labeling rate constants with certain rhodamine substrates, which are more than 2 orders of magnitude higher than those of SNAP-tag for the corresponding substrates. SNAP-tag labeling rate constants, however, are less affected by the structure of the label than those of HaloTag7, which vary over 6 orders of magnitude for commonly employed substrates. Determining the crystal structures of HaloTag7 and SNAP-tag labeled with fluorescent substrates allowed us to rationalize their substrate preferences. We also demonstrate how these insights can be exploited to design substrates with improved labeling kinetics.ISSN:0006-2960ISSN:1520-499

Comparison of Arginine Vasopressin, Terlipressin, or Epinephrine to Correct Hypotension in a Model of Anaphylactic Shock in Anesthetized Brown Norway Rats

Background: Arginine vasopressin (AVP) and terlipressin were proposed as alternatives to catecholamines in shock states characterized by decreased plasma AVP concentrations. The endogenous plasma AVP profile in anaphylactic shock is unknown. In an ovalbumin-sensitized anesthetized anaphylactic shock rat model, the authors investigated (1) plasma AVP concentrations and (2) the dose versus mean arterial pressure response for exogenous AVP and terlipressin and compared them with those of epinephrine. Methods: In a first series of rats (n ‫؍‬ 12), endogenous plasma AVP concentrations were compared with a model of pharmacologically induced hypotension (nicardipine, n ‫؍‬ 12). A second series was randomly assigned to three groups (AVP, n ‫؍‬ 7; terlipressin, n ‫؍‬ 7; epinephrine, n ‫؍‬ 7) and dose (AVP: 8 doses, 0.03-100 U/kg; terlipressin: 7 doses, 0.03-30 g/kg; epinephrine: 7 doses, 0.3-300 g/kg)-response mean arterial pressure curves were plotted. Data are expressed as mean ؎ SD. Results: Endogenous plasma AVP concentrations were significantly lower in anaphylactic shock (57 ؎ 26 pg/ml) than in the nicardipine group (91 ؎ 43 pg/ml; P < 0.05). The ED 50 was 10.6 g/kg (95% confidence interval, 7.1-15.9) for epinephrine and 4.1 U/kg (95% confidence interval, 3.0 -5.6) for AVP. Terlipressin did not change mean arterial pressure, regardless of the dose used. Conclusions: In a rat model, anaphylactic shock is associated with inadequately low plasma AVP concentrations. For clinically relevant doses, AVP and epinephrine had comparable effects on mean arterial pressure and heart rate values, whereas, unexpectedly, terlipressin was ineffective. These results are consistent with reports in humans experiencing anaphylaxis where AVP injection restored arterial pressure