Lanthanide modulation of the orientation of macromolecules induced by purple membrane.

Addition of Tb3+ to purple membrane (PM) suspensions changes the orientation of the menbrane normal from parallel to perpendicular with respect to the magnetic field. Residual dipolar couplings measured in protein L in the presence of PM are scaled by a factor of -1/2. NMR line broadening and cross-correlation effects induced by the addition of PM are partially reversed by Tb3+ but not by Tm3+ that has no effect on the orientation of PM. This is interpreted as the result of anisotropically restricted motion of protein L in the transiently PM-bound form.     

Solvothermal Synthesis, Crystal Structure, and Properties of the First Zinc Containing Thioantimonate(III) [Zn( tren)] 2Sb 4S 8·0.75 H 2O

Yellow crystals of the title compound were obtained under solvothermal conditions reacting elemental Zn, Sb, and S in a solution of tris(2-aminoethyl)amine (=tren) and water. The compound crystallises in the monoclinic space group P2₁/c with a=13.0247(7), b=22.308(2), c=12.1776(6) Å, and =105.352(6)°. In the structure of [Zn(tren)]₂Sb₄S₈·0.75 H₂O two [Zn(tren)]²⁺ cations are bound to the [Sb₄S₈]^4– anion via S atoms. The Zn²⁺ ions are in a trigonal bipyramidal environment of four N atoms of the tetradentate tren ligand and one S atom of the [Sb₄S₈]^4– anion. The anion is formed by SbS₃ and SbS₄ units which share common corners and edges. The interconnection mode yields three different non-planar Sb₂S₂ heterorings. The shortest intermolecular Sb–S distance amounts to about 3.7Å, and taking this long separation into account undulated chains running along [001] are formed with the water molecules residing in the pocket-like cavities. Upon heating the compound decomposes in one step starting at about 240°C. The final decomposition product was identified as ZnS and Sb₂S₃ by X-ray powder diffractometry. Additionally, spectroscopic data as well as synthetic procedures for [Zn(tren)]₂Sb₄S₈·0.75 H₂O are reported.     

Effect of operating parameters on selective separation of heavy metals from binary mixtures via polymer enhanced ultrafiltration

Performance of continuous polymer enhanced ultrafiltration (PEUF) method was investigated for removal of mercury and cadmium from binary mixtures. This method includes the addition of polyethyleneimine (PEI) as a water soluble polymer to bind the metals, which was followed by ultrafiltration operation performed on both laboratory and pilot scale systems. The influence of various operating parameters such as temperature, metal/polymer ratio, presence of calcium ions and pH on retention of metals and permeate flux was investigated. To investigate the possibility of selective separation of mercury and cadmium, experiments were conducted for binary solutions at different pH and loading ratios. It was seen that the retention of mercury decreased and permeate flux increased when the temperature increased. The increased pH and decreased metal/polymer ratio, loading (L), resulted in higher retention of both metals. Shapes of retention vs. pH or L curves were very similar for both metals. Retentions stay almost constant at a value very close to unity until a critical L or pH value was reached, then, R decreases almost linearly with L or pH. However, retention of cadmium was affected more than that of mercury as the pH decreased and L increased. This leads to the selective separation of mercury and cadmium. At low pH values (about 5) and at high L values (about 0.3), mercury was removed by ultrafiltration operation while almost all cadmium passed through the membrane. At pH 5.5 and cadmium/polymer ratio about 0.35 and mercury/polymer ratio about 0.39, the highest separation factor was obtained as 49.     

Automated and enhanced extraction of a small molecule-drug conjugate using an enzyme-inhibitor interaction based SPME tool followed by direct analysis by ESI-MS

We report a novel, fast, and automatic SPME-based method capable of extracting a small molecule-drug conjugate (SMDC) from biological matrices. Our method relies on the extraction of the drug conjugate followed by direct elution into an electrospray mass spectrometer (ESI-MS) source for qualitative and quantitative analysis. We designed a tool for extracting the targeting head of a recently synthesized SMDC, which includes acetazolamide (AAZ) as high-affinity ligand specific to carbonic anhydrase IX. Specificity of the extraction was achieved through systematic optimization. The design of the extraction tool is based on noncovalent and reversible interaction between AAZ and CAII that is immobilized on the SPME extraction phase. Using this approach, we showed a 330% rise in extracted AAZ signal intensity compared to a control, which was performed in the absence of CAII. A linear dynamic range from 1.2 to 25 μg/ml was found. The limits of detection (LOD) of extracted AAZ from phosphate-buffered saline (PBS) and human plasma were 0.4 and 1.2 μg/ml, respectively. This with a relative standard deviation of less than 14% (n = 40) covers the therapeutic range.

Graphical abstract

     

Biocomposites of covalently linked glucose oxidase on carbon nanotubes for glucose biosensor

The formation of covalently linked composites of multi–walled carbon nanotubes (MWCNT) and glucose oxidase (GOD) with high-function density for use as a biosensing interface is described. The reaction intermediates and the final product were characterized by using FT–IR spectroscopy, and the MWCNT-coated GOD nanocomposites were examined by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Interestingly, it was found that the GOD–MWCNT composites are highly water soluble. Electrochemical characterization of the GOD–MWCNT composites that were modified on a glassy carbon electrode shows that the covalently linked GOD retains its bioactivity and can specifically catalyze the oxidation of glucose. The oxidation current shows a linear dependence on the glucose concentration in the solution in the range of 0.5–40 mM with a detection limit of 30 μM and a detection sensitivity of 11.3 μA/mMcm². The present method may provide a way to synthesize MWCNT related composites with other biomolecules and for the construction of enzymatic reaction-based biofuel cells and biosensors. Supported by grants from the National Natural Science Foundation of China (NSFC, No. 20125515; 90206037; 20375016) and the Natural Science Foundation of Jiangsu Province (Grant No. BK 2004210)     

Determination of the thiol redox state of organisms: new oxidative stress indicators

This study describes a new methodology by which the concentrations of non-protein (NP) thiols glutathione (GSH), cysteine (CSH), N-acetylcysteine (AcCSH), and protein (P) thiols (PSH), as well as the contribution of these components to symmetric and mixed disulfides (NPSSR, NPSSC, NPSSCAc, PSSR, PSSC, PSSCAc, PSSP) can reliably be measured. The methodology consists of a strict sequence of methods which are applied to every sample. Free thiols at any given state of the procedure are measured by Ellmans assay, the CSH fraction is measured by its unique response in the ninhydrin assay, AcCSH is selectively measured with ninhydrin after enzymatic deacylation, proteins are separated from non-protein thiols/disulfides by precipitation with trichloroacetic or perchloric acid, disulfides are reduced into free thiols with borohydride, mixed disulfides between a protein and a non-protein component are measured by extracting the non-protein thiol from the protein pellet after borohydride treatment, and protein thiols/disulfides are measured after resolubilization of the protein pellet.When this method was applied to animal and fungal tissue, new molecular indicators of the thiol redox state of living cells were identified. The findings of the present study clearly show that the new parameters are very sensitive indicators of redox state, while at the same time the traditional parameters GSH and GSSG often remain constant even upon dramatic changes in the overall redox state of biological tissue. Therefore, unbiased assessment of the redox state also requires explicit measurement of its most sensitive thiol indicators.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

Synthesis of macrocyclic tetraamides derived from α-amino acids and their investigations using ESI-MS technique

Chiral α,ω-diesters react under high-pressure conditions (10 kbar) with α,ω-diamines to give chiral cyclic tetraamides of C₂-symmetry. The complexation properties of tetraamides towards alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) were estimated on the basis of ESI-MS spectra.     

Skeletal Isomerization of <Emphasis Type="Italic">n</Emphasis>-butenes over Solid Acid Catalysts

Conversion reactions of n-butenes over zeolites and amorphous catalysts have been investigated to deduce the factor that determines the selectivity for the skeletal isomerization producing isobutene. The effects of pore structure and acid site concentration on the selectivity for the skeletal isomerization are discussed on various catalysts. The pore structures of FER and CLI zeolites induce the distant locations of butene molecules, accelerating monomolecular skeletal isomerization. On the other hand, acid site concentration determines the preferred reaction path of n-butenes on amorphous catalysts. Oligomerization followed by cracking that produces various hydrocarbons is suppressed on the catalyst with low acid site concentration, resulting in high selectivity for isobutene. The feasibility of monomolecular skeletal isomerization on zeolites and amorphous catalysts is confirmed by its reversibility with high selectivity.     

Enzymatic kinetic of cellulose hydrolysis

The ethanol effect on the Trichoderma reesei cellulases was studied to quantify and clarify this inhibition type. To determine inhibition parameters of crude cellulase and purified exoglucanase Cel7A, integrated Michaelis-Menten equations were used assuming the presence of two inhibitors: cellobiose as the reaction product and ethanol as a possible bioproduct of cellulose fermentation. It was found that hydrolysis of cellulose by crude enzyme follows a model that considers noncompetitive inhibition by ethanol, whereas Cel7A is very slightly competitively inhibited. Crude cellulase is much more inhibited (K _iul=K _icl=151.9 mM) than exoglucanase Cel7A (K _icl=1.6 × 10¹⁵ mM). Also, calculated inhibition constants showed that cellobiose inhibition is more potent than ethanol inhibition both for the crude enzyme as well as exoglucanase Cel7A.