Peptide‐Directed DNA‐Templated Protein Labelling for The Assembly of a Pseudo‐IgM

The development of methods for conjugation of DNA to proteins is of high relevance for the integration of protein function and DNA structures. Here, we demonstrate that protein‐binding peptides can direct a DNA‐templated reaction, selectively furnishing DNA–protein conjugates with one DNA label. Quantitative conversion of oligonucleotides is achieved at low stoichiometries and the reaction can be performed in complex biological matrixes, such as cell lysates. Further, we have used a star‐like pentameric DNA nanostructure to assemble five DNA–Rituximab conjugates, made by our reported method, into a pseudo‐IgM antibody structure that was subsequently characterized by negative‐stain transmission electron microscopy (nsTEM) analysis.     

Nickel(II)‐Komplexe von Oxalamidinen und Oxalamidinaten mit zusätzlichen R2P‐Donorgruppen

Complexes of Nickel(II) with Oxalic Amidines and Oxalic Amidinates with Additonal R₂P‐Donor Groups Oxalamidines R¹N=C(NHR²)‐C(=NHR²)=NR¹, which bear additional donor atoms at two of the four N substituents ( H₂A : R¹ = mesityl, R² = ‐(CH₂)₃‐PPh_2; H₂B : R¹ = tolyl, R² = ‐(CH₂)₃‐PMe₂) form binuclear complexes with Nickel(II) in which very different coordination modes are realized. In the complex [ (A) Ni₂Br₂] (1) the two nickel atoms at each side of the bridge are in a square‐planar environment, coordinated by the two N donor atoms of the oxalic amidinate framework, a bromide and a Ph₂P group. An analogous coordination has the organometallic compound [ (A) Ni₂Me₂] (2) . In contrast, the two nickel atoms in the compound {[( B )][Ni(acac)]₂} (5) differ in their coordinative environment. At one side of the oxalic amidinate bridging ligand a (acac)Ni fragment is coordinated by the two N donor atoms resulting in a square‐planar environment. At the opposite side the (acac)Ni fragment is coordinated at the both N donor ligands of the bridging ligand as well as at the two PMe₂ groups of the side chains resulting in an octahedral coordination for this nickel atom.     

The crystal structure determinations and refinements of K2S2O7, KNaS2O7 and Na2S2O7 from X-ray powder and single crystal diffraction data

The crystal structures of K₂S₂O₇, KNaS₂O₇ and Na₂S₂O₇ have been solved and/or refined from X-ray synchrotron powder diffraction data and conventional single-crystal data. K₂S₂O₇: From powder diffraction data, monoclinic C2/c, Z=4, a=12.3653(2), b=7.3122(1), , β=93.0792(7)°, R_Bragg=0.096. KNaS₂O₇: From powder diffraction data; triclinic , Z=2, a=5.90476(9), b=7.2008(1), , α=101.7074(9), β=90.6960(7), γ=94.2403(9)°, R_Bragg=0.075. Na₂S₂O₇: From single-crystal data; triclinic , Z=2, a=6.7702(9), b=6.7975(10), , α=116.779(2), β=96.089(3), γ=84.000(3)°, R_F=0.033. The disulphate anions are essentially eclipsed. All three structures can be described as dichromate-like, where the alkali cations coordinate oxygens of the isolated disulphate groups in three-dimensional networks. The K-O and Na-O coordinations were determined from electron density topology and coordination geometry. The three structures have a cation-disulphate chain in common. In K₂S₂O₇ and Na₂S₂O₇ the neighbouring chains are antiparallel, while in KNaS₂O₇ the chains are parallel. The differences between the K₂S₂O₇ and Na₂S₂O₇ structures, with double-, respectively single-sided chain connections and straight, respectively, corrugated structural layers can be understood in terms of the differences in size and coordinating ability of the cations.     

Cation Complexation by a Lower Rim Calix(4)arene Derivative: Structural,Electrochemical and Thermodynamic Studies

The synthesis and characterization (¹H and ¹³C NMR) of a partially substituted lower rim p-tert-butylcalix(4)arene, namely, 5,11,17,23-tetra-4-tert-butyl-25,27-bis(diethylphosphate amino)ethoxy-26,28-dihydroxycalix[4]arene (1), are reported. The solution thermodynamics of the ligand in a variety of solvents at 298.15?K was investigated through solubility (hence standard Gibbs energy of solution) measurements while the calorimetric technique was used to derive the standard solution enthalpy. These data were used to calculate the standard entropy of solution. An enthalpy–entropy compensation effect is shown and, as a result, slight variations are observed in the transfer Gibbs energies of this ligand from the reference to other solvents. ¹H NMR, conductance and calorimetric measurements were carried out to establish the degree of interaction of the ligand with univalent (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and Ag⁺) and bivalent (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Cd²⁺, Hg²⁺, Cu²⁺, Zn²⁺) cations in acetonitrile, methanol, N,N-dimethylformamide and propylene carbonate. No complexation was found between this ligand and univalent cations in these solvents. As far as the bivalent cations are concerned, interaction between 1 and these cations was found only in acetonitrile. The versatile behaviour of this ligand with bivalent cations in this solvent is reflected by the formation of complexes of different stoichiometry. Thus the interaction of 1 with alkaline-earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) and Pb²⁺ metal cations leads to the formation of 1:2 (cation:ligand) complexes. However, for other bivalent metal cations (Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺) the complex stoichiometry was found to be 1:1. The results are discussed in terms of the key role played by acetonitrile in processes involving calix[4]arene derivatives.     

Towards validating a method for two-dimensional electrophoresis/silver staining

Two-dimensional electrophoresis (2-DE) is a technique involving numerous steps, many of them to be performed manually. Hence, some operator dependency must be taken into account. An attempt to elucidate the reliability of 2-DE combined with silver staining is presented, employing the general practice to validate a method in pharmaceutical analysis. Most proteomic studies employing 2-DE aim at qualitative or quantitative differences in protein expression. One of the most sensitive and broadly applied staining techniques is silver staining. In order to gain information on accuracy, precision, linearity, and ruggedness of this technique, gels were run in replicates with different amounts of protein from a complex standard sample. In addition, sets of gels were repeated by two different operators in a second independent laboratory equipped with identical hardware and software. Our results show that reliable qualitative data on differential protein expression can be obtained by 2-DE, nevertheless replicate gels should be run and experimental conditions have to be kept stringently to a standardized protocol. Quantitative data are just achievable with spots, which are well-resolved, of high quality, with an optical density (OD) above a certain threshold (OD > 10), and which show a linear response. Quantitative differences occurring due to method-derived deviations may easily be misinterpreted as true changes in protein expression. After normalization, relative standard deviation (RSD) values of approximately 30% (n = 4) could be obtained, therefore minor changes (< 50%) should be critically reviewed.     

Gaussian charge polarizable interaction potential for carbon dioxide

A number of simple pair interaction potentials of the carbon dioxide molecule are investigated and found to underestimate the magnitude of the second virial coefficient in the temperature interval 220-448 K by up to 20%. Also the third virial coefficient is underestimated by these models. A rigid, polarizable, three-site interaction potential reproduces the experimental second and third virial coefficients to within a few percent. It is based on the modified Buckingham exp-6 potential, an anisotropic Axilrod-Teller correction, and Gaussian charge densities on the atomic sites with an inducible dipole at the center of mass. The electric quadrupole moment, polarizability, and bond distances are set to equal experiment. Density of the fluid at 200 and 800 bars pressure is reproduced to within some percent of observation over the temperature range 250-310 K. The dimer structure is in passable agreement with electronically resolved quantum-mechanical calculations in the literature, as are those of the monohydrated monomer and dimer complexes using the Gaussian charge polarizable model water potential. Qualitative agreement with experiment is also obtained, when quantum corrections are included, for the relative stability of the trimer conformations, which is not the case for the pair potentials.     

Sekundäre Phosphinchalkogenide. VII. Synthese von Bis(tert.-butylphosphino)ethan,ButHPCH2CH2PHBut,und 1-tert.-Butylphosphino-2-diphenylphosphino-ethan,Ph2PCH2CH2PHBut,sowie deren sekundäre Phosphinchalkogenide

Secondary Phosphine Chalcogenides. VII. Synthesis of Bis(tert.-butylphosphino)thane, Bu^tHPCH₂CH₂PHBu^t, and 1-tert.-Butylphosphino-2-diphenylphosphinoethane, Ph₂PCH₂CH₂PHBu^t, as well as their Secondary Phosphine Chalcogenides The reaction of Cl₂PCH₂CH₂PCl₂ with Bu^tMgCl gives Bu^tClPCH₂CH₂PClBu^t which is either hydrolysed to yield Bu^tH(O)PCH₂CH₂P(O)HBu^t or reduced to give Bu^tHPCH₂CH₂PHBu^t. This phosphine reacts with sulfur or selenium to give Bu^tH(E)PCH₂CH₂P(E)HBu^t (E = S, Se). Treatment of Ph₂PCH₂CH₂Cl with LiPHBu^t results Ph₂PCH₂CH₂PHBu^t which is oxidized to give Ph₂(E)PCH₂CH₂P(E)HBu^t (E = O, S, Se). The Ph₂P group appears to be oxidized primarily. The compounds obtained are characterized by means of I.R. ¹H and ³¹P-N.M.R. spectroscopy.     

Electric potential distributions around discrete charges in a dielectric membrane—electrolyte solution system

Within the framework of the linearized Debye-Hückel theory an exact solution of the problem of calculating the electric potential caused by discrete fixed charges located at arbitrary positions with respect to a dielectric membrane-solution interface is presented. It takes into account the existence of an electrolyte solution on both sides of the membrane. Asymmetric ionic conditions are allowed for. For some interesting typical cases of fixed charge locations and electrolyte ionic strengths electric potential distributions were calculated and discussed. It is shown that, if the fixed charges were at or in front of the membrane surface, the characteristic distance of the electric potential decay was comparable to the Debye-Hückel length. At the opposite membrane surface only very small electric potentials can be observed. If, however, the fixed charge was placed below the membrane surface the electric potential in lateral direction and towards the other membrane surface largely increased. This effect was very sensitive to the position of the fixed charge with respect to the membrane surface.     

DNA–Polymer Nanostructures by RAFT Polymerization and Polymerization‐Induced Self‐Assembly

Nanostructures derived from amphiphilic DNA–polymer conjugates have emerged prominently due to their rich self‐assembly behavior; however, their synthesis is traditionally challenging. Here, we report a novel platform technology towards DNA–polymer nanostructures of various shapes by leveraging polymerization‐induced self‐assembly (PISA) for polymerization from single‐stranded DNA (ssDNA). A “grafting from” protocol for thermal RAFT polymerization from ssDNA under ambient conditions was developed and utilized for the synthesis of functional DNA–polymer conjugates and DNA–diblock conjugates derived from acrylates and acrylamides. Using this method, PISA was applied to manufacture isotropic and anisotropic DNA–polymer nanostructures by varying the chain length of the polymer block. The resulting nanostructures were further functionalized by hybridization with a dye‐labelled complementary ssDNA, thus establishing PISA as a powerful route towards intrinsically functional DNA–polymer nanostructures.