Noncovalent Bond Lengths and Their Cooperative Shortening: Dimers of Vancomycin Group Antibiotics in Crystals and in Solution

A wide range of dimerisation constants (K_dim ca. 10¹–10⁶ M ^?1) for various glycopeptide antibiotics have been determined. We consider these dimerisation constants in the light of the published X‐ray structures of the antibiotics, in particular, the relationship between K _dim and the length of a specified distance at the dimer interface. In the crystals, we find that this distance is smaller for strongly dimerising antibiotics and larger for weakly dimerising antibiotics. Thus, the dimerisation constant is correlated with tightness at the dimer interface. Despite the crystal‐packing forces exerted between adjacent dimer molecules in the crystals, the noncovalent bond distances at the dimer interface are correlated with the distances in solution (inferred from solution NMR data). These observations can account for the benefits in enthalpy, and costs in entropy, associated with positively cooperative binding.     

Reaktionen des Cumalinsäure-methylesters und Cumalinaldehyds mit ambidenten Nucleophilen

Reactions of Methyl Coumalate and Coumalaldehyde with Ambident Nucleophiles Methyl coumalate and coumalaldehyde show great diversity in their reactions with ambident nucleophiles both depending upon the 2H-pyran-2-one derivative and the nature of the ambident nucleophile used. The products are either pyridine or pyrimidine derivatives.     

Tungsten hexachloride alone as a catalyst for the metathetic polymerization of cyclic olefins

The polymerization of cyclic olefins may be initiated by tungsten hexachloride alone. The rate of polymerization is less than that normally obtained with bimetallic catalysts but the equilibrium conversion monomer is of the same order.     

Low-cost Imaging of Fluorescent DNA in Agarose Gel Electrophoresis using Raspberry Pi cameras

Low-cost analytical solutions built around microcomputers like the Raspberry Pi help to facilitate laboratory investigations in resource limited venues. Here, three camera modules (V1.3 with and without filter, as well as NoIR) that work with this microcomputer were assessed for their suitability in imaging fluorescent DNA following agarose gel electrophoresis. Evaluation of their utility was based on signal-to-noise (SNR) and noise variance metrics that were developed. Experiments conducted with samples were subjected to Polymerase Chain Reaction (PCR), and the amplified products were separated using gel electrophoresis and stained with Midori green. Image analysis revealed the NoIR camera performed the best with SNR and noise variance values of 21.7 and 0.222 respectively. In experiments conducted using UV LED lighting to simulate ethidium bromide (EtBr) excitation, the NoIR and V1.3 with filter removed cameras showed comparable SNR values.

     

Minimalist and convenient mode changing off-axis digital holography

Basic issues in creating practical setups for off-axis digital holography involve having (i) convenient switch of imaging in the transmission and reflection modes, (ii) reduction in stray light reflection, (iii) immunity against environmental noise, and (iv) efficient usage of light output from the laser source. These exigencies are addressed using a free-space setup described here that applies a minimal number of optical components. Experimental results are presented to verify the approach.     

A study of the formation and application of new chiral water soluble lanthanoid benzoates using real-time infrared spectroscopy

A range of water soluble lanthanoid benzoate complexes of composition [Ln(Bz)₃(H₂O)_n] (Ln = La, Gd, Ho and Yb; Bz = 3,5-bis((R)-2,3-dihydroxypropoxy)benzoate and 3,4,5-tris((R)-2,3-dihydroxypropoxy)benzoate) have been prepared by reaction of lanthanoid bicarbonates with three equivalents of the corresponding optically active benzoic acid in water. Application of [Ln(Bz)₃(H₂O)_n] as asymmetric catalysts for epoxide ring opening reactions has been investigated using styrene oxide, showing complete conversion after 20 h, albeit with no significant enantiomeric excess observed. The formation of the lanthanoid complexes and subsequent catalytic conversion of styrene oxide to phenylethane-1,2-diol were monitored using real-time infrared (RTIR) spectroscopy, yielding information about reaction pathways and intermediates.     

An improved method for determining zeta potential and pore conductivity of porous materials

An improved method based on streaming potential and streaming current was proposed to determine zeta potential and surface conductance of porous material simultaneously. In the electrokinetic generation mode, a resistor is connected to the generator and by measuring the voltage drop across resistors with different resistance, a true streaming current can be determined. The zeta potential and surface conductivity can be obtained simultaneously from their relation to streaming potential and streaming current. The electrode and ion concentration polarization effects during the measurement were also discussed. The resistance from channel ends to electrodes, which has typically been ignored in the literature, was shown to have a significant influence on the calculated zeta potential and surface conductance. Ignorance of this resistance would lead to underestimation of both zeta potential and surface conductance values.     

The diversity challenge in directed protein evolution

Over the past decade, we have witnessed a bloom in the field of evolutive protein engineering which is fueled by advances in molecular biology techniques and high-throughput screening technology. Directed protein evolution is a powerful algorithm using iterative cycles of random mutagenesis and screening for tailoring protein properties to our needs in industrial applications and for elucidating proteins' structure function relationships. This review summarizes, categorizes and discusses advantages and disadvantages of random mutagenesis methods used for generating genetic diversity. These random mutagenesis methods have been classified into four main categories depending on the method employed for nucleotide substitutions: enzyme based methods (Category I), synthetic chemistry based methods (Category II), whole cell methods (Category III) and combined methods (Category I-II, I-III and II-III). The basic principle of each method is discussed and varied mutagenic conditions are summarized in Tables and compared (benchmarked) to each other in terms of: mutational bias, controllable mutation frequency, ability to generate consecutive nucleotide substitutions and subset diversity, dependency on gene length, technical simplicity/robustness and cost-effectiveness. The latter comparison shows how highly-biased and limited current diversity creating methods are. Based on these limitations, strategies for generating diverse mutant libraries are proposed and discussed (RaMuS-Flowchart; KISS principle). We hope that this review provides, especially for researchers just entering the field of directed evolution, a guide for developing successful directed evolution strategies by selecting complementary methods for generating diverse mutant libraries.     

Modulating the activity of membrane-active peptides through Zn(II) complexation

Seeking to increase the selectivity of antimicrobial peptides for prokaryotic cells, we incorporated a bis-dipicolyl amine (bis-DPA) ligand at the N-terminus of de novo designed model peptides. The Zn₂·bisDPA complex increases the interaction of peptides with anionic model membranes, while decreasing interactions with zwitterionic model membranes. Further, it improves the peptides’ antimicrobial activity and decreases their hemolytic activity without substantial changes to their secondary structure. Therefore, incorporating a Zn₂·bisDPA complex is a useful strategy to enhance the selectivity of antimicrobial peptides.     

How surface tension of surfactant solutions influences the characteristics of sprays produced by hydraulic nozzles used for pesticide application

The sprays produced by hydraulic agricultural nozzles are influenced by the surface tension of the spray liquid, but models of spray formation relate only to pure liquids with constant surface tension. The way surfactant solutions affect spray formation is studied by investigating sprays of pure liquids compared with a range of surfactant solutions. Some surfactants caused changes in the appearance of the liquid sheet produced by the nozzles, which did not occur with pure liquids, and smaller spray drop sizes than pure liquids, suggesting that other surface properties may also be important.