Field regulation of single-molecule conductivity by a charged surface atom

Electrical transport through molecules has been much studied since it was proposed that individual molecules might behave like basic electronic devices, and intriguing single-molecule electronic effects have been demonstrated. But because transport properties are sensitive to structural variations on the atomic scale, further progress calls for detailed knowledge of how the functional properties of molecules depend on structural features. The characterization of two-terminal structures has become increasingly robust and reproducible, and for some systems detailed structural characterization of molecules on electrodes or insulators is available. Here we present scanning tunnelling microscopy observations and classical electrostatic and quantum mechanical modelling results that show that the electrostatic field emanating from a fixed point charge regulates the conductivity of nearby substrate-bound molecules. We find that the onset of molecular conduction is shifted by changing the charge state of a silicon surface atom, or by varying the spatial relationship between the molecule and that charged centre. Because the shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature.     

Zeitbedarf der Längsteilung von miteinander verzwirnten Fadenmolekülen

Summary The time requirement is treated for a longitudinal fission by Brownian movement of a very long particle consisting of two or more filaments twisted a great number of times round each other to form a double spiral. It is shown that a comparatively swift disintegration is obtained by partial rotation or torsion round the axis of the spiral, resulting in a loosing of the spiral structure and subsequent separation of the constituents by translational Brownian movement. The time required to separate a double spiral consisting of about 900 turns of a height of 3.4 × 10⁻⁷ cm and a radius of 10⁻⁷ cm, thus having a length of 3 × 10⁻⁴ cm being realized approximately by deoxyribonucleic acid is found by this mechanism to be about 50 to 80 s. The time required to undo the same spiral by unwrapping it turn by turn would be about 150 days. The result of the considerations is related to observations published byAlexander andSteacy on deoxyribonucleic acid. An additional remark stresses the importance of stereochemical asymmetry for the practicability of the mechanism and therefore the importance of optical activity for the time requirement of such disintegrations or transformations of high polymer material occurring in living organisms.      

Different rhinovirus serotypes neutralized by antipeptide antibodies

Recently, Rossman et al. have described the three-dimensional structure of a human rhinovirus. A possible host cell surface receptor binding site was identified with a cleft on each icosahedral face. Two highly conserved amino-acid sequences found in rhino-, polio-, and foot-and-mouth disease (FMD) viruses are located near the base of this site and could be important in maintaining its topology. We have prepared site-specific antibodies to two synthetic peptides which include these sequences. The antibodies bind to the predicted capsid proteins of rhinovirus and neutralize approximately 60% of 48 rhinovirus serotypes tested. These results could provide a route to a rhinovirus vaccine effective against most of the numerous serotypes of this virus.     

Electron cryo-microscopy shows how strong binding of myosin to actin releases nucleotide

Muscle contraction involves the cyclic interaction of the myosin cross-bridges with the actin filament, which is coupled to steps in the hydrolysis of ATP. While bound to actin each cross-bridge undergoes a conformational change, often referred to as the "power stroke", which moves the actin filament past the myosin filaments; this is associated with the release of the products of ATP hydrolysis and a stronger binding of myosin to actin. The association of a new ATP molecule weakens the binding again, and the attached cross-bridge rapidly dissociates from actin. The nucleotide is then hydrolysed, the conformational change reverses, and the myosin cross-bridge reattaches to actin. X-ray crystallography has determined the structural basis of the power stroke, but it is still not clear why the binding of actin weakens that of the nucleotide and vice versa. Here we describe, by fitting atomic models of actin and the myosin cross-bridge into high-resolution electron cryo-microscopy three-dimensional reconstructions, the molecular basis of this linkage. The closing of the actin-binding cleft when actin binds is structurally coupled to the opening of the nucleotide-binding pocket.     

Ein neuer,bisher unbekannter Entwicklungsmodus bei einem Scyphopolypen

Summary A new solitary scyphopolyp from submarine caves of the rocky shore near Marseille has been observed to exhibit a new mode of development which is characterized by a reduction of the normally free medusa generation. By the process of strobilation, a chain of sessile hermaphroditic eumedusoids is originated. The germ cells are fertilized and develop into planulae within the gastral room. Self-fertilization has been observed.