Molecular signaling tuning

For pump-probe photoionization (PPI, Fig.l) the first laser pulse is tuned into resonance with the (vibrationless) electronic transition of the molecule, the second pulse is red-shifted in wavelength, so that the enhanced (1+1 ) photoion signal can be easily identified. When a time-of-flight mass spectrometer is used for detection the mass-selective photoion signal as a function of time delay can be recorded as the RCS spectrum of the electronically excited state, which is particularly useful for the specific investigation of molecular clusters. 

The time modulation of transmitter signals, through pulsations of different durations and shapes may lead to frequency and amplitude coding of signalling events, the detection requiring molecular receivers suitably tuned to frequency patterns and thresholds. Such processes occur in intercellular communication by cell to cell signalling [8.243]. 

The identifications of atomic and molecular species is undertaken with a variety of mass spectroscopies. Time-of-flight (TOF) mass spectroscopy is of value for very short lived or highly peaked emissions. More sustained emissions are more readily studied with a quadrupole mass spectrometer (QMS), which can be tuned to a single mass peak. The time evolution (on a microsecond time scale) of a particular mass emission can be determined from the observed signals. Under the appropriate conditions, both these tools can be applied to studies of neutral emission (with ionizer) and positive or negative ion emission (without ionizer). 

Table 1 Amino acids observed as calciiun-binding ligands in 567 EF-hand sequences. (Reproduced from J.J. Falke, S.K. Drake, A.L. Flazard, O.B. Peersen, Molecular tuning of ion binding to calcium signalling proteins. Q, Rev. Biophys. 27(3) 219-90 by permission of Cambridge University Press)...

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