Experimental and theoretical investigations on the ultrafast photoinduced decomposition of three tert-butyl peroxides of general structure R-C(O)O-O-tert-butyl with R ) phenyloxy, benzyl, or naphthyloxy in solution are presented. Photoinduced O-O bond scission occurs within the time resolution (200 fs) of the pumpprobe experiment. The subsequent dissociation of photochemically excited carbonyloxy radicals, R-CO 2 , has been monitored on a picosecond time scale by transient absorption at wavelengths between 290 and 1000 nm. The measured decay of R-CO 2 is simulated via statistical unimolecular rate theory using molecular energies, geometries, and vibrational frequencies obtained from density functional theory (DFT) calculations. The results are compared with recent data for tert-butyl peroxybenzoate (R ) phenyl). While benzoyloxy radicals exhibit nanosecond to microsecond lifetimes at ambient temperature, insertion of an oxygen atom or a methylene group between the phenyl or naphthyl chromophore and the CO 2 moiety significantly decreases the stability and thus lowers the lifetime of the carbonyloxy radicals in solution to picoseconds. The reasons behind this structural effect on decomposition rate are discussed in terms of barrier heights for decarboxylation on the ground-state potential energy surface and of a fast reaction channel via electronically excited states of carbonyloxy radicals. Arrhenius parameters are reported for thermal rate constants, k(T), of R-CO 2 decarboxylation as deduced from modeling of the time-resolved experimental data in conjunction with the DFT calculations.

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In 2004, the FDA published a guideline to implement process analytical technologies (PAT) in biopharmaceutical processes for process monitoring to gain process understanding and for the control of important process parameters. Viable cell concentration (VCC) is one of the most important key performance indicator (KPI) during mammalian cell cultivation processes. Commonly, this is measured offline. In this work, we demonstrated the comparability and scalability of linear regression models derived from online capacitance measurements. The linear regressions were used to predict the VCC and other familiar offline biomass indicators, like the viable cell volume (VCV) and the wet cell weight (WCW), in two different industrially relevant CHO cell culture processes (Process A and Process B). Therefore, different single-use bioreactor scales (50–2000 L) were used to prove feasibility and scalability of the in-line sensor integration. Coefficient of determinations of 0.79 for Process A and 0.99 for Process B for the WCW were achieved. The VCV was described with high coefficients of determination of 0.96 (Process A) and 0.98 (Process B), respectively. In agreement with other work from the literature, the VCC was only described within the exponential growth phase, but resulting in excellent coefficients of determination of 0.99 (Process A) and 0.96 (Process B), respectively. Monitoring these KPIs online using linear regression models appeared to be scale-independent, enabled deeper process understanding (e.g. here demonstrated in monitoring, the feeding profile) and showed the potential of this method for process control.

The photodissociation of diiodomethane following excitation at 305 nm in supercritical CO2 was investigated by femtosecond pump‐probe absorption spectroscopy at pressures between 10 and 100 MPa. As in liquid solution, transient absorption signals in the wavelength range from 350 to 450 nm generally show an instantaneous peak, followed by a fast initial decay (200–300 fs) and a subsequent rise on a 10‐ps timescale. The initial fast decay time is found to be linearly dependent on viscosity, suggesting that dissociative motion on the repulsive surface is damped by solvent friction. Both amplitude and formation rate of the rising component, which is assigned to formation of iso‐diiodomethane within the solvent cage, increase with increasing pressure. Spectral narrowing of the transient absorption band indicates vibrational cooling of hot isomer by energy transfer to CO2 in about 20–40 ps. Immediately after excitation, this band shows absorption anisotropy for about 3 ps. The anisotropy decay rate increases from 3·1011 s−1 to 2·1012 s−1 as the pressure is lowered from 80 to 10 MPa. It is tentatively assigned to rotational relaxation of “hot” CH2I radicals generated in ultrafast photodissociation of the parent molecule. The observed density dependence of formation rate and relative yield of iso‐diiodomethane are described in terms of a simple kinetic model.

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