The low‐temperature phase transition of 9‐methylfluoren‐9‐ol: comparison of the crystal structures at 100 and 200 K

Crystals of 9‐methyl­fluoren‐9‐ol, C₁₄H₁₂O, undergo a reversible phase transition at 176 (2) K. The structure of the high‐temperature α form at 200 K is compared with that of the low‐temperature β form at 100 K. Both polymorphs crystallize in space group P with Z = 4 and contain discrete hydrogen‐bonded R(8) ring tetramers arranged around crystallographic inversion centres. The most obvious changes observed on cooling the crystals to below 176 K are an abrupt increase of ca 0.5 Å in the shortest lattice translation, and a thermal transition with ΔH = 1 kJ mol^?1.     

Performance monitoring of a mammalian cell based bioprocess using Raman spectroscopy

Being able to predict the final product yield at all stages in long-running, industrial, mammalian cell culture processes is vital for both operational efficiency, process consistency, and the implementation of quality by design (QbD) practices. Here we used Raman spectroscopy to monitor (in terms of glycoprotein yield prediction) a fed-batch fermentation from start to finish. Raman data were collected from 12 different time points in a Chinese hamster ovary (CHO) based manufacturing process and across 37 separate production runs. The samples comprised of clarified bioprocess broths extracted from the CHO cell based process with varying amounts of fresh and spent cell culture media. Competitive adaptive reweighted sampling (CoAdReS) and ant colony optimization (ACO) variable selection methods were used to enhance the predictive ability of the chemometric models by removing unnecessary spectral information. Using CoAdReS accurate prediction models (relative error of predictions between 2.1% and 3.3%) were built for the final glycoprotein yield at every stage of the bioprocess from small scale up to the final 5000 L bioreactor. This result reinforces our previous studies which indicate that media quality is one of the most significant factors determining the efficiency of industrial CHO-cell processes. This Raman based approach could thus be used to manage production in terms of selecting which small scale batches are progressed to large-scale manufacture, thus improving process efficiency significantly.     

Cleaning requirements for silica‐coated sensors used in optical waveguide lightmode spectroscopy

Optical waveguide lightmode spectroscopy (OWLS), based on the incoupling of laser light into a waveguide sensor by an optical grating, allows for the in situ measurement of protein adsorption. Few reports have described cleaning methods for the surfaces of such sensors, and in this investigation, we compare common methods for cleaning of silica surfaces in relation to their effectiveness for cleaning silica‐coated waveguide sensors used in OWLS. For this purpose, atomic force microscopy (AFM) analysis of surface morphology and OWLS detection of protein adsorption kinetics were used to evaluate waveguide sensors before and after cleaning. While AFM line scans showed a substantial increase in average waveguide peak‐to‐valley height after RCA cleaning relative to all other methods tested, chemical etching owing to the alkaline component of the rolling circle amplification method rendered the waveguide unusable for detection of protein adsorption with OWLS. A revised method, based on replacement of the alkaline step with immersion in sodium dodecyl sulfate, was not only effective at cleaning OWLS waveguides off‐the‐shelf but also showed excellent protein adsorption reproducibility after ex situ cleaning. Moreover, the revised method showed excellent reproducibility when applied in situ, between repeated adsorption‐elution cycles. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluating the influence of deposition conditions on solvation of reactive conducting polymers with neutron reflectivity

We describe in situ neutron reflectivity (NR) and RAIRS studies of the chemical modification of films of a polypyrrole-based conducting polymer derived from the pentafluorophenyl ester of poly(pyrrole-N-propanoic acid) (PFP) electrodeposited on electrode surfaces. We explore the role of the solvent in controlling the rate of reaction with solution-based nucleophiles (amines, which react with the ester to form amides). By varying the identity of the solvent (water vs acetonitrile) and the neutron contrast (deuteration), we find that both the identity of the solvent and its population within the film are paramount in determining chemical reactivity and electroactivity. IR signatures allow monitoring of the reaction of solution-based amine-tagged species such as amino-terminated poly(propylene glycol), ferrocene ethylamine, and lysine with film-based ester functionalities: the carbonyl bands show ester/amide interconversion and some hydrolysis to acid. Time-dependent spectral analysis shows marked variations in reaction rate with (i) (co-)polymer composition (replacement of some fluorinated ester-functionalized pyrrole with unfunctionalized pyrrole), (ii) the solvent to which the polymer film is exposed, and (iii) the rate of polymer deposition. NR data provide solvent profiles as a function of distance perpendicular to the interface, the variations of which provide an explanation for film reactivity patterns. Homopolymer films are relatively hydrophobic, thus hindering reaction with species present in water solutions. Incorporating pyrrole groups raises the solvent population-dramatically for water-thereby facilitating entry and reaction of aqueous-based lysine. Changing film deposition rate yields films with different absolute levels of solvent and reactivity patterns that are dependent on the size of the reactant molecules: more rapid deposition of polymer gives films with a more open structure leading to a higher solvent content and thence increased reactivity. These results, supported by XPS and AFM data, allow assembly of composition-structure-reactivity correlations, in which the controlling feature is film solvation.     

Spin-rotation coupling and Fermi–Walker transport

It is demonstrated that a spin-rotation coupling term only appears in the Hamiltonian of a Dirac particle if the rotating frame obeys the rules of Fermi–Walker transport. This is illustrated by examples in Minkowski space and the paper concludes with some speculations about spin-rotation coupling in Kerr space-time.     

Anisotropy resolved multidimensional emission spectroscopy (ARMES): A new tool for protein analysis

Structural analysis of proteins using the emission of intrinsic fluorophores is complicated by spectral overlap. Anisotropy resolved multidimensional emission spectroscopy (ARMES) overcame the overlap problem by the use of anisotropy, with chemometric analysis, to better resolve emission from different fluorophores. Total synchronous fluorescence scan (TSFS) provided information about all the fluorophores that contributed to emission while anisotropy provided information about the environment of each fluorophore. Here the utility of ARMES was demonstrated via study of the chemical and thermal denaturation of human serum albumin (HSA).