Real sample temperature: a critical issue in the experiments of nuclear resonant vibrational spectroscopy on biological samples

Abstract

The real sample temperatures during the nuclear resonant vibrational spectroscopy on biological samples have been assessed and significantly reduced (116 → 52 K) by improving the sample-loading procedures.

A strenuous experimental journey searching for spectroscopic evidence of a bridging nickel–iron–hydride in [NiFe] hydrogenase

“…The real sample temperatures were much higher than 6-9 K, e.g. 50-70 K (Wang et al, 2012). This standard NRVS setup has been used in many NRVS measurements in the past and their details are discussed elsewhere (Cramer et al, 2007;Pelmenschikov et al, 2011;Wang et al, 2012Wang et al, , 2014.…”

“…The spectral conversion was optimized when the observed Stokes/anti-Stokes imbalance matched the imbalance calculated using the entered temperature as a parameter. The real sample temperatures were thus obtainable with the measured NRVS's Stokes/anti-Stokes imbalance (Wang et al, 2012).…”

NRVS for Fe in Biology: Experiment and Basic Interpretation

“…Due to favorable physical properties, particularly a melting point of 147 K, 1-propanol is considered one of the best mounting liquids. 13 The true sample temperature can be obtained by fitting the ratio of phonon annihilation events to creation events using the PHOENIX software and is approximated by a Maxwell-Boltzmann distribution. 14 To ensure the temperature can be approximated, a standard NRVS spectrum is usually collected slightly below the elastic resonance at −180 cm −1 (annihilation of phonons), through the elastic resonance, and at energies higher than the resonance into the region of interest (creation of phonons).…”

A Practical Guide for Nuclear Resonance Vibrational Spectroscopy (NRVS) of Biochemical Samples and Model Compounds

“…The samples are either attached using screws or using a cryogenic adhesive. In the latter procedure, the samples are briefly warmed up above the effective melting point of the cryogenic adhesive, which is ~175K for low temperature grease and 147K for 1-proanol) (2). Once cooled below those temperatures, the samples are held firmly in place, usually with better thermal contact than provided by mechanical screws or clamps.…”

“…However, given the current price and shortages of liquid He, you can expect a shift towards use of closed-cycle cryo-coolers. In addition, as discussed above, sample loading medium and method are also critical to real sample temperatures (2). …”