Validation of energy expenditure and macronutrient oxidation measured by two new whole-room indirect calorimeters.

OBJECTIVE: The aim of this study was to validate two new whole-room indirfect calorimeters according to Room Indirect Calorimetry Operating and Reporting Standards (RICORS 1.0). METHODS: For technical validation, 16 propane combustion tests were performed to determine accuracy and precision of energy expenditure (EE) and ventilation rates of oxygen (VO2 ), carbon dioxide (VCO2 ), and respiratory exchange ratio (VCO2 /VO2 ). For biological validation, eight participants (mean [SD], age 24.1 [2.5] years; BMI 24.3 [3.1] kg/m2 ) underwent four 24-hour protocols under highly standardized conditions: (1) isocaloric sedentary, (2) fasting sedentary, (3) isocaloric active, and (4) fasting active. Reliability (coefficients of variation [CV]) and minimal detectable changes (MDC) were calculated for 24-hour EE, sleeping metabolic rate (SMR), physical activity energy expenditure (PAEE), thermic effect of food (TEF), and macronutrient oxidation rates. RESULTS: Technical validation showed high reliability and recovery rates for VO2 (0.75% and 100.8%, respectively), VCO2 (0.49% and 100.6%), and EE (0.54% and 98.2%). Biological validation revealed CV and MDC for active conditions of 1.4% and 4.3% for 24-hour EE, 1.7% and 5.9% for SMR, and 30.2% and 38.4% for TEF, as well as 5.8% and 10.5% for PAEE, respectively. Mean CV and MDC for macronutrient oxidation rates were 9.9% and 22.9%, respectively. CONCLUSIONS: The precision of 24-hour EE and SMR was high, whereas it was lower for PAEE and poor for TEF.

Validation of whole room indirect calorimeters: refinement of current methodologies.

Whole room indirect calorimeter (WRIC) validation techniques consist of propane combustion (PC) or infusion of mixed carbon dioxide (CO2) and nitrogen (N2) by a precision blender (PB). To determine the best method, PC of 6, 10, 22-h and PB infusions of 6, 10, and 14-h, were conducted. The 14-h infusion consisted of two metabolic settings. Energy expenditure (EE; kJ), ventilation (V; liters/min) of oxygen (VO2), VCO2, and respiratory quotient (VCO2/VO2) obtained from the WRIC were extrapolated to the respective test durations and compared to similarly calculated values. Moreover, accurate equations (AE) were derived to correct infusions for additional N2 As a final evaluation of a PC validated WRIC, weight maintenance (WM), energy balance (EB), respiratory quotient (RQ), and food quotients (FQ) were determined in 22 subjects who had repeat 24-h EE measurements. Statistical analyses (P < 0.05) were conducted (SPSS, version 23). Significant differences in RQ existed between PC and stoichiometry after 6-h. Errors for the rest of the PC tests ranged from -1.5 ± 2.4 (VCO2) to 2.8 ± 4.6% (EE). When compared with the WRIC, all uncorrected metabolic parameters for six and 10-h PB infusions were significantly different with errors from -12.8 ± 1.6 (VO2) to 6.0 ± 2.8% (RQ). The AE reduced the magnitude of errors to -12.4 ± 1.5 (RQ) to 2.2 ± 3.0% (RQ). The PB infusion with two settings showed similar performance. No differences in WM, EB, RQ, or FQ existed in the subjects. In conclusion, 10-h PC tests are sufficient for validating WRICs.

Why are trimethylsilyl groups asymmetrically coordinated? Gas-phase molecular structures of 1-trimethylsilyl-1,2,3-benzotriazole and 2-trimethylsilyl-1,3-thiazole.

The structures of 1-trimethylsilyl-1,2,3-benzotriazole and 2-trimethylsilyl-1,3-thiazole have been determined by gas electron diffraction and computational methods. While 1-trimethylsilyl-1,2,3-benzotriazole shows a significant asymmetry in the way the SiMe(3) groups bonds to the ring system, the same is not true for 2-trimethylsilyl-1,3-thiazole. However, it has been shown that when the positions of formal single and double bonds in the rings systems are considered, the silyl groups in both compounds are displaced towards the neighbouring ring nitrogen atom. Calculated structures of a series of analogous compounds with different substituents on silicon show only minor variations in the extent of the distortion, although with hydrogen instead of a silyl group the displacement is significantly smaller.

Extremely narrow SiON angles in siloxy-substituted nitrogen-containing rings: a computational investigation.

Quantum chemical calculations have been performed for a number of siloxy derivatives of pyrrolidine and piperidine in an attempt to gauge the effect of the saturated ring on the SiON angle. Most derivatives of pyrrolidine had SiON angles comparable to those previously observed for substituted N,N-dimethylhydroxylamines. However, piperidine derivatives were predicted to have particularly narrow SiON angles. Anti, anti, axial-F(3)SiO-piperidine was found to have an angle of 82.9 degrees , smaller than the narrowest angle observed by experiment in the gas phase, for (F(3)C)F(2)SiONMe(2). The size of the ring and, in particular, the CNC angle appears to play a crucial role in determining the SiON angle. Further calculations including other heterocyclic rings were therefore performed to help explain this finding. Using the (F(3)C)F(2)SiO- group as a substituent on nitrogen allowed SiON angles of less than 80 degrees to be calculated for several five-, six- and seven-membered rings.

Highly asymmetric coordination of trimethylsilyl groups to tetrazole and triazole rings: an experimental and computational study in gaseous and crystalline phases.

1-Trimethylsilyltetrazole, 1, has been synthesised from chlorotrimethylsilane and tetrazole in the presence of triethylamine as an auxiliary base. The structure of this compound has been determined in the crystalline phase by X-ray diffraction of a crystal grown in situ. The gas-phase structures of 1 and 1-trimethylsilyl-1,2,4-triazole, 2, have been determined by gas-phase electron diffraction (GED). An extensive investigation of these and related compounds by ab initio calculations is also reported. The angles between the rings and the substituents on N were of particular interest. It was found that the calculated difference of 15.5 degrees between the CNSi and NNSi angles in 1 was mostly, but not entirely, an inherent property of the tetrazole ring and not due to a short SiN interaction.

(Dimethylaminomethyl)trifluorosilane, Me2NCH2SiF3--a model for the alpha-effect in aminomethylsilanes.

F3SiCH2NMe2 was prepared as a model for the investigation of the nature of the alpha-effect in alpha-aminosilanes, by fluorination of Cl3SiCH2NMe2 with SbF3. Under less mild conditions Si--C bond cleavage was also observed, leading to the double adduct F4Si(Me2NCH2SiF3)2, which was characterised by a crystal structure analysis showing that the central SiF4 unit is connected to Me2NCH2SiF3 via SiN dative bonds and FSi contacts. F3SiCH2NMe2 was characterised by multinuclear NMR spectroscopy (1H, 13C, 15N, 19F and 29Si), gas-phase IR spectroscopy and mass spectrometry. It is a dimer in the crystal (X-ray diffraction, crystal grown in situ), held together by two Si--N dative bonds. In solution and in the gas phase the compound is monomeric. The structure of the free molecule, determined by gas-phase electron diffraction, showed that, in contrast to former postulates, there are no attractive SiN interactions. Ab initio calculations have been carried out to explain the nature of the bonding. F3SiCH2NMe2 has an extremely flat bending potential for the Si-C-N angle; the high degree of charge transfer from the Si to the N atoms which occurs upon closing the Si-C-N angle is in the opposite direction to that expected for a dative bond. The topology of the electron density of F3SiCH2NMe2 was analysed. Solvent simulation calculations have shown virtually no structural dependence on the medium surrounding the molecule. The earlier postulate of Si-->N dative bonds in SiCN systems is discussed critically in light of the new results.

Three-membered ring or open chain molecule - (F3C)F2SiONMe2 a model for the alpha-effect in silicon chemistry.

(F3C)F2SiONMe2 was prepared from LiONMe2 and F3CSiF3. It was characterized by gas IR and multinuclear solution NMR spectroscopy and by mass spectrometry. Its structure was elucidated by single crystal X-ray crystallography and by gas electron diffraction. (It exists as a conformer mixture.) Important findings were extremely acute SiON angles [solid 74.1(1) degrees , gas anti 84.4(32) degrees and gauche 87.8(20) degrees] and short Si...N distances [solid 1.904(2) A]. The bending potential of the SiON unit was calculated at the MP2/6-311++G(3df,2dp) level of theory and appears very flat and highly asymmetric. The calculated atomic charges (NPA) are counterintuitive to the expected behavior for a classical Si-N dative bond, as upon formation of the Si...N bond electron density is transferred mainly from oxygen to nitrogen, while the silicon charge is almost unaffected. Despite the molecular topology of a three-membered ring, the topology of the electron density shows neither a bond critical point between Si and N atoms nor a ring critical point, but the electron density and Laplacian values are related to other hypercoordinate Si compounds. The electronic properties of (F3C)F2SiONMe2 were compared to those of the adduct (F3C)F2(MeO)Si-NMe3, whose properties and structure were also calculated. The charge distribution and Laplacian values along the Si-N vectors in both molecules are similar but not equivalent. (F3C)F2SiONMe2 contains thus a nonclassical Si...N bond, and its properties can be regarded as a new model for the explanation of the old postulate of an alpha-effect in silicon chemistry, explaining the behavior of compounds with geminal Si and N atoms.