Comprehensive solid-state NMR analysis reveals the effects of N-methylation on the molecular dynamics of glycine

High-temperature rotation-vibration spectrum of iminosilylene (HNSi)

Iminosilylene (HNSi) has been observed in the laboratory and is expected to occur in the envelopes of carbon-rich stars. However, the lack of spectroscopic information for HNSi has hampered its further astrophysical detection. Using robust ab initio methods, we present the first and comprehensive molecular line list for HNSi (X 1Σ+). The new line list contains almost 3.36 billion transitions between 1.57 million levels with rotational excitation up to J = 160. It is suitable for temperatures up to 3000 K and covers the wavenumber range of 0-9000 cm-1 (wavelengths λ > 1.11 μm). This new line list can be helpful for the future spectroscopic characterization and molecular detection of HNSi in the laboratory and interstellar space.

NMR crystallography of amino acids

The development of NMR crystallography methods requires a reliable database of chemical shifts measured for systems with known crystal structure. We measured and assigned carbon and hydrogen chemical shifts of twenty solid natural amino acids of known polymorphic structure, meticulously determined using powder X-ray diffraction. We then correlated the experimental data with DFT-calculated isotropic shieldings. The small size of the unit cell of most amino acids allowed for advanced computations using various families of DFT functionals, including generalized gradient approximation (GGA), meta-GGA and hybrid DFT functionals. We tested several combinations of functionals for geometry optimizations and NMR calculations. For carbon shieldings, the widely used GGA functional PBE performed very well, although an improvement could be achieved by adding shielding corrections calculated for isolated molecules using a hybrid functional. For hydrogen nuclei, we observed the best performance for NMR calculations carried out with structures optimized at the hybrid DFT level. The high fidelity of the calculations made it possible to assign additional signals that could not be assigned based on experiments alone, for example signals of two non-equivalent molecules in the unit cell of some of the amino acids.

Sarcosine as a potential prostate cancer biomarker--a review

Prostate cancer (CaP) is the most common type of tumour disease in men. Early diagnosis of cancer of the prostate is very important, because the sooner the cancer is detected, the better it is treated. According to that fact, there is great interest in the finding of new markers including amino acids, proteins or nucleic acids. Prostate specific antigen (PSA) is commonly used and is the most important biomarker of CaP. This marker can only be detected in blood and its sensitivity is approximately 80%. Moreover, early stages cannot be diagnosed using this protein. Currently, there does not exist a test for diagnosis of early stages of prostate cancer. This fact motivates us to find markers sensitive to the early stages of CaP, which are easily detected in body fluids including urine. A potential is therefore attributed to the non-protein amino acid sarcosine, which is generated by glycine-N-methyltransferase in its biochemical cycle. In this review, we summarize analytical methods for quantification of sarcosine as a CaP marker. Moreover, pathways of the connection of synthesis of sarcosine and CaP development are discussed.

Solid-state NMR analyses reveal the structure dependence of the molecular dynamics for ω-amino acids

The molecular dynamics of metabolites is structure dependent and vitally important for the interactive functions in their potential applications as natural materials. To understand the relationship between molecular structure and dynamics, the molecular motions of four structurally related ω-amino acids (β-alanine, γ-aminobutyric acid, 5-aminovaleric acid, and 6-aminocaproic acid) were investigated by measuring their proton spin-lattice relaxation times (T(1), T(1ρ)) as a function of temperature (180-440 K). (13)C CPMAS NMR and DSC analyses were performed to obtain complementary information. All of these ω-amino acids showed no phase transition in the temperature range studied but had outstandingly long proton T(1) at 300 MHz and even at 20 MHz for the deuterated forms. The molecular dynamics of all these ω-amino acids were dominated by the reorientation motions of amino groups and backbone motions except in β-alanine. The activation energies for amino group reorientations were positively correlated with the strength of hydrogen bonds involving these groups in the crystals and the carbon-chain lengths, whereas such energies for the backbone motions were inversely correlated with the carbon-chain lengths. These findings provided essential information for the molecular dynamics of ω-amino acids and demonstrated the combined solid-state NMR methods as a useful approach for understanding the structural dependence of molecular dynamics.