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PMC:7594251 / 107950-115010 JSONTXT 9 Projects

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Id Subject Object Predicate Lexical cue
T722 0-2 Sentence denotes 5.
T723 3-16 Sentence denotes Final Remarks
T724 17-118 Sentence denotes As we have attempted to emphasize and demonstrate, NMR has a powerful and unique role in drug design.
T725 119-274 Sentence denotes NMR provides detailed structural information about a molecule along with kinetic information over extended time periods, i.e., not just a snapshot [24,25].
T726 275-454 Sentence denotes Moreover, NMR is quantitative and highly reproducible, allowing applications in diverse fields such as relaxometry, combinatorial chemistry, fluxomics, and targeted analysis [91].
T727 455-599 Sentence denotes NMR can be combined with other analytical techniques, such as mass spectrometry “in tandem” analysis of the molecules of interest [436,437,438].
T728 600-793 Sentence denotes 1H 1D-NMR is used particularly in the analysis of metabolites, while the strength and intensity of the recorded signals is directly proportional to the concentration of the sample [44,439,440].
T729 794-881 Sentence denotes 1H 1D-NMR can also be used to follow “real-time” analysis of different molecules [441].
T730 882-1088 Sentence denotes In the 1D 1H-NMR experiment, there are no polarization transfer techniques required (the 1H atom is already highly sensitive) and covers a spread of interesting nuclei in the molecule(s) being studied [91].
T731 1089-1267 Sentence denotes Assuming that the sample can be stored stably for extended periods of time, the non-destructive nature of NMR permits the re-use on the sample for different experiments [50,442].
T732 1268-1376 Sentence denotes Aiding in the reproducibility of NMR [91], sample-recycling offers a significant advantage of NMR [443,444].
T733 1377-1504 Sentence denotes While always important in drug design, sensitivity and resolution of NMR are two major factors that need special consideration.
T734 1505-1647 Sentence denotes Since both factors improve with increasing magnetic field strength, we have seen a spike in the demand for ultra-high-field NMR spectrometers.
T735 1648-2007 Sentence denotes Recently, 28.2 T (i.e., 1.2 GHz for 1H) magnets have become commercially available, and with recent advances in magnet technology, such as liquid helium recycling and magnetic field shielding [91], NMR has begun to offer far better resolution and higher sensitivity while reducing the substantial costs of maintaining the instruments compared to past decades.
T736 2008-2294 Sentence denotes Other steps have been taken to enhance the sensitivity of NMR including: the development of cryoprobes increasing the signal to noise ratio 3 to 4 times, and micro-coil probes that not only increased sensitivity but also reduced the amount of sample required for the measurements [445].
T737 2295-2422 Sentence denotes From another perspective, one can further optimize the process of obtaining spectra by using different methods of measurements.
T738 2423-2604 Sentence denotes One of these, called SOFAST, helps to reduce the delay between scans resulting in lowering acquisition time for 2D experiments such as HMQC utilizing 1H,15N or 1H,13C [117,446,447].
T739 2605-2886 Sentence denotes The basic principle of this method is to use selective 1H pulses that will excite only a small portion of the available nuclei pool, while the unperturbed spins provide a magnetization “heat sink” thus improving the spin-lattice relaxation (T1) rate via dipolar interactions [446].
T740 2887-2985 Sentence denotes These methods can be highly efficient when studying drug binding and molecular interactions [117].
T741 2986-3141 Sentence denotes Another method, called ultrafast 2D NMR, enables obtaining a 2D spectra within a single scan but with the associated cost of reduced sensitivity [117,448].
T742 3142-3352 Sentence denotes The principle of this method is to divide the sample into n number of fractions, and apply the appropriate incremental aspect to each fraction, while recording them all simultaneously within the one scan [448].
T743 3353-3477 Sentence denotes This method has been applied to many metabolomic studies [177,447,449] as well as in the analysis of natural products [450].
T744 3478-3581 Sentence denotes The difficulty is that the effective concentration of the sample is lowered by the fractionation level.
T745 3582-3686 Sentence denotes The more slices the sample is split into, the greater the reduction of combined signal that is obtained.
T746 3687-3861 Sentence denotes Lastly, a method termed non-uniform sampling (NUS) may provide an advantage by reducing the total time for measurement while maintaining the same resolution of spectra [117].
T747 3862-3963 Sentence denotes NUS effectively skips over parts of the total dataset, collecting only around 20 to 30% of the total.
T748 3964-4114 Sentence denotes Usually sections containing higher concentrations of signal (over noise) are emphasized in the selection scheme, known as non-linear data acquisition.
T749 4115-4450 Sentence denotes These methods reconstruct the complete data subset by applying various algorithms such as multidimensional decomposition (MDD), which essentially separates the sets of multidimensional data into one dimensional problems that are much easier to solve given the common process of signal overlapping in multidimensional NMR spectra [117].
T750 4451-4680 Sentence denotes Other algorithms such as compressed sensing (CS), Maximum entropy method (Max Ent) and Iterative soft threshold (IST) each have their own advantages but all focus on decreasing the time needed for collection of spectra [117,451].
T751 4681-4748 Sentence denotes The cost is in signal to noise, as no gain is ever absolutely free.
T752 4749-4931 Sentence denotes The inherent advantages of NMR do not eliminate the disadvantages (Table 3), which are namely being limited for some nuclei, and inherent insensitivity for many types of experiments.
T753 4932-5057 Sentence denotes NMR can provide high quality resolution and sensitivity for some experiments [91,452] but the application can be challenging.
T754 5058-5377 Sentence denotes When the experiments become multidimensional, there is often a tradeoff between the improved higher resolution and/or the resulting sensitivity and/or the amount of time an experiment takes, i.e., high-quality spectra for multidimensional experiments take much longer than their simple 1D counterparts [117] (Scheme 2).
T755 5378-5502 Sentence denotes One must always choose between resolution, sensitivity, and the amount time; as you can only ever have two out of the three.
T756 5503-5688 Sentence denotes Unfortunately, in the real world, when working with NMR spectroscopy, we are mainly forced to choose between high or low precision data (Scheme 2) with fixed available instrument times.
T757 5689-5782 Sentence denotes Scheme 2 can be useful, when choosing NMR technique and/or method/approaches in drug studies.
T758 5783-6055 Sentence denotes It shows the general representation of different NMR techniques and method/approaches in cost-time matrix, bearing in mind that the exact position in the matrix can be influenced by the environmental conditions, pulse sequence and sample preparation (e.g., concentration).
T759 6056-6156 Sentence denotes Regarding, NMR methods/approaches, the exact position depends on the choice of proper NMR technique.
T760 6157-6256 Sentence denotes For the purposes of Scheme 2, the 2D techniques were chosen as described in the practical examples.
T761 6257-6439 Sentence denotes Nevertheless, with relatively short times and at low cost, we can acquire numerous data sets and therefore the low precision can be partially compensated for by statistical analysis.
T762 6440-6639 Sentence denotes Fortunately, significant efforts have been undertaken to reduce the amount of time it takes to record multidimensional spectra, especially for 2D NMR, and still obtain high quality spectra (Table 3).
T763 6640-6725 Sentence denotes Novel pulse sequences have been developed to decouple nuclei in Pure-shift NMR [117].
T764 6726-6856 Sentence denotes Dynamic Nuclear Polarization (DNP) can induce hyper-polarization in atoms (13C, 15N) with an inherently low sensitivity [453,454].
T765 6857-7060 Sentence denotes Parahydrogen-Induced Polarization (PHIP) and Signal Amplification by Reversible Exchange (SABRE) are other polarization techniques used to increase the sensitivity of inherently insensitive nuclei [455].