Direct and simultaneous quantification of ATP, ADP and AMP by (1)H and (31)P Nuclear Magnetic Resonance spectroscopy

Latest assessment methods for mitochondrial homeostasis in cognitive diseases

Mitochondria play an essential role in neural function, such as supporting normal energy metabolism, regulating reactive oxygen species, buffering physiological calcium loads, and maintaining the balance of morphology, subcellular distribution, and overall health through mitochondrial dynamics. Given the recent technological advances in the assessment of mitochondrial structure and functions, mitochondrial dysfunction has been regarded as the early and key pathophysiological mechanism of cognitive disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, mild cognitive impairment, and postoperative cognitive dysfunction. This review will focus on the recent advances in mitochondrial medicine and research methodology in the field of cognitive sciences, from the perspectives of energy metabolism, oxidative stress, calcium homeostasis, and mitochondrial dynamics (including fission-fusion, transport, and mitophagy).

Bipolar hemicyanine cationic probe for simultaneous sensing of ATP and GTP

Adenosine 5'-triphosphate (ATP) and guanosine 5'-triphosphate (GTP) are the most essential energy source in enormous biological processes. Various probes for ATP or GTP sensing, have been widely established, but the probe that could simultaneously monitor ATP and GTP is still rarely reported. Herein, we report a bipolar hemicyanine cationic probe for simultaneous sensing of ATP and GTP via a one-step monitoring process. This probe exhibited strong affinity to ATP and GTP through intramolecular electrostatic and π-π stacking interactions, which the binding constant on each step were determined as 6.15 × 107 M-1 and 1.57 × 106 M-1 for ATP, 3.19 × 107 M-1 and 3.81 × 106 M-1 for GTP. The sensitivity and specificity of this probe toward ATP or GTP over other twelve biological analogues (adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP), guanosine 5'-diphosphate (GDP), guanosine 5'-monophosphate (GMP), Etc.) have also been successfully demonstrated. Furthermore, due to the rapid response rate (within 10 s), we also proved that this probe could be employed as a monitor tool during the ATP or GTP-related enzymatic reaction process.

Cu2+-mediated turn-on fluorescence biosensor based on DNA-templated silver nanoclusters for label-free and sensitive detection of adenosine triphosphate

A Cu²⁺-mediated turn-on fluorescence biosensor based on the DNA-templated green-emitting silver nanoclusters (DNA@g-AgNCs) was developed for label-free and sensitive detection of adenosine 5'-triphosphate (ATP). Cu²⁺ was able to quench the bright green fluorescence of DNA@g-AgNCs because of the coordination and photoinduced electron transfer between DNA@g-AgNCs and Cu²⁺. Therefore, a unique and effective fluorescence biosensor can be constructed with the formation of DNA@g-AgNCs/Cu²⁺/ATP ternary-competition system. With the introduction of ATP, the DNA@g-AgNCs/Cu²⁺ fluorescence sensing system will be disrupted and the fluorescence of DNA@g-AgNCs was recovered due to higher affinity of ATP towards Cu²⁺. On the basis of this feature, the DNA@g-AgNCs/Cu²⁺ fluorescence sensing system demonstrated quantitative determination of ATP in the range 0.05 - 3 μM and a detection limit of 16 nM. Moreover, the fluorescence sensing system was successfully applied to the quantitative determination of ATP in human urine and serum samples with recoveries ranging from 98.6 to 106.5%, showing great promise to provide  a label-free, cost-efficient, and rapid platform for ATP-related clinical disease diagnosis.

Approaches to monitor ATP levels in living cells: where do we stand?

ATP is the most universal and essential energy molecule in cells. This is due to its ability to store cellular energy in form of high-energy phosphate bonds, which are extremely stable and readily usable by the cell. This energy is key for a variety of biological functions such as cell growth and division, metabolism, and signaling, and for the turnover of biomolecules. Understanding how ATP is produced and hydrolyzed with a spatiotemporal resolution is necessary to understand its functions both in physiological and in pathological contexts. In this review, first we will describe the organization of the electron transport chain and ATP synthase, the main molecular motor for ATP production in mitochondria. Second, we will review the biochemical assays currently available to estimate ATP quantities in cells, and we will compare their readouts, strengths, and weaknesses. Finally, we will explore the palette of genetically encoded biosensors designed for microscopy-based approaches, and show how their spatiotemporal resolution opened up the possibility to follow ATP levels in living cells.

Validated quantitative 31P NMR spectroscopy for positional isomeric impurity determination in L-α-glycerylphosphorylcholine (L-α-GPC)

In this study a quantitative ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy method was described to determine positional isomeric impurity β-GPC in commercial products of L-α-GPC. The samples were dissolved in D₂O and trimethyl phosphate (TMP) was selected as an internal calibrant. The measurements were performed on a Bruker 500 MHz spectrometer and the spectra were recorded under optimized process conditions. A good linear relationship was constructed for β-GPC in the range of 62.7-528.0 µg·mL^-1, i.e. 0.03-0.25 % (w/w %, in relative to L-α-GPC) with a correlative coefficient of 0.9996. The limit of quantification (LOQ) and limit of detection (LOD) were 62.7 µg·mL^-1 and 20.9 µg·mL^-1 with signal to noise of 3 and 10, respectively. The spiked recoveries were in the range of 98.17-99.78 % with the relative standard deviation (RSD %) less than 1.0 %. Therefore, it could be supposed that the ³¹P NMR was a promising alternative method for sensitive determination of β-GPC for strict quality control of L-α-GPC.

Determination of Isotope Abundance for Deuterium-labeled Compounds by Quantitative 1 H NMR + 2 H NMR

Deuterated reagents have been used in many research fields. Isotope abundance, as the feature parameter of deuterated reagents, the precise quantification is of great importance. Based on quantitative nuclear magnetic resonance technology, a novel method that combines ¹ H NMR + ² H NMR was systematically established to determine the isotopic abundance of deuterated reagents. The results showed that the isotopic abundance of partially labeled and fully labeled compounds calculated by this new method was even more accurate than that calculated by classical ¹ H NMR and MS methods. In brief, this new method is a robust strategy for the determination of isotope abundance in large-scale deuterated reagents.

Genetically Encoded ATP Biosensors for Direct Monitoring of Cellular ATP Dynamics

Adenosine 5'-triphosphate, or ATP, is the primary molecule for storing and transferring energy in cells. ATP is mainly produced via oxidative phosphorylation in mitochondria, and to a lesser extent, via glycolysis in the cytosol. In general, cytosolic glycolysis is the primary ATP producer in proliferative cells or cells subjected to hypoxia. On the other hand, mitochondria produce over 90% of cellular ATP in differentiated cells under normoxic conditions. Under pathological conditions, ATP demand rises to meet the needs of biosynthesis for cellular repair, signaling transduction for stress responses, and biochemical processes. These changes affect how mitochondria and cytosolic glycolysis function and communicate. Mitochondria undergo remodeling to adapt to the imbalanced demand and supply of ATP. Otherwise, a severe ATP deficit will impair cellular function and eventually cause cell death. It is suggested that ATP from different cellular compartments can dynamically communicate and coordinate to adapt to the needs in each cellular compartment. Thus, a better understanding of ATP dynamics is crucial to revealing the differences in cellular metabolic processes across various cell types and conditions. This requires innovative methodologies to record real-time spatiotemporal ATP changes in subcellular regions of living cells. Over the recent decades, numerous methods have been developed and utilized to accomplish this task. However, this is not an easy feat. This review evaluates innovative genetically encoded biosensors available for visualizing ATP in living cells, their potential use in the setting of human disease, and identifies where we could improve and expand our abilities.

Live Cells Extracts of Freshly Cut Chicken and Baby Sprouts of Mung Beans Detected with UV Absorption and Proton NMR Spectra

Background:

This article discloses information related to a recent patent filed by the author on extracts of freshly cut farm birds and animals.

Objective:

The objective was to evaluate “Liquid-Protein” extracts obtained from live cells of protein-rich meat of farm birds or animals as well as from baby plants of pulses.

Method:

Freshly cut meat pieces or sprouts of pulses were put in water and pulse-heated for 30 minutes. The nutritious water extract of these was taken that contained amino-acids/proteins and some signaling chemicals emitting from the stressed live cells.

Results:

The heat-stressed animal cells (of Chicken) released creatine and many other nutrients in the extract along with Guanosine triphosphate/Guanosine diphosphate/ Guanosine monophosphate/ Inosine Mono Phosphate (GTP/GDP/ GMP/IMP), showing a UV absorption peak at 249 nm. This paper analyses the UV-Visual Absorption spectra and proton NMR data for the extracts. It is disclosed that the vegetarian baby plant cells of pulse seeds released (ATP) Adenosine Tri Phosphate (264 nm peak) along with Resveratrol (306 nm peak) but did not produce creatine, and such an extract exhibited side effects.

Conclusion:

Cells of birds/animals are similar to those of humans, and the signaling chemicals in the non-vegetarian extract are non-toxic and 100% compatible with humans as compared to plant cell extracts with incompatible chemicals. Since meat cells manage to “live” for longer than 10 hours without blood/oxygen supply, in anaerobic cell respiration involving creatine and GTP/GDP/GMP/IMP, the extract of these meat cells plays a key role in metabolic cell repair, inducing anti-aging effects in humans.

Colorimetric detection of ATP by inhibiting the Peroxidase-like activity of carbon dots

Adenosine triphosphate (ATP) is the main energy currency for cells and an important biomolecule involved in cellular reactions, whose abnormal levels are closely related to physical disease, thus it is extremely important to establish a convenient, fast and simple ATP monitoring method. Toward this end, we developed a facile method for colorimetric detection of ATP on the basis of the inhibiting effect of ATP on the peroxidase-like activity of carbon dots (CDs). The detection principle of this method was utilizing the peroxidase-like activity of CDs, which catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H₂O₂ to generate blue products. However, the introduction of ATP in the system can inhibit the generation of blue products, so ATP can be colorimetric detected. This method exhibited high sensitivity with a detection limit of 34 nM and a wide linear range (0.050-2.0 μM). The as-proposed colorimetric ATP sensor was capable of detecting ATP in real samples accurately.

Controlled release and characterisation of photocaged molecules using in situ LED illumination in solution NMR spectroscopy

We demonstrate that photo-uncaging reactions triggered by LED illumination can be conveniently monitored in situ by solution NMR, offering new ways to characterise and optimise photocages.

Accurate detection of perchlorate in epoxy resins via chlorine-35 quantitative quadrupolar NMR (qQNMR)

We present herein the application of a qQNMR method that uses a quadrupolar nucleus such as chlorine-35 for the quantification of perchlorate in epoxy resins.

Quantitative Quadrupolar NMR (qQNMR) via nitrogen-14 for the accurate control of L-carnitine in food supplements

A qQNMR methodology using nitrogen-14 as the quadrupolar nucleus of choice has been introduced for the first time as a robust and validated method to determine and quantify L-carnitine in food supplements. The quantification has been carried out by the alternative use of a calibration curve or by addition of ammonium chloride as internal standard. The method was validated at seven concentration levels in the range of 5.58-99.26 mM, affording intra- and inter day accuracies lower than 6.84% (expressed in CV), robustness towards temperature and recycle delay, limit of detection (LOD) of 2.48 mM, limit of quantification (LOQ) of 5.58 mM and remarkably with absence of matrix effect.

NMR of 31P nuclear spin singlet states in organic diphosphates

³¹P NMR and MRI are commonly used to study organophosphates that are central to cellular energy metabolism. In some molecules of interest, such as adenosine diphosphate (ADP) and nicotinamide adenine dinucleotide (NAD), pairs of coupled ³¹P nuclei in the diphosphate moiety should enable the creation of nuclear spin singlet states, which may be long-lived and can be selectively detected via quantum filters. Here, we show that ³¹P singlet states can be created on ADP and NAD, but their lifetimes are shorter than T₁ and are strongly sensitive to pH. Nevertheless, the singlet states were used with a quantum filter to successfully isolate the ³¹P NMR spectra of those molecules from the adenosine triphosphate (ATP) background signal.

1H HR-MAS NMR Based Metabolic Profiling of Lung Cancer Cells with Induced and De-Induced Cisplatin Resistance to Reveal Metabolic Resistance Adaptations

Cisplatin (cisPt) is an important drug that is used against various cancers, including advanced lung cancer. However, drug resistance is still a major ongoing problem and its investigation is of paramount interest. Here, a high-resolution magic angle spinning (HR-MAS) NMR study is presented deciphering the metabolic profile of non-small cell lung cancer (NSCLC) cells and metabolic adaptations at different levels of induced cisPt-resistance, as well as in their de-induced counterparts (cells cultivated in absence of cisPt). In total, fifty-three metabolites were identified and quantified in the ¹H-HR-MAS NMR cell spectra. Metabolic adaptations to cisPt-resistance were detected, which correlated with the degree of resistance. Importantly, de-induced cell lines demonstrated similar metabolic adaptations as the corresponding cisPt-resistant cell lines. Metabolites predominantly changed in cisPt resistant cells and their de-induced counterparts include glutathione and taurine. Characteristic metabolic patterns for cisPt resistance may become relevant as biomarkers in cancer medicine.

The lipopolysaccharide-transporter complex LptB2FG also displays adenylate kinase activity in vitro dependent on the binding partners LptC/LptA

Lipopolysaccharide (LPS) is an essential glycolipid that covers the surface of gram-negative bacteria. The transport of LPS involves a dedicated seven-protein transporter system called the lipopolysaccharide transport system (Lpt) machinery that physically spans the entire cell envelope. The LptB₂FG complex is an ABC transporter that hydrolyzes ATP to extract LPS from the inner membrane for transport to the outer membrane. Here, we extracted LptB₂FG directly from the inner membrane with its original lipid environment using styrene-maleic acid polymers. We found that styrene-maleic acid polymers–LptB₂FG in nanodiscs display not only ATPase activity but also a previously uncharacterized adenylate kinase (AK) activity, as it catalyzed phosphotransfer between two ADP molecules to generate ATP and AMP. The ATPase and AK activities of LptB₂FG were both stimulated by the interaction on the periplasmic side with the periplasmic LPS transport proteins LptC and LptA and inhibited by the presence of the LptC transmembrane helix. We determined that the isolated ATPase module (LptB) had weak AK activity in the absence of transmembrane proteins LptF and LptG, and one mutation in LptB that weakens its affinity for ADP led to AK activity similar to that of fully assembled complex. Thus, we conclude that LptB₂FG is capable of producing ATP from ADP, depending on the assembly of the Lpt bridge, and that this AK activity might be important to ensure efficient LPS transport in the fully assembled Lpt system.

Quantitative quadrupolar NMR (qQNMR) using nitrogen-14 for the determination of choline in complex matrixes

NMR offers the unique potential to selectively excite the chosen nuclei avoiding in an extraordinary way the matrix effect. Quantitative Nitrogen-14 NMR (¹⁴N qNMR) spectroscopy has been introduced for the first time as a robust and validated method to determine choline in a variety of matrixes including quinoa grains, instant coffee and food supplements. A study about the ion pairing of choline bitartrate in aqueous solution by means of diffusion PGSE, NOESY and HOESY NMR have been also provided. Validation of the method within eight concentrations levels (from 1.58 to 79.0 mM) afforded a limit of detection of 400 μg/mL (1.58 mM), a quantification limit of 1000 μg/mL (3.95 mM), excellent linearity (R² higher than 0.999), intra-/inter-day precisions lower than 1.24% (CV), recoveries of 93.5%-102.5%, and complete absence of matrix effect. The fast and reliable quantification of choline together with the accuracy and simplicity of this new approach make it useful in the development of analytical procedures that could dramatically affect traditional analysis.

Quantification of 13C, 15N labelled compounds with 13C, 15N edited 1H Nuclear Magnetic Resonance spectroscopy

It was significant to detect isotope labelled compounds in biology and pharmacy. Based on a novel ¹H Nuclear Magnetic Resonance (¹H-NMR) technique, a simple, fast and green method has been successfully established to quantitatively detect ¹³C, ¹⁵N isotope labelled compounds. In this protocol, the couples between ¹H and ¹³C, ¹⁵N nearby were removed, which greatly simplified the spectrum. At mean time, the multiple peaks led by ¹³C and ¹⁵N were combined into one peak, so the signal intensity was also significantly enhanced. Melamine was selected as the internal standard and five ¹³C, ¹⁵N isotope labelled compounds showed excellent linearity from 0.001 mM to 100 mM. A real polypeptide sample has quantitatively been detected.

Selective monitoring ATP using a fluorogenic Al(III)-probe complex in aqueous medium

A simple commercially available probe 8-hydroxyjulolidine-9-aldehyde (HJ) has been developed as a turn-on fluorescent probe specifically for Al³⁺ and characterized systemically. The probe HJ for Al³⁺ ion exhibits strong green fluorescence under ultraviolet light. The HJ acted as an OFF-ON-OFF type fluorescent probe for Al³⁺ and ATP in nearly 100% aqueous media. The 1:1 binding stoichiometry between probe and Al³⁺ has been established from Job's plot and HRMS studies. The limit of detection for Al³⁺ ion is found to be 5.75 × 10^-8 M. The large association constant between HJ and Al³⁺ ion is 1.05 × 10⁵ M^-1. Detailed insights of probe-metal interaction mechanisms have been studied by the density functional theory (DFT) as well as the time dependent-DFT (TDDFT) calculations. Moreover, benefiting from the water solubility and biocompatibility of the probe HJ and its HJ-Al³⁺ complex, they have also been successfully applied to detect Al³⁺ and ATP by bioimaging in onion epidermal cells and adult zebrafish respectively.

Phosphate-sensing with (di-(2-picolyl)amino)quinazolines based on a fluorescence on–off system

Detection and visualization of phosphates such as ATP in living organisms can facilitate the elucidation of various biological events. Although substantial efforts had been made in this area, present methods have disadvantages such as the need for specialized equipment and poor sensitivities. To address these limitations, novel fluorescent probes, (di-(2-picolyl)amino)quinazolines, were developed for application in ATP detection. They selectively recognized copper ions by fluorescence quenching, and their copper complexes displayed fluorescence enhancement in the presence of phosphoric acid derivatives. This fluorescence on–off system enabled highly sensitive fluorescence detection of ATP when combined with a phenyl boronic acid-modified γ-cyclodextrin through a plausible multipoint recognition system.

Supramolecular probe Cu-dpa-QZ2/FPB-γ-CyD recognized ATP with high sensitivity.

The clinical application of purine nucleosides as biomarkers of tissue Ischemia and hypoxia in humans in vivo

During periods of ischemia and hypoxia, intracellular adenosine triphosphate stores are rapidly depleted. Its metabolism results in release of purine nucleosides into the systemic circulation. While the potential of purine nucleosides as a biomarker of ischemia has long been recognized, this has been limited by their complex physiological role and inherent instability leading to problematic sampling and prolonged, complex analysis procedures. Purine release has been demonstrated from cerebral tissue in patients undergoing carotid endarterectomy and patients presenting to hospital with stroke and transient ischemic attack. Rises in purine nucleosides have also been demonstrated in patients with angina and myocardial infarction, during systemic hypoxia, exercise, in patients with peripheral arterial disease and during surgery. This article reviews purine nucleoside production in ischemia, the development of purine analysis technology and details results of the studies investigating purine nucleosides as a biomarker of ischemia with suggestions for areas of future research.

Monitoring ADP and ATP in vivo using a fluorescent Ga(iii)-probe complex

A naphthol-based sensor (L) was designed and synthesized for the specific recognition of Ga3+ using fluorescence enhancement. An in situ generated L-Ga3+ ensemble detected ADP and ATP more selectively through a fluorescence "switch off" response, which was confirmed both in cells and in adult zebrafish.

Pushing the frontiers: boron-11 NMR as a method for quantitative boron analysis and its application to determine boric acid in commercial biocides

Quantitative boron-11 NMR (11B qNMR) spectroscopy has been introduced for the first time as a method to determine boric acid content in commercial biocides. Validation of the method affords a limit of detection of 0.02% w/w and a limit of quantification of 0.04% w/w, which are low enough to determine boric acid in commercial biocides. Other figures of merit such as linearity (R2 > 0.99), recovery (93.6%-106.2%), intra- and inter-day precision (from 0.7 to 2.0%), uncertainty (3.7 to 4.4%) and matrix effects were also evaluated. This method was successfully applied to determine boric acid in five different commercial biocides in a wide range of concentrations (<0.05 to 10% w/w) providing excellent results when they were compared with those obtained using inductively coupled plasma-mass spectrometry (ICP-MS). The suitability of this method for a fast and reliable quantification of boric acid in commercial biocide preparations has been demonstrated. The absence of the matrix effect allows the application of this validated method for the determination of boric acid in other matrices of diverse composition.

An ''off-on'' phosphorescent aptasensor switch for the detection of ATP

An "off-on" phosphorescent aptasensor based on the 3-mercaptopropionic acid (MPA) capped Mn-doped ZnS quantum dots (MPA-Mn:ZnS QDs)/aptamer hybrid system was developed to detect adenosine triphosphate (ATP) in biological fluids. The phosphorescence of MPA-Mn:ZnS QDs was obviously quenched when ATP aptamer was added due to the aggregation induced effect. ATP aptamer, adsorbed on the surface of the phosphorescent MPA-Mn:ZnS QDs, has a high affinity for ATP. And then, with the addition of ATP, phosphorescence was gradually recovered because of the stronger special binding interaction between ATP and ATP aptamer than that between QDs and ATP aptamer. In this case, a high sensitivity and selectivity of phosphorescent aptasensor for the detection of ATP has constructed with a low detection limit of 0.9 nM and a wide linear range from 2 nM to 9 µM. What's more, the phosphorescent aptasensor does not require complex pretreatments and can effectively eliminate the interference from auto fluorescence and scattering light.

Study of Al3+ interaction with AMP, ADP and ATP in aqueous solution

The interaction of Al³⁺ and nucleotide ligands, namely adenosine-5'-monophosphate, (AMP), adenosine-5'-diphosphate, (ADP), adenosine-5'-triphosphate, (ATP), has been studied in aqueous solution at T = 298.15 K and I = 0.15 mol L^-1 in NaCl (only for Al³⁺-ATP system at I = 0.1 mol L^-1). Formation constants and speciation models for the species formed are discussed on the basis of potentiometric results. The speciation models found for the three systems include ML and ML₂ species in all the cases, and for Al³⁺-ADP and ATP systems, MLH, MLOH and ML₂OH species as well. The formation constant value for ML species shows the trend, AMP < ADP < ATP. ¹H NMR spectroscopy was also employed for the study of Al³⁺-ATP system. The ¹H NMR results are in agreement with the speciation model obtained from analysis of potentiometric titration data, confirming the stabilities of the main species. Enthalpy change values were obtained by titration calorimetry; for the main Al³⁺-ATP species (at T = 298.15 K and I = 0.1 mol L^-1 in NaCl), they resulted always higher than zero, as typical for hard-hard interactions. The dependence of formation constants on ionic strength over the range I = 0.1 to 1 mol L^-1 in NaCl is also reported for Al³⁺-ATP system. The sequestering ability of the nucleotides under study towards Al³⁺ was also evaluated by the empirical parameter pL_0.5.

Quantitative determination and validation of octreotide acetate using 1 H-NMR spectroscopy with internal standard method

Quantitative nuclear magnetic resonance (qNMR) is a well-established technique in quantitative analysis. We presented a validated ¹ H-qNMR method for assay of octreotide acetate, a kind of cyclic octopeptide. Deuterium oxide was used to remove the undesired exchangeable peaks, which was referred to as proton exchange, in order to make the quantitative signals isolated in the crowded spectrum of the peptide and ensure precise quantitative analysis. Gemcitabine hydrochloride was chosen as the suitable internal standard. Experimental conditions, including relaxation delay time, the numbers of scans, and pulse angle, were optimized first. Then method validation was carried out in terms of selectivity, stability, linearity, precision, and robustness. The assay result was compared with that by means of high performance liquid chromatography, which is provided by Chinese Pharmacopoeia. The statistical F test, Student's t test, and nonparametric test at 95% confidence level indicate that there was no significant difference between these two methods. qNMR is a simple and accurate quantitative tool with no need for specific corresponding reference standards. It has the potential of the quantitative analysis of other peptide drugs and standardization of the corresponding reference standards.

pH detection in biological samples by 1D and 2D 1H-31P NMR

The chemical shifts of several important endogenous phosphorus compounds under different pH conditions were explored, including adenosine-5'-triphosphate, adenosine-5'-diphosphate, adenosine-5'-monophosphate, phosphorylcholine and phosphorylethanolamine. Their ³¹P NMR and ¹H NMR chemical shifts were all pH-sensitive in the similar pH range. Two dimensional (2D) ¹H-³¹P NMR spectra were found helpful to identify these endogenous phosphorus markers in biological samples from rather complicated NMR spectra. Herein, for the first time, a pH sensor based on 2D ¹H-³¹P NMR was established and applied to biological samples analysis with pH values determined in good agreement with those by potentiometric method. Apart from being simple, green, rapid and less sample-consuming, information concerning both the endogenous phosphorus markers and pH status could be attained in a single NMR run, which demonstrated the great potential of this method in rare sample analysis and even disease diagnosis.

Improved workflow for the efficient preparation of ready to use CMP-activated sialic acids

Natural and synthetically modified cytidine monophosphate activated sialic acids (CMP-Sias) are essential research assets in the field of glycobiology: among other applications, they can be used to probe glycans, detect sialylation defects at the cell surface or carry out detailed studies of sialyltransferase activities. However, these chemical tools are notoriously unstable because of hydrolytic decomposition, and are very time-consuming and costly to obtain. They are nigh impossible to store with satisfactory purity, and their preparation requires multiple laborious purification steps that usually lead to heavy product loss. Using in situ time-resolved ³¹P phosphorus nuclear magnetic resonance (³¹P NMR), we precisely established the kinetics of formation and degradation of a number of CMP-Sias including CMP-Neu5Ac, CMP-Neu5Gc, CMP-SiaNAl and CMP-SiaNAz in several experimental conditions. ³¹P NMR can be carried out in undeuterated solvents and is a sensitive and nondestructive technique that allows for direct in situ monitoring and optimization of chemo-enzymatic syntheses that involve phosphorus-containing species. Thus, we showed that CMP-sialic acid derivatives can be robustly obtained in high yields using the readily available Neisseria meningitidis CMP-sialic acid synthase. This integrated workflow takes less than an hour, and the freshly prepared CMP-Sias can be directly transferred to sialylation biological assays without any purification step.