Limits in Proton Nuclear Singlet-State Lifetimes Measured with para-Hydrogen-Induced Polarization

Vertical Excitation Energies and Lifetimes of the Two Lowest Singlet Excited States of Cytosine, 5-Aza-cytosine, and the Triazine Family: Quantum Mechanics-Molecular Mechanics Studies

A swarm of semi-classical quantum mechanics/molecular mechanics molecular-dynamics simulations where OM2/MNDO is combined with the Gromacs program for consideration of explicit water is performed, solving the time-dependent Schrödinger equation in each step of the trajectories together with the Tully's fewest switches algorithm. Within this stochastic treatment, time dependent probabilities of the three lowest electronic states are determined. The fact that nucleobases are quickly deactivated is confirmed in the cytosine case where our best lifetime estimation is τ₁=0.82 ps for the model with 100 water molecules with the SPCE force field and a time step of 0.1 fs. Lifetimes of the remaining molecules are visibly longer: 5-azacytosine, 2,4-diamino-1,3,5-triazine (DT), and 2,4,6-triamino-1,3,5-triazine (TT) molecules have an S₁ → S₀ de-excitation time of slightly above 10 ps. The lifetimes of the triazine family increases with the increasing number of exocyclic amino groups, that is, s-triazine < 2-amino-1,3,5-triazine < DT < TT. This can be explained by a higher mobility of the carbon-bonded hydrogen atoms in comparison with heavier amino groups since their movement is slowed down due to a substantially higher mass than hydrogen atoms, which can easier reach the out-of-plane positions required in the conical intersection structures. Moreover, bulkier NH₂ ligands suffer due to greater friction caused by the surrounding water environment. These mechanical aspects caused a change in the explored lifetime dependences in comparison with our previous gas-phase study.

Long-Lived States Provide Insights from NMR into the β-Cyclodextrin Drug Assemblies

In the last two decades, extending spin memory in NMR has been used for several purposes. Long-lived states (LLS) or singlet states are one of the first spin memory enhancement techniques used. LLS have the potential to extract structural information and intra- and intermolecular interactions of complex systems other than studying slow phenomenon. The motional regime of β-cyclodextrin (β-CD) drug inclusion complexes generally lies in the intermediate region, where ωτ_c ≈ 1, and the standard methods of studying these interactions, i.e., NOE and chemical shift monitoring, suffer from insufficient output information. The sensitivity of LLS toward the environmental changes is utilized here to gain insights into the drug assemblies formed by β-CD. One can use change in relaxation of LLS to study the structural changes during complexation. The examples of β-CD with the drugs indomethacin, paracetamol, gliclazide, and CI-933 (a precursor 4-methoxybenzamide) were studied. Indomethacin, paracetamol, and 4-methoxybenzamide show strong interaction through the para-substituted benzene ring, unlike gliclazide. Relaxation of LLS in β-CD-drug complexes is modeled using standard Redfield Relaxation Theory. Computational studies performed support the experimental observations. Docking and molecular dynamics simulation provided the explanation of the relaxation properties of these drug molecules.

Prediction of 1H Singlet Relaxation via Intermolecular Dipolar Couplings Using the Molecular Dynamics Method

Dissolution dynamic nuclear polarization has been applied in various fields, including chemistry, biology, and medical science. To expand the scope of these applications, the nuclear singlet state, which is decoherence-free against dipolar relaxation between spin pairs, has been studied experimentally, theoretically, and numerically. The singlet state composed of proton spins is used in several applications, such as enhanced polarization preservation, molecular tagging to probe slow dynamic processes, and detection of ligand-protein complexes. In this study, we predict the lifetimes of the nuclear spin states composed of proton spin pairs using the molecular dynamics method and quantum chemistry simulations. We consider intramolecular dipolar, intermolecular dipolar between solvent and solute, chemical shift anisotropy, and spin-rotation interactions. In particular, the relaxation rate of intermolecular dipolar interactions is calculated using the molecular dynamics method for various solvents. The calculated values and the experimental values are of the same order of magnitude. Our program would provide insight into the molecular design of several NMR applications and would be helpful in predicting the nuclear spin relaxation time of synthetic molecules in advance.

Weak nuclear spin singlet relaxation mechanisms revealed by experiment and computation

Nuclear spin singlet states are often found to allow long-lived storage of nuclear magnetization, which can form the basis of novel applications in spectroscopy, imaging, and in studies of dynamic...

Bimodal fluorescence/magnetic resonance molecular probes with extended spin lifetimes

Bimodal molecular probes combining nuclear magnetic resonance (NMR) and fluorescence have been widely studied in basic science, as well as clinical research. The investigation of spin phenomena holds promise to broaden the scope of available probes allowing deeper insights into physiological processes. Herein, a class of molecules with a bimodal character with respect to fluorescence and nuclear spin singlet states is introduced. Singlet states are NMR silent but can be probed indirectly. Symmetric, perdeuterated molecules, in which the singlet states can be populated by vanishingly small electron‐mediated couplings (below 1 Hz) are reported. The lifetimes of these states are an order of magnitude longer than the longitudinal relaxation times and up to four minutes at 7 T. Moreover, these molecules show either aggregation induced emission (AIE) or aggregation caused quenching (ACQ) with respect to their fluorescence. In the latter case, the existence of excited dimers, which are proposed to use in a switchable manner in combination with the quenching of nuclear spin singlet states, is observed

Exotic nuclear spin behavior in dendritic macromolecules

Dendrimers are a class of branched, highly symmetric macromolecules that have been shown to be useful for a vast number of different applications. Potential uses as fluorescence sensors, in catalysis and perhaps most importantly in medical applications as drug delivery systems or cytotoxica have been proposed. Herein we report on an exotic behaviour of the nuclear spins in a dendritic macromolecule in the presence of different paramagnetic ions. We show that the stability of the long lived nuclear singlet state, is affected by the presence of Cu(II), whereas other ions did not have any influence at all. This effect could not be observed in the case of a simple tripeptide, in which the nuclear singlet stability was influenced by all investigated paramagnetic ions, a potentially useful effect in the development of Cu(II) selective probes. By adding a fluorescent marker to our molecule we could show that the nuclear singlet multimer (NUSIMER) is taken up by living cells. Furthermore we were able to show that nuclear singlet state NMR can be used to investigate the NUSIMER in the presence of living cells, showing that an application in in vivo NMR can be feasible.

Nuclear singlet relaxation by chemical exchange

The population imbalance between nuclear singlet states and triplet states of strongly coupled spin-1/2 pairs, also known as nuclear singlet order, is well protected against several common relaxation mechanisms. We study the nuclear singlet relaxation of ¹³C pairs in aqueous solutions of 1,2-¹³C₂ squarate over a range of pH values. The ¹³C singlet order is accessed by introducing ¹⁸O nuclei in order to break the chemical equivalence. The squarate dianion is in chemical equilibrium with hydrogen-squarate (SqH^-) and squaric acid (SqH₂) characterized by the dissociation constants pK₁ = 1.5 and pK₂ = 3.4. Surprisingly, we observe a striking increase in the singlet decay time constants T_S when the pH of the solution exceeds ∼10, which is far above the acid-base equilibrium points. We derive general rate expressions for chemical-exchange-induced nuclear singlet relaxation and provide a qualitative explanation of the T_S behavior of the squarate dianion. We identify a kinetic contribution to the singlet relaxation rate constant, which explicitly depends on kinetic rate constants. Qualitative agreement is achieved between the theory and the experimental data. This study shows that infrequent chemical events may have a strong effect on the relaxation of nuclear singlet order.

31P nuclear spin singlet lifetimes in a system with switchable magnetic inequivalence: experiment and simulation

³¹P NMR spectroscopy and the study of nuclear spin singlet relaxation phenomena are of interest in particular due to the importance of phosphorus-containing compounds in physiology. We report the generation and measurement of relaxation of ³¹P singlet order in a chemically equivalent but magnetically inequivalent case. Nuclear magnetic resonance singlet state lifetimes of ³¹P pairs have heretofore not been reported. Couplings between ¹H and ³¹P nuclei lead to magnetic inequivalence and serve as a mechanism of singlet state population conversion within this molecule. We show that in this molecule singlet relaxation occurs at a rate significantly faster than spin-lattice relaxation, and that anticorrelated chemical shift anisotropy can account for this observation. Calculations of this mechanism, with the help of molecular dynamics simulations and ab initio calculations, provide excellent agreement with the experimental findings. This study could provide guidance for the study of ³¹P singlets within other compounds, including biomolecules.

Nuclear Spin Relaxation of Longitudinal and Singlet Order in Liquid-CO2 Solutions

Hyperpolarization techniques can enormously enhance the NMR signal thus allowing the exploitation of hyperpolarized substrates for in-vivo MRI applications. The short lifetime of hyperpolarized spin order poses significant limitations in such applications. Spin order storage can be prolonged through the use of long-lived spin states. Additionally, the storage of spin polarization-either in the form of longitudinal or singlet order-can be prolonged in low viscosity solutions. Here, we report the use of low viscosity liquid-CO₂ solutions to store nuclear spin polarization in the form of longitudinal and singlet order for extended periods. Our results demonstrate that this storage time can be considerably sustained in liquid-CO₂ solutions in comparison to other low viscosity solvents, opening up the possibility of new, exciting storage experiments in the future.

Single-scan measurements of nuclear spin singlet order decay rates

Measurements of singlet spin order decay rates are time consuming due to the long-lived nature of this form of order and the typical pseudo-2D mode of acquisition. Additionally, this acquisition modality is not ideal for experiments run on hyperpolarized order because of the single-shot nature of hyperpolarization techniques. We present a methodology based on spatial encoding that not only significantly reduces the duration of these experiments but also confers compatibility using spin hyperpolarization techniques. The method condenses in a single shot the variable delay array used to measure decay rates in conventional pseudo-2D relaxation experiments. This results in a substantial time saving factor and, more importantly, makes the experiment compatible with hyperpolarization techniques since only a single hyperpolarized sample is required. Furthermore, the presented method, besides offering savings on time and costs, avoids reproducibility concerns associated with repetition in the hyperpolarization procedure. The method accelerates the measurement and characterization of singlet order decay times, and, when coupled with hyperpolarization techniques, can facilitate the quest for systems with very long decay times.

Design of Nuclear Magnetic Resonance Molecular Probes for Hyperpolarized Bioimaging

Nuclear hyperpolarization has emerged as a method to dramatically enhance the sensitivity of NMR spectroscopy. By application of this powerful tool, small molecules with stable isotopes have been used for highly sensitive biomedical molecular imaging. The recent development of molecular probes for hyperpolarized in vivo analysis has demonstrated the ability of this technique to provide unique metabolic and physiological information. This review presents a brief introduction of hyperpolarization technology, approaches to the rational design of molecular probes for hyperpolarized analysis, and examples of molecules that have met with success in vitro or in vivo.

Radiofrequency encoded Only Parahydrogen SpectroscopY

A new pulse sequence aimed to filter out NMR signals coming from thermally polarized protons in PHIP experiments based on the OPSY pulse sequence (Only Parahydrogen SpectroscopY) is presented. In analogy to OPSY, which removes thermal polarization by using a pair of magnetic field gradient pulses with an intensity ratio 1:2 and equal duration, the same effect can be achieved using inhomogeneous radiofrequency fields. The spatial dependence of the radiofrequency field is used to control the Hamiltonian, which results in an effective suppression of thermal contributions in the NMR signal, while PHIP originated signals remain unmodified. A theoretical model for the radiofrequency encoded only parahydrogen (REOPSY) sequence is presented along with an experimental implementation on a birdcage coil in a 7 T magnetic field. The control level achieved by this strategy allows the inclusion of a long train of refocusing pulses. Therefore, the new sequence can be combined with the parahydrogen discriminated PHIP (PhD-PHIP) pulse sequence as a detection block to improve sensitivity and resolution in a single-scan experiment. Experiments with REOPSY and REOPSY+PhD-PHIP are presented in thermally and hyperpolarized samples.

Parahydrogen-Induced Polarization of Diethyl Ether Anesthetic

The growing interest in magnetic resonance imaging (MRI) for assessing regional lung function relies on the use of nuclear spin hyperpolarized gas as a contrast agent. The long gas-phase lifetimes of hyperpolarized 129 Xe make this inhalable contrast agent acceptable for clinical research today despite limitations such as high cost, low throughput of production and challenges of 129 Xe imaging on clinical MRI scanners, which are normally equipped with proton detection only. We report on low-cost and high-throughput preparation of proton-hyperpolarized diethyl ether, which can be potentially employed for pulmonary imaging with a nontoxic, simple, and sensitive overall strategy using proton detection commonly available on all clinical MRI scanners. Diethyl ether is hyperpolarized by pairwise parahydrogen addition to vinyl ethyl ether and characterized by 1 H NMR spectroscopy. Proton polarization levels exceeding 8 % are achieved at near complete chemical conversion within seconds, causing the activation of radio amplification by stimulated emission radiation (RASER) throughout detection. Although gas-phase T1 relaxation of hyperpolarized diethyl ether (at partial pressure of 0.5 bar) is very efficient, with T1 of ca. 1.2 second, we demonstrate that, at low magnetic fields, the use of long-lived singlet states created via pairwise parahydrogen addition extends the relaxation decay by approximately threefold, paving the way to bioimaging applications and beyond.

Algorithmic cooling of nuclear spins using long-lived singlet order

Algorithmic cooling methods manipulate an open quantum system in order to lower its temperature below that of the environment. We achieve significant cooling of an ensemble of nuclear spin-pair systems by exploiting the long-lived nuclear singlet state, which is an antisymmetric quantum superposition of the "up" and "down" Zeeman states. The effect is demonstrated by nuclear magnetic resonance experiments on a molecular system containing a coupled pair of near-equivalent ¹³C nuclei. The populations of the system are subjected to a repeating sequence of cyclic permutations separated by relaxation intervals. The long-lived nuclear singlet order is pumped well beyond the unitary limit. The pumped singlet order is converted into nuclear magnetization which is enhanced by 21% relative to its thermal equilibrium value.

A versatile synthetic route to the preparation of 15 N heterocycles

A robust medium-scale (approximately 3 g) synthetic method for 15 N labeling of pyridine (15 N-Py) is reported based on the Zincke reaction. 15 N enrichment in excess of 81% was achieved with approximately 33% yield. 15 N-Py serves as a standard substrate in a wide range of studies employing a hyperpolarization technique for efficient polarization transfer from parahydrogen to heteronuclei; this technique, called SABRE (signal amplification by reversible exchange), employs a simultaneous chemical exchange of parahydrogen and a to-be-hyperpolarized substrate (e.g., pyridine) on metal centers. In studies aimed at the development of hyperpolarized contrast agents for in vivo molecular imaging, pyridine is often employed either as a model substrate (for hyperpolarization technique development, quality assurance, and phantom imaging studies) or as a co-substrate to facilitate more efficient hyperpolarization of a wide range of emerging contrast agents (e.g., nicotinamide). Here, the produced 15 N-Py was used for the feasibility study of spontaneous 15 N hyperpolarization at high magnetic (HF) fields (7 T and 9.4 T) of an NMR spectrometer and an MRI scanner. SABRE hyperpolarization enabled acquisition of 2D MRI imaging of catalyst-bound 15 N-pyridine with 75 × 75 mm2 field of view (FOV), 32 × 32 matrix size, demonstrating the feasibility of 15 N HF-SABRE molecular imaging with 2.4 × 2.4 mm2 spatial resolution.

Long live the singlet state!

The field of long-lived states in NMR is reviewed. The relationship of long-lived-state phenomena to those associated with spin isomerism is discussed. A brief overview is given of key developments in the field of long-lived states, including chemical symmetry-switching, the role of magnetic equivalence and magnetic inequivalence, long-lived coherences, hyperpolarized NMR involving long-lived states, quantum-rotor-induced polarization, and parahydrogen-induced hyperpolarization. Current application areas of long-lived states are reviewed, and a peer into the crystal ball reveals future developments in the field.

Clinical-Scale Batch-Mode Production of Hyperpolarized Propane Gas for MRI

NMR spectroscopy and imaging (MRI) are two of the most important methods to study structure, function, and dynamics from atom to organism scale. NMR approaches often suffer from an insufficient sensitivity, which, however, can be transiently boosted using hyperpolarization techniques. One of these techniques is parahydrogen-induced polarization, which has been used to produce catalyst-free hyperpolarized propane gas with proton polarization that is 3 orders of magnitude greater than equilibrium thermal polarization at a 1.5 T field of a clinical MRI scanner. Here we show that more than 0.3 L of hyperpolarized propane gas can be produced in 2 s. This production rate is more than an order of magnitude greater than that demonstrated previously, and the reported production rate is comparable to that employed for in-human MRI using HP noble gas (e.g., ¹²⁹Xe) produced via a spin exchange optical pumping (SEOP) hyperpolarization technique. We show that high polarization values can be retained despite the significant increase in the production rate of hyperpolarized propane. The enhanced signals of produced hyperpolarized propane gas were revealed by stopped-flow MRI visualization at 4.7 T. Achieving this high production rate enables the future use of this compound (already approved for unlimited use in foods by the corresponding regulating agencies, e.g., FDA in the USA, and more broadly as an E944 food additive) as a new inhalable contrast agent for diagnostic detection via MRI.

Nuclear singlet relaxation by scalar relaxation of the second kind in the slow-fluctuation regime

The singlet state of nuclear spin-1/2 pairs is protected against many common relaxation mechanisms. Singlet order, which is defined as the population difference between the nuclear singlet and triplet states, usually decays more slowly than the nuclear magnetization. Nevertheless, some decay mechanisms for nuclear singlet order persist. One such mechanism is called scalar relaxation of the second kind (SR2K) and involves the relaxation of additional nuclei ("third spins") which have scalar couplings to the spin-1/2 pair. This mechanism requires a difference between the couplings of at least one third spin with the two members of the spin-1/2 pair, and depends on the longitudinal relaxation time of the third spin. The SR2K mechanism of nuclear singlet relaxation has previously been examined in the case where the relaxation rate of the additional spins is on the time scale of the nuclear Larmor frequency. In this paper, we consider a different regime, in which the longitudinal relaxation of the third spins is on a similar time scale to the J-coupling between the members of the spin pair. This regime is often encountered when the spin-1/2 pair has scalar couplings to nearby deuterium nuclei. We show that the SR2K mechanism may be suppressed in this regime by applying a radiofrequency field which is resonant either with the members of the spin pair, or with the third spins. These phenomena are analyzed theoretically and by numerical simulations, and demonstrated experimentally on a diester of [¹³C₂, ²H₂]-labeled fumarate in solution.

Nuclear singlet multimers (NUSIMERs) with long-lived singlet states

Magnetic resonance (NMR) is a powerful tool in chemical analysis, structure determination and in medical diagnostics. Developing novel biological sensors for this field holds promise to better investigate protein structures or target diseases more efficiently. Herein, we explore nuclear spin singlet states in dendritic macromolecules as a platform molecule to develop stimuli responsive probes. We have developed a nuclear singlet multimer (NUSIMER) based on a generation 5 poly(amidoamine) dendrimer (PAMAM) which contains on average about 90 accessible nuclear spin singlet states with lifetimes up to 10-fold longer than the T 1 relaxation times (up to 10 seconds T s vs. T 1 < 0.5 seconds) in a single molecule. We demonstrate little influence on the singlet lifetime in phosphate buffer (H2O) and a high viscosity gel environment in the presence of paramagnetic oxygen. Additionally, we demonstrate an increase in singlet lifetime upon the release of a protective chemical moiety from the NUSIMER following a stimulus, whereby no change in longitudinal relaxation time is observed. The robustness and change in singlet lifetime of the NUSIMER holds promise for the development of a novel type of biosensors.

Experimental evidence for the role of paramagnetic oxygen concentration on the decay of long-lived nuclear spin order

The sensitivity of longitudinal magnetization and singlet order to relaxation from dissolved paramagnetic oxygen sources in solution is investigated experimentally.

Singlet excitation in the intermediate magnetic equivalence regime and field-dependent study of singlet–triplet leakage

Measuring field-dependence of singlet lifetimes in the intermediate magnetic equivalence regime.

Parahydrogen-Based Hyperpolarization for Biomedicine

Magnetic resonance (MR) is one of the most versatile and useful physical effects used for human imaging, chemical analysis, and the elucidation of molecular structures. However, its full potential is rarely used, because only a small fraction of the nuclear spin ensemble is polarized, that is, aligned with the applied static magnetic field. Hyperpolarization methods seek other means to increase the polarization and thus the MR signal. A unique source of pure spin order is the entangled singlet spin state of dihydrogen, parahydrogen (pH2 ), which is inherently stable and long-lived. When brought into contact with another molecule, this "spin order on demand" allows the MR signal to be enhanced by several orders of magnitude. Considerable progress has been made in the past decade in the area of pH2 -based hyperpolarization techniques for biomedical applications. It is the goal of this Review to provide a selective overview of these developments, covering the areas of spin physics, catalysis, instrumentation, preparation of the contrast agents, and applications.

Nuclear spin singlet states as magnetic on/off probes in self-assembling systems

Nuclear singlet states in thermo-responsive peptides are introduced as magnetic on/off switches.

Hyperpolarized fumarate via parahydrogen

We produce hyperpolarized [1-¹³C]fumarate in the proton nuclear spin singlet state by pairwise trans-addition of parahydrogen to a molecular precursor using a ruthenium-based catalyst in water.

Effect of convection and B1 inhomogeneity on singlet relaxation experiments

Nuclear spin singlet lifetimes can often exceed the T₁ length scales by a large factor. This property makes them suitable for polarization storage. The measurement of such long lifetimes itself can become challenging due to the influence of even very weak relaxation mechanisms. Here we show that a judicious choice of the singlet-to-triplet conversion method is highly important in order to achieve reliable singlet relaxation measurements. In particular, we identify thermal convection, in connection with B₁ field gradients, asa significant apparent decay mechanism, which limits the ability to measure the true singlet state lifetimes. Highly B₁-compensated broadband singlet excitation/detection sequences are shown to minimize the influence of macroscopic molecular motion and B₁ inhomogeneity.

Extending the Lifetime of Hyperpolarized Propane Gas through Reversible Dissolution

Hyperpolarized (HP) propane produced by the parahydrogen-induced polarization (PHIP) technique has been recently introduced as a promising contrast agent for functional lung magnetic resonance (MR) imaging. However, its short lifetime due to a spin-lattice relaxation time T₁ of less than 1 s in the gas phase is a significant translational challenge for its potential biomedical applications. The previously demonstrated approach for extending the lifetime of the HP propane state through long-lived spin states allows the HP propane lifetime to be increased by a factor of ∼3. Here, we demonstrate that a remarkable increase in the propane hyperpolarization decay time at high magnetic field (7.1 T) can be achieved by its dissolution in deuterated organic solvents (acetone-d₆ or methanol-d₄). The approximate values of the HP decay time for propane dissolved in acetone-d₆ are 35.1 and 28.6 s for the CH₂ group and the CH₃ group, respectively (similar values were obtained for propane dissolved in methanol-d₄), which are ∼50 times larger than the gaseous propane T₁ value. Furthermore, we show that it is possible to retrieve HP propane from solution to the gas phase with the preservation of hyperpolarization.

Singlet order conversion and parahydrogen-induced hyperpolarization of 13C nuclei in near-equivalent spin systems

We have demonstrated two radiofrequency pulse methods which convert the nuclear singlet order of proton spin pairs into the magnetisation of nearby ¹³C nuclei. These irradiation schemes work well in the near-equivalence regime of the three-spin system, which applies when the difference in the two ¹H-¹³C couplings is much smaller than the ¹H-¹H coupling. We use pulse sequences to generate thermally polarized singlet states in a reproducible manner, and study the singlet-to-magnetisation transfer step. Preliminary results demonstrate a parahydrogen-enhanced ¹³C polarization level of at least 9%, providing a signal enhancement factor of more than 9000, using 50% enriched parahydrogen.

Prediction of low-field nuclear singlet lifetimes with molecular dynamics and quantum-chemical property surface

Molecular dynamics and quantum chemistry methods are implemented to quantify nuclear spin-1/2 pair singlet-state relaxation rates. Illustrated is the relevant spin-internal-motion mechanism (SIM).

Versatile magnetic resonance singlet tags compatible with biological conditions

The long lifetime of nuclear singlet states holds promise for the development of molecular tracers to study motional processes in proteins with increased precision or to act as imaging contrast agents.

NMR SLIC Sensing of Hydrogenation Reactions Using Parahydrogen in Low Magnetic Fields

Parahydrogen-induced polarization (PHIP) is an NMR hyperpolarization technique that increases nuclear spin polarization by orders of magnitude, and it is particularly well-suited to study hydrogenation reactions. However, the use of high-field NMR spectroscopy is not always possible, especially in the context of potential industrial-scale reactor applications. On the other hand, the direct low-field NMR detection of reaction products with enhanced nuclear spin polarization is challenging due to near complete signal cancellation from nascent parahydrogen protons. We show that hydrogenation products prepared by PHIP can be irradiated with weak (on the order of spin-spin couplings of a few hertz) alternating magnetic field (called Spin-Lock Induced Crossing or SLIC) and consequently efficiently detected at low magnetic field (e.g., 0.05 T used here) using examples of several types of organic molecules containing a vinyl moiety. The detected hyperpolarized signals from several reaction products at tens of millimolar concentrations were enhanced by 10000-fold, producing NMR signals an order of magnitude greater than the background signal from protonated solvents.