13 research outputs found
Configuration and Performance of a Mobile 129Xe Polarizer
A stand-alone, self-contained and transportable system for the polarization of (129)Xe by spin exchange optical pumping with Rb is described. This mobile polarizer may be operated in batch or continuous flow modes with medium amounts of hyperpolarized (129)Xe for spectroscopic or small animal applications. A key element is an online nuclear magnetic resonance module which facilitates continuous monitoring of polarization generation in the pumping cell as well as the calculation of the absolute (129)Xe polarization. The performance of the polarizer with respect to the crucial parameters temperature, xenon and nitrogen partial pressures, and the total gas flow is discussed. In batch mode the highest (129)Xe polarization of P(Xe) = 40 % was achieved using 0.1 mbar xenon partial pressure. For a xenon flow of 6.5 and 26 mln/min, P(Xe) = 25 % and P(Xe) = 13 % were reached, respectively. The mobile polarizer may be a practical and efficient means to make the applicability of hyperpolarized (129)Xe more widespread
Recommended from our members
Production of highly concentrated and hyperpolarized metabolites within seconds in high and low magnetic fields
Hyperpolarized metabolites are very attractive contrast agents for in vivo magnetic resonance imaging studies enabling early diagnosis of cancer, for example. Real-time production of concentrated solutions of metabolites is a desired goal that will enable new applications such as the continuous investigation of metabolic changes. To this end, we are introducing two NMR experiments that allow us to deliver high levels of polarization at high concentrations (50 mM) of an acetate precursor (55% 13C polarization) and acetate (17% 13C polarization) utilizing 83% para-state enriched hydrogen within seconds at high magnetic field (7 T). Furthermore, we have translated these experiments to a portable low-field spectrometer with a permanent magnet operating at 1 T. The presented developments pave the way for a rapid and affordable production of hyperpolarized metabolites that can be implemented in e.g. metabolomics labs and for medical diagnosis
Influence of spin 1/2 hetero-nuclei on spin relaxation and polarization transfer among strongly coupled protons
Effects of spin-spin interactions on the nuclear magnetic relaxation
dispersion (NMRD) of protons were studied in a situation where spin ½ hetero-
nuclei are present in the molecule. As in earlier works [K. L. Ivanov, A. V.
Yurkovskaya, and H.-M. Vieth, J. Chem. Phys.129, 234513
(2008)10.1063/1.3040272;S. E. Korchak, K. L. Ivanov, A. V. Yurkovskaya, and
H.-M. Vieth, J. Chem. Phys.133, 194502 (2010)10.1063/1.3495988], spin-spin
interactions have a pronounced effect on the relaxivity tending to equalize
the longitudinal relaxation times once the spins become strongly coupled at a
sufficiently low magnetic field. In addition, we have found influence of 19F
nuclei on the proton NMRD, although in the whole field range, studied protons
and fluorine spins were only weakly coupled. In particular, pronounced
features in the proton NMRD were found; but each feature was predominantly
observed only for particular spin states of the hetero-nuclei. The features
are explained theoretically; it is shown that hetero-nuclei can affect the
proton NMRD even in the limit of weak coupling when (i) protons are coupled
strongly and (ii) have spin-spin interactions of different strengths with the
hetero-nuclei. We also show that by choosing the proper magnetic field
strength, one can selectively transfer proton spin magnetization between
spectral components of choice
Оценка влияния динамики инвестиций на рост валового регионального продукта в регионах Севера и Арктической зоны Российской Федерации
This article presents results of a study conducted using mathematical and statistical modelling of regional economic specifics of the Russian Northern and Arctic regions in comparison to the national economic trend. The research continues a series of works on modelling the dynamics of GRP production aimed at improving the measurement quality of the interaction between the main production factors and assessing the specificity of their influence on the economic growth in the regions under review. The article considers the impact of investments on the GRP production in the Northern and Arctic regions is argued which is determined by a new approach to the management of these territories through the formation of support zones of development based on the implementation of interconnected different scale investment projects. Mathematical and statistical modelling of GRP production in the Northern and Arctic regions and the Russian Federation as a whole was carried out using the multiplicative production function and the CES production function. For the eight regions of the North [Karelia, Komi Republic, Arkhangelsk region, Nenets autonomous area, Yamal-Nenets autonomous area, Republic of Tuva, Republic of Sakha (Yakutia), Kamchatka territory, and Magadan region] and for the Russian Federation as a whole, were matched variants of a model, linking GRP with investments. For four constituent entities (Murmansk region, Sakhalin region, Khanty-Mansi autonomous area - Yugra, and Chukotka autonomous area), it was not possible to select such variants of the model. In this regard the authors point out that there is a need for further improvement of mathematical and statistical modelling of the dependence of economic development of the regions on the dynamics of investment activity.Данная публикация отражает результаты исследования с использованием математико-статистического моделирования региональных особенностей экономического развития Севера и Арктической зоны Российской Федерации в сравнении с общероссийским экономическим трендом. Исследование продолжает серию работ авторов по моделированию динамики производства на основе показателя валового регионального продукта (ВРП) с целью повышения качества измерения взаимодействия основных факторов производства, адекватной оценки специфики их влияния на экономический рост в рассматриваемых регионах страны. Аргументирована актуальность анализа влияния инвестиций на производство ВРП, определяемая новым подходом к управлению северными и арктическими территориями России посредством формирования опорных зон развития на основе реализации взаимосвязанных инвестиционных проектов разного масштаба. Проведено математико-статистическое моделирование факторов динамики производства ВРП в регионах Севера, Арктики и Российской Федерации в целом с использованием мультипликативной производственной функции и производственной функции CES. Для восьми регионов Севера [Республика Карелия, Республика Коми, Архангельская область, Ненецкий автономный округ, Ямало-Ненецкий автономный округ, Республика Тыва, Республика Саха (Якутия), Камчатский край, Магаданская область] и Российской Федерации в целом были подобраны варианты модели, отображающие взаимосвязь роста ВРП и динамики инвестиций. Для четырех субъектов Российской Федерации - Мурманской и Сахалинской областей, Ханты-Мансийского автономного округа - Югры, Чукотского автономного округа - адекватные варианты моделей подобрать не удалось. В этой связи авторами обоснована необходимость дальнейшего совершенствования математико-статистического моделирования зависимости экономического развития регионов от динамики инвестиционной деятельности
Hyperpolarisation in gekoppelten Vielspinsystemen
Introduction 1 1\. Hyperpolarization of nuclear spins 4 1.1 Chemically induced
dynamic nuclear polarization 4 1.2 Dynamic nuclear polarization 11 1.3
Parahydrogen induced polarization 14 1.4 Hyperpolarization transfer among
coupled spins 18 1.5 Nuclear magnetic relaxation dispersion in scalar coupled
systems 25 2\. Experimental setup 28 2.1 Spectrometer control unit: DAMARIS 28
2.2 Field-cycling part 33 General description 35 Auxiliary magnetic system 36
Mechanical shuttling system 38 Light irradiation 39 Probehead 39 Influence of
magnetic susceptibility 40 Reduction of eddy currents 43 Mathematical
correction of FID 44 Summary 45 2.3 High field time-resolved CIDNP setup 46
2.4 DNP setup 48 3\. Polarization transfer in scalar coupled multi spin
systems 51 3.1 Photo-CIDNP transfer in AMP, N-acetylhistidine and
cycloundecanone 52 Experimental part 52 Photo-CIDNP transfer in AMP 53 Photo-
CIDNP transfer in N-acetylhistidine 56 Long-range polarization transfer in
cycloundecanone 58 Summary and conclusions 60 3.2 Relaxation experiments with
scalar coupled spin systems 61 Experimental part 61 Coherent polarization
transfer during relaxation in two-spin system 63 Relaxation dispersion of two-
spin 1/2 system 66 Relaxation dispersion of three-spin 1/2 system 68
Relaxation dispersion of two-proton and two-fluorine system 71 Relaxation
dispersion of N-acetylhistidine (five coupled spins 1/2) 74 Summary and
conclusions 80 4\. Parahydrogen induced polarization in the hydrogenation
reaction of styrene 81 Experimental part 82 Results and discussion 85 Summary
and conclusions 90 5\. Dynamic nuclear polarization 93 Experimental part 94
Theoretical description of the pulsed DNP experiment 97 DNP spectra 102 DNP
effect as resonance phenomenon 106 Exploiting coherent spin motion for
optimizing DNP efficiency 107 Summary and conclusions 112 6\. Application of
CIDNP to biomolecules (amino acids and peptides) 115 Experimental part 116 6.1
Methionine, N-acetylmethionine and 3-(methylthio)propylamine 117 CIDNP spectra
119 CIDNP field dependence 123 CIDNP kinetics 129 6.2 Met-Gly, Gly-Met
dipeptides 141 Transient radicals in the photo-oxidation of Gly-Met 141
Transient radicals in the photo-oxidation of Met-Gly 145 Summary and
conclusions 154 7\. Conclusions and outlook 157 Curriculum Vitae 161
Publications 162 Acknowledgements 166 Bibliography 167Nuclear magnetic resonance experiments on multi-spin systems using variation
of the external magnetic field were performed with high spectral resolution.
The main focus was investigating the behaviour of hyperpolarized nuclear spin
states in the coupled spin systems in its dependence on the strength of the
magnetic field in order to discriminate field dependent effects from others
and to optimize the hyperpolarization (HP) yield. The experimental method of
the field dependent measurements employs fast transfer of the spins between
two field positions: the desired field at which the system is studied and the
constant detection field. Extensive improvements of the field-cycling setup
were introduced making the field variation faster and enhancing the spectral
resolution. For this task, a novel material with compensated magnetic
susceptibility was developed and a probehead with reduced metallic parts was
constructed in order to suppress eddy currents and their magnetic field and,
thus, preserve the detection field from disturbances. A new control unit of
the experimental setup was devised allowing a better timing control of the
experiments. Thus, for the first time variable field measurements were
obtained with high spectral resolution that allow distinguishing signals of
individual nuclei in the molecules at a controllable time profile of field
variation in a range between 100 T and 7 T. All experiments were done on
liquid state solutions, thus, the main interaction between the spins was
scalar spin-spin coupling, which is not averaged in low viscosity liquids in
contrast to dipolar spin-spin interaction. It was demonstrated that scalar
coupling despite its small value has a high impact on the hyperpolarization
experiments. At sufficiently low magnetic field the spins reach the regime of
strong coupling where all hyperpolarization measurements as well as relaxation
experiments are affected by the scalar interaction In the nuclear magnetic
relaxation dispersion (NMRD), i.e. in the dependence of the relaxation rate on
the field strength, strong coupling in multi-spin systems was shown to lead to
several distinct features that have to be taken into account in a quantitative
analysis. For instance, strongly coupled spins tend to relax with a common
rate even when at high field their relaxation is distinctly different. Also,
pronounced peaks and dips were observed in the NMRD curves of systems with
more than two nuclear spins 1/2 that were attributed to spin level anti-
crossings. In addition, a site specific influence of paramagnetic additives in
the solution on the NMRD of the solute was analysed. It was possible to
separate this paramagnetic effect from the strong coupling effect. Several
methods of hyperpolarization were explored: Chemically Induced Dynamic Nuclear
Polarization (CIDNP), Parahydrogen Induced Polarization (PHIP), and Dynamic
Nuclear Polarization (DNP). Experiments were performed with the aim to
manipulate hyperpolarization by control of spin coherences and to exploit the
encoded information for analytical purposes. In all cases it was found that
hyperpolarization is distributed among coupled spins when they are in the
strong coupling regime. It was proven that the transfer has a coherent nature
that manifests itself as quantum beats in the NMR signal amplitude upon
changing the spin evolution time at the polarization field and subsequent non-
adiabatic field variation to the high detection field. Such oscillations were
observed both in CIDNP experiments and in relaxation measurements. Criteria
for the polarization manipulation at variable field were derived and
experimentally checked. The DNP experiments were conducted with driving the
electronic spins off equilibrium by applying a train of radio-frequency pulses
in comparison with cw irradiation. The electron pumping was done at low field
where the coupling factor is close to its theoretical maximum. Length,
amplitude and repetition time of the pulses were optimized to achieve maximal
DNP while keeping the average pumping power constant. For analyzing the data
an adequate theoretical approach to pulsed DNP was developed. Optimal
conditions for getting maximum signal enhancement at minimal microwave power
and thus avoiding sample heating were studied on solute and solvent molecules.
Strong hyperpolarization was obtained in the hydrogenation reaction of styrene
with the singlet spin isomer of hydrogen gas (parahydrogen) and studied at
variable field. While for the protons originating from parahydrogen the high
polarization was observed at all field amplitudes, in low field also
polarization of the phenyl ring protons of the product was detected as a
result of polarization transfer among strongly coupled spins. The highest
transfer efficiency was seen at the field of spin level anti-crossing. The
theoretical simulations reproduce the shape of the PHIP spectra in excellent
agreement with the experimental data. CIDNP techniques were applied to amino
acids, nucleotides and cycloketones. The most extensive investigation was
performed on radical intermediates of the essential amino acid methionine and
of methionine containing peptides. Their reactions with photo-exited dye
molecules were investigated by combining field dependent and time-resolved
CIDNP that allowed revealing the radical structure and the reaction kinetics.
It was found that in aqueous solution the pH influences the branching of the
radical formation not only through the protonation state of the precursor but
also through the reaction intermediates. Exploiting these results formation of
four methionine radicals was observed. Simple methionine containing dipeptides
chosen to model the behaviour of methionine residues in proteins showed a
behaviour similar to that of the free amino acid although they have several
additional peculiarities. It was shown that the effects of neighbouring
groups, of position at N vs C terminus, and of degenerate electron transfer
have to be taken into account when studying proteins by CIDNP. The kinetic
constants of the radical reaction as well as the nuclear relaxation times at
the radical stage were determined from the CIDNP kinetics. In summary, it was
shown that field variation can be used for optimizing the generation of
hyperpolarization, for preserving it from relaxation and for transferring it
to target nuclei of interest. In addition, the hyperpolarization methods in
combination with high spectral resolution were demonstrated to be versatile
tools that allow extracting structural and dynamic information on diamagnetic
molecules and on short-lived radical intermediates.Kernspinresonanz-Experimente an skalar gekoppelten Vielspinsystemen wurden
erstmals bei Variation des äußeren Magnetfelds in Kombination mit hoher
spektraler Auflösung durchgeführt. Schwerpunkt dabei war die Untersuchung von
hyperpolarisierten Kernspin-zuständen in den gekoppelten Systemen als Funktion
der Feldstärke, um feldabhängige Effekte von feldunabhängigen zu unterscheiden
und den Polarisationsgrad zu optimieren. Die experimentelle Realisierung der
Feldvariation basiert auf schnellem mechanischen Transfer der Spins zwischen
Positionen unterschiedlicher Feldstärke: für die gewünschte Spinevolution im
variablem Feld bzw. den optimierten Nachweis im konstanten Hochfeld.
Umfangreiche apparative Verbesserungen der Feldzyklisierung werden
beschrieben, die insbesondere zu einer erheblichen Verbesserung der Auflösung
und zur Erhöhung der Transfer-Geschwindigkeit bei genauerer Kontrolle des
zeitlichen Ablaufs geführt haben. Zu diesem Zweck wurde unter anderem ein
neuartiges Kompositmaterial mit verschwindender magnetischer Suszeptibilität
entwickelt und für einen NMR-Probenkopf verwendet, dessen Metallteile zudem
reduziert waren, um Wirbelstrom-Effekte beim Feldschalten zu unterdrücken.
Außerdem wurde die Rechnersteuerung des Spektrometers komplett erneuert.
Dadurch gelang es die Signale der unterschiedlichen Spinpositionen im Molekül
bei zeitlich genau gesteuerter Feldvariation im Bereich zwischen 100 T und 7T
mit einer Auflösung von 10-9 nachzuweisen. Alle Untersuchungen fanden an
flüssigen Proben statt, wo die Wechselwirkungung unter den Spins durch skalare
Kopplung gegeben ist, die in niederviskosen Flüssigkeiten im Gegensatz zu
dipolarer Kopplung nicht ausgemittelt ist. Die Messungen zeigen, dass die
skalare Kopplung trotz ihrer geringen Stärke große Auswirkungen auf die
Evolution von Spinpolarisation hat, insbesondere wenn die Spinzustände
Populationsverteilungen fernab vom thermischen Gleichgewicht aufweisen. Bei
ausreichend kleiner externer Feldstärke wird der sogenannte Fall starker
Kopplung erreicht, bei dem die Spin-Spin-Kopplung dominant wird und alle
Hyperpolarisations- und Relaxationsexperimente beeinflusst. So führt bei der
Magnetfeldabhängigkeit der Spin-Gitter-Relaxation, der sogenannten
Relaxationsdispersion (NMRD) die skalare Kopplung dazu, dass in
Vielspinsystemen bei starker Kopplung sich die Relaxationsraten einander
annähern, selbst wenn im Fall schwacher Kopplung die Raten der einzelnen Spins
deutlich verschieden sind. Darüber hinaus wurden scharfe Strukturen in den
Dispersionskurven nachgewiesen, die bei Feldern in der Nähe von
Niveaukreuzungen (level anti-crossings) auftreten. Der Effekt der starken
Spinkopplung konnte von dem feldabhängigen Einfluss paramagnetischer
Metallionen auf die Relaxationsdispersion diskriminiert werden. In einer
weiteren Gruppe von Experimenten wurden verschiedene Methoden zur Erzeugung
von Hyperpolarisation untersucht: Chemisch induzierte dynamische
Kernspinpolarisation (CIDNP), Parawasserstoff-induzierte Polarisation (PHIP)
und dynamische Kernspinpolarisation vom Overhauser-Typ (DNP). Diese
Experimente hatten das Ziel die Hyperpolarisation durch Steuerung von
Spinkohärenzen zu manipulieren sowie die im Polarisationsprozess
verschlüsselte Information für analytische Zwecke zu nutzen. In diesem
Zusammenhang ließ sich nachweisen, dass sich die Hyperpolarisation auf alle
gekoppelten Spins verteilt, wenn der Fall starker Kopplung gegeben ist. Die
Untersuchungen ergaben, dass dieser Verteilungsprozess von kohärenter Natur
ist und sich in Oszillationen der NMR-Signalamplitude niederschlägt, wenn die
Dauer der Spinevolution im Niederfeld systematisch verändert wird, wobei der
Transfer ins Nachweisfeld nicht-adiabatisch durchgeführt muss. Derartige
Oszillationen konnten sowohl in CIDNP Experimenten als auch bei
Relaxationsmessungen aufgezeigt werden. Bei den DNP-Untersuchungen ging es
hauptsächlich um die Überprüfung, inwieweit das elektronische Spinsystem durch
gepulste Anregung und damit durch Ausnutzung kohärenter Spinbewegung
effizienter aus dem thermischen Gleichgewicht getrieben werden kann als durch
konstantes Pumpen. Ziel war unter es anderem, bei gleichem Polarisationsgrad
die Erwärmung der Probe zu vermindern. Im Niederfeld sind die Bedingungen für
solche Messungen wesentlich günstiger als im Hochfeld. Eine besonders hohe
Polarisation (PHIP) wurde mit Hilfe von Parawasserstoff erzielt, dem
Singulett-Spinisomer von Wasserstoffgas, das sich bei tiefen Temperaturen
anreichern lässt und zur Hydrierung von Styrol zu Ethylbenzol verwendet wurde.
Der Einbau der beiden singulett-korrelierten H-Atome führt zu spektralen
Polarisationsmustern, deren Änderung als Funktion des Magnetfeldes untersucht
wurde. Insbesondere der Polarisationtransfer auf benachbarte Kerne ist von
großem Interesse im Hinblick auf Kontrastmittel in der Kernspintomographie.
Hier konnte gezeigt werden, dass solch ein Transfer besonders effektiv im
Bereich von Level-Crossings ist. Numerische Simulationen konnten das gemessene
Polarisationsmuster und seine Feldabhängigkeit mit hoher Genauigkeit
reproduzieren. Die Einsatzmöglichkeiten von Hyperpolarisation zur Analyse von
chemischen Reaktionen wurden vor allem durch Kombination mehrer CIDNP-
Techniken aufgezeigt. Untersuchungsobjekte waren Aminosäuren, Nukleotide und
zyklische Ketone. Die umfangreichsten Studien betreffen kurzlebige Radikale
der essentiellen Aminosäure Methionin und verschiedener Peptide mit Methionin-
Residuen, die bei Photoreaktionen mit Triplett-angeregten Farbstoffmolekülen
entstehen. Dabei wurden sowohl Feldabhängigkeit als auch Zeitverlauf der dabei
erzeugten Hyperpolarisation gemessen, um daraus Struktur der Radikale
einerseits und Reaktionswege und -kinetik andererseits zu bestimmen. Die
Ergebnisse zeigen unter anderem, dass in wässriger Lösung der pH-Wert das
Verzweigungsverhältnis verschiedener Reaktionswege nicht nur über den
Protonierungszustand der Ausgangssubstanz, sondern auch über die
Reaktionsintermediate beeinflusst. Aufgrund dieser Kenntnis war es möglich
vier verschiedene Methionin-Radikale nachzuweisen und mithilfe ihrer
magnetischen Parameter (Hyperfeinkopplung, g-Faktor) zu charakterisieren. Bei
den Peptiden konnten außerdem Effekte von Nachbargruppen oder der Einfluss von
C und N Terminus gezeigt werden. Insgesamt gesehen erwies sich die Variation
der Magnetfeldstärke in Kombination mit hochauflösendem NMR-Nachweis als sehr
vielseitige und aussagekräftige Methode, die sowohl für die optimale
Generierung von Hyperpolarisation, für der Verlängerung ihrer Lebensdauer und
beim Transfer auf gewünschte Spins eingesetzt werden, die aber auch bei der
Analyse komplexer Reaktionen und der dabei auftretenden Zwischenprodukte
wertvolle Informationen bringen kann
Dynamic Real-Time Magnetic Resonance at Very Low Magnetic Fields
The phenomenon of nuclear magnetic resonance (NMR) is widely applied in biomedical and
biological science to study structures and dynamics of proteins and their reactions. Despite
its impact, NMR is an inherently insensitive phenomenon and has driven the field to construct
spectrometers with increasingly higher magnetic fields leading to more detection sensitivity.
Here, we are demonstrating that enzymatic reactions can be followed in real-time at millitesla
fields, 1000-fold lower than state-of-the-art spectrometers. This requires signal-enhancing
samples via hyperpolarization. Within seconds, we have enhanced the signals of 2-
13Cpyruvate, an important metabolite to probe cancer metabolism, in 22 mM concentrations (up
to 10.1%±0.1% polarization) and show that such a large signal allows for the real-time
detection of enzymatic conversion of pyruvate to lactate. This development paves the
pathways for biological studies in portable and affordable NMR systems with a potential for
medical diagnostics. <br /
Nuclear hyperpolarization of (1-<sup>13</sup>C)-pyruvate in aqueous solution by proton-relayed side-Arm hydrogenation
We employ Parahydrogen Induced Polarization with Side-Arm Hydrogenation (PHIP-SAH) to polarize (1-13C)-pyruvate. We introduce a new method called proton-relayed side-Arm hydrogenation (PR-SAH) in which an intermediate proton is used to transfer polarization from the side-Arm to the 13C-labelled site of the pyruvate before hydrolysis. This significantly reduces the cost and effort needed to prepare the precursor for radio-frequency transfer experiments while still maintaining acceptable polarization transfer efficiency. Experimentally we have attained on average 4.33% 13C polarization in an aqueous solution of (1-13C)-pyruvate after about 10 seconds of cleavage and extraction. PR-SAH is a promising pulsed NMR method for hyperpolarizing 13C-labelled metabolites in solution, conducted entirely in high magnetic field.</p
High resolution NMR study of T1magnetic relaxation dispersion. III. Influence of spin 1/2 hetero-nuclei on spin relaxation and polarization transfer among strongly coupled protons
Effects of spin-spin interactions on the nuclear magnetic relaxation dispersion (NMRD) of protons were studied in a situation where spin ½ hetero-nuclei are present in the molecule. As in earlier works [K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 129, 234513 (2008)10.1063/1.3040272; S. E. Korchak, K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 133, 194502 (2010)10.1063/1.3495988], spin-spin interactions have a pronounced effect on the relaxivity tending to equalize the longitudinal relaxation times once the spins become strongly coupled at a sufficiently low magnetic field. In addition, we have found influence of 19F nuclei on the proton NMRD, although in the whole field range, studied protons and fluorine spins were only weakly coupled. In particular, pronounced features in the proton NMRD were found; but each feature was predominantly observed only for particular spin states of the hetero-nuclei. The features are explained theoretically; it is shown that hetero-nuclei can affect the proton NMRD even in the limit of weak coupling when (i) protons are coupled strongly and (ii) have spin-spin interactions of different strengths with the hetero-nuclei. We also show that by choosing the proper magnetic field strength, one can selectively transfer proton spin magnetization between spectral components of choic