239
DOSY experiment the chemical shift is shown along the detected
F2 axis (x-axis) and diffusion coefficient is along the other F1 axis
(y-axis). Although in some cases we will be referred to BRUKER
NMR spectrometer, the instructions can be generalized and applied
for all NMR spectrometers (Fig. 3).
The goal of the 2D DOSY experiment is to separate species
spectroscopically (not physically) present in a mixture of compounds.
For this reason 2D DOSY is also termed “NMR chromatography.”
For acquiring better results the diffusion coefficients of the components of the mixture are desirable to differ significantly [12].
One interesting experiment for checking the formation of the
complex between an organic molecule and supramolecule is the
2D DOSY (diffusion-ordered spectroscopy). In this chapter we
provide details for obtaining a decent spectrum in which the useful
parameter diffusion coefficient can be calculated.
Some terms are provided to understand the physics behind the
experiment. The experiment is based on the application of gradients. Let us consider spatially homogeneous B 0 to be oriented in
the z-direction, and ω is the same throughout the sample. In addition to B 0 there is a spatially dependent magnetic field gradient g
(T m
−1
):
ω
ω γ
eff
,
n r
n
gr
( ) =
+ ( )
(
)
0
. ,
(1)
where g is defined by the grad of the gradient field component
parallel to B 0 , i.e.,
g
B
Bz
x
i
Bz
y
j
Bz
z
k
= ∇ =
∂
∂
+
∂
∂
+
∂
∂
0
,
(2)
where i, j, and k are unit vectors of the laboratory frame of reference. The important point is that if a homogeneous gradient of
known magnitude is imposed throughout the sample, the Larmor
frequency becomes a spatial label with respect to the direction of
the gradient.
The pulse sequence for the most frequently used ledbpgp2S
experiment is given below (which is installed inside the Bruker
NMR spectrometer library) (Fig. 4).
δ is the duration of the gradient pulse. Δ is the delay that takes
place during the diffusion and g is the gradient strength (ramped
in a series of experiments). Important parameters that must be
adjusted during the experiment are the diffusion delay (d20 in
Bruker instruments) and gradient duration (p30 in Bruker instruments). In the pulse sequence bpg stands for bipolar gradients.
These gradients modify the known LED gradient pulse sequence
replaced by two pulses of different polarity separated by a 180°
pulse. This replacement offers two advantages: (a) eddy currents
are reduced to a minimum and (b) the effective gradient output is
double. Ledbgp is useful for relatively low diffusion coefficients
2D DOSY NMR: A Valuable Tool to Confirm the Complexation in Drug Delivery Systems
DOSY experiment the chemical shift is shown along the detected
F2 axis (x-axis) and diffusion coefficient is along the other F1 axis
(y-axis). Although in some cases we will be referred to BRUKER
NMR spectrometer, the instructions can be generalized and applied
for all NMR spectrometers (Fig. 3).
The goal of the 2D DOSY experiment is to separate species
spectroscopically (not physically) present in a mixture of compounds.
For this reason 2D DOSY is also termed “NMR chromatography.”
For acquiring better results the diffusion coefficients of the components of the mixture are desirable to differ significantly [12].
One interesting experiment for checking the formation of the
complex between an organic molecule and supramolecule is the
2D DOSY (diffusion-ordered spectroscopy). In this chapter we
provide details for obtaining a decent spectrum in which the useful
parameter diffusion coefficient can be calculated.
Some terms are provided to understand the physics behind the
experiment. The experiment is based on the application of gradients. Let us consider spatially homogeneous B 0 to be oriented in
the z-direction, and ω is the same throughout the sample. In addition to B 0 there is a spatially dependent magnetic field gradient g
(T m
−1
):
ω
ω γ
eff
,
n r
n
gr
( ) =
+ ( )
(
)
0
. ,
(1)
where g is defined by the grad of the gradient field component
parallel to B 0 , i.e.,
g
B
Bz
x
i
Bz
y
j
Bz
z
k
= ∇ =
∂
∂
+
∂
∂
+
∂
∂
0
,
(2)
where i, j, and k are unit vectors of the laboratory frame of reference. The important point is that if a homogeneous gradient of
known magnitude is imposed throughout the sample, the Larmor
frequency becomes a spatial label with respect to the direction of
the gradient.
The pulse sequence for the most frequently used ledbpgp2S
experiment is given below (which is installed inside the Bruker
NMR spectrometer library) (Fig. 4).
δ is the duration of the gradient pulse. Δ is the delay that takes
place during the diffusion and g is the gradient strength (ramped
in a series of experiments). Important parameters that must be
adjusted during the experiment are the diffusion delay (d20 in
Bruker instruments) and gradient duration (p30 in Bruker instruments). In the pulse sequence bpg stands for bipolar gradients.
These gradients modify the known LED gradient pulse sequence
replaced by two pulses of different polarity separated by a 180°
pulse. This replacement offers two advantages: (a) eddy currents
are reduced to a minimum and (b) the effective gradient output is
double. Ledbgp is useful for relatively low diffusion coefficients
2D DOSY NMR: A Valuable Tool to Confirm the Complexation in Drug Delivery Systems