|
Current
Analytical Chemistry
ISSN: 1573-4110
Current Analytical Chemistry
Volume 4, Number 1, January 2008
Contents
Membrane Domain Distributions: Analysis of Fluorescence
Sterol Ex-change Kinetics
Pp.1-7
Adalberto M. Gallegos, Barbara P. Atshaves, Avery L. McIntosh
Stephen M. Storey, Judith L. Ball, Ann B. Kier and Friedhelm
Schroeder
[Abstract]
T2p
and T2p
Adiabatic Relaxations and Contrasts Pp. 8-25
Shalom Michaeli, Dennis J. Sorce and Michael Garwood
[Abstract]
Structural Analyses of Carbohydrate Moieties of Glycoproteins
by Microwave-Assisted Partial Acid Hydrolysis and Mass Spectrometry
Pp. 26-39
Bao-Shiang Lee, Sangeeth Krishnanchettiar, G.D. Lasanthi
P. Jayathilaka, Syed Salman Lateef and Shalini Gupta
[Abstract]
Magnetic Resonance Spectroscopy with Longitudinal
Multispin Orders Pp. 40-54
S. Sendhil Velan, Kumar Pichumani, David Murray, Raymond
R. Raylman, Tricia Scott, Ayyakannu Manivannan and Larry Halliburton
[Abstract]
Experimental Design Techniques for Optimization of
Analytical Methods. Part I: Separation and Sample Preparation
Techniques Pp. 55-74
Federica Bianchi and Maria Careri
[Abstract]
Abstracts
[Back to top]
Membrane Domain Distributions: Analysis of
Fluorescence Sterol Ex-change Kinetics
Adalberto M. Gallegos, Barbara P. Atshaves, Avery L. McIntosh,
Stephen M. Storey, Judith L. Ball, Ann B. Kier and Friedhelm
Schroeder
It is well known that cholesterol is localized in a non-random
distribution within and across biological membranes. The importance
of the cholesterol-enriched domains, also termed rafts, is
evident from the fact that non-receptor- mediated cholesterol
uptake and reverse cholesterol transport also occur through
select plasma membrane domains. However, despite much effort
to resolve the mechanisms that explain the origin, function,
and regulation of membrane cholesterol lateral and transbilayer
asymmetric distribution into domains, these phenomena remain
largely unresolved. As well, progress in understanding the
pathways of intracellular cholesterol trafficking, and the
ultimate cellular fate of that cholesterol, has been sparse.
Understanding the above-named phenomena and processes is itself
crucial to resolving the molecular mechanisms of cholesterol
uptake, reverse cholesterol transport, modulation of membrane
function, and steroidogenesis. These ongoing efforts to elucidate
the nature of cholesterol distribution and dynamics within
the cell, have necessitated devising new ways to investigate
the trafficking of cholesterol. To that end, fluorescent kinetic
exchange assays have been developed to probe the nature of
sterol transfer between biological membranes, i.e. endoplasmic
reticulum, lysosomes, mitochondria, plasma membrane, and caveolae/lipid
rafts (i.e., distinct sub-domains of the plasma membrane).
These exchange assays make use of spectroscopic properties,
such as polarization, to investigate the nature and distribution
of sterol within biological membranes. These assays demonstrate
that: cholesterol is distributed within the plane of biomembrane
layers into dynamic and static domains, with the latter predominating,
and that regulation of the size and kinetics of biomembrane
cholesterol domains might be determining factors in intracellular
cholesterol trafficking, targeting, and efflux.
[Back to top]
T2pand
T2p
Adiabatic Relaxations and Contrasts
Shalom Michaeli, Dennis J. Sorce and Michael Garwood
Transverse relaxation in the rotating frame (T2p)
is the dominant relaxation mechanism during a train of adiabatic
full passage (AFP) radiofrequency (RF) pulses with no interpulse
time intervals placed after the 900
excitation pulse. The magnetization components remain transverse
to the time-dependent effective field and undergo relaxation
with the time constant T2p
Longitudinal relaxation in the rotating frame (T1p)
is the dominant relaxation mechanism during a train of AFP
RF pulses placed prior to an excitation pulse. Here, magnetization
is aligned along the time-dependent effective field during
adiabatic rotation undergoes relaxation with the time constant
T1p. A detailed
description of rotating frame relaxations due to dipolar interactions
and exchange during adiabatic pulses is presented herein.
The exchange-induced and dipolar interaction contributions
depend on the modulation functions of the adiabatic pulses
used. The intrinsic rotating frame relaxation rate constant
is sensitive to fluctuations at the effective frequencey (ωeff)
in the rotating frame, and this is modulated differently during
the two types of AFP pulses. This may lead to the possibility
to assess T1p and T2p
relaxation influenced by dipolar relaxation pathways and exchange
in human brain tissue and provide a means to generate T1p
and T2p
contrasts in MRI.
[Back to top]
Structural Analyses of Carbohydrate Moieties of Glycoproteins
by Microwave-Assisted Partial Acid Hydrolysis and Mass Spectrometry
Bao-Shiang Lee, Sangeeth Krishnanchettiar, G.D. Lasanthi
P. Jayathilaka, Syed Salman Lateef and Shalini Gupta
Characterization of carbohydrate moieties of glycoproteins
using microwave-assisted partial acid hydrolysis (MAPAH) and
mass spectrometry (MS) are described in this review. Acids
including hydrochloric acid (HCl), trifluoroacetic acid (TFA),
and phosphoric acid (H3 PO4)
can be used to induce partial hydrolysis of the carbohydrate
moieties of glycoproteins in as short as 30 s of microwave
exposure. High resolving power of MS allows distinction between
different glycopeptide fragments. Several glycoproteins including
bovine pancreatic ribonuclease B (RNase B, MW ~15
kDa), egg white avidin (MW ~16 kDa), human serum α1-acid
glycoprotein (α1-AGP,
MW ~36 kDa), horseradish peroxidase (HRP, MW ~44 kDa), fetal
calf serum fetuin (BSF, MW ~45 kDa), and glucose oxidase from
Aspergillus niger (GO, MW ~75 kDa), are used to demonstrate
this technique. Information of the sugar composition and/or
arrangement of the carbohydrate moieties can be readily obtained
either from glycoproteins directly or digested glycopeptides
of the glycoproteins. This method is fast, sensitive, and
a reliable technique. Challenges when working on larger and
heavily glycosylated glycoproteins are discussed.
[Back to top]
Magnetic Resonance Spectroscopy with Longitudinal Multispin
Orders
S. Sendhil Velan, Kumar Pichumani, David Murray, Raymond
R. Raylman, Tricia Scott, Ayyakannu Manivannan and Larry Halliburton
Longitudinal multispin orders can be created in spin
systems that exhibit scalar, dipolar or quadrupolar couplings.
They provide an effective way for measurement of scalar couplings
and also to probe molecular interactions and dynamics. They
cannot be separated by phase cycling or gradient selection
methods which are the only known modes of separating different
coherences. In this review we describe the frequency cycling
procedure for separating various orders in weakly and strongly
coupled spin systems. We provide the analytical solutions
that permit determination of the frequency cycle for different
spin systems. We also discuss the creation of longitudinal
orders through relaxation. Finally we highlight the potential
applications including spectral editing, measurement of relative
signs of scalar couplings and structural properties of molecules.
[Back to top]
Experimental Design Techniques for Optimization of Analytical
Methods. Part I: Separation and Sample Preparation Techniques
Federica Bianchi and Maria Careri
A review is presented on recent applications of experimental
design and optimization techniques for the analysis of compounds
of food, biomedical, toxicological and environmental concern.
The main features and the significant advantages of chemometric
approaches are discussed.
Examples related to the determination of substances like xenobiotics
or naturally occurring compounds using different analytical
techniques, i.e. gas chromatography (GC), liquid chromatography
(LC) and capillary electrophoresis (CE) are provided in this
Part. The use of experimental design techniques for optimization
of extraction techniques is emphasized as well as the importance
of experimental design in checking robustness of analytical
methods.
This survey will attempt to cover the state-of-the-art from
2004 to 2006.
|
