A simple method for the preparation of pseudopure states in nuclear magnetic resonance quantum information processing.

The use of nuclear magnetic resonance (NMR) to carry out quantum information processing (QIP) often requires the preparation, transformation, and detection of pseudopure states. In our previous work, it was shown that the use of pairs of pseudopure states (POPS) as a basis for QIP is very convenient because of the simplicity in experimental execution. It is now further demonstrated that the product of the NMR spectra corresponding to two sets of POPS that share a common pseudopure state has the same peak frequencies as those of the common (single) pseudopure state. Examples of applying two different quantum logic gates to a 5-qubit system are given.

Selective excitation in spin systems with homogeneous broadening.

We have found that the application of a weak radio frequency (rf) pulse to a spin system with indirect spin-spin (J) couplings can produce a narrow inverted peak in spectral regions where there are many overlapping peaks. Examples of three compounds with (1)H-(1)H J couplings and one with (1)H-(13)C J couplings are given. The dependences of the signals on the frequency, duration, and amplitude of the weak rf irradiation have been studied. For an rf power of gammaB(1)/2pi=1.0 Hz, pulse widths longer than 0.25 s consistently produce inverted narrow peaks in spectral regions with unresolved peaks. An interpretation of the origin of this unusual result of selective excitation in spin systems with homogeneous broadening is given: the inverted signal observed can be considered as a cumulative effect of the weak rf irradiation acting on many uncorrelated transitions that are slightly off resonance on both sides of the irradiating frequency; the only role of the J couplings (or dipolar couplings in liquid crystals) is to produce a large number of closely spaced peaks that overlap with each other. Computer simulations of both coupled and noninteracting spin systems have been carried out, and the results support this interpretation.

The presence of long-lived spin states in organic solids with rapid molecular motions.

For organic solids with sufficiently mobile molecular segments, the application of a long and weak pulse (gammaB1/2pi approximately Hz) can yield inverted sharp peaks with linewidths of approximately 100 Hz in the 1H NMR spectra, and the use of multi-frequency weak pulses can excite multiple inverted sharp peaks. For these compounds, the normal 1H free induction decay (FID) of a static sample contains a slowly decaying part, which can be detected by acquisition delay up to about 2 ms. The presence of highly mobile molecular segments can also be identified by using a "dipolar filter."

A simple method for NMR photography.

The application of a multi-frequency weak pulse to a liquid crystal can excite narrow 1H NMR peaks at the applied frequencies. By using two-level amplitude coding, namely setting the amplitudes of some of the harmonics to zero, this method can be used to store up to 1024 bits of binary information in the liquid crystal molecules. When the information is retrieved in the form of a spectrum, which is plotted as an array of 32 or 16 segments, the stack of spectral segments reproduces a 2D input pattern quite well. This technique is called "NMR photography." The original method was a pseudo-2D technique that applies the 1024-frequency pulse in the first step, and reads the signal row-by-row in the second step. The present improvement involves subtracting two spectra obtained with the same 1024-frequency pulse but with different durations, so that the method becomes a 1D technique, with a tremendous saving of experimental time. Several examples are given to illustrate the results.

Phospholipid bicelles that align with their normals parallel to the magnetic field.

We have recently reported phospholipid bicelles (bilayered micelles) that have positive anisotropy of the magnetic susceptibility and align with their normals parallel to an external magnetic field [J. Am. Chem. Soc. 2001, 123, 1537]. Improvements have been made via the synthesis of a new phospholipid, 1-dodecanoyl-2-(4-(4-biphenyl)butanoyl)-sn-glycero-3-phosphocholine (DBBPC). Bicelles can be formed by mixing DBBPC with a short-chain phospholipid, 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) in a ratio between 5.1:1 and 6.5:1 in an aqueous medium. The (31)P NMR spectra clearly show that these bicelles align with their principal axes parallel to the magnetic field within a wide temperature range. The (31)P chemical shifts indicate that the conformation of the polar headgroup in these bicelles may be different from that in common bicelles. The phase behavior of a mixture of DBBPC/DHPC with 6:1 mole ratio was investigated in the temperature range of 10-75 degrees C using (31)P, (2)H, and (23)Na NMR. At lower temperatures (10-54 degrees C), the system is dominated by the bicellar phase. At higher temperatures (54-75 degrees C), isotropic micelles are formed and coexist with the bicelles. The partial alignment of maltotriose in the DBBPC/DHPC system was studied at three temperatures, and the (1)H-(13)C dipolar coupling constants are compared with those obtained for two other bicelle solutions.

14N chemical shifts and quadrupole coupling constants of inorganic nitrates.

The isotropic chemical shift and the nuclear quadrupole coupling constant for (14)N were obtained for 14 inorganic nitrates by solid-state MAS NMR measurements at two different field strengths, 9.4 and 11.7 T. The compounds studied were polycrystalline powders of AgNO(3), Al(NO(3))(3), Ba(NO(3))(2), Ca(NO(3))(2), CsNO(3), KNO(3), LiNO(3), Mg(NO(3))(2), NaNO(3), Pb(NO(3))(2), RbNO(3), Sr(NO(3))(2), Th(NO(3))(4)center dot4H(2)O, and UO(2)(NO(3))(2)center dot3H(2)O. Even though the spectra show broadening due to (14)N quadrupole interactions, linewidths of a few hundred hertz and a good signal-to-noise ratio were achieved. From the position of the central peaks at the two fields, the chemical shifts and the nuclear quadrupole coupling constants were calculated. The chemical shifts for all compounds studied range from 282 to 342 ppm with respect to NH(4)Cl. The nuclear quadrupole coupling constants range from 429 kHz for AgNO(3) to 993 kHz for LiNO(3). These data are compared with those available in the literature.

NMR implementation of a parallel search algorithm.

Recently it has been shown that the dynamics of a cluster of dipolar-coupled spins can be manipulated to store and process a large amount of information in a parallel way [Chem. Phys. Lett. 360, 161 (2002)]]. Here it is further demonstrated that it is possible to realize a cascade of parallel bitwise operations on a spin cluster so that an algorithm of parallel search can be experimentally implemented by means of nuclear magnetic resonance.

Indirect NMR detection in solids with multiple cross-polarization periods.

The use of indirect detection for signal enhancement in solids is much less common than in liquids, but has attracted renewed interest recently. In this work we describe an indirect detection scheme that offers a large signal enhancement for rare spins in solids. The method uses multiple periods of cross polarization, each followed by an evolution period. The latter is increased stepwise in a pseudo 2D experiment, in which the signal of the rare spin is detected as modulation of the abundant spin. As an illustration of this method, the natural abundance deuterium NMR spectrum of a static powder sample of 1,2,4,5-tetramethylbenzene is presented.

Filtering of spinning sidebands in 1D MAS NMR spectra.

Spinning sidebands (SSBs) in the MAS NMR spectrum of a polycrystalline solid are related to the principal values of the chemical shift or quadrupole coupling tensors. At present, 2D methods are widely used to sort out the SSBs for each isotropic peak. Here a simple and efficient method for separating the SSBs in 1D MAS NMR spectra is described. It is based on finding the optimal spinning rate with a mathematical algorithm and subsequently treating the spectra with filtering functions.

An improved broadband decoupling sequence for liquid crystals and solids.

Recently we developed an efficient broadband decoupling sequence called SPARC-16 for liquid crystals ¿J. Magn. Reson. 130, 317 (1998). The sequence is based upon a 16-step phase cycling of the 2-step TPPM decoupling method for solids ¿J. Chem. Phys. 103, 6951 (1995). Since then, we have found that a stepwise variation of the phase angle in the TPPM sequence offers even better results. The application of this new method to a liquid crystalline compound, 4-n-pentyl-4'-cyanobiphenyl, and a solid, L-tyrosine hydrochloride, is reported. The reason for the improvement is explained by an analysis of the problem in the rotating frame.

An efficient broadband decoupling sequence for liquid crystals.

A new and efficient broadband decoupling sequence is presented. It is based on the phase cycling of two pulses with small phase angles. The pulse width is 180 degrees +/- 30 degrees, and the phase angle is +/-10 degrees-12 degrees. The sequence contains 16 elements, and is called SPARC-16 as an abbreviation for small phase angle rapid cycling. The application of this sequence to a liquid crystalline compound, 4-n-pentyl-4'-cyanobiphenyl (5CB), is reported. The signal-to-noise ratios and the linewidths of the 13C peaks of 5CB with SPARC-16 decoupling and with other decoupling methods are compared. The results show that the broadband decoupling efficiency of SPARC-16 is considerably better than those of other methods.

Thrombolysis using liposomal-encapsulated streptokinase: an in vitro study.

The clot-lysing ability of streptokinase (SK) was examined using membrane-bound thrombi. Encapsulation of SK in large unilamellar phospholipid vesicles (liposomes) resulted in entrapping approximately 30% of its original activity. Measurements of streptokinase activity for liposomal-encapsulated streptokinase (LESK) indicated little loss of activity or leakage in Tris-buffered saline over a 24-hr period at temperatures of 4 and 23 degrees C. However, incubation of free SK and LESK in platelet-poor plasma (PPP) at 37 degrees C resulted in a decrease of SK activity. The retention of SK activity in LESK was considerably higher than that of unentrapped SK. Clot-dissolving time (CDT) was measured by monitoring the pressure drop during slow filtration in plasma through membrane-bound thrombi. The results indicated that both LESK and free SK were able to activate the fibrinolytic system. Without prior incubation in PPP at 37 degrees C, the CDT of a SK and PPP mixture (SK/PPP) was 10.7 +/- 1.9 min (n = 12), while that of a LESK and PPP mixture (LESK/PPP) was 12.4 +/- 1.7 min (n = 12). The CDT-detected clot-lysing abilities of both SK and LESK were diminished by incubation in PPP, but to different extents. After 15- and 30-min incubations, the CDT of SK/PPP increased significantly to 15.5 +/- 1.5 and 24.1 +/- 2.4 min (n = 5, P less than 0.05), respectively. In contrast, the CDT of LESK/PPP increased to 13.3 +/- 0.8 min (n = 5) after 15 min of incubation and to 16.0 +/- 1.1 min (n = 5, P less than 0.05) after a 30-min incubation. These results suggest that entrapment of SK in liposomes preserves the thrombolytic potential of the plasminogen activator by limiting its exposure to the components of the plasma.

Dynamic evaluation of clotting phenomena in vitro and perfluorochemical oxygen transport across a membrane-bound thrombus model.

Citrated platelet-rich plasma was used to occlude 3-microns and 10-microns poresize Nuclepore membranes after recalcification as a thrombus model. Morphologic studies, using both light microscopy and scanning electron microscopy, indicated that over 90 percent of the number of pores available for filtration in hydrophilic and hydrophobic membranes were occluded either partially or completely. Results of transient and steady state pressure drop measurements supported the morphologic studies. It was found that the percentage of oxygen transported across the occluded membranes was greater for filtration of red blood cell suspensions diluted with a perfluorochemical emulsion than that of those diluted with Ringers. The findings in this study suggested that perfluorochemical emulsions might transport oxygen across a thrombus to maintain tissue viability during acute ischemic events.

Interaction between erythrocytes and a perfluorochemical blood substitute.

Perfluorochemicals (PFCs) are being widely developed for use as erythrocyte substitutes to carry oxygen to tissue in acute crises. Oxypherol, a commercially available PFC preparation commonly used for animal tests, reduces erythrocyte deformability in the presence of plasma. This undesirable effect further complicates oxygen delivery by erythrocytes. Our experiments indicate that one or more plasma proteins must be present to observe Oxypherol-induced reduction in erythrocyte deformability, but the latter is not protein specific. Neither platelet activation nor enhanced protein adsorption could account for the mechanism of altered erythrocyte flexibility. Using fluorine-19 NMR, it was found that a small amount of Oxypherol droplets is adsorbed on the surface of the erythrocytes. The amount of adsorbed droplets increases when Oxypherol is incubated with the erythrocytes in the presence of plasma, in parallel with a decrease in erythrocyte deformability. Therefore, it seems likely that the loss of deformability of the erythrocytes is caused by the adsorption of small Oxypherol droplets on the erythrocytes.

Plasma-mediated alterations of erythrocyte deformability by perfluorochemical blood substitutes.

The effect of perfluorochemical blood substitutes (eg, Oxypherol or Fluosol-DA) on red cell deformability was investigated because these emulsions are in direct contact with red cells when they are used as temporary circulatory aids. Erythrocyte deformability was assessed by a constant volumetric flow rate filtration method. The results of in vitro incubation experiments indicate that perfluorotributylamine causes the deformability of human red cells to decrease significantly in the presence of plasma. However, there is no obvious loss in the deformability when washed cells are used. Neither mean cell volume nor white cells appear to be responsible for the observed effects of perfluorotributylamine. Perfluorodecalin and perfluorotripropylamine, two perfluorochemical compounds that are widely applied clinically, do not induce significant changes in red cell deformability with or without plasma. These results indicate the need for in vitro testing in the development of perfluorochemicals as blood substitutes.

The effect of ATP concentration on the rate of actin polymerization.

It was found that the rate of polymerization of G-actin increased with the decrease of ATP concentration. When excess ATP was replaced by chloride through anion-exchange treatment, the extent of actin polymerization did not change provided that the ionic strength was raised immediately after the treatment. In the meantime, the rate of actin polymerization was greatly enhanced after the removal of excess ATP. The rate enhancement was much less when both excess Ca2+ and excess ATP were removed. G-actin with excess ATP replaced by chloride had larger light scattering and showed a "catalytic" effect on the polymerization of normal G-actin. The inhibition of actin polymerization by cytochalasin B in 100 mM KCl was much more obvious for G-actin with excess ATP removed than for normal G-actin. It is suggested that the reduction of excess ATP concentration in a G-actin solution increases the binding of weak-affinity Ca2+ and promotes the formation of oligomeric actin (actin nuclei).