Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

ESI‐MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Investigating the vortex melting phenomenon in BSCCO crystals using magneto-optical imaging technique

Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals of Bi₂Sr₂CaCu₂O₈ (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local melting temperature/field, we have constructed maps of the melting landscape T _m(H, r), viz., the melting temperature (T _m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite effects on the local melting transition.     

Tri-partite complex for axonal transport drug delivery achieves pharmacological effect

Background

Targeted delivery of pharmaceutical agents into selected populations of CNS (Central Nervous System) neurons is an extremely compelling goal. Currently, systemic methods are generally used for delivery of pain medications, anti-virals for treatment of dermatomal infections, anti-spasmodics, and neuroprotectants. Systemic side effects or undesirable effects on parts of the CNS that are not involved in the pathology limit efficacy and limit clinical utility for many classes of pharmaceuticals. Axonal transport from the periphery offers a possible selective route, but there has been little progress towards design of agents that can accomplish targeted delivery via this intraneural route. To achieve this goal, we developed a tripartite molecular construction concept involving an axonal transport facilitator molecule, a polymer linker, and a large number of drug molecules conjugated to the linker, then sought to evaluate its neurobiology and pharmacological behavior.

Results

We developed chemical synthesis methodologies for assembling these tripartite complexes using a variety of axonal transport facilitators including nerve growth factor, wheat germ agglutinin, and synthetic facilitators derived from phage display work. Loading of up to 100 drug molecules per complex was achieved. Conjugation methods were used that allowed the drugs to be released in active form inside the cell body after transport. Intramuscular and intradermal injection proved effective for introducing pharmacologically effective doses into selected populations of CNS neurons. Pharmacological efficacy with gabapentin in a paw withdrawal latency model revealed a ten fold increase in half life and a 300 fold decrease in necessary dose relative to systemic administration for gabapentin when the drug was delivered by axonal transport using the tripartite vehicle.

Conclusion

Specific targeting of selected subpopulations of CNS neurons for drug delivery by axonal transport holds great promise. The data shown here provide a basic framework for the intraneural pharmacology of this tripartite complex. The pharmacologically efficacious drug delivery demonstrated here verify the fundamental feasibility of using axonal transport for targeted drug delivery.     

Investigation of water bound to photosystem I with multiquantum filtered 17 O nuclear magnetic resonance

A new analytical approach was developed to characterize the properties of water molecules bound to macromolecules in solution using 17 O nuclear magnetic resonance (NMR) relaxation. A combination of conventional (single-quantum) and triple-quantum filtered Hahn echo and inversion recovery measurements was employed. From measured relaxation rate constants, the fraction and the correlation time of bound H2 17 O molecules and the relaxation rate constant of bulk water in solution were calculated. This was done by solving analytically a set of nonlinear equations describing the overall relaxation rate constants in the presence of chemical exchange between bulk and bound water. The analytical approach shows the uniqueness of the solution for a given set of three relaxation rate constants. This important result sheds light on the data reduction problem from 17 O NMR experiments on biological systems. Water bound in photosystem I isolated from the wild type and rubA variant of the cyanobacterium Synechocystis species PCC 7002 was investigated for the first time. The analysis revealed that photosystem I isolated from the wild type binds 1720+/-110 water molecules, whereas photosystem I isolated from the rubA variant binds only 1310+/-170. The accuracy of the method proposed can be increased by further 17 O enrichment. The methodology, established for the first time in this work, allows the study of a diverse range of biological samples regardless of their size and molecular weight. Applied initially to photosystem I, this novel method has important consequences for the future investigation of the assembly of biological molecules.     

Investigation of the Stationary and Transient A 1 ·− Radical in Trp → Phe Mutants of Photosystem I

Photosystem I (PS I) contains two symmetric branches of electron transfer cofactors. In both the A- and B-branches, the phylloquinone in the A₁ site is π-stacked with a tryptophan residue and is H-bonded to the backbone nitrogen of a leucine residue. In this work, we use optical and electron paramagnetic resonance (EPR) spectroscopies to investigate cyanobacterial PS I complexes, where these tryptophan residues are changed to phenylalanine. The time-resolved optical data show that backward electron transfer from the terminal electron acceptors to P₇₀₀^·+ is affected in the A- and B-branch mutants, both at ambient and cryogenic temperatures. These results suggest that the quinones in both branches take part in electron transport at all temperatures. The electron-nuclear double resonance (ENDOR) spectra of the spin-correlated radical pair P₇₀₀^·+A₁^·− and the photoaccumulated radical anion A₁^·−, recorded at cryogenic temperature, allowed the identification of characteristic resonances belonging to protons of the methyl group, some of the ring protons and the proton hydrogen-bonded to phylloquinone in the wild type and both mutants. Significant changes in PS I isolated from the A-branch mutant are detected, while PS I isolated from the B-branch mutant shows the spectral characteristics of wild-type PS I. A possible short-lived B-branch radical pair cannot be detected by EPR due to the available time resolution; therefore, only the A-branch quinone is observed under conditions typically employed for EPR and ENDOR spectroscopies.     

Absolute signs of hyperfine coupling constants as determined by pulse ENDOR of polarized radical pairs

A novel method that allows the determination of absolute signs of hyperfine coupling constants in polarized radical pair (RP) pulse electron-nuclear double resonance (ENDOR) spectra is presented, The variable mixing time (VMT) ENDOR method used here leads to a separation of ENDOR transitions originating from different electron spin manifolds by employing their dependence on the time-dependent parameters of the pulse sequence. The simple kinetic model of the RP VMT ENDOR experiment shows very good agreement with the experiments performed on the P ₇₀₀ ^.+ A ₁ ^.- RP in photosystem I. This method relies on the selective excitation of absorptive or emissive lines of one radical in the RP EPR spectrum and therefore requires high spectral resolution. This condition was fulfilled for the system studied at the low-field edge of the RP EPR spectrum obtained at Q-band. The method presented here has a very high sensitivity and does not require any equipment additional to the one used for RP pulse ENDOR. The VMT ENDOR method offers the possibility for selective suppression of signals from different electron spin manifolds.     

Accuracy of the multipole expansion applied to a sphere in a creeping flow parallel to a wall

An example system is studied to discuss precision of the multipoleexpansion, applied to determine forces exerted on particlesby a viscous low-Reynolds-number fluid flow. A single spherein an ambient flow (pure shear, quadratic, and modulated shear)parallel to a close plane wall is considered. Forces and torquesexerted by the ambient flow on a motionless sphere are evaluated.Their precision is determined and related to a multipole orderof the truncation. Similar analysis is performed for a movingsphere with no ambient flow and for a freely moving sphere.Relative motion of the sphere with respect to the wall givesrise to strong lubrication interactions. It is analysed howthese interactions affect accuracy of the pure multipole expansion,and what are the smallest distances where it becomes insufficient.An alternative precise method is applied, in which lubricationexpressions are subtracted from the hydrodynamic forces andtorques, and the residue is evaluated as a fast-convergent seriesof inverse powers of the distance between the sphere centreand the wall. The accuracy of this procedure is carefully analysed.