Biomedical subjects

Jeffrey I Zink

Publications and source records attributed to Jeffrey I Zink.

At least 19 recordsLinked to original sources

PubMed2007

Design and optimization of molecular nanovalves based on redox-switchable bistable rotaxanes.

Redox-controllable molecular nanovalves based on mesoporous silica nanoparticles have been fabricated, using two bistable [2]rotaxanes with different spacer lengths between their recognition sites as the gatekeepers. Three different linkers with varying chain lengths have been employed to attach the bistable [2]rotaxane molecules covalently to the silica substrate. These nanovalves can be classified as having IN or OUT locations, based on the positions of the tethered bistable [2]rotaxanes with respect to the entrances to the nanopores. The nanovalves are more efficient when the bistable [2]rotaxane-based gatekeepers are anchored deep within (IN) the pores than when they are attached closer to (OUT) the pores' orifices. The silica nanopores can be closed and opened by moving the mechanically interlocked ring component of the bistable [2]rotaxane closer to and away from the pores' orifices, respectively, a process which allows luminescent probe molecules, such as coumarins, tris(2-phenylpyridine)iridium, and rhodamine B, to be loaded into or released from the mesoporous silica substrate on demand. The lengths of the linkers between the surface and the rotaxane molecules also play a critical role in determining the effectiveness of the nanovalves. The shorter the linkers, the less leaky are the nanovalves. However, the distance between the recognition units on the rod section of the rotaxane molecules does not have any significant influence on the nanovalves' leakiness. The controlled release of the probe molecules was investigated by measuring their luminescence intensities in response to ascorbic acid, which induces the ring's movement away from the pores' orifices, and consequently opens the nanovalves.

Journal Article↗

PubMed2006

Excited-state mixed-valence distortions in a diisopropyl diphenyl hydrazine cation.

Excited-state mixed valence (ESMV) occurs in the 1,2-diphenyl-1,2-diisopropyl hydrazine radical cation, a molecule in which the ground state has a symmetrical charge distribution localized primarily on the hydrazine, but the phenyl to hydrazine charge-transfer excited state has two interchangeably equivalent phenyl groups that have different formal oxidation states. Electronic absorption and resonance Raman spectra are presented. The neighboring orbital model is employed to interpret the absorption spectrum and coupling. Resonance Raman spectroscopy is used to determine the excited-state distortions. The frequencies of the enhanced modes from the resonance Raman spectra are used together with the time-dependent theory of spectroscopy to fit the two observed absorption bands that have resolved vibronic structure. The origins of the vibronic structure and relationships with the neighboring orbital model are discussed.

Cations↗

PubMed2006

Photoisomerization of azobenzene derivatives in nanostructured silica.

A series of derivatized azobenzene molecules are synthesized such that one of the phenyl groups can be chemically bonded to mesostructured silica and the other, derivatized with dendrons, is free to undergo large-amplitude light-driven motion. The silica frameworks on which the motion takes place are either 150 nm thick films containing ordered hexagonal arrays of tubes (inner diameter about 2 nm) containing the bonded azobenzenes, or particles (about 500 nm in diameter) containing the same ordered arrays of functionalized tubes. The photoisomerization yields and the rate constants for the thermal cis to trans back-reaction of the azobenzenes in the tubes are measured and compared to those of the molecules in solution. The rate constants decrease with increasing size of the dendrons. Fluorescence spectra of the cis and trans isomers in the pores show that the photoisomerization in the nanostructured materials is selectively driven by specific wavelengths of light and is reversible.

Journal Article↗

PubMed2006

The vault exterior shell is a dynamic structure that allows incorporation of vault-associated proteins into its interior.

Vaults are 13 million Da ribonucleoprotein particles with a highly conserved structure. Expression and assembly by multimerization of an estimated 96 copies of a single protein, termed the major vault protein (MVP), is sufficient to form the minimal structure and entire exterior shell of the barrel-shaped vault particle. Multiple copies of two additional proteins, VPARP and TEP1, and a small untranslated vault RNA are also associated with vaults. We used the Sf9 insect cell expression system to form MVP-only recombinant vaults and performed a series of protein-mixing experiments to test whether this particle shell is able to exclude exogenous proteins from interacting with the vault interior. Surprisingly, we found that VPARP and TEP1 are able to incorporate into vaults even after the formation of the MVP vault particle shell is complete. Electrospray molecular mobility analysis and spectroscopic studies of vault-interacting proteins were used to confirm this result. Our results demonstrate that the protein shell of the recombinant vault particle is a dynamic structure and suggest a possible mechanism for in vivo assembly of vault-interacting proteins into preformed vaults. Finally, this study suggests that the vault interior may functionally interact with the cellular milieu.

Animals↗

PubMed2006

Excited-state mixed valence in transition metal complexes.

Mixed valence in the lowest-energy metal-to-ligand charge-transfer excited state of di-(4-acetylpyridine)tetraammineruthenium(II) complexes is defined and analyzed. The excited state has two interchangeably equivalent ligands with different oxidation states. The electronic absorption band energies, selection rules, and bandwidths are analyzed quantitatively in terms of the signs and orientations of the transition dipole moments, sign and magnitude of the coupling, and resonance Raman analysis of displaced normal modes.

Journal Article↗

PubMed2006

Construction of a pH-driven supramolecular nanovalve.

[Structure: see text] The versatility of supramolecular chemistry has been exploited in constructing nanovalves based on mesoporous silica MCM-41 and the mutual recognition between secondary dialkylammonium ions and dibenzo[24]crown-8 (DB24C8). Naphthalene-containing dialkylammonium threads were tethered to the MCM-41, followed by loading with coumarin 460 and capping with DB24C8. Controlled release of coumarin 460 from the pores of MCM-41 was demonstrated using different bases. The rate of release of coumarin 460 from the nanovalves depends on the size of the base.

Coumarins↗

PubMed2006

Wavelength dependent photofragmentation patterns of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)Ln (III) (Ln = Eu, Tb, Gd) in a molecular beam.

Laser photoionization and ligand photodissociation in Ln(thd)(3) (Ln = Eu, Tb, Gd; thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) are studied in a molecular beam via time-of-flight mass spectrometry. The fragmentation patterns are strongly wavelength dependent. With 355 nm excitation, the mass spectrum is dominated by Ln(2+), Ln(+), and LnO(+) fragments. The bare Ln ions are believed to arise from photoionization of neutral Ln atoms. The Ln atoms, in turn, are produced from the Ln(thd)(3) complex in a sequence of Ln reductions (through ligand-to-metal charge-transfer transitions), with each reduction being accompanied by the dissociation of a neutral ligand radical. In contrast, under visible-light (410-450 nm) excitation, a significant Ln(thd)(n)(+) signal is observed (where n = 2,3 for Ln = Tb,Gd and n = 1-3 for Ln = Eu). Thus, with visible excitation, photoionization of Ln(thd)(n) competes effectively with the Ln-reduction/ligand-dissociation sequence that leads to the dominant bare Ln-ion signal seen with 355 nm excitation. The fact that monoligated Ln(thd)(+) is observed only for Ln = Eu is interpreted in terms of the relative accessibility of an excited ligand-to-metal charge-transfer state from the ground electronic state of neutral Ln(thd).

Ketones↗

PubMed2006

Optical spectra of protected diamine 10-bond-bridged intervalence radical cations related to N,N,N'N'-tetraalkylbenzidine.

The optical absorption spectra of the delocalized intervalence radical cations of seven o,o'-linked benzidine derivatives that have the nitrogens protected as 9-(9-aza-bicyclo[3.3.1]nonan-3-one) derivatives are discussed and compared with that of the p-phenylene radical cation. The linking units are CH2, CH2CH2, NMe, S, SO2, and C=O, and we also studied H,H (the unlinked benzidine). The lowest-energy absorption band is assigned as the transition from the antibonding combination of symmetrical N and aromatic orbitals to the antibonding combination of the antisymmetric N and aromatic orbitals using TD-DFT calculations, and a good correlation between the observed transition energies and those calculated using the simple Koopmans theorem-based "neutral in-cation geometry" calculations on the UB3LYP/6-31G* structures is found. The use of the two-state model that equates the electronic interaction through the bridge between the amino groups with half of the lowest transition energy is seriously incorrect for these and other delocalized intervalence compounds. The problem of extracting the electronic interactions that actually are involved from calculated transition energies is discussed.

Journal Article↗

PubMed2006

Photoinduced electron transfer in 2-tert-butyl-3-(anthracen-9-yl)-2,3-diazabicyclo[2.2.2]octane.

Intramolecular photoinduced electron transfer from a hydrazine unit to an aromatic group is studied by resonance Raman spectroscopy and electronic absorption spectroscopy. Substituted hydrazine functional groups have played an important role in studies of electron-transfer reactions, photoinduced intramolecular electron transfer, and of mixed valence. A prototypical compound, 2-tert-butyl-3-(anthracen-9-yl)-2,3-diazabicyclo[2.2.2]octane, that has the hydrazine-to-anthracene charge-transfer band in a region of the visible spectrum suitable for detailed resonance Raman spectroscopy is studied in detail. Excitation profiles are obtained, calculated quantitatively by using time-dependent theoretical methods, and interpreted with the assistance of molecular orbital calculations. Excited-state distortions are calculated. The largest distortions occur on the hydrazine unit; the normal mode showing the largest distortion (659 cm(-1), calculated at 665 cm(-1)) involves an out-of-plane C-N-N-C bend consistent with removing an electron from the N-N pi antibonding orbital. Anthracene ring-centered C-C stretches also are enhanced, consistent with populating an antibonding pi orbital centered on the ring. Excellent fits to all of the excitation profiles and to the absorption band are obtained using one set of excited-state potential surfaces.

Journal Article↗

PubMed2006

Interpretation of unusual absorption bandwidths and resonance Raman intensities in excited state mixed valence.

Excited state mixed valence (ESMV) occurs in molecules in which the ground state has a symmetrical charge distribution but the excited state possesses two or more interchangeably equivalent sites that have different formal oxidation states. Although mixed valence excited states are relatively common in both organic and inorganic molecules, their properties have only recently been explored, primarily because their spectroscopic features are usually overlapped or obscured by other transitions in the molecule. The mixed valence excited state absorption bands of 2,3-di-p-anisyl-2,3-diazabicyclo[2.2.2]octane radical cation are well-separated from others in the absorption spectrum and are particularly well-suited for detailed analysis using the ESMV model. Excited state coupling splits the absorption band into two components. The lower energy component is broader and more intense than the higher energy component. The absorption bandwidths are caused by progressions in totally symmetric modes, and the difference in bandwidths is caused by the coordinate dependence of the excited state coupling. The Raman intensities obtained in resonance with the high and low energy components differ significantly from those expected based on the oscillator strengths of the bands. This unexpected observation is a result of the excited state coupling and is explained by both the averaging of the transition dipole moment orientation over all angles for the two types of spectroscopies and the coordinate-dependent coupling. The absorption spectrum is fit using a coupled two-state model in which both symmetric and asymmetric coordinates are included. The physical meaning of the observed resonance Raman intensity trends is discussed along with the origin of the coordinate-dependent coupling. The well-separated mixed valence excited state spectroscopic components enable detailed electronic and resonance Raman data to be obtained from which the model can be more fully developed and tested.

Journal Article↗

PubMed2005

Photochemical charge separation within aromatic hydrazines and the effect of excited-state intervalence in dihydrazines.

Photolysis into the longest wavelength absorption band of 2-tert-butyl-2,3-diazabicyclo[2.2.2]oct-3-yl hydrazine (Hy) substituted naphthalenes causes aryl group reduction electron transfer to give (+)Hy-Ar(-). Electrooptical absorption measurements characterize the charge separation properties from these bands. Emission studies demonstrate that the separation between absorption and emission maxima for symmetrically disubstituted compounds is smaller than that for monosubstituted compounds, which is attributed to excited-state intervalence. The excited-state diabatic surfaces may be described as a Hy(+)-NA(- )-Hy(0), Hy(0)-NA(-)-Hy(+) pair, for which electronic interaction produces a double minimum that qualitatively resembles that in the ground state of the disubstituted intervalence radical cations.

Journal Article↗

PubMed2005

A photoactive molecular triad as a nanoscale power supply for a supramolecular machine.

A tetrathiafulvalene-porphyrin-fullerene (TTF-P-C(60)) molecular triad, which generates electrical current by harnessing light energy when self-assembled onto gold electrodes, has been developed. The triad, composed of three unique electroactive components, namely, 1) an electron-donating TTF unit, 2) a chromophoric porphyrin unit, and 3) an electron-accepting C(60) unit, has been synthesized in a modular fashion. A disulfide-based anchoring group was tagged to the TTF end of the molecule in order to allow its self-assembly on gold surfaces. The surface coverage by the triad in a self-assembled monolayer (SAM) was estimated to be 1.4 nm(2) per molecule, a density which is consistent with hexagonal close-packing of the spherical C(60) component (diameter approximately 1 nm). In a closed electronic circuit, a triad-SAM functionalized working-electrode generates a switchable photocurrent of approximately 1.5 microA cm(-2) when irradiated with a 413 nm Kr-ion laser, a wavelength which is close to the porphyrin chromophore's absorption maximum peak at 420 nm. The electrical energy generated by the triad at the expense of the light energy is ultimately exploited to drive a supramolecular machine in the form of a [2]pseudorotaxane comprised of a pi-electron-deficient tetracationic cyclobis(paraquat-p-phenylene) (CBPQT(4+)) cyclophane and a pi-electron-rich 1,5-bis[(2-hydroxyethoxy) ethoxy]naphthalene (BHEEN) thread. The redox-induced dethreading of the CBPQT(4+) cyclophane from the BHEEN thread can be monitored by measuring the increase in the fluorescence intensity of the BHEEN unit. A gradual increase in the fluorescence intensity of the BHEEN unit concomitant with the photocurrent generation, even at a potential (0 V) much lower than that required (-300 mV) for the direct reduction of the CBPQT(4+) unit, confirms that the dethreading process is driven by the photocurrent generated by the triad-SAM.

Nanotechnology↗

PubMed2005

Optical spectra of delocalized dinitroaromatic radical anions revisited.

The optical spectra of nine dinitroaromatic radical anions (1,2- and 1,4-dinitrobenzene, 1,5- and 2,6-dinitro naphthalene, 4,4'-dinitrobiphenyl, 2,7-dinitro-9,9-dimethylfluorene, 2,6-dinitroanthracene, and 2,7- and 1,8-dinitrobiphenylene) in dimethylformamide are reported and analyzed. All have delocalized charge distribution, as demonstrated by the vibrational fine structure that is observed in their optical spectra: All show lowest energy absorption bands that correspond to an alpha-homo (highest occupied molecular orbital) to alpha-lumo (lowest unoccupied) transition, as shown by Koopmans-based UB3LYP calculation of the orbital separation of the neutral at the geometry of the radical anion. These single-point calculations are shown to be significantly more accurate for five of these compounds than the much more complex and expensive TD-DFT method. The two-state model should not be used to estimate the electronic coupling in delocalized intervalence compounds such as these. Neighboring orbital estimation of the electronic couplings show that using the two-state model greatly underestimates electronic coupling here.

Journal Article↗

PubMed2005

A reversible molecular valve.

In everyday life, a macroscopic valve is a device with a movable control element that regulates the flow of gases or liquids by blocking and opening passageways. Construction of such a device on the nanoscale level requires (i) suitably proportioned movable control elements, (ii) a method for operating them on demand, and (iii) appropriately sized passageways. These three conditions can be fulfilled by attaching organic, mechanically interlocked, linear motor molecules that can be operated under chemical, electrical, or optical stimuli to stable inorganic porous frameworks (i.e., by self-assembling organic machinery on top of an inorganic chassis). In this article, we demonstrate a reversibly operating nanovalve that can be turned on and off by redox chemistry. It traps and releases molecules from a maze of nanoscopic passageways in silica by controlling the operation of redox-activated bistable [2]rotaxane molecules tethered to the openings of nanopores leading out of a nanoscale reservoir.

Models, Chemical↗

PubMed2005

Formation of titanium nitride nanoparticles within mesoporous silica SBA-15.

We report the first synthesis of titanium nitride (TiN) nanoparticles inside the nanoscale channels of mesoporous silica SBA-15. The TiN precursor, Ti(NMe(2))(4) in toluene, was incorporated into the methyl group-modified channels of the SBA-15 powder. The functionalization of pore surfaces with methyl groups generates hydrophobic surfaces that facilitate impregnation with Ti(NMe(2))(4) and minimizes reactions between the TiN precursor and the hydroxyl groups on the surface of SBA-15. Formation of TiN nanoparticles inside the mesoporous channels of SBA-15 was carried out by subsequent ammonolysis at high temperatures (700-750 degrees C). The final products have been characterized by TEM and EELS images, powder XRD patterns, FTIR spectra, UV-vis absorption spectra, and nitrogen adsorption isotherm measurements to confirm the presence and distribution of TiN nanoparticles in the SBA-15 samples.

Journal Article↗

PubMed2005

Engineering of vault nanocapsules with enzymatic and fluorescent properties.

One of the central issues facing the emerging field of nanotechnology is cellular compatibility. Nanoparticles have been proposed for diagnostic and therapeutic applications, including drug delivery, gene therapy, biological sensors, and controlled catalysis. Viruses, liposomes, peptides, and synthetic and natural polymers have been engineered for these applications, yet significant limitations continue to prevent their use. Avoidance of the body's natural immune system, lack of targeting specificity, and the inability to control packaging and release are remaining obstacles. We have explored the use of a naturally occurring cellular nanoparticle known as the vault, which is named for its morphology with multiple arches reminiscent of cathedral ceilings. Vaults are 13-MDa ribonucleoprotein particles with an internal cavity large enough to sequester hundreds of proteins. Here, we report a strategy to target and sequester biologically active materials within the vault cavity. Attachment of a vault-targeting peptide to two proteins, luciferase and a variant of GFP, resulted in their sequestration within the vault cavity. The targeted proteins confer enzymatic and fluorescent properties on the recombinant vaults, both of which can be detected by their emission of light. The modified vaults are compatible with living cells. The ability to engineer vault particles with designed properties and functionalities represents an important step toward development of a biocompatible nanocapsule.

Biological Transport, Active↗

PubMed2005

Multiply doped nanostructured silicate sol-gel thin films: spatial segregation of dopants, energy transfer, and distance measurements.

Physical and chemical strategies that place designed molecules in spatially separated regions of surfactant-templated mesostructured silicate thin films are used to prepare films containing rhodamine 6G (R6G), lanthanide complexes, and both simultaneously. Fluorescence and photoexcitation spectra of R6G in amorphous and structured thin films show that it is located inside the surfactant micelles of structured thin films. A silylated ligand that binds lanthanides condenses to form part of the silica framework and causes the lanthanide to localize in the silica. Luminescence and photoexcitation spectra show that energy transfer from the metal complex to R6G occurs in the films. R6G quenches Tb emission in a concentration-dependent manner. Energy transfer efficiency is calculated using the Tb luminescence lifetime, and this quantity is used to calculate the distance between Tb and R6G with the aid of Forster theory.

Journal Article↗

PubMed2005

Excited-state mixed valence in a diphenyl hydrazine cation: Spectroscopic consequences of coupling and transition dipole moment orientation.

A quantitative model of mixed-valence excited-state spectroscopy is developed and applied to 2,3-diphenyl-2,3-diazabicyclo[2.2.2]octane. The lowest-energy excited state of this molecule arises from a transition from the ground state, where the charge is located on the hydrazine bridge, to an excited state where the charge is associated with one phenyl group or the other. Coupling splits the absorption band into two components with the lower-energy component being the most intense. The sign of the coupling, derived by using a neighboring orbital model, is positive. The transition dipole moments consist of parallel and antiparallel vector components, and selection rules for each are derived. Bandwidths are caused by progressions in totally symmetric modes determined from resonance Raman spectroscopic analysis. The absorption, emission, and Raman spectra are fit simultaneously with one parameter set.

Cations↗