Biomedical subjects

Kenneth S Suslick

Publications and source records attributed to Kenneth S Suslick.

31 records · Page 2Linked to original sources

PubMed2005

Microporous porphyrin solids.

Metalloporphyrins are exceedingly useful building blocks for the design and synthesis of molecularly based solids. The use of hydrogen bonding or metal ion coordination provides a wide range of framework solids. Using various polyfunctionalized porphyrins, we have created porous solids that are thermally robust and that retain their internal porosity upon loss of solvates. Their pore dimensions are comparable to zeolites, and they show shape and size selectivity in sorption of guest molecules and in epoxidation of alkenes.

Crystallography, X-Ray↗

PubMed2004

High velocity interparticle collisions driven by ultrasound.

Ultrasonic irradiation of slurries produces high velocity impacts between solid metal particles that are sufficient to cause interparticle melting. Sonication of 5 mum Zn powder as a slurry in alkanes, for example, produces dense agglomerates 50 mum in diameter consisting of approximately 1000 fused particles. Particle size was found to be the most influential parameter in inducing local melting during interparticle collisions. Ultrasonic irradiation of mixed powders resulted in formation of agglomerates with larger Zn particles "soldered" by the smaller ones. A simple kinematic model of the ultrasound-driven interparticle fusion predicts a melting criterion that is nonmonotonically dependent on particle size and is shown to be in agreement with experiment.

Journal Article↗

PubMed2004

An optoelectronic nose: "seeing" smells by means of colorimetric sensor arrays.

A new approach to general sensors for odors and volatile organic compounds (VOCs) using thin films of chemically responsive dyes as a colorimetric sensor array is described. This optoelectronic "nose," by using an array of multiple dyes whose colors change based on the full range of intermolecular interactions, provides enormous discriminatory power among odorants in a simple device that can be easily digitally imaged. High sensitivities (ppb) have been demonstrated for the detection of biologically important analytes such as amines, carboxylic acids, and thiols. By the proper choice of dyes and substrate, the array can be made essentially nonresponsive to changes in humidity.

Biosensing Techniques↗

PubMed2003

A robust microporous zinc porphyrin framework solid.

A robust microporous zinc(II) metalloporphyrin framework solid has been synthesized. The proposed structural model developed from X-ray single crystal data has an interpenetrated three-dimensional framework of zinc trans-biscarboxylate tetraarylporphyrins whose carboxylates coordinate the six edges of tetrahedral Zn(4)O(6+) clusters, maintaining a charge-neutral framework. This cubic framework has 74% free volume and 4 x 7 A pores. N(2) adsorption gives a type I isotherm with a surface area of 800 m(2)/g, which is greater than that of a typical zeolite. Experimental evidence indicates that the interpenetrated frameworks of the evacuated solid remain intact and retain a microporous structure. This is a versatile framework system: alteration of the metal in the porphyrin may create a catalytically active solid, and modification of the 10-, 20-substituents of the porphyrin can provide control over both the polarity and the size of the pores.

Crystallography, X-Ray↗

PubMed2003

Molecular imprinting inside dendrimers.

Synthetic hosts capable of binding porphyrins have been produced by a mixed-covalent-noncovalent imprinting process wherein a single binding site is created within cross-linked dendrimers. Two synthetic hosts were prepared, using as templates 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin and 5,10,15,20-tetrakis(3,5-dihydroxyphenyl)porphyrin. These two templates were esterified with, respectively, fourth- and third-generation Fréchet-type dendrons containing homoallyl end-groups. The resulting tetra- and octadendron macromolecules underwent the ring-closing metathesis reaction using Grubbs' Type I catalyst, RuCl(2)(P(C(6)H(5))(3))(2)(CHCH(2)C(6)H(5)), to give extensive interdendron cross-linking. Hydrolytic removal of the porphyrin cores afforded imprinted hosts whose ability to bind porphyrins with various peripheral substituents was investigated by UV-visible spectrophotometric titrations and size exclusion chromatography. The results indicate a high yield of imprinted sites that show high selectivity for binding of porphyrins capable of making at least four hydrogen bonds, but only a moderate degree of shape selectivity.

Binding Sites↗

PubMed2003

De novo designed cyclic-peptide heme complexes.

The structural characterization of de novo designed metalloproteins together with determination of chemical reactivity can provide a detailed understanding of the relationship between protein structure and functional properties. Toward this goal, we have prepared a series of cyclic peptides that bind to water-soluble metalloporphyrins (FeIII and CoIII). Neutral and positively charged histidine-containing peptides bind with a high affinity, whereas anionic peptides bind only weakly to the negatively charged metalloporphyrin. Additionally, it was found that the peptide becomes helical only in the presence of the metalloporphyrin. CD experiments confirm that the metalloporphyrin binds specific cyclic peptides with high affinity and with isodichroic behavior. Thermal unfolding experiments show that the complex has "native-like" properties. Finally, NMR spectroscopy produced well dispersed spectra and experimental restraints that provide a high-resolution solution structure of the complexed peptide.

Amino Acid Sequence↗

PubMed2003

Sonochemistry and sonoluminescence of room-temperature ionic liquids.

The sonication of ionic organic liquids leads to decomposition of the liquids. Multibubble sonoluminescence spectra and headgas analysis reveal a variety of decomposition products from the sonolysis of N,N'-dialkylimidazolium ionic liquids. The decomposition is a result of acoustic cavitation, which generates localized hot spots from the implosive collapse of bubbles in the ionic liquids. Despite the negligible vapor pressure of the ionic liquids, reaction still occurs in a heated shell of the bubbles or from microdroplets thrown into the collapsing bubbles.

Journal Article↗

PubMed2003

Engineered microsphere contrast agents for optical coherence tomography.

Contrast agents are utilized in virtually every imaging modality to enhance diagnostic capabilities. We introduce a novel class of optical contrast agent, namely, encapsulating microspheres, that are based not on fluorescence but on scattering nanoparticles within the shell or core. The agents are suitable for reflection- or scattering-based techniques such as optical coherence tomography, light microscopy, and reflectance confocal microscopy. We characterize the optical properties of gold-, melanin-, and carbon-shelled contrast agents and demonstrate enhancement of optical coherence tomography imaging after intravenous injection of such an agent into a mouse.

Animals↗

PubMed2003

Is the olfactory receptor a metalloprotein?

The sense of smell is arguably our most primal faculty and also the least understood. Even our own olfactorily impaired species is capable of detecting approximately 10,000 distinct scents [Buck, L. & Axel, R. (1991) Cell 65, 175-187]. To achieve that amazing diversity, mammals have approximately 1,000 olfactory genes, which accounts for approximately 3% of their entire genome [Mombaerts, P. (1999) Science 286, 707-711]. The olfactory receptors (ORs) are believed to be seven-helix transmembrane proteins, with an odorant-binding site on the periplasmic domain and a G protein-binding site on the cytoplasmic domain. Odorants first bind to an OR, which then undergoes some structural change that triggers the G protein activation and the following cascade of events leading to nerve cell activity. The structural details of ORs, however, remain to be determined. In this paper, we will describe a hypothesis in which metal ions play an important role for odorant recognition. We analyze the predicted structure and consensus sequence of the ORs and propose a metal-binding site in the loop between fourth and fifth helix (4-5 loop). We have prepared synthetically a pentapeptide that contains this putative binding site and find that it not only has high affinity for binding Cu(II) and Zn(II) ions, but that it also undergoes a dramatic transition to an alpha-helical structure upon metal ion binding. Based on these observations, we propose a "shuttlecock" mechanism for the possible structural change in ORs upon odorant binding. This mechanism involves membrane penetration of the 4-5 loop after residue charge neutralization by metal ion binding.

Amino Acid Sequence↗

PubMed2002

Cyclic and hairpin peptide complexes of heme.

We have synthesized and characterized a new class of heme-peptide complexes using disulfide-linked hairpin-turn and cyclic peptides and compared these to their linear analogues. The binding affinities, helicities, and mechanism of binding of linear, hairpin, and cyclic peptides to [FeIII(coproporphyrin-I)]+ have been determined. In a minimalist approach, we utilize amphiphilic peptide sequences (15-mers), where a central histidine provides heme ligation, and the hydrophobic effect is used to optimize heme-peptide complex stability. We have incorporated disulfide bridges between amphiphilic peptides to make hairpin and even cyclic peptides that bind heme extremely well, roughly 5 x 106 times more strongly than histidine itself. CD studies show that the cyclic peptide heme complexes are completely alpha-helical. NMR spectra of paramagnetic complexes of the peptides show that the 15-mer peptides bind sequentially, with an observable monopeptide, high-spin intermediate. In contrast, the cyclic peptide complexes ligate both imidazoles cooperatively to the heme, producing only a low-spin complex. Electrochemical measurements of the E1/2 of the FeIII(coproporphyrin-I)+ complexes of these peptides are all at fairly low potentials, ranging from -215 to -252 mV versus NHE at pH 7.

Disulfides↗

PubMed2002

Synthetic hosts by monomolecular imprinting inside dendrimers.

Synthetic host systems capable of selectively binding guest molecules are of interest for applications ranging from separations and chemical or biological sensing to the development of biomedical materials. Such host systems can be efficiently prepared by 'imprinting' polymers or inorganic materials with template molecules, which, upon removal, leave behind spatially arranged functional groups that act as recognition sites. However, molecularly imprinted polymers have limitations, including incomplete template removal, broad guest affinities and selectivities, and slow mass transfer. An alternative strategy for moulding desired recognition sites uses combinatorial libraries of assemblies that are made of a relatively small number of molecules, interconverting in dynamic equilibrium; upon addition of a target molecule, the library equilibrium shifts towards the best hosts. Here we describe the dynamic imprinting of dendritic macromolecules with porphyrin templates to yield synthetic host molecules containing one binding site each. The process is based on our general strategy to prepare cored dendrimers, and involves covalent attachment of dendrons to a porphyrin core, cross-linking of the end-groups of the dendrons, and removal of the porphyrin template by hydrolysis. In contrast to more traditional polymer imprinting, our approach ensures nearly homogeneous binding sites and quantitative template removal. Moreover, the hosts are soluble in common organic solvents and amenable to the incorporation of other functional groups, which should facilitate further development of this system for novel applications.

Benzene↗

PubMed2002

The energy efficiency of formation of photons, radicals and ions during single-bubble cavitation.

It is extremely difficult to perform a quantitative analysis of the chemistry associated with multibubble cavitation: unknown parameters include the number of active bubbles, the acoustic pressure acting on each bubble and the bubble size distribution. Single-bubble sonoluminescence (characterized by the emission of picosecond flashes of light) results from nonlinear pulsations of an isolated vapour-gas bubble in an acoustic field. Although the latter offers a much simpler environment in which to study the chemical activity of cavitation, quantitative measurements have been hindered by the tiny amount of reacting gas within a single bubble (typically <10(-13) mol). Here we demonstrate the existence of chemical reactions within a single cavitating bubble, and quantify the sources of energy dissipation during bubble collapse. We measure the yields of nitrite ions, hydroxyl radicals and photons. The energy efficiency of hydroxyl radical formation is comparable to that in multibubble cavitation, but the energy efficiency of light emission is much higher. The observed rate of nitrite formation is in good agreement with the calculated diffusion rate of nitrogen into the bubble. We note that the temperatures attained in single-bubble cavitation in liquids with significant vapour pressures will be substantially limited by the endothermic chemical reactions of the polyatomic species inside the collapsing bubble.

Journal Article↗

PubMed2002

A functional zeolite analogue assembled from metalloporphyrins.

The assembly of molecular building blocks with metal ions generating microporous network solids has been the focus of intense activity. Because of their potential applications associated with channels and cavities, such materials have been examined for size- and shape-selective catalysis, separations, sensors, molecular recognition and nanoscale reactors. Within this context, assemblies of robust and chemically versatile porphyrin and metalloporphyrin building blocks remain rare. Supramolecular architectures of porphyrin solids based on weak van der Waals interactions, hydrogen bonding and metal-ligand coordination networks have been reported. Although there are frequent allusions to zeolite-like microporosity from crystallography and loss of initial guest solvent molecules, evidence of functional microporous behaviour is scarce. We have demonstrated repeatable sorption-desorption with high selectivity on the basis of size, shape and functional group of the sorbate by a microporous metalloporphyrin solid in analogy to zeolites.

Adsorption↗