Improved conductivity of carbon nanotube networks by in situ polymerization of a thin skin of conducting polymer

The overall conductivity of SWNT networks is dominated by the existence of high resistance and tunneling/Schottky barriers at the intertube junctions in the network. Here we report that in situ polymerization of a highly conductive self-doped conducting polymer "skin" around and along single stranded DNA dispersed and functionalized single wall carbon nanotubes can greatly decrease the contact resistance. The polymer skin also acts as "conductive glue" effectively assembling the SWNTs into a conductive network, which decreases the amount of SWNTs needed to reach the high conductive regime of the network. The conductance of the composite network after the percolation threshold can be 2 orders of magnitude higher than the network formed from SWNTs alone.

Structural characterization of the monolayer-multilayer transition in a pulmonary surfactant model: IR studies of films transferred at continuously varying surface pressures

The four-component system acyl chain perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC)/1,2-dipalmitoylphosphatidylglycerol/ (DPPG)/pulmonary surfactant protein SP-C/cholesterol provides a useful model for in vitro biophysical studies of the reversible monolayer to multilayer transition that occurs during compression <--> expansion cycles in the lung. Monolayer films of this mixture (with chain perdeuterated DPPC-d62) at the air/water interface have been transferred to solid substrates under conditions of continuously varying surface pressure, an approach termed COVASP (continuously varying surface pressures) (Langmuir 2007, 23, 4958). The thermodynamic properties of the Langmuir films have been examined with pressure-area isotherms, while the molecular properties of the film constituents in the transferred films in the monolayer and multilayer phases have been examined with IR spectroscopy. Quantitative intensity measurements of the DPPC-d62, DPPG, and SP-C components in each phase reveal that the DPPG and SP-C constituents are relatively enriched in the multilayer compared with the DPPC-d62, although all three species are present in both phases. Some molecular structure information is available from the surface-pressure-induced variation in IR parameters. The DPPC-d62 exhibits slightly increased conformational order in the multilayer phase as detected from decreases in the CD2 stretching frequencies upon compression, while the lipid phosphate residues become dehydrated, as deduced from increases in the 1245 cm-1 symmetric PO2- stretching frequency. A small increase is observed in the protein amide I frequency; possible interpretations of these changes are presented. The current observations are compared with ideas contained in the "squeeze-out hypothesis" (Handbook of Physiology, The Respiratory System; American Physiological Society Press: Bethesda, MD, 1986; Vol. III, p 247) and in the "liquid crystalline collapse" model (Biophys. J. 2003, 84, 3792). Within the limitation of the current procedures, the data contain elements from both these descriptions of the monolayer transformation. Extensions and possible limitations of the COVASP-IR method are discussed.

Complex N-glycan and metabolic control in tumor cells

Golgi beta1,6N-acetylglucosaminyltransferase V (Mgat5) produces beta1,6GlcNAc-branched complex N-glycans on cell surface glycoproteins that bind to galectins and promote surface residency of glycoproteins, including cytokine receptors. Carcinoma cells from polyomavirus middle T (PyMT) transgenic mice on a Mgat5-/- background have reduced surface levels of epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) receptors and are less sensitive to acute stimulation by cytokines in vitro compared with PyMT Mgat5+/+ tumor cells but are nonetheless tumorigenic when injected into mice. Here, we report that PyMT Mgat5-/- cells are reduced in size, checkpoint impaired, and following serum withdrawal, fail to down-regulate glucose transport, protein synthesis, reactive oxygen species (ROS), and activation of Akt and extracellular signal-regulated kinase. To further characterize Mgat5+/+ and Mgat5-/- tumor cells, a screen of pharmacologically active compounds was done. Mgat5-/- tumor cells were comparatively hypersensitive to the ROS inducer 2,3-dimethoxy-1,4-naphthoquinone, hyposensitive to tyrosine kinase inhibitors, to Golgi disruption by brefeldin A, and to mitotic arrest by colcemid, hydroxyurea, and camptothecin. Finally, regulation of ROS, glucose uptake, and sensitivities to EGF and TGF-beta were rescued by Mgat5 expression or by hexosamine supplementation to complex N-glycan biosynthesis in Mgat5-/- cells. Our results suggest that complex N-glycans sensitize tumor cells to growth factors, and Mgat5 is required to balance responsiveness to growth and arrest cues downstream of metabolic flux.

Tracking the dephosphorylation of resveratrol triphosphate in skin by confocal Raman microscopy

Polyphenolic resveratrol has been identified as a potent antioxidant acting as both a free radical scavenger and an inhibitor of enzyme oxidative activity. However, the reactive propensity of resveratrol also limits its use in topical formulations. A transient derivative of resveratrol, resveratrol triphosphate, has been designed to provide a means for the delayed delivery of the active compound in skin tissue where endogenous enzymes capable of dephosphorylation reside. Confocal Raman microscopy studies of intact pigskin biopsies treated with modified resveratrol provided information about the spatial distribution and time-dependence of permeation and conversion to the native active form. Conversion to the active form was not observed when skin samples were exposed to steam, a procedure that likely inactivates endogenous skin enzymes. In addition, treatment with the triphosphate compared to the parent compound revealed a more homogeneous distribution of resveratrol throughout the stratum corneum and viable epidermis when the former was applied. Thus, the bioavailability of resveratrol in the epidermis appears to be enhanced upon application of the pro-molecule compared to resveratrol.

FTIR studies of collagen model peptides: complementary experimental and simulation approaches to conformation and unfolding

X-ray crystallography of collagen model peptides has provided high-resolution structures of the basic triple-helical conformation and its water-mediated hydration network. Vibrational spectroscopy provides a useful bridge for transferring the structural information from X-ray diffraction to collagen in its native environment. The vibrational mode most useful for this purpose is the amide I mode (mostly peptide bond C=O stretch) near 1650 cm-1. The current study refines and extends the range of utility of a novel simulation method that accurately predicts the infrared (IR) amide I spectral contour from the three-dimensional structure of a protein or peptide. The approach is demonstrated through accurate simulation of the experimental amide I contour in solution for both a standard triple helix, (Pro-Pro-Gly)10, and a second peptide with a Gly --> Ala substitution in the middle of the chain that models the effect of a mutation in the native collagen sequence. Monitoring the major amide I peak as a function of temperature gives sharp thermal transitions for both peptides, similar to those obtained by circular dichroism spectroscopy, and the Fourier transform infrared (FTIR) spectra of the unfolded states were compared with polyproline II. The simulation studies were extended to model early stages of thermal denaturation of (Pro-Pro-Gly)10. Dihedral angle changes suggested by molecular dynamics simulations were made in a stepwise fashion to generate peptide unwinding from each end, which emulates the effect of increasing temperature. Simulated bands from these new structures were then compared to the experimental bands obtained as temperature was increased. The similarity between the simulated and experimental IR spectra lends credence to the simulation method and paves the way for a variety of applications.

Control of T Cell-mediated autoimmunity by metabolite flux to N-glycan biosynthesis

Autoimmunity is a complex trait disease where the environment influences susceptibility to disease by unclear mechanisms. T cell receptor clustering and signaling at the immune synapse, T cell proliferation, CTLA-4 endocytosis, T(H)1 differentiation, and autoimmunity are negatively regulated by beta1,6GlcNAc-branched N-glycans attached to cell surface glycoproteins. Beta1,6GlcNAc-branched N-glycan expression in T cells is dependent on metabolite supply to UDP-GlcNAc biosynthesis (hexosamine pathway) and in turn to Golgi N-acetylglucosaminyltransferases Mgat1, -2, -4, and -5. In Jurkat T cells, beta1,6GlcNAc-branching in N-glycans is stimulated by metabolites supplying the hexosamine pathway including glucose, GlcNAc, acetoacetate, glutamine, ammonia, or uridine but not by control metabolites mannosamine, galactose, mannose, succinate, or pyruvate. Hexosamine supplementation in vitro and in vivo also increases beta1,6GlcNAc-branched N-glycans in naïve mouse T cells and suppresses T cell receptor signaling, T cell proliferation, CTLA-4 endocytosis, T(H)1 differentiation, experimental autoimmune encephalomyelitis, and autoimmune diabetes in non-obese diabetic mice. Our results indicate that metabolite flux through the hexosamine and N-glycan pathways conditionally regulates autoimmunity by modulating multiple T cell functionalities downstream of beta1,6GlcNAc-branched N-glycans. This suggests metabolic therapy as a potential treatment for autoimmune disease.

Maturational changes in dentin mineral properties

In this study the changes in properties of the maturing mantle and circumpulpal dentin were quantitatively analyzed. Sections from six fetal bovine undecalcified incisors were used. Regions of mantle and circumpulpal dentin of sequential maturation stages were identified on spectroscopic images acquired by Fourier Transform Infrared Imaging. Spectroscopic parameters corresponding to mineral properties at these stages were analyzed and reported as a function of distance from the cervix of the incisor, the latter representing tissue age. Mineral parameters were correlated with distance from the cervix. Values of these parameters in mantle and circumpulpal dentin were compared. A multi-phasic pattern of changes was found for all the parameters examined, with most of the alterations occurring in the initial maturation period. The patterns of temporal variation in mantle and circumpulpal dentin mineral properties show distinct developmental stages and were not identical for the two dentin compartments. The study showed that mineral maturation in dentin is not a linear process and that mantle dentin is developmentally distinct from circumpulpal dentin, presenting at certain stages different physicochemical events during the maturation of the tissue.

Langmuir-Blodgett films formed by continuously varying surface pressure. Characterization by IR spectroscopy and epifluorescence microscopy

Monolayer films of phospholipids at the air-water interface have been transferred to solid substrates under conditions of continuously varying surface pressure, an approach termed COVASP. The molecular and supramolecular properties of the film constituents have been characterized with two complementary techniques. IR spectroscopy was used to monitor chain conformation as a function of transfer surface pressure. Results were compared to those from Langmuir films determined directly at the A/W interface by IR reflection-absorption spectroscopy (IRRAS). The methylene stretching frequencies for both proteated and acyl chain perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC and DPPC-d62) in the transferred molecules indicate that the phospholipids retain at least, in part, their surface pressure-dependent chain-conformational order characteristics. The line widths of these modes are somewhat reduced, suggestive of slower rates of reorientational motion in the Langmuir-Blodgett (LB) films. Epifluorescence microscopy reveals a progressive condensation gradient, including nucleation and growth of probe-excluding condensed domains along the transfer line. DPPC condensation, observed along a single LB film, was qualitatively comparable to compression-driven condensation as observed in situ or in conventional LB films transferred at constant pressures. However, condensation along the compression isotherm in COVASP-LB films was reduced by 15-20% as compared to films equilibrated at different constant pressures, probably the result of kinetic differences in equilibration processes. As a preliminary demonstration of the utility of this new approach, the monolayer --> multilayer transition known to occur (Eur. Biophys. J. 2005, 34, 243) in a four-component model for pulmonary surfactant has been examined. IR parameters from both the lipid and the protein constituents of the film all indicate that the transition persists during the transfer process. This new approach for the study of transferred films will permit the efficient characterization of lipid-protein interactions and structural transitions occurring in pulmonary surfactant films subjected to dynamic compression.

Studies of the minimum hydrophobicity of alpha-helical peptides required to maintain a stable transmembrane association with phospholipid bilayer membranes

The effects of the hydrophobicity and the distribution of hydrophobic residues on the surfaces of some designed alpha-helical transmembrane peptides (acetyl-K2-L(m)-A(n)-K2-amide, where m + n = 24) on their solution behavior and interactions with phospholipids were examined. We find that although these peptides exhibit strong alpha-helix forming propensities in water, membrane-mimetic media, and lipid model membranes, the stability of the helices decreases as the Leu content decreases. Also, their binding to reversed phase high-performance liquid chromatography columns is largely determined by their hydrophobicity and generally decreases with decreases in the Leu/Ala ratio. However, the retention of these peptides by such columns is also affected by the distribution of hydrophobic residues on their helical surfaces, being further enhanced when peptide helical hydrophobic moments are increased by clustering hydrophobic residues on one side of the helix. This clustering of hydrophobic residues also increases peptide propensity for self-aggregation in aqueous media and enhances partitioning of the peptide into lipid bilayer membranes. We also find that the peptides LA3LA2 [acetyl-K2-(LAAALAA)3LAA-K2-amide] and particularly LA6 [acetyl-K2-(LAAAAAA)3LAA-K2-amide] associate less strongly with and perturb the thermotropic phase behavior of phosphatidylcholine bilayers much less than peptides with higher L/A ratios. These results are consistent with free energies calculated for the partitioning of these peptides between water and phospholipid bilayers, which suggest that LA3LA2 has an equal tendency to partition into water and into the hydrophobic core of phospholipid model membranes, whereas LA6 should strongly prefer the aqueous phase. We conclude that for alpha-helical peptides of this type, Leu/Ala ratios of greater than 7/17 are required for stable transmembrane associations with phospholipid bilayers.

Imaging the prodrug-to-drug transformation of a 5-fluorouracil derivative in skin by confocal Raman microscopy

The widespread adoption of transdermal drug delivery has been limited by the barrier properties of the outermost layer of the epidermis, the stratum corneum (SC). A variety of approaches have been developed to overcome the barrier, including the use of a prodrug form of an active therapeutic agent to enhance transdermal delivery. Once in the epidermis, the pro-molecule is converted to the active drug by endogenous enzymes or simple chemical hydrolysis. The prodrug selected for the current studies, 1-ethyloxycarbonyl-5-fluorouracil, is known to enhance transdermal delivery of 5-fluorouracil, an important systemic antitumor drug. Using confocal Raman microscopy on pigskin biopsies treated with prodrug, we are able to image the spatial distribution of both prodrug and drug in the SC and viable epidermis, thereby providing information about permeation and metabolism. This approach may readily be extended to a variety of dermatological processes.

Vibrational microscopy and imaging of skin: from single cells to intact tissue

Vibrational microscopy and imaging offer several advantages for a variety of dermatological applications, ranging from studies of isolated single cells (corneocytes) to characterization of endogenous components in intact tissue. Two applications are described to illustrate the power of these techniques for skin research. First, the feasibility of tracking structural alterations in the components of individual corneocytes is demonstrated. Two solvents, DMSO and chloroform/methanol, commonly used in dermatological research, are shown to induce large reversible alterations (α-helix to β-sheet) in the secondary structure of keratin in isolated corneocytes. Second, factor analysis of image planes acquired with confocal Raman microscopy to a depth of 70 μm in intact pigskin, demonstrates the delineation of specific skin regions. Two particular components that are difficult to identify by other means were observed in the epidermis. One small region was formed from a conformationally ordered lipid phase containing cholesterol. In addition, the presence of nucleated cells in the tissue (most likely keratinocytes) was revealed by the spectral signatures of the phosphodiester and cytosine moieties of cellular DNA.

Infrared kinetic/structural studies of barrier reformation in intact stratum corneum following thermal perturbation

Stratum corneum, the outermost layer of the epidermis, constitutes the main barrier to permeability in skin. As such, it has been the target of many approaches for transdermal drug delivery based on methods involving transient modifications of the barrier. An infrared (IR) spectroscopic method has been developed to monitor the kinetics of barrier restoration following an external perturbation. In the current case, temperature perturbation was selected as a convenient means to induce structural changes in the barrier. The method is based on the observation that the ordered lipid phases of the barrier in isolated human stratum corneum exist in part in orthorhombically packed subcells. Such phases display a characteristic splitting of the CH2 rocking vibrations with component frequencies at 720 and 729 cm(-1). The latter is reliably diagnostic for orthorhombic phases and is markedly reduced in intensity following a thermal perturbation to 55 degrees C. The kinetics of barrier recovery following quenching to either 25 degrees C or 30 degrees C were monitored by tracking the restoration of the 729 cm(-1) band intensity. The kinetics were dominated by exponential growth in the initial stages, followed by linear increases at longer times. The half lives for exponential growth regimes were 52.4 h for the 25 degrees C quench and 13.8 h for the 30 degrees C quench. These values are in reasonable accord with those determined with more phenomenological approaches, typically based on restoration of some barrier function. This novel method for monitoring structural reorganization kinetics in intact stratum corneum can readily be extended to evaluate barrier recovery following a variety of treatments used to enhance drug delivery.

Surfactant protein C and lung function: new insights into the role of α-helical length and palmitoylation

Surfactant protein C (SP-C) is known to be essential for lung function and the formation of a surface confined reservoir at the alveolar interface. The structural features relevant for the peptide's extraordinary ability to form extended three-dimensional structures were systematically investigated and are summarized in the present paper. The influence of palmitoylation was studied for full length SP-Cs as well as truncated variants with the N-terminal residues 1-17 and 1-13, respectively. The combined results from film balance measurements, fluorescence microscopy (FLM) and scanning force microscopy (SFM) reveal a fine-tuned balance between the influence of the palmitoyl chains and alpha-helical length. Native SP-C added to DPPC/DPPG monolayers (molar ratio 80:20) induced the formation of the surface confined reservoir independent of its palmitoylation degree. However, topographic images revealed that only bilayers and not multilayers where formed when the acyl chains were missing. The influence of palmitoylation increased when alpha-helical length was considerably reduced to 17 or even 13 amino acid residues. In these strongly truncated SP-C peptides palmitoyl chains increased monolayer stability and anchored the peptides in the lipid film. However, no multilayer formation was observed at all for all shortened peptides. The alpha-helix of SP-C seems to be a prerequisite for the formation of extended three-dimensional structures and obviously has to be able to span a lipid bilayer. Palmitoylation obviously mediates interactions between lipids and/or peptides not only within a protein/lipid film but also between neighbouring layers and induces a stacking of bilayers.

In Situ Fabrication of A Water-Soluble, Self-Doped Polyaniline Nanocomposite: The Unique Role of DNA Functionalized Single-Walled Carbon Nanotubes

Dispersion of carbon nanotubes into solvents affects their surface chemistries, electronic structures, and subsequent functionalization. In this Communication, a water-soluble self-doped polyaniline nanocomposite was fabricated by in situ polymerization of the 3-aminophenylboronic acid monomers in the presence of single-stranded DNA dispersed- and functionalized-single-walled carbon nanotubes. For the first time, we found that the carbon nanotubes became novel active stabilizers owing to the DNA functionalization. The nanotubes reduced the polyaniline backbone from the unstable, degradable, fully oxidized pernigraniline state to the stable, conducting emeraldine state because of their reductive ability, which could improve the chemical stability of the self-doped polyaniline. Electrical measurements demonstrate that the conductivity of the nanocomposite was much higher than that of the pure self-doped polyaniline in both acidic and neutral solutions.

Vibrational microspectroscopy and imaging of molecular composition and structure during human corneocyte maturation

The outermost region of the epidermis, the stratum corneum (SC), provides an essential barrier to water loss and protects against exogenous substances. The functional integrity of the SC depends on a complex maturation and exfoliation process, which is often perturbed in skin diseases. The maturation of corneocytes isolated from different depths in healthy human SC was investigated using infrared (IR) spectroscopic imaging and Raman microscopy. Both IR and Raman spectral quality of individual corneocytes was high and revealed depth-dependent variations in molecular composition. Spectral changes were identified as arising from alterations in the concentration of the major constituents of natural moisturizing factor (NMF), important in maintaining SC hydration. A significant decrease in the concentration of NMF was observed for corneocytes isolated from superficial compared to deeper SC layers (layer 3 vs. layer 11, respectively). An IR parameter that measures the relative NMF concentration in corneocytes is introduced. The potential role of vibrational imaging to evaluate corneocyte composition and molecular structure in the treatment of NMF-related diseases is discussed.

Determination of molecular conformation and permeation in skin via IR spectroscopy, microscopy, and imaging

Skin tissue, in addition to its specific use in dermal research, provides an excellent model for developing the techniques of vibrational microscopy and imaging for biomedical applications. In addition to permitting characterization of various regions of skin, the relative paucity of major biological constituents in the stratum corneum (the outermost layer of skin), permits us to image, with microscopic resolution, conformational alterations and concentration variations in both the lipid and protein components. Thus we are able to monitor the effects of exogenous materials such as models for drug delivery agents (liposomes) and permeation enhancers (DMSO) on stratum corneum lipid organization and protein structure. In addition, we are able to monitor protein conformational changes in single corneocytes. The current article demonstrates these procedures, ranging from direct univariate measures of lipid chain conformational disorder, to factor analysis which permits us to image conformational differences between liposomes that have permeated through the stratum corneum from those which have remained on the surface in a reservoir outside the skin.

Kinetics of Membrane Raft Formation: Fatty Acid Domains in Stratum Corneum Lipid Models

The major barrier to permeability in skin resides in the outermost layer of the epidermis, the stratum corneum (SC). The major SC lipid components are ceramides, free fatty acids, and cholesterol. Ternary mixtures containing these constituents are widely used for physicochemical characterization of the barrier. Prior X-ray diffraction and IR spectroscopy studies have revealed the existence of ordered lipid chains packed in orthorhombic subcells. To monitor the kinetics of formation of regions rich in fatty acids, the current study utilizes a modification of the method (J. Phys. Chem. 1992, 96, 10008) developed to monitor component demixing in n-alkane mixtures. The approach is based on changes in the scissoring or rocking mode contours in the IR spectra of (orthorhombically packed) ordered chains. In the current study, equimolar mixtures of ceramides (either non-hydroxy fatty acid sphingosine ceramide or alpha-hydroxy fatty acid sphingosine ceramide) with chain perdeuterated fatty acids (either palmitic or stearic acid) and cholesterol reveal a time evolution of the scissoring contour of the deuterated fatty acid chains following quenching from relatively high temperatures where random mixing occurs. Segregation of domains enriched in the fatty acid component is observed. The kinetics of segregation are sensitive to the quenching temperature and to the chemical composition of the mixture. The kinetic regimes are conveniently catalogued with a power law of the form P=Ktalpha where P is a (measured) property related to domain composition. The time scales for demixing in these experiments are similar to times observed in several studies that have tracked the restoration of the in vivo permeability barrier following nonthermal challenges to SC integrity. Further evidence for the physiological importance of the current measurements is the detection of these phases in native SC. The current work constitutes the first direct, structure-based determination of the kinetics of barrier formation in relevant skin lipid barrier models.

Comparison of mineral quality and quantity in iliac crest biopsies from high- and low-turnover osteoporosis: an FT-IR microspectroscopic investigation

Fourier-transform infrared microspectroscopy (FTIRM) allows analysis of mineral content, mineral crystal maturity and mineral composition at approximately 10-micron spatial resolution. Previous FTIRM analyses comparing 4-micron thick sections from non-decalcified iliac crest biopsies from women with post-menopausal osteoporosis, as contrasted with iliac crest tissue from individuals without evidence of metabolic bone disease, demonstrated significant differences in average mineral content (decreased in osteoporosis) and mineral crystal size/perfection (increased in osteoporosis). More importantly, these parameters, which vary throughout the tissue in relation to the tissue age in healthy bone, showed no such variation in bone biopsies from patients with osteoporosis. The present study compares the spatial and temporal variation in mineral quantity and properties in trabecular bone in high- and low-turnover osteoporosis. Specifically, six biopsies from women (n=5) and one man with high-turnover osteoporosis (age range 39-77) and four women and two men with low turnover osteoporosis (age range 37-63) were compared to ten "normal" biopsies from three men and seven woman (age range: 27-69). "High turnover" was defined as the presence of increased resorptive surface, higher than normal numbers of osteoclasts and greater than or equal to normal osteoblastic activity. "Low turnover" was defined as lower than normal resorptive surface, decreased osteoclast number and less than normal osteoblastic activity. Comparing variations in FTIR-derived values for each of the parameters measured at the surfaces of the trabecular bone to the maximum value observed in multiple trabeculae from each person, the high-turnover samples showed little change in the mineral: matrix ratio, carbonate: amide I ratio, crystallinity and acid phosphate content. The low-turnover samples also showed little change in these parameters, but in contrast to the high-turnover samples, the low-turnover samples showed a slight increase in these parameters, indicative of retarded, but existent resorption and formation. These data indicate that FTIR microspectroscopy can provide quantitative information on mineral changes in osteoporosis that are consistent with proposed mechanisms of bone loss.

Investigation of Iminosulfuranes as Novel Transdermal Penetration Enhancers: Enhancement Activity and Cytotoxicity

PURPOSE

Very few chemical enhancers for transdermal drug delivery have been approved for clinical use due to irritancy and toxicity concerns. Novel chemical enhancers (iminosulfuranes) were synthesized and studied for their activity and toxicity.

METHODS

Skin was treated with 0.4 M 1-5 for 1 h before hydrocortisone was applied. Samples were taken over 24 h and analyzed by high-performance liquid chromatography. Dermal fibroblasts and epidermal keratinocytes were treated with 0-1.2 M 1-5 for 24 h and cytotoxicity assay [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)] was performed. Furthermore, enhancement activity of 0-0.4 M 2 was studied. Partition coefficient of the model drugs into stratum corneum (SC) was measured and confocal Raman microscopy was used to study the penetration process and possible mechanisms of action of the enhancers. Quantitative structure-activity relationship (QSAR) was analyzed to study the contribution of different intramolecular descriptors to enhancement activity.

RESULTS

Iminosulfurane 2 showed the highest enhancement activity. All compounds below 0.2 M were safe to skin cells, and 2 was effective at the concentration of 0.1 and 0.2 M. Mechanisms of action of 2 may include increasing partition coefficient of the model drug into SC and interaction between the enhancer and lipids and protein in the SC. QSAR study indicated contribution of several factors to activity: partition coefficient, hydrogen-bond acceptor, and optimal molecular size.

CONCLUSIONS

Enhancement activity of 2 was achieved without any cytotoxicity.

Infrared spectroscopic characterization of mineralized tissues

Vibrational spectroscopy (Infrared and Raman), and in particular micro-spectroscopy and micro-spectroscopic imaging has been used to characterize developmental changes in bone and other mineralized tissues, to monitor these changes in cell cultures, and to detect disease and drug-induced modifications. Examples of the use of infrared micro-spectroscopy and micro-spectroscopic imaging are discussed in this review.

Infrared analysis of bone in health and disease

Infrared spectroscopy, microspectroscopy, and microspectroscopic imaging have been used to probe the composition and physicochemical status of mineral and matrix of bone in normal and diseased tissues using a series of validated parameters that reflect quantitative and qualitative properties. In this review, emphasis is placed on changes in bone's composition and physiochemical status during osteoporosis and the impact of currently used therapeutics on these parameters, although the impact of infrared microscopy in other pathological states is briefly discussed.

Feasibility of Tracking Phospholipid Permeation into Skin Using Infrared and Raman Microscopic Imaging

The feasibility of monitoring the permeation of chain perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC-d62) and 1-palmitoyl-d31, 2-oleoylphosphatidylcholine (P-d31OPC) vesicles into pigskin using infrared (IR) microscopic imaging and confocal Raman microscopy was demonstrated. The former technique permits the examination of the relative concentration of molecular species (e.g., endogenous and exogenous lipids and proteins) over spatial areas, approximately 1 mm, with a spatial resolution of approximately 10-12 microm. In contrast, Raman microscopy allows the confocal examination of tissue at depths up to 100 microm with a pixel size of about 2-3 microm3. Spectral signal/noise, however, is reduced from IR and significantly smaller areas are generally monitored. The permeation of the gel phase DPPC-d62 was limited to approximately 5-15 microm, whereas the liquid-crystalline phase P-d31OPC permeated to substantially greater depths (35-100 microm), at times ranging up to 24 h after application. The results are generally in accord with literature values. In addition, the state of the P-d31OPC (intact vesicles or molecularly dispersed with skin constituents) was evaluated from the spatial dependence of the deuteriopalmitate chain conformational order. Upon permeation, the chains became more ordered. The advantages and limitations of these imaging technologies are discussed.