Solvent‐tunable morphology and emission of pyrene‐dipeptide organogels

Two pyrene based organogelators in which the pyrene moiety has been linked to the diphenylalanine dipeptide have been synthesized. We show how the solvent can tune both the morphology and the optical properties of the organogels: spherical aggregates with quenched emission were obtained in acetonitrile, whereas an entangled fibrillar network with enhanced emission was formed in o‐dichlorobenzene. Fourier transform infrared spectroscopy, circular dichroism and nuclear magnetic resonance spectroscopy experiments suggest that both π–π stacking and hydrogen bonding contribute to the formation of the supramolecular networks. Ultraviolet–visible and steady state emission studies demonstrated the formation of I‐aggregates in acetonitrile. In contrast, in o‐dichlorobenzene, the formation of J‐type aggregates leads to assemblies with enhanced emission. These results give some insight into the important role of the gelling solvent in the morphology of the supramolecular gels and may help in the design of new soft‐materials. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

A Series of Pyrene‐Substituted Silicon Phthalocyanines as Near‐IR Sensitizers in Organic Ternary Solar Cells

An attractive method to broaden the absorption bandwidth of polymer/fullerene‐based bulk heterojunction (BHJ) solar cells is to blend near infrared (near‐IR) sensitizers into the host system. Axial substitution of silicon phthalocyanines (Pcs) opens a possibility to modify the chemical, thermodynamic, electronic, and optical properties. Different axial substitutions are already designed to modify the thermodynamic properties of Pcs, but the impact of extending the π‐conjugation of the axial ligand on the opto‐electronic properties, as a function of the length of the alkyl spacer, has not been investigated yet. For this purpose, a novel series of pyrene‐substituted silicon phthalocyanines (SiPc‐Pys) with varying lengths of alkyl chain tethers are synthesized. The UV–vis and external quantum efficiency (EQE) results exhibit an efficient near IR sensitization up to 800 nm, clearly establishing the impact of the pyrene substitution. This yields an increase of over 20% in the short circuit current density (J _SC) and over 50% in the power conversion efficiency (PCE) for the dye‐sensitized ternary device. Charge generation, transport properties, and microstructure are studied using different advanced technologies. Remarkably, these results provide guidance for the diverse and judicious selection of dye sensitizers to overcome the absorption limitation and achieve high efficiency ternary solar cells.     

Synthesis and Biophysical Studies of Bis‐Macrocyclic Cobalt/Copper(II) Complexes Having a Pyridine Spacer with CT DNA and 5′‐GMP

New bis‐macrocyclic complexes of Co^III, 1 , Ni^II, 2 , and Cu^II, 3 , containing pyridyl bridges between 13‐membered macrocyclic subunits, have been synthesized via an in situ one‐pot template condensation reaction (IOPTCR). The proposed structures of these new dinuclear complexes are consistent with the data obtained from elemental analysis, molar conductance, IR, EPR, UV/VIS, ¹H‐ and ¹³C‐NMR, and ESI‐MS. The complexes 2 and 3 possess square‐planar geometry with four secondary N‐atoms coordinated to the metal ion, while complex 1 reveals octahedral geometry in solution due to coordinated H₂O molecules. DNA‐Binding properties of the complexes 1 and 3 were investigated by absorption and emission titrations, cyclic voltammetry, and viscosity measurements. Complexes 1 and 3 are strong DNA binders with binding constants, K_b, of 1.64×10⁵ and 2.05×10⁵ M ^?1, respectively. Hyperchromism, decrease in emission intensity of DNA‐bound ethidium bromide (EB), and changes observed in the viscosity and cyclic voltammograms in the presence of added metal complexes reveals that the complexes bind to DNA predominantly by electrostatic attraction, substantiated by absorption titration with 5′‐GMP.     

A comparative study of one- and two-photon absorption properties of pyrene and perylene diimide derivatives

Two important classes of organic molecules, perylene diimide (PDI) and pyrene derivatives have been found to possess relatively excellent photophysical and photochemical properties and especially high two-photon absorption cross sections (δ ^T _max). Herein, one-photon absorption (OPA) and two-photon absorption (TPA) properties of some novel PDI and pyrene derivatives were comparatively investigated by the density functional theory (DFT) and Zerner’s intermediate neglect of differential overlap (ZINDO) methods. The calculated results indicate that with respect to PDI derivatives, the maximum TPA cross-sections for pyrene compounds increase obviously, the maximum peaks of OPA and TPA spectra are blue-shifted, the ΔE _H-L (energy gaps between the highest occupied orbital and the lowest unoccupied orbital) increase. The different π-conjugated bridges (fluorene and pyrene) and terminal groups have slight effect on the OPA properties. Nevertheless, the molecules bearing 1,6-disubstituted pyrene as the π-conjugated bridge display the largest δ ^T _max in both series of compounds 3 and 4. Moreover, the δ ^T _max values of molecules with benzothiazole-substituted terminal groups are larger than those of the molecules with diphenylamine, which is attributed to benzothiazole groups stabilizing the planarity of the branch parts, extending the conjugated length and increasing the π-electron delocalized extent. Furthermore, the molecular size has marked effect on OPA and TPA properties. It is worthy to mention that cruciform 8 displays the largest δ ^T _max among all the studied molecules in the range of 600–1100 nm. This research could provide a better understanding for the origin of the linear and nonlinear optical properties, and it would be helpful to gain more information about designing two-photon absorption materials with large δ ^T _max.     

Synthesis of novel bispyrene diamines and their application as ratiometric fluorescent probes for detection of DNA

Fluorescent DNA probes with 1,6-hexanediyl as the linker between two pyrenes, phenylpyrenes or phenylethynyl pyrene fluorophores were synthesized (Py-1, Py-2 and Py-3) and their interactions with DNA were studied by UV–vis absorption spectra, fluorescence spectra and viscosity measurements. The probes show red-shifted emission compared with pyrene (up to 20 nm). We found the interaction of these probes with DNA can be either intercalation or groove binding. Ratiometric fluorometry (ratio of the monomer and excimer emission intensity versus concentration of DNA) was achieved with these probes for DNA quantification (with limit of detection, LOD, up to 0.1 μg/mL). We also found that the undesired oxygen sensitivity of the emission intensity of pyrene fluorophore can be greatly suppressed by extending the π-conjugation framework of pyrene (the I_Ar/I_air value is decreased from 8.10 for pyrene to less than 2.20 for the DNA probes described herein).     

Synthesis,characterization and sol–gel entrapment of a crown ether‐styryl fluoroionophore

The synthesis and initial evaluation of a new dye‐functionalized crown‐ether, 2‐[2‐(2,3,5,6,8,9,11,12,14,15‐decahydro‐1,4,7,10,13,16‐benzohexaoxacyclooctadecin)ethenyl]‐3‐methyl benzothiazolium iodide (denoted BSD), are reported. This molecule contains a benzyl 18‐crown‐6 moiety as the ionophore and a benzothiazolium to spectrally transduce ion binding. Binding of K⁺ to BSD in methanol causes shifts in the both absorbance and fluorescence emission maxima, as well as changes in the molar absorptivity and the emission intensity. Apparent dissociation constants (K_d) in the range 30–65 µ m were measured. In water and neutral buffer, K_d values were approximately 1 m m . BSD was entrapped in sol–gel films composed of methyltriethoxysilane (MTES) and tetraethylorthosilicate (TEOS) with retention of its spectral properties and minimal leaching. K⁺ binding to BSD in sol–gel films immersed in pH 7.4 buffer causes significant fluorescence quenching, with an apparent response time of approximately 2 min and an apparent K_d of 1.5 m m . Copyright © 2009 John Wiley & Sons, Ltd.     

Reductive dehalogenation of brominated ethenes by Sulfurospirillum multivorans and Desulfitobacterium hafniense PCE‐S

Sulfurospirillum multivorans and Desulfitobacterium hafniense PCE‐S are anaerobes that can utilize tetrachloroethene (PCE) as an electron acceptor in their energy metabolism. The end‐product of PCE reduction for both organisms is cis‐1,2‐dichloroethene, which is formed via trichloroethene as the intermediate. The bacteria were able to dehalogenate cis‐ and trans‐1,2‐dibromoethene (cDBE and tDBE) in growing cultures and cell extracts. Dibromoethene supported growth of both organisms. The organisms debrominated cDBE and tDBE to vinyl bromide (VB); D. hafniense PCE‐S also produced ethene in addition to VB. The PCE reductive dehalogenases (PCE dehalogenases) of S. multivorans and D. hafniense PCE‐S mediated the debromination of tribromoethene (TBE) and both isomers of 1,2‐DBE, indicating that this enzyme was responsible for the reductive dehalogenation of brominated ethenes. cDBE, tDBE, 1,1‐DBE and VB were formed upon TBE debromination; VB was the major end‐product. The PCE dehalogenase of D. hafniense PCE‐S also formed ethene. With the purified enzymes from both organisms the kinetic properties of dehalogenation of brominated alkenes were studied and compared with those of their chlorinated analogues.     

Luminescent properties of a novel fluorene organic material

The photo‐physical properties of 6,6′‐(9H‐fluoren‐9,9‐diyl)bis(2,3‐bis(9,9‐dihexyl‐9H‐fluoren‐2‐yl)quinoxaline) (BFLBBFLYQ) and its blend doped with N′‐biphenyl‐N,N′‐bis‐(3‐methylphenyl)‐1,1′‐biphenyl‐4,4′‐diamine (TPD) were investigated. The absorption, photoluminescence (PL) and electroluminescence (EL) properties of pristine BFLBBFLYQ and blend in solution and spin‐coated film are outlined, including a discussion of charge‐transfer (CT) exciplex emission of BFLBBFLYQ:TPD blend in the solid state. The luminescent properties of BFLBBFLYQ films using different deposition processes were studied. It was found that the low‐energy emission bands at 530–570 nm appeared in the PL spectra of BFLBBFLYQ evaporated films in ultra‐high vacuum. Also, the low‐energy band was the exclusive emission in the EL spectra of BFLBBFLYQ films. Copyright © 2008 John Wiley & Sons, Ltd.     

Self quenching of chlorosome chlorophylls in water and hexanol-saturated water

The optical properties of a methyl ester homolog of bacteriochlorophylld (BChld _M ) and bacteriochlorophyllc (BChlc) in H₂O, hexanol-saturated H₂O and methanol were studied by absorption, fluorescence emission, and circular dichroism (CD). In H₂O, BChld _M spontaneously forms an aggregate similar to that formed in hexane, with absorption maximum at 730 nm and fluorescence emission at 748 nm. For the pigment sample in hexanol-saturated H₂O, while the absorption peaks at 661 nm, only slightly red-shifted compared to the monomer, the fluorescence emission is highly quenched. When diluted 2–3 fold with H₂O, the absorption returns to around 720 nm, characteristic of an aggregate. The CD spectrum of the H₂O aggregate exhibits a derivative-shaped feature with positive and negative peaks, while the amplitude is lower than that of chlorosomes. The Fourier transform infrared spectra of BChld _M aggregates in H₂O and hexane were measured. A 1644 cm^–1 band, indicative of a bonded 13¹-keto group, is detected for both samples. A marker band for 5-coordinated Mg was observed at 1611 cm^–1 for the two samples as well. To study the kinetic behavior of the samples, both single-photon counting (SPC) fluorescence and transient absorption difference spectroscopic measurements were performed. For BChld _M in hexanol-saturated H₂O, a fast decay component with a lifetime of 10 to 14 ps was detected using the two different techniques. The fast decay could be explained by the concentration quenching phenomenon due to a high local pigment concentration. For the pigment sample in H₂O, SPC gave a 16 ps component, whereas global analysis of transient absorption data generated two fast components: 3.5 and 26 ps. The difference may arise from the different excitation intensities. With a much higher excitation in the latter measurements, other quenching processes, e.g. annihilation, might be introduced, giving the 3.5 ps component. Finally, atomic force microscopy was used to examine the ultrastructure of BChld _M in H₂O and hexanol-saturated H₂O. Pigment clusters with diameters ranging from 15 to 45 nm were observed in both samples.     

Role of caffeine in DNA recognition of a potential food‐carcinogen benzo[a]pyrene and UVA induced DNA damage

Electron transfer (ET) reactions are important for their implications in both oxidative and reductive DNA damages. The current contribution investigates the efficacy of caffeine, a xanthine alkaloid in preventing UVA radiation induced ET from a carcinogen, benzo[a]pyrene (BP) to DNA by forming stable caffeine–BP complexes. While steady‐state emission and absorption results emphasize the role of caffeine in hosting BP in aqueous medium, the molecular modeling studies propose the energetically favorable structure of caffeine–BP complex. The picosecond‐resolved emission spectroscopic studies precisely explore the caffeine‐mediated inhibition of ET from BP to DNA under UVA radiation. The potential therapeutic activity of caffeine in preventing DNA damage has been ensured by agarose gel electrophoresis. Furthermore, time‐gated fluorescence microscopy has been used to monitor caffeine‐mediated exclusion of BP from various cell lines including squamous epithelial cells, WI‐38 (fibroblast), MCF‐7 (breast cancer) and HeLa (cervical cancer) cells. Our in vitro and ex vivo experimental results provide imperative evidences about the role of caffeine in modified biomolecular recognition of a model carcinogen BP by DNA resulting dissociation of the carcinogen from various cell lines, implicating its potential medicinal applications in the prevention of other toxic organic molecule induced cellular damages. Copyright © 2014 John Wiley & Sons, Ltd.     

Oligomeric fluorescent labels for DNA

In an effort to find fluorescent labels that have large Stokes shifts and increased emission intensity, a strategy for fluorescence labeling of DNA was explored in which multiple individual fluorophores are incorporated at adjacent positions at the end of a DNA probe. To encourage close interactions, hydrocarbon and heterocycle fluorophores were substituted at C-1 of deoxyribose, replacing the DNA base. The C-glycosides studied contained the well-known fluorophores terphenyl, pyrene, and terthiophene. For comparison, a commercial fluorescein-dU nucleotide was examined. Oligomeric labels containing up to five fluorophores were tested. Interestingly, all four dyes behaved differently on multiple substitution. Fluorescein displayed strong self-quenching properties, with the quantum yield dropping severalfold with each additional substitution and with a constant, small Stokes shift. In contrast, pyrene showed increases in quantum yield on addition of more than one fluorophore and yielded efficient long-wavelength emission on multiple substitution, with Stokes shifts of >130 nm. Oligomeric terphenyl labels gave a small progressive red shift in absorption and a marked red shift in emission wavelength and showed a strong increase in brightness with more monomers. Finally, terthiophene oligomers showed self-quenching combined with increasing Stokes shifts. Overall, the results suggest that some oligomeric fluorescent labels exhibit properties not available in common fluorescein class (or other commercial) labels, such as large Stokes shifts and increasing brightness with increasing substitution.     

Thermoluminescence and photoluminescence studies on γ‐ray‐irradiated Ce3+,Tb3+‐doped potassium chloride single crystals

Single crystals of KCl doped with Ce³⁺,Tb³⁺ were grown using the Bridgeman–Stockbarger technique. Thermoluminescence (TL), optical absorption, photoluminescence (PL), photo‐stimulated luminescence (PSL), and thermal‐stimulated luminescence (TSL) properties were studied after γ‐ray irradiation at room temperature. The glow curve of the γ‐ray‐irradiated crystal exhibits three peaks at 420, 470 and 525 K. F‐Light bleaching (560 nm) leads to a drastic change in the TL glow curve. The optical absorption measurements indicate that F‐ and V‐centres are formed in the crystal during γ‐ray irradiation. It was attempted to incorporate a broad band of cerium activator into the narrow band of terbium in the KCl host without a reduction in the emission intensity. Cerium co‐doped KCl:Tb crystals showed broad band emission due to the d–f transition of cerium and a reduction in the intensity of the emission peak due to ⁵D₃–⁷F_j (j = 3, 4) transition of terbium, when excited at 330 nm. These results support that energy transfer occurs from cerium to terbium in the KCl host. Co‐doping Ce³⁺ ions greatly intensified the excitation peak at 339 nm for the emission at 400 nm of Tb³⁺. The emission due to Tb³⁺ ions was confirmed by PSL and TSL spectra. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and optical properties of alloyed ZnxCd1‐xS/alginate core/shell nanoparticles

Zn_xCd_1‐xS/alginate core/shell nanoparticles were synthesized via a colloidal route by reacting zinc and cadmium ions with sulfide ions, followed by coating with alginate. The crystal structure, morphology, size and optical properties of the core/shell nanoparticles were characterized by X‐ray diffraction, transmission electron microscopy, UV/vis and photoluminescent spectra, respectively. The Zn_xCd_1‐xS nanoparticles are spherical and have a cubic structure with a mean crystalline size of 2–4 nm. The band gap of Zn_xCd_1‐xS/alginate core/shell nanoparticles increases with increasing Zn/Cd molar ratio, and the UV/vis absorption blue‐shifts correspondingly. Two emissions related to zinc and sulfide ion vacancies were observed for the Zn_xCd_1‐xS/alginate core/shell nanoparticles due to the surface changes from the alginate coating. A cadmium‐related emission was observed for both the uncovered Zn_xCd_1‐xS and Zn_xCd_1‐xS/alginate core/shell nanoparticles, which has a significant blue‐shift with increasing Zn/Cd molar ratio. Copyright © 2014 John Wiley & Sons, Ltd.     

Assessment of spectroscopic parameters of solvated Eu(dmh)3phen organometallic complex in various basic and acidic solvents

We report on the comprehension of novel europium activated hybrid organic Eu(dmh)₃phen (Eu: europium, dmh: 2,6‐dimethyl‐3,5‐heptanedione, phen: 1,10 phenanthroline) organo‐metallic complexes, synthesized at different pH values by the solution technique. Photo physical properties of these complexes in various basic and acidic solvents were probed by UV–vis optical absorption and photoluminescence (PL) spectra. Minute differences in optical absorption peaks with variable optical densities were encountered with the variation in solvent from basic (chloroform, toluene, tetrahydrofuran) to acidic (acetic acid) media, revealing bathochromic shift in the absorption peaks. The PL spectra of the complex in various acidic and basic organic solvents revealed the position of the emission peak at 613 nm irrespective of the changes in solvents whereas the excitation spectrum almost matched with that of the UV–vis absorption data. The optical density was found to be maximum for the complex with pH 7.0 whereas it gradually decreased when pH was lowered to 6.0 or raised to 8.0 at an interval of 0.5, demonstrating its pH sensitive nature. Several spectroscopic parameters related to probability of transition such as absorbance A(λ), Napierian absorption coefficient α(λ), molecular absorption cross‐section σ(λ), radiative lifetime (τ₀) and oscillator strength (f) were calculated from UV–vis spectra. The relative intensity ratio (R‐ratio), calculated from the emission spectra was found to be almost the same in all the organic solvents. The optical energy gap, calculated for the designed complexes were found to be well in accordance with the ideal acceptance value of energy gap of the emissive materials used for fabrication of red organic light‐emitting diode (OLED). The relation between Stoke's shift and solvent polarity function was established by Lippert–Mataga plot. This remarkable independence of the electronic absorption spectra of Eu complexes on the nature of the solvent with unique emission wavelength furnishes its potential to serve as a red light emitter for solution processed OLEDs, display panels and solid‐state lighting.     

One‐Pot Solvent Free Synthesis and DNA Binding Studies of Thieno[2,3‐b]‐1,8‐Naphthyridines

Abstract

With the aim of evaluating interaction between double‐stranded calf thymus (ds)DNA and sulphur containing fused planar rings, the derivatives of 1,8‐naphthyridine containing thiono groups were synthesized by the condensation of 2‐mercapto‐3‐formyl[1,8]naphthyridines using 1‐chloroacetone, 2‐chloroacetamide, chloroaceticacid, and 2‐chloro‐1‐phenylethanone in the presence of anhydrous potassium carbonate as s catalyst under solvent free microwave irradiation. The structures of the compounds were elucidated on the basis of elemental analysis, IR, ¹H NMR, and mass spectra. The interaction of thieno[2,3‐b]‐1,8‐naphthyridine‐2‐carboxylic acid (TNC) (3a) with ct‐DNA was studied by UV‐Vis spectrophotometry, viscosity, thermal denaturation, as well as cyclic voltammetry experiments. On binding to DNA, the absorption spectrum underwent bathochromic and hypochromic shifts. Binding parameters, determined from spectrophotometric measurements indicated a binding constant of K _b =2.1×10⁶ M^?1. The thieno[2,3‐b]‐1,8‐naphthyridine‐2‐carboxylic acid (3a) increases the viscosity of sonicated rod‐like DNA fragments. The binding of TNC to DNA increased the melting temperature by about 4°C. The decrease in peak current heights and shifts of peak potential values are observed by the addition of calf thymus DNA in cyclic voltammetry studies.     

Hybridization of European oaks (Quercus ilex × Q. robur) results in a mixed isoprenoid emitter type

European oaks have been reported to emit isoprene or monoterpenes derived from recently fixed photosynthetic carbon. The emission type is plant species specific and can be used as chemo‐taxonomic marker. In the present article the isoprenoid biochemical properties of mature Quercus × turneri‘Pseudoturneri’ hybrids resulting from a crossing of a Mediterranean evergreen monoterpene‐emitting species (subgenus Sclerophyllodrys; Quercus ilex L.) and an isoprene‐emitting deciduous oak species (subgenus Lepidobalanus; Quercus robur L.) are described. Both species are compared with respect to the capacity for isoprenoid synthesis and the actual isoprenoid emission pattern of different tree‐types. The analysis showed that the oak hybrid combines properties of both parental species. Furthermore, it could be shown that the enzyme activities of isoprene synthase and monoterpene synthases are reflected in the isoprenoid emission pattern of the hybrids as well as in the observed emission rates.     

The structure of a far‐red fluorescent protein,AQ143, shows evidence in support of reported red‐shifting chromophore interactions

Engineering fluorescent proteins (FPs) to emit light at longer wavelengths is a significant focus in the development of the next generation of fluorescent biomarkers, as far‐red light penetrates tissue with minimal absorption, allowing better imaging inside of biological hosts. Structure‐guided design and directed evolution have led to the discovery of red FPs with significant bathochromic shifts to their emission. Here, we present the crystal structure of one of the most bathochromically shifted FPs reported to date, AQ143, a nine‐point mutant of aeCP597, a chromoprotein from Actinia equina. The 2.19 Å resolution structure reveals several important chromophore interactions that contribute to the protein's far‐red emission and shows dual occupancy of the green and red chromophores.     

Circularly polarized luminescence of helically assembled pyrene π‐stacks on RNA and DNA duplexes

In this report, we describe the circularly polarized luminescence (CPL) of the RNA duplexes having one to four 2′‐O‐pyrene modified uridines ( Upy ) and the DNA duplexes having two, four, and six pyrene modified non‐nucleosidic linkers ( Py ). Both the pyrene π‐stack arrays formed on the RNA and DNA double helical structures exhibited pyrene excimer fluorescence. In the pyrene‐modified RNA systems, the RNA duplex having four Upy s gives CPL emission with g_lum value of <0.01 at 480 nm. The structure of pyrene stacks on the RNA duplex may be rigidly regulated with increase in the Upy domains, which resulted in the CPL emission. In the DNA systems, the pyrene‐modified duplexes containing two and four Pys exhibited CPL emission with g_lum values of <0.001 at 505 nm. The pyrene π‐stack arrays presented here show CPL emission. However, the g_lum values are relatively small when compared with our previous system consisting of the pyrene‐zipper arrays on RNA.     

Controls of the quantum yield and saturation light of isoprene emission in different‐aged aspen leaves

Leaf age alters the balance between the use of end‐product of plastidic isoprenoid synthesis pathway, dimethylallyl diphosphate (DMADP), in prenyltransferase reactions leading to synthesis of pigments of photosynthetic machinery and in isoprene synthesis, but the implications of such changes on environmental responses of isoprene emission have not been studied. Because under light‐limited conditions, isoprene emission rate is controlled by DMADP pool size (S_DMADP), shifts in the share of different processes are expected to particularly strongly alter the light dependency of isoprene emission. We examined light responses of isoprene emission in young fully expanded, mature and old non‐senescent leaves of hybrid aspen (Populus tremula x P. tremuloides) and estimated in vivo S_DMADP and isoprene synthase activity from post‐illumination isoprene release. Isoprene emission capacity was 1.5‐fold larger in mature than in young and old leaves. The initial quantum yield of isoprene emission (α_I) increased by 2.5‐fold with increasing leaf age primarily as the result of increasing S_DMADP. The saturating light intensity (Q_I90) decreased by 2.3‐fold with increasing leaf age, and this mainly reflected limited light‐dependent increase of S_DMADP possibly due to feedback inhibition by DMADP. These major age‐dependent changes in the shape of the light response need consideration in modelling canopy isoprene emission.     

A proton magnetic resonance study of water in human stratum corneum

Proton magnetic resonance spectroscopy has been used to study the nature of water in human stratum corneum. For a single planar sheet of stratum corneum mounted at a specific orientation to the applied magnetic field, three distinct absorptions may be seen having different chemical shifts and spin-lattice relaxation times (T₁). All T₁ values for these resonances are smaller than that for normal liquid water. One absorption is unusual in that the resonance position is dependent upon the orientation of the sample within the field.