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At least 577 records · Page 32Linked to original sources
PubMed2001

Thermodynamic formalism of the harmonic measure of diffusion limited aggregates: phase transition.

We study the nature of the phase transition in the multifractal formalism of the harmonic measure of diffusion limited aggregates. Contrary to previous work that relied on random walk simulations or ad hoc models to estimate the low probability events of deep fjord penetration, we employ the method of iterated conformal maps to obtain an accurate computation of the probability of the rarest events. We resolve probabilities as small as 10(-35). We show that the generalized dimensions D(q) are infinite for q<q*, where q* = -0.18+/-0.04. In the language of f(alpha) this means that alpha(max) is finite. We present a converged f(alpha) curve.

Journal Article↗
PubMed2002

Fluctuation-driven quantum phase transitions in clean itinerant ferromagnets.

The quantum phase transition in clean itinerant ferromagnets is analyzed. It is shown that soft particle-hole modes invalidate Hertz's mean-field theory for d< or =3. A renormalized mean-field theory predicts a fluctuation-induced first order transition for 1<d< or =3, whose stability is analyzed by renormalization group techniques. Depending on microscopic parameter values, the first order transition can be stable, or be preempted by a fluctuation-induced second order transition. The critical behavior at the latter is determined. The results are in agreement with recent experiments.

Journal Article↗
PubMed1986

The effect of pH on the phase transition temperature of dipalmitoylphosphatidylcholine-palmitic acid liposomes.

The shift in the gel-liquid crystal phase transition temperature (tm) of dipalmitoylphosphatidylcholine liposomes induced by incorporation of 10 mol% palmitic acid, was measured by 90 degrees light scattering at different bulk pH values. It has been found that the tm shift decreases sigmoidally from 4.7 to -0.3 degrees C as the bulk pH is raised from 5 to 11. Since it is in this range that the carboxyl group of a membrane-bound fatty acid should ionize, our results can be interpreted to mean that there is relationship between the tm shift and the degree of dissociation of palmitic acid, the uncharged fatty acid increasing tm and its conjugate, anionic form, slightly decreasing the transition temperature of dipalmitoylphosphatidylcholine liposomes. The experimental results are fitted by a modified form of the Henderson-Hasselbach equilibrium expression which takes into account the effect of the anionic fatty acid on the surface potential and hence, on the surface pH of liposomes, according to Gouy-Chapman and Boltzmann equations, respectively. Best fit between theory and experiments is found when the intrinsic interfacial pK of palmitic acid is set equal to 7.7. This high pK value can be explained as due to the effect of the lower dielectric constant of the interfacial region, as compared to bulk water, on the acid-base dissociation of the carboxyl group. The results presented here show that upon incorporation of palmitic acid, the phase transition of dipalmitoylphosphatidylcholine bilayers becomes extremely sensitive to changes of pH in the vicinity of the physiological range. This property is not shown by the pure phospholipid bilayers in the same pH range.

1,2-Dipalmitoylphosphatidylcholine↗
PubMedDate not supplied

[Study of the aqueous phase transition in a collagen--water system by the calorimetric and NMR methods].

Heat capacity and line width of proton magnetic resonance of collagen were studied by means of low-temperature calorimatry and high resolution NMR spectroscopy at different values of moisture in the temperature range of ice-water phase transition. Peculiarities of water phase transition in the presence of biopolymers were revealed. It was shown that a definite part of H2O in the "hydration layers" of the macromolecules (0.35 g of H2O/g of protein) is not transformed into ice even at a temperature decrease up to 4 K. The NMR data show that the total mobility of the bound water molecules remains high enough up to the water concentration at which the inner hydration layer of the macromolecule is formed. After the formation of hydrogen-bound water chains in the hydrate layers of collagen the mobility of the bound water molecules decreases.

Calorimetry↗
PubMed1997

The Valence-Detrapping Phase Transition in a Crystal of the Mixed-Valence Trinuclear Iron Cyanoacetate Complex [Fe(3)O(O(2)CCH(2)CN)(6)(H(2)O)(3)].

A mixed-valence trinuclear iron cyanoacetate complex, [Fe(3)O(O(2)CCH(2)CN)(6)(H(2)O)(3)] (1), was prepared, and the nature of the electron-detrapping phase transition was studied by a multitemperature single-crystal X-ray structure determination (296, 135, and 100 K) and calorimetry by comparison with an isostructural mixed-metal complex, [CoFe(2)O(O(2)CCH(2)CN)(6)(H(2)O)(3)] (2). The mixed-valence states at various temperatures were also determined by (57)Fe Mössbauer spectroscopy. The Mössbauer spectrum of 1 showed a valence-detrapped state at room temperature. With decreasing temperature the spectrum was abruptly transformed into a valence-trapped state around 129 K, well corresponding to the heat-capacity anomaly due to the phase transition (T(trs) = 128.2 K) observed in the calorimetry. The single-crystal X-ray structure determination revealed that 1 has an equilateral structure at 296 and 135 K, and that the structure changes into an isosceles one at 100 K due to the electron trapping. The crystal system of 1 at 296 K is rhombohedral, space group R&thremacr; with Z = 6 and a = 20.026(1) Å, c = 12.292(2) Å; at 135 K, a = 19.965(3) Å, c = 12.145(4) Å; and at 100 K, the crystal system changes into triclinic system, space group P&onemacr;, with Z = 2 and a = 12.094(2) Å, b = 12.182(3) Å, c = 12.208(3) Å, alpha = 110.04(2) degrees, beta = 108.71(2) degrees, gamma = 109.59(2) degrees. The X-ray structure determination at 100 K suggests that the electronically trapped phase of 1 at low temperature is an antiferroelectrically ordered phase, because the distorted Fe(3)O molecules, which are expected to possess a nonzero electronic dipole moment, oriented alternatively in the opposite direction with respect to the center of symmetry. On the other hand, no heat-capacity anomaly was observed in 2 between 7 and 300 K, and X-ray structure determination indicated that 2 shows no structure change when the temperature is decreased from 296 K down to 102 K. The crystal system of 2 at 296 K is rhombohedral, space group R&thremacr; with Z = 6 and a = 19.999(1) Å, c = 12.259(1) Å; at 102 K, a = 19.915(2) Å, c = 12.061(1) Å. Even at 102 K the CoFe(2)O complex still has a C(3) axis, and the three metal ion sites are crystallographically equivalent because of a static positional disorder of two Fe(III) ions and one Co(II) ion. The activation energy of intramolecular electron transfer of 1 in the high-temperature disordered phase was estimated to be 3.99 kJ mol(-)(1) from the temperature dependence of the Mössbauer spectra with the aid of the spectral simulation including the relaxation effect of intramolecular electron transfer. Finally the phase-transition mechanism of 1 was discussed in connection with the intermolecular dielectric interaction.

Journal Article↗
PubMed1998

Expression patterns of cyclin D1 and related proteins regulating G1-S phase transition in uveal melanoma and retinoblastoma.

BACKGROUND/AIMS: A checkpoint mechanism in late G1, whose regulation via loss of retinoblastoma protein (pRB) or p16, or overexpression of cyclin D1 or cyclin dependent kinase 4 (CDK4), has been proposed to constitute a common pathway to malignancy. The aims of this study were (a) to compare markers of cell cycle G1-S phase transition in an intraocular tumour with known pRB deficiency (retinoblastoma) and compare it with one with an apparently functional pRB (uveal melanoma); (b) to determine if one of these markers may have a role in the pathogenesis of uveal melanoma; and (c) to determine if there is a difference in cell cycle marker expression following treatment of uveal melanoma and retinoblastoma. METHODS: 90 eyes were enucleated from 89 patients for retinoblastoma (n = 24) or for choroidal or ciliary body melanoma (n = 66). Conventional paraffin sections were assessed for cell type and degree of differentiation. Additional slides were investigated applying standard immunohistochemical methods with antibodies specific for cyclin D1 protein, pRB, p53, p21, p16, BCL-2, and MIB-1. RESULTS: Cyclin D1 protein and pRB were negative in retinoblastoma using the applied antibodies. In contrast, cyclin D1 protein expression was observed in 65% of uveal melanomas; a positive correlation between cyclin D1 cell positivity and tumour cell type, location, growth fraction, as well as with pRB positivity was observed. p53, p21, and p16 could be demonstrated in both tumours. An inverse relation between p53 and p21 expression was demonstrated in most choroidal melanomas and in some retinoblastomas. Apart from a decrease in the growth fractions of the tumours as determined by MIB-1, a significant difference in the expression of G1-S phase transition markers in vital areas of uveal melanoma and retinoblastoma following treatment with radiotherapy and/or chemotherapy was not observed. CONCLUSION: Retinoblastomas and uveal melanomas, two tumours of differing pRB status, differ also in their immunohistochemical pattern for markers of the G1-S phase transition of the cell cycle. The results of the present study support the concept of (a) an autoregulatory loop between pRB and cyclin D1 in tumours with a functional pRB and the disruption of this loop in the presence of pRB mutation, as well as (b) a checkpoint mechanism in late G1, whose regulation via loss of p16 or pRB, or overexpression of cyclin D1 constitutes a common pathway to malignancy. Further, the results raise the possibility of cyclin D1 overexpression having a role in the pathogenesis of uveal melanoma.

Adolescent↗
PubMed2000

Phase transitions in the common brainstem and related systems investigated by nonstationary time series analysis.

Neuronal activities of the reticular formation (RF) of the lower brainstem and the nucleus tractus solitarii (NTS, first relay station of baroreceptor afferents) were recorded together in the anesthized dog with related parameters of EEG, respiration and cardiovascular system. The RF neurons are part of the common brainstem system (CBS) which participates in regulation and coordination of cardiovascular, respiratory, somatomotor systems, and vigilance. Multiple time series of these physiological subsystems yield useful information about internal dynamic coordination of the organism. Essential problems are nonlinearity and instationarity of the signals, due to the dynamic complexity of the systems. Several time-resolving methods are presented to describe nonlinear dynamic couplings in the time course, particularly during phase transitions. The methods are applied to the recorded signals representing the complex couplings of the physiological subsystems. Phase transitions in these systems are detected by recurrence plots of the instationary signals. The pointwise transinformation and the pointwise conditional coupling divergence are measures of the mutual interaction of the subsystems in the state space. If the signals show marked rhythms, instantaneous frequencies and their shiftings are demonstrated by time frequency distributions, and instantaneous phase differences show couplings of oscillating subsystems. Transient signal components are reconstructed by wavelet packet time selective transient reconstruction. These methods are useful means for analyzing coupling characteristics of the complex physiological system, and detailed analyses of internal dynamic coordination of subsystems become possible. During phase transitions of the functional organization (a) the rhythms of the central neuronal activities and the peripheral systems are altered, (b) changes in the coupling between CBS neurons and cardiovascular signals, respiration and the EEG, and (c) between NTS neurons (influenced by baroreceptor afferents) and CBS neurons occur, and (d) the processing of baroreceptor input at the NTS neurons changes. The results of this complex analysis, which could not be done formerly in this manner, confirm and complete former investigations on the dynamic organization of the CBS with its changing relations to peripheral and other central nervous subsystems.

Action Potentials↗
PubMed2002

Nonequilibrium phase transitions in a model for the origin of life.

The requisites for the persistence of small colonies of self-replicating molecules living in a two-dimensional lattice are investigated analytically in the infinite diffusion or mean-field limit and through Monte Carlo simulations in the position-fixed or contact process limit. The molecules are modeled by hypercyclic replicators A that are capable of replicating via binary fission A+E-->2A with production rate s, as well as via catalytically assisted replication 2A+E-->3A with rate c. In addition, a molecule can degrade into its source materials E with rate gamma. In the asymptotic regime, the system can be characterized by the presence (active phase) and the absence (empty phase) of replicators in the lattice. In both diffusion regimes, we find that for small values of the ratio c/gamma these phases are separated by a second-order phase transition that is in the universality class of the directed percolation, while for small values of s/gamma the phase transition is of first order. Furthermore, we show the suitability of the dynamic Monte Carlo method, which is based on the analysis of the spreading behavior of a few active cells in the center of an otherwise infinite empty lattice, to address the problem of the emergence of replicators. Rather surprisingly, we show that this method allows an unambiguous identification of the order of the nonequilibrium phase transition.

Biophysical Phenomena↗
PubMed2002

Theory of structural transformations in ferrofluids: chains and "gas-liquid" phase transitions.

We consider a ferrofluid consisting of identical spherical particles with a permanent magnetic moment. Under the assumption that linear flexible chains can appear in the ferrofluid, we estimate the distribution function of the number of particles inside the chain. The analysis is done and simple expressions for the size distribution function are obtained in asymptotics of a strong magnetic interaction between the particles inside one chain. We studied the influence of the linear chains on conditions and scenarios of bulk "gas-liquid" phase transition in the ensemble of the particles under an infinitely strong magnetic field. In order to study the influence of the chains on bulk "gas-liquid" phase transition in the ensemble of the particles, their chemical potential mu is calculated in the model of separate interacting particles as well as in the model with chains, taking into account the interaction between them. When the temperature is low enough, van der Waals loops appear on the plots of mu versus volume concentration phi of the particles in the first model; function mu(phi) increases monotonically in the second model for all examined temperatures. This means that the condensation "gas-liquid" phase transition can take place in the model of individual particles; however, formation of the chains in real ferrofluids prevents the appearance of this transition.

Journal Article↗
PubMed2006

Influence of pressure on the electric-field-induced phase transitions in liquid crystals.

Within the framework of Landau-de-Gennes formulation, we analyse the effect of pressure on electric-field-induced phase transitions in a liquid crystal which shows spontaneously an isotropic-smectic A transition. Inferring from the experimental pressure dependences on the layer spacing in smectic A phase, as well as the nematic-smectic A metastable temperature T*(AN), we incorporated the pressure dependence in the free energy through (the surface energy term) and the coupling between the quadrupolar nematic ordering Q(ij) and the smectic order parameter psi. From the S-T phase diagram, we found that the stability of field-induced nematic phase increases with pressure, whereas the discontinuity of the transition decreases. Also, the region where paranematic phase transits directly to smectic A phase increases with pressure.

Electricity↗
PubMed2006

Solid-state phase transition induced by pressure in LiOH x H2O.

When the free energy surface of the lithium hydroxide monohydrate crystal was explored, the high-pressure solid-state phase transition was determined. The high-pressure phase has been obtained through ab initio Car-Parrinello molecular dynamics simulation in the isothermic-isobaric ensemble. The recent metadynamics method has been applied to overcome the high activation energy barriers typical of rare events, like solid-state phase transition at high pressures. In the LiOH x H2O system, there are two kinds of H bonds: water-water and hydroxyl-water. The effect of the pressure has been investigated, to give further insight into the high-pressure phase. The strengthening of the H bonds of the system produces modifications in the water and the hydroxyl ion dipole electronic environment. The infrared spectra of both phases have been calculated and compared with experiments, and the assignment of the external modes has been discussed.

Lithium Compounds↗
PubMed1976

31P NMR studies of unsonicated aqueous dispersions of neutral and acidic phospholipids. Effects of phase transitions, p2H and divalent cations on the motion in the phosphate region of the polar headgroup.

1. The 129 MHz (non-proton decoupled) and 36.4 MHz (proton decoupled) 31P NMR spectra arising from unsonicated aqueous dispersions of well defined species of phospholipid have been investigated. The phospholipids employed (and the parameters varied) include phosphatidylcholine (temperature), phosphatidylethanolamine (temperature), phosphatidic acid (temperature and p2H) and phosphatidylglycerol (temperature, p2H and Ca2+ (or Mg2+)) concentration. 2. At p2H = 7 the 31 P MNR spectra arising from saturated species of phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol become progressively broader as the temperature is reduced below the phase transition, demonstrating reduced motion in the phosphate region of the polar headgroup. 3. In the liquid crystalline state at p2H = 7 the molecular dipolar order parameters obtained for saturated species of phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol and very similar, and are independent of the acyl chain length for species derived from lauric and myristic acid. Thus the motion in the methylene-phosphate-methylene region is similar for these different liquid crystaline phospholipid species. 4. The 31 P NMR spectra of aqueous dispersions of 14:0/14:0 phosphatidic acid display anomalous temperature and p2H dependences. The effective chemical shift anistropy (delta v CSA EFF) at 5 degrees C varies from 71 ppm at p2H = 8.5 to 38 ppm at p2H = 2.5. Further, the motion in the phosphate region is relatively insensitive to the gel or liquid crystalline nature of the hydrocarbon chains. 5. The addition of 40 mol% Ca2+ (or Mg2+) to saturated species of phosphatidylglycerol causes an increase of approx. 20 degrees C in the hydrocarbon phase transition temperature as indicated by 31 P NMR. Equimolar concentrations of Ca2+ increase the transition temperature by approx. 70 degrees C, and no 31P NMR signal could be observed for the very condensed precipitate formed below this temperature. In the liquid crystalline state the motion in the phosphate region of the polar headgroup is not significantly affected by the presence of Ca+ or Mg2+. 6. The 31P NMR spectra obtained from 18 : 1c/18 : 1c phosphatidylethanolamine are consistent with a phase transition from a lamellar to an hexagonal (HII) phase in the region 10-15 degrees C. 7. The observed narrowing of the 31 P NMR spectra of aqueous dispersions of phospholipids as the temperature is raised toward the hydrocarbon transition temperature is discussed in terms of the "pretransition" observed in calorimetric studies.

Binding Sites↗
PubMed1978

Fluorine-19 nuclear magnetic resonance studies of lipid phase transitions in model and biological membranes.

Fluorinated fatty acids of the general formula CH3(CH2)13-mCF2(CH2)m-2COOH are informative spectroscopic probes of the gel to liquid-crystalline phase transitions in phospholipid dispersions and in biological membranes. We present theoretical considerations to suggest that the 19F nuclear magnetic resonance line shapes are very different for frozen and fluid lipid regions. Our studies confirm this expectation for mixed phospholipid multilamellar dispersions containing a trace of difluoromyristate. The method correctly measures the onset and completion temperatures of the transition in the well-studied dimyristoylphosphaditylcholine distearoylphosphatidylcholine system and also describes the motional behavior of the solid and fluid phases within the transition. Lipids extracted from Escherichia coli membranes show similar motional phenomena through the transition-temperature range according to 19F nuclear magnetic resonance studies of difluoromyristate biosynthetically incorporated into the K1060B5 strain, an unsaturated fatty acid auxotroph. Intact cells or membrane vesicles show substantially different behavior from extracted lipids, indicating that membrane proteins significantly perturb the phase transition. Evidence presented in this paper also shows that the 19F resonance from Escherichia coli phospholipids is sensitive to various intramembrane interactions. There is a general decrease in restriction of motion due to neutral lipids and an opposite effect due to the architecture of the native membrane. Neither effect is temperature sensitive. However, there are interactions in the intact membrane, affecting the 19F resonance, that are temperature dependent both due to the phase-transition process and due to processes occurring at high temperatures.

Cell Membrane↗
PubMed2005

Chiral phase transition in two-dimensional supramolecular assemblies of prochiral molecules.

The self-assembly of the rodlike two-dimensional chiral molecule 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid on the Cu(100) surface has been investigated by scanning tunneling microscopy. Upon adsorption at T>or=300 K, the molecules are deprotonated and assemble in parquet patterns when the coverage remains below a critical value. Corresponding high-resolution data reveal that the ordering implies mesoscopic chiral resolution as a result of chiroselective interactions (i.e., two domains comprise exclusively one enantiomer). When the critical coverage is exceeded, an abrupt transition to a single racemic phase is observed with a different lateral molecular coupling scheme. The shifting of the subtle balance between the weak lateral coupling, substrate bonding, and the packing requirements encountered with the increased molecular coverage is suggested to be the driving force for this homochiral-to-heterochiral phase transition.

Journal Article↗
PubMed2004

Phase transitions and hindered rotation in dimethylacetylene at high pressures probed by Raman spectroscopy.

We present Raman spectroscopy experiments in dimethylacetylene (DMA) using a sapphire anvil cell up to 4 GPa at room temperature. DMA presents phase transitions at 0.2 GPa (liquid to phase I) and 0.9 GPa, which have been characterized by changes in the Raman spectrum of the sample. At pressures above 2.6 GPa several bands split into two components, suggesting an additional phase transition. The Raman spectrum of the sample above 2.6 GPa is identical to that found for the monoclinic phase II (C2/m) at low temperatures, except for an additional splitting of the band assigned to the fourfold degenerated asymmetric methyl stretch. The global analysis of the Raman spectra suggests that the observed splitting is due to the loss of degeneracy of the methyl groups of the DMA molecule in phase II. According to the above interpretation, crystal phase II of DMA extends from 0.9 GPa to pressures close to 4 GPa. Between 0.9 and 2.6 GPa, the methyl groups of the DMA molecules rotate almost freely, but the rotation is hindered on further compression.

Journal Article↗
PubMed2004

Influence of ammonium nitrate in phase transitions of Langmuir and Langmuir-Blodgett films at air/solution and solid/solution interfaces.

The effect of ammonium nitrate on the phase transitions in Langmuir films of amphiphiles-stearic acid, stearyl amine (STAM), stearyl alcohol, dihexadecylphosphate, and the quarternized ammonium salt dioctadecyldimethylammonium bromide have been studied at air/water interface and in local ordering of their Langmuir-Blodgett films (LB films). The study shows that except for the stearyl amine (STAM) all other monolayers exhibit a liquid-expanded to liquid-condensed transition with slight expansion in area in the presence of ammonium nitrate. STAM monolayers show a new phase transition, which possibly arises due to the differently ionized amino groups, and change in solvation sheath due to an ion-dipole type interaction between the amino groups and the ammonium ion in the subphase. Mixed films of the amine with the acid and alcohol did not show such intermediate phases indicating that competing H-bonds between polar groups themselves and dipolar couplings between the polar groups and ammonium nitrate play a major role in the organization of the molecules at the interface. The above effect resulting in a change in the local order is borne out by Brewster angle micrographs (BAM) of the Langmuir films of STAM at air/solution interface. Such behavior is also seen at solid/liquid interfaces where the polar component of surface energy undergoes a drastic change for the amine films transferred onto solid substrates from the air/ammonium nitrate solution interface.

Journal Article↗
PubMed1985

Fluorescence decay of pyrene in small and large unilamellar L, alpha-dipalmitoylphosphatidylcholine vesicles above and below the phase transition temperature.

The fluorescence decays of pyrene in small and large unilamellar L, alpha-dipalmitoylphosphatidylcholine vesicles have been investigated as a function of probe concentration and temperature. When the molar ratio of pyrene to phospholipid equals 1:3000, no excimer emission is observed and the fluorescence decays are mono-exponential. When this ratio is equal to or higher than 1:120, excimer formation is observed. Above the phase transition temperature the observed fluorescence decays of monomer and excimer can be adequately described by a bi-exponential function. The monomer decays can be equally well fitted to a decay law which takes into account a time-dependence in the probe diffusion rate constant. The fluorescence decay kinetics are compatible with the excimer formation scheme which is valid in an isotropic medium. The excimer lifetime and the (apparent) rate constant of excimer formation have been determined as a function of probe concentration at different temperatures above the phase transition temperature. The activation energy of excimer formation is found to be 29.4 +/- 1.3 kJ/mol. In small unilamellar vesicles the diffusion constant associated with the pyrene excimer formation process varies from 8.0 X 10(-7) cm2/s at 40 degrees C to 2.2 X 10(-6) cm2/s at 70 degrees C. Below the phase transition temperature the monomer decays can be described by a decay law which takes into account a time dependence of the rate constant of excimer formation. The lateral diffusion coefficient of pyrene calculated from the decay fitting parameters of the monomer region varies from 4.0 X 10(-9) cm2/s at 20 degrees C to 7.9 X 10(-8) cm2/s at 35 degrees C. No significant difference could be observed between the pyrene fluorescence decay kinetics in small and large unilamellar vesicles.

Diffusion↗
PubMed2003

Fluorescent molecular thermometers based on polymers showing temperature-induced phase transitions and labeled with polarity-responsive benzofurazans.

Poly(N-isopropylacrylamide) in aqueous solution undergoes a phase transition at approximately 32 degrees C. The fluorescence properties of benzofurazans are affected by solvent polarity. We combine these two characteristics for the first time to develop sensitive fluorescent molecular thermometers. Five fluorescent monomers having a benzofurazan skeleton were synthesized, and the copolymers of N-isopropylacrylamide (NIPAM) and a small quantity of the fluorescent monomer were obtained to investigate their fluorescence properties. With increase in temperature, the copolymers in water showed the temperature-induced phase transition at approximately 32 degrees C and the fluorescence intensities of the copolymers concurrently increased. Especially, for the copolymer of 4-N-(2-acryloyloxyethyl)-N-methylamino-7-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole and NIPAM, the fluorescence intensity at 37 degrees C was 13.3-fold that seen at 29 degrees C. The sensitive range of temperature of these fluorescent molecular thermometers is changed by the replacement of the NIPAM units by N-isopropylmethacrylamide or N-n-propylacrylamide units in the copolymers. The basis of these fluorescent molecular thermometers is the decrease in the microenvironmental polarities near the main chains of the copolymers with increasing temperature, as confirmed from the maximum emission wavelengths of the benzofurazan units in the copolymers. The responses from the copolymers to the change in temperature are reversible and exactly repeatable during at least 10 cycles of heating and cooling.

Journal Article↗