Thermal Reversibility Research Articles

Novel Nanostructures from Self‐Assembly of Chiral Block Copolymers

A diblock copolymer system constituting both achiral and chiral blocks, polystyrene-block-poly(L-lactide) (PS-PLLA), was designed for the examination of chiral effects on the self-assembly of block copolymers (BCPs). A unique phase with three-dimensional hexagonally packed PLLA helices in PS matrix, a helical phase (H*), can be obtained from the self-assembly of PS-rich PS-PLLA with volume fraction of PLLA f PLLAv = 0.34, whereas no such phase was found in racemic polystyrene-block-poly(D.L-lactide) (PS-PLA) BCPs. Moreover, various interesting crystalline PS-PLLA nanostructures can be obtained by controlling the crystallization temperature of PLLA (T(c,PLLA) ), leading to the formation of crystalline helices (PLLA crystallization directed by helical confined microdomain) and crystalline cylinders (phase transformation of helical nanostructure dictated by crystallization) when T(c,PLLA) < T(g,PS) (the glass transition temperature of PS) and T(c,PLLA) ≧ T(g,PS) , respectively. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation (i.e., stretching) of helices and to result in crystalline cylinders. For PS-PLLA with PLLA-rich fraction (f PLLAv = 0.65), another unique phase, a hexagonally packed core-shell cylinder phase with helical sense (CS*), in which the PS microdomains appear as shells and PLLA microdomains appear as matrix and cores, can be found in the self-assembly of PLLA-rich PS-PLLA BCPs. The formation of those novel phases: helix and core-shell cylinder is attributed to the chiral effect on the self-assembly of BCPs, so we named this PS-PLLA BCP as chiral BCP (BCP*). For potential applications of those materials, the spring-like behavior with thermal reversibility might provide a method for the design of switchable nanodevices, such as nanoscale actuators. In addition, the PLLA blocks can be hydrolyzed. After hydrolysis, helical nanoporous PS bulk and PS tubular texture can be obtained and used as templates for the formation of nanocomposites.

Thermosensitive hydrogels synthesized by fast Diels–Alder reaction in water

Novel thermosensitive hydrogels have been synthesized by aqueous Diels–Alder reaction of poly(N,N-dimethylacrylamide-co-furfuryl methacrylate) and N-[4-(formyl polyethylene glycol ester) bismaleimide. The gelation time was measured by a vial inversion method and the swelling behavior of dried hydrogel was studied by a general gravimetric method. It was found that water can accelerate Diels–Alder reaction while DMF can accelerate retro-Diels–Alder reaction. The gelation time decreases with the increase of temperature. Swelling/shrinking kinetics indicates that the as-prepared hydrogels have high swelling ratio and can respond to temperature. The strategy described here provides several advantages for the hydrogel formation including mild reaction conditions, no initiator or catalyzer, no organic solvent, tunable gelation rate, and thermal reversibility.

Towards self-replicating materials of DNA-functionalized colloids

We report the first results of ongoing research that involves the creation of a new class of non-biological materials designed to self-replicate and, as a result, to grow exponentially. We propose a system design that exploits the strong specificity and thermal reversibility of the interactions between colloidal particles functionalized with complementary single-stranded DNA ‘sticky ends’. Here, we experimentally test the fundamentals of the different steps that constitute the self-replication scheme. First of all, we quantitatively study the equilibrium and kinetic aspects of the aggregation–dissociation behavior of the particles. We find that the dissociation transition is very sharp (∼1 °C) and that it occurs at unexpectedly low temperatures, with the dissociation temperature shifting further down when the fraction of sticky ends becomes smaller. The sharpness of the transition and its sensitivity to the sticky end fraction are important control parameters in our self-replication scheme. We further find that for our present purposes it is best to use a DNA construct with a double-stranded backbone, as this largely prevents unwanted hybridization events, such as secondary structure formation. The latter is seen to lead to peculiar aggregation kinetics, due to a competition between inter- and intra-particle hybridization. Finally, we show how one can obtain dual recognition at different temperatures by functionalizing a single particle species with two distinct DNA sequences and we demonstrate the formation of permanent bonds, using the chemical intercalator psoralen and long-wavelength UV exposure.

Thermochromic core–shell nanofibers fabricated by melt coaxial electrospinning

AbstractMicrocapsule/nanocapsule and encapsulation techniques have great potential for devices of functional materials. Also, electrospinning has attracted great attention for the fabrication of microstructures and nanostructures. The fluidity after melting limits the application of phase‐transformation thermochromic materials. In this study, with the melt coaxial electrospinning technique, a phase‐transformation thermochromic material was encapsulated in poly(methyl methacrylate) nanofibers. A device of this phase‐transformation thermochromic material was realized. With a poly(methyl methacrylate) shell with good optical transmission and a thermoresponsive core made of crystal violet lactone, bisphenol A, and 1‐tetradecanol core, the fibers had good thermal energy management, fluorescent thermochromism, and reversibility. The fabrication of thermochromic core–shell nanofibers has further potential in the preparation of temperature sensors with good fluorescence signals and body‐temperature calefactive materials with intelligent thermal energy absorption, retention, and release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Preparation and properties of a novel remendable coating concept

Key properties of organic coatings, such as mechanical strength and solvent resistance, are greatly influenced by the structure of the polymeric binder. In general, a 3-dimensional polymeric network gives the best properties and therefore most performance coatings have a 3-dimensional network structure. However, 3-dimensional networks cannot easily be repaired. Through molecular design in combination with different synthetic routes, a series of new building blocks has been prepared that render conventional coating types thermally remendable. Damage can be repaired through thermally reversible cross-linking of the coating through reversible bond scission within these specially designed building blocks. At room temperature, a fully cross-linked network is present, whereas at elevated temperatures the cross-link density becomes much lower and the system becomes mouldable or low viscous. This self-healing concept was proven by various techniques. Both the thermal reversibility window and the final coating properties can be tuned by careful design of the system.

Click chemistry‐assisted triazole‐substituted azobenzene and fulgimide units in the pendant‐based copoly(decyloxymethacrylate)s for dual‐mode optical switches

AbstractCopolymer containing new thermally reversible click chemistry‐assisted triazole‐substituted azobenzene and fulgimide units in the pendant F‐co‐A was prepared by free‐radical solution addition polymerization technique. The F and A were also prepared for comparison. The DSC analysis of F indicates that the polymer possessing the C‐form of fulgimide unit exhibited higher Tm than that of E‐form of the same polymer and revealed that the C‐form of fulgimide unit in F is highly ordered. The cis‐trans back isomerization behavior of the click chemistry‐assisted triazole‐substituted azobenzene unit in film A has thermal irreversibility, while in F‐co‐A it exhibited thermal reversibility. The UV‐exposed film of F‐co‐A heated around Tg leads to cis‐trans back isomerization of azobenzene unit and thermally stable C‐form of fulgimide which retains its conjugated structure where both the photochromic units are converted into planar conformations and exhibit high fluorescence properties. The fluorescence maxima of C‐form in F‐co‐A red shifted compared with F, because the substituted triazole ring in the azobenzene unit stabilized the C‐form of fulgimide unit. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7843–7860, 2008

DNA and DNAzyme-Mediated 2D Colloidal Assembly

DNA-mediated interactions present a significant opportunity for controlling colloidal self-assembly. Using microcontact printing to achieve spatial control of DNA-surface patterning and DNA-functionalized polystyrene colloids, we report that DNA hybridization can be utilized for sequence-specific reversible self-assembly of well-ordered 2D colloidal arrays. Two essential indicators of DNA-hybridization mediated assembly were confirmed: thermal reversibility and sequence specificity. The arrays melted at 50 degrees C and reassembled when introduced to fresh colloid suspension, and sequence specificity with <1% nonspecific binding was confirmed using fluorescent polystyrene colloids. The real-time assembly of the colloids onto the periodically patterned substrate was monitored by simple laser diffraction to obtain assembly kinetics. Maximum surface coverage of DNA-mediated assembly was determined to be 0.593 for DNA-functionalized 100 nm polystyrene colloids, and 90% of the assembly was complete after 6.25 h of hybridization in 50 mM NaCl Tris buffer. We also demonstrate that DNAzymes, catalytic DNA molecules, can be incorporated into the design, and in the presence of 10 microM Pb(2+), the hybridization-induced array assembly can be disrupted via DNAzyme activity.

Study of protein conformational stability and integrity using calorimetry and FT-Raman spectroscopy correlated with enzymatic activity

Maintaining protein conformational stability and integrity during formulation is critical for developing protein pharmaceuticals. Accordingly, high sensitivity differential scanning calorimetry (HSDSC) and Fourier transform (FT)-Raman spectroscopy were employed to assess conformational stabilities (thermal stability and folding reversibility) and structural integrities, respectively, for three model proteins: lysozyme, deoxyribonuclease I (DNase I) and lactate dehydrogenase (LDH) in lyophilised (as received) and spray-dried forms. Enzymatic assay after cooling of thermally denatured protein solutions from HSDSC determined if thermal transition reversibility was related to biological activity. HSDSC data showed that molecules from lyophilised lysozyme were able to refold better than the spray-dried form. This was confirmed by enzymatic assay. Moreover, enzymatic assay results revealed that lysozyme folding reversibility was related to the native structure of the protein that is essential for the biological activity. Thermal denaturation of DNase I and LDH samples in HSDSC was not reversible upon cooling of thermally denatured proteins (in contrast to lysozyme). Hence, it was decided to identify the effect of protein initial structures on its propensity to thermal denaturation via FT-Raman spectroscopy. In other words, proteins may denature with structural alterations due to stresses such as heat and the protein loses its enzymatic activity. Consequently, FT-Raman investigated the effects of spray drying and heating of solid DNase I and LDH samples, from differential scanning calorimetry, on protein conformational integrities. Lyophilised and spray-dried DNase I and LDH solid samples were heated to two temperatures, one before the apparent denaturation temperatures ( T m) and the other after the T m. Samples heated below their T m showed some alterations of the secondary structure and some enzymatic activity. HSDSC and FT-Raman spectroscopy are useful techniques to study protein conformations and their results correlate with those of enzymatic activity.

Novel poly(fluorene-alt-squaraine) derivatives having large coverage with solar spectrum

AbstractNovel main-chain-conjugated poly(fluorene-alt-squaraine) using vinyl as linkage group were synthesized through direct condensation of 9,9’-dioctylfluorene derivates and squaric acid. The resulting polyfluorenes were characterized by NMR and FT-IR. They have good solubility in common organic solvents, good thermal stability and electrochemical reversibility. The structure of donor-acceptor-donor interaction in the polymer backbone resulted in much more red-shifted absorption spectra of 500-1000 nm, and extremely low band gaps of ~1.2 eV have been obtained. Their absorption spectra have large coverage with solar spectrum, suggesting that they are potential materials that can be used in photovoltaic devices.

The Isolated System of Quantifiable Experiences in the 1783 "Mémoire sur la chaleur" of Lavoisier and Laplace

The thesis of the present paper is that the famous memoir of Antoine-Laurent Lavoisier and Pierre Simon Laplace of 1783 inaugurated the study of a new unit of experimentation, the isolated system of quantifiable experiences. It was defined by a linear equation, ruled by a principle of thermal reversibility and realised experimentally by a calorimetric apparatus. This notion took its origins from a specific context of studies of heat and its quantification that involved the two scientists from 1777: attempts to verify the mechanisms of combustion and animal respiration. Born from an original interpretation of the principle of conservation of vires vivae, the concept of system is deeply connected with the formulation of a new way to quantify chemical reactions. This method leaves nonquantifiable entities out of consideration and is the basis of the subsequent principle of conservation of matter. This paper argues that the Lavoisierian concept of system arises from the eighteenth-century studies on heat and from an experimental approach different from that of the quantitative chemistry of the Scottish tradition. Following this new logic, the transformation of vital air into fixed air was proved to be the effect of combinations between specific basis and heat, not determined by the addition/subtraction of matter: the combustion of bodies and animal respiration could never be considered mere inflammatory processes.

Thermal Characterization of Self-Assembled Monolayers of Dialkyl Disulfides Containing the Urea Moiety

Thermal behaviors of urea-containing dialkyl disulfides 4-(3-octadecylureido)phenyl disulfide (ODPD) and 3-(octadecylureido)ethane disulfide (ODED) and octadecyl disulfide (ODDS) self-assembled monolayers (SAMs) were investigated by infrared reflection-absorption spectroscopy (IRRAS). Among the SAMs, the alkyl chain of ODPD is thermally reversible in the temperature region between 30 and 138 degrees C, whereas alkyl chains of ODED and ODDS are irreversible. With regard to the thermal stability of alkyl chains, ODED is superior to ODPD and ODDS. It is considered that the good thermal reversibility of the ODPD SAM is due to the rigid phenyl ring and the good thermal stability of the ODED SAM is due to the flexible ethylene linker. Moreover, 2D correlation analysis provides an enhancement of spectral resolution in amide II and CH2 antisymmetric stretching bands and suggests from the comparison of sequences of spectral events of ODPD and ODED SAMs that the last reorientation of the phenyl ring in the ODPD SAM is responsible for the good thermal reversibility.

Biophysical Comparability of the Same Protein From Different Manufacturers: A Case Study Using Epoetin Alfa From Epogen® and Eprex®

This study focuses on the development and application of biophysical methodology to characterize conformations of Epogen® and Eprex®, the injectable formulations of recombinant human Epoetin alfa produced by different manufacturers and commonly used for the treatment of renal anemia. In these studies Eprex, from prefilled syringes, and Epogen bulk product formulated in a buffer similar to the Eprex formulation, were purified by anion-exchange chromatography. Analytical ultracentrifugation studies of the purified main peak from each sample demonstrated that Epogen contains a single component with an s value of 2.51 while Eprex contains a single component with the same molecular weight but with an s value of 2.44 suggesting a slight difference in hydrodynamic structure. The degree of α-helicity was compared by far-UV circular dichroism and shown to contain slight differences. Intrinsic tryptophan fluorescence and near-UV circular dichroism were assessed and demonstrated additional differences between the proteins. Finally, the global stability of the proteins was monitored using thermal unfolding monitored by far-UV circular dichroism. The Epoetin alfa of Epogen demonstrated complete reversibility while the Epoetin alfa purified from Eprex demonstrated only 80%–85% thermal reversibility when heated to 100°C. Together the data indicate that the proteins are not structurally identical.

Thermal reversibility and bistability in photochromic diarylethenes

An account is given of the research work in progress in the authors’ laboratory on the photochromic behaviour (photocyclization) of diarylethenes structurally constrained to the cis geometry. Depending on the aromaticity of the aryl groups, the photoreaction can be thermoreversible, photoreversible or both. Examples of different photochromic behaviours of two series of photochromic diarylethenes (dipyrrolylperfluorocyclopentenes, which are thermally and photochemically reversible, and dithienyldithiolthiones, which are thermally stable and photoreversible) are investigated here by steady state and time-resolved spectroscopy to obtain information about their photochemistry and the competitive relaxation paths of their electronically excited states.

The studies on structural and thermal properties of delithiated Li xNi 1/3Co 1/3Mn 1/3O 2 (0 < x ≤ 1) as a cathode material in lithium ion batteries

The structural and thermal properties of the delithiated Li x Ni 1/3Co 1/3Mn 1/3O 2 (0 < x ≤ 1) material have been investigated by using diffraction and thermoanalytical techniques such as XRD and TG-DSC methods. XRD result shows that the delithiated materials maintain the O3-type structure with defined stoichiometric number at the range of 0.24 < x ≤ 1, exhibiting good crystal structural stability. The cobalt and nickel ions in the delithiated materials change their valence state (i.e. Co 3+ to Co 4+ and Ni 3+ to Ni 4+) when x < 0.49; the irreversible changes of the transformation may affect the first cycle of charge–discharge efficiency of the materials. A comparison of the results of TG-DSC with TPD-MS shows that the irreversible change of oxygen species during the delithiation process of Li x Ni 1/3Co 1/3Mn 1/3O 2 have great influence on the structural and thermal stability and reversibility of the materials.

Lyotropic Liquid Crystals from Designed Helical β-Peptides

We demonstrate that 14-helical beta-peptides can self-assemble to form lyotropic liquid crystalline (LC) phases in water. beta-Peptides 1-4 were designed to form globally amphiphilic 14-helices of increasing length. Optical microscopy showed that several of these beta-peptides formed LC phases in aqueous solutions at concentrations as low as 2.5 wt % (15 mM). Liquid crystallinity appears to require the adoption of a globally amphiphilic conformation because a scrambled sequence, 5, does not display LC behavior. Thermal stability and reversibility of LC phase formation were assessed by variable temperature 2H NMR spectroscopy and optical microscopy. The LC phase formed by beta-peptide 3 at 10 wt % is disrupted above 40 degrees C in D2O and re-forms within minutes upon cooling. LC phase behavior for solutions of 3 is influenced by concentration and net charge. These studies demonstrate that highly folded 14-helical beta-peptides can produce LC phases at shorter lengths than do alpha-helical alpha-peptide mesogens and can provide a basis for tailoring properties of LC phases for future applications.

Temperature dependent infrared spectroscopy of proton conducting alkali thio-hydroxogermanates

We have investigated the thermal stability and reversibility upon dehydration and re-hydration of a novel class of proton conducting alkali thio-hydroxogermanates. The results indicate that no phase transitions or structural degradation occur in the temperature range 25 to 300 °C, and that repeated dehydration and subsequent re-hydration is a reversible process. The dehydration occurs gradually with increasing temperature, starting at about 80 °C. For temperatures above 180 °C the materials are dry, as all molecular water has been dried off. The dehydration process is shown to be reversible and the material can be rehydrated by exposure to air. The thermal stability and reversibility of the dehydration–rehydration process are attractive properties of functional materials, making the proton conducting alkali thio-hydroxogermanates to potential fuel cell electrolytes.

Thermally reversible cross-linked polyamides and thermo-responsive gels by means of Diels–Alder reaction

Cross-linked polyamides and polyamide gels were prepared from maleimide-containing polyamides and a tri-functional furan compound and showed thermal reversibility in cross-linking behavior and in gel formation through Diels–Alder (DA) and retro-DA reactions. The rate constant k of the DA cross-linking reaction were 1.25–4.83×10 −5 dm 3 mol −1 s −1 in the temperature range of 20–60 °C with an activation energy of 32.1 kJ mol −1. The cross-linking densities, thermal properties, and thermal reversibility of the polyamides/furan polymers were adjustable with the contents of maleimide groups in polyamides.

Prevention of thermal induced aggregation of cytochrome c at isoelectric pH values by polyanions

Differential scanning calorimetry, viscometry, optical and CD spectroscopy were used to characterize the influence of two polyanions, poly(vinylsulfate) (PVS), and poly(4-styrene-sulfonate) (PSS) on thermal transition reversibility of ferricytochrome c at or near isoelectric pH. In these conditions, both PVS and PSS enhance the thermal transition reversibility of cytochrome c by preventing the aggregation of denatured protein molecules. Data indicate that the polyanions are in complex with cytochrome c that is stabilized by synergistic effect of Coulombic and non-Coulombic interactions.

Photoinduced Magnetization in Copper Octacyanomolybdate

This article describes the studies of a photomagnetic cyanide-bridged Cu-Mo bimetallic assembly, Cu(II)(2)[Mo(IV)(CN)(8)].8H(2)O (Cu(II), S = (1)/(2); Mo(IV), S = 0) (1), which has an intervalence transfer (IT) band from Mo(IV)-CN-Cu(II) to Mo(V)-CN-Cu(I) around 480 nm. Wide-angle X-ray scattering and X-ray spectroscopic studies provide precise information about the 3D connectivity and the local environment of the transition metal ions. Irradiating with blue light causes solid 1 to exhibit a spontaneous magnetization (Curie temperature = 25 K). The thermal reversibility is carefully studied and shows the long-time stability of the photoinduced state up to 100 K. Photoreversibility is also observed; i.e., the magnetization is induced by irradiation with light below 520 nm, while the magnetization is reduced by irradiation with light above 520 nm. The UV-vis absorption spectrum after irradiation shows a decrease of the IT band and the appearance of the reverse-IT band in the region of 600-900 nm (lambda(max) = 710 nm). This UV-vis absorption spectrum is recovered to the original spectrum by irradiation with 658-, 785-, and 840-nm light. In this photomagnetic effect, the excitation of the IT band causes an electron transfer from Mo(IV) to Cu(II), producing a ferromagnetic mixed-valence isomer of Cu(I)Cu(II)[Mo(V)(CN)(8)].8H(2)O (Cu(I), S = 0; Cu(II), S = (1)/(2); Mo(V), S = (1)/(2)) (1'). 1' returns to 1 by irradiation of the reverse-IT band, which obeys the scheme for the potential energy surface in mixed-valence class II compounds.

Temperature-Induced Molten Globule-like State in Human α1-Acid Glycoprotein: An Infrared Spectroscopic Study

Despite extensive investigations on thermal denaturation of alpha(1)-acid glycoprotein (AGP) using a variety of techniques, structural features of the folded-unfolded state in terms of residual secondary structures and the structural transitions involved in this process have not been fully characterized. In this study we employed FT-IR spectroscopy to investigate the thermal unfolding and reversibility of temperature-induced changes in AGP. The data revealed a fully reversible beta-sheet-rich protein which exhibits a molten globule-like state, an important protein folding intermediate. 2D-IR COS revealed the sequence of the conformational changes occurring before denaturation and confirmed the formation of this intermediate which was further supported by CD spectroscopy. On account of the similarities in the FT-IR spectra of AGP with those of porcine odorant-binding protein (OBP), homology modeling of AGP using OBP as template was performed. The resemblance of AGP and OBP 3D structures confirmed the similarities of data obtained using FT-IR spectroscopy. Overall, FT-IR spectroscopy appears to be useful for investigating the structural characteristics and stability of proteins whose 3D structures are unavailable and for assessing the molten globule-like state in small beta-sheet-rich proteins.