Stepwise Melting Research Articles

Temperature Dependence of the Vibrational Spectra of Thallium(I) Alkanoates

IR spectroscopy has been used to model the stepwise melting process of nine T1(I) n-alkanoate salts from the solid phase into the isotropic liquid. This study has provided an explanation of the thermal effect observed by differential scanning and adiabatic calorimetry as an enhancement in the normal sigmate shape heat-capacity morphology. Infrared spectra show that these salts exist at low temperature as crystals with a subcell different from orthorhombic or monoclinic formation (no factor group splitting observed). In the lowest solid-to-solid phase transitions, the alkyl chains remain, mainly, in a totally trans-planar conformation, but the concentration of nonplanar conformers increases continuously as the temperature rises, and at a particular value (different for each compound), the CH2 wagging progression bands disappear. The temperature range at which this chain “melting” takes place coincides with the final steps of the calorimetric enhancement of the heat capacity. Changes in wavenumbers of some characteristic bands are observed in the infrared spectra at several phase transitions found by calorimetry. Because of its enhanced sensitivity to conformational order, Raman spectroscopy also was used for several alkanoate salts.

Effect of various anions on the stepwise melting of plasmid DNA.

Differential scanning calorimetry (DSC) was carried out for the study on the effect of various anions on the melting of plasmid pJL3-TB5 DNA (5, 277 base pairs in length). In the presence of halide ions such as Cl-, Br-, or I- in citrate buffer solutions, seven separate peaks caused by the stepwise melting of the DNA molecule were found in the DSC curve. Similar profile of the DSC curve was also found in the presence of SCN-. Such a characteristic melting profile was not observed, when some other buffer solutions such as phosphate, borate, and acetate buffers were used. These ions affected significantly the melting profile of DNA; the height of the peaks seen in the high temperature range decreased and broadened. The presence of the anions such as NO3-, ClO4-, SO42- and IO3- instead of Cl- in the saline-sodium citrate (SSC) buffer solution also affected the DSC curves in the high temperature range in the similar manner to phosphate, borate, and acetate buffers. These results indicate that the type of anions in the solution as well as that of cations is very important for the melting of DNA. Since anions are known to alter the structure of water, it is suggested that these results are closely related to alteration of the structure of water caused by the interaction between anions and water, rather than the direct interaction between anions and DNA. The borate buffer solutions also showed not only clearly separated peaks, but also excellent reversibility for the melting of the DNA.

Differential scanning calorimetric study of the effect of intercalators and other kinds of DNA-binding drugs on the stepwise melting of plasmid DNA

The effect of intercalating drugs (the anthracycline group of antibiotics, ethidium bromide, actinomycin D) on stepwise melting of DNA was studied by differential scanning calorimetry (DSC). The DSC DNA melting profile of plasmid pJL3-TB5 DNA (5277 base-pairs in length) consists of seven peaks, and all the intercalators caused shifting of these peaks, particularly those formed at the high temperature ranges, to the higher temperature ranges in a characteristic manner depending upon the binding strength of the drug. The analysis of the anthracycline group of antibiotics, such as aclacinomycin A, daunomycin, adriamycin and pyrarubicin, indicates that the difference in binding is due to the sugar moiety at position O-7 of the chromophore in these antibiotics. Analysis on the basis of the helix-coil transition theory suggests that the anthracycline group of antibiotics interact preferentially with the 5'-CG-3' sequences. The effect of various DNA-binding drugs other than intercalators on stepwise melting of DNA was then studied by DSC. The representative drugs examined were distamycin A, peplomycin, cis-dichlorodiamine-platinum(II) (cis-DDP or cis-Platin) and mitomycin C, which differ in their mode of interaction with DNA; namely, minor groove binding, strand cleavage and intrastrand or interstrand cross-linking. Distamycin A caused shifting of the DSC peaks at the low temperature ranges to a higher temperature range, whereas peplomycin and cis-DDP caused shifting of all the DSC peaks to form a broad peak at a lower temperature range, suggesting that the DSC DNA melting profiles are affected in a characteristic manner depending upon the interaction mode of the drug.

Interaction of an anthracycline antibiotic, 4'-0-tetrahydropyranyladriamycin (pyrarubicin), with plasmid pJL3-TB5 DNA

The effect of an anthracycline antibiotic 4'-0-tetrahydropyranyladriamycin (pyrarubicin) on the stepwise melting of plasmid pJL3-TB5 DNA by means of differential scanning calorimetry. The peaks seen at higher temperature ranges of the DSC curve of the DNA were affected by the addition of pyrarubicin in a manner essentially similar to the other anthracycline antibiotics (daunomycin, adriamycin, aclacinomycin A), suggesting that pyrarubicin binds to the 5'-CG-3' sequences of DNA. However, pyrarubicin broadened the peak at the highest temperature and shifted the peak in a manner different from other antibiotics. This suggests that the sugar moiety attached to the chromophores of pyrarubicin play an important role in binding probably to the minor groove of DNA.

Phase behaviour of lithium and sodium salts of phenylstearic acid

Abstract Phenylstearic acid, prepared from oleic acid and benzene, using the Friedel-Crafts reaction, has been confirmed to be a reproducible mixture of twelve positional isomers. Lithium and sodium salts of this acid are semi-crystalline solids which behave in many ways like pure single substances. The thermotropic polymorphism of these soaps has been studied using DSC and polarizing microscopy (as well as X-ray diffraction and 7Li NMR spectroscopy for the former soap). Both soaps exhibit characteristic stepwise melting behaviour and form stable reversed hexagonal mesophases at elevated temperatures, in contrast to the lamellar phases exhibited by the unsubstituted soaps.

Automated purity determination by stepwise melting in differential scanning calorimetry

Automated purity determination by stepwise melting in differential scanning calorimetry

An X-Ray Study of the Stepwise Melting of Anhydrous Sodium Palmitate

X-ray powder patterns on anhydrous sodium palmitate show that the five phases already known to occur between crystal and isotropic melt can be grouped into two basic structures. Both structures are liquid crystalline, i.e., crystalline in the direction of the long spacing and liquid-like laterally. Between the lower temperature ``waxy'' structure, which includes the previously known subwaxy, waxy, and superwaxy phases, and the higher temperature ``neat'' structure, which includes subneat and neat, there is a pronounced break in the curve of long spacing vs. temperature; in addition, the three waxy phases exhibit two diffuse short spacing rings, whereas the neat phases exhibit only one. These pattern differences lead to the interpretation that the waxy phases contain structural restraints on molecular position and motion not present in the neat phases.