Novel cellulose derivatives. III. Thermal analysis of mixed esters with butyric and hexanoic acid

Cellulose derivatives with low degrees of substitution (i.e., DS < 1.5) often fail to reveal glass transition temperatures (T_g) by virtue of their tenacious adherence to moisture, thus preventing systematic analysis of substituent effects (size and DS) on T_g and T_m transitions. On the other hand, cellulose triesters have T_ms that decline with acyl substituent size except when the substituent size becomes very large (i.e., > C₆), and they have T_gs within 5–20°C of their T_ms. This proximity is unusual for a semicrystalline material, and it interferes with the crystallization process that occurs between T_m and T_g. Triesters of cellulose with mixed acyl substituents (one smaller and one larger) allow not only unambiguous observation of T_gs and T_ms but also an adjustable Δ(T_m ? T_g) window that depends upon the size and the DS of the larger substituent. The materials studied including cellulose acetate butyrate triesters (DS_bu 0.8–2.6), cellulose acetate hexanoate triesters (DS_hex 0–3.0), and cellulose acetate (DS_ac 2.44), revealed that only the mixed esters, in which the bulkier acyl group is in the range of DS 0.3–1.0, had a Δ(T_m ? T_g) value in excess of 40°C. Although the T_m of cellulose acetate hexanoate declined by ca. 150°C per unit of DS_hex as DS_hex rose from 0 to 1, this was only ca. 25°C between DS_hex of 1 and 3. Frequently observed dual-melt endotherms were attributed to two separate crystal morphologies. ©1995 John Wiley & Sons, Inc.     

Modelling the thermal behaviour of carboxylic acid derivatives with cylcodextrins in the solid-state

The application of classical QSAR and molecular modelling to the inclusion complexation of natural and modified cyclodextrins (CDs) with carboxylic acid derivatives as guest molecules was examined. Information was available on the thermal behaviour, in the solid-state of benzoic acid (BA), salicylic acid (SA), and various substituted aminosalicylic acids (3-aminosalicylic acid, 3-ASA, 4-aminosalicylic acid, 4-ASA and 5-aminosalicylic acid, 5-ASA), as well as on the thermal behaviour of 1:1 molar ratio physical and kneaded mixtures of these acids with each of three different cyclodextrins, β-, (BCD) 2-hydroxypropyl-β-, (HPBCD) and γ-cyclodextrin (GCD). The thermal behaviour of the binary (1:1 stoichiometry) mixtures was modelled using stepwise multiple regression (SMR). Two models for the prediction of the percentage mass loss and enthalpy of dehydration of the physical mixtures were established with correlation coefficients (r) of 0.79 and 0.92, respectively. Decreased correlation in the thermal behaviour of kneaded mixtures indicated significant interaction and possible formation of inclusion complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal stability of ferrocene derivatives and ferrocene-containing polyamides

Thermogravimetric data and the kinetic interpretation of the curves of mass loss for ferrocene, ferrocenecarboxylic and ferrocenedicarboxylic acids and a series of ferrocene-containing polyamides are presented. The results indicate that the degradation process occurred with more than one stage of thermal degradation. The apparent activation energy values and the FTIR spectra of the degradation products suggest that the degradation mechanism occurred by either scission of weak links or by random scission of the chain. Apparently, the N-vicinal methylene group was the primary site of attack of oxygen on the polymer chain. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal stability and degradation of starch derivatives

Thermal behaviour of different starch derivatives, i.e. starch esters and ethers having degree of substitution (DS) in the range of 0.02–0.18 were studied. Potato, maize and wheat starches were used. Measurements were carried out by coupled thermal analysis/ mass spectrometry method (STA-MS) in air atmosphere. The major DTG peak during the investigation for starch derivatives is observed below 300°C. The mass loss up to a temperature of 300°C is about 50%. The most abundant ions found areH₂O⁺ and CO₂ ⁺. For the studied starch derivatives with a low degree of substitution (DS<0.18) no correlation was found between thermal stability and the level of substitution regardless of the nature of substitution.     

Investigation of molecular interactions in the complex formation of tartaric acid derivatives with di(2-ethylhexyl) phosphoric acid

The molecular interactions in the complex formation of two tartaric acid derivatives with di(2-ethylhexyl) phosphoric acid are investigated. The complex formation with a 1:1 stoichiometry between tartaric acid derivatives and D2EHPA can be obtained through UV-Vis titration, NMR chemical shifts and molecular dynamic simulations. Furthermore, the differences of the two complexes on the binding constants and strength of hydrogen bonds can also be determined. Such research will ideally provide insight into ways of regulating the complex forming properties of tartaric acid derivatives for composing or syn- thesizing new chiral resolving agents.     

Synthesis of glycyrrhetic acid derivatives

11-Deoxyglycyrrhetinic acid (DGA) (2) was produced by Clemmensen reduction of the C-11 carbonyl of 18β-glycyrrhetic acid (GA) (1). Four derivatives of GA and DGA (3a–3d) were synthesized. Their structures were elucidated using spectral data (IR, mass, ¹H, ¹³C NMR). __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 153–155, March–April, 2008.     

Comparative study of GQ and QG indices as potentially favorable molecular descriptors

In chemical graph theory, several degree-based topological indices are introduced and put forward in the development of quantitative structure-property relationships (QSPR)/quantitative structure-activity relationships (QSAR) studies. However, only a few of them are considered employable in the prediction of physical and chemical properties and biological activities of molecular compounds. Here, we focus our attention on some foremost characteristics of newly defined Geometric–Quadratic $$ and Quadratic–Geometric $$ indices such as prediction power, degeneracy and structure sensitivity. Based on these attributes, we discuss their comparison with other well-established degree-based topological indices with the help of statistical analysis and computational techniques on the data sets of octane, nonane and decane isomers. Some of the graphical approaches, statistical outcomes and computational tests exhibit the dominating nature of the $$ and $$ indices over other topological indices.     

Synthesis, spectral description, and lipophilicity parameters determination of phenylcarbamic acid derivatives with integrated N-phenylpiperazine moiety in the structure

The phenylcarbamic acid derivatives with N-phenylpiperazine moiety in the molecule have been prepared. The structure has been confirmed by elemental analysis, IR, ¹H NMR, and mass spectral data. For the prepared set of the compounds the lipophilicity parameters have been determined. The experimentally obtained lipophilicity parameters have been correlated with theoretical entries obtained by different computer programs based on the neural network and fragmental methods.