John H. van der Maas

Factors Associated with Dough Stickiness as Sensed by Attenuated Total Reflectance Infrared Spectroscopy

ABSTRACT Attenuated total reflectance (ATR) and Fourier transform infrared (FTIR) spectroscopy have been applied in the characterization of sticky dough surfaces. The characterization provides insight in the chemical distribution of gluten protein, starch, water, and fat during dough kneading. ATR is especially useful for selective sampling of dough surfaces because the depth of penetration of radiation is quite shallow. For dough, it is calculated to be in the order of 0.5–4 μm in the mid-infrared, ideal for measurements of stickiness effects, where only the dough surface is of interest. To investigate the cohesive and adhesive properties of the individual dough constituents, dough was peeled from the ATR plate to study the material that adhered to it. The infrared spectra obtained indicate that fat and gluten protein appear to be located at the outer sticky dough surfaces, rather than water and starch. In comparison with gluten, the fatty component showed relatively strong adhesive forces to the ATR pla...

Spectroscopic evidence for CH⋯ interaction in crystalline steroids and reference compounds

Abstract The attractive interaction between CH donors and oxygen acceptors is demonstrated for a number of compounds measured as liquid, solid and in non-polar solution. Reference values for the “free” (isolated) molecules are derived from gas-phase or solution measurements. Infrared spectral data for the CH stretching mode of a series of compounds with geminal-substituted hydroxyl and ethynyl groups, are reported. Both the Δν SC ( ν CCl 4 − ν solid ) and Δν T ( ν 300 K − ν 100 K ) values are shown to be indicative of the strength of the CH⋯O interaction. For a limited number of steroids an attempt is made to correlate the H⋯O distance with the frequency shift, Δν SC . The steric effect of neighbouring alkyl groups is shown for some cyclohexanol and adamantanol derivatives.

Conformational isomerism and self-association of calixarene building blocks in non-polar solution studied by Fourier transform infrared spectrometry

In order to establish the conformational equilibrium of calix[6]arene derivatives, a series of phenolic building blocks differing in chain length (oligomers) have been studied in solution by Fourier transform infrared spectrometry (FT-IR). Different intramolecular OH ? X interactions have been established in the calixarene building blocks, i.e. OH ? ?, OH ? OH, OH ? OCH3 and a bifurcated OH ? OH/OCH3 or OH ? OH/OH one. Concentration-dependent measurements show that the ?biphenol? and ?triphenol? oligomers form cyclic dimers even at very low concentration ( 10?2 M). Preliminary MM3 calculations were performed to support conformational assignment.

Weak hydrogen bonding. Part 5. Experimental evidence for the long-range nature of CC–H ⋯π interactions: crystallographic and spectroscopic studies of three terminal alkynes

In the crystal structures of three terminal alkynes, long CC–H ⋯ CC contacts with H ⋯ C separations in the range 2.7–3.1 A are observed. Despite the long distances, these contacts possess the characteristic infrared spectroscopic features of weak hydrogen bonds. This provides direct evidence that the range of C–H ⋯π interactions donated by sufficiently acidic C–H groups extends beyond van der Waals separation. In two of the crystal structures, the C–H ⋯π interactions form interconnected systems CC–H ⋯ CC–H ⋯ CC–H.

Artificial intelligence for the interpretation of combined spectral data Design and development of a spectrum interpreter

Abstract The design of a knowledge-based system for the interpretation of combined spectral data for structure elucidation (EXSPEC) is described. Some basic design features are discussed and the functioning of the knowledge base, inference mechanism and user-interface is outlined. Attention is focussed on the development of a spectrum interpreter for infrared and mass spectral data. Interpretation of spectra for 120 liquid alcohols used for rule generation was successful. The system can be run on a Macintosh II or, more slowly, on a Macintosh Plus.

The sensorial potentials of the OH stretching mode

Abstract The OH stretching band of 57 selected saturated alcohols has been investigated in two different apolar solvents, CCl4 and CS2, as an initial step to recognise and understand weak hydrogen bonding phenomena. Based on rotamer classification and mathematical curve fitting, complex OH bandshapes have been unraveled successfully. A detailed analysis shows that ten different classes of rotamers, AK, suffice to correlate molecular structure and band parameters. The sensing properties for variation in the local molecular structure are shown to be reflected in the band maximum, v OH , the half band with, HBWCCl4OH and the solvent shift value, v d . A scheme is presented to classify saturated mono-hydroxy alcohols. For bicyclic alcohols and adamantanol-2 derivatives a sterical lever effect is established. No experimental evidence is found to support the involvement of an oxygen lone pair·CαH of primary and secondary alcohols in the band maximum nor in the relative intensity of the rotamers.

Vibrational spectroscopic characteristics of CH ⋯ O and NH ⋯ π interaction in crystalline N-(2,6-dimethylphenyl)-5-methylisoxazole-3-carboxamide

Abstract Infrared and Raman spectra have been scrutinised for features reflecting the presence of a very short CH ⋯ O contact in crystalline N-(2,6-dimethylphenyl)-5-methylisoxazole-3-carboxamide (D2624). A tentative assignment of infrared and Raman bands is presented for the pure and partly deuterated compound measured in the solid state and in the non-polar solution. The intensity increase of the C4H stretching vibration upon changing the matrix from a solution to the crystalline state, is the most prominent feature particularly in infrared. The temperature sensitivity was determined for the C4H and NH stretching vibration; the wavenumber-temperature coefficients (WTc) are significant but small, 0.0137 and 0.0143 cm−1 K−1, respectively. The presence of an NH ⋯ π interaction in the crystalline phase is established by mimicking this type of interaction in solution. Infrared measurements at temperatures above the melting point show that an intermolecular NH ⋯ OC amide bond is present in the liquid phase. Upon cooling (crystallisation) this typical energetically favourable amide bond is disrupted as a result of several competing attractive forces (intermolecular CH ⋯ O and NH ⋯ π interaction, intramolecular N8-H ⋯ N2) and the effect of steric shielding of the amide functionality by the 2,6-dimethylphenyl group.

First example of cooperative O–H⋯CC–H⋯Ph hydrogen bonding: crystalline 7-ethynyl-6,8-diphenyl-7H-benzocyclohepten-7-ol

In the crystalline title compound, molecular dimers are joined by a system of interconnected O–H⋯CC–H and CC–H⋯Ph hydrogen bonds for which IR spectra indicate considerable strength; this hydrogen-bond configuration has not been observed previously.

On the competitive intramolecular H-bonding in alcohols with two accepting sites

Abstract Alcohols with two accepting sites were studied in dilute CCl 4 solution by infrared spectroscopy. The results showed that conformer populations based on peak intensities can lead to erroneous conclusions regarding preferred interactions, when the effects of entropy and structural degeneracy become important. For quantitative calculations, peak areas are to be preferred over peak heights.

Spectroscopic and structural evidence for the hydrogen bond nature of CCH…CC contacts in ethynyl steroids

Abstract Structural and IR-spectroscopic evidence is given that directed contacts from terminal alkynes to CC double bonds possess the essential characteristics of weak hydrogen bonds. The contacts are directed at the center of the π-bond rather than at one of the individual C-atoms. The contact distances from H to the center of the CC bond are typically 2.8 A, with the shortest distances being ∼2.5 A . The interaction is of pronounced long-range nature and can be detected in the infrared spectrum even with a long H…π distance of almost 3.0 A. The sample used is mainly composed of ethynyl steroids belonging to the progestine family.