Interplay of thermochemistry and Structural Chemistry,the journal (volume 28, 2017, issues 3–4) and the discipline

Structural Chemistry - The contents of issues 3 and 4 of Structural Chemistry from the calendar year 2017 are summarized in the present review. A brief thermochemical commentary and recommendations...     

Interplay of thermochemistry and Structural Chemistry, the journal (Volume 26, 2015, Issues 1–2) and the discipline

Structural Chemistry - The contents of issues 1 and 2 of Structural Chemistry from the calendar year 2015 are summarized in the present review. A brief thermochemical commentary and possible...     

HIGH PERFORMANCE LIQUID CHROMATOGRAPHY OF PIGMENTS FROM GUARD CELL PROTOPLASTS AND MESOPHYLL TISSUE OF Vicia faba L.

Abstract— Pigments extracted from guard cell protoplasts (GCP) and mesophyll tissue from Vicia faba L., were separated by high performance liquid chromatography and identified by absorbance spectroscopy. Water soluble, UV-absorbing pigments, presumably flavonoids, were present in the GCP in large amounts. Chlorophyll and carotenoid content in GCP and mesophyll tissue was qualitatively similar, with both cell types having chlorophylls, xanthophylls and carotenes. Some quantitative differences were found. Beta-carotene was less abundant in the GCP, while some of the xanthophylls, notably violaxanthin and lutein-antheraxanthin, were more abundant. Lutein and neoxanthin occurred in similar amounts. The similarity between the action spectrum for the stimulation of stomatal conductances by blue light and the absorbance spectrum of guard cell carotenoids points to carotenoids as putative photoreceptors in the stomatal response to blue light.     

On dos languages and dos mappings

Roughly speaking,DOS systems formalize the notion of generatively deterministic context free grammars. We explore the containment relationships among the class of languages generated byDOS systems and other subclasses of the class of context free languages. Leaving the axiom of aDOS system unspecified yields aDOS scheme, which defines a mapping from words to languages over a given alphabet. We explore the algebraic properties ofDOS mappings and obtain an algebraic characterization of a fundamental subclass of theDOS mappings generated byDOS schemes which are propagating (non erasing) and have no cycles of derivability among letters of the alphabet. We apply this characterization to show that the mapping equivalence problem for propagatingDOS schemes is decidable.     

Cooperative calcium phosphate nucleation within collagen fibrils

Although "chaperone molecules" rich in negatively charged residues (i.e., glutamic and aspartic acid) are known to play important roles in the biomineralization process, the precise mechanism by which type I collagen acquires intrafibrillar mineral via these chaperone molecules remains unknown. This study demonstrates a mechanism of cooperative nucleation in which three key components (collagen, chaperone molecules, and Ca(2+) and PO(4)(3-)) interact simultaneously. The mineralization of collagen under conditions in which collagen was exposed to pAsp, Ca(2+), and PO(4)(3-) simultaneously or pretreated with the chaperone molecule (in this case, poly(aspartic acid)) before any exposure to the mineralizing solution was compared to deduce the mineralization mechanism. Depending on the exact conditions, intrafibrillar mineral formation could be reduced or even eliminated through pretreatment with the chaperone molecule. Through the use of a fluorescently tagged polymer, it was determined that the adsorption of the chaperone molecule to the collagen surface retarded further adsorption of subsequent molecules, explaining the reduced mineralization rate in pretreated samples. This finding is significant because it indicates that chaperone molecules must interact simultaneously with the ions in solution and collagen for biomimetic mineralization to occur and that the rate of mineralization is highly dependent upon the interaction of collagen with its environment.     

THE BLUE LIGHT RESPONSE OF STOMATA: PULSE KINETICS AND SOME MECHANISTIC IMPLICATIONS*

Abstract— Intact leaves of Commelina communis irradiated with high fluence rates of red light, showed discrete increases in stomatal conductance in response to pulses (1-100 s) of blue light (250 μmol m^?2 s^?1). Red light pulses were ineffective, indicating that the conductance increases were not mediated by photosynthesis and that they constitute a specific stomatal response to blue light. The response peaked 15 min after the pulse and was completed within50–60 min. Conductance increases were proportional to pulse duration up to about 30 s and saturated at longer exposures. The relationship between stomatal responses and pulse duration approximately fitted an exponential function, with a t 9s. Pulse responses at two different fluences indicated that reciprocity held. Responses to two consecutive pulses varied with time between pulses. A saturating pulse applied immediately after a preceding one induced no additional response; two saturating pulses 50 min apart caused two identical, consecutive responses. Total increases in conductance induced by two pulses separated by intermediate time intervals increased with time between pulses with a = 9 min. These results point to a blue light-dependent photoconversion of a molecular form, with the activity of the photoconversion product decaying in a thermal reaction. Under continuous blue light, prevailing fluence rates and rates of the light and thermal reactions are postulated to determine steady-state activities of the photoconversion product and proportional increases in conductance levels. These findings have implications for the environmental and metabolic roles of the stomatal response to blue light.