Djelovanje karboksilnih kiselina na crveno obojenje cvjetova žutinice

Eight carboxylic acids were fed at 1-10000 pM to the flower pastes from fresh dyer’s saffron (Carthamus tinctorius L.) capitula and their effects on the red colouration investigated. Glyoxyllic acid, glycolic acid, oxaloacetic acid, 2-oxoglutaric acid and gluconic acid were found to be positive stimulators for the reaction, while succinic acid, malic acid and citric acid inhibited the colour change.Svojim ranijim istraživanjima autori su pokazali da usitnjeni cvjetovi žutinice (Carthamus tinctorius L.) poprime crvenu boju ako na njih djeluju otopine aminokiselina. Učinkovitost pojedine aminokiseline ovisi o tipu: kisele amino- kiseline bile su najučinkovitije, neutralne nešto manje, one s aromatičnim skupinama ili skupinama sa sumporom još manje, dok su bazične aminokiseline bile najmanje učinkovite. Za objašnjenje ovih rezultata bilo je potrebno da se ustanove još drugi metaboliti koji biokatalitički utječu na promjenu boje cvjetova. U ovom prilogu autori objavljuju podatke o promjenama boje nakon primjene karboksilnih kiselina. U tu svrhu istražili su djelovanje osam karboksilnih kiselina u koncentracijama od 1 - 10000 pM na kašu od zdrobljenih cvjetova žutinice (Carthamus tinctorius L.). Postignuti rezultati su pokazali da glioksilna, glikolna, oksalooc- tena, 2-oksoglutarna i glukonska kiselina pospješuju reakciju stvaranja crvenog bojila, dok jantarna, jabučna i limunska kiselina tu reakciju inhibiraju. U radu se navode točni podaci o materijalu, metodama rada i rezultatima koji su prikazani u preglednoj tabeli. Rezultate autori kratko komentiraju uz razmišljanja da bi kemijske strukture karboksilnih kiselina mogle biti uže povezane s procesima promjene bojila, iako je sam mehanizam reakcije zasad još nepoznat

An N-heterocyclic boryloxy ligand isoelectronic with N-heterocyclic imines: access to an acyclic dioxysilylene and its heavier congeners

We introduce a new type of strongly donating N-heterocyclic boryloxy (NHBO) ligand, [(HCDippN)₂BO]¯, which is isoelectronic with the well-known N-heterocyclic iminato (NHI) donor class. This 1,3,2-diazaborole functionalized oxy ligand can be employed to stabilize the first acyclic two-coordinate dioxysilylene and its Ge, Sn and Pb congeners, thereby presenting the first complete series of heavier group 14 dioxycarbene analogues. All four compounds have been characterized by X-ray crystallography and Density Functional Theory (DFT), enabling analysis of periodic trends: the potential for the [(HCDippN)₂BO]¯ ligand to subtly vary its electronic donor capabilities is revealed via snapshots revealing gradual evolution of arene π-coordination on going from Si to Pb

N‐nacnac stabilized tetrelenes: formation of an N,P‐Heterocyclic germylene via C–C bond Insertion

The use of an amino‐functionalized β‐diketiminate (“N‐nacnac”) ligand in low‐valent germanium chemistry is reported, with a view to comparison with “conventional” nacnac systems. Transmetallation of the N‐nacnac ligand from lithium allows access to a versatile chlorogermylene system, and subsequent substituent exchange processes are used to generate related hydrido‐, and phosphaketenyl‐germylenes. The latter undergoes photolytically‐induced cleavage of the P–CO bond to yield an unusual imine‐coordinated N,P‐heterocyclic germylene. On the basis of DFT calculations this transformation is proposed to occur via concerted attack by the electron‐rich carbon–carbon bond of the N‐nacnac backbone accompanying CO loss, rather than via the generation of a free phosphinidene

N-H cleavage vs. Werner complex formation: reactivity of cationic group 14 tetrelenes towards amines

β-Diketiminate ligands featuring backbone NMe2 groups have been exploited to access a series of two-coordinate cations of the type [(N-nacnac)E]+ (E = Si, Ge, Sn), whose reactivity towards N-H bonds has been investigated. While the heavier group 14 systems react via simple adduct formation, N-H oxidative addition occurs for E = Si consistent with differences in EII/EIV redox potentials. The structurally characterized Ge/Sn adducts can be viewed as models for the corresponding (transient) Si systems [(N-nacnac)Si·(NH2R)]+ (R = H, tBu) - which are potential intermediates in the formation of [(N-nacnac)Si(H)(NHR)]+ via a proton-shuttling mechanism

An acid-free anionic oxoborane isoelectronic with carbonyl: facile access and transfer of a terminal B═O double bond

We disclose the synthesis and structural characterization of the first acid-free anionic oxoborane, [K(2.2.2-crypt)][(HCDippN)2BO] (1) (Dipp = 2,6- iPr2C6H3), which is isoelectronic with classical carbonyl compounds. 1 can readily be accessed from its borinic acid by a simple deprotonation/sequestration sequence. Crystallographic and density functional theory (DFT) analyses support the presence of a polarized terminal B═O double bond. Subsequent π bond metathesis converts the B═O bond to a heavier B═S containing system, affording the first anionic thioxoborane [K(2.2.2-crypt)][(HCDippN)2BS] (2), isoelectronic with thiocarbonyls. Facile B═O bond cleavage can also be achieved to access B-H and B-Cl bonds and, via a remarkable oxide (O2-) ion abstraction, to generate a borenium cation [(HCDippN)2B(NC5H5)][OTf] (4). By extension, 1 can act as an oxide transfer agent to organic substrates, a synthetic role traditionally associated with transition-metal compounds. Hence we show that B-O linkages, which are often considered to be thermodynamic sinks, can be activated under mild conditions toward bond cleavage and transfer, by exploiting the higher reactivity inherent in the B═O double bond

N‐nacnac stabilized tetrelenes: formation of an N,P‐Heterocyclic germylene via C–C bond Insertion

The use of an amino‐functionalized β‐diketiminate (“N‐nacnac”) ligand in low‐valent germanium chemistry is reported, with a view to comparison with “conventional” nacnac systems. Transmetallation of the N‐nacnac ligand from lithium allows access to a versatile chlorogermylene system, and subsequent substituent exchange processes are used to generate related hydrido‐, and phosphaketenyl‐germylenes. The latter undergoes photolytically‐induced cleavage of the P–CO bond to yield an unusual imine‐coordinated N,P‐heterocyclic germylene. On the basis of DFT calculations this transformation is proposed to occur via concerted attack by the electron‐rich carbon–carbon bond of the N‐nacnac backbone accompanying CO loss, rather than via the generation of a free phosphinidene

Reduction of carbon oxides by an acyclic silylene: reductive coupling of CO

Reactions of a boryl-substituted acyclic silylene with carbon dioxide and monoxide are reported. The former proceeds through oxygen atom abstraction, generating CO (with rearrangement of the putative silanone product through silyl-group transfer). The latter is characterized by reductive coupling of CO to give an ethynediolate fragment, which undergoes formal insertion into the Si-B bond. The net conversion of carbon dioxide with two equivalents of silylene offers a route for the three-electron reduction of CO2 to [C2 O2 ]2-

Reduction of carbon oxides by an acyclic silylene: reductive coupling of CO

Reactions of a boryl-substituted acyclic silylene with carbon dioxide and monoxide are reported. The former proceeds through oxygen atom abstraction, generating CO (with rearrangement of the putative silanone product through silyl-group transfer). The latter is characterized by reductive coupling of CO to give an ethynediolate fragment, which undergoes formal insertion into the Si-B bond. The net conversion of carbon dioxide with two equivalents of silylene offers a route for the three-electron reduction of CO2 to [C2 O2 ]2-

A β-diketiminate-stabilized sila-acyl chloride: systematic access to base-stabilized silicon analogues of classical carbonyl compounds

An oxidation/substitution strategy for the synthesis of silicon analogues of classical organic carbonyl compounds is reported, by making use of a novel β-diketiminate-supported sila-acyl chloride-the first example of such a compound isolated without the use of a stabilizing Lewis acid. Nucleophilic substitution at the SiIV center allows direct access to the corresponding sila-aldehyde and sila-ester. An alternative approach utilizing the reverse order of synthetic steps is thwarted by the facile rearrangement of the corresponding SiII systems featuring either H or OR substituents. As such, the isolation of (N-nacnac)Si(O)Cl represents a key step forward in enabling the synthesis of sila-carbonyl compounds by a synthetic approach ubiquitous in organic chemistry