Interstellar formation of lactaldehyde, a key intermediate in the methylglyoxal pathway.

Aldehydes are ubiquitous in star-forming regions and carbonaceous chondrites, serving as essential intermediates in metabolic pathways and molecular mass growth processes to vital biomolecules necessary for the origins of life. However, their interstellar formation mechanisms have remained largely elusive. Here, we unveil the formation of lactaldehyde (CHCH(OH)CHO) by barrierless recombination of formyl (HĊO) and 1-hydroxyethyl (CHĊHOH) radicals in interstellar ice analogs composed of carbon monoxide (CO) and ethanol (CHCHOH).

Gas-phase synthesis of racemic helicenes and their potential role in the enantiomeric enrichment of sugars and amino acids in meteorites.

The molecular origins of homochirality on Earth is not understood well, particularly how enantiomerically enriched molecules of astrobiological significance like sugars and amino acids might have been synthesized on icy grains in space preceding their delivery to Earth. Polycyclic aromatic hydrocarbons (PAHs) identified in carbonaceous chondrites could have been processed in molecular clouds by circularly polarized light prior to the depletion of enantiomerically enriched helicenes onto carbonaceous grains resulting in chiral islands. However, the fundamental low temperature reaction mechanisms leading to racemic helicenes are still unknown.

A molecular beam and computational study on the barrierless gas phase formation of (iso)quinoline in low temperature extraterrestrial environments.

Despite remarkable progress toward the understanding of the formation pathways leading to polycyclic aromatic hydrocarbons (PAHs) in combustion systems and in deep space, the complex reaction pathways leading to nitrogen-substituted PAHs (NPAHs) at low temperatures of molecular clouds and hydrocarbon-rich, nitrogen-containing atmospheres of planets and their moons like Titan have remained largely obscure. Here, we demonstrate through laboratory experiments and computations that the simplest prototype of NPAHs - quinoline and isoquinoline (CHN) - can be synthesized via rapid and de-facto barrier-less reactions involving o-, m- and p-pyridinyl radicals (CHN˙) with vinylacetylene (CH) under low-temperature conditions.

Gas phase formation of cyclopentanaphthalene (benzindene) isomers reactions of 5- and 6-indenyl radicals with vinylacetylene.

The tricyclic polycyclic aromatic hydrocarbons (PAHs) 3H-cyclopenta[a]naphthalene (C13H10), 1H-cyclopenta[b]naphthalene (C13H10) and 1H-cyclopenta[a]naphthalene (C13H10) along with their indene-based bicyclic isomers (E)-5-(but-1-en-3-yn-1-yl)-1H-indene, (E)-6-(but-1-en-3-yn-1-yl)-1H-indene, 5-(but-3-ene-1-yn-1-yl)-1H-in-dene, and 6-(but-3-ene-1-yn-1-yl)-1H-indene were formed via a "directed synthesis" in a high-temperature chemical micro reactor at the temperature of 1300 ± 10 K through the reactions of the 5- and 6-indenyl radicals (C9H7˙) with vinylacetylene (C4H4). The isomer distributions were probed utilizing tunable vacuum ultraviolet light by recording the photoionization efficiency curves at mass-to-charge of m/z = 166 (C13H10) and 167 (13CC12H10) of the products in a supersonic molecular beam. The underlying reaction mechanisms involve the initial formation of van-der-Waals complexes followed by addition of the 5- and 6-indenyl radicals to vinylacetylene via submerged barriers, followed by isomerization (hydrogen shifts, ring closures), and termination via atomic hydrogen elimination accompanied by aromatization.

A Free-Radical Prompted Barrierless Gas-Phase Synthesis of Pentacene.

A representative, low-temperature gas-phase reaction mechanism synthesizing polyacenes via ring annulation exemplified by the formation of pentacene (C H ) along with its benzo[a]tetracene isomer (C H ) is unraveled by probing the elementary reaction of the 2-tetracenyl radical (C H ) with vinylacetylene (C H ). The pathway to pentacene-a prototype polyacene and a fundamental molecular building block in graphenes, fullerenes, and carbon nanotubes-is facilitated by a barrierless, vinylacetylene mediated gas-phase process thus disputing conventional hypotheses that synthesis of polycyclic aromatic hydrocarbons (PAHs) solely proceeds at elevated temperatures. This low-temperature pathway can launch isomer-selective routes to aromatic structures through submerged reaction barriers, resonantly stabilized free-radical intermediates, and methodical ring annulation in deep space eventually changing our perception about the chemistry of carbon in our universe.

A Unified Mechanism on the Formation of Acenes, Helicenes, and Phenacenes in the Gas Phase.

A unified low-temperature reaction mechanism on the formation of acenes, phenacenes, and helicenes-polycyclic aromatic hydrocarbons (PAHs) that are distinct via the linear, zigzag, and ortho-condensed arrangements of fused benzene rings-is revealed. This mechanism is mediated through a barrierless, vinylacetylene mediated gas-phase chemistry utilizing tetracene, [4]phenacene, and [4]helicene as benchmarks contesting established ideas that molecular mass growth processes to PAHs transpire at elevated temperatures. This mechanism opens up an isomer-selective route to aromatic structures involving submerged reaction barriers, resonantly stabilized free-radical intermediates, and systematic ring annulation potentially yielding molecular wires along with racemic mixtures of helicenes in deep space.

Gas phase synthesis of [4]-helicene.

A synthetic route to racemic helicenes via a vinylacetylene mediated gas phase chemistry involving elementary reactions with aryl radicals is presented. In contrast to traditional synthetic routes involving solution chemistry and ionic reaction intermediates, the gas phase synthesis involves a targeted ring annulation involving free radical intermediates. Exploiting the simplest helicene as a benchmark, we show that the gas phase reaction of the 4-phenanthrenyl radical ([CH]) with vinylacetylene (CH) yields [4]-helicene (CH) along with atomic hydrogen via a low-barrier mechanism through a resonance-stabilized free radical intermediate (CH).

Gas-Phase Synthesis of Triphenylene (C H ).

For the last decades, the hydrogen-abstraction-acetylene-addition (HACA) mechanism has been widely invoked to rationalize the high-temperature synthesis of PAHs as detected in carbonaceous meteorites (CM) and proposed to exist in the interstellar medium (ISM). By unravelling the chemistry of the 9-phenanthrenyl radical ([C H ] ) with vinylacetylene (C H ), we present the first compelling evidence of a barrier-less pathway leading to a prototype tetracyclic PAH - triphenylene (C H ) - via an unconventional hydrogen abstraction-vinylacetylene addition (HAVA) mechanism operational at temperatures as low as 10 K. The barrier-less, exoergic nature of the reaction reveals HAVA as a versatile reaction mechanism that may drive molecular mass growth processes to PAHs and even two-dimensional, graphene-type nanostructures in cold environments in deep space thus leading to a better understanding of the carbon chemistry in our universe through the untangling of elementary reactions on the most fundamental level.

[Pyoinflammatory complications of the permanent vascular hemodialysis access].

Of 315 patients with permanent vascular hemodialysis access, 23 (7,3%) patients developed pyoinflammatory complications in various terms after the operation. Angiogenic sepsis was registered in 73,9% of them. Lethality among patients with pyoinflammatory complications of the vascular access was 69,6%.

[Radical operative treatment of perforative gastroduodenal ulcer disease].

Data of 363 patients operated on for perforated gastric or duodenal ulcers were analyzed. Immediate and follow-up results were obtained after simple suture plication, Jadd's ulcer excision combined with stem vagotomy and after distal gastric resection. Predictors of the unfavourable outcome were determined.

[Choice of treatment method at acute gastroduodenal ulcerous bleedings].

Experience of treatment of 1307 patients with acute gastroduodenal ulcerous bleedings is analyzed. Three variants of treatment tactics are compared: expectant, active and differential. Differential tactics based on prediction of bleeding recurrence and assessment of patient's condition severity permit to improve the treatment results.

[Antisecretory therapy as a component of hemostasis in acute gastroduodenal ulcer bleedings].

Results of antisecretory therapy (pyrenzepin, H(2)-blockers, inhibitors of proton pump, octreotid) in 962 patients with acute gastroduodenal ulcer bleedings (AGDUB) were analyzed over 14-years period. Antisecretory treatment in AGDUB has principally different goals and potential depending on risk of bleeding's recurrence and morphological changes in tissue of gastroduodenal ulcer. Antisecretory therapy is the main treatment in high risk of AGDUB recurrence or before urgent surgery.

[Pathogenesis of recurrences of acute gastroduodenal ulcerous bleedings].

Based on analysis of morphologic data, oxygen regime and redox potential it is demonstrated that progressive ischemic necrosis in periulcerous zone is the basis of recurrence of gastroduodenal ulcerous bleedings. Systemic hemostatic therapy, antisecretion drugs, endoscopic methods of hemostasis don't guarantee absence of bleeding recurrence. Prognosis of recurrence of gastroduodenal ulcerous bleedings must be based on evaluation of clinical and endoscopic data.

[Recurrence of acute gastroduodenal ulcer bleedings].

Multifactor analysis of 818 cases of acute gastroduodenal ulcer bleedings (clinical and laboratory examination, gastroscopy, morphological studies) was carried out, 97 of these patients had recurrence of bleeding. It is demonstrated that recurrence of gastroduodenal ulcer bleeding is cause by progressed ischemic necrosis in periulcerous zone in condition of local hypoperfusion as a result of systemic hemodynamic disorders due to acute blood loss syndrome and chronic ischemia dueto ulcerous process. Systemic hemostatic therapy, antisecretory drugs, methods of endoscopic hemostasis don't guarantee absence of bleeding recurrence.

[Features of surgical strategy in acute cholecystitis in old patients].

Results of treatment of 197 patients at the age of 75-years and older with acute cholecystitis in terms of active (early operations) and active-delaying (delayed and elective operations) policy were analyzed. It was established that changes of gall bladder wall in old patients with acute cholecystitis are of ischemic genesis, of primary-destructive and irreversible nature leading to gangrene and phlegmon of gall bladder wall in 84% cases. In 2/3 cases clinical picture doesn't reflect destructive nature of the disease.