bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continuous Separation of Racemic 3,5‐Dinitrobenzoyl‐Amino Acids in a Centrifugal Contact Separator with the Aid of Cinchona‐Based Chiral Host Compounds
Authors: Hallett Andrew J. , Kwant Gerard J. , de Vries Johannes G. 
Published: January 2009

AbstractResolution through revolution: It is possible to extract 3,5‐dinitrobenzoyl‐protected amino acids enantioselectively with the aid of a table‐top centrifugal contact separator and a catalytic amount of a chiral host compound based on the Cinchona alkaloids. Enantioselectivities of up to 80 % could be reached in a single pass. This allows the development of a process for the continuous separation of racemates.magnified imageThe resolution of racemates is mostly performed by crystallisation of diastereomeric salts. Direct physical separation could be much more efficient, but so far most concepts, with the exception of SMB, have proven to be non‐scaleable. Here we report the first scalable process for the resolution of N‐protected amino acid derivatives through selective extraction, with the aid of a catalytic amount of a chiral host compound based on Cinchona alkaloids. The method hinges on the use of centrifugal contact separators (CCSs) for fast mixing and separation. Although the highest ee obtained was only 80 %, the concept can be extended through the use of a series of CCSs in countercurrent mode to effect full separation.
The Interplay between Steric and Electronic Effects in SN2 Reactions
Authors: Fernández Israel , Frenking Gernot , Uggerud Einar 
Published: January 2009

AbstractMyths of steric hindrance: In contrast with current opinion, energy decomposition analysis shows that the presence of bulky substituents at carbon leads to the release of steric repulsion in the transition state shown in the graphic. It is rather the weakening of the electrostatic attraction, and in particular the loss of attractive orbital interactions, that are responsible for the activation barrier.magnified imageQuantum chemical calculations for SN2 reactions of H3EX/X− systems, in which E=C or Si and X=F or Cl, are reported. In the case of the carbon system we also report on bulkier species in which the hydrogen atoms are substituted by methyl groups. It is shown how the variation in the individual energy terms of the Morokuma/Ziegler energy decomposition analysis (EDA) scheme along the reaction coordinate from reactants to products provides valuable insight into the essential changes that occur in the bond‐breaking/bond‐forming process during SN2 reactions. The EDA results for the prototypical SN2 reaction of the systems [X⋅⋅⋅R3E⋅⋅⋅X]−, in which the interacting fragments are [X⋅⋅⋅X]2− and [R3E]+, have given rise to a new interpretation of the factors governing the reaction course. The EDA results for the carbon system (E=C) show that there is less steric repulsion and stronger electrostatic attraction in the transition structure than in the precursor complex and that the energy increase comes mainly from weaker orbital interactions. The larger barriers for systems in which R3 is bulkier also do not arise from increased steric repulsion, which is actually released in the transition structure. It is rather the weakening of the electrostatic attraction, and in particular the loss of attractive orbital interactions, that are responsible for the activation barrier. The D3h energy minima of the silicon homologues [XH3SiX]− is driven by the large increase in the electrostatic attractions and also of stronger orbital interactions, while the steric interactions is destabilizing.
Reviewing the Polyolefin Cyclization Reaction of the C35 Polyprene Catalyzed by Squalene‐Hopene Cyclase
Authors: Hoshino Tsutomu , Kumai Yuko , Sato Tsutomu 
Published: January 2009

AbstractA review of the polycyclization reaction of the C35 polyprenoid by squalene‐hopene cyclase: Surprisingly, our results completely disagree with a previous publication in which it was reported that a hexacyclic skeleton was constructed as the single product. In our work many tri‐ and tetracyclic scaffolds were isolated, but no penta‐ or hexacycles. The reasons for the different results and the mechanism of the polycyclization reaction are discussed (see figure).magnified imageSqualene‐hopene cyclase (SHC) catalyzes the polycyclization of squalene (C30) to the pentacyclic hopene with regio‐ and stereochemical specificity. In this study, we reviewed the polycyclization reaction of the C35 polyprenoid catalyzed by SHC. Surprisingly, our results completely disagreed with a previous publication in which it was reported that a hexacyclic skeleton was constructed as the single product in 10 % yield (I. Abe, H. Tanaka, H. Noguchi, J. Am. Chem. Soc. 2002, 124, 14514–14515). Our experimental results showed that many tri‐ and tetracyclic products, up to 12, including novel carbocyclic cores, were generated in a high conversion ratio (97 %), but no detectable amounts of the penta‐ and hexacycle were produced. The mechanisms for the formation of the C35 polyprene products isolated by us are discussed in this paper. The following four conformations were generated during the polycyclization cascade: chair‐chair‐boat, chair‐chair‐chair, chair‐chair‐chair‐boat, and chair‐chair‐chair‐chair. Larger amounts of the false intermediates with 13α‐H (tricycle) and 17α‐H (tetracycle) were produced compared with the true intermediates (13β‐H and 17β‐H), which indicates that the C35 polyprene cannot fold correctly in the enzyme cavity due to the extra C5 unit appended to squalene. This would have promoted the formation of the aborted cyclization products with tri‐ and tetracycles. In addition, the fact that no penta‐ or hexacyclic products were formed further indicates that SHC does not have sufficient space to accommodate the entire carbon framework of C35.
Diaminoterephthalates: Scaffolds for Combinatorial Chemistry
Authors: Pflantz Rebekka , Christoffers Jens 
Published: January 2009

AbstractFluorescent building blocks: Tetracarboxyamides with a central fluorescent diaminoterephthalate unit were prepared from succinyl succinates following a combinatorial‐like strategy. The 2,5‐diaminoterephthalates (see scheme; PG=protecting group) possess four points of diversification and are introduced as new scaffolds for combinatorial chemistry.magnified image2,5‐Diaminoterephthalates that possess four points of diversification are introduced as new scaffolds for combinatorial chemistry. A straightforward synthesis of an orthogonally protected platform compound was developed. This platform was transformed by stepwise deprotection and amidation of the two amino and two carboxylic acid moieties into tetra‐amides with a central aromatic ring as a fluorescence chromophore.
Structure and Electronic Configuration of an Iron(II) Complex in a LIESST State: A Pump and Probe Method
Authors: Sheu Chou‐Fu , Chen Kowa , Chen Szu‐Miao , Wen Yuh‐Sheng , Lee Gene‐Hsiang , Chen Jin‐Ming , Lee Jyh‐Fu , Cheng Bing‐Ming , Sheu Hwo‐Shuenn , Yasuda Nobuhiro , Ozawa Yoshiki , Toriumi Koshiro , Wang Yu 
Published: January 2009

AbstractSwitchable molecules: The electronic configurations of the Fe center in trans‐[Fe(tzpy)2(NCS)2] in low‐spin, high‐spin, and LIESST states (LIESST=light‐induced excited spin‐state trapping) were confirmed by K‐ and L‐edge X‐ray absorption and magnetic measurements. The molecular structures at 40 K before and after irradiation are superimposed in the picture, which demonstrates a single‐crystal‐to‐single‐crystal transition by irradiation.magnified imageTwo polymorphs of mononuclear six‐coordinate iron(II) spin‐crossover complex trans‐[Fe(tzpy)2(NCS)2] (tzpy=3‐(2‐pyridyl)[1,2,3]triazolo[1,5‐a]pyridine) (1) were isolated and structurally characterized. According to the thermally dependent magnetic measurements, polymorph A undergoes a gradual spin transition from a paramagnetic high‐spin state (5T2, S=2, HS‐1) above 200 K to a diamagnetic low‐spin state (1 A1, S=0, LS‐1) below 120 K, whereas polymorph B shows an abrupt spin transition with T1/2 at 102 K. Molecular and crystal structures of polymorph A in the HS‐1 and LS‐1 states were studied at 300 and 40 K, respectively. Significant differences in FeN distances and coordination geometries of Fe were found between the two spin states, as expected. Light‐induced excited spin state trapping (LIESST) was observed upon irradiating the crystal with 532 nm laser light at 40 K, whereupon a metastable high‐spin state (HS‐2) was formed; the molecular and crystal structure of this metastable state were investigated by a pump and probe method because of its relatively fast relaxation. The electronic configuration of the Fe center in the HS‐1, LS‐1, and LIESST (HS‐2) states were further confirmed by Fe K‐ and L‐edge absorption spectroscopy. In addition, the CN stretching frequency on the ligand can also be followed through the spin transition. The excitation and relaxation process concerning such metastable state were followed by the CN stretching frequency and magnetic susceptibility measurements in the temperature ranges 15–55 K and 5–80 K, respectively. The structure and electronic configuration of the LIESST state of polymorph A were firmly established by X‐ray diffraction, X‐ray absorption, infrared absorption, and magnetic measurements. A single‐crystal‐to‐single‐crystal transition through irradiation was demonstrated. The changes in structure and electronic configuration as a result of the spin transition are believed to occur concurrently.
Synthesis of Tricyclic Fused 3‐Aminopyridines through Intramolecular CoI‐Catalyzed [2+2+2] Cycloaddition between Ynamides, Nitriles, and Alkynes
Authors: Garcia Pierre , Moulin Solenne , Miclo Yves , Leboeuf David , Gandon Vincent , Aubert Corinne , Malacria Max 
Published: January 2009

AbstractThree‐ring circus: An expedient route to tricyclic fused 2‐trimethylsilyl‐3‐aminopyridines exhibiting unprecedented skeletons is described. The key step is a very efficient cobalt‐catalyzed [2+2+2] cycloaddition of a polyunsaturated compound displaying an ynamide, an alkyne, and a nitrile functionality (see picture).magnified imageThe first [2+2+2] cocyclizations between ynamides, nitriles, and alkynes are reported. They open a new access to unprecedented nitrogen‐containing heterocycles of type 2‐trimethylsilyl‐3‐aminopyridines. Such frameworks, which can be found in various compounds of biological interest, are very difficult to prepare by conventional methods. However, using [CpCo(C2H4)2] (Cp=cyclopentadienyl) as catalyst, the intramolecular cyclizations could be achieved in up to 100 % yield. The presence of the trimethylsilyl group allowed a rare type of Hiyama cross‐coupling: one of the silylated pyridines could be coupled with p‐iodoanisole to give a new type of biaryl system.
ChemInform Abstract: Structure Effect of TsDPEN Derivatives on Enantioselectivity of Asymmetric Transfer Hydrogenation.
Authors: Liu Juntao , Wu Yinuo , Li Xingshu , Chan Albert S. C. 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Ionic Polymer‐Supported Copper(I): A Reusable Catalyst for Huisgen′s 1,3‐Dipolar Cycloaddition.
Authors: Sirion Uthaiwan , Bae Yu Jin , Lee Byoung Se , Chi Dae Yoon 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Synthesis of Novel Bis‐1,3,4‐thiadiazoles, Bis‐1,2,4‐triazoles and Their Antimicrobial Activity.
Authors: Burghate Megha K. , Burghate S. K. , Berad B. N. 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: A Highly Efficient Catalyst‐Free Cycloisomerization Approach to Indolizinones.
Authors: Kim Ikyon , Choi Jihyun , Lee Sunkyung , Lee Ge Hyeong 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Magnetism in Graphene Systems
Authors: Kan Erjun , Li Zhenyu , Yang Jinlong 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Solid‐State Ionic Devices
Authors: Wachsman Eric D. , Traversa Enrico 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Supramolecular Coordination Chemistry: The Synergistic Effect of Serendipity and Rational Design
Authors: Saalfrank Rolf W. , Maid Harald , Scheurer Andreas 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Bidentate Ligands Containing a Heteroatom—Phosphorus Bond
Authors: Kok Stanton H. L. , Au‐Yeung Terry T.‐L. , Cheung Hong Yee , Lam Wing Sze , Chan Shu Sun , Chan Albert S. C. 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Metal—Organic Frameworks for Asymmetric Catalysis and Chiral Separations
Authors: Lin Wenbin 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Bile Acid Scaffolds in Supramolecular Chemistry: The Interplay of Design and Synthesis
Authors: Davis Anthony P. 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Thermodynamically Controlled Deracemization Utilizing Inclusion Complexation
Authors: Kaku Hiroto 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Sesquiterpene Lactones and Their Precursors as Chemosystematic Markers in the Tribe Cichorieae of the Asteraceae
Authors: Zidorn Christian 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Large‐Scale Recordings for Drug Screening in Neural Circuit Systems
Authors: Ikegaya Yuji 
Published: January 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Angiographic and Clinical Implications of Combined ST‐segment Elevation in Anterior and Inferior Leads in Acute Myocardial Infarction
Authors: Jim Man‐Hong , Chan Annie On‐On , Tang Man‐Oi , Siu Chung‐Wah , Lee Stephen Wai‐Luen , Lau Chu‐Pak 
Published: January 2009

AbstractBackgroundThe clinical and angiographic findings of patients suffered from acute myocardial infarction (MI) and presented with combined ST elevation in both anterior and inferior leads remain unclear.HypothesisThese patients might have ≥ 1 coronary arteries occluded.MethodsFrom January 2002 to December 2006, 49 consecutive patients were found to have ST elevation in both anterior and inferior leads during myocardial infarction. Patients who had left circumflex artery occlusion (acute or chronic) were excluded. These patients were divided into 4 types according to the infarct‐related artery (IRA) and status of the contralateral vessel patency: left anterior descending artery (LAD) as the IRA with a patent right coronary artery (RCA) (type 1A, n = 25); LAD as IRA with an occluded RCA (type 1B, n = 1); RCA as IRA with a patent LAD (type 2A, n = 19); and RCA as IRA with an occluded LAD (type 2B, n = 4).ResultsSingle vessel occlusion (type A angiographic pattern) was found in 90% of patients. Type 1A patients had a larger infarct size than that of 2A. ST elevation in V2 ≥ V3 identified RCA as the IRA with a high specificity (92%) and sensitivity (74%). Type 2B patients (2‐vessel occlusion) had a larger infarct size than that of 2A; however, no electrocardiogram (ECG) criteria could reliably differentiate them.ConclusionIn a real world situation, single vessel occlusion is found in the majority of cases of combined ST elevation in anterior and inferior leads. ST elevation in V2 ≥ V3 distinguishes RCA against LAD as the IRA with high accuracy. Copyright © 2009 Wiley Periodicals, Inc.
Target‐organ protection with combination renin‐angiotensin‐system blockade
Authors: PrisantMD L. Michael 
Published: January 2009

AbstractPharmacologic blockade of the renin‐angiotensin‐aldosterone system (RAS) has antihypertensive, anti‐atherogenic, antioxidant, and anti‐inflammatory effects. Treatment with angiotensin‐converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) has been demonstrated to prevent atrial fibrillation and new‐onset diabetes, and provide cardiac, cerebral, and renal protection. Combination therapy with ACEIs and ARBs, compared with monotherapy, provides enhanced reno‐ and cardioprotection, although available data indicate that combination RAS blockade may be beneficial only in select patient groups, such as those with diabetes mellitus, chronic kidney disease, or heart failure (HF). In certain high‐risk patients, the use of ARBs provides comparable efficacy to that observed with ACEIs. The efficacy of these agents may stem from pleiotropic effects beyond blood pressure (BP) reduction. Several studies demonstrate achievement of clinical endpoints without significant effects on BP. Copyright © 2009 Wiley Periodicals, Inc.
Utility of implantable loop recorders for diagnosing unexplained syncope in clinical practice
Authors: Entem Felipe R. , Enriquez Susana G. , Cobo Manuel , Expósito Víctor , Llano Miguel , Ruiz Marta , Jose Olalla Juan , Otero‐Fernandez Macarena 
Published: January 2009

AbstractBackgroundEstablishing a symptom–rhythm correlation in patients with unexplained syncope is complicated because of its sporadic, infrequent, and unpredictable nature. Prolonged monitoring with an implantable loop recorder (ILR) allows the recording of electrocardiogram (ECG) data from a spontaneous syncopal event.HypothesisThe aim of this study was to evaluate the usefulness of the ILR for the diagnosis of syncope of unknown origin after conventional management in clinical practice.MethodsWe reviewed the results with ILR implantation in patients with syncope of unknown origin after conventional management in the cardiology department at HU Marques de Valdecilla (Santander, Cantabria, Spain).ResultsOne hundred and forty patients (age 64 ± 16 y; 86 male [62%]) with syncope of unknown etiology after conventional work‐up underwent prolonged monitoring with an ILR from September 1998 to February 2006; 46 patients (33%) had structural heart disease. During a mean follow‐up of 346 ± 160 d, 51 patients (36.5%) had recurrent syncope with diagnostic ECG recording. An arrhythmic cause for syncope was found in 33 of them (64.5%), with bradycardia present in 27 (53%) and tachycardia in 6 (11%). There were no sudden deaths, and 1 patient suffered a complication related to a recurrence of syncope.ConclusionLong‐time experience with the ILR confirmed the utility of this device in the diagnosis of unexplained syncope in clinical practice. Most of these patients had syncope of arrhythmogenic etiology that could be successfully treated. This strategy of prolonged monitoring is safe even in patients with structural heart disease. Copyright © 2009 Wiley Periodicals, Inc.
Current trends in heart failure readmission rates: analysis of medicare data
Authors: Aranda Juan M. , Johnson James W. , Conti Jamie B. 
Published: January 2009

AbstractBackgroundDespite advances in optimal pharmacologic therapy, patients with heart failure (HF) continue to have significant rehospitalization rates.HypothesisWe sought to provide current estimates on rates of readmission for Medicare patients with HF, and identify factors associated with an increased chance of readmission.MethodsWe used Medicare data from the 5% sample Standard Analytical File Limited Data Set for the years 2002 through 2004 to calculate readmission rates for HF. Clinical factors associated with readmission rates were identified using multivariate logistic regression.ResultsWe identified 28,919 patients accounting for 38,849 HF hospitalizations in the 5% sample for 2003. These numbers project to an estimated 578,380 patients with 776,980 HF hospitalizations. In‐hospital mortality was 4.4% with an average length of stay of 5.5 ± 5.4 d. In the 6—9 mo following the initial HF admission, 60% of patients had 1 or more readmissions for any cause. Heart failure accounted for 28% of all readmissions. Factors associated with readmission for HF after the initial HF hospitalization included age < 65 y, geographic location, previous hospitalization, length of stay of initial HF hospitalization > 7 d, not receiving a cardiac device implant at the time of initial HF hospitalization, and history of comorbidities including diabetes, myocardial infarction, peripheral vascular disease, and stroke.ConclusionsMedicare patients with HF continue to have significant morbidity and one of the highest in‐hospital mortality rates of any HF patient population. Factors associated with worse outcomes after an initial HF hospitalization can be used to identify patients who require aggressive therapy and follow‐up. Copyright © 2009 Wiley Periodicals, Inc.