bluuebunny/crossref_metadata_2025 huggingface dataset:
Does Impaired Left Ventricular Relaxation Affect P Wave Dispersion in Patients with Hypertension?
Authors: Dogan Abdullah , Mehmet Ozaydin , Cem Nazli , Ahmet Altinbas , Omer Gedikli , Ozan Kinay , Oktay Ergene
Published: July 2003

Objective: P wave dispersion (PD) is considered to reflect the heterogeneous conduction in atria. We investigated whether there was a correlation between the left ventricular (LV) relaxation and PD.

Method and Results: Fifty‐three hypertensive patients ≤60 years old were divided into two groups: Group A, 27 patients, aged 54 ± 5 years with the impaired LV relaxation and Group B, 26 patients, aged 51 ± 8 years with normal LV relaxation. The P wave durations were measured in all 12 leads of ECG and PD was defined as the difference between maximum and minimum P wave duration (Pmax−Pmin). Mitral inflow velocities (E and A), E deceleration time (DT), isovolumic relaxation time (IVRT), left atrial and ventricular diameters, and wall thickness of LV were obtained by echocardiography. Clinical characteristics of both groups were comparable. The wall thickness of LV, Pmax, and left atrial dimension were not different in both groups. A velocity was higher (P < 0.001), but E velocity (P = 0.03) and E/A ratio (P < 0.001) were lower in group A than in group B. IVRT and DT were also significantly longer in group A. PD was significantly higher in group A compared to group B (51 ± 9 vs 41 ± 11 ms, P = 0.01). This difference resulted from the Pmin (61 ± 10 vs 67 ± 9 ms, P = 0.03, respectively). Multivariate analysis revealed a significant correlation between PD and A velocity (r = 0.46, P = 0.01), E/A ratio (r =−0.53, P = 0.001), DT (r = 0.65, P < 0.001), and IVRT (r = 0.73, P < 0.001).

Conclusion: This study suggests that impaired LV relaxation contributes to the heterogeneous atrial conduction in hypertensive patients.
Automatic Cardiac Event Recorders Reveal Paroxysmal Atrial Fibrillation after Unexplained Strokes or Transient Ischemic Attacks
Authors: Barthélémy Jean‐Claude , Féasson‐Gérard Séverine , Garnier Pierre , Gaspoz Jean‐Michel , Costa Antoine Da , Michel Daniel , Roche Frédéric
Published: July 2003

Background: The etiology of stroke or transitory ischemic attack (TIA) remains frequently unknown. While paroxysmal atrial fibrillation (PAF) is often suspected, its presence remains difficult to establish. Therefore, we investigated the occurrence of PAF episodes in such a population using a long‐term automatic cardiac event recorder.

Methods: We prospectively investigated 60 consecutive subjects admitted in our university hospital for stroke (n = 44) or TIA (n = 16), adding long‐term automatic cardiac event recorders, with a target duration of 4 days, to standard investigations, which included 12‐lead ECGs and 24‐hour Holter recordings.

Results: In 28 patients no etiology was found for their stroke or TIA. However, one or more than one PAF episode was found in 4 of them (14.3%) using the long‐term automatic event recorder. In the 32 remaining patients, 8 presented with PAF, and this was considered as the cause of their stroke. In both groups, AF was paroxysmal. The PAF episodes' duration went from 1 to 96 hours (mean ± standard deviation, 18 hours and 30 minutes ± 30 hours).

Conclusions: Patients suffering PAF episodes after ischemic stroke or TIA were statistically less often recognized using the 24‐hour Holter ECG recording alone than the R‐Test Evolution alone.
ST Segment Analysis by Holter Monitoring:
Authors: Bjerregaard Preben , El‐Shafei Amr , Kotar Susan L. , Labovitz Arthur J.
Published: July 2003

Background: There has been a renewed interest in ST segment analysis by Holter Monitoring, especially in multicenter clinical trials, but consensus on how to define an ischemic event is missing. We conducted a survey of European and U.S. publications involving ST segment analysis by Holter monitoring from 1975 to 2002 and found no notation of any correction for baseline ST segment depression in 52% of them. In 45% J‐point depression was required in addition to ST segment depression measured either 60 ms (24%) or 80 ms (76%) after the J point. In 28% ST segment elevations were included.

Method: Four different criteria for an ischemic event found in our survey were applied to Holter recordings from 66 patients with acute ischemic syndrome enrolled in the Esmolol Myocardial Ischemia Trial (EMIT). Only lead CM5 was used and the analyzer was a Reynolds Medical Pathfinder 600.

Results: By the most sensitive method (J + 80), there were 16 (24%) patients who had ischemic events in their Holter recording compared to only 10 (15%) patients if J‐point depression was also required. If corrections were made for baseline ST segment depression, only 3 (4.5%) recordings were positive for ischemia.

Conclusion: The outcome of Holter analysis for ischemic events is greatly dependent upon how an ischemic event is defined. Consensus on how to define an ischemic event is urgently needed.
Effect of Phenylephrine Provocation on Dispersion of Repolarization in Congenital Long QT Syndrome
Authors: Khositseth Anant , Nemec Jan , Hejlik Joseph , Shen Win K. , Ackerman Michael J.
Published: July 2003

Introduction: Syncope and sudden death are associated with sympathetic stimulation in LQT1 while LQT2 patients are more susceptible to arrhythmias during nonexertional states. Abnormal spatial (QTd)‐ and transmural (TDR)‐dispersion of repolarization may indicate increased arrhythmogenicity. This study compares the effect of phenylephrine on QTd and TDR in genotyped LQTS to control (C).

Methods and Results: Seventeen LQT1, 12 LQT2, and 18 age‐ and sex‐matched normal controls received 2 mcg/kg of phenylephrine intravenously. At baseline and peak phenylephrine effect, BP, QT, RR, Bazett's QTc, precordial QTd (QTmax−QTmin), and T‐peak to T‐end (Tp‐e) intervals were determined blinded to the patient's clinical and genotype status. Baseline QT intervals and QTc were significantly longer in LQT1 and LQT2 compared to C. Baseline QTd and Tp‐e were greater in LQT2 than either LQT1 or C: QTd = 79 ± 29 ms (LQT2), 53 ± 26 (LQT1), and 45 ± 15 (C) and Tp‐e = 120 ± 30 ms (LQT2), 99 ± 20 (LQT1), and 90 ± 11 (C). Overall, phenylephrine exerted no significant effect on either QTd or Tp‐e except with subgroup analysis of symptomatic LQTS where LQT1 and LQT2 patients had a divergent response with TDR.

Conclusions: Phenylephrine‐induced bradycardia decreased TDR in symptomatic LQT1 but increased TDR in symptomatic LQT2. The observed effects of phenylephrine are consistent with the protective effect of beta‐blocker in LQT1 and the increased arrhythmogenicity noted during nonexertional states in LQT2.
P Wave Amplitude and Duration may Predict Immediate Recurrence of Atrial Fibrillation After Internal Cardioversion
Authors: Gorenek Bulent , Birdane Alpaslan , Kudaiberdieva Gulmira , Goktekin Omer , Cavusoglu Yuksel , Unalir Ahmet , Ata Necmi , Timuralp Bilgin
Published: July 2003

Background: Although internal cardioversion (IC) for atrial fibrillation (AF) is effective at restoring sinus rhythm, immediate recurrence (IR) of AF after IC is a major and largely unpredictable clinical problem. The purpose of the study was to determine the role of P wave duration and amplitude in prediction of IR of AF after IC. Forty‐five consecutive patients undergoing IC for chronic AF were evaluated.

Material and Methods: After successful IC, 1‐minute ECG recording was obtained in all patients. P wave duration and amplitude in Lead II and V1 were measured using computer. Forty patients (88%) had successful IC. Thirteen patients experienced IR of AF within 1 minute of restoring sinus rhythm.

Results and Conclusion: As a result, the incidence of IR of AF after IC was higher in the patients with shorter P wave amplitude (for lead II P < 0.01, for V1P < 0.01) and larger P wave duration (for lead II P < 0.01, for V1P < 0.05).
Prevalence of Sensing Abnormalities in Dual Chamber Implantable Cardioverter Defibrillators
Authors: Saeed Mohammad , Jin Anna , Pontone Gregory , Higgins Steve , Gold Michael , Harari David , Nunley Steven , Link Mark S. , Homoud Munther K. , Estes N.A. Mark , Wang Paul J. ,   the LESS Investigators
Published: July 2003

Background: The clinical efficacy of ICD therapy depends on accurate sensing of intracardiac signals and sensing algorithms. We investigated the occurrence of sensing abnormalities in patients with dual chamber ICDs.

Methods: The study group consisted of all patients with dual chamber ICDs enrolled in the LESS trial and patients implanted with dual chamber ICDs at a single center between January 1997 and July 2000. Electrograms of spontaneous ventricular arrhythmias requiring device intervention were analyzed.

Results: A total of 48 patients met the criteria for enrollment. Among the 244 episodes, 215 (88%) were due to ventricular tachycardia and 29 (12%) were due to ventricular fibrillation. Overall undersensing was infrequent with 12 (20%) patients exhibiting on average 2.2 undersensed beats during 26 episodes of ventricular arrhythmias. There was no delay in therapy due to undersensing. Oversensing occurred in 5 (10%) patients resulting in 13 (2.7%) episodes of inappropriate therapy. None of the patients had any lead abnormalities and oversensing resolved after device reprogramming in 4 patients while 1 patient required a separate rate sensing lead. Among patients with oversensing, 4 out of 5 were pacing before the index event while among patients with no oversensing only 5 out of 42 were pacing (P < 0.001).

Conclusions: Dual chamber ICDs demonstrate outstanding accuracy of sensing. However, because of the selection of patient population requiring more frequent pacing, oversensing occurs with a significant frequency. Meticulous evaluation in such patients is necessary to minimize the likelihood of oversensing and inappropriate shocks.
Heart Rate Variability Declines with Increasing Age and CTG Repeat Length in Patients with Myotonic Dystrophy Type 1
Authors: Hardin Bradley A. , Lowe Miriam R. , Bhakta Deepak , Groh William J.
Published: July 2003

Background: Cardiac myopathy manifesting as arrhythmias is common in the neurological disease, myotonic dystrophy type 1 (DM1). The purpose of the present study was to evaluate heart rate variability (HRV) in patients with DM1.

Methods: In a multicenter study, history, ECG, and genetic testing were performed in DM1 patients.

Results: In 289 patients in whom the diagnosis of DM1 was confirmed by a prolonged cytosine‐thymine‐guanine (CTG) repeat length the most common ambulatory ECG abnormality was frequent ventricular ectopy (16.3%). The 24‐hour time domain parameters of SDNN (SD of the NN interval) and SDANN (SD of the mean NN, 5‐minute interval) declined as age and CTG repeat length increased (SDNN: −8.5 ms per decade, 95% confidence intervals [CI]−12.9, −4.2, −8.7 ms per 500 CTG repeats, CI −15.7, −1.8, r = 0.24, P < 0.001; SDANN: −8.1 ms per decade, CI −12.4, −3.8, −8.8 ms per 500 CTG repeats, CI −15.7, −1.9, r = 0.23, P < 0.001). Short‐term frequency domain parameters declined with age only (total power: −658 ms2 per decade, CI: −984, −331, r = 0.23, P < 0.001; low frequency (LF) power −287 ms2 per decade, CI: −397, −178, r = 0.30, P < 0.001; high frequency (HF) power: −267 ms2 per decade, CI: −386, −144, r = 0.25, P < 0.001). The LF/HF ratio increased as the patient aged (0.5 per decade, CI: 0.1, 0.9, r = 0.13, P = 0.03).

Conclusions: In DM1 patients a decline in HRV is observed as the patient ages and CTG repeat length increases.          A.N.E. 2003; 8(3):227‐232
Predictive Value of P‐Wave Signal‐Averaged Electrocardiogram for Atrial Fibrillation in Acute Myocardial Infarction
Authors: Çiçek Dilek , Çamsari Ahmet , Pekdemir Hasan , Kiykim Ahmet , Akkuş Necdet , Sezer Kerem , Diker Erdem
Published: July 2003

Background: Atrial fibrillation (AF) is a common complication of acute myocardial infarction (AMI) with a reported incidence of 7–18%. Recently, P‐wave signal‐averaged electrocardiogram (P‐SAECG) has been used to assess the risk of paroxysmal AF attacks in some diseases. The aim of this study was to determine prospectively whether patients with AMI at risk for paroxysmal AF would be identified by P‐SAECG and other clinical variables.

Methods: A total of 100 patients (mean age: 59 ± 12, 77 male, 23 female) with ST segment elevation AMI were enrolled in this study. Patients with chronic AF were excluded. At entry, all patients underwent standard 12‐lead ECG and in the first 24 hours, P‐SAECG was taken, and echocardiography and coronary angiography were performed on the patients. Patients are followed for a month in terms of paroxysmal AF attacks and mortality.

Results: AF was determined in 19 patients (19%). In patients with AF, abnormal P‐SAECG more frequently occurred than in patients without AF (37% vs 15%, P < 0.05). Patients with AF were older (70 ± 14 vs 56 ± 10, P < 0.001) and had lower left ventricular ejection fraction (42%± 8 vs 49%± 11, P < 0.05). AF was less common in thrombolysis‐treated patients (47% vs 74%, P <0.05). Thirty‐day mortality was higher in patients with AF (16% vs 2%, P = 0.05).

Conclusions: An abnormal P‐SAECG may be a predictor of paroxysmal AF in patients with AMI. Advanced age and systolic heart failure were detected as two important clinical risk factors for the development of AF.
Diagnosis of Arrhythmogenic Right Ventricular Dysplasia‐Cardiomyopathy: Value of Standard ECG Revisited
Authors: Peters Stefan , Trümmel Martina
Published: July 2003

Background: The diagnostic dilemma in arrhythmogenic right ventricular dysplasia‐cardiomyopathy (ARVD/C) is that a single diagnostic test does not exist and that there is a need for broadening diagnostic criteria. As standard ECG contributes significantly to clinical diagnosis and represents a tool for screening in family studies ECG data should be revisited.

Methods and Results: In a cohort of 265 patients (159 males, mean age 46.8 years) with ISFC/ESC criteria of ARVD/C ECG features were reevaluated.

QRS duration in (V1 + V2 + V3)/(V4 + V5 + V6) ≥ 1.2—called localized right precordial QRS prolongation—was present in 261/265 patients (98%) and represents the essential finding. Right precordial epsilon potentials were found in 23% in standard and in 75% in highly amplified and modified recording technique. Right precordial T wave inversions were present in 143 cases (54%) and ST‐segment elevation of different types in 66 patients (25%). Localized prolongation of inferior QRS complexes could be found in 58 cases (22%), complete right bundle branch block with T inversions beyond V2 in most cases in 17 patients (6%), incomplete right bundle branch block in 38 cases (14%), pseudo‐incomplete right bundle branch block in 8 patients (3%), and right precordial R wave reduction in 14 cases (5%).

Conclusion: With regard to sensitivity and already known specificity an ECG score for the diagnosis of ARVD/C was developed with high probability of ARVD/C in cases with ≥4 points, possibly without the need for an additional imaging technique.

Standard ECG with additional highly amplified and modified recording technique represents a single diagnostic test with high value in the clinical diagnosis of ARVD/C and should be used as a first line tool in noninvasive family screening.          A.N.E. 2003; 8(3):238‐245
Novel Compound Heterozygous Mutations in the KCNQ1 Gene Associated with Autosomal Recessive Long QT Syndrome (Jervell and Lange‐Nielsen syndrome)
Authors: Ning Li , Moss Arthur J. , Zareba Wojciech , Robinson Jennifer , Rosero Spencer , Ryan Dan , Qi Ming
Published: July 2003

Background: The Jervell and Lange‐Nielsen syndrome (JLNS) is the autosomal recessive form of long QT syndrome (LQTS)—a familial cardiac disorder that causes syncope, seizures, and sudden death from ventricular arrhythmias, specifically torsade de pointes. JLNS is associated with sensorineural deafness and has been shown to occur with homozygous mutations in KCNQ1 or KCNE1 in JLNS families in which QTc prolongation is inherited as a dominant trait. This study investigated the molecular pathology of a family with clinical evidence of JLNS.

Methods and Results: Single‐strand conformation polymorphism, denaturing high performance liquid chromatography, and DNA sequencing analyses were used to screen for KCNQ1 mutations. Novel compound heterozygous nonsense mutations R518X/Q530X in the C‐terminus of KCNQ1 were identified in both affected dizygotic twins; both the parents and a sibling each carried only one of the mutant alleles and were asymptomatic with modestly prolonged QTc intervals (0.46, 0.50, and 0.45 seconds, respectively). These two nonsense mutations lead to premature termination of C‐terminus with truncation of the postulated assembly domain.

Conclusion: Novel compound heterozygous nonsense mutations in C‐terminus of KCNQ1 can cause JLNS.               A.N.E 2003;8(3):246‐250
Giant J Wave on 12‐Lead Electrocardiogram in Hypothermia
Authors: Kanna Balavenkatesh , Wani Sachin
Published: July 2003

Findings on standard 12‐lead electrocardiogram in patients with hypothermia include sinus bradycardia, prolonged QT and PR interval, wide QRS complex, supraventricular and ventricular arrhythmia, and the most striking electrocardiographic abnormality, the J wave. Although characteristic of hypothermia, J wave also occurs in other conditions. The electro‐physiologic basis of J wave in hypothermia has been recently elucidated. We present a case of giant J wave due to accidental hypothermia and in addition discuss the features, mechanism, and significance of J wave in hypothermia.          A.N.E. 2003; 8(3):262‐265
Reaction paths based on mean first-passage times
Authors: Park Sanghyun , Sener Melih K. , Lu Deyu , Schulten Klaus
Published: July 2003

Finding representative reaction pathways is important for understanding the mechanism of molecular processes. We propose a new approach for constructing reaction paths based on mean first-passage times. This approach incorporates information about all possible reaction events as well as the effect of temperature. As an application of this method, we study representative pathways of excitation migration in a photosynthetic light-harvesting complex, photosystem I. The paths thus computed provide a complete, yet distilled, representation of the kinetic flow of excitation toward the reaction center, thereby succinctly characterizing the function of the system.
Surrogate Hamiltonian study of electronic relaxation in the femtosecond laser induced desorption of NO/NiO(100)
Authors: Koch Christiane P. , Klüner Thorsten , Freund Hans-Joachim , Kosloff Ronnie
Published: July 2003

A microscopic model for electronic quenching in the photodesorption of NO from NiO(100) is developed. The quenching is caused by the interaction of the excited adsorbate–substrate complex with electron hole pairs (O 2p→Ni 3d states) in the surface. The electron hole pairs are described as a bath of two level systems which are characterized by an excitation energy and a dipole charge. The parameters are connected to estimates from photoemission spectroscopy and configuration interaction calculations. Due to the localized electronic structure of NiO a direct optical excitation mechanism can be assumed, and a reliable potential energy surface for the excited state is available. Thus a treatment of all steps in the photodesorption event from first principles becomes possible for the first time. The surrogate Hamiltonian method, which allows one to monitor convergence, is employed to calculate the desorption dynamics. Desorption probabilities of the right order of magnitude and velocities in the experimentally observed range are obtained.
Temperature effects during Ostwald ripening
Authors: Madras Giridhar , McCoy Benjamin J.
Published: July 2003

Temperature influences Ostwald ripening through its effect on interfacial energy, growth rate coefficients, and equilibrium solubility. We have applied a distribution kinetics model to examine such temperature effects. The model accounts for the Gibbs–Thomson influence that favors growth of larger particles, and the dissolution of unstable particles smaller than critical nucleus size. Scaled equations for the particle size distribution and solution concentration as functions of time are solved numerically. Moments of the distribution show the temporal evolution of number and mass concentration, average particle size, and polydispersity index. Parametric and asymptotic trends are plotted and discussed in relation to reported observations. Temperature programming is proposed as a potential method to control the size distribution during the phase transition. We also explore how two crystal polymorphs can be separated by a temperature program based on different interfacial properties of the crystal forms.
Two-dimensional spectroscopy for a two-dimensional rotator coupled to a Gaussian–Markovian noise bath
Authors: Suzuki Yoko , Tanimura Yoshitaka
Published: July 2003

The dynamics of a system in the condensed phase are more clearly characterized by multitime correlation functions of physical observables than by two-time ones. We investigate a two-dimensional motion of a rigid rotator coupled to a Gaussian–Markovian harmonic oscillator bath to probe this issue. The analytical expression of a four-time correlation function of a dipole that is the observable of two-dimensional microwave or far-infrared spectroscopy is obtained from a generating functional approach. The spectra in the absence of damping are discrete and reveal transitions between eigenstates of the angular momentum quantized due to the cyclic boundary condition. For a weakly damped case, the two-dimensional spectrum predicts three echolike peaks corresponding to transition processes between the rotational energy levels, which cannot be observed in one-dimensional (linear-absorption) spectroscopy related to the two-time correlation function of the dipole [J. Phys. Soc. Jpn. 71, 2414 (2002)]. The two-dimensional spectra are more sensitive to the noise effects than the one-dimensional spectra. It is because the effects of the initial thermal distribution determine the profile of the continuous line shape in one-dimensional spectroscopy, while such thermal effects are canceled through the higher-order optical transition process in two-dimensional spectroscopy. If the rotator system is strongly coupled to the colored noise bath, the system exhibits one overdamped and other oscillatory motions. We observe peaks arising from interaction between these two modes in the two-dimensional spectra, which are difficult to distinguish in one-dimensional spectra.
Quantum Monte Carlo study of singlet–triplet transition in ethylene
Authors: El Akramine O. , Kollias A. C. , Lester W. A.
Published: July 2003

A theoretical study is reported of the transition between the ground state (1Ag) and the lowest triplet state (1 3B1u) of ethylene based on the diffusion Monte Carlo (DMC) variant of the quantum Monte Carlo method. Using DMC trial functions constructed from Hartree–Fock calculations, complete active-space self-consistent field and multiconfiguration self-consistent field wave functions, we have computed the atomization energy and heat of formation of both states and the adiabatic and vertical energy differences between these states using both all-electron and effective core potential DMC methods. The ground-state atomization energy and heat of formation are found to agree with experiment to within the error bounds of the computation and experiment. Predictions by the DMC method of the triplet-state atomization energy and heat of formation are presented. The adiabatic singlet–triplet energy difference is found to differ by 5 kcal/mol from the value obtained in a recent photodissociation experiment.
On the inversion of the 1 Bu and 2 Ag electronic states in α,ω-diphenylpolyenes
Authors: Catalán J.
Published: July 2003

An alternative model to that of the inversion of the states 1 Bu and 2 Ag is proposed for interpreting the photophysics of the α,ω-diphenylpolyenes. This model is based upon the existence of two chemical structures with Bu symmetry, which may be ascribed to the same excited electronic state 1 Bu. One of the two chemical structures corresponds to the Franck–Condon structure with conjugated single and double bonds for the polyene chain, and another consists of a nearly equivalent series of partial double bonds along the polyene chain. The latter relaxed structure is consistent with the observation of high torsional energy barriers and low photoisomerization quantum yields for diphenylhexatriene in the singlet excited state manifold. Interestingly, such a simple quantum model as that of the particle in a one-dimensional box provides quite an accurate description of the absorption spectroscopic properties of these major compounds. This is partly the result of the most stable structures for these compounds being of the all-trans type; such structures increase in length as additional ethylene units are added, which makes them very similar to a one-dimensional box becoming increasingly longer.
Predicting aqueous solubilities from aqueous free energies of solvation and experimental or calculated vapor pressures of pure substances
Authors: Thompson Jason D. , Cramer Christopher J. , Truhlar Donald G.
Published: July 2003

In this work, we explore the possibility of making predictions of solubilities from free-energy calculations by utilizing the relationship between solubility, free energy of solvation, and solute vapor pressure. Because this relationship is only strictly valid when all activity and fugacity coefficients are unity, it is not clear when it will hold and when it will break down for a given solute–solvent system. So we have tested the validity of this relationship using a variety of liquid solutes and solid solutes in liquid water solvent. In particular, we used a test set of 75 liquid solutes and 15 solid solutes composed of H, C, N, O, F, and Cl. First we compared aqueous free energies of solvation calculated from experimental solute vapor pressures and aqueous solubilities to experimental aqueous free energies of solvation for the 90 solutes in the test set and obtained a mean-unsigned error (MUE) of 0.26 kcal/mol. Second, we compared aqueous solubilities calculated from experimental solute vapor pressures and aqueous free energies of solvation to experimental aqueous solubilities for the 90 solutes in the test set and obtained a mean-unsigned error of the logarithm (MUEL) of the aqueous solubility of 0.20. These results indicate that the relation has useful accuracy. Using this relationship, we have also investigated the utility of three continuum solvation models, in particular Solvation Model 5.42R implemented at the Hartree–Fock, Becke-3–Lee–Yang–Parr, and Austin Model 1 levels (SM5.42R/HF, SM5.42R/B3LYP, and SM5.42R/AM1, respectively) to predict aqueous solubilities of liquid solutes and solid solutes in water solvent. The SM5.42R solvation model can predict the aqueous free energy of solvation and, given several solvent descriptors, it can also predict the free energy of self-solvation (which can be converted to a solute vapor pressure). We compared aqueous solubilities calculated from experimental solute vapor pressures and SM5.42R aqueous free energies of solvation to experimental aqueous solubilities for the 90 solutes in the test set and obtained an MUEL of the aqueous solubility of 0.40 for SM5.42R/HF, 0.35 for SM5.42R/B3LYP, and 0.43 for SM5.42R/AM1. We also compared aqueous solubilities calculated from SM5.42R aqueous free energies of solvation and SM5.42R vapor pressures to experimental aqueous solubilities for all 75 liquid solutes and the 7 solid solutes for which vapor pressures can be predicted by the SM5.42R solvation model; these computations yielded an MUEL of the solubility of 0.39 for SM5.42R/HF, 0.37 for SM5.42R/B3LYP, and 0.36 for SM5.42R/AM1.
A many-body model to study proteins. I. Applications to MLnm+ complexes, Mm+=Li+, Na+, K+, Mg2+, Ca2+, and Zn2+, L=H2O, CH3OH, HCONH2, n=1–6, and to small hydrogen bonded systems
Authors: Masella Michel , Cuniasse Philippe
Published: July 2003

A new model to study proteinic systems including a many-body polarization and a hydrogen bond energy contribution is presented. This model represents an extension of an earlier water many-body model [M. Masella and J.-P. Flament, J. Chem. Phys. 107 9105 (1997)]. As in this earlier model, the new model is developed to reproduce quantum computations on small molecular aggregates, and, in this first paper, we focus our efforts in developing an accurate potential to describe interactions among all nonbonded atoms occurring in proteins, and among those atoms and six cations of biological interest: Li+, Na+, K+, Mg2+, Ca2+, and Zn2+. Intramolecular degrees of freedom are described as in classical two-body force fields. In the present paper, the new model is applied to investigate the properties of small ion–neutral [M,Ln]m+ complexes and of small hydrogen-bonded systems. The results showed that this model is able to reproduce most of the theoretical quantum predictions and experimental data published until now regarding those systems.
A many-body model to study proteins. II. Incidence of many-body polarization effects on the interaction of the calmodulin protein with four Ca2+ dications and with a target enzyme peptide
Authors: Cuniasse Philippe , Masella Michel
Published: July 2003

The origin of the interactions occurring in the calmodulin protein interacting with one of its target peptide and counterions, and binding four calcium dications, has been investigated in the gas phase, using the many-body model presented in Paper I [Masella and Cuniasse, J. Chem. Phys. 119, 1866 (2003)] and a classical pairwise force field. As compared to the latter force field, the many-body model is shown to provide a geometrical description of the calmodulin/target peptide structure in better agreement with the x-ray experimental one, and a better description of the Ca2+ binding sites (as compared to “small molecule” structures reported in the Cambridge Structural Database). Regarding the energy, both models provide qualitatively a similar description of the interactions occurring in the calmodulin/target peptide system. However, quantitatively, the pairwise model predicts interaction energies greater by about 25% as compared to the many-body one in the case of calmodulin/Ca2+ interactions. This is due to the inability of pairwise force fields to account for the strong anticooperative effects predicted to occur in [Ca,(carboxylate)n]2−n systems by both the many-body model and quantum computations. Hence, the new many-body model appears to be well suited for describing proteinic systems interacting with cations, both in terms of geometry and energy.
Where the linearized Poisson–Boltzmann cell model fails: Spurious phase separation in charged colloidal suspensions
Authors: Tamashiro M. N. , Schiessel H.
Published: July 2003

The Poisson–Boltzmann (PB) spherical Wigner–Seitz cell model—introduced to theoretically describe suspensions of spherical charged colloidal particles—is investigated at the nonlinear and linearized levels. The linearization of the mean-field PB functional yields linearized Debye–Hückel-type equations agreeing asymptotically with the nonlinear PB results in the weak-coupling (high-temperature) limit. Both the canonical (fixed number of microions) as well as the semigrand-canonical (in contact with an infinite salt reservoir) cases are considered and discussed in a unified linearized framework. In disagreement with the exact nonlinear PB solution inside a Wigner–Seitz cell, the linearized theory predicts the occurrence of a thermodynamical instability with an associated phase separation of the homogeneous suspension into dilute (gas) and dense (liquid) phases, being thus a spurious result of the linearization. We show that these artifacts, although thermodynamically consistent with quadratic expansions of the nonlinear functional and osmotic pressure, may be traced back to the nonfulfillment of the underlying assumptions of the linearization. This raises questions about the reliability of the prediction of gas/liquid-like phase separation in deionized aqueous suspensions of charged colloids mediated by monovalent counterions obtained by linearized theories.
Investigation of structural fluctuation of supercritical benzene by small-angle x-ray scattering
Authors: Arai Asako Ayusawa , Morita Takeshi , Nishikawa Keiko
Published: July 2003

With the aim of studying molecular size effect on structural fluctuation, small-angle x-ray scattering (SAXS) experiments for supercritical benzene were performed for various pressures along three isothermal conditions at Tr=T/Tc=1.02, 1.04, and 1.06. From analysis of the SAXS intensities, density fluctuation 〈(ΔN)2〉/〈N〉 and correlation length ξ were obtained, which are closely related to many physicochemical properties of supercritical fluids. In order to relate the correlation length with the density fluctuation, direct-correlation range R was also obtained, which is defined by ξ2=R2〈(ΔN)2〉/〈N〉. The values of R are linearly dependent on density, and its isotherms agree with each other in the wider temperature and density ranges than the previous reports on critical phenomena. With regard to the substance dependence of structural fluctuation, the correlation length of supercritical benzene shows larger values than those of CO2, CHF3, and C2H4, while the density fluctuation of the former exhibits the same trend as the latter. The correlation lengths normalized by respective molecular sizes are in good agreement among CO2, CHF3, and C2H4 and benzene, except for H2O. As a result, the normalization is necessary for the discussion on universality of the correlation length.
Self-consistent nonperturbative theory: Treatment of colloidal-type interactions
Authors: Serrano-Illán J. , Navascués G. , Velasco E. , Mederos L.
Published: July 2003

We generalize a recently proposed self-consistent nonperturbative theory for classical systems by introducing the effect of the interaction potential in the functional form of the correlation function. The theory may be relevant for colloidal systems characterized by interactions that can be expressed in terms of a hard core plus a short-ranged term, and it is applied to two- and three-dimensional systems with Yukawa interactions. The results for the correlation function are in very good agreement with simulations, which confirms the suitability of the functional form that we propose. The thermodynamic properties are also in fair agreement with the predictions obtained by simulation, and this agreement goes over to the complete phase diagram. We believe that the theory is capable of providing more reliable results than simulation in fluid regions of the phase diagram where signals of crystalization make it difficult to accurately obtain the location of the fluid-to-solid phase transition. The theoretical predictions remain accurate even at relatively low fluid densities, a region where the theory is not intended to perform well, and an explanation based on clustering effects is provided.
Inelastic x-ray scattering from stretch-oriented polyethylene
Authors: Mermet A. , David L. , Lorenzen M. , Krisch M.
Published: July 2003

The phonon dynamics in hydrogenated stretched polyethylene was investigated using inelastic x-ray scattering. The dispersion curve of longitudinal acoustic modes describing intrachain collective motions was measured in the first Brillouin zone, and compared to inelastic neutron scattering data on deuterated similar samples. This first exploration of the collective dynamics within the first Brillouin zone reveals the presence of an additional low energy component. In spite of its large energy distribution, this feature is seen to slightly disperse with momentum transfer Q. The possible origins of this low energy scattering are discussed; arguments converge towards the collective dynamics of the amorphous regions.
Adiabatic change in the Smoluchowski equation: Orientational diffusion of polar particles
Authors: Jones R. B.
Published: July 2003

A system described by a Smoluchowski equation in configuration space is subject to slow change of external fields. The distribution function is studied by expanding it in instantaneous eigenfunctions of the adjoint Smoluchowski operator leading to an adiabatic approximation for the distribution function which is linear in the rates of change of external fields. The general result is applied to a magnetic dipole subject to slowly changing external magnetic field. Both eigenvalues and eigenfunctions are obtained analytically by a series expansion method. For slow change of field magnitude, the eigenfunction solution is compared numerically with the adiabatic approximation and with an independent numerical solution of the Smoluchowski equation. The case of slow rotation of a field of constant magnitude and an example of cyclic change involving both change of magnitude and direction of the field are studied. Significant nonequilibrium components of magnetization are generated and persist throughout the duration of slow change of external field. For the system to be regarded as in thermal equilibrium in the instantaneous external field, the rate of change of the external field must be very much slower than the intrinsic decay rates of the system.
Nucleation in confined ideal binary mixtures: The Renninger–Wilemski problem revisited
Authors: Reguera David , Reiss Howard
Published: July 2003

This paper addresses fundamental issues and models that have been used in the theory of nucleation in binary vapor systems. The meaning in thermodynamics of models is discussed, and three purely thermodynamic models are analyzed and compared. For the binary condensation nucleus, these are the capillarity model of classical nucleation theory, the modified capillarity model due to Renninger and Wilemski (RW), and the Gibbs model (usually referred to as the Gibbs theory). The Gibbs model is of course the most sophisticated and general, but its application requires more information than is available in macroscopic thermodynamic observables. Consistent thermodynamic analyses of the capillarity and RW models are performed and, for argon–krypton binary system, the two are compared with Monte Carlo simulation to assess which is the more accurate. Despite the genuinely inspired idea of the RW model, the classical model proves, by far, to be the most accurate. Finally, the extended modified liquid drop model, which is an augmentation of the classical capillarity model by an inclusion of statistical ideas such as fluctuations, is applied to the argon–krypton system. This model, which uses only macroscopic thermodynamic parameters and does not require knowledge of intermolecular potentials, predicts behavior that agrees remarkably well with the results of simulation. Its accuracy in this respect could be general enough to render it applicable to a large number of binary systems. In general the analysis in this paper makes use of fluids confined to a spherical container. This approach offers the great advantage of allowing the “nucleus” to be dealt with as a thermodynamically stable entity.
Photoinduced dynamics of the valence states of ethene: A six-dimensional potential-energy surface of three electronic states with several conical intersections
Authors: Krawczyk Robert P. , Viel Alexandra , Manthe Uwe , Domcke Wolfgang
Published: July 2003

A six-dimensional analytic potential-energy surface of the three valence states (N, V, Z) of ethene has been constructed on the basis of complete-active-space ab initio calculations and ab initio calculations with perturbation theory of second order based on a complete active reference space. The nuclear coordinate space is spanned by the torsion, the C–C stretch coordinate, the left and right pyramidalization and the symmetric and antisymmetric scissor coordinates. The C–H stretch coordinates and the CH2 rocking angles are kept frozen at their ground-state equilibrium value. A diabatic representation of the valence states of ethene has been constructed within the framework of a Hückel-type model. The diabatic potential-energy elements are represented as analytic functions of the relevant coordinates. The parameters of the analytic functions have been determined by a least-squares fit of the eigenvalues of the diabatic potential-energy matrix to the ab initio data for one-dimensional and two-dimensional cuts of the six-dimensional surface. As a function of the torsion, the analytic potential-energy surface describes the intersections of the V and Z states for torsional angles near 90°, which are converted into conical intersections by the antisymmetric scissor mode. As a function of pyramidalization of perpendicular ethene, it describes the intersections of the diabatic N and Z states, which are converted into conical intersections by displacements in the torsional mode. The analytic potential-energy surfaces can provide the basis for a quantum wave packet description of the internal conversion of photoexcited ethene to the electronic ground state via conical intersections.
Comparison between hydrogen and dihydrogen bonds among H3BNH3, H2BNH2, and NH3
Authors: Kar Tapas , Scheiner Steve
Published: July 2003

Several possible binary complexes among ammonia-borane, aminoborane, and ammonia, via hydrogen and/or dihydrogen bonds, have been investigated to understand the effect of different hybridization. Møller–Plesset second-order perturbation theory with aug-cc-pVDZ basis set was used. The interaction energy is corrected for basis set superposition error, and the Morokuma–Kitaura method was employed to decompose the total interaction energy. Like H3BNH3, the sp2 hybridized H2BNH2 also participates in H- and dihydrogen bond formation. However, such bonds are weaker than their sp3 analogs. The contractions of BN bonds are associated with blueshift in vibrational frequency and stretches of BH and NH bonds with redshift. The polarization, charge transfer, correlation, and higher-order energy components are larger in dihydrogen bonded complexes, compared to classical H-bonded ammonia dimers.
Geometrical optimization for strictly localized structures
Authors: Mo Yirong
Published: July 2003

Recently we proposed the block localized wavefunction (BLW) approach which takes the advantages of valence bond theory and molecular orbital theory and defines the wavefunctions for resonance structures based on the assumption that all electrons and orbitals are partitioned into a few subgroups. In this work, we implement the geometrical optimization of the BLW method based on the algorithm proposed by Gianinetti and coworkers. Thus, we can study the conjugation effect on not only the molecular stability, but also the molecular geometry. With this capability, the π conjugation effect in trans-polyenes C2nH2n+2 (n=2–5) as well as in formamide and its analogs are studied by optimizing their delocalized and strictly localized forms with the 6-31G(d) and 6-311+G(d,p) basis sets. Although it has been well presumed that the π resonance shortens the single bonds and lengthens the double bonds with the delocalization of π electrons across the whole line in polyenes, our optimization of the strictly localized structures quantitatively shows that when the conjugation effect is “turned off,” the double bond lengths will be identical to the CC bond length in ethylene and the single Csp2–Csp2 bond length will be about 1.513–1.517 Å. In agreement with the classical Hückel theory, the resonance energies in polyenes are approximately in proportion to the number of double bonds. Similarly, resonance is responsible not only for the planarity of formamide, thioformamide, and selenoformamide, but also for the lengthening of the CX (X=O,S,Se) double bond and the shortening of the CN bonds. Although it is assumed that the CX bond polarization decreases in the order of O>S>Se, the π electronic delocalization increases in the opposite order, i.e., formamide<thioformamide<selenoformamide. All calculations with the 6-31G(d) and 6-311+G(d,p) basis sets show that there is no noticeable basis set dependence for the results.
High resolution photoemission study of CdSe and CdSe/ZnS core-shell nanocrystals
Authors: Borchert H. , Talapin D. V. , McGinley C. , Adam S. , Lobo A. , de Castro A. R. B. , Möller T. , Weller H.
Published: July 2003

Colloidally prepared CdSe and CdSe/ZnS core-shell nanocrystals passivated with trioctylphosphine/trioctylphosphine oxide and hexadecylamine have been studied by photoelectron spectroscopy with tuneable synchrotron radiation. High-resolution spectra of the Se 3d level in CdSe nanocrystals indicate the bonding of organic ligands not only to surface Cd but also to surface Se atoms. The investigation of the CdSe/ZnS core-shell nanocrystals allows us to determine the average thickness of the ZnS shell and to study the interface between the two semiconductor nanomaterials. The photoemission spectra indicate a rather well ordered interface. No evidence for interfacial bonds other than Cd–S and Se–Zn is found.
Clarification of oxygen bonding on diamond surfaces by low energy electron stimulated desorption and high resolution electron energy loss spectroscopy
Authors: Laikhtman A. , Lafosse A. , Le Coat Y. , Azria R. , Hoffman A.
Published: July 2003

In this work we correlate between O− electron stimulated desorption (ESD) from hydrogenated and bare polycrystalline diamond films exposed to thermally activated oxygen for incident electron energies in the 4–23 eV range and vibrational electron energy losses. By utilizing the previously established mechanism of low energy ESD of O− from diamond surfaces and high resolution electron energy loss spectroscopy carried out at an incident energy below the threshold for ion desorption, the surface bonding configuration of oxygen is discussed. Such analysis reveals formation of C=O and C–O–C bonds on the bare diamond surface, as well as some adsorbed CO molecules. The bonding configuration of the hydrogenated surface before and after exposure to oxygen is found to be dependent on the hydrogenation method: ex situ microwave plasma versus in situ treatment using a hot tungsten filament for gas activation. Oxygen-related features on the ex situ hydrogenated surface are attributed to formation of C=O and C–O–H bonds, whereas in situ hydrogen treatment retains some bare parts on the film surface where C–O–C bonds can be found alongside C=O and C–O–H.
Origin of particle clustering in a simulated polymer nanocomposite and its impact on rheology
Authors: Starr Francis W. , Douglas Jack F. , Glotzer Sharon C.
Published: July 2003

Many nanoparticles have short-range interactions relative to their size, and these interactions tend to be “patchy” since the interatomic spacing is comparable to the nanoparticle size. For a dispersion of such particles, it is not a priori obvious what mechanism will control the clustering of the nanoparticles, and how the clustering will be affected by tuning various control parameters. To gain insight into these questions, we perform molecular dynamics simulations of polyhedral nanoparticles in a dense bead–spring polymer melt under both quiescent and steady shear conditions. We explore the mechanism that controls nanoparticle clustering and find that the crossover from dispersed to clustered states is consistent with the predictions for equilibrium particle association or equilibrium polymerization, and that the crossover does not appear to match the expectations for first-order phase separation typical for binary mixtures in the region of the phase diagram where we can equilibrate the system. At the same time, we cannot rule out the possibility of phase separation at a lower temperature. Utilizing the existing framework for dynamic clustering transitions offers the possibility of more rationally controlling the dispersion and properties of nanocomposite materials. Finally, we examine how nanocomposite rheology depends on the state of equilibrium clustering. We find that the shear viscosity for dispersed configurations is larger than that for clustered configurations, in contrast to expectations based on macroscopic colloidal dispersions. We explain this result by the alteration of the polymer matrix properties in the vicinity of the nanoparticles. We also show that shear tends to disperse clustered nanoparticle configurations in our system, an effect particularly important for processing.