Publications by authors named "Mohamed Abdel-Mottaleb"

22 Publications

  • Page 1 of 1

Convolutional neural networks for breast cancer detection in mammography: A survey.

Comput Biol Med 2021 Apr 9;131:104248. Epub 2021 Feb 9.

University of Miami, Department of Electrical and Computer Engineering, Memorial Dr, Coral Gables, FL, 33146, USA. Electronic address:

Despite its proven record as a breast cancer screening tool, mammography remains labor-intensive and has recognized limitations, including low sensitivity in women with dense breast tissue. In the last ten years, Neural Network advances have been applied to mammography to help radiologists increase their efficiency and accuracy. This survey aims to present, in an organized and structured manner, the current knowledge base of convolutional neural networks (CNNs) in mammography. The survey first discusses traditional Computer Assisted Detection (CAD) and more recently developed CNN-based models for computer vision in mammography. It then presents and discusses the literature on available mammography training datasets. The survey then presents and discusses current literature on CNNs for four distinct mammography tasks: (1) breast density classification, (2) breast asymmetry detection and classification, (3) calcification detection and classification, and (4) mass detection and classification, including presenting and comparing the reported quantitative results for each task and the pros and cons of the different CNN-based approaches. Then, it offers real-world applications of CNN CAD algorithms by discussing current Food and Drug Administration (FDA) approved models. Finally, this survey highlights the potential opportunities for future work in this field. The material presented and discussed in this survey could serve as a road map for developing CNN-based solutions to improve mammographic detection of breast cancer further.
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http://dx.doi.org/10.1016/j.compbiomed.2021.104248DOI Listing
April 2021

Multidisease Deep Learning Neural Network for the Diagnosis of Corneal Diseases.

Am J Ophthalmol 2021 Jan 30;226:252-261. Epub 2021 Jan 30.

Bascom Palmer Eye institute, Miller School of Medicine, University of Miami, Miami; Electrical and Computer Engineering, University of Miami, Coral Gables; Biomedical Engineering, University of Miami, Coral Gables, Florida, USA. Electronic address:

Purpose: To report a multidisease deep learning diagnostic network (MDDN) of common corneal diseases: dry eye syndrome (DES), Fuchs endothelial dystrophy (FED), and keratoconus (KCN) using anterior segment optical coherence tomography (AS-OCT) images.

Study Design: Development of a deep learning neural network diagnosis algorithm.

Methods: A total of 158,220 AS-OCT images from 879 eyes of 478 subjects were used to develop and validate a classification deep network. After a quality check, the network was trained and validated using 134,460 images. We tested the network using a test set of consecutive patients involving 23,760 AS-OCT images of 132 eyes of 69 patients. The area under receiver operating characteristic curve (AUROC), area under precision-recall curve (AUPRC), and F1 score and 95% confidence intervals (CIs) were computed.

Results: The MDDN achieved eye-level AUROCs >0.99 (95% CI: 0.90, 1.0), AUPRCs > 0.96 (95% CI: 0.90, 1.0), and F1 scores > 0.90 (95% CI: 0.81, 1.0) for DES, FED, and KCN, respectively.

Conclusions: MDDN is a novel diagnostic tool for corneal diseases that can be used to automatically diagnose KCN, FED, and DES using only AS-OCT images.
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http://dx.doi.org/10.1016/j.ajo.2021.01.018DOI Listing
January 2021

Correcting Higher Order Aberrations Using Image Processing.

IEEE Trans Image Process 2021 26;30:2276-2287. Epub 2021 Jan 26.

Higher Order Aberrations (HOAs) are complex refractive errors in the human eye that cannot be corrected by regular lens systems. Researchers have developed numerous approaches to analyze the effect of these refractive errors; the most popular among these approaches use Zernike polynomial approximation to describe the shape of the wavefront of light exiting the pupil after it has been altered by the refractive errors. We use this wavefront shape to create a linear imaging system that simulates how the eye perceives source images at the retina. With phase information from this system, we create a second linear imaging system to modify source images so that they would be perceived by the retina without distortion. By modifying source images, the visual process cascades two optical systems before the light reaches the retina, a technique that counteracts the effect of the refractive errors. While our method effectively compensates for distortions induced by HOAs, it also introduces blurring and loss of contrast; a problem that we address with Total Variation Regularization. With this technique, we optimize source images so that they are perceived at the retina as close as possible to the original source image. To measure the effectiveness of our methods, we compute the Euclidean error between the source images and the images perceived at the retina. When comparing our results with existing corrective methods that use deconvolution and total variation regularization, we achieve an average of 50% reduction in error with lower computational costs.
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http://dx.doi.org/10.1109/TIP.2021.3051499DOI Listing
January 2021

3DCD: Scene Independent End-to-End Spatiotemporal Feature Learning Framework for Change Detection in Unseen Videos.

IEEE Trans Image Process 2021 24;30:546-558. Epub 2020 Nov 24.

Change detection is an elementary task in computer vision and video processing applications. Recently, a number of supervised methods based on convolutional neural networks have reported high performance over the benchmark dataset. However, their success depends upon the availability of certain proportions of annotated frames from test video during training. Thus, their performance on completely unseen videos or scene independent setup is undocumented in the literature. In this work, we present a scene independent evaluation (SIE) framework to test the supervised methods in completely unseen videos to obtain generalized models for change detection. In addition, a scene dependent evaluation (SDE) is also performed to document the comparative analysis with the existing approaches. We propose a fast (speed-25 fps) and lightweight (0.13 million parameters, model size-1.16 MB) end-to-end 3D-CNN based change detection network (3DCD) with multiple spatiotemporal learning blocks. The proposed 3DCD consists of a gradual reductionist block for background estimation from past temporal history. It also enables motion saliency estimation, multi-schematic feature encoding-decoding, and finally foreground segmentation through several modular blocks. The proposed 3DCD outperforms the existing state-of-the-art approaches evaluated in both SIE and SDE setup over the benchmark CDnet 2014, LASIESTA and SBMI2015 datasets. To the best of our knowledge, this is a first attempt to present results in clearly defined SDE and SIE setups in three change detection datasets.
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http://dx.doi.org/10.1109/TIP.2020.3037472DOI Listing
November 2020

Pathological-Corneas Layer Segmentation and Thickness Measurement in OCT Images.

Transl Vis Sci Technol 2020 10 21;9(11):24. Epub 2020 Oct 21.

Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Miami, FL, USA.

Purpose: The purpose of this study was to propose a new algorithm for the segmentation and thickness measurement of pathological corneas with irregular layers using a two-stage graph search and ray tracing.

Methods: In the first stage, a graph, with only gradient edge-cost, is used to segment the air-epithelium and endothelium-aqueous boundaries. In the second stage, a graph, with gradient, directional, and multiplier edge-cost, is used to correct segmentation. The optical coherence tomography (OCT) image is flattened using the air-epithelium boundary and a graph search is used to segment the epithelium-Bowman's and Bowman's-stroma boundaries. Then, the OCT image is flattened using the endothelium-aqueous boundary and a graph search is used to segment the Descemet's membrane. Ray tracing is used to correct the inter-boundary distances, then the thickness is measured using the shortest distance. The proposed algorithm was trained and evaluated using 190 OCT images manually segmented by trained operators.

Results: The mean and standard deviation of the unsigned errors of the algorithm-operator and inter-operator were 0.89 ± 1.03 and 0.77 ± 0.68 pixels in segmentation and 3.62 ± 3.98 and 2.95 ± 2.52 µm in thickness measurement.

Conclusions: Our proposed algorithm can produce accurate segmentation and thickness measurements compared with the manual operators.

Translational Relevance: Our algorithm could be potentially useful in the clinical practice.
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http://dx.doi.org/10.1167/tvst.9.11.24DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7594599PMC
October 2020

DU-Net: Convolutional Network for the Detection of Arterial Calcifications in Mammograms.

IEEE Trans Med Imaging 2020 10 23;39(10):3240-3249. Epub 2020 Apr 23.

Breast arterial calcifications (BACs) are part of several benign findings present on some mammograms. Previous studies have indicated that BAC may provide evidence of general atherosclerotic vascular disease, and potentially be a useful marker of cardiovascular disease (CVD). Currently, there is no technique in use for the automatic detection of BAC in mammograms. Since a majority of women over the age of 40 already undergo breast cancer screening with mammography, detecting BAC may offer a method to screen women for CVD in a way that is effective, efficient, and broad reaching, at no additional cost or radiation. In this paper, we present a deep learning approach for detecting BACs in mammograms. Inspired by the promising results achieved using the U-Net model in many biomedical segmentation problems and the DenseNet in semantic segmentation, we extend the U-Net model with dense connectivity to automatically detect BACs in mammograms. The presented model helps to facilitate the reuse of computation and improve the flow of gradients, leading to better accuracy and easier training of the model. We evaluate the performance using a set of full-field digital mammograms collected and prepared for this task from a publicly available dataset. Experimental results demonstrate that the presented model outperforms human experts as well as the other related deep learning models. This confirms the effectiveness of our model in the BACs detection task, which is a promising step in providing a cost-effective risk assessment tool for CVD.
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http://dx.doi.org/10.1109/TMI.2020.2989737DOI Listing
October 2020

Expansion of Peripheral Visual Field with Novel Virtual Reality Digital Spectacles.

Am J Ophthalmol 2020 02 15;210:125-135. Epub 2019 Oct 15.

Bascom Palmer Eye Institute, University of Miami, Miami, Florida, USA; Department of Electrical and Computer Engineering, University of Miami, Miami, Florida, USA; Biomedical Engineering Department, University of Miami, Miami, Florida, USA. Electronic address:

Purpose: To examine an image remapping method for peripheral visual field (VF) expansion with novel virtual reality digital spectacles (DSpecs) to improve visual awareness in glaucoma patients.

Design: Prospective case series.

Methods: Monocular peripheral VF defects were measured and defined with a head-mounted display diagnostic algorithm. The monocular VF was used to calculate remapping parameters with a customized algorithm to relocate and resize unseen peripheral targets within the remaining VF. The sequence of monocular VF was tested and customized image remapping was carried out in 23 patients with typical glaucomatous defects. Test images demonstrating roads and cars were used to determine increased awareness of peripheral hazards while wearing the DSpecs. Patients' scores in identifying and counting peripheral objects with the remapped images were the main outcome measurements.

Results: The diagnostic monocular VF testing algorithm was comparable to standard automated perimetric determination of threshold sensitivity based on point-by-point assessment. Eighteen of 23 patients (78%) could identify safety hazards with the DSpecs that they could not previously. The ability to identify peripheral objects improved with the use of the DSpecs (P = 0.024, chi-square test). Quantification of the number of peripheral objects improved with the DSpecs (P = 0.0026, Wilcoxon rank sum test).

Conclusions: These novel spectacles may enhance peripheral objects awareness by enlarging the functional field of view in glaucoma patients.
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http://dx.doi.org/10.1016/j.ajo.2019.10.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7002244PMC
February 2020

Toward Improving the Mobility of Patients with Peripheral Visual Field Defects with Novel Digital Spectacles.

Am J Ophthalmol 2020 02 10;210:136-145. Epub 2019 Oct 10.

Bascom Palmer Eye Institute, University of Miami, Miami, Florida, USA; Department of Electrical and Computer Engineering, University of Miami, Miami, Florida, USA; Biomedical Engineering Department, University of Miami, Miami, Florida, USA. Electronic address:

Purpose: To assess the efficacy of novel Digital spectacles (DSpecs) to improve mobility of patients with peripheral visual field (VF) loss.

Design: Prospective case series.

Methods: Binocular VF defects were quantified with the DSpecs testing strategy. An algorithm was implemented that generated personalized visual augmentation profiles based on the measured VF. These profiles were achieved by relocating and resizing video signals to fit within the remaining VF in real time. Twenty patients with known binocular VF defects were tested using static test images, followed by dynamic walking simulations to determine if they could identify objects and avoid obstacles in an environment mimicking a real-life situation. The effect of the DSpecs were assessed for visual/hand coordination with object-grasping tests. Patients performed these tests with and without the DSpecs correction profile.

Results: The diagnostic binocular VF testing with the DSpecs was comparable to the integrated monocular standard automated perimetry based on point-by-point assessment with a mismatch error of 7.0%. Eighteen of 20 patients (90%) could identify peripheral objects in test images with the DSpecs that they could not previously. Visual/hand coordination was successful for 17 patients (85%) from the first trial. The object-grasping performance improved to 100% by the third trial. Patient performance, judged by finding and identifying objects in the periphery in a simulated walking environment, was significantly better with the DSpecs (P = 0.02, Wilcoxon rank sum test).

Conclusions: DSpecs may improve mobility by facilitating the ability of patients to better identify moving peripheral hazardous objects.
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http://dx.doi.org/10.1016/j.ajo.2019.10.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7002240PMC
February 2020

Automatic Segmentation of Corneal Microlayers on Optical Coherence Tomography Images.

Transl Vis Sci Technol 2019 May 11;8(3):39. Epub 2019 Jun 11.

Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Miami, FL, USA.

Purpose: To propose automatic segmentation algorithm (AUS) for corneal microlayers on optical coherence tomography (OCT) images.

Methods: Eighty-two corneal OCT scans were obtained from 45 patients with normal and abnormal corneas. Three testing data sets totaling 75 OCT images were randomly selected. Initially, corneal epithelium and endothelium microlayers are estimated using a corneal mask and locally refined to obtain final segmentation. Flat-epithelium and flat-endothelium images are obtained and vertically projected to locate inner corneal microlayers. Inner microlayers are estimated by translating epithelium and endothelium microlayers to detected locations then refined to obtain final segmentation. Images were segmented by trained manual operators (TMOs) and by the algorithm to assess repeatability (i.e., intraoperator error), reproducibility (i.e., interoperator and segmentation errors), and running time. A random masked subjective test was conducted by corneal specialists to subjectively grade the segmentation algorithm.

Results: Compared with the TMOs, the AUS had significantly less mean intraoperator error (0.53 ± 1.80 vs. 2.32 ± 2.39 pixels; < 0.0001), it had significantly different mean segmentation error (3.44 ± 3.46 vs. 2.93 ± 3.02 pixels; < 0.0001), and it had significantly less running time per image (0.19 ± 0.07 vs. 193.95 ± 194.53 seconds; < 0.0001). The AUS had insignificant subjective grading for microlayer-segmentation grading (4.94 ± 0.32 vs. 4.96 ± 0.24; = 0.5081), but it had significant subjective grading for regional-segmentation grading (4.96 ± 0.26 vs. 4.79 ± 0.60; = 0.025).

Conclusions: The AUS can reproduce the manual segmentation of corneal microlayers with comparable accuracy in almost real-time and with significantly better repeatability.

Translational Relevance: The AUS can be useful in clinical settings and can aid the diagnosis of corneal diseases by measuring thickness of segmented corneal microlayers.
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http://dx.doi.org/10.1167/tvst.8.3.39DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6561132PMC
May 2019

Evaluation of endothelial/Descemet membrane complex of eye bank donor corneas using enhanced depth imaging optical coherence tomography.

Clin Ophthalmol 2019 8;13:789-794. Epub 2019 May 8.

Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, FL, USA.

We present a novel method for screening eye bank donor corneas using high definition optical coherence tomography (HD-OCT). This technology allows for the quantification of endothelial/Descemet membrane (En/DM) complex thickness ex vivo. Prospective interventional study. Fifty-two corneal grafts from 27 donors were included in this study. Twenty additional control eyes and 11 eyes with Fuchs' endothelial corneal dystrophy were also evaluated for comparison. A custom built, high speed HD-OCT device (Envisu R2210, Bioptigen, Buffalo Grove, IL, USA) was used to obtain images, and custom-made graph-based segmentation software was used to automatically deconstruct corneal images into micro-layers. HD-OCT imaging was used to scan through the sealed sterile case of donor corneas stored in McCarey-Kaufman medium to image their En/DM complex through the center of the cornea. This technology allowed for quantification of En/DM complex thickness in all donor corneas through the sealed sterile container used to transport graft tissue. Mean En/DM complex thickness of donor corneas was 17±4 μm. The difference between donor cornea En/DM thickness and that of control subjects (16±2 μm) was not statistically significant (=0.3), suggesting that the transport container and media do not affect measurements. There was a significant difference between En/DM thickness of Fuchs' endothelial corneal dystrophy eyes (25±5 μm) and both donor corneas (<0.0001) and control subjects (<0.0001). We have described a new technique to measure En/DM complex thickness in eye bank donor corneas stored in a sealed sterile case. This may represent a novel adjunctive approach to screen corneal grafts for early endothelial disease.
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http://dx.doi.org/10.2147/OPTH.S185455DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6514128PMC
May 2019

Novel chitosan-ZnO based nanocomposites as luminescent tags for cellulosic materials.

Carbohydr Polym 2014 Jan 6;99:817-24. Epub 2013 Sep 6.

Department of Forgery and Counterfeiting Research, Forensic Medicine Authority, Ministry of Justice, El-Sayeda Zeinab, 11461 Cairo, Egypt. Electronic address:

Novel chitosan-ZnO composites have been synthesized as luminescent taggants for cellulosic materials. The synthesized chitosan-ZnO nanospheres (CS-ZnO NS), chitosan-ZnO-oleic acid quantum dots (CS-ZnO-oleic QD) and chitosan-ZnO-oleic acid:Eu(3+) doped nanorods (CS-ZnO-oleic:Eu(3+) NR) were characterized by X-ray diffraction, photoluminescence spectroscopy, FTIR spectroscopy and transmission electron microscopy. The prepared luminescent CS-ZnO composites were used in printing paste and applied to different types of papers and textiles by using screen printing technique. The colorimetric values of the printed CS-ZnO-oleic acid and CS-ZnO-oleic:Eu(3+) showed that printing caused slightly change in color values. Scanning electron microscopy images and color values of the printed surface showed that CS-ZnO-oleic QD and highly luminescence CS-ZnO-olic:Eu(3+) NR are suitable for use as a printed security feature.
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http://dx.doi.org/10.1016/j.carbpol.2013.08.096DOI Listing
January 2014

Formation principles and ligand dynamics of nanoassemblies of CdSe quantum dots and functionalised dye molecules.

Chemphyschem 2012 Mar 23;13(4):959-72. Epub 2011 Dec 23.

Chemnitz University of Technology, Institute of Physics and Center for Nanostructured, Materials and Analytics (nanoMA), Reichenhainer Str. 70, 09107 Chemnitz, Germany.

Functional dye molecules, such as porphyrins, attached to CdSe quantum dots (QDs) through anchoring meso-pyridyl substituents, form quasi-stable nanoassemblies. This fact results in photoluminescence (PL) quenching of the QDs both due to Förster resonance energy transfer (FRET) and the formation of non-radiative surface states under conditions of quantum confinement (non-FRET). The formation process is in competition with the ligand dynamics. At least two timescales are found for the formation of the assemblies: 1) one faster than 60 s attributed to saturation of empty attachment sites and 2) one slower than 600 s, which is attributed to a reorganisation of the tri-n-octylphosphine oxide (TOPO) ligand shell. Finally, this process results in almost complete exchange of the TOPO shell by porphyrin dye molecules. Following a Stern-Volmer analysis, we established a microscopic description of PL quenching and assembly formation. Based on this formalism, we determined the equilibrium constant for assembly formation between QDs and the pyridyl-functionalised dye molecules to be K ≈ 10(5) - 10(7)  M(-1), which is several orders of magnitude larger than that of the TOPO ligands. Our results give additional insights into the non-FRET PL quenching processes involved and show that the QD surface is inhomogeneous with respect to the involved attachment and detachment processes. In comparison with other methods, such as NMR spectroscopy, the advantage of our approach is that ligand dynamics can be investigated at extremely low ratios of dye molecules to QDs.
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http://dx.doi.org/10.1002/cphc.201100711DOI Listing
March 2012

Identification of different donor-acceptor structures via Förster Resonance Energy Transfer (FRET) in quantum-dot-perylene bisimide assemblies.

Int J Mol Sci 2009 Dec 1;10(12):5239-56. Epub 2009 Dec 1.

Institute of Physics and nanoMA, Center for Nanostructured Materials and Analytics, University of Technology, Chemnitz, Germany.

Nanoassemblies are formed via self-assembly of ZnS capped CdSe quantum dots (QD) and perylene bisimide (PBI) dyes. Upon assembly formation the QD photoluminescence is quenched, as can be detected both via single particle detection and ensemble experiments in solution. Quenching has been assigned to FRET and NON-FRET processes. Analysis of FRET allows for a distinction between different geometries of the QD dye assemblies. Time-resolved single molecule spectroscopy reveals intrinsic fluctuations of the PBI fluorescence lifetime and spectrum, caused by rearrangement of the phenoxy side groups. The distribution of such molecular conformations and their changed dynamics upon assembly formation are discussed in the scope of FRET efficiency and surface ligand density.
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http://dx.doi.org/10.3390/ijms10125239DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2801993PMC
December 2009

Molecule-molecule versus molecule-substrate interactions in the assembly of oligothiophenes at surfaces.

J Phys Chem B 2006 Apr;110(15):7898-908

Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.

In this paper we present a joint experimental and theoretical approach for the study of the assembly of end-substituted oligothiophenes at surfaces with different polarities (i.e., mica vs graphite). Scanning probe microscopy studies of (sub)monolayer deposits show various types of structures (one-dimensional fibrils, two-dimensional regular layers, and monolayers), depending on the nature of the end groups and the substrate. Using molecular modeling with an atomistic approach, we focus on the interplay between the molecule-molecule (and segment-segment) interactions and the molecule-substrate interactions and their influence on the observed morphologies and the stacking geometry. Such information is relevant for controlling the structural order in thin layers of thiophene oligomers for use in field-effect transistor applications, for example, by modifying the nature of dielectric material over which those compounds are deposited.
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http://dx.doi.org/10.1021/jp056824qDOI Listing
April 2006

Influence of halogen substituents on the self-assembly of oligothiophenes--a combined STM and theoretical approach.

Langmuir 2006 Feb;22(4):1443-8

Abteilung Organische Chemie II, Universitat Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.

Iodinated quaterthiophenes 2-3 have been synthesized and their self-assembling behavior investigated at the liquid-solid interface by means of high-resolution scanning tunneling microscopy in comparison to parent oligothiophene 1. All three compounds spontaneously give well-ordered 2D crystalline monolayers at the graphite surface and order in a lamella-type arrangement of the conjugated backbones concomitant with an interlocking of the alkyl side chains. Symmetrically substituted oligothiophenes 1 and 3 without a relevant dipole moment self-assemble in a similar fashion, exhibiting comparable unit cells, whereas monoiodo derivative 2 arranges as pairs along the lamella axis due to the presence of a permanent dipole moment induced by the polarizable halogen group. Corroborated by quantum chemical calculations, novel head-to-head (iodo-iodo) intermolecular interactions were found to take place for this unsymmetrical derivative. The investigation of mixed solutions clearly reveals that at the solid-liquid interface a homogeneous layer of this compound is formed, which comprises the highest packing density leading to a separation process at the interface.
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http://dx.doi.org/10.1021/la052566cDOI Listing
February 2006

A nanoscale view of supramolecular stereochemistry in self-assembled monolayers of enantiomers and racemates.

Langmuir 2004 Oct;20(22):9628-35

Laboratory of Photochemistry and Spectroscopy, Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200-F, 3001, Leuven, Belgium.

The effect that molecular chirality has on the formation of monolayer structures by pure enantiomers and their racemates at the liquid/solid interface has been investigated for two chiral compounds (1 and 2) which differ from each other by the presence or absence of an ester function in their respective molecular structures. 1 shows pseudoracemate formation when the achiral graphite support is exposed to a solution containing a racemate while 2 shows racemic conglomerate formation. This difference is rationalized in terms of the orientation of the pure enantiomers with respect to the graphite substrate and highlights the importance of molecular structure and its influence on balancing the interplay between molecular conformation and molecular packing on the surface. For 1, nonstoichiometric mixtures of both enantiomers have been investigated, and the results are discussed in the framework of the sergeant and soldiers principle. These results are important for the understanding and prediction of spontaneous resolution in monolayer systems.
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http://dx.doi.org/10.1021/la048141sDOI Listing
October 2004

Metal ion complexation: a route to 2 D templates?

Chemistry 2004 Mar;10(5):1124-32

Katholieke Universiteit Leuven, Department of Chemistry, Celestijnenlaan 200 F, 3001 Leuven, Belgium.

The two-dimensional ordering of a number of 2,2'-bipyridine derivatives at the liquid/solid interface has been investigated by scanning tunneling microscopy. By appropriate functionalization of the bipyridine units, their intermolecular distance can be tuned, which has proved to be crucial for complexation with metal ions. The in situ addition of metal salts (Pd(2+), Cu(2+)), leading to the formation of metal-bipyridine complexes, has a dramatic influence on the two-dimensional ordering of the molecules and suggests that these complexes could be used as templates.
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http://dx.doi.org/10.1002/chem.200305424DOI Listing
March 2004

Synthesis, separation, and isomer-dependent packing in two dimensions--detected by scanning tunnelling microscopy--of a TTF derivative.

Chem Commun (Camb) 2003 Apr(7):906-7

Institut de Ciència de Materials de Barcelona (CSIC), Campus Universitari, 08193 Bellaterra, Catalonia, Spain.

The synthesis, isolation and STM imaging on graphite of the cis and trans isomers of a TTF reveal isomer-dependent packing, and constitutes a way to study the non-covalent interactions at play in these systems.
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http://dx.doi.org/10.1039/b300731fDOI Listing
April 2003

Supramolecular control of two-dimensional phase behavior.

Chemistry 2003 Mar;9(5):1198-206

Katholieke Universiteit Leuven, Departement Scheikunde Celestijnenlaan 200 F, 3001 Leuven, Belgium.

We have used directed two-component self-assembly to "pattern" organic monolayers on the nanometer scale at the liquid/solid interface. The ability of the scanning tunneling microscope to investigate structural details in these adlayers was used to gain insight into the two-component two-dimensional phase behavior. The components are symmetrically alkylated bisurea derivatives (R1-urea-spacer-urea-R2; R1, R2=alkyl, spacer=alkyl or bisthiophene). The bisthiophene unit acts as a marker and its bisurea derivative (T2) is a component in all the mixtures investigated. By varying the position of the hydrogen-bond forming urea groups along the molecule and the length of the alkyl chains of the other components, the effect of 1) hydrogen bonding, 2) molecule length, 3) odd-even effects, and 4) shape complementarity on the two-dimensional phase behavior was investigated. Insight into the effect of these parameters leads to the control of the two-dimensional patterning: from randomly intermixed systems to phase separation.
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http://dx.doi.org/10.1002/chem.200390137DOI Listing
March 2003

19F NMR spectrometric determination of the partition coefficients of some fluorinated psychotropic drugs between phosphatidylcholine bilayer vesicles and water.

J Pharm Biomed Anal 2002 Nov;30(4):1087-92

Kyoto Pharmaceutical University, 5 Nakauchicho, Misasagi, Yamashina-ku, 607-8414, Kyoto, Japan.

A simple 19F NMR spectrometric method was proposed for the determination of the partition coefficients of fluorinated psychotropic drugs, trifluoperazine (TFPZ), flunitrazepam (FNZ) and flurazepam (FZ) between phosphatidylcholine (PC) bilayer of small unilamellar vesicles (SUVs) and water (buffer). Each 19F NMR spectrum of these drugs in the presence of PC SUV showed a single signal accompanying a PC concentration-depending shift change and broadening, which indicated a fast exchange of these drugs between the water phase and the PC bilayer of SUV. From the relationship between the 19F chemical shift change (Deltadelta) of each drug and the PC concentration, the molar partition coefficients (K(p)'s) were calculated and obtained with a good precision of RSD below 6%. The fractions of the partitioned drugs calculated by using the obtained K(p)-values were in a good agreement with the experimental values. The results demonstrate that the 19F NMR method can be usefully applied to the determination of partition coefficients of many drugs having fluorine atom(s) without any separation procedure, especially for drugs which do not have absorption in the ultraviolet or visible region, or those having absorption but show insignificant spectral changes according to their incorporation to PC bilayers (e.g. FNZ).
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http://dx.doi.org/10.1016/s0731-7085(02)00438-7DOI Listing
November 2002

Submolecular visualisation of palladium acetate complexation with a bipyridine derivative at a graphite surface.

Chem Commun (Camb) 2002 Sep(17):1894-5

University of Leuven (KULeuven), Department of Chemistry, Laboratory of Molecular Dynamics and Spectroscopy, Celestijnenlaan 200-F, 3001 Heverlee, Belgium.

In situ complexation of palladium acetate by a monolayer of a bipyridine derivative at a graphite/liquid interface has been observed using scanning tunneling microscopy.
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http://dx.doi.org/10.1039/b205240gDOI Listing
September 2002

Effect of phosphatidylserine content on the partition coefficients of diazepam and flurazepam between phosphatidylcholine-phosphatidylserine bilayer of small unilamellar vesicles and water studied by second derivative spectrophotometry.

Chem Pharm Bull (Tokyo) 2002 Mar;50(3):312-5

Kyoto Pharmaceutical University, Japan.

The affinity of the psychotropic benzodiazepine drugs diazepam (DZ) and flurazepam (FZ) to phosphatidylserine (PS) was examined since PS is abundantly contained in brain membranes. The effect of PS content on the partition coefficients (K(p)s) of these drugs between phosphatidylcholine (PC)-PS bilayer membranes of small unilamellar vesicles (SUV) and water was measured using second derivative spectrophotometry. The second derivative spectra of DZ and FZ measured in the solutions containing various amounts of PC-PS SUV clearly showed derivative isosbestic points and a distinct derivative intensity change depending on the amount of the SUV added. The derivative intensity differences (AD) of the drugs before and after addition of the SUV suspension were measured at a specific wavelength. Using the AD values, the Kp values were calculated and obtained with relative standard deviation of below 10%. The Kp values of both drugs increased according to the PS content in the PS-PC bilayer membranes of the SUV proving that both have higher affinity to the PC-PS bilayer membranes than to PC membranes. The effect was much larger for FZ, i.e., the Kp value of FZ at 30 mol% PS content increased to about five times the value for the PC SUV. This can be explained by the fact that at the experimental pH of 7.4, 80% of FZ molecules are in a cationic form (pKa=8.1), so that these molecules are highly accessible to the negatively charged PS molecules. The results support the rapid and high distribution of DZ and FZ in the central nervous system after their administration.
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http://dx.doi.org/10.1248/cpb.50.312DOI Listing
March 2002